Friday, March 16, 2018

Suit and Habitat Atmospheres 2018

This article takes on the best available information regarding selection of pure oxygen space suit pressure levels,  and how they relate to space habitation atmosphere composition and fire dangers.  The previous related articles posted on this site all share the same basic methodologies and calculation methods. 

The fundamental methodology here is to calculate both atmospheres and design criteria in terms of the wet in-lung partial pressure of oxygen,  which in turn is what actually drives the diffusion of oxygen across the lung tissues into the blood. 

In the earlier articles,  there were unresolved issues with “pre-breathe” (decompression) criteria,  and with fire danger criteria,  that have since been resolved or sidestepped.  This article brings,  as a new item,  a “leak-down” suit pressure factor,  and also brings additional supporting data for the selected suit pressures,  which are lower than is typical of NASA practice today.  Lower pressures make space suits more comfortable to wear,  and easier to design.

Lists of the previous articles follow.  The most recent,  superseded by this one are:

“A Better Version of the MCP Space Suit?” 11-23-2017
“Suits and Atmospheres for Space” 2-15-2016

Those two in turn superseded these earlier articles:

Space Suit and Habitat Atmospheres” 11-17-2014
“On Orbit Repair and Assembly Facility” 2-11-2014
“Fundamental Design Criteria for Alternative Space Suit Approaches” 1-21-2011

The best way to find any of these is to use the date/title navigation tool at the left.  Click on the desired year,  then on the desired month.  If the article is not top of the list (in view),  click on its title. 

To view any or all of the figures enlarged,  click on any of the figures.  You may then scroll through all of them in enlarged format.  Once done,  you can return to the article by “X-ing-out” of the enlarged figures screen. 

Another way is to find one,  then click on the “space program” keyword.  Then you will see only those articles with that search keyword,  which these all share.  An alternative keyword is “space suit”,  but I’m not sure that all of them share this search keyword.  The more recent ones do,  for sure.

Wet In-Lung Oxygenation is Not the Oxygen Content of What You Breathe

Atmospheric pressure is easily determined versus altitude using published atmosphere tables.  It doesn’t vary much from model to model.  The model used here is the US 1962 Standard Day,  which for altitudes up to about 65,000 feet,  is identical to the ICAO Standard Day. 

Air composition is fairly standard as follows.  It is oxygen,  diluted with mostly nitrogen.  The largest trace ingredient is argon.  Whether given as fractions or percentages,  these compositions are usually given in volume format,  which is also molar.  True “synthetic air” is the two-gas mix of oxygen and nitrogen,  at the same oxygen content as real air.  Other ratios are also feasible,  for different purposes.  The standard air oxygen content used for this article is 0.20946 = 20.946% by volume.

Gas                      Vol %
Oxygen                20.95
Nitrogen              78.09
Argon                   0.93
Carbon dioxide   0.03 (older figure,  has since risen to 0.04)
Trace gases         0.018 or less

These figures are for dry air (no humidity).  The presence of water vapor displaces dry air,  so that the total of their pressures adds to the atmospheric pressure.  The water of interest here is that within the lungs,  with liquid moisture present at body temperature.  If one assumes the vapor is in equilibrium with the warm liquid,  then the vapor pressure in the lungs is the standard steam table value at body temperature:

                Pvap = 47.07 mm Hg = 0.061934 atm 
at T = 37.0 C = 98.6 F (human body temperature)

The oxygen partial pressure in the dry air is the dry air pressure multiplied by the volume fraction of oxygen.  In the atmosphere tables,  the pressure ratio to standard sea level pressure is numerically equal to the altitude pressure in atm.  Dry air oxygen partial pressure,  atm,  is thus 0.20946 * (P/PSL).

In Figure 1,  oxygen partial pressure in the dry air is plotted versus a wide range of altitudes.  To calculate wet in-lung oxygen partial pressure,  you reduce the dry air pressure by the water vapor pressure,  then apply the oxygen fraction to that reduced value.  Both are plotted in Figure 1.  The difference between then becomes increasingly significant as altitude increases,  because water vapor pressure depends on only body temperature,  and is thus an ever-larger portion of the atmospheric pressure as altitude increases.

There are several notes added to the figure.  First is that US Navy pilots are required to start using supplemental oxygen when they exceed 5000 feet altitude.  Second is that USAF pilots,  and FAA civilian pilots,  must use supplemental oxygen when above 10,000 feet.  In the civilian case,  this is coupled with a time limit,  so that oxygen is not required if above 10,000 feet,  until the time is exceeded.  But oxygen is always required if above 14,000 feet.

