Thursday, July 30, 2015

New Cactus Tool Website

If you need to clear cactus from farm or ranch pastures,  please read on.  There is a new website for a mechanical method using a tool I developed.

Used properly,  it literally kills the prickly pear,  eradicating it permanently,  without pickup-and-disposal,  without chemicals,  and without disturbing the grass.  And your effort is reduced to driving your tractor around.  The end result is far better than any of the chemical or mechanical control methods that I have ever found.

This new site is something my son and I have been working on,  to greatly expand the cactus tool business I have operated for over a decade now.  Since I am retiring,  I can devote more time and effort to building and selling these very simple and effective tools.  Most people find it hard to believe how effective this approach is;  I could hardly believe it myself when I accidentally discovered how to do this.  But it is true:  this is really effective,  and without so much onerous work.

The new site is now operational as “”.  It is a turnkey site designed specifically for online browsing,  information-gathering,  customization of your tool with options,  and secure purchasing.  Prices and options posted there supersede all others published elsewhere.  The information posted there will allow you to evaluate for yourself the relative economics of chemical sprays versus the purchase of a well-proven mechanical eradication tool. 

There are two basic tool models:  the plain tool and the hydraulic tool.  Each comes with multiple options,  and each is equally durable.  The plain tool has no moving parts,  and is less expensive because it is simpler.  The hydraulic tool has hydraulically-operated transport wheels that enable it to “step over” the occasional bale of debris under the tool,  without manual clearing of that debris.  It is more complicated and expensive,  but is more capable of saving the owner time and effort.

The new site is jam-packed with text,  picture,  and video-clip information.  Go visit it and learn how you can clear your farm or ranch pastureland of prickly-pear cactus,  permanently. 


Sunday, June 28, 2015

Loss of Falcon-9 Launch to ISS

Observation and Condolences

The Sunday morning launch of a Falcon-9 / Dragon spacecraft supply mission to the ISS ended abruptly in an explosion a couple of minutes after launch.  My condolences to Spacex over this,  and may God speed their efforts to find out what caused this,  and to fix it. 

We will need them flying again,  sooner rather than later,  to send supplies to the ISS,  and later,  to send astronauts there.  With both them and Orbital ATK “down” with vehicle explosions,  the only other way to send supplies is via the Russian Soyuz / Progress cargo vehicle,  which itself has had a fatal problem just a few months back.

The ISS crew has sufficient supplies through to October.  After that,  they would be forced to abandon and come home in the emergency Soyuz craft docked to the station.  Somebody has to be flying and make a successful trip by then.   We really do need all three outfits up-and-flying. 

Suggestions and Recommendations

If I were them,  I'd be looking real hard at propellant leaks in the second stage.  Early at lower altitude I saw signs of propellant flash-burning erratically alongside the rear end of the first stage.  Then I saw flashes of white "cloud" moving down the side of the vehicle coming from the interstage. 

The higher the altitude and thinner the air,  the more of this leaking "something" I saw.  When the explosion occurred,  I saw "for sure" in the video that the first stage was still intact with all engines firing,  for a finite amount of time.  It was the second stage that exploded first. 

That suggests to me that something reactive was leaking from the second stage into the interstage volume around that engine.  You need that protected space to have a fume buildup that can be ignited.  They were approaching the staging point,  and systems were firing up electrically to make that happen.  Electricity and loose propellants are an explosive combination. 

It couldn't have been just kerosene,  there's almost no air up there with which it could burn. You can see that by the first stage rocket plumes ballooning out in the nearly-zero backpressure. 

It had to be both kerosene and liquid oxygen that were leaking!  Holes in both tanks cannot be ruled out,  but that seems most unlikely.  Especially as there is no internal path to get leakage from the forward tank into that interstage. 

I'd be looking very,  very seriously at the propellant line stop valves to the turbopumps (or even the engine chamber itself) that might have opened prematurely somehow. 

UPDATE 7-23-15

Elon Musk recently said the best of their thinking is that a strut internal to the second stage LOX tank failed,  releasing a container of helium pressurant,  which leaked,  causing the tank to overpressurize and burst within seconds.  His message said they use lots of these internal struts.  This one seems to have failed at 5 times lower force that it is rated to carry,  according to Musk.   

They'll have to figure that one out,  for sure.   If the failure of one small part can be catastrophic,  then some sort of redundancy seems to be called for.  At least somebody should be looking at that issue.  

The other issue is what they (Spacex) seem to be focused upon:  how to prevent installation of  low-strength parts.  This is very important:  the environment is extreme.  LOX is very cold,  a temperature at which all materials behave in a brittle fashion.  Plus,  rocket vehicles inherently suffer vibration.  Vibration + brittleness is a recipe for bad outcomes in flight vehicles.


Saturday, June 13, 2015


I first wrote this little commentary in July 2006,  in response to questions from friends and colleagues,  regarding the Airbus crash in NYC,  where the vertical fin came off under hard rudder application during climb-out from takeoff.  I used to send it by email as a small file.

This topic of properly joining composite structures to metal (or to other composite structures) with fasteners,  just keeps coming up,  again and again.  I have noticed that a lot of outfits still fail to do this job properly.  So,  I thought I would put this article up for interested persons to use.  Knowing the truth might save a life.

Original 12 July 2006 article ----

Here is how we used to build composite rocket motor cases with pinned closures at the old McGregor rocket plant (see Figure 1,  where the "shims" are thin sheet steel stock).  Weight was at a premium,  as was reliability.  We used these for up to 5-inch diameter motors up to 4000 psi maximum expected operating pressure with wall thicknesses away from the joint under 0.10 inch.  We even used these externally un-insulated in situations with Mach 5 aero-heating by friction.  (Typically,  these had around 0.1 inches of rubber insulation on the inside to hold the 5000-6000 F fire away from the carbon-epoxy that degraded at about 300 F.)  None of our pinned joints ever failed.

    Figure 1 -- Pinned Joint in Composite Rocket Motor Cases

This (Figure 2) is typical of general industry practice joining composite (or plastic) to metal.  This concept has long been used in automotive and consumer products,  because it is cheap.  It has also long been known to be very failure-prone.  The idea is to try to spread the loads for lower stresses with a big washer,  but it never really works that way.  It always starts at a single point on each washer,  unzips around it,  then unzips from washer to washer.

   Figure 2 - Typical Industry Practice,  Subject to "Unzip" Failure

The recent (as of 2006) fatal crash in NYC of an Airbus airliner operated by American Airlines,  with a composite vertical fin,  points out the need to do this joint correctly.  It is necessary that there be some sort of metal attachment fittings for a bolted joint.  These fittings would be “glassed-in” or otherwise made part of the composite fin structure. 

Such reports as are given to the public do not indicate exactly how this was done in the Airbus design.  That design must lie somewhere between the extremes (“good” vs “bad”) pictured above. 

However,  reports do indicate that these attachment fittings tore out of the composite fin structure,  and were found still bolted securely to the fuselage,  sans fin.  Reports also indicate that one of the pilots applied full rudder deflection to correct an upset at low altitude climb-out conditions. 

The ability to use rudder,  aileron,  or elevator controls at full deflection,  anywhere in the flight envelope,  without fear of losing tail surfaces,  has been taken for granted in American aircraft design practice since the early days of commercial travel.  (This stricture does not apply to wings,  of course.)

Reports since the crash tell of a dispute between Airbus,  American Airlines,  and the pilots’ union over who was supposed to tell the pilots they could not use full rudder deflection during climb-out,  and whether or not they were even told at all by anyone.  This is proof of the foreign design not meeting generally accepted US expectations.  It thus may not strictly meet FAR Part 25,  either:  a reciprocity issue needing swift resolution.

The attachments tore out under side load to the fin.  These conditions put tension on the interface between the composite structure and the attachment fittings somewhere.  That it failed,  and that it needs an unusual flight restriction,  together are proof that the attachment design had insufficient means of spreading a tensile attachment force into the composite structure of the fin.  Thus it is probably not the right joint design.

