Tuesday, July 17, 2018


Mr. Trump has apparently stepped across the line into treason.  Many observers have noted serious wrongdoing,  a few so far have even used the word “treason”. 

Mr. Trump has weakened the western alliance for Mr. Putin by denigrating the allies at every turn (the G-7 meeting in Canada,  the NATO summit in Brussels,  his visit to the UK,  etc),  and imposing unnecessary tariffs,  trying to start trade wars with them. 

Soviet Russia and now Putin’s Russia has been trying to weaken our alliance unsuccessfully for over 7 decades.  Mr. Trump has done it for them in only a year and a half. 

At the Helsinki summit news conference,  Mr. Trump then gut-punched his own intelligence community to stick up for Putin.  He defended Putin against reporters’ questions.  The smirk on Putin's face was evident.

At the same news conference,  Mr. Trump then tried to blame poor relations with Russia on Mueller's investigation.  He so obviously still believes the fiction that Mueller's investigation is solely just a witch hunt against him.  It is not. 

Mueller’s investigation began before Mr. Trump became President,  and its charter was to find out what exactly happened regarding election meddling,  how they did it,  who exactly did it,  and did they have any help on the US side?   Exactly as it should be. 

The “collusion” thing is but a small piece of that investigation,  dealing with the “did they have any help on the US side?” question.    That’s no witch hunt,  that’s quite a proper question to investigate. 

Billions have seen this play out on live television the last couple of weeks.  Weakening the western alliance for Putin’s Russia is at the very least “providing aid and comfort to the enemy”,  as one of the two Constitutional definitions of treason has it.  Only two witnesses are required.

The House of Representatives brings the charges as Articles of Impeachment.  The Senate then tries the case,  with the Chief Justice of the Supreme Court presiding,  not the Vice President.  It takes a 2/3 majority to convict.  That is what the Constitution says.

It is now urgent for the House and Senate to deal with this apparent treason.  If they do not deal with this fairly quickly,  they are complicit in it,  by any possible reasonable standard.  And you,  the American people,  must hold them accountable at election time.  This is way more important than any conceivable party politics. 

Update 7-19-18:  Notwithstanding the various quite pathetic walk-backs of what Trump said in Helsinki and afterwards,  it is quite clear what he said and meant in Helsinki,  and to the allies in the month preceding.  If that combination is not treason of the “aid and comfort” type,  it is perilously close,  and merits severe corrective action. 

There is no question that the House and Senate need to deal with this,  and quickly,  and it appears that the majority of Americans are aware of this.  The fate of the western alliance that has kept the world more-or-less at peace for 70 years is at stake.  But what I see are politicians mostly scrambling to give misbehaving Trump another “pass” for their own political advantage,  instead of doing their sworn duty for the American people.  They are thus complicit in Trump’s treason,  in my opinion.

At this point,  all I can recommend is voting for “the other guy”,  no matter who it is,  in every election from 2018 onward.  I don’t see how we could do any worse.  We might do a lot better.  This is way beyond any party politics in its seriousness,  which is exactly why who the “other guy” is,  does not matter.  Just replace the whole misbehaving lot!

Saturday, July 7, 2018

Immigration Politics and the Nazification of America

This article appeared in essentially its submitted form,  in the Waco Tribune-Herald,  on Saturday,  July 7,  2018.  It takes on the immigration and refugee problems,  which are but one piece of a larger pattern that I see as the gradual nazification of America.  That is a path to our destruction as a nation.


The Immigration Problem 

There are really three separate parts to the general immigrant problem:  temporary guest workers,  refugees (asylum),  and undocumented children (DACA).  These are all quite different.  There is no one-size-fits-all thing to do about them,  no matter how inconvenient that might be for politics.

Temporary Guest Workers:

There two categories here, termed “skilled” and “unskilled” workers.  Skilled workers (and families) get H2 visas,  and there aren’t very many of these.  This category is not a worry for our purposes here.

Unskilled workers also divide into “agricultural” and “other”.  The agricultural workers and their families get H1A visas,  and are also known as “migrant farm workers”.  The “other” get H1B visas,  and many of these also bring their families. 

Most of these “other” are in construction work,  and more recently lawn care and many other unskilled jobs.  The quota for H1A and H1B visas is not strictly enforced (there being some exceptions granted once the cap is reached),  but generally speaking,  there are only something like 100,000 to 150,000 of these in any given year.  The term of the visa is only a year.  The idea behind them is “seasonal work”.

The size of the labor market these people fill is a big chunk of the number of undocumented aliens in the US:  something like 10 or 12 million people.  Assuming an immigrant family is two adults and 4 kids,  and that both adults work,  that’s at least about 3-4 million jobs they fill.  Fewer kids,  more jobs.

The market demand is thus quite out-of-line with the legal supply:  3-4 million jobs to fill,  versus 100,000 to 150,000 guest worker visas available,  in any given year.  These people have to eat,  so they will come to the US for that work,  they have no other feasible choice. 

They will come legally if possible,  illegal if not,  precisely because they have no real choice.  These numbers say most will have to come illegally,  as forced by the unrealistically low quotas.

This has been going on for many decades.  No one should be in the least surprised by this!  For those same many decades,  congresses and administrations,  one after another,  have failed us on this issue.

Because these workers are largely illegal,  it is easy to extort hard work out of them for really crummy pay.  That is definitely unethical,  if not illegal,  abuse.  If these workers were legal,  pay in those jobs would likely be higher,  and some Americans might even want some of those jobs. 

As it is,  most Americans do not want those jobs at all,  precisely because the work is hard,  the conditions very bad,  and the pay really lousy.

The common-sense “fix” is easy:  raise the visa quotas to be in-line with the size of the labor market these workers serve.  This will cost you a few more government workers to process and manage the visas,  but as guest worker pay improves,  you will need to supply less welfare support to their families.   The size of this population may drop some,  over time,  as more Americans take some of those jobs.

Demonizing for political purposes this population of guest workers,  mostly from Mexico,  is nothing but racism masquerading as national security or public safety,  there can be no doubt about that.  The statistics prove there are actually fewer real criminals among this population,  than among Americans at large.  That eliminates the only “excuse”.

Fixing this problem properly is the “right thing to do”,  and it is actually a moral imperative.  Hold your representation accountable:  it is their job to fix this,  and they have not.  And there is no defendable excuse for that lack.

Refugees (asylum):

This is a different problem,  and a different (much smaller) population of people.  These are mostly people from a handful of failed-state Central American countries,  who are fleeing for their very lives.  The types and kinds of violence vary,  but the effect is the same:  certain death.

Under our laws and policies as they have been until very recently,  every such refugee has the right to come to our border and ask for asylum.  They have the right to have an immigration judge decide their case in a timely fashion.  Since there is no one to ask on the Mexican side,  they have the implied right to step over our border and ask an official on the American side.

It is easy enough to tell who the bona fide refugees really are.  A child will cling to its real parent,  but will have to be restrained by any bad actor using that child as a means of disguise.  A nursing mother is no smuggler,  trafficker,  or gang member.  Many of these people may have been brought here by such,  but they are not such.  (The same is true of illegal guest workers.)

This does require a real,  mature,  experienced human being to decide properly,  not some underpaid dropout with nothing but a rule book to follow by rote. 

Recently,  we have seen an unfolding crisis on our border with an unconscionable change in policy. 

Policy now criminalizes any non-citizen stepping over the border for any purpose.  Thus these people were arrested for prosecution and their children taken from them.  This was explicitly stated by some in the administration to be a deterrent to other border crossers,  including future refugees seeking asylum.

A court has recently ordered these children be reunited with their parents.  The government’s obvious difficulties tracing where these kids actually are,  speaks directly to the intended harsh policy:  there never was any original intention to reunite anybody.  Instead,  children were to be taken and essentially interned or fostered-out,  and the adults summarily deported.  The President has as much as said so.

I have to point out this evil for what it actually is:  abusing refugees,  particularly children,  for nothing but political gain.  The second House immigration bill that recently failed has exactly that political gain embedded in it:  getting Democrats to agree to fund the border wall that we really do not need,  using both DACA and these interned children as bait.  Even the moderate Republicans backed away from this evil,  which is why it failed by a large margin.  And evil it is,  to ruin lives for political gain.