Also shown on the figure is the usual airliner cabin pressure altitude practice,  which is 10,000 to about 15,000 feet equivalent.  The 10,000 foot condition is rather close to the elevation of the city of Leadville,  Colorado (USA).  The 15,000 foot condition is rather close to the elevation of the city of Daocheng,  Sichuan (China).  La Paz,  Bolivia,  is not shown,  but has an elevation in the middle of the cabin pressure altitude range,  at 13,323 feet.  These are all cities where people live perfectly normal lives.

Equivalent wet in-lung oxygen partial pressure is also shown in the figure as the arrows A and B for the effects of a (vented) supplemental oxygen mask at 40,000 feet,  and at 45,000 feet,  respectively.   These masks seem quite adequate for long flight times at 40,000 feet,  for which wet in-lung oxygen falls in the cabin pressure altitude range at just about 12,000 foot equivalent.  They are recommended only for short exposures at 45,000 feet,  which seems about equivalent to 20,000 feet.  Only a few genetically-adapted herders live and work at this altitude,  in the Andes and the Himalayas.  

Thus wet in-lung oxygen partial pressures equivalent to 15,000 feet or lower are quite consistent with standard high-altitude flying practices. 

 Figure 1 – Wet In-Lung Oxygen from Atmospheric Air,  as a Function of Altitude

The calculation for the two supplemental oxygen mask points was a little different.  The calculated curves and some notes are given in Figure 2.  The big assumption was that 100% dry oxygen was in the mask,  at the altitude atmospheric pressure.  Offsetting this down by the vapor pressure gives the wet in-lung oxygen partial pressure,  as given in the figure. 

The assumption about 100% oxygen inside the mask is probably pretty good at the higher altitudes,  and probably not so good at lower altitudes.  The pressure drop from the supply to the mask is high enough to ensure choked flow somewhere in the equipment,  so that the delivered oxygen massflow is fixed,  and thus independent of the delivered density conditions in the mask. 

The delivered density is lower at high altitudes,  which for the same massflow is larger volume flow.  If that volume flow is large enough,  it overwhelms the effects of imperfect sealing of the mask to the face,  and of the diluting effect of the exhaled gases.  At those conditions,  the mask is filled with very nearly pure oxygen.  This would certainly be the case at the highest altitudes for which the mask is considered effective.  Those would be long exposures at 40,000 feet,  and short exposures as high as 45,000 feet.  Military flying practice requires pressure breathing equipment above those altitudes;  effectively,  some kind of pressure suit.

It is these wet in-lung oxygen partial pressures from the supplemental oxygen mask at 40,000 and 45,000 feet that was the objective here.  Those are the points A and B in Figure 1 above.  The possible error at low altitudes is irrelevant to the discussions here.

Figure 2 – Wet In-Lung Oxygen from a Vented Pure-Oxygen Mask,  as a Function of Altitude

How to Use Altitude Equivalence for Oxygen Suit Pressure Selection

Figures 3 and 4 show this process for two slightly-different suit design pressures.  You start with an assumed design altitude in Earthly air (for which you can also figure its dry oxygen partial pressure if you want,  but we don’t use that in this calculation),  and offset the ambient pressure down by the water vapor pressure,  to the wet in-lung dry air partial pressure.  Use the oxygen fraction against the dry air partial pressure to calculate the wet in-lung oxygen partial pressure.  Use this wet in-lung oxygen partial pressure as the wet in-lung result to be obtained by your suit.  Add to it the water vapor pressure,  and that is your dry oxygen suit pressure at design conditions. 

Then,  ratio-down that suit pressure by your leak-down margin factor (in this case 1.10) to the min tolerable dry sit pressure.  Offset that down by the water vapor pressure to obtain the min tolerable wet in-lung oxygen partial pressure.  This needs to fall in an acceptable range (generally that defined by the wet in-lung oxygen partial pressure at cabin pressure altitudes,  or 10,000-to-15,000 feet equivalent). 

Now,  divide that min tolerable wet in-lung partial pressure of oxygen by the volume fraction of oxygen in dry air,  to obtain the wet in-lung partial pressure of dry air.  Add to that the water vapor pressure to obtain the Earthly dry air pressure at altitude.  Reverse the table lookup to determine the equivalent altitude for your min tolerable leak-down condition.  If you did this right,  it will fall in the 10,000 to 15,000 foot range of acceptable cabin pressure altitudes. 