The right way to attach a composite fin to a metal fuselage is pictured below (Figure 3).  This is an adaptation of the well-proven layered interface used in the rocket motor pinned closure joint.  The key criteria are (1) provide adequate adhesive shear area to spread the tensile (and compressive and shear) loads into the composite structure by shear,  and (2) size the members and the adhesive bond areas to take full deflection forces everywhere in the expected flight envelope,  and a little beyond it,   for safety.

   Figure 3 - Correct Way to Join Composite Structure to Other Structure with Fasteners

Saturday, April 11, 2015

Radiation Risks for Mars Trip

I used NASA’s own data and criteria,  obtained as they published it,  on the internet.  There are two types to worry about:  (1) galactic cosmic radiation (GCR),  and (2) major solar flare events (SFE).  These data (and shielding material effectiveness data) are available in both text and graphical form at,  in an article titled “Space Travel Radiation Risks”,  dated 5-2-12.  There is a by-date navigation tool on the left side of the website page. 

Update 4-12-15 in the conclusions section below.

The NASA data were obtained from, titled Spaceflight Radiation Health Program at JSC  

Update 4-15-15 in the conclusions below.

The Nature of the Problem

GCR is a slow but varying drizzle of really high energy particles for which ready-to-use shielding technologies are relatively ineffective.  If you have too much passive shielding material,  the secondary particle shower effects can negate the value of your shield. 

The Van Allen belts provide shielding for much of this,  which is why astronauts in low Earth orbit have relatively little risk.  Earth’s atmosphere is a really good shield,  so that GCR contributes only a little to the natural background for people on the surface. 

When the sun is most active,  GCR is minimized at around 25 REM per year (“roentgen equivalent man”,  a unit of measure that also factors in the different damage caused by the different types of radiation).  When the sun is quiet,  GCR maximizes at around 60 REM per year.  This varies with the sunspot cycle.  Figures are for Earth’s vicinity in the solar system,  which should not be drastically different at Mars. 

GCR,  REM/year = 42.5 + 17.5 sin (2 π (t, yr) / T)  where T = 11 years approximately,  but it does vary

SFE are relatively random in occurrence and strength.  Between 1968 and 1971,  several events occurred,  all under 100 REM accumulated over the course of a few hours.  Very large events occurred in February 1956,  November 1960,  and August 1972,  that last being between the Apollo 16 and 17 missions to the moon.  That 1972 event accumulated about 3400 REM over the course of several hours,  far beyond a lethal dose for an unprotected person. 

Allowable Doses

Lethal doses start at about 500 REM whole body over a short interval (hours to days).  Allowable exposures are far lower.  Different figures are published for skin,  eye,  and 5 cm inside the body.  The 5 cm deep exposures are the smallest allowable,  and thus the most conservative to use. 

The other issue to consider is timing:  how quickly does the dose accumulate?  NASA uses a short-term 30 day basis,  an annual (1-year) basis,  and a career limit (accumulated over multiple years).  The career limits depend upon age and gender.  These are for astronauts,  and are higher than for civilians on the ground.  They correspond to an estimated 3% higher incidence of cancer late in life,  compared to ordinary civilians. 

30 day short term NASA limit (5 cm)  =  25 REM whole body
Annual (1 year) NASA limit (5 cm)      =  50 REM whole body
Career limit for males: 200 + 7.5(age – 30)  REM; 400 REM max at estimated age 57
Career limit for females: 200 + 7.5(age – 38)  REM; 400 REM max at estimated age 65

Mars Trip Exposures

With the kinds of spacecraft we can build at this time in history,  a trip to Mars will be 6 to 8.5 months one-way,  with about a year or more at the planet waiting for the orbits to be “right” for a return.  The trip home is also 6 to 8.5 months one way.  That’s a 2 to 3 year mission.  For comparison,  missions to the moon were at most 2 weeks. 

Mars has a very thin atmosphere.  Even so,  it is a fairly effective shield against the radiation threats.  Protection varies a lot with thicker or thinner Martian “air” from place to place,  but it does cut the threat by at least half.  So,  that year or so spent at Mars,  could be at most half-exposure,  if spent on the surface.  If spent in orbit,  the exposure there is full space exposure:  Mars has no analog to the Van Allen belts that help shield Earth.  For very low orbits,  there is a shielding effect from the presence of the adjacent planet,  but to be conservative,  I neglect that effect. 

For my figures here,  I assume two transits at 8.5 months each,  and 13 months at Mars,  half of it in orbit,  half on the surface (two alternating surface crews for visits lasting a week to a month).  That’s a 2.5 year (30 month) mission.  That should be a reasonably realistic,  yet very conservative,  exposure estimate.  I will further assume GCR to be the maximum 60 REM per year,  and I will assume one lethal SFE,  and two 100-REM SFE’s,  all spaced months apart. 

The lethal SFE absolutely requires me to provide a radiation shelter of some kind,  but most of the time,  I assume my astronauts are outside of it.  I do assume they take shelter for any SFE,  not just the lethal ones. 

The first year’s exposure to GCR is 8.5 months full exposure,  plus 3.5 months at reduced exposure,  accounting for time on the surface.  The second year’s exposure is 9.5 months at reduced exposure accounting for surface time,  plus 2.5 months exposure at full in-space strength to start the voyage home.  The third year is just 6 months’ in-space exposure during the voyage home. 

I assumed one SFE in each exposure year.  There are two minor events each at 100 REM accumulated (unshielded),  plus one major event at 3400 REM (unshielded,  comparable to the August 1972 event).  It is the major event that we have to worry about from a shielding standpoint,  and it could happen in any of the three exposure years.  So I looked at all three possible cases. 

Shielding Data

The NASA data that I obtained addresses two scenarios:  (1) thicknesses of aluminum,  water,  and liquid hydrogen required to reduce exposure to GCR,  and (2) mass per unit area of aluminum required to attenuate the three largest known SFE events (which includes the August 1972 event,  the largest of all).  One can convert mass per unit area (g/cm2) of shielding to its thickness (cm) by dividing by the density (g/cm3). 

Looking at NASA’s GCR shielding effects data,  it is easy to see that the best shielding agent is liquid hydrogen,   with aluminum the worst of the three.  Their other plot shows 15 g/cm2 aluminum provides attenuation of the three large SFE events down to about 25 REM,  for shield knockdown factor of 0.0074 and an aluminum thickness of about 5.5 cm.  About 50 g/cm2 (18.5 cm) aluminum knocks the dose from the August 1972 event down to around 2.5 REM,  a 10-fold improvement. 

You can also see from the GCR shielding data that the thickness of water that is required is around 80% or less than the thickness of aluminum required,  for the same effect.  I used 80% as conservative.  The plots say that for 60 REM/year GCR,  that to hit 50 REM/year,  you need 7-8 cm aluminum,  4-5 cm water,  or about 2 cm liquid hydrogen.  The same curves say that 15 cm aluminum knocks 60 REM down to 42 REM,  that 15 cm water knocks it down to 33 REM,  and that 15 cm liquid hydrogen knocks it down to 14 REM.  And,  1 cm aluminum knocks 60 REM down to about 59 REM,  1 cm water knocks it down to 56 REM,  and 1 cm liquid hydrogen knocks it down to 50 REM. 

I’d rather use water supplies,  wastewater awaiting treatment,  and water-bearing foodstuffs as the shielding material.  Aluminum is likely to be there in shell structures of thin sheet,  not plates several cm thick,  in any practical vehicle design.  I rather doubt the wisdom of having liquid hydrogen in close proximity to the crew.  So,  water it is. 

I’d recommend placing the shielding around the flight control station,  so that maneuvers can be made even if an SFE hits at the time the maneuver is required.  If that’s not enough radiation shielding,  the next priority is shielding around the sleeping quarters. 