You fix this by not criminalizing stepping across the border to ask for asylum.  The demand is higher of late,  so you simply put more immigration judges in place to still get this done in a timely fashion.  That actually greatly reduces detention housing costs while the cases are considered.  And,  you quit putting conditions on the kind of violence we will accept as a justification:  death is just death.  That certainty is what those people fled in the first place,  in spite of the dangers along the way.

Since both laws and policies require change,  this is something that both congress and the administration must do,  no one else can.  Hold them accountable:  there is an election this fall! 

Undocumented Children (DACA):

These are the children brought here illegally,  mostly by illegal guest workers.  These children had no choice.  They fell into a sort-of unaddressed limbo in our immigration policies and laws.  Congress after congress,  and president after president, failed to deal with this.  The previous President tried a stopgap measure.  The current President is undoing that,  and is using this issue as part of the bait to get what he wants politically. 

The statistics show that the vast majority of these kids have well-assimilated into America,  getting educated,  getting jobs.  They have become exactly what we like to see in our citizenry.  There needs to be a way to make citizens of people like that,  and currently there is not one.  That is what you fix.

It starts with some sort of interview or hearing to weed out the bad actors,  but we have to ensure that this process cannot be abused the way the asylum process recently has been.  That’s the short-term solution.  It requires actions from both congress and the administration,  and only you (at the ballot box) can hold them accountable for it.

The long-term solution depends upon properly solving the other two problems:  temporary guest workers,  and refugees seeking asylum.  Solve those properly,  and the undocumented child (DACA) problem naturally goes away,  in about a generation.  At that point,  your only remaining illegals really will be the smugglers,  traffickers,  and gang members.

How to Get These Done

Step 1.  No matter which party you favor,  ditch the politics!  Don’t fall for the propaganda from either side (and it is loud and voluminous)!  Find out the facts for yourself.  Use your logic and your knowledge of people to figure out what the truth really is,  which is always one whale-of-a-lot more complicated than some idiotic political sound-bite slogan.  If you really do this,  I think you will reach conclusions fairly similar to mine.

Step 2. Decide what you want done about these problems.  I think that if you really honestly did step 1,  you will pretty much generate the same to-do list that I did. 

Step 3. Communicate what you want done,  and why,  to your representation in Congress and in the White House.  In that communication,  let them know that you are watching for outcomes,  and that you will hold them accountable.  The addresses are well known,  and obtainable on the internet.  You can now contact them by email,  but a paper letter sent by surface mail is still more impressive.

Step 4. Actually hold them accountable at election time!  If they cannot be statesmen and do the people’s business instead of politics-as-usual,  they are just not someone you want to hold the offices,  so try somebody else.  Simple as that. 

The next election is this November.


These immigration/refugee issues are just one piece of the ongoing nazification of America.  There is also the leader-who-can-do-no-wrong cult.  And there is chronic and widespread government lying about what is being done and why.   The means and details are different than 1930's Germany,  but the overall strategies and outcomes are exactly the same.

First,  there is the in-group/out-group thing to inflame passionate support.  Groups are selected for scapegoating,  then demonization,  then abuse,  then elimination.  Same pattern as Nazi Germany,  only the details are different:  for immigrants,  separations and deportations instead of gas chambers and ovens.  Note also what is being said about political opponents.  This is quite widespread.

Second,  there is the leader-who-can-do-no-wrong cult,  which historically always leads to dictatorship.  Followers support him rabidly,  despite all facts,  and all the evident harm he brings them.  Exact same pattern as Nazi Germany.  Only the details are different,  and not by very much. 

Examples include tariffs in a trade war that will destroy heartland businesses,  a huge increase in the national debt to “finance” a tax cut that is 90+% for the super-rich,  and borderline treason by a leader who cozies up to vicious dictators like Putin and Kim Jong Un,  while insulting the leaders of our allies,  and damaging those alliance relationships. 

That is something Soviet Russia,  and now Putin’s Russia,  has tried to do without success for 70+ years:  weaken the Western Alliances.  Think “aid and comfort to the enemy”,  as one of two Constitutional definitions of treason has it.

Third,  there is constant lying by officials and staff,  although we don't call them "ministers of propaganda".  No effective difference there at all to Nazi Germany.  You can believe essentially nothing the government says.  That is EXACTLY what happened after 1933 in Germany.

If we continue down this path,  America will end up doing very great evils,  and will eventually be destroyed for it,  as was Nazi Germany.  It's the same path,  leading to the same ugly place.  Only the details are different.  And not by so very much.

My fellow citizens,  wake up!  See this evil for what it really is!  Rise up and make things different!  The Declaration of Independence says explicitly that we really can do this.  The Second Amendment to the Constitution gives you the means to make your uprising credible,  if all else fails. 

But start at the ballot box this November!  Vote for ANY alternative to this evil!  You could hardly do worse,  if you did only that.  Changing the government at the ballot box is much preferred over armed revolution,  if only because there is less mess to clean up afterwards. 

Your personal party preferences and personal ideologies have little to do with this.  Stopping the evil of nazification is far more important than any other consideration.  Simple as that. 

You all have been warned!!!!  On your heads be it,  if you do nothing!

Tuesday, July 3, 2018

Typical Texas Signs

Warning signs typical of Texas,  where you are expected to have at least a little bit of common sense:

I actually have one like this in my shop,  in two copies:

But I like this one even better:

Tuesday, June 19, 2018

History Begins to Repeat Itself!

This is what separating and detaining families looks like at the US southern border.  This is also what US officials look like when lying about what they are doing and why.  

This is Auschwitz,  another place where families were separated and detained.  And,  where officials also lied about what they were doing and why.  

Trump’s story that the Democrats forced his hand to do this has been thoroughly debunked.  He could stop this evil with a single word. 

What this is really all about is holding children hostage to extort the money from Democrats in Congress to build the border wall that we do not need.  That has been verified.

My fellow citizens,  rise up and put a stop to this evil!  Contact your senators and representatives,  and insist that they stop this. 

If they do not,  replace them at the earliest election,  or other recall opportunity,  with someone who will.   It really is that simple.

Update 6-24-18:  I have not seen one single thing in any of the governmental actions,  or in any of the commentary,  that would induce me to change my assessment of this problem.  It is indeed a manufactured crisis to gain a political end,  and it is a real,  verifiable human rights abuse,  motivated by a political propaganda message that is essentially Hitlerian Nazi in its fundamental character.  I have also seen not one ounce of the courage required in Congress to oppose this evil,  with very few individual exceptions.  Maybe a small single handful so far.

Update 7-3-18:  I have still seen nothing to change my assessment of this situation.  As of yesterday,  it was reported that family separations finally (!!!) stopped.  But the number of children actually reunited with their parents is still,  as of today,  a number less than 10 out of over 2000 so separated.  Border crossing arrests are also reported to be down,  so this does seem to work as a deterrent,  at least short term.  But I find the cost of this "deterrent" to be totally unacceptable from a moral and ethical standpoint.  It is a human rights violation.  It is far outside that behavior recommended by all the great religions.

Update 7-6-18 There is definitely a pattern to the delays correcting by court order this atrocity.

That pattern includes and encompasses the more recent story about immigrant recruits being discharged from the military.  They were promised a path to citizenship if they enlisted.  The government has just reneged on that promise.  Can you conceive of why?

It also encompasses the toleration of Nazis and KKK'ers marching in Charlottesville,  as if their ideologies were as valid as anyone else's,  although few yet make that particular connection.  Sound familiar?  It should!

That pattern is:  select a scapegoat population,  such as immigrants,  especially those of color.  Then demonize them.  Then abuse them.  Finally,  get rid of them.  Sound familiar?  It should!

Another piece is the "beloved-leader" cult of the strongman leader.  Followers support him rabidly,  no matter how much harm he does them. Logic and facts cannot dissuade them.  Sound familiar?  It should!

Consider the effects of the trade war on the heartland figures who are Trump's political base (and largely the extreme-right wing of the GOP's base,  these days).  Or the 1.5 trillion dollars added to the national debt to "finance" tax cuts that were 90+% for the super-rich,  not them.