Figure 3 does this for an 8700 foot equivalent suit design at 0.2004 atm = 2.945 psia that leaks down by factor 1.10 to a 12,000 foot equivalent design at 0.1822 atm = 2.678 psia.  Figure 4 does this for a 10,000 foot equivalent suit design at 0.1930 atm = 2.836 psia that leaks down by 1.10 to an equivalent 13,300 foot design at 0.1755 atm = 2.579 psia.  Both fall within the cabin pressure altitude range or lower,  for acceptable wet in-lung oxygen partial pressures,  considered adequate for pilots.  The 13,300 foot condition is also equivalent to the major city of La Paz,  Bolivia,  to which tourists acclimatize very quickly.   

Either design,  or an even-higher pressure design,  are all quite acceptable for life support and fully-functional human cognition in a space suit.  The lower pressures allow easier suit design,  and more comfortable suits.  So,  unless there is an overriding need for higher pressures,  these lower pressure designs are to be preferred. 

 Figure 4 – Relating Design and Leaked-Down Suit Oxygenation to Equivalent Air at Altitude:  10/13.3 kft

Relating Suit Design Pressure to Two-Gas Habitat Atmospheres:  Fire Danger and Pre-Breathe Criteria

There are two issues that relate oxygen suit pressure to the pressure and composition of a two-gas habitat atmosphere.  One is the “pre-breathe” factor,  the other is the enhanced fire danger posed by a too-oxygen-enriched atmosphere. 

The pre-breathe factor used by NASA was originally developed for the US Navy,  for oxygen-nitrogen two-gas mixtures.  If in the dry habitat atmosphere the partial pressure of nitrogen is at or below factor 1.20 times the pure oxygen suit pressure,  then no decompression time is needed breathing pure oxygen to blow off the nitrogen in the blood.  That decompression time is the “pre-breathe time”. 

As an example,  for a two-gas oxygen-nitrogen atmosphere at 1 atm pressure and 20.946% oxygen by volume (“synthetic air” at 1 atm),  the nitrogen partial pressure is 0.79054 atm.  For a pure oxygen suit at 3.8-4.2 psia,  the dry oxygen partial pressure is 0.2586-.2858 atm.  The ratio of nitrogen to suit oxygen pressures is 3.057-2.766.  This range of values far exceeds the 1.20 criterion,  so significant hours of pre-breathe time are required.  This is pretty much current NASA practice at the ISS (space station).

In the earlier articles,  it was unknown to me whether that factor of 1.2 applied to individual dilution gas partial pressures,  or to the aggregate sum of their partial pressures.  I still do not know,  but I sidestepped that issue entirely by only considering two-gas mixtures of oxygen and nitrogen here. 

It is also fairly obvious that reducing habitat atmosphere pressure reduces the dilution gas partial pressure,  thus reducing its ratio to suit oxygen pressure.  It is also fairly obvious that increasing the oxygen fraction of the habitat atmosphere also reduces the ratio.  Thus,  reduced habitat atmosphere pressures at higher-than-Earthly oxygen content seems to be indicated for lowering or eliminating pre-breathe times. 

However,  increasing oxygen content runs afoul of enhanced fire danger.  I have read of two ways to judge the fire danger.  One is that the percent (by volume) oxygen for air pressures near 1 atm should be under 30% at most,  and preferably nearer the 20.946% of ordinary air. 

Percent oxygen is independent of total pressure,  but partial pressure of oxygen is not.  The second way to judge the danger is a limit on oxygen partial pressure,  limited to about sea level Earth normal. 

After thinking about this,  I realized that the enhanced fire danger resulting from the enhanced oxygen is really faster chemical reaction rates,  leading to very much-accelerated phenomena and enhanced energy release rates.  For an overall empirical model of a fuel-air chemical reaction rate,  a second-order two-component one-step Arrhenius model is often used:

Rate = k Cf^r Co^(n-r) exp[Ea/RT] 
where n ~ 2 and r ~ 1, 
with Cf and Co measured as mass/vol

That suggests the real criterion might be the oxygen concentration Co,  expressed in mass per unit volume units.  If this concentration were no worse than that of Earthly air,  then the fire reaction rates should be unaccelerated relative to those seen in Earthly air.  Both volume fraction oxygen and atmosphere pressure get into this concentration calculation. 

The volume fractions of the two gases,  and their molecular weights,  give you the molecular weight of the synthetic air mix:

                MW-O2 * vol frac O2 + MW-N2 * vol frac N2 = MW-air * 1

The molecular weight ratio and volume fraction of O2 give you the mass fraction of the air that is oxygen:

                (MW-O2 / MW-air) * vol frac O2 = mass frac O2

Because the pressure ratio to standard pressure P/Pstd is numerically the pressure in atm,  you can use the habitat pressure expressed this way,  and its temperature,  to correct standard air density to habitat atmosphere conditions.  The ignores the difference between the synthetic air and actual air,  but that is trivial:

                Dens-hab = density-std * (P/Pstd) * (Tstd/Thab)

Multiplying habitat density by the mass fraction of oxygen gives you the oxygen concentration:

                C-O2 = dens-hab * mass frac O2  (suggested units kg/cu.m)

For Earthly air at sea level pressure and standard temperature,  the density is 1.225 kg/cu.m,  and the concentration of oxygen is 0.275 kg/cu.m.  If the habitat oxygen concentration is that value or less,  the fire reaction speeds and energy release rates should be as slow (or slower) than on Earth.

