Friday, January 15, 2016

Astronaut Facing Drowning Points Out Need for Better Space Suit

Note updates 1-29-16 in red below.

Astronauts Tim Peake and Tim Kopra were forced to cut short an EVA due to water leaking into Kopra’s helmet.  This is the very same suit worn by astronaut Parmitano in 2013,  who nearly drowned from a water leak into the helmet.  That suit was extensively refurbished after the 2013 incident,  but clearly there is still a risk associated with its water cooling system.

So,  do all spacesuits need water cooling systems?  No.  The fundamental job is providing a way for you to breathe,  and surprisingly enough,  that does not necessarily mean protecting you from exposure to vacuum.

As long as your heat is beating and your blood pressure hasn’t zeroed,  exposure to vacuum is not fatal and your blood does not boil.  Nothing “explodes” either.  Nor do you instantly freeze or fry,  something that takes longer than anoxia death in vacuum.  The various science fiction shows have lied to you. 

You will start to die within about 2 minutes or so of whole-body exposure to vacuum,  because of nothing more than anoxia,  since oxygen at zero pressure will not diffuse across your lung membranes into your blood. 

In point of fact,  the reverse diffusion of oxygen from your blood to the environment in vacuum is quite enhanced over what we normally experience down here on the surface of the Earth.  So anoxia sets-in quicker upon exposure to vacuum “out there”,  than it does by gross strangulation down here (usually about 4 minutes,  but it can take twice that long,  depending upon your initial blood oxygen levels). 

In experiments and accidents,  people and animals have survived whole-body exposure to vacuum for up to about 2 minutes.  And that’s a fact,  Jack!  This has been known since the 1960’s. 

What’s minimally required to survive in space is an oxygen supply at sufficient pressure to cause adequate diffusion of oxygen across the lung membranes into the blood.  Nothing more than that.  For most folks,  this is in the neighborhood of 2-3 psi pressure of pure oxygen,  or 2-3 psi “partial pressure” of oxygen in a more complicated atmosphere. 

Sea level air has just about 3 psi partial pressure of oxygen,  while air at 10,000 feet elevations has about 2.1 psi.  Some folks are adapted to 15,000,  even 20,000 foot elevations.   That last is about 1.4 psi partial pressure of oxygen.  That’s about the utter minimum for survivable breathing gas pressure,  even if pure oxygen.  But it is based on actual people living active lives at such conditions.

The most immediate idea that comes to mind is just to breathe oxygen at 2 to 3 psi pressure,  with a mask sealed tightly to your face.  This is called "pressure breathing".  
  
There is an immediate danger with "pressure breathing":  if oxygen pressure in the lungs exceeds about 2 psi without counterbalancing pressure within the body,  the lung tissues rupture in an event called "pneumo-thorax".  This is fatal and irreversible and immediate,  you drown in your own blood.  It is a well known risk among scuba divers.

There is a another complication that requires time:  counter-pressure must be exerted upon the body that is more-or-less equal to the breathing gas pressure,  or else those breathing gases will diffuse out of the blood into the spaces between cells in the body,  causing swelling,  disability,  even death.  We have known that since the late 1940’s.

It takes about 30 minutes for significant swelling to happen to a vacuum-exposed small body part like a hand or foot.  It happens much quicker (5-10 minutes) if the whole body is uncompressed while breathing oxygen at pressure.  We learned these figures by hard experience,  since the late 1940’s.  They are accurate. 

There is also a mitigating factor:  the body “does not care one whit” how this counterbalancing pressure is applied!  It can be the pressure of the gas within the current modern space pressure suit,  or it can be a mechanical “squeeze” exerted by other means,  as long as it is applied whole-body.  Pressure is pressure,  no matter how it is applied! 

Our cells are essentially little water balloons:  the pressure in them,  and between them,  goes up whether we put them inside a container at some gas pressure,  or if we simply grab them and physically squeeze them (like a water balloon) in our hands.  Doesn’t matter,  as long as it gets done.

Modern space suits are what we call “full pressure suits”,  which means they are literally gas-tight balloons whose internal gas pressure is the compression the body needs to counterbalance the breathing gas pressure.  These suits isolate you chemically and thermally from your environment;  one layer is quite literally a gas-impermeable rubber balloon.  

It is difficult at best to expel from such a suit the heat your body produces,  especially if you are active.  Your breath and your sweat fill your suit (and your helmet) with moisture,  thus fogging your visor.  There is also carbon dioxide to absorb.  We have fully understood this since the 1950’s at the very latest.  Our first efforts date to the 1930’s. 

The heat problem requires water-cooled underwear to carry your body heat to your backpack,  where some sort of “air conditioner” equipment expels that heat to space.  Likewise,  your breathing gas requires considerable regeneratable dessicant to get rid of the moisture load from your breath,  and more especially,  your body sweat (the larger of the two sources).    The carbon dioxide absorbent also needs to be regeneratable. 

Your makeup oxygen supply is not lightweight,  all by itself,  although makeup from a flask of liquid oxygen is the most efficient.  The combination of all this plus adequate insulation against hot and cold makes your suit,  and your life support backpack,  quite heavy.  It’s been like that since the 200+ pound Apollo moonsuit,  all through the space shuttle program (300+ pounds),  and is still like that on the international space station (ISS) today (close to 400 pounds). 

But,  what if you relied on mechanical-physical compression by a tight garment instead?  This was exactly how the early “partial pressure” suits worked,  and they worked quite well,  actually,  for 10-minute bailouts,  beginning in the late 1940’s.  Hands and feet were uncompressed,  and compression over the limbs and body was rather uneven,  but it worked for 10 minutes anyway. 

Such a compression garment need not hold gas pressure at all,  it can be entirely porous!  You can sweat right through it into vacuum,  which is actually more efficient cooling than here on Earth,  because of inherent moisture vaporization into vacuum.  So you need no mechanical cooling system at all,  and your moisture load is only breath,  not breath-plus-sweat.  Your life support backpack reduces to just the makeup oxygen,  plus minimal dessicant,  and the same carbon dioxide absorbent. 