We've seen this evil before,  and spent the best part of half a million lives and most of our treasure trying to eradicate it,  7.5 decades ago.  THAT is why I specifically picked the comparison to the Nazis.  The parallel between today's America and 1930's Germany is quite eerie,  at the very least!

Saturday, June 2, 2018

Yet Still Another School Shooting

The following is a column I wrote for the Waco paper,  which they chose not to use.  I wrote it in the days immediately following the school shooting in Santa Fe,  Texas.  I,  too,  am tired of seeing our schools shot up.  Here is the real,  time-proven solution to that problem,  and more such venues besides. It's not what you think.  Unless you have read some unvarnished American history.


The mass shooting problem has been hyped and politicized into a pro-gun/anti-gun debate.  That does not address the problem.  It’s past time to point out that we need to recognize exactly what the problem really is!

Just about every single mass shooting for the last several years has been some public venue that was a sitting-duck target.  Sitting-duck targets are the real issue,  and what we should do to change that,  is the problem at hand. 

Both the crazies and the terrorists are inevitably drawn to sitting-duck targets,  because they are easy to attack.  It really is that simple.  They are sitting-duck targets precisely because they were undefended,  or at best inadequately-defended,  gun-free zones.

Why the Usual Gun Control Ideas Won’t Work

The guns are already out there in the society.  It is far,  far too late to try banning guns,  which would require major changes to the Constitution.  Fat chance of that!  But,  if you did ban guns,  all you would accomplish is making the entire country a sitting-duck target. 

Here is why the entire country becomes a sitting-duck target:  the guns already out there would tend to fall into the hands of criminals and terrorists,  and then get sold black-market to crazies.  Nothing really changes except the rate of such mass shootings vastly increases.  You made it worse with your gun ban.

This last incident in the Santa Fe,  Texas,  school,  wasn't even an "assault weapon" thing.  He had a simple shotgun and a simple revolver.  Didn’t make much difference,  did it?  So,  what then is the real point of an “assault weapons” ban?  Or a clip size limit?

The main gun control idea that I see as making any significant difference would be to revise the process of keeping guns out of the hands of crazies,  with some sort of “red flag” alert process.  But that doesn’t address terrorism,  which is on the rise.

The only other useful one would be to outlaw bump stocks and trigger cranks,  which violate the spirit of the machine gun ban,  which really has worked.

A Pertinent Lesson From American History

Now,  what's forgotten here is a lesson from the 19th century gun-free American frontier towns that actually worked,  and quite well.  There are actually very good reasons to have gun-free zones,  and in a variety of venues,  not just schools.  (But that’s another topic.)

What is totally forgotten today:  once you declare a gun-free zone,  you are obligated to defend it,  in order to prevent the sitting-duck target effect.   That really is the fundamental problem we as a nation so perversely refuse to face today.

The Santa Fe school apparently had one (and only one) campus cop who actually confronted the shooter in a timely fashion.  That cop was armed,  mostly likely only with a revolver.  The shooter got him before he could take out the shooter.  Which is proof that,  in this case,  the school’s defense was inadequate. 

One cop,  if taken out,  leaves no defense.  The 19th century town sheriffs and town marshals always had a significant number of deputies.  Nobody went alone to quell problems.  It worked then,  why not now? 

News reports indicate the school officials thought they were adequately hardened against shooter attack,  because they employed two armed guards.  But,  so very clearly,  only one of those guards made it to the initial confrontation,  and he got taken out before he do anything to stop the shooter early. 


You simply need more guards than shooters,  and your guards also need to outgun the shooters.  Period!  But there are also a couple more well-proven nuances to this prescription.

One critical 19th century rule-of-thumb was “60 seconds max” to the scene of the problem.  That limits casualties,  and well-proven it was,  too.  No police department today could possibly respond that fast!

The other facet of the 19th century solution was using real peace officers actually accountable to the people,  not just hiring some outlaw gunman for protection.  Any gun-free zone guard will inevitably serve in the capacity of a peace officer.  There is no way around that. 

Applying the Prescription

The hardest part of applying that today is the 60 second rule-of-thumb to limit casualties.  Most places no longer resemble small frontier towns only 2 to 4 city blocks in size.  Adapting to the 21st century,  it means if your gun-free venue is large,  you need more than one guardhouse. 

That inevitably costs more than it did in the 19th century,  but here is where my acid test for ethics in public officials comes to the fore:  what does your official value more?  Money?  Or lives?  Look at what is done,  not what is said.  Talk is cheap. 

The mistake I see so often made today is the concept of arming teachers,  and counting on them to be your defense.  That teachers already have way too much to do is beside the point here,  that’s another article at some other time. 

Armed teachers will only have some sort of handgun.  They will not generally outgun the shooters,  even if they do outnumber the shooters.  This fails the prescription outlined above,  so it probably won’t work well enough most of the time.  In the long run,  it just gets more people killed.

So,  just do it right!  You need multiple well-armed guards,  trained to be real peace officers,  as they will inevitably be called upon to serve that role.  You need them located in enough places so that two or more can respond anywhere in the venue within a minute.   Make sure they have better guns than any of the shooters we have seen.

Why does everyone make this so hard,  when it really is so stinking easy?  JUST LEARN FROM HISTORY !!!  Don't politicize this,  just do it!

Other articles on this site related to guns,  gun violence,  mass shootings,  and gun control:

Gun Articles as of 6-1-18 (this one highlighted):
6-1-18 Yet Still Another School Shooting
2-24-18 Yet another School Shooting
10-2-17 Machine Guns in Las Vegas?
6-21-16 What the Gun Violence Data Really Say 
10-7-15 Oregon Mass Shooting and Gun Control
5-31-14 On Calls for More Gun Control
10-1-13 Government Shutdown,  Default!  Again?  No!!!
9-20-13 More Gun Control?  No Way!
2-5-13 Real Problems with the Proposed Gun Control Legislation Items
12-20-12 On the Tragedy in Connecticut
12-14-12 School Shooting in Connecticut
8-9-12 Mass Murder Shooters and Gun Control
1-13-11 On the Shooting Rampage in Tucson

Friday, May 4, 2018

Some Thoughts on the Anniversary of the West Explosion

I wrote this article on 23 April,  2018.  A slightly-edited form of it appeared in the Waco "Tribune-Herald" on 26 April,  2018.  By way of disclosure,  I am on the board of contributors for that newspaper.  And a few years ago,  I worked in fire protection engineering,  which gave me much more than just a nodding familiarity with the various fire codes.

For those from out-of-state,  the "Trib" is the Waco,  Texas,  USA,  newspaper.  The agricultural plant in nearby West,  Texas,  caught fire and suffered an ammonium nitrate fertilizer explosion,  some 5 years ago.  Recovery from that devastation is now complete. And devastation it was.


The 5 year anniversary of the West fertilizer plant explosion recently passed,  with excellent coverage on TV and in the newspaper regarding recovery since.  That recovery is now said to be complete,  and is a testimony to the people of West,  and to all who helped them.

Many things in life are a sort of “double-edged sword” that can either help you or hurt you.  Ammonium nitrate is one of those things.  It makes a wonderful fertilizer as a source of fixed nitrogen.  It is also a mass-detonable explosive in its pure form,  which is type 100-0-0 fertilizer,  something well-known from a long history of such explosions.

When combined with other fertilizer compounds as something other than 100-0-0 fertilizer,  the explosive risk goes away.  But there is still an enhanced fire danger,  as the ammonium nitrate decomposes when exposed to fire,  releasing oxygen into the fire.  That makes the fire very intense.

Now,  neat 100-0-0 ammonium nitrate fertilizer is hard to detonate,  requiring either the same sort of detonator as dynamite (just larger),  or confinement when decomposing in a fire.  Without confinement,  decomposing the material in a deliberate fire is actually the best way to dispose of mass quantities. 

The confinement comes from anything heavy resting on top of the fertilizer (including large amounts of the fertilizer itself,  as at Texas City),  or containing the fertilizer within some physical structure as it decomposes from the heat of a fire.  The fertilizer itself doesn’t burn,  it decomposes. It also melts and runs as a liquid down into any holes or spaces,  even floor drains.