Mission Accumulation Calculations – Flight Control Station as Radiation Shelter

I assumed no shielding effects for GCR,  other than time spent on the surface at half exposure.  I went to 50 g/cm2 aluminum equivalent (as 15 cm water) to reduce some serious violations of NASA’s annual limit of 50 REM.  This assumes no shielding about the sleeping quarters.  Here is what I found,  dependent upon which year gets the major SFE:

Maj SFE ....year 1...year 2...year
1st ..............58..........48..........30........136

In all three cases,  year 1 exceeds the nominal annual maximum of 50 REM by some margin.  If the major SFE hits during year 2,  that year also exceeds the standard by a trivial amount.  The worst exposure for year 1 is the case with the major SFE hitting during year 1.  Yet,  with 15 cm of water shield available,  we do not exceed the limit by a huge amount.  This does indicate that we should place shielding around the sleeping quarters,  which is one third of the day cycle while in space. 

None of the individual months come close to the 25 REM in one month limit,  at this level of shielding (15 cm water equivalent to 50 g/cm2 aluminum).  If we were to reduce the shielding to 15 g/cm2 aluminum equivalent,  we would violate the monthly limit in that month when the major SFE occurs.  So we really do need the thicker shielding. 

The mission totals are actually rather modest,  at 136 REM no matter when the major SFE occurs.  Using NASA’s equations and the assumptions of astronauts who are 25 years old (min credible) to 50 years old (more typical),  I get the following career limit accumulated REM:

 Male......age 25...age 30...age 40...age 50
 Female..age 25...age 30...age 40...age 50

It is fairly clear that females should be older than 30 to make this trip.  Younger astronauts up to about age 30-something if male,  40-something female,  should not make this trip but once,  without violating career exposure,  as long as the accumulations prior to the trip are negligible.  Older astronauts might make this trip twice,  if prior accumulations were near zero. 

Mission Accumulation Calculations – Flight Control Station and Sleeping Quarters as Radiation Shelter

What I assumed for this comes direct from NASA’s data for GCR shielding effects.  At 15 cm water shield thickness,  their curves say 60 REM per year is reduced to 33 REM per year.  If we put that 15 cm of water around the sleeping quarters in addition to the flight control station,  then (1) we have more SFE shelter space available,  and (2) we reduce GCR exposure by the time spent sleeping,  while in space.  I applied this to transits,  but not to time spent in Mars orbit,  just to be conservative.  I also used 8 hours out of every 24 spent in sleeping quarters. 

Major SFE....year 1...year 2...year

That brings the annual exposures into compliance with the 50 REM limit,  unless the major SFE occurs in the first year,  and then the deviation is rather small.  Remember,  my numbers are conservative!  It is fairly likely that the 52 REM that I show in year 1 for a year-1 major SFE is really under the 50 REM limit. 

Note also that the lower mission accumulation makes it feasible to fly female astronauts as young as about age 27.  And,  the age beyond which two such trips become feasible is now very clearly 30-something male,  and 40-something female. 


For the sake of safety-of-flight,  I’d say we must shield the flight control station so that critical maneuvers may be flown no matter the solar weather.  But adding shielding to the sleeping quarters to reduce GCR exposure in peak years makes a big difference to annual and mission accumulations.  I would very strenuously recommend shielding both zones!

Note that in min GCR years,  this entire radiation exposure question becomes far less relevant (25 REM per year GCR versus 60 REM/year).  In max GCR years,  the toughest issues are yearly exposure limits,  and the monthly limit for the month in which the major SFE occurs.  Only young female astronauts run into career limit exposures for one such flight.  Older astronauts could make two flights without violating career limits.  

Mission durations to the main asteroid belt would likely be around twice these Mars mission durations.  With the flight control plus sleeping quarters shielding recommended here,  it seems likely that older astronauts could make a main belt trip without violating any radiation exposure limits.  I have not investigated that to be sure,  though. 

Finally, these numbers show that radiation exposure is not a credible excuse for not sending men to Mars,  even in a peak GCR year.  The shielding requirements to stay within exposure limits are actually rather modest at 15 cm water thickness equivalent around only two zones in the vehicle. 

Update 4-15-15:  my own recommendation would be to use a bit more water shielding at 20 cm thickness,  not just 15.  That lets even very young females make the trip safely,  and all astronauts with low career accumulations could make such a trip twice.  A reminder:  water,  wastewater,  and non-freeze dried foodstuffs all qualify as "water shielding".  Use them all.  

But without it,  you will likely violate the limits from GCR exposure (a dead certainty in a peak GCR year),  and you will very likely kill a crew from exposure to an SFE event.

There is nothing as expensive as a dead crew. 

Update 4-12-15:

These calculations really provide an upper bound,  because of the mission architecture assumed,  not just the conservative assumptions made.  That architecture is an orbit-based mission sending down alternating crews to the surface at multiple sites.  Spending all the time at Mars on the surface reduces mission radiation-exposure accumulations still further,  because of the shielding effects of the Martian atmosphere.  There also is "wiggle-room" in year 3 exposures to handle longer trips.  

Calculation Details

These follow in the images of 6 spreadsheet pages.  I did sheets for shielding only the flight control station with major SFE in years 3,  2,  and 1;  and for shielding both the flight control deck and the sleeping quarters,  with major SFE in years 3,  2,and 1.  These are given in Figures 1 through 6. 

 Figure 1 – Shield Only Flight Control Station,  Major SFE in Year 3

 Figure 2 – Shield Only Flight Control Station,  Major SFE in Year 2

 Figure 3 – Shield Only Flight Control Station,  Major SFE in Year 1

 Figure 4 – Shield Flight Control Station and Sleeping Quarters,  Major SFE in Year 3

 Figure 5 – Shield Flight Control Station and Sleeping Quarters,  Major SFE in Year 2

Figure 6 – Shield Flight Control Station and Sleeping Quarters,  Major SFE in Year 1

Saturday, January 17, 2015

Stagnation In Space?

Has anybody noticed that NASA has sent men nowhere off-world to explore,  in over 4 decades?  NASA is about much more than manned spaceflight,  but that is its “front-burner” mission,  its reason-for-being,  and has been,  since it was created in 1958. 

NASA was originally formed to put man in orbit,  and carry out science and aeronautics,  too.  But the “prime show” or “front-burner project” was manned spaceflight.  3 years later,  that mission got upgraded to the far more demanding man-on-the-moon,  which really energized the little agency.

In those days,  NASA was rather small,  very heavy on engineering talent,  had a definite front-burner mission,  money was no object,  and no one told them how to do their jobs.  They got to figure that all out themselves.  And,  miss-steps notwithstanding,  it worked quite well.  It was only 8 years from assigning the moon-as-mission to the agency,  until two men first walked there. 

It might have taken perhaps 5 extra years to do this,  had budgets been a problem,  but that basic approach of assigning the mission and then “stand back and let them do it” works really well either way. 

In those days,  there were dozens of prime contractors to let contracts to,  competitively.  Cost-plus is quite appropriate when doing things never before done.  Fixed-price would have been egregious mismanagement.  

All that changed in the middle of the moon landings in 1972 (there should have been missions through Apollo 22,  not 17),  when Apollo got cancelled early and all manned flight outside Earth orbit forbidden by presidential order.  NASA has never had a front-burner mission,  an agency reason-to-be,  ever since.  They have only had major projects mandated upon them mostly by Congress,  with some from the various presidents.  Projects like Space Shuttle,  like ISS,  like X-30,  like X-33,  etc. 

Science and aeronautics are still small-time background,  but by dint of the successes of the probes (which derives mostly from being left alone by Congress),  the planetary probe program kind-of falls in-between,  in that spectrum.  Some of these projects,  like the Mars landers and Hubble,  turn out to be quite popular with the public,  too popular to kill,  even though Congress often tries. 

Two of these mandated projects flew men in space (Shuttle and ISS),  the rest didn’t.  There were some tests (like X-43A) that never led anywhere.  But,  none of these were actually managed in an overall sense by the agency.  Instead,  the project,  its detailed objectives,  how it would be done,  and where things would be built (by that I mean in whose districts) were all mandated by Congress.  That’s exactly what Constellation was,  and what its resurrected form Orion/SLS is.  There is no one in Congress at all competent to do any of this work,  which is precisely why their mandated project plans are so egregiously ineffective and nonsensical. 