You still need protection against hot and cold,  but this can be an over-garment.  It simply need not be part of your compression garment!  Think vacuum-protective underwear,  overlain by whatever insulation,  at whatever level you need,  for the job at hand. 

That gives you the freedom to dress in layers,  just like down here on Earth!  In point of fact,  you can use ordinary Earth garments for this insulation function.  Coveralls,  aprons,  coats,  pants,  shoes,  and gloves,  all exactly the same as we wear down here. 

Believe it or not,  this notion of vacuum-protective underwear (known as “mechanical counter-pressure” or “MCP”) was tested and somewhat-developed in the late 1960’s,  quite successfully,  by Dr. Paul Webb.  The compression garment,  breathing helmet,  and oxygen backpack that he tested totaled 85 pounds. In its final form,  the difficulty of breathing while wearing a very tight garment was eased by incorporating a breathing tidal-volume bag on the chest within a non-elastic restraining jacket,  instead of garment compression.

Add 5-15 lb of insulating garments,  gloves,  and boots,  and you are talking about a spacesuit that weighs around 100 pounds,  not the 300-400 pounds currently in use!  Plus,  it is a whole lot more dexterous:  you can bend sharply over,  climb ladders,  and crawl into small spaces,  something not at all possible with a “normal” modern spacesuit. If you fall over in a 400 pound full pressure suit,  it is likely you cannot get up on your feet again very effectively.  If there is no one close by,  you may lay there till you die.  That doesn't happen in a supple,  100-pound MCP suit.

This stuff worked long ago:  I have seen the 1968-vintage video of Dr. Webb’s test subject in a vacuum tank,  pedaling a bicycle ergonometer for half an hour,  and wearing nothing but 6-7 layers of tight pantyhose material and a breathing helmet.  The simulated altitude was 87,000 feet,  where even a pure oxygen atmosphere would still only be 0.293 psia.  If there were a problem with this approach,  it would have shown up in that half an hour:  no problems showed up! 

This test effort was partially-funded by NASA:  they have known that this alternative works for almost half a century.  Irrational attitudes and monied interests,  not actual facts,  prevent its application today.  Small amounts of grant money to Dr. Dava Newman at MIT have supported some work on this “MCP” suit concept,  but nothing at any of NASA’s favored spacesuit contractors.  Dr. Newman has since been hired by NASA,  but there is still no development effort for an MCP suit.  

Here's one more advantage of MCP over a standard full pressure suit.  If you puncture a full pressure suit,  and you cannot get inside before it deflates,  you are dead.  If you puncture an MCP suit,  nothing happens,  because the garment does not contain any gas under pressure at all.  If the hole is smaller than about 0.1 inch in size,  you may ignore it completely,  and just sew it up later.  If it's a bigger tear,  a tight wrap of duct tape will protect the exposed skin from localized vacuum damage until you can go inside and make repairs.  

This MCP suit is the dexterous,  easily-launderable spacesuit we have always dreamed of!  There is simply no excuse not to do this!  So what if it takes some time and effort to don such tight layers?  Further,  if you figure out some scheme to relax and apply the fabric tension “at will”,  even that objection goes away. 

And,  with MCP,  there is zero risk of drowning an astronaut,  because there is no water-cooled underwear!  Astronaut Kopra on the ISS is just the latest to face this lethal risk.  

Related articles on this site:

Date           title

11-17-14    Space Suit and Habitat Atmospheres

2-11-14      On-Orbit Repair and Assembly Facility
                  
1-21-11     Fundamental Design Criteria for Alternative Space Suit Approaches

Edits/updates:

1-16-16 two new lead-in paragraphs,  plus rewording of final paragraph,  plus new paragraph 9 about pneumo-thorax.

1-29-16  added information in multiple locations,  red text.



Monday, December 21, 2015

Facts Must Trump Politics


The matter of fact or fiction should be an objective decision.  Politics (or any other predilection) has nothing to do with whether something is factual or not.  This is something far too often ignored by politicians and appointed officials.   It is ignored by too many voters,  as well. 

Finger on the Nuclear Button

Anybody with their finger on the nuclear trigger button needs to base their decisions on real,  verifiable facts.  If they have a predilection for fictions instead of fact,  they are not qualified to hold that position.  Too much is stake to allow “convenient lies”,  or election-campaign “sound bites”,  or party agenda to substitute for rational and informed thought. 

Immigration

Anybody with decision-making authority about immigration needs to base their decisions on real,  verifiable facts.   It is simply too easy to discriminate arbitrarily if these decisions are made based on political fictions.   This evil usually takes the form of a scapegoat group to be blamed for all ills,  which is really how you recognize when you are being lied to.   The last notable example was Adolf Hitler,  who blamed Jews for everything wrong in Germany after World War 1.  And then he tried to kill them all.   And we all know how well that episode turned out. 

Safety Net Programs

Anybody making decisions about the social safety nets we choose to employ (such as Social Security and Medicare) needs to make those decisions upon verifiable facts.  To do otherwise is egregious discrimination against those who happen not to be so very wealthy.   Such discrimination is wrong,  no matter what form it takes.

Regulations on the Economy

Anyone making decisions about the regulations upon our economy needs to base their decisions upon verifiable fact,  including the historically-demonstrated fact that completely-unregulated capitalism has always degenerated into piracy and economic slavery.  It’s simply not a fair market if there are no rules to ensure fair play. 

Regulated to avoid these abuses,  capitalism then takes its rightful place as the most powerful engine of creation ever devised by man.  These are the “two-sides-of-the-same-coin” facts that should never be “trumped” by political ideologies.  From any party,  or any sub-group.

Climate Change

Anybody making decisions about what to do in response to climate change needs to base their decisions upon verifiable facts,  including the demonstrated reality of climate change,  regardless of who or what might be causing it.  Much more than just this year’s bottom lines for some giant corporations is involved with this issue. 