In a building fire such as happened at the West fertilizer plant,  the confinement is generated by either (1) the burning building collapses down upon the decomposing fertilizer,  or (2) the melted fertilizer flows down a floor drain into a pipe.  Either will start the tremendous explosion. 

At the West fertilizer plant,  it was the building collapse that prompted the explosion.  This event actually happened after the majority of the stored fertilizer had already decomposed in the building fire.  Had it happened sooner,  much more of (perhaps all) the town of West would have been obliterated,  and the death toll would have been much,  much higher.

The way to positively prevent ammonium nitrate explosions is to positively prevent the building fire from collapsing the building in the first place.  Wooden structures,  feed,  and grain,  plus other building interior furnishings,  are all flammable:  fuel for the fire. 

In a new facility,  you simply eliminate all those materials from where ammonium nitrate is processed and stored.  But because the fertilizer is stored in paper bags,  there is still fuel next to the fertilizer that enhances the fire. 

So,  you fire-sprinkle the building according to the specific standards for fertilizer storage (and these already exist,  courtesy of the National Fire Protection Association).  There is no other way to be certain.

In an existing facility,  there are likely to be wooden floors,  wooden building structure,  wooden storage racks or pallets,  and perhaps even wooden handling and process equipment.  These are all flammable,  fuel for the fire.  That makes the fire-sprinkling of the building even more crucial,  plus it is prudent to seriously over-design the sprinkler system.

Most of these facilities now lie within the city limits of small towns all over Texas.  Many of them were outside the city limits when originally built,  putting them under county (or state) jurisdiction.  If there is no authorization for a county to impose the fire code standards upon these facilities,  then it is the Legislature’s job to authorize them to do so,  or else to make it a statewide mandate. 

And,  believe me,  they should do so!  There have been many of these explosions over the past century.  There is no excuse to let money trump public safety.  Official both in public service and in private organizations should be judged by how they prioritize public safety versus profit.

There is also the problem of urban sprawl.  As already mentioned,  towns grow toward and engulf these facilities.  Without thinking about the threat,  residences,  businesses,  and schools get built right next to facilities handling what amounts to a high explosive,  if mishandled. 

What that really means is that local officials need to understand the true nature of the threat from ammonium nitrate.  They need to zone around these facilities as their locations are annexed into the city,  to restrict development to a safe distance.  This has not been happening,  but ignorance should not be an excuse!

As for anhydrous ammonia,  it poses much less of an explosion hazard,  but something of a toxic gas release hazard,  even in a plant fire.  However,  there are standards for these,  too.  If applied,  the risks are reduced quite effectively.  Again,  this starts as a county or state requirement for rural construction,  and those same requirements should be applied by the cities as they engulf these facilities,  as well as proper zoning.

Citizens,  you render your judgements at the polls!

Tuesday, April 17, 2018

Reverse-Engineering the 2017 Version of the Spacex BFR

I visited the Spacex website in April 2018 and recovered from it the revised characteristics of the large BFR Mars vehicle,  as presented during 2017.  These characteristics are somewhat downsized from those in the 2016 presentation given in Guadalajara.  Thus this article supersedes the previous article posted on this site 10-23-17,  titled “Reverse Engineering the ITS/Second Stage of the Spacex BFR/ITS System”.  Both articles share the search keywords “launch”,  “Mars”,  and “space program”.  The older article has been updated to redirect readers here.

Data From the Spacex Website

What is listed includes a basic vehicle diameter of 9 meters (both first stage booster and second stage spacecraft),  a booster length of 58 m,  and a spacecraft length of 48 m.  The forward half of the crewed spacecraft includes an unpressurized cargo bay,  and over 825 cubic meters of pressurized space for the crew and passengers.  The rest is propellant tankage and engines. 

No data are given for the uncrewed cargo version,  but it appears quite similar overall,  with a giant clamshell door to open the entire space corresponding to the crewed vehicle’s unpressurized and pressurized payload spaces.

For the crewed vehicle,  payload mass is listed as 150 metric tons to low Earth orbit,  and the same on to Mars with refilling on-orbit.  Return payload (presumably from Mars) is listed as 50 tons,  with refilling done on Mars by in-situ propellant manufacture from local ice deposits and atmospheric carbon dioxide.  The cargo deliverable to orbit by the uncrewed cargo version is also said to be 150 tons.

The crewed spacecraft is listed as having an 85 ton inert structure weight.  Musk says the data right now actually say 75 tons,  but that always grows as development proceeds.  Propellant loadout in the tanks is 240 tons of liquid methane,  and 860 tons of liquid oxygen (1100 total),  both superchilled to a higher density than in normal usage.  The listed data imply similar numbers for the uncrewed cargo version.

Basic weight statements for the crewed vehicle (implied to operable either manned or unmanned by the mission planning) would then be as follows (all masses are metric tons):

Item                     at launch             ign. in LEO           ign. on Mars
Payload                150                         150                         50
Inert                      85                           85                           85
Dry                      235                         235                         135
Prop.                  1100                       1100                       1100
Ign.                    1335                       1335                       1235

 There are not enough data given to establish a weight statement for the first stage booster,  because no inert weight was given.  Only the gross takeoff mass (for 150 tons of payload) was given to be 4400 metric tons.  The inert fraction of the crewed spaceship is a bit over 6%.  Falcon-9 first stages seem to be just under 5%. 

On the assumption that the inert mass fraction of the BFR first stage is 5%,  given the 1335 ton max weight of the second stage,  then the first stage inert mass should be near 220 metric tons.  Under that assumption,  its weight statement would be approximately:

Payload (second stage at max)                   1335
Inert                                                              220
Dry                                                               1555
Propellant                                                    2845
Ignition                                                        4400

The first stage is listed as having some 31 sea level Raptor engines.  The second stage spacecraft is listed as having 2 sea level Raptor engines of high gimballing capacity,  and 4 vacuum Raptor engines of limited gimballing capacity.  The two versions differ only in the expansion bell size,  very much like the Merlin engines used on the Falcon 9 and Heavy. 

Design chamber pressure is listed as 250 bar,  with growth eventually anticipated to 300 bar.  The engines are said to be throttleable from 20% to 100% of rated thrust.  The given specific impulses (Isp) apply to 100% thrust at 250 bar,  and should decrease slightly as thrust is throttled down.  No data are given for that Isp reduction.  It is a relatively minor effect at this level of analysis,  and is ignored in my reverse-engineering analysis here.

Data as listed for the individual Raptor engines are as follows.  The sea level design data as presented do not report vacuum thrust,  but an exit diameter is given,  so that it may be calculated using sea level air pressure of 101.325 KPa.  I did this in my reverse-engineering analysis.  Only vacuum performance is listed for the vacuum design.  Listed data are for one engine. 

The data on the site claim a vacuum engine exit diameter too big to fit a 9 m diameter vehicle;  that has to be a typographical error!  Because the vacuum design is never operated with backpressure (excepting 6 mbar on Mars,  essentially negligible),  the lack of a reliable vacuum exit diameter does not impact my estimates.  

Version                                sea level                               vacuum
Vacuum Isp, s                     356                                         375
Vacuum thrust, KN          not given                                 1900
Sea level Isp, s                   330                                         not given
Sea level thrust, KN         1700                                         not given
Exit dia, m                           1.3                                        12.4 (typo !!!)

The presentation as given on the Spacex website does show the reentry sequence as currently envisioned at Mars.  This shows direct entry from an interplanetary trajectory,  with an entry interface speed up to about 7.5 km/s.  Initially the vehicle is flown inverted for downlift,  presumably to keep it from “bouncing off” the Martian atmosphere while traveling faster than Martian escape speed.  Later in the entry trajectory,  the vehicle rolls upright for uplift, in order to shape the trajectory. 

By the time the hypersonics are ending at about 0.7 km/s (local Mach 3) speeds,  the vehicle is within 4-5 km of the surface,  and climbing upward towards about 10 km altitude.  It reverses to tail first for the retropropulsive burn,  all the way to landing.  The presentation claims max 5 gees deceleration during entry sequence while hypersonic.

No data is given at all for the return entry at Earth.  Presumably,  this would also be direct from the interplanetary trajectory,  with entry interface speeds somewhere in the vicinity of 17 km/s.  This will be a very high-gee entry,  as return from the moon with Apollo was 11 gees at 11 km/s entry interface speed.  12-15 gees (or more) is nothing but a gut-feel guess.