Meanwhile the agency has grown to enormous size,  trying to be “everything to everybody” in lieu of a front-burner mission / reason-to-be.  Once an organization gets too large,  it gets very inefficient,  worrying more about preserving departments,  people,  and budgets than actually doing anything real anymore.  NASA is no exception.  There’s more managers and support functions at NASA these days than there are real engineers.  That’s not a good recipe to get anything major,  actually done.  Not in industry,  not in government. 

When you add bureaucratic inertia to mandated-but-nonsensical-projects to be done,  you have what we see now:  no man has flown beyond Earth orbit,  or explored anything off-world,  in person,  since 1972.  And with the mandated projects they have to do sopping-up most of the available money,  we’re having a hard time not spending trillions just to go back to moon,   the same moon that we visited over 4 decades ago!  None of the stuff they are doing now (with the serious money) can take a crew to Mars alive,  much less land there. 

I’m talking about Orion/SLS as a “Mars rocket”,  of course.   The PR about that is nothing but lies.  And everybody who knows much at all about these things knows it.  Most within the agency are too afraid to “tell the emperor that he has no clothes”,  though.  And as an agency,  NASA is afraid to tell Congress that it,  too,  has no clothes. 

Meanwhile,  Congress and the various presidents have let the available contractors "consolidate" into a monopoly supplier.  With only a monopoly available,  the distinction between fixed price and cost plus is functionally irrelevant.  With only a monopoly available,  the incentive to actually do something never done before is greatly reduced.  Recently,  upstarts like Spacex have attempted to break these monopolies,  but with limited success.  This basic situation is not NASA's fault,  but their rules are rigged to favor the monopoly.  

There are small groups within NASA that are working on the right kinds of things for men to go beyond Earth orbit again.  But these are not funded with any serious money.  Some of these groups are better managed than others.  Some of these groups have better talent than others.  So,  their ideas and plans vary considerably in practicality and feasibility.  That should not be unexpected,  given the situation.  But until these things get the money and attention to perfect them,  they will take no one anywhere.  That,  you can count on.

And in conclusion,  that complicated description is fundamentally why what is funded seriously at NASA often makes no sense.  A lot of you may have noticed that,  or at least know that something is wrong.  Nothing about that situation will change,  until the operating model for NASA-as-an-agency goes back to that 1958 version.  They need a front burner mission as a reason-to-be,  and they need to be left alone to accomplish it.  Period. That mission has been known for at least 2 centuries:  Mars.   

Unfortunately,  Congress craves ever-more control,  not less.  Ergo,  no change is forseeable.  So,  no Mars.

Thursday, January 8, 2015

Kactus Kicker Development

This article recounting progress with Kactus Kicker models is the latest among a series of earlier articles posted on this website.  That list is as follows (the date is highlighted on this one).  Watch for an update to this article giving links to a new website dedicated to these tools. 

Updates 7-30-15 in red below.

1-8-15……Kactus Kicker Development
………………production prototype & 1st production article
1-8-14……Kactus Kicker: Recent Progress
…………..….testing a revised wheeled design (experimental)
10-12-13..Construction of the Tool
………………building a “Kactus Kicker” (plain tool)
5-9-13…….Loading Steel Safely
……………….transport and storage of materials
12-19-12…Using the Cactus Tool or Tools
…………… the tool is employed (applies to any model)
11-1-12….About the Kactus Kicker
..…………….painting and rigging finished tools (plain tool)
12-28-11..Latest Production Version
………………new bigger snout and barge front (plain tool)

General Background

A little over 10 years ago,  I accidentally figured out how to permanently kill prickly pear cactus out of farm and ranch pastures.  I built myself an experimental tool and a couple of early production prototypes,  and I started building and selling these things to people who need them.  I have done this ever since then,  and steadily improved the design of the tools. 

My good friend Dave Gross of Oglesby,  Texas,  was impressed enough with this tool to want to do cactus eradication for hire as a service.  He’s retired now,  but for over the decade that he did this,  we built him a series of heavy-duty tools,  to which we added transport wheels.  His “commercial” tool became the genesis of the hydraulic tool I now offer in addition to the plain tool.  What I had to address was supplying the same strength and utility,  but with greatly-improved producibility. 

Recent History

The second article in the list above (Kactus Kicker:  Recent Progress,  1-8-14) describes my work up through last winter on an experimental wheeled prototype,  including field testing.  That experimental prototype proved to need some design changes,  beyond just the narrow stance corrected to wide stance as described in an update to that earlier article.  The towbar option I put on it wasn’t very good,  for one thing.  The wheelbarrow wheels I used weren’t tough enough,  for another. 

But,  that experience led to a real production prototype,  which is insignificantly different from the actual production models.  I did add rain drain holes to both (and to the production hydraulic design).  From that production prototype result,  I revised my experimental prototype to the production configuration,  except for its hydraulic pressure rating and its wheels.  Both are shown in Figure 1.

Figure 1 – Experimental Prototype (near) and Production Prototype (far) Hydraulic Tools

Figure 2 shows a close-up of the production prototype from its right side.  The longer hydraulic snout has 3 plates instead of two as on the plain tool.  On the plain tool,  one is a mini-“barge front” for wedging over obstructions,  the other is the ground-contact “slider”.  On the hydraulic tool,  two slider plates are needed,  mounted at slight angles.  One is for cactus-killing with the wheels raised,  the other (in the middle) is for smooth sliding with the wheels down for transport or “stepping-over” obstructions. 

This prototype is fitted with the optional towbar hitch,  providing a standard trailer-ball hook-up for faster transport across the pasture behind the tractor.  This is not intended for towing while killing cactus,  because the forces are too high,  and the leading edge gap under the tool deck is too large to efficiently break up plants.  The real advantage of the towbar hitch option is being able to back the tool up,  something not possible when towing only on the chain.  

The hitch tongue extends by sliding,  and is secured with a hitch pin in either position.  The upside-down cross-mounted channel is a jack point,  with which one uses the hydraulic bottle jack (resting on the tool deck).  This raises the trailer hitch up over the ball for connection and disconnection.  I supply the bottle jack with the towbar option.  It outlives most crank-type trailer jacks. 

The towbar hitch is an option,  because the tool can be transported on its wheels sliding on the snout plate,  simply towing with the tow chain bridle.  Transport speed is a little slower this way,  but still faster than towing the tool with the wheels up.  Things bounce when you tow too fast,  in any case.

 Figure 2 – Close-Up of Production Prototype Showing Hydraulic Snout and Towbar Option

Figures 3 and 4 show the production prototype hitched-up for chain tow to kill cactus.  The big triangular tow chain bridle flips over any trailer ball or tow hook on the drawbar assembly of any tractor.  Figure 3 shows the wheels-up/tool-down-on-the-ground configuration for killing prickly pear cactus.  Like the plain tool,  at the recommended tow speed of no more than 3 mph,  tow loads are usually around half a ton,  for a drawbar horsepower figure in the 10-12 HP range (8-10 for the lighter plain tool).  The left side chain helps guide and support the hydraulic hoses that extend forward to the tractor.  

You can see the cross-chain that runs from one side to the other,  through the snout assembly.  This cross chain helps limit pitching motions on rough ground,  but more importantly,  it forms the lift sling.  If you pull the tow chains together over the cylinder and deck behind the snout,  the two tow chains form two legs of a 3-way sling to pick up the tool.  The cross chain forms the third leg of that 3-way sling,  holding up the snout. 

One single bolt (which I supply) is all that is needed to pin the chains together to form this lift sling.  With it,  the hydraulic digging bucket (that most modern tractors have) can be used to pick the tool up and set it anywhere you want,  such as on a flatbed farm trailer. 

The center chain is a safety chain,  exactly like that on a trailer.  It will take tow tension if your tow bridle should break,  preventing the hoses from being damaged.  The tool tows unstably from its snout,  so you will notice if this happens.  This gives you time to stop and make a minor repair instead of a major one.