In General

Similar considerations apply to any issue one cares to raise.   Facts are key,  and what is fact is not a political decision. 

My message is this:  pay attention to fact-checking when political campaigns go on.  You will have to take off your political blinders and propaganda lenses to do this effectively.  Ditch the political belief systems.  Do not believe the propaganda.  Look only at what actually “is”.  Candidates who play fast and loose with facts are simply not qualified to make decisions about your lives.   Do not vote for them.

So few elected (or appointed) officials qualify today as people who deal in real facts.  That is why I have generally not voted “for” anyone in decades.  I generally vote instead only for the lesser of the evils available,  and evil they usually are,  because of the money that buys elections.  The common man cannot afford to run for office in our USA.  That has been true for about 200 years now,  and it desperately needs to be changed. 


If in doubt,  I vote “no” or “against”.  That policy has served me well.  

Update:  Specifics for Election Year 2016

Donald J. TrumpNO!!!!  Here’s why:  complete denial of facts on every issue listed above,  which means he is completely unqualified to be making decisions affecting the entire country.  His shifting and extreme positions are designed to create buzz,  not solutions.  Putin likes the idea of President Trump,  because it would be easy to push a publicity-hound clown around,  and with him,  the entire country.   Trump is unstable and extremist enough that I absolutely do not want his finger on the nuclear button! 

Ted CruzNO!!!!  Here’s why:  the not-Trump choice for the GOP is really just a Trump “mini-me”.  He has exactly the same problems with denial of facts and with extremist nonsense to create buzz,  not solutions.  Therefore,  he is similarly not qualified to be making decisions for the entire country.  He’s a tea party favorite (infamous for their “my way or the highway” approach to things that prevents effective governance),  and would govern for party advantage at the expense of the people (a real evil bordering upon treason during wartime).   He has already demonstrated this by orchestrating the government shutdown.  He is far too extremist to have his finger on the nuclear button. 

Marco Rubio – He might be acceptable as long he does not have a party majority in both houses of Congress to support him.  His approaches to many issues seem reasoned and reasonable.  But he’s awfully young:  I’d like to see him serve another term in the Senate before attempting the Presidency.   That is the problem we already just had with Obama (who also should have gained more experience in the Senate before becoming President).   I don’t know enough about him to trust that he will govern for the benefit of all,  and not just govern for party advantage at the expense of the people,  which is why I don’t want his party in control of both houses if he were President. 

Jeb Bush – Seems to be similar in many ways to Rubio,  plus he has real experience at governing that Rubio does not have.  I know enough about him to think that he would try to govern for the benefit of all,  and not just for party advantage,  but only so long as he surrounds himself with a diversity of advisors.  His brother (Bush 43) already made that mistake:  surrounded by nothing but neocons who wanted to wage war for oil,  that’s what “W” did.  Jeb is not “W”,  but the same risk is still there.  So I’d rather not see him supported by a party majority in both houses of Congress,  should he be elected.

Chris Christie – This one may be the best the Republicans have to offer,  by far.  He has experience governing,  he has the backbone to be forceful in foreign affairs,  and he has the wisdom to set aside party considerations and govern for the benefit of all (demonstrated during Hurricane Sandy).  I suspect he would make an acceptable president regardless of who controls Congress.   He might even be a good one.  I do hope the Republicans avoid the Trump vs “not-Trump” Cruz choice at their convention,  by drafting Christie. 

Hillary Clinton – She certainly has the experience in governance,  and she certainly has the backbone to deal with foreign affairs.  But she is demonstrably afflicted with a bad case of “shyster-lawyer” attitude:  (1) a predilection for lying,  and (2) a disregard for the rules.  This shows up as low rating for trust in the polls.  She was the brains and ambition behind Bill,  but does not have Bill’s grasp of doing right by the people (a sort of “noblesse oblige”).  I think she would not go off “half-cocked” on the nuclear button.  She might be acceptable as President,  but the shyster-lawyer effect will cause her to have scandal after scandal,  just as it always has since Bill was President.  So there are very definite and serious pluses and minuses with her. 

Bernie Sanders – I don’t yet know a lot about him.  He seems quite personable and reasonable,  just to hear him talk.  A self-described “democratic socialist”,  I’m not at all sure he is as far-left as he seems to many.  He’s probably only “left-center” for the New England region he comes from.  He does have experience in government,  and is demonstrably independent-of-party enough to trust that he would try to govern for the benefit of all of us.  Might actually be an acceptable President.  I think he would be trustable with the nuclear button. 

Republican Agenda – as a broad-brush generalization:  tax breaks that almost exclusively favor the rich,  justified by “trickle-down economics” (something tried since Reagan and it has never,  ever worked).  These tax breaks are a reward for campaign contributions from those same rich entities.  The Republicans talk a lot about reducing the size and expense of government,  but never actually do it.  They do tend to be stronger and more forceful as regards foreign affairs,  although this sometimes gets us into deep trouble (example:  recent neocon wars for oil in the middle east under Bush 43). 

Problem:  the Republican party is tearing itself apart without actually splitting.  The extremist right wing coalition (of tea party political extremists and extremist Christians) has the party hog-tied into a turn to the extreme right,  without actually being a majority within the party.  If the split were actually to happen,  neither group would have the following to be a factor in national politics,  which is precisely why they have not yet split.  Eventually,  they will,  or else the Republicans will eventually fade from national significance.  Most Americans have a distaste for extremism. 

Most of their social agenda (top issues:  overturning abortion and Obamacare) I vehemently disagree with:  I think Roe vs Wade better represents the majority of Americans,  and I have seen no concrete proposals to replace Obamacare.  They do support Second Amendment gun rights,  which I agree with. 

Democrat Agenda – I pretty much agree with their social agenda,  excepting increased gun control,  which I utterly abhor.  The party tends to adopt measures immediately,  with the promise to figure out how to fund it later,  which they never do (neither do the Republicans).  They do tend to believe in a larger,  more-activist government,  and the more left-leaning members are more willing to experiment with social engineering,  something I don’t think wise.  (Actually,  the far-right Republicans also want to experiment with social engineering,  just different in the details,  but just as unwise.) 