The data on the site show 4 landing legs whose span is 3 or 4 times less than the length of the crewed second stage vehicle.  Cargo is lowered to the ground from the cargo bay door with a crane.  People would leave the vehicle by the same means,  and reverse the crane to return to it.

Organizing the Analysis

The Spacex website presentation claims refilling on orbit from uncrewed tanker vehicles.  The illustrations show variously 4 to 5 such tankers,  but no data are given.  Propellant transfer is by tail-to-tail docking,  with thruster-induced microgravity driving propellant flow from one vehicle to the other.  It is unclear whether the tanker is an unmanned crewed vehicle or the cargo vehicle,  and it is unclear whether propellant is loaded as cargo,  or is leftover in the tanks after flying to orbit with no payload.

The tanker performance problem is not analyzed here.  

The analyses here were made using simple rocket equation estimates modified with realistic “jigger factors” for gravity and drag losses.  Because of the long times in interplanetary flight with cryogenic propellants,  other “jigger factors” get included to account for boiloff effects and midcourse correction budgets.  And because retropropulsive landings must have a margin to adjust touchdown if obstacles are encountered,  yet another “jigger factor” must be included to model the need to hover and/or redirect touchdown laterally some distance away. 

For Earth launch with slender,  “clean” vehicle shapes,  something like 2.5% gravity loss and 2.5% drag loss provide realistic first estimates.  The two add to 5%,  which gets incorporated into a “jigger factor” of 1.05,  that multiplies the kinematic delta-vee requirement,  making it suitably larger to cover gravity and drag losses in the simple rocket equation.  At Mars,  gravity is weaker and the air much thinner,  so I reduce the gravity percentage by a factor of 0.384 (Mars surface gravity in gees),  and the drag percentage by a factor of 0.007 (Mars surface density ratioed to Earth standard).  In retropropulsion,  drag helps rather than hinders,  so the two percentages subtract instead of adding. 

I assumed a factor of 1.1 increase on the already “jigger-factored” propellant weight (out of the rocket equation for that burn) to include a “kitty” for minor midcourse corrections,  and the same for long-term propellant boiloff effects in transit.  I also assumed a hover/redirect factor of 1.5,  to multiply the same already-factored propellant weight,  during landing burns. 

These calculations can be made by hand,  but are very conveniently entered into a spreadsheet,  for rapid changes and refinements.  That is what I did for this analysis.  Its results were incorporated into a series of figures.

First Stage Problem

The first stage problem has but one payload,  a weight statement based on the 5% inert fraction assumption,  and suitable sea level and vacuum engine performance data for the sea level Raptor engine design.  The website presentation does not give any indication of the staging speed or altitude,  only depictions showing the trajectory bent over almost level by the time staging occurs. 

This is complicated by the need to fly the booster back to launch site,  and land it there,  very much like the Falcon-9 first stages.  Therefore,  beyond just reaching staging speed against realistic gravity and drag losses,  enough propellant must remain on board after staging,  for the stage (with no payload) to more-than-“kill” its flight velocity with a boostback burn,  ease the entry heating with a shock-penetrating entry burn,  and conduct the final touchdown burn. 

I made the “reasonable” guesses of allowing 0.99 km/s worth of delta-vee for the touchdown burn,  an arbitrary 0.10 km/s delta vee for the entry burn,  and a boostback delta-vee equal to,  or slightly exceeding,  the speed at staging.  I assumed staging altitude to be essentially in vacuum,  so that the average of the sea level and vacuum Isp’s could be used to represent average booster performance. 

Staging speed was an input assumed value,  since it was not specified in the presentations on the website.  I iteratively modified this value until the 3 flyback burns all had reasonable delta-vee values.  The boostback kinematic delta-vee is the staging speed.  It is figured for the ascent weight statement,  “jiggered” by factor 1.05,  and then plugged into the rocket equation for a mass ratio less than what the stage provides overall.  Dividing launch mass by that ratio gets the burnout mass,  and the difference is the ascent boost propellant mass burned to reach staging speed.

Deleting the payload mass (second stage) gives a new weight statement for booster inert and the mass of propellant still on board.  It corresponds to a certain delta-vee from the rocket equation,  “jigger-factored” down by 1.025,  since there is no drag outside the atmosphere.  Subtracting 0.99 km/s for the touchdown burn,  and 0.10 km/s for the entry burn,  leaves the delta-vee benefit available for the boostback burn.  I adjusted my assumed staging speed until my boostback delta-vee equaled or slightly exceeded this staging speed value. 

At launch,  the sea level thrust of the 31 sea level Raptor engines totals to 5375 metric tons-force (force in KN/9.805).  The website data lists 5400 tons of thrust,  close enough.  The thrust/weight ratio minus unity gives the kinematic acceleration straight upwards,  in gees.  At staging,  one must correct to vacuum thrust of the sea level engines,  and since the trajectory is nearly level,  the thrust/weight ratio is the pathwise kinematic acceleration in gees.  These values can be factored by the throttle percentage expressed as a fraction,  if needed.  I bounded the burnout accelerations by calculating values at 100% and 20% thrust.

Those results are summarized in Figure 1.

 Figure 1 – Results for the Booster Problem with Flyback Recovery

Going to Mars After Refilling in Earth Orbit

This is not quite straightforward,  because you cannot use all your propellant to go to Mars.  You must have enough propellant still on board after departure,  to enable the landing on Mars.  That means you analyze the Mars landing first,  and then the departure burn from Earth orbit. 

You have to analyze from dry tanks at touchdown on Mars back to the landing burn ignition conditions,  complete with Mars retropropulsion gravity/drag effects,  for the min propellant needed to land.  Then you scale that amount of propellant up with the hover/redirect factor on your delta-vee for a realistic propellant budget to land from the rocket equation.

Then you scale that realistic landing budget up with the boiloff factor and the midcourse factor to find the actual reserve propellant that you must still have on board after the departure burn.  That is what sets your weight statement for the departure burn. 

These results for the Mars landing are given in Figure 2.

 Figure 2 – Results of the Analysis of the Mars Landing

The departure burn from Earth orbit sees an Earth gravity loss,  but no drag loss.  The usable delta-vee from it adds to the Earth orbit velocity for a velocity Vdep at that Earth orbit location.  A little farther from Earth,  you figure a velocity-at-infinity as Vinf = (Vdep^2 + Vesc^2)^0.5.  Then you add Earth’s orbital speed to that value for the vehicle speed with respect to the sun Vwrt sun. 

For a min energy Hohmann-type transfer ellipse orbit there is a perigee velocity,  which varies with planetary positioning along their ellipses.  I used the worst case (highest) value.  The vehicle velocity with respect to the sun Vwrt sun,  minus the Hohmann transfer perigee speed Vper-HOH,  is the margin you have,  that might be used to fly a faster trajectory.  Hohmann transfer is about 8.5 months one way. 

These results for the departure from Earth orbit are given in Figure 3.

Figure 3 – Results for the Analysis of Departure from Earth Orbit

Returning From Mars

Very similarly to the trip outbound to Mars,  one must analyze first the landing on Earth,  to define the propellant needed to land there,  jigger that up for the transit,  and have that quantity in reserve after the Mars departure burn.  So you analyze the Earth landing first,  then the departure from Mars,  which is a direct ascent into the interplanetary trajectory.

I used the same basic end-of-hypersonics at 0.7 km/s (local Mach 3) as my kinematic definition of min landing delta-vee.  This just happens at higher altitude,  and in much thicker air,  on Earth.  Unlike Mars,  it is quite feasible to fall a long way in the transonic/low-supersonic flight speed range,  before reversing vehicle orientation to tail-first for the touchdown burn. 

You “jigger-up” this min delta vee by a gravity-drag factor (near 1 in retropropulsion on Earth) and by the hover/redirect factor (I used the same factor 1.5 for this).  That much larger delta-vee goes through the rocket equation for a mass ratio from dry tanks at touchdown.  This leads to a realistic landing propellant budget.  Then you factor that up for boiloff and midcourse,  to find the reserve propellant that must be on board after the Mars departure burn. 