 Figure 3 – Production Prototype Hitched Up for Chain Tow,  Wheels-Up for Killing Cactus

In Figure 4,  the tool has been raised by putting its wheels down.  You can see how it now rests on the center snout slider plate,  instead of the aft one.  That way,  the snout does not “dig into” the dirt and damage your pasture.  This is what you do (1) to transport the tool from one place to another in the pasture,  (2) to “step-over” obstructions,  or (3) to “step off of” debris bales that sometimes form underneath the tool deck. 

The “barge front” on the hydraulic tool is exactly the same as the one on the plain tool.  It will wedge either tool over any obstructions (like outcrops or small stumps) that are shorter in height than the barge front top edge:  6 inches maxAnything taller than that,  you must go around

You are towing on a chain with no “give” to it.  If you hang up on something solid,  a piece of steel somewhere is going to break,  faster than you can be aware that it is happening.  I tried to make that the easily-fixed chain,  but there can be no guarantees about that;  every place’s hazards are different.  

 Figure 4 – Production Prototype Hitched-Up for Chain Tow,  Wheels-Down for “Step-Overs”

In Figure 5,  the production prototype hydraulic tool is in the foreground at my shop,  and two production plain tools in the background,  tipped on edge for storage.  As can be seen by close inspection,  these two versions share exactly the same deck,  crush rail,  ballast bar,  and barge front.  The plain tool has a slightly-shorter two-plate snout.  You can’t really tell from the photos,  but both versions use exactly the same chain towers,  skids,  and snout attachment brackets now.  I have discontinued the older brackets made of angle stock,  in favor of triangular flat-plate brackets with shear tabs.  These are just as strong,  and far more producible. 

Plain tools readily store tipped-up like that.  You should support them for safety,  with a 26 inch piece of any size angle iron,  under one of the skids.  This does require a stout 6-foot prybar.  It is also how you clear debris bales from underneath the plain tool.  

 Figure 5 – Production Prototype Hydraulic Tool with Two Plain Tools at My Shop

The Production Hydraulic Version of the Tool

Actual production hydraulic tools differ very little from production prototype pictured here.  I did change the angle slightly between the two snout slider plates,  as it was “close” but not quite right on the prototype.  I have since built jigs for assembling plain and hydraulic snouts rapidly,  and in exactly the right geometry,  every time.  

The cross-over valve in the deck-mounted hydraulic plumbing is backwards on the production prototype.  In the closed position,  its handle points forward,  vulnerable to hanging-up in low-hanging brush.  In Figure 6,  you can see the production prototype in the foreground,  and the first production hydraulic tool in the background.  The yellow valve handles point in opposite directions,  as you can see.  The correct installation is on the first production article.  That way,  the handle points rearward with the valve closed.

The weight of the wheels when raised,  or the weight of the tool standing on its wheels,  acts to pressurize the main hydraulic hoses.  You relieve this by opening the cross-over valve,  so that the hoses may be connected or disconnected.  When you store the tool,  with the valve open,  the wheels rest freely upon the ground behind the tool.  Coil the hoses on the deck.  

 Figure 6 – Hydraulic Tools:  Production Prototype (near) and First Production Article (far)

Also in Figure 6,  you can see an old cat litter bucket on the deck of the production prototype.  I use this to store my bottle jack,  its handle,  spare hydraulic fittings,  and any tools,  out of the weather.  I have taken to spray-painting these plastic buckets to extend their useful life in this kind of service (sunlight destroys plastics).  A “cheapie” storage bucket like this turns out to be a really handy item.

The rain drain holes do tend to get clogged with pasture debris.  One of the “tools” I keep in my storage bucket is an old nail,  perfect for clearing those drain holes.  Otherwise,  rain water puddles-up on the deck behind the barge front. 

The two main hydraulic hoses are manufactured with half-inch male pipe thread connections.  My “stock” fittings are Pioneer 4000-series quick-disconnects,  but John Deere fittings are also available (same idea as the Pioneer,  but a tapered geometry instead of straight).  I keep some plugged-up male fittings in my storage bucket along with some rags or paper towels.  I keep the fittings cleaned with the towels,  and the female fittings plugged with those extra plugged-up male fittings,  as dust covers.  It’s a very practical solution.  I use a universal hydraulic oil that is compatible with both John Deere and everybody else.  It takes about 3-quarts-to-a-gallon to fill a tool and its hoses. 

The hydraulic cylinder was carefully chosen,  and its installation geometry carefully designed,  so that no physical stops were needed in the hydraulic wheel assembly,  and so that any tractor hydraulic system,  even antique low-pressure ones,  could power the wheels. 

The motion stops are the inherent stroke limits of the cylinder itself,  so the wheel assembly sees no end-of-travel overloads,  in either direction.  The cylinder stroke and wheel structure gives me 100 degrees of wheel strut rotation.  This allows a 10-degree “up-sweep” of the raised wheels,  providing much better clearance going over rough ground and obstructions. 

The maximum hydraulic pressure that this system is rated for is 2500 psig.  All the components are good for that or slightly higher.  However,  the cylinder size is such that it will work acceptably well even at only 300 psig.  My antique Farmall-H had a one-way hydraulic system that I converted to two-way with a log-splitter valve and a return line down the oil fill pipe.  At low rpm it operates at about 300-400 psig,  and at higher rpm near 600-800 psig.  These tools work just fine with it.  I see more influence of lower pump flow rate at low rpm than I do pressure. 

Items Now Available For Sale

My son and I are currently trying to expand this cactus tool business (the new website is now operational,  and I have the outside vendors lined-up for higher production rates and deliveries).  A brand new website is under development,  watch for an update,  here and at the TXIDEAFARM site,  for links to it.  Hopefully it will be up-and-running in February 2015,  but no guarantees! 

Up to now,  I have sold plain tool plans for very distant customers,  and also up to now I have built plain tools built speculatively.  With delivery now available,  I no longer offer plans at all.  The greater expenses of the hydraulic tool require me to demand half the money up front,  and I build-to-specific-order only.  I have custom-shipped one plain tool to a customer in Florida. I have built and delivered one hydraulic tool.  

Plans for an older model of the plain tool will continue to be available only until the last of the shipping issues are resolved.  No plans are available for the hydraulic tool.  Once shipping is resolved,  I will literally be able to ship anywhere.  This will be part of the total package pricing on the new website.  Once it is operational,  I will no longer offer any plans at all. 

What I currently offer for hardware is two basic models now built with a common chassis when they were not before (plain tool and hydraulic tool).  Prices are always subject to some change,  especially so as I will have to contract-out more of the fabrication labor,  so do please check with me for current prices,  until the new website is operational.  What will be is posted there will be is current. That site is "".

Some options are available at extra cost right now.  More will become available soon.  The towbar hitch (only on the hydraulic tool) is one.  Adding trailer ball mounts to tow other things behind either model is another.  An added fence at the left and right edges is a third,  that helps keep items stowed on the tool deck from rattling off when operating on rough ground;  this is available on both models. We also have an option for a "real" tool box that secures to the deck,  doing what the scrap cat litter bucket did,  just better.  Soon there will be an option for a remote-viewing camera.  

The very oldest form of my plain tool predates the addition of the “barge front” for wedging over obstructions.  There are photos of these on the TXIDEAFARM site,  at least right now.  I had few-to-no obstructions on my place;  however most places have outcrops and stumps.  That’s why the two standard models today both have “barge fronts”.  I no longer offer plain tools without “barge fronts”.  I have never offered any hydraulic tools without “barge fronts”. 

For a list of current offerings,  which models they fit,  and current prices as of this writing,  see Figure 7.  See "" for current prices and prices and options.  The site is designed for direct on-line customization and secure purchase.  

(Fig 7 deleted)

As for effectiveness,  see the earlier articles here on “exrocketman” per the article list above,  at the beginning of this article,  and the write-ups on “TXIDEAFARM”.  The fun photo in Figure 8 is overstated,  of course.  But what I say about the effectiveness of these tools in those articles is not! 

Update with links to new website

This new website is currently still under construction.  But watch for it.  An update with those links will be posted here and on “TXIDEAFARM”.  Everything you need to choose,  customize,  and buy a tool will be is there.  