My own take on this is mixed:  there are things that only government can do,  and there are things that are better-supplied by our free market business communities.  Wisdom lies in knowing which is which,  a decision that should be objective and not political.  Government exists to provide those necessary things that business either cannot or will not supply.  Both parties have very serious failings regarding this.  The Democrats create more government offices and programs,  but (just like the Republicans) never act to eliminate them,  once they are no longer useful. 

The Democrats are stereotyped as “soft” on foreign affairs,  although FDR,  Harry Truman,  JFK,  LBJ,  and Barack Obama are all “exceptions”,  in my opinion.   (I include Obama because he has killed more people with drone attacks than George W. Bush ever even thought about.)  I really think this is more determined by individual personalities than it is by any sort of party agenda. 

I don’t like the way the Democrats (under LBJ) took the social security trust fund and made it part of the federal government general fund.  This is in large part why the social security program is now perceived as going broke.  This was done for political expedience,  and is only one example (among many) of why I think prioritizing party advantage above the good of all the people is tantamount to treason.

My hopes

I am not classifiable as either Republican or Democrat.  I am a “dyed-in-the-wool” independent.  I am an American,  first and foremost.  You might as well know that,  if you have not yet guessed. 

I hope the Democrats draft Joe Biden at their convention as the “not-Hillary” candidate who could actually win the election.  He is a decent,  thoughtful man,  with lots of direct relevant experience in government.  He could be a good President,  perhaps even a great one,  occasional “foot-in-mouth disease” notwithstanding.  He can be trusted with the nuclear button.  I think he can be trusted to prioritize serving all the people above party advantage. 

I hope the Republicans draft Chris Christie at their convention as the (1) not-Trump,  and (2) not Trump‘s “mini-me” (meaning Cruz) candidate.  Christie could actually win the election.  As described above,  I think he could be a good President.  Essentially,  these are the same reasons that underlie my opinion of Biden.

I don’t know anything about any of the other candidates not named above.  Accordingly,  my rule-of-thumb would be vote “against”.  I’m sorry if that offends,  but my policy of voting “no” or “against” when I don’t know,  has served me well for a very long time now. 

Best-case scenario:  the election is Biden versus Christie.  Either could serve well,  regardless of who controls the houses of Congress.  I would hope that both men have the wisdom to include the other man as a major figure in his government,  whichever man wins.  Nothing could be more healing of the division among Americans,  both symbolically,  and in a very real-and-practical sense. 

Worst-case scenario:  the election is Trump versus Hillary.  I’d have to vote for Hillary as the lesser of two considerable evils.  I think I can trust her finger on the nuclear button.  Trump,  I do not trust at all,  with the nuclear button. 

Update 2-9-16:  I see no reason to change any of these evaluations.  


Tuesday, December 15, 2015

"White Trash Christmas" 2015

This is the Christmas 2015 version of what has become our traditional Christmas yard display at the Johnson household.  We call it "White Trash Christmas".

The tree is something I built for the City of McGregor some years ago,  something I call the "Iron Christmas Tree".   The city doesn't use it anymore,  so we do.  It erects easily,  but knocks down to store in a very small space.  I made it out of rebar and all-thread rod,  plus some odds and ends for fittings.

The Santa-and-reindeer paraody is a cheap plastic Santa with a light inside,  using a wheelbarrow as his sleigh,  and a garbage bag in an old steel trash can as his bag of toys.  The reindeer team is a set of plastic lawn flamingoes with pipe-cleaner "antlers",  all lit up internally,  and all "hitched" to the "sleigh" with yellow caution tape.

You'll notice there are 10 flamingoes,  not eight.  The lone leader is "Rudolph",  followed by four pairs for eight,  all named as in the poem,  and a lone follower named "Bambi".  I haven't figured out yet how to give "Rudolph" a glowing red nose (beak).

This display has been our yard decoration since about 1997 or 1998.  It has taken multiple forms over the years,  but this seems to be the funniest.  I hope you like it as well as we do.



Thursday, November 26, 2015

Bounding Analysis: Single Stage to Orbit Spaceplane, Vertical Launch

The question at hand is:  how feasible is a single-stage spaceplane to orbit and back,  that has airliner-like characteristics in order to lower ticket costs for passengers,  or per-pound costs for cargo (or any other effectiveness criterion, including the difficulty and cost of military missions).  The notion behind this question is that until spaceships can be operated like airplanes,  costs of access to orbit will simply be too high to do anything but the most critical tasks there,  the ones for which cost is ignored. 

To answer the question at hand I did a little approximate bounding calculation.  I used the weight statement of a well-proven,  long-serving airliner as the weight statement for my spaceplane.  I assumed a vertical launch,  non-lifting ballistic fast ascent to minimize gravity and drag losses at about 10% of the orbital speed to be achieved.  (If you stay low at very high speed,  the drag losses can easily exceed 100%-300% of orbit speed.)  I also assumed on-orbit,  de-orbit,  and go-around-at-landing propulsion weights to be part of the inert weights on ascent (!!!!). 

Some may argue with my using the high inert weight fraction of the airliner for the spaceplane.  But I would remind them that if you want true airliner characteristics,  then the vehicle must be able serve for about half a century and about 40,000 landing/take-off cycles,  without a single major airframe rebuild.  That’s what airliners do,  and their airframes not subjected to the abusive loads that a spacecraft must endure.  We are talking about an aluminum airframe whose entire exterior must be protected by some sort of reusable heat shield (which must serve just as long without a rebuild).  The 5-10% inert fractions of rocket stages are just entirely inappropriate assumptions to make for a winged spaceplane. 

The analysis uses the rocket equation with a corrected delta-vee requirement.  I used 25,000 ft/sec as the velocity to be achieved (maybe 26,000 is better,  but so what?).  This is for a low Earth orbit eastward at no more than about 23 degrees inclination.  Orbital altitude might be around 100-300 statute miles. 