The Earth landing results are given in Figure 4.

 Figure 4 – Results for the Earth Landing Analysis

This Earth landing propellant budget at Mars departure then adjusts the weight statement of the refilled craft upon Mars,  in addition to the stated reduction in return payload.    This is a direct departure:  the weight statement and choice of engines finds the ideal delta-vee,  adjusted downward by the Mars gravity-drag factor to a realistic delta-vee.  We are not stopping in Mars orbit,  this realistic delta-vee becomes the speed of the vehicle near Mars.  It is adjusted using Mars escape velocity to find the Vinf in the vicinity of Mars.  That is in turn subtracted from Mars’s orbital velocity to find the velocity with respect to the sun.  This is compared to the Hohmann min energy transfer orbit’s apogee velocity,  to determine any margin available for a faster trip home. 

These numbers indicate little or no potential for a fast return home.  The results are given in Figure 5. 

Figure 5 – Results of the Mars Departure Analysis


Using Spacex’s own data  plus some reasonable assumptions regarding gravity and drag losses,  and hover requirements for retropropulsive landings,  and for boiloff and midcourse budgets,  I calculated performances estimates,  for the big Spacex Mars vehicle as presented in 2017, that are not very far at all from what is claimed in their 2017 presentation. 

I show some potential for a slightly-faster trajectory to Mars than min energy Hohmann transfer.  I show very little,  essentially zero,  potential for a faster return trajectory from Mars,  compared to min energy Hohmann transfer. 

To get these data,  I had to assume that the inert mass fraction of the BFR first stage is 5%,  and I had to assume that the BFR stages at just about 2.55 km/s flight speed,  outside the sensible atmosphere,  and already almost level. 

I used the reported engine performance data for the sea level and vacuum forms of the Raptor engine,  operating at 250 bar chamber pressure at full thrust.  If the chamber pressure can be raised closer to 300 bar (as Spacex wants),  some of the faster-trip performance shortfalls ease.  I did not analyze these data to quantify that effect.

Gravity and drag loss effects upon ideal rocket equation delta vee are assumed at 2.5% each here on Earth,  and ratioed down by 0.384 for gravity,  and 0.007 for drag,  at Mars.  Propellant quantities coming from the rocket equation mass ratio and appropriate weight statements get ratioed by an assumed factor of 1.5 for retropropulsion hover/redirect effects,  by a factor of 1.1 for boiloff effects in transit,  and by a factor of 1.1 for budgeting midcourse correction propellant. 

To correct sea level thrust of a sea level Raptor engine to vacuum conditions,  add a force equal to the exit area multiplied by Earth sea level air pressure.  This does not affect rocket equation results,  but it does affect vehicle acceleration-capability calculations.  These help you choose which engines to burn,  and what levels of throttling to use.

Spacex has posted data for anticipated Mars entry from the interplanetary trajectory,  but not for Earth entry from the interplanetary trajectory.  It is peak entry deceleration gees during the return to Earth that is very probably the highest gee requirement for occupants to endure.  This is not something controllable with engine thrust,  as there is no propellant available to budget for this purpose. 

Earth entry deceleration from Mars (on a direct entry from the interplanetary trajectory) is quite likely to be far more severe than the Apollo 11-gee peak deceleration coming back from the moon at an entry interface speed of 11 km/s.  Coming back direct from Mars,  entry interface speed is likely to be in the vicinity of 17 km/s.  The crew simply must be very physically-fit to endure this.  This is a serious issue yet to be addressed in the Spacex presentations.

Landing stability of a relatively tall and narrow vehicle,  on unprepared rough ground on Mars,  is not addressed here.  This is another serious issue yet to be addressed in the Spacex presentations.

Update 4-18-18 artificial gravity

For Spacex’s mission plan with its BFR vehicle,  the health risk for high gee entry occurs at Earth return.  It cannot be avoided.  The occupants so exposed will have endured months-to-years of low Mars gravity (0.384 gee),  followed by about 8 to 8.5 months exposure to zero-gee on the transit home.  They are very unlikely to be physically fit for an 11+ gee entry,  even if Mars gravity is found to be fully therapeutic for microgravity diseases.   

The support for that assertion comes from years of orbital experiences at zero gee.  Astronauts exposed to zero gee for times on the order of 6 months to a year have proven to be fit enough to endure a 4 gee ride down from Earth orbit,  with an entry speed of 8 km/s.  We have absolutely nothing to point at,  to support the assumption that higher gee levels are safely endurable in that physical state!   Coming from Mars is a faster entry at about 17 km/s than from the moon,  and that was an 11 gee ride at 11 km/s.

Given that risk,  artificial gravity for at least the voyage home seems prudent.  This could possibly be accomplished by having two ships make the return voyage together.  Taking advantage of the refilling plans and procedures,  dock the two ships tail-to-tail during the long coasting transit.  Spin them up end-over-end with the attitude thrusters.  At the nominal 4 rpm spin limit,  near-Earth gee levels are obtained as shown in Figure 5. 

Figure 5 – Obtaining Spin Gravity in Two BFR Ships Docked Tail-to-Tail

The 4 rpm limit is a “fuzzy” limit.  If a very slightly-higher spin rate (maybe 4.6 or 4.7 rpm) is tolerable to the balance organs in the middle ear,   then very near full Earth gravity can be simulated in the occupied decks.  This is also shown in Figure 5 as the data in parentheses.  This is an artifact of the size of the BFR vehicle.  Achieved gee level is proportional to spin radius,  and to spin rate squared.  A nominal reference point is 1 gee at 56 m radius and 4 rpm.

There are two inconvenient design issues with this notion,  but they are not “show-stoppers”.  One is the reversed directions for up and down,  sitting on the landing legs versus spinning for artificial gravity.  What were floors become ceilings,  and vice versa.  All the interior equipment and appurtenances will have to be reversible physically,  or “double-ended” if not. 

The other is the solar panel fans that Spacex shows for powering these vehicles with electricity.  The presentations show them deployed near the tail of the vehicle while in space (free fall).  These will have to be strong enough to deploy properly,  and stay in position,  while exposed to low levels of effective gravity while spinning.  As shown in Figure 5,  these levels of gravity will be less than lunar gravity.  Capture of solar energy for conversion to electricity will usually be intermittent,  at the spin rate.

These are design inconveniences,  to be sure.  But in comparison to losing occupants due to heart failure at high entry gee,  just minutes from returning to Earth,  these are minor inconveniences.  I am fond of reminding people that “there is nothing as expensive as a dead crew”. 

Update 4-19-18 landing stability etc:

Landing stability on Mars is associated with overturning issues,  landing pad penetration into soil,  and the perturbing dynamics of trying to land among rocks.  There are also issues with the jet blast flinging debris where it is not wanted,  although these only arise with subsequent ships landing near the first ship or any other structures or equipment already there. 

From an analysis standpoint,  there are static effects and dynamic effects.  From a mission standpoint,  there is a landing at low weight,  and a takeoff at high weight.  For the takeoff,  there are few,  if any dynamic effects to worry about.

Landing Statics

This topic divides into static overturn stability,  and the soil bearing pressure underneath the landing leg pads.  Static overturn stability simply requires that the weight vector fall within the polygon defined by the landing pads,  no matter how off-angle the ship sits,  such as on inclined ground.  As shown in Figure 6 below,  this isn’t much of an issue for inclinations oriented directly toward a pad,  as illustrated. 

The center of gravity position in the figure is only a guess,  but a realistic one.  The span pad-to-pad is only a guess,  but also a realistic one.  The ground could incline some 18 degrees directly toward a pad,  and still be stable,  as shown in the figure.   If the inclination is directly between two pads,  the lateral distance is 70% of the value shown,  for a max inclination angle of about 13 degrees.

13 degrees is a rather steep local slope on terrain chosen to be flat.  We can conclude that the otherwise tall BFR spaceship is at relatively lower risk of simple static overturn,  as long as small localized hazards like a pad coming down in a dry stream gully can be avoided.  That might be very challenging to satisfy in a robotic landing,  though.  Hopefully the available stroke in each landing leg exceeds the roughly 2 m shown in the figure.  That should take care of most of the localized roughness hazards.  Stroke rate capability should be comparable to ship speed just as it touches down.