Update 6-21-15:

The new website is not quite operational yet,  but will be found very soon as  as".  Everything you need to select and customize a tool with options will be is there.  Everything you need to place an order will be is there.  Even the estimates for shipping to distant locations will be are there.  

My son and I anticipate higher production rates once this website goes operational.  Accordingly,  I am lining-up parts manufacturing vendors to make the parts for these tools,  additional welders,  and workers to paint and rig these tools.  The job has already gotten far bigger than I alone can handle,  and we anticipate bigger still.  We have established a relationship with YRC (formerly Yellow Freight) to ship tools to distant customers on a routine basis.  

With more outside vendors and activities,  prices will be substantially higher than were quoted here until today.  Freight charges are not cheap either,  a couple of years ago it cost me about a $1000 to ship a plain tool to Florida.  So,  contact me (or consult the new website once it's "up") to get current prices.  

With shipping to distant customers in place,  I no longer offer plans.  That was how I serviced distant customers before.  (I still do rentals for folks close enough to me to come pick up a tool at my shop.)

Figure 8 – Don’t We All Wish ………

Monday, November 17, 2014

Space Suit and Habitat Atmospheres

See also updates 11-20-14 and 11-26-14 and 1-1-15 at end.

Spacesuits are usually designed for pure oxygen “atmospheres“ supplied as breathing gas.  This is especially important to full pressure suit designs,  as lower pressures can be used with pure oxygen,  which eases the joint restriction design problem.  However,  long-term breathing of pure oxygen is detrimental to human health.  Plus,  it is a very serious fire hazard:  flammability and explosiveness are greatly amplified in pure oxygen at full atmospheric pressure. 

All of that taken together means that the habitation for astronauts (be it a ship,  a space station,  or a base on another planet) needs a suitable diluent gas.  Such atmospheres are thus inherently two (or more) gas systems.  We evolved in an atmosphere of 20.946 volume percent oxygen,  about 78% nitrogen,  and around 1% argon,  plus some other trace gases. 

Although sea level pressure is “the standard”,  there are many human communities living at altitudes where pressures are substantially lower.  Many large populations live near 10,000 feet elevation,  some near 15,000 feet,  and a very few approaching 20,000 feet.  Air pressure,  and oxygen partial pressure,  are both substantially lower at altitude. 

The pilots of aircraft are required to use supplemental oxygen when flying above certain altitudes.  The exact standards vary,  but the US Navy uses 5000 feet as the altitude above which oxygen must be used.  Most other authorities use 10,000 feet as the “trigger” for mandating oxygen.  Below those altitudes,  pilots seem to be fully functional.  Therefore,  atmospheric oxygen concentrations resembling those in the 5000-10,000 feet altitude range make pretty good criteria for the minimum life support requirements of any space suit design.  See also Figure 1.  These data were also used in “Fundamental Design Criteria for Alternative Spacesuit Approaches”,  posted this site 1-21-11.  

 Figure 1 -- Life Support Experiences

Suit Criteria

The Earth’s atmosphere has very variable humidity.  Dry air composition is 20.946 volume percent oxygen.  Water vapor acts to “displace” dry air,  so there is a slightly-lower oxygen partial pressure to breathe on very humid days versus very dry days,  at any altitude.  At human body temperature,  the steam tables show the partial pressure of saturated water vapor to be just about 47.06 mm mercury. 

Respiration depends upon the partial pressure of oxygen in the air we breathe,  not the volume percent.  This is because so many biochemical processes are driven by osmotic pressure differences. 

These two effects (water vapor displacement and partial pressure-driven osmosis) taken together say that the actual oxygen requirement,  when designing space suit and habitat atmospheres,  is the partial pressure of oxygen in the near-equilibrium saturated environment of the lungs.  This same water vapor displacement effect must be taken into account in selecting the pressure of the pure dry oxygen in the suit.  (There are other displacement effects,  but all are far less significant than this water vapor effect.)

The other factor to consider is leakage from the suit.  Suit pressures can be increased to compensate for losses that might (or might not) occur.  The “usual” factor seems to be 1.10 for leakage effects.  The suit oxygen pressure selection approach is shown in Figure 2,  Figure 3 presents the actual data.  This applies to any type of suit,  not just the full pressure suits that have been standard. 

Suit designs that supply pure oxygen at compression pressures between 147 mm mercury (10,000 feet) and 167 mm mercury (5000 feet) would thus seem to be quite adequate.  196 mm mercury corresponds to full sea level oxygen.  Those figures include the water vapor displacement effectbut not the increase for leak compensation.  Using a factor of 1.10 as leak compensation,  the design suit pressures become 216 mm mercury for sea level-based,  187 mm mercury for 5000 ft-based,  and 161 mm mercury for 10,000 foot-based designs.  

Figure 2 – Selecting Pressure in a Pure Oxygen Suit

 Figure 3 – Pressures in a Pure Oxygen Suit of Any Type.

Getting from Suit to Habitat Atmosphere

Since we evolved to breathe them,  oxygen,  nitrogen,  and argon make pretty good choices for the gases in the atmosphere of any astronaut habitat.  This is important because interplanetary missions will require living in such habitats for years at a time.  Oxygen-nitrogen is a basic two-gas system.  We might add substantial argon as an additional diluent for reducing the risk of fire. 

The problem going from a two-gas system in the habitat to pure oxygen in the suit is a requirement to “blow off” the nitrogen (and any third diluent gas) dissolved in the blood,  without risking “the bends”.  This is “pre-breathe” time,  and it is quite significant with the atmospheres used in the ISS and associated spacesuits.  There is a tested criterion for this:  if habitat partial pressure of nitrogen ≤ 1.20 suit pure oxygen pressure,  then no pre-breathe is needed. 

So,  once a design suit pressure has been selected,  this factor of 1.2 should be used to determine the maximum partial pressure of nitrogen in the habitat atmosphere.  Suit and habitat share the same in-lung wet partial pressure of oxygen.  The in-lung wet and habitat dry atmospheres share the same total pressure.  If this a multiple-gas atmosphere in the habitat,  then we know its total pressure as the sum of the wet O2 and N2 (and Argon,  if any) partial pressures,  and can figure the volume percentage of oxygen in the dry mix as its partial pressure divided by the total.  That process logic is a part of Figure 4,  with the numbers as a function of suit pressure in Figure 5. 

As a two-gas system,  all the suit pressure designs under these criteria share the same habitat atmosphere oxygen percentage:  45%.  That sounds like a high fire risk,  unless low total pressure mitigates it.  These total pressures are much lower than standard atmospheric:  ranging from only 6.86 psia for the 15,000 foot-based design up to only 9.19 psia for the sea-level-based design. 

These total pressure and oxygen percent data and the oxygen partial pressure can be used to evaluate fire risks.  I have no ready criteria for this myself.  It can be tested experimentally in test chambers right here on Earth,  however.  Adding argon lowers the percentage oxygen (but not its partial pressure),  and raises habitat total pressure.  

 Figure 4 – Scaling Up from Suit to Habitat to Avoid Pre-Breathe Requirements

Figure 5 – Basic Two-Gas Habitat Atmospheres as a Function of Design Suit Pressure

Three-Gas System for Reducing Fire Risks?

I do not know of a pre-breathe criterion factor for argon.  One might assume the same 1.2 factor over suit oxygen pressure applies,  so that one can add substantial argon to the mix,  at a partial pressure equal to that of the nitrogen. 

On the other hand,  monatomic argon has a molecular weight near 39,  versus diatomic nitrogen’s molecular weight of 28.  If osmotic rates depend directly upon molecular weight,  then argon should be slower than nitrogen to dissolve into,  and out of,  the blood.  Then perhaps the pre-breathe criterion for argon should be nearer 0.86 than nitrogen’s 1.20.  We just don’t know.  But,  that assumption lowers the argon content,  which is in the safer direction.  Results are in Figure 6.

Figure 6 – Three-Gas Atmospheres as a Function of Design Suit Pressure


#1. Go with the Navy oxygen mask criterion of 5000 feet as slightly more conservative than the 10,000 foot criterion.   Your suit (whatever its design) is then at-minimum pure O2 at 3.28 psia.  Factored up for leaks,  this is 3.61 psia.  Even full pressure suits can be somewhat supple at pressures this low. 