I used customary US units for this;  metric conversions for mass in lbm (usually the meaning of weights in lb) are 2.205 lbm = 1.0 kg.  Conversions for thrust:  1.0 lb = 4.45 Newtons.  Weight (mass) ratios and Isp,  sec need no conversion.  For lengths,  1.0 meter = 3.2808333 feet.  I did approximate the rocket exhaust velocity as Isp x standard acceleration of gravity.  1 statute mile = 1.609 km. 

The situation and aircraft data that I used are given in Figure 1.  The spaceplane specific impulse (Isp) requirements shown there are to be interpreted as an average for the entire ascent trajectory.  Note that the max cargo weight and max fuel capacity of the Boeing 747-100 airplane cannot both be had,  simultaneously.  The gross weight limitation restricts the sum of these to a fixed amount shown in the figure. 

I went ahead and used these limitations to figure my spaceplane at max payload and at max fuel load.  I solved the rocket equation for a given mass ratio and theoretical delta-vee,  for the exhaust velocity required to accomplish the mission,  and then converted that to a trajectory-averaged specific impulse (Isp) requirement.  At modest acceleration,  you leave the air at about Mach 2 / 130,000 feet conditions,  still near vertical.    The depression to horizontal and acceleration to high speed occurs exoatmospheric. 


There is a thrust greater than weight requirement for vertical takeoff that combines with a diameter limit,  into a frontal thrust density that must be equaled or exceeded in order to lift off.  Later in the trajectory,  because the ascent is still near-vertical,  thrust minus drag and that same diameter combine so that the same frontal net force density must still be exceeded in order to continue climbing.  Those estimates are also given in the figure.  

 Figure 1 – The Data Used for the Bounding Analysis

I did not even try to estimate drag data.  But,  on a frontal cross section area basis (not wing planform area !!!!),  it would be very hard indeed to imagine any shape with a drag coefficient averaging less than 0.4 across the speed range from launch to atmospheric exit at around Mach 2-ish.  Drag is a very significant force,  especially around Mach 0.9 to 1.3 (transonic).  At Mach 1 and 45,000 ft conditions,  that would be 5000-6000 lb of drag at the very least,  even without considering that in the real world very few drag coefficients would be under 1.2 (not 0.4) at Mach 1 speeds.  The drag could easily be 3-4 times larger than those numbers. 

It is very important to understand that there are both specific impulse and frontal thrust density requirements that simultaneously must be met,  in order to achieve results in this scenario.  These have to be met on a trajectory that begins at zero speed,  vertical,  at sea level,  and that leaves the sensible atmosphere at about Mach 2 (2000 ft/sec),  still near-vertical,  at around 130,000 feet or so. 

                Trajectory averaged Isp, sec                       
                >1469/min payload         
                >4002/max payload

                Launch frontal thrust density, psf             
                >3900/min payload         
                >3900/max payload

                M=1 @ 45 kft net force density, psf         
                >3900/min payload         
                >3900/max payload

So,  what are the possible propulsion concepts,  and what are their characteristics,  as expressed in these terms?  For my bounding calculation,  I looked at technologies we actually have,  and at technologies we don’t actually have,  but which we could actually develop.  That excludes “Star Trek” warp and impulse drives,  and other similar things,  for which there exists no science.  The list is:

                Chemical rocket propulsion (as demonstrated,  not theoretical things which proved impossible)
                Nuclear-thermal rocket propulsion (including both solid and gas core concepts)
                Chemical airbreathers (ramjet,  gas turbine,  and scramjet)
                Nuclear airbreathers (nuclear scramjet)
                Nuclear pulse (explosion) propulsion (included with the rocket data as “rocket-like”)

Figure 2 contains the typical characteristics of three common chemical rocket systems,  the projected characteristics of multiple nuclear thermal rocket concepts as best we know them,  and the typical characteristics quoted for nuclear pulse propulsion as it was proposed circa 1959 during Project Orion.  There are all the rocket reaction propulsion concepts that we have,  aside from the extremely low-thrust electric concepts,  which are clearly not candidates for this application. 

The chemical rocket systems have the thrust density to take off vertically and accelerate upward,  but they lack the required specific impulse capability by a very large margin.  The one nuclear thermal rocket for which we have real test data likely cannot meet the thrust density requirement to take off and climb due to its low engine thrust/weight ratio,  plus,  it lacks the specific impulse capability to meet the needs of the low payload fraction case.

The gas core nuclear thermal rocket concepts are exactly that:  concepts.  None has ever been built and tested.  So the data are just best guesses.   These concepts very likely have much better engine thrust/weight ratios,  so that frontal thrust density requirements might be met,  as long as no waste heat radiator is required.   The closed-cycle gas core “nuclear light bulb” engine comes close to meeting specific impulse requirements with a clean exhaust for the low payload fraction case.  The open-cycle gas core engine definitely satisfies the impulse for the low payload fraction case,  but has a radioactive exhaust plume.  None meet requirements for the high payload fraction case,  for which the economics would be more feasible. 

Only nuclear pulse propulsion meets the impulse requirements and the frontal thrust density requirements,  and for both cases:  low and high payload fraction.  There are two very serious downsides:  the vehicle must be very large (over 5000 tons at launch,  preferably over 10,000 tons),  and the “exhaust stream” is quite literally a series of nuclear explosions in the atmosphere,  starting with a surface burst.  Not only is there radiation released,  there is a very destructive EMP.

 Figure 2 – Characteristics of Rocket and Pulse Propulsion Systems

Therefore,  of the rocket and rocket-like concepts,  only the “nuclear lightbulb” engine might possibly serve,  and then only if the weight statement can be adjusted to make 1300 sec Isp feasible.  This will be a difficult design to do,  without a lot of margin,  and with a reduced payload fraction that makes the economics more difficult.  Such a weight statement might be ascent inerts 0.40,  ascent propellant 0.50,  and payload 0.10,  remembering that “ascent inerts” includes on-orbit,  de-orbit,  and landing go-around propulsion that is not the nuclear ascent engine. 