At landing,  with the full 150 ton payload and 85 tons of inert,  the ship at “dry tanks” masses 235 metric tons.  If the landing is “perfect” and does not use any of the hover/redirect allowance built into the propellant budget,  there might still be something like 53 tons of propellant on board at touchdown,  bringing the as-landed mass to 288 tons as a maximum.  At Mars 0.384 gee,  the corresponding weight on the landing legs is 1084 KN. 

If evenly distributed among the 4 landing legs,  and if the total pad area is 10 sq.m as shown in the figure,  then the bearing pressure exerted upon the soil after landing is 108-109 KPa.  If all the propellant is used,  the bearing pressure is the lesser 88.5 KPa shown in the figure. 

The figure shows typical soil bearing pressure capabilities for two soils that might be like soils that could be encountered on the plains of Mars.  One is soft fine sand,  like many deserts with sand dunes on Earth,  capable of from 100-200 Kpa.  The other is more like desert hardpan on Earth,  with lots of gravel mixed into coarse sand and relatively-compacted:  some 380-480 KPa.  Excluding dynamic effects,  even the soft fine sand seems capable of supporting the low weight of the as-landed ship.

Landing Dynamics

If there is some inclination,  it will tend to throw some of the ship’s weight toward the downslope pad or pads.  Landing impact dynamics could possibly double the static forces on a short transient.  If we double the static bearing pressures,  this should typically “cover” the landing impact dynamics and any small inclination effects.  For a ship with residual propellants on board,  the doubled static bearing pressures are in the 220 KPa class. 

That rules out soft fine sand by considerable margin.  Any landing site must be desert hardpan or better in terms of soil bearing strength,  or else the landing pads had better total far more than 10 square meters of bearing area (something difficult to achieve).  Thus it would pay to select a landing site already visited by an earlier probe or rover,  whose visit could verify soil type and estimated strength. 

Once the equipment is in place to prepare hard-paved landing sites ahead of time,  this restriction loosens.

About the worst conceivable landing dynamics event is for one pad to touch down on a boulder,  and then slip off during the touchdown,  leaving the vehicle temporarily unsupported on that side.  If that happens to be downslope,  the vehicle will start to topple that way,  while the leg strokes to reach the actual surface. 

If one assumes a realistic 5 degree local slope down toward the pad that hits and slips off a 1 m boulder,  then for the max landed weight of 1084 KN (as calculated above),  a side force at the center of gravity of about 95 KN acts to topple the vehicle.  This is on an effective moment arm of 22 m,  using the surface as the coordinate reference.  That torque is 2090 KN-m = 2.09 million N-m.

Approximating the vehicle as a solid bar 48 m long of mass 288 metric tons,  its moment of inertia is roughly (1/12) m L^2 = 55.3 million kg-sq.m.  The resulting angular acceleration is something like 0.0378 rad/sq.sec or 2.16 deg/sq.sec. 

Ignoring the recovering stroke rate of the slipped leg,  the vehicle could rotate through about 5 degrees for that pad to actually strike the real surface.  Adding the inclination of 5 degrees,  that’s 10 degrees out-of-plumb,  within the 18 degree limit for one pad directly downslope,  and also within the limit for two pads downslope. 

Now,  in this transient as the slipped pad hit surface,  the vehicle is already moving,  and is going to take time to stop moving once the pad is on solid ground to resist.  Crudely speaking,  the time for the pad to strike the surface is near 2.15 sec,  and the ship will be moving at about 4.6 deg/s.  The pad support force has to stop this motion in its 1 remaining m of stroke. 

That pad force will be in the neighborhood of 279 KN,  just ratioed from the disturbing force by the ratio of moment arms,  and acting upon about 2.5 sq.m for one pad.  The vehicle will move another 5 degrees during this deceleration transient.

At the end of this transient,  the vehicle is about 15 degrees out-of-plumb,  dangerously close to the 18 degree limit directly toward 1 pad,  and beyond the 13 degree limit directly between two pads.  The bearing pressure under the pad exerting the restoring force is in the neighborhood of 112 KPa plus the allocated static weight pressure for the vehicle at rest (109 KPa):  a total near 221 KPa. 

From an inclination standpoint during this transient,  the vehicle is dangerously close to toppling over,  even if the soil is infinitely strong and hard.  If the soil resembles packed coarse sand with gravel,  it is theoretically strong enough to resist serious compaction under the pad exerting the restoring force,  but whatever compaction does occur allows the vehicle to incline just that much more.  If the soil resembles more soft fine sand in strength,  the restoring pad will inevitably dig in,  without being able to exert enough restoring force,  and so the vehicle will indeed topple over and be destroyed. 

The toppling risk is high if a pad strikes an obstruction of any significant size (in this example,  a boulder 1 m in dimension).  Things of this size are difficult to observe by remote sensing from orbit.  The risk situation is quite similar to the boulder field encountered during the Apollo 11 moon landing,  and requires a hover and redirect action away from the threat.

The BFR vehicle obviously needs some sort of “see-and-avoid” capability at touchdown.  This would be direct vision with a human pilot,  or something very sophisticated indeed built-in for a robotic landing.  If the vehicle were not so tall,  the moment arm of the disturbing force would not amplify the toppling effect so much.  That is why the Apollo LM and all the Mars landers have had a height/span ratio under 1.   That number is 3+ for this vehicle.

Figure 6 – Data to Support Statics and Dynamic Calculations

Takeoff Statics (Only)

At takeoff,  payload is reduced to 50 tons,  inert is the same 85 tons,  and the refilled propellant load is the maximum 1100 metric tons.  The vehicle mass at takeoff is then 1235 metric tons.  At Mars 0.384 gee,  the vehicle weight is near 4650 KN.  Evenly distributed onto a nominal total of 10 sq.m of pad area,  the exerted bearing pressure is 465 KPa.

The soil upon which it rests had better not be similar to fine soft sand,  or the landing legs will sink deeply into the soil as propellant is loaded. 

This could lead to landing leg damage as the ship launches,  or even prevent its launch,  given the high extraction forces trying to pull out deeply-embedded pads.  If the soil properties vary on a 5 m scale,  the legs could embed unevenly.  That could risk toppling over with propellants on board,  leading to a huge explosion.

If the soil resembles gravel embedded in packed coarse sand,  the static bearing pressure at launch falls within the range of soil bearing strengths,  before the safety factor of 2 is applied.  That means it is very likely that the pads will sink a bit into the soil,  although not likely enough to run the embedding risk.  If the soil properties vary on a 5 m scale,  this sink-in will be uneven,  adding to the vehicle inclination. 

Given those outcomes,  it would be wise to design larger pads on the landing legs,  or use more than the 4 legs depicted in the website presentations.   This size and shape of vehicle is more safely operated from a very level,  hard-paved pad,  or from level,  flat solid rock. 

I do recommend using the coarse sand/gravel soil strength as representative of the sand/rock mix we see on Mars.  The minimum Earthly strength of that material is about 380 KPa,  with around 480 KPa as the max strength.  I also recommend using at least a factor of 2 upon exerted pad pressures to model inclination and sudden-impact effects on landing.  Best practice would apply that to takeoff as well,  although perhaps a factor nearer 1.1 might be adequate. 

The landing leg and pad depictions on the website are very generic and lack detail.  I don’t believe this part of the vehicle has yet received much in the way of design attention.  I presumed 10 sq.m of pad area,  and it is really not enough.  This part of the design needs such attention,  as it will be difficult to incorporate 14+ sq.m of flat pad area on the ends of 4 landing legs,  and still stow these away successfully for hypersonic entry aerobrake events.  If circular,  that 14 sq.m of pad area corresponds to pads about 2.1 m in diameter.  Even my 10 sq.m analysis implies circular pads 1.8 m diameter.

Debris Flung By Jet Blast

The force exerted on the surface by the rocket streams as the vehicle touches down is just about equal to the engine thrust.  At landing on Mars,  this would be the vacuum thrust of two sea level Raptor engines.  This is about 3670 KN.  It would be exerted over an area on the ground comparable to the exit area of the engines,  or maybe a little more.  That would be something in the vicinity of 3 sq.m.  That effective average pressure is near 1220 KPa. 