#2. For a two-gas habitat atmosphere,  use a pre-breathe factor of 1.20 for nitrogen as well-supported.  Use the in-lung wet suit oxygen partial pressure as the in-lung wet habitat partial pressure of oxygen.  Results are given in figure 5 for all the suit designs.  For the recommended 5000 foot-based suit design and the two-gas system,  your habitat atmosphere is 45.45% O2 and 54.55% N2,  at 6.13 psia,  with zero pre-breathe time required to don the spacesuitThe 45% O2 is rather alarming as a fire hazard.  It is at best unclear whether the low pressure of 6.13 psia could mitigate this risk.  At worst,  this is simply too severe a fire hazard. 

#3. For a 3-gas habitat atmosphere,  we use all the same design factors,  plus we set the argon pre-breathe factor at about 0.86.  Results are given for all the suit designs in Figure 6.  For the 5000 foot-based design,  we are looking at a habitat atmosphere that is 32.68 volume % O2,  39.22% N2,  and 28.10% Ar,  at a total pressure of 8.16 psia,  again with zero pre-breathe time required to don the spacesuit.  Adding the third gas greatly reduced the objectionable high volume percent oxygen.  But it is unclear whether this is enough reduction. 

#4. It is entirely possible that more argon could be used,  once a pre-breathe limit factor has been established for it.  That would act to lower oxygen percentage and raise habitat total pressure,  but would not affect the suit design. 

#5. It might also be possible to add a fourth gas (preferably an inert one,  and one not linked to the biology of life as CO2 is).    This would also lower oxygen percentage and increase habitat total pressure,  without changing the suit design.  One candidate might be helium,  which has been used in deep sea diving.  It takes longer to decompress than nitrogen in that application,  which means its pre-breathe factor is lower than nitrogen’s,  in spite of the low molecular weight. 

#6. Note that in the tables given in Figures 5 and 6,  that oxygen percentages are constant,  regardless of the suit design pressure.  Raising suit pressure will not cut oxygen percentage in the habitat,  without violating the pre-breathe factors that make EVA’s into practical operations. 


Assume as a wild guess that the pre-breathe factor for helium is 0.5Assume also that the pre-breathe factor for argon is closer to that of nitrogen,  for about 1.0.  Under those conditions,  a hand calculation for the 5000 foot-based suit design gives a habitat atmosphere of 27.03% O2,  32.43% N2,  27.03% Ar,  and 13.51%% He,  at 9.68 psia.  Earth-normal oxygen percentage is nearly 21%,  so surely this 4-gas atmosphere would be far less risky in terms of fire. 


Determine reliable pre-breathe factors for argon and helium.

Identify other candidate gases that could be added to the mix,  and determine the pre-breathe factors for them. 

Final Note:

The atmosphere we evolved with (20.946% O2 78% N2,  and 1% argon) at 14.7 sea level psia could be a habitat atmosphere as safe as here at home,  in terms of fire risk and any long-term medical risks.  The nitrogen pre-breathe factor of 1.2 says the spacesuit pure oxygen pressure would have to be about 9.55 psi in order to avoid pre-breathe time donning the suit. 

That’s impossibly high,  even for a full pressure suit.  Our astronauts have severe mobility restrictions at about half that pressure currently.  The ISS uses near Earth-normal air,  and hours of pre-breathe time,  to use a suit at about 4.85 psi.    

Something has to change,  or these EVA-practicality issues will stymie us.  

Update 11-20-14:

The preceding calculations and graphs were made under the assumption that we wanted a minimal suit pressure,  and that we calculated habit atmospheres to match the wet in-lung oxygen partial pressure of the suit  Only 3 and 4-gas atmospheres were considered (oxygen,  nitrogen,  and argon,  plus maybe helium).

For this update,  I looked at setting habitat atmospheric oxygen to something very near Earth-normal oxygen 20.946 volume % for fire protection,  and added two more noble gases to the mix,  resulting in a 6-gas mixture.  All the inert gases added to inert nitrogen are chemically-inert noble gases.  In order,  the diluents are nitrogen,  argon,  helium,  neon,  and krypton.  There are more noble gases available (xenon and radon),  but these are becoming radioactive items,  and are to be avoided. 

I used the same pre-breathe factor of 1.2 on the nitrogen that has been proven.  The other factors are speculative.  I used a factor of 1.0 for the argon,  and 0.5 for helium and the other noble gases.  This is an arbitrary selection,  but should be in the ballpark (so something like this mix will work.)  The last noble gas (krypton) I allowed to fall a tiny bit short of its max pre-breathe factor to balance the mix at 100%. 

I did not use exactly the Earth-normal oxygen percentage,  because I could not quite achieve mathematical closure with a 6-gas mix.  But since the next noble gases are radioactive,  I did not use them.  Instead I picked an oxygen percentage very close to a nominal 21 volume percent,  which should present exactly the same fire hazard as Earth-normal air.  My number was exactly 21.28% oxygen. 

I forced the wet in-lung oxygen partial pressure of the mix to match that from sea level Earth-normal air at 149.33 mm mercury.  Removing the water vapor but retaining the mixture total pressure gives this dry habitat atmosphere:

                Gas        Pp,  mm Hg         vol%
                O2          159.34                   21.28  compare to 20.946% for sea-level Earth-normal air
                N2          191.21                   25.54
                Ar           159.34                   21.28
                He          79.67                    10.64
                Ne          79.67                     10.64
                Kr            74.55                     10.62
                Dry tot  748.80                   100.

The habitat atmosphere works out to 0.9853 atm = 14.48 psia,  very close to Earth-normal air.  The difference is 5 diluent gases at significant concentrations,  instead of just one.  None of the 5 will have large concentrations (or osmotic pressures) in the blood.  Thus,  there should be little or no risk of “the bends” going straight from this atmosphere to the corresponding suit,  assuming my pre-breathe factors are anywhere close to right.  But,  it will take experiment to find out what the real factors are. 

In the wet-lung environment,  water vapor pressure displaces part of this dry atmosphere,  lowering the partial pressures.  I assume equilibrium water vapor pressure at body temperature.  Those adjusted data look like this:

                Gas                                        Pp, mmHg
                O2                                          149.33  same as sea-level Earth-normal air in the wet lungs
                N2                                          179.20
                Ar                                           149.33
                He                                            74.67
                Ne                                          74.67
                Kr                                            74.55
                Water vapor                       47.06
                Total                                      748.80  = 0.9853 atm = 14.48 psia

We want the pure-oxygen suit to match wet in-lung oxygen partial pressures,  so that tissue oxygenation and resistance to hypoxia issues is the same,  in the suit as in the habitat.  Because the suit is a 1-gas system,  you just add the water vapor partial pressure to the wet in-lung oxygen partial pressure to determine total suit pressure. 

                149.33 + 47.06 = 196.39 mm Hg = 0.2584 atm = 3.798 psia  

Even if you add a factor 1.10 increase to counter leakage,  the suit pressure is still only 216.03 mm Hg = 0.2842 atm = 4.177 psia.  That is far lower than current practice on the ISS. 


#1. It is quite feasible to have habitat atmosphere at very nearly Earth-normal pressure and Earth-normal oxygen percentages,  and yet avoid high nitrogen concentrations,  by going to a multi-gas mixture.

#2. It is very likely feasible to do this in a way that avoids the long pre-breathe times associated with the high nitrogen concentration in Earth-normal air.

#3. If you do it as a multi-gas system,  there is no need for a high-pressure space suit,  just to lower (but not eliminate) the pre-breathe times using Earth-normal air. 

#4. The lowered suit pressure requirement makes full pressure suits more supple,  and makes mechanical counterpressure suits immediately feasible with compression levels already easily achieved.

Final Note: 

My pre-breathe factors for all but nitrogen are probably only ballpark,  but certainly not exactly correct.  The research to quantify these factors correctly can be done on the ground.  Thus there is no excuse not to research this,  the payoff is simply too attractive. 