The airbreathers are summarized in Figure 3.  At first glance,  the Isp’s of the ramjet and the gas turbines looks attractive,  but upon further inspection the frontal thrust densities are clearly not feasible.  Further,  the impulses are only attractive in a narrow band of speeds.  Variable inlets do not change this.

The ramjet depicted is a supersonic design with a minimum operating Mach number of 2,  which happens just as the vertically-launched spaceplane is leaving the sensible atmosphere somewhere above 100,000 feet.  A subsonic design that could ignite somewhere around Mach 0.7 and burn to about Mach 2-2.5 usefully,  but would have about half to two-thirds the listed impulse capability,  which renders it infeasible.  At altitude,  the frontal thrust densities are also completely infeasible,  unless these were staged-off strap-ons very much larger than the spaceplane’s fuselage.  It is staging we are trying to get away from here! 

Neither gas turbine design has the frontal thrust density to take off vertically at all,  so this kind of propulsion would also have to be gigantic strap-ons that get staged off.  Not feasible by definition. 

The basic message here seems to be that the airbreathers are very probably not very useful for vertically-launched fast ascent trajectories if no staging is allowable.  They might well be useful for a horizontal-takeoff,  depressed-trajectory design,  at the cost of enormous drag losses.  But that is a different scenario!

Figure 3 – Characteristics of Existing Airbreather Systems (Ramjet and Gas Turbine)

A nuclear ramjet is no better:  although its effective specific impulses are higher (you need to look at air specific impulse instead of fuel specific impulse to compare fairly,  the fuel air ratio embodied in the chemical ramjet data is .074),  the frontal thrust density is no better than the chemical ramjet.  It may well be worse due to the impact of a very heavy core on engine sizing.  Plus,  its exhaust stream is intensely radioactive,  based upon the Project Pluto nuclear ramjet ground tests decades ago. 

The best-guess estimates for scramjet characteristics are given in Figure 4.  These are impulse and frontal thrust densities similar to ramjet,  but achieved only at Mach numbers larger than 4,  the utter-minimum takeover speed.  These Mach numbers are simply incompatible with the vertical launch scenario.  The impulses look marginally-attractive in a narrow range of speeds,  but the frontal thrust densities at stratospheric altitudes are infeasible.  Going nuclear does not help the fundamental incompatibility  of a very high-speed airbreather on this trajectory.  Where the vehicle reaches these speeds,  there is no air!

Figure 4 – Guessed Data for Supersonic-Combustion Ramjet (Scramjet) Systems (Chemical and Nuclear)

So,  there are only two known propulsion concepts that could support a vertically-launched single stage spaceplane with operating characteristics of an airliner.  One is the “nuclear light bulb” version of the gas core nuclear thermal rocket,  which likely could support payload fractions around 5-10%,  if it actually existed,  which it does not.  What that really says is that this “nuclear light bulb” engine ought to be a major development priority.  It is not. 

The other is nuclear pulse propulsion,  which would only work in vehicle sizes far beyond anything ever before constructed,  and at the social cost of uncontained nuclear explosions in the atmosphere.  The EMP is probably actually more dangerous than the radioactivity,  but the radioactivity will be the political killer of this idea. 


So that leaves only the “nuclear light bulb” as a feasible propulsion for this kind of spaceplane.  But for vertically-launched fast ascent,  this looks to be entirely feasible.  Which means that its mythical engine should be a high-priority development.  

The only other approach to a single stage spaceplane to orbit would be a horizontally-launched craft with a depressed trajectory to make airbreathers feasible for a small portion of the ascent,  trading their impulse advantage against the enormous drag losses of flying fast down in the atmosphere.  The last program to attempt that approach was X-30,  which failed.  (It is very difficult to do realistic estimates for that kind of trajectory,  unlike this scenario.)  

PS:  The ramjet data were obtained with my latest version of the high-speed range cycle codes for sizing and performance.  

Tuesday, November 17, 2015

Why Air Is Hot When You Fly Fast

This article is for readers who are not trained in high speed compressible aerothermodynamics,  but who wish to understand why air friction and capture processes make air so very hot when you fly very fast through it.  The article explains why there is no such thing as cooling air,  once you have busted Mach to any significant amount.  

Captured Air (Scooped-Up by Any Sort of Inlet,  Including Cooling Air Inlets)

In order to do anything with atmospheric air inside a flight vehicle,  you have to scoop it up,  and decelerate it relative to yourself.  The air has a certain internal energy associated with its temperature,  plus some pressure energy associated with its ambient pressure.  Lumped together,  these are the air’s “enthalpy”,  the energy of its existence at those conditions. 

From your point of view inside the vehicle,  the air,  which has that certain enthalpy,  is also moving toward you very fast,  which is a kinetic energy.  Looked at from the air’s point of view,  it has to pick up an enormous speed in order to come aboard your vehicle.  Either way,  it is the same increment of kinetic energy. 

You add the kinetic energy change to the original enthalpy,  and that is the new enthalpy of the captured air at rest aboard your vehicle.  This enthalpy translates directly into a temperature measurement at the pressure conditions aboard your vehicle,  which are quite often different that in the ambient atmosphere.  What happens here is conservation of energy.  

Because of these changes in pressure,  it is more convenient to figure things directly from enthalpy,  symbolized as h in most textbooks on thermodynamics:

                h = m Cp T  (defined this simply only for absolute temperature)

where m is the mass,  Cp is the specific heat at constant pressure,  and T is the static (thermodynamic) temperature.  The energy that is conserved is the enthalpy h:

                h(ambient) + KE = h(on board)

where KE is the kinetic energy of the air 0.5 m V2,  and V is the absolute velocity of the vehicle.  If the velocity of the air once it is on-board is zero relative to the vehicle,  then its calculated temperature is maximum,  which we call the “total” or “stagnation” temperature.