That pressure is so far above the soil bearing strength,  even for coarse sand with gravel,  that the sand will get flung as a supersonic sandstorm,  and rocks of substantial size are going to get torn loose and flung with considerable force,  albeit at a rather low launch angle. 

For a 10 cm rock,  the cross section area is about 0.00785 sq.m.  The jet blast pressure acting on that area produces a force in the vicinity of 9.6 KN.  At specific gravity 2.5,  such a rock should mass something in the vicinity of 1.3 kg,  and on Mars would weigh something like 4.9N.  The force to weight ratio is huge at nearly 2000 to 1. 

Using impulse and momentum,  with a wild-guessed action time on the order of 0.01 sec,  the thrown velocity of this rock would be on the order of 75 m/s.  If the elevation angle were 10 degrees,  the range at which the rock comes down would be around 0.5 km.  These crude estimates could easily be too conservative. 

Loss of a Ship Leading to Explosion

If a ship should topple over and explode,  or crash and explode,  large debris will be flung with incredible force.  Based partly on half the speed of the military fragment impact tests,  the velocity of such debris might be in the vicinity of 1.2 km/s.  It will leave the scene at all elevation angles from zero to straight up.  In the low gravity on Mars, such debris flung at 45 degrees will travel over 350 km.

It will be almost impossible to protect from debris flung nearly vertically,  which will come down close to the site.  It would be possible to intercept the low-angle debris with an earthen embankment bulldozed around the landing pad.  That might protect neighboring ships on adjacent pads,  or base buildings erected nearby,  acting as a shadow shield.  Based on what I have seen published about the base to eventually be constructed with these BFR ships,  I don’t think this issue has yet been considered at all.  Yet,  such an explosion is inevitable over the long haul,  even if very rare. 

Conclusions and Recommendations

It is probably too late in the design process to adjust vehicle length and diameter to a shorter,  fatter proportion.  That means the landing pads must exceed about 14 sq.m total area in actual contact with the ground,  if my soil strength estimates have any reality at all.

I strongly recommend to Spacex that they start looking closely at these issues of landing and takeoff statics,  and the landing dynamics.  From what has been published so far,  I have to conclude that they have not addressed these particular issues in any detail,  yet. 

I would definitely,  and very strongly,  recommend that BFR landing sites be at least 1 km away (preferably 2+ km) from other grounded ships or any other structures or equipment,  to mitigate the flung rock hazard.  This would be true until such time as hard paved landing pads can be constructed.  “Hard” means materials with compressive and shear strengths both exceeding about 1500 KPa = 1.5 MPa.  Such will automatically satisfy needed bearing strength.

I would also recommend to Spacex that they begin considering the possible effects of a ship explosion upon adjacent ships,  base buildings,  and other nearby equipment.  Berms around hard-paved pads are highly recommended.  Such high-velocity debris will travel a long way in Mars’s low gravity,  and some of these pieces will be quite large.   Such events may actually be exceedingly rare,  but the results are unacceptably catastrophic,  no matter how rare.  Probability x cost is NOT the way to judge this.

Update 4-21-18 speculations on the tanker issue:

This update presents very speculative numbers I ran trying to understand the tanker vehicle issue.  This includes both the design of the tanker,  and how many are needed to fully refill a crewed BFR second stage vehicle in Earth orbit. 

Spacex presents on its website estimated weights data for the crewed vehicle,  and not for the cargo-only unmanned vehicle (or the tanker).  The implication is that the cargo vehicle overall characteristics are similar to the crewed vehicle.  There is no clue given as to the identity or characteristics of the tanker. 

It would make sense that the same engine section and propellant tank section would be used in both (or all three),  just with different forward section structures,  although with the same heat shield.  That is the “justification” for using the same inert weights,  propellant weights,  and payload weights for crewed and cargo vehicles in the original portion of this article.  In particular,  the inert weights are likely not to be the same,  although they are likely to be crudely similar.

Here in this update,  I extend that inert weight assumption to any potential third configuration that would serve as a dedicated tanker.  It would have additional tanks holding 150 tons of propellant mounted in the forward section,  and plumbed into the other tanks.  The other competing idea is to fly a crewed BFR unmanned,  or a cargo BFR,  but both with zero payload on board.  If fully loaded with propellant in the tanks,  either of these would arrive on orbit with considerable unused propellant beyond the landing budget (effectively the “tanker load”).

All the assumptions and engine performance data are the same as I already used in the original portion of this article.  The same basic mission analysis consideration applies:  hold enough propellant in reserve to land.  The difference here is that the landing is made with zero payload on board,  which reduces the necessary budget for landing propellant.  Plus,  no budgets need be maintained for long-term boiloff effects, or for deep space midcourse maneuvers.  Thus the reduced figure of 32.6 tons of landing propellant will suffice to land at zero payload,  even with factor 1.5 on the landing delta-vee to cover any “hover and redirect” effects. 

Similar to what I did in the original portion of the article,  we start with the landing to determine that landing propellant budget.  With all three designs sharing the same overall weight statement,  all three then share the same dry-tanks weight at landing,  and thus the same landing propellant budget.   Then we apply that reserve to each of the three tanker configuration candidates to determine how much deliverable propellant they can provide on orbit.  Assumptions are shown in Figure 7,  results in Figure 8.

 Figure 7 – Assumptions Made to Model the Tanker Problem Two Ways

Figure 8 – Results Obtained Modeling the Tanker Problem Two Ways

Applicable overall weight statements (metric tons) are:

                                crewed                 cargo                     ded. tanker
inert                      85                           85                           85 (#1)
payload                0 (#3)                    0 (#3)                    150 (#2)
b.o.                        85                           85                           235
propellant           1100                       1100                       1100
ign                          1185                       1185                       1335

#1. incl extra tanks
#2. payload is propellant
#3. capable of 150 tons, flown here at 0

The resulting as-flown weight statements are:

                                Crewed                cargo                     ded.tanker
Ign                          1185                       1185                       1335
Asc.prop              925.6                     925.6                     1042.8
b.o.                        259.4                     259.4                     292.2
less del.prop      141.8                     141.8                     174.6 (#1)
land.ign.               117.6                     117.6                     117.6
land.prop            32.6                        32.6                        32.6
b.o. (inert)          85                           85                           85

#1. 141.8 left in main tanks excl. landing prop.
#1. 24.6 left in main tanks excl. land.,  plus 150 in payload tanks

The “dedicated tanker” configuration with extra tanks holding 150 tons in the forward section is the most efficient tanker of the three candidates.  It takes 6.3 of these to completely refill a crewed BFR vehicle in low Earth orbit,  using that 150 tons plus the excess in the main tanks beyond the landing budget.  The downside of this design is a third configuration to account fir in manufacturing.  It wouldn’t take much design refinement to eliminate the “.3” and get to 6 tanker flights. The target is 183-184 tons delivered to low Earth orbit.  The design (as crude as it is) delivers 175.

Provided that the crewed and cargo vehicles share the same inert masses,  then if flown at zero payload,  they arrive with enough excess propellant in the main tanks beyond the landing budget,  to enable complete refilling of a crewed vehicle in low Earth orbit,  if flown some 7.8 times.  This approach is less efficient from a number of flights standpoint,  but allows the advantage of having to account for only two configurations in the manufacturing effort.  It is probably not possible to get enough design refinement to eliminate the “.8” and get to 7 tanker flights.  8 flights is likely realistic.

The “real” numbers are going to be different,  once revealed by Spacex,  because these configurations will not all share the same inert weight as was assumed here.  The “flown-at-zero-payload” potential is close enough to the “dedicated tanker” potential that perhaps Spacex should investigate this possibility closer,  before “freezing” the crewed and cargo designs,  in spite of the inefficiency of flying with such large volumes of empty space on board.

Note also in the results figure that gee loads have been held to very tolerable values with very simple choices of engines and throttle settings.  In particular,  the landing settings have been chosen to enable either a 1-engine or 2-engine touchdown from the very same point in the descent trajectory.  You plan on flying as 2-engine,  but if one fails to ignite,  you just immediately double the thrust setting on the remaining engine.  The throttle margins are there to support that.