Update 11-26-14:

Once again,  my pre-breathe limit factors for all but nitrogen are guesses requiring experiment before application!  I have heard that the US Navy knows the pre-breathe factors for at least some of the noble gases that I proposed using here,  and has experience with actual use of multiple diluent gases,  exactly as proposed here.  The pre-breathe factor of 1.2 for nitrogen is in fact a US Navy value.

While not conclusive as presented here,  this does make my analysis seem at least ballpark correct.

Use the Navy's factors,  and this becomes possible as a 4-, 5-,  or at most 6-gas system.  You will be at no more at risk of fire than here on Earth with 21% by volume oxygen,  and you can use a lower-pressure,  more-supple pressure suit in the vicinity of at most 4 psia (for a sea-level-equivalent oxygenation design plus leak margin).

And,  best of all,  you need no long pre-breathe times to avoid the bends.  That is completely unlike current practice on the ISS.

Or even better than a supple full pressure suit,  you can use a really supple mechanical counterpressure suit at the same low pressure.  Such a low-pressure suit is technologically feasible right now,  and has been since 1968,  in one form or another.  3 to 4 psia compression has been well demonstrated as feasible in that approach,  with two disparate technologies.  

There is simply no excuse not to try all of this out.  The payoff,  in terms of basic astronaut mobility,  and in terms of effective human exploration capability,  is just too great.  Not to mention enabling feasible and practical designs for habitats and bases on other celestial bodies of all kinds.  And,  enabling far more effective assembly and repair operations by humans in space!

Any space agency,  public or private,  that is really interested in manned travel beyond cis-lunar space should be looking very seriously at the issues and possibilities raised here.

As for the rest of us,  we can safely conclude that agencies not looking very seriously at these same issues and possibilities,  are simply not yet serious about manned travel beyond cis-lunar space.

Update 1-1-15:

I have run across documents about what the Navy pre-breathe factor work really involved.  They looked at decompression needs coming from higher-than-1-atm pressures,  which is for deep sea diving.  What they found for that regime was that the prebreathe factor of 1.2 applies to the sum of all the diluent gas partial pressures:  sum Pp diluents / low total pressure = 1.2.  A lot of experiments were conducted to confirm this.

The low-pressure regime has not been explored experimentally yet.  When decompressing from near 1 atm to low total pressures in a pure oxygen suit,  the question is this:  does the prebreathe factor still apply to the sum of all diluent gas pressures taken together,  or can you use a separate factor for each diluent gas,  or does it correlate as something in-between these extremes?  That would be a good topic for someone research experimentally.  

However,  the Navy result is suggestive that using multiple diluent gases does you no real good,  because the factor of 1.2 applies to the sum of diluent partial pressures,  not those pressures individually.  That runs counter to what I explored above.

If that is indeed the case,  then the decompression problem revolves around this choice:  either (1) you choose a habitat atmosphere (the usual choice is Earth-normal sea level air) and design suits to match it that require no pre-breathe time,  or (2) you figure out what suits you really want,  and use the pre-breathe factor criterion to design your habitat atmosphere to be compatible.  That bounds the problem,  and the answer lies between those extremes,  very sensitive to the assumptions you actually make.

There is context to consider surrounding this choice and the assumptions.  As pointed out above,  full sea level air pressure is not really necessary.  NASA is working on full pressure suit designs with more dexterous joints and gloves,  even at higher suit pressures (in the 8-9 psia range).  NASA cannot accept oxygen concentrations beyond about 30%,  as being too much of a fire hazard.  With MCP suits,  existing technologies would only support about 0.25 to 0.30 atm compression.  MCP is inherently more dexterous,  and far more fault-tolerant of punctures and rips,  offers the possibility of being machine-washable,  but is far more difficult and time-consuming to don.  Those are just the facts of life with which we must deal.

habitat-first approach with full Earth-normal air:

Assume Earth-normal air as "synthetic air":  0.209 atm oxygen and 0.791 atm nitrogen.  Using a pre-breathe factor of 1.2 on the nitrogen partial pressure gives a required suit pressure of 0.659 atm pure oxygen.  That high a suit pressure (9.69 psia) presents extreme challenges designing-in glove dexterity in full pressure suits.  That high a compression level also rules out using MCP without major technological breakthroughs in materials.  Assuming 10% loss from leaks says your min allowable suit pressure is 0.599 atm.  With suit oxygen pressures in the 0.6 atm range,  there are medical worries about exposure to too much oxygen,  if exposure times are long.  On the ISS,  we use essentially Earth-normal air.  Accordingly,  we have long decompression pre-breathe times,  because current suit pressures are not that high.

suit-first approach using only what is needed for oxygen in the suit:

Assume your suit pressure (full pressure suit or MCP) is 0.209 atm pure oxygen,  same as Earth-normal air.  10% for leaks gives you 0.190 atm,  corresponding to the oxygen content in Earth-normal air at about 3000 feet above sea level.  That's just fine.  Using the factor of 1.2 on the design suit pressure of 0.209 atm  sets the habitat atmosphere nitrogen at 0.251 atm.  Using max allowable 30% oxygen sets the oxygen pressure at 0.108 atm,  and the habitat "air" pressure at 0.359 atm.  That level of oxygenation is still just too low,  being equivalent to Earth air at about 17,000 feet elevation.

compromise with reduced-pressure but otherwise earth-normal air in habitat:

In flying,  pilots must use oxygen above 10,000 feet elevation,  below that altitude,  they do not have to use it,  which presumes adequate oxygenation,  something proven by long experience.  The air pressure at 10,000 feet is 0.6878 atm. Assuming synthetic air at 20.9% oxygen,  that's 0.1438 atm oxygen and 0.5440 atm nitrogen.  That would be adequate as habitat air.  Using the pre-breathe factor on that nitrogen,  we get a pure-oxygen suit pressure of 0.4533 atm (6.66 psia).  That's still a considerable design challenge for dexterous full pressure suit (although NASA is working on glove designs for 8-9 psia).  It still rules-out using MCP without decompression time.  We are still very limited,  and would need decompression pre-breathe times to use MCP technology as it exists.  But this possibly could eliminate pre-breathe requirements with existing full pressure suits,  especially if refitted with more dexterous gloves.

same reduced-pressure habitat but with max oxygen allowable for fire safety:

Require the same oxygen as Earth-normal air at 10,000 feet:  0.1438 atm oxygen.  At 30% oxygen,  the habitat pressure is 0.4793 atm,  and the nitrogen is the other 70% at 0.3355 atm.  Using the pre-breathe factor on that nitrogen gets you a suit pressure of 0.2796 atm (4.11 psia).  That falls to 0.2542 atm with 10% leakage,  still quite adequate.  With suit pressures near 4 psia,  the new more-dexterous glove designs for full pressure suits will be far more effective,  and the compression levels are achievable with MCP.  Both kinds could be used with no decompression pre-breathe time requirement.

conclusions and recommendations:

What this does is bound the problem and show feasibility by making more appropriate initial assumptions.  The water-vapor displacement effect inside the lungs has not been taken into account,  and must be,  in any final design.  But those results should not be very far from these.  I'd guess the habitat and suit pressures to be just slightly higher than these bounds.

The "feasibility" shown here is threefold:  (1) we can dispense with the decompression pre-breathe times by using a significantly lowered habitat pressure,  and with the oxygen content still within known fire safety criteria,  (2) we can immediately add existing materials technology-based MCP suit designs to the mix of things available to the astronauts,  and (3) the more dexterous glove designs being developed for the full pressure suits will be even more effective at reduced suit pressures.  Those are all very favorable outcomes,  and they are also incredible enabling factors for astronauts to be far more effective when working in vacuum.

The only thing currently going on is the more-dexterous glove design for full pressure suits being done by NASA.  No experimentation is going on with habitat atmospheres on the ISS,  it's close to Earth-normal air almost by default.  MCP suits are still not seriously funded.

I see some things here that should be going on,  if we ever expect to explore other bodies like Mars more effectively.