If the air is still in motion aboard the vehicle at some velocity v,  then it still has some kinetic energy as measured on-board:

                KE(on board) = 0.5 m v2

Which must be subtracted from the on-board h in order to calculate the actual thermodynamic (“static”) air temperature.  That is why static temperature is always less than total temperature:  some of the energy that could have been enthalpy is still kinetic energy instead. 

Hot Boundary Layer Adjacent to Vehicle Skin

This phenomenon works by dissipation (waste) of energy,  instead of conservation of energy.  It is only readily apparent once vehicle flight speeds exceed transonic.  It has increasing effect very rapidly as supersonic speeds increase.  The effect is quite dominant in the hypersonic speed range. 

Understanding this effect requires the same “book-keeping” of static versus total temperature as before,  plus another calculated temperature called the “recovery temperature”.  This is an empirical concept that correlates how viscous dissipation converts KE to waste heat in the intense fluid shear zone that is a boundary layer adjacent to a flight vehicle’s lateral skin.  Yet the recovery temperature is an item that actually does physically exist,  and can be measured within that boundary layer. 

The difference between static temperature T and total temperature Tt is a measure of the air’s kinetic energy,  as already discussed above.  This increment represents the maximum possible energy that could be dissipated by viscous friction in the boundary layer.  Not all of it is wasted (although most of it is),  which is why recovery temperatures fall between static and total temperatures.

How much energy gets dissipated,  showing up as recovery temperature,  depends upon whether flow is laminar or turbulent.  For vehicles of ordinary size,  such flow is nearly always turbulent,  for reasons beyond scope here.

The correlation depends upon a property of the air called Prandtl number,  which for air is in the vicinity of 0.7.  The recovery factor applied to the total-minus-static temperature difference in the correlation for turbulent flow is the cube root of the Prandtl number (square root if laminar).  

Recovery temperatures Tr are the adjusted difference added to the static value.  These are very close to total temperatures,  the recovery factor being about 89% in turbulent flow.

The high-velocity dissipative boundary layer concept is shown in Figure 1What drives heat transfer to or from the skin is not the difference between skin and ambient temperatures,  but the difference between the skin and the (much higher) recovery temperature. 

I have plotted in Figures 2, 3, and 4 recovery (Tr) and total (Tt) temperatures vs flight Mach number at 3 different altitudes for a particular model of the atmosphere.  The ambient air static temperature T is different at each altitude.  Figure 5 shows how T varies with altitude in that model atmosphere (the US 1962 Standard Day model,  extended to the edge of space).  

The higher the ambient static temperature,  the higher the trend of Tr and Tt,  compared at the same flight Mach number.  Yet it is flight Mach number that dominates,  regardless.  If you are scooping cooling air,  and that air must be below boiling water temperatures to do its job,  then there is no such thing as cooling air for you at speeds between Mach 1.2 and 2,  regardless of which figure you examine.  Because the ambient static temperatures are the same,  the 110,000 ft data in Figure 4 looks just like data for 28,000 feet.  

If you look at the Tr or Tt data in the vicinity of Mach 6 in any of these figures,  you see temperatures in the vicinity of 3000 deg F.  For reference,  the meltpoint of iron and steel is 2935 F.  That,  more than anything else,  is why hypersonic flight is so very difficult.  

I apologize to readers who prefer metric units,  because these plots are not in metric units.  Here is the conversion information for you:

Deg F     the normal Fahrenheit non-metric temperature scale (corresponds to deg C in metric)
Deg R    the absolute Rankine non-metric temperature scale (corresponds to deg K in metric)
F and R use same size degree but different zero points,  0 R is absolute zero = -459.67 F

C and K use same size degree but different zero points,  0 K is absolute zero = -273.15 C
Deg K = deg R/1.8
Deg C = (deg F - 32)/1.8

Figure 1 -- Boundary Layer in High-Speed Flow

Figure 2 -- Temperatures vs Mach at Sea Level
Figure 3 -- Temperatures vs Mach in the Stratosphere

Figure 4 -- Temperatures vs Mach at Very High Flight Altitude

Figure 5 -- Temperatures vs Altitude in the Standard Day Model



Wednesday, October 7, 2015

Oregon Mass Shooting and Gun Control

Update 12-3-2015:  

I still see absolutely nothing to change any of my views.  Please also see the yellow-highlighted text in the original posting below.  It is the fact set that supports my contention that stricter gun control is utter nonsense.

The shooter at the Planned Parenthood clinic in Colorado has turned out to be a locally-known nutcase who was never judged insane by a court.  Hence,  he could legally own and buy guns.  The way we choose to "keep guns out of the hands of the insane" is therefore so very clearly wrong.  Change that,  and most of this last year's mass shooting incidents go away.  But you MUST do something different about the way you keep guns out of the hands of crazy people!!!  Face facts!!!

The most recent attack in San Bernadino seems to be turning out to be a self-radicalized local citizen and his wife here on a "fiance visa".  It doesn't actually matter what sets them off,  once they believe in a radical creed which teaches that one must kill outsiders for God.  That simply isn't God they are listening to,  and until such teachings are eliminated from our midst,  we will always have this problem.  The problem is NOT the guns,  it IS the radical creeds.  All religions have them,  not just Islam,  although Islam is the source of our biggest radical creed problem in recent years.

The Planned Parenthood center in Colorado,  the government facility in San Bernadino,  and all the others we have witnessed (Newtown,  Gabby Giffords,  Columbine,  all of them),  were gun-free zones attacked by someone with a motive that made some sort of sense to them.  Every single one of these was effectively undefended,  a sitting-duck target.  THAT is why each was selected for attack by their respective perpetrators,  regardless of detailed motive.

This derives from a lesson that many Americans learned the hard way in the 19th century,  but is also a lesson so very clearly completely forgotten today.  There are perfectly-good reasons to have gun-free zones.  But,  once you create one,  you are obligated to defend it (the part which is so completely forgotten today).  The criterion for defending a gun-free zone that worked acceptably well in 19th century frontier America was very simple:   having an armed peace officer responding within 60 seconds,  no longer.  Period.  End of issue.

Fix THAT,  and you will greatly-reduce this wave of mass shootings in America.  Dealing properly with keeping guns out of the hands of crazy people will reduce it further.  But,  you will NOT stop them ALL,  until you completely eliminate all radical evil creeds from the entire world.   Yep,  the entire world!!!  Religious,  political,  makes no difference.  Evil creeds do evil.  Simple as that.

And,  by the way,  fearing Syrian refugees is nonsense.  No matter how effective or ineffective the refugee vetting process has been,  the fact is that not one refugee has caused a terrorist or mass shooting incident here.  All of our perpetrators have been either domestic citizens or persons here on some kind of visa.  That ought to tell you where the worst "leaks" requiring "fixes" really are.  Everything claimed otherwise is nothing but election-year political BS.

Update 11-16-2015:  I have seen nothing to change any of these opinions or conclusions.

Original Posting:

Yet another mass shooting (this one at a community college on Oregon) prompts yet again calls for stricter gun control laws.  That’s the “usual response”,  and it is wrong.  Here’s why….

If stricter gun control laws were actually successful at reducing violence,  then Chicago and Washington DC would be the safest cities in America in which to live,  precisely because they have the strictest gun control laws.  They are actually the most violent cities in America by the statistics,  and by far. 

So,  clearly,  this approach is wrong,  it does not work.  QED.  Get over it! 

Look a bit deeper than the customary knee-jerk reaction,  for something that might actually work,  and try that instead!  To keep trying something again and again,  that does not bring about what you want,  is a pretty good operational definition of insanity.  Just how insane are you,  my neighbors?

This means that you look for what might actually be causing the problem,  and do something about that,  instead.  You will not find it by listening to knee jerk reactions and political sound bites. 

You might try history instead,  but you’ll have to be read between the lines to find any truth in history.  It’s written only by the winners/survivors. 

If you look at mass shooting incidents over the last several years,  there are really only two common threads.  And that’s a good place to start.  (1) With one exception,  every one of these incidents is an example of people known to have mental problems getting guns legally.  (2) Without exception,  every single one of these was a gun-free zone that was not adequately defended. 

The exception to (1) was the Newtown school incident,  where the perpetrator obtained his guns illegally.  He killed his mother,  so he could get access to her guns,  otherwise locked up beyond his reach.  That right there ought to tell you something! 

Current laws are based on a federal standard that is essentially an “on-off switch” with too high a bar.  To be prevented from obtaining guns,  a crazy person must be judged crazy by a judge in a court of law.  Otherwise,  he may buy the gun legally,  and the seller has no grounds not to sell it to him.  Period. 

That’s demonstrably the wrong standard.  It was written that way to make things easy and convenient for lawyers and judges.  Yet it quite demonstrably kills people.  The people who sold “xxx” the gun with which he shot congresswoman Gabby Giffords were uncomfortable selling him a gun,  but they had no choice.  That is a matter of public record. 

It is simply outside my expertise to give you practical details,  but I do suggest a staged,  multi-step approach to this.  If a seller is uncomfortable,  that should spark a deeper investigation by local law enforcement than just a review of existing paperwork on file.  Family,  friends,  and colleagues should be questioned about just how well we can trust “xxx” to behave responsibly with his weapons. 

As for item (2) defense of a gun free zone,  we have the example of the 19th century American frontier.  There are perfectly-good reasons to establish gun-free zones,  well-known since long before that time.  It actually works quite well to reduce violence,  if done correctly.  Not done correctly,  this approach demonstrably does not work.

There are two items,  completely forgotten today,  that are required to do a gun-free zone correctly.  (1) An easy way to comply by checking your weapons with local law enforcement when you enter the gun-free zone,  with easy retrieval when you leave.  (2) Timely defense of the gun-free zone (extremely crucial).  Of the two,  (2) is more important,  but both are actually crucial to success.  

The history of the 19th century American frontier confirms this assessment,  if and only if you look very closely at it. 

Today,  we completely ignore item (1),  and force people who are armed to leave their guns at home,  or (more damaging to us all),  in their cars.  Guns left in cars are targets for criminals who steal them and use them to commit violent crimes.  Period.  End of issue.  Not to mention terrorists. 

We have known this since the 19th century.  That’s why back then,  you checked your guns with the local sheriff/town marshal/constable (pick a name) when you entered town.  You knew they would be safe in his custody.  And you knew you could drop by his office and pick them up easily when you left town.  This stopped a huge proportion of the drunken-cowboy gunfights in saloons. 

Item (2) is more arguable today.  Back then,  a town was a physically-small thing around 2,  or at most 3,  modern city blocks in dimension.  An armed deputy could arrive anywhere in town within about 60 seconds,  at a dog trot. 

This standard of response time actually worked quite well.  It did not prevent every problem,   but it did prevent the vast majority of them.  That’s the real truth of our history. 

There’s absolutely nothing in any of the accounts to suggest that anything is any different today.  In point of fact,  the longer the response time,  the worse the typical outcome.  5 minutes is too long.  20+ minutes is way too long.  Period.

Now,  the mistake made at every mass shooting site in the last several years is not defending the gun-free zone adequately (essentially a 60-second response).    

In Oregon,  they not only declined to have an armed officer on site,  they declined to have an unarmed officer on site (all this is a matter of public record).  Just how stupid is that?

So,  what do you defend your gun-free zone with?  I suggest that only folks with actual peace officer training qualify.  You are quite literally counting on whoever might be armed to do a peace officer’s job. 

The holder of a concealed-carry permit might be trained in what he can and cannot do with his firearm,  but HE HAS NOT BEEN TRAINED TO BE A PEACE OFFICERThere’s quite a difference. 


What that says is that Donald Trump is wrong when he says the faculty should have been armed at the community college in Oregon.  It takes a real peace officer to defend a gun-free zone,  just like it did in the 19th century American  frontier.