Now,  using exactly the pre-breathe limit factor of 1.20,  you want your habitat atmosphere to equal the selected value of suit dry oxygen pressure,  and so the habitat nitrogen pressure is 1.2 times that oxygen pressure.  That is the inherently-high oxygen volume fraction of 1/(1 + 1.2) = 0.4545,  but the atmospheric pressures being considered here are well below sea level. 

For a range of suit oxygen pressures from about 0.13 atm up to about 0.24 atm,  habitat pressures vary strongly,  and so does oxygen concentration.  This is shown in Figure 5.  The note regarding “synthetic air” refers to a synthetic Earthly air,  at 20.946% oxygen,  with the remainder all nitrogen.  The habitat atmospheres considered here all have more oxygen content and less nitrogen content than a true synthetic Earthly air. 

Referring again to Figure 5,  the derived habitat atmospheres as a function of oxygen suit pressure reach the Earthly oxygen concentration limit of 0.275 kg/cu.m at a suit pressure of 0.2165 atm,  and a habitat atmosphere pressure of 0.4663 atm.  That’s your upper limit for fire reaction rates equal to Earthly rates at sea level.  It corresponds to a suit pressure lower than current practices,  and 45.45% oxygen by volume in the habitat two-gas mix. 

Note in Figure 5 that the volume percent-as-fire-criteria is always violated,  while in this pressure range,  the partial-pressure-of-oxygen criterion is satisfied until you get very close to the concentration criterion limit.   Yet,  it is these two items working together that actually determine the concentration-driven reaction rates in the fire chemistry.  Thus it is oxygen concentration that is the real fire danger criterion,  and it should not exceed sea level Earthly values,  for fires not to exceed familiar Earthly rates.  By this criterion,  you may actually have a slightly-higher suit pressure than by the partial pressure criterion.  But you may not lower it without triggering pre-breathe time requirements. 

Figure 5 – Comparing Fire Danger Criteria from Increased Oxygen Content

In view of that result,  what you really want to do is identify a minimum suit pressure design that you want to accommodate,  and use it to set your habitat atmosphere.  That way,  for that suit,  and for any higher pressure designs,  you will not trigger any pre-breathe time.  This is based on the design pressure,  not the factor-1.10 leaked-down pressure.  This is shown in Figure 6 for two candidate designs:  the 8.7 kft equivalent “A”,  and the 10 kft equivalent “B”,  with the habitat atmosphere “set” by the lower-pressure 10 kft equivalent design.  Both the 1.10 leak-down and 1.20 pre-breathe factors were applied. 

Doing this produced the results tabulated in the figure:  all the pre-breathe factors were at,  or under,  1.20,  all the way up to (and beyond) the “limit” suit design pressure of 0.2165 atm.   There is nothing about this selection which precludes suit pressures as high as current practice!

Note that the factor 1.10 leak-down points are also shown.  Decompression down to them is not an issue;  you will only be recompressing from them up to habitat pressure. 
 Figure 6 – Relating Oxygen Suit Pressures to Habitat Synthetic Air Compositions Subject to Fire Safety

Final Results:

These were calculated with a spreadsheet,  and are given in Figure 7.  The habitat atmosphere data is given in the upper part,  and the data for the A and B suit designs (design and leaked-down)in the lower part,  along with the “limit” suit design (at design only).  Bear in mind that the habitat atmosphere is a two-gas oxygen-nitrogen mix set at 45.45% volume percent oxygen,  it is fixed.  Bear also in mind that still-higher suit pressures,  are also compatible with this. 

Figure 7 gives suit and habitat pressures in a variety of measurement units for a variety of readers.  Note that the wet-in-lung partial pressure of oxygen in the habitat atmosphere is identical to that from the min-pressure design suit (the 10 kft B design).  This fell within the cabin pressure altitude range considered adequate for a pilot’s cognition (10,000 feet,  actually). 

The habitat atmosphere is 0.4242 atm (6.420 psia),  and 45.45% oxygen,  the rest nitrogen.  The lowest compatible (no pre-breathe required) oxygen suit pressure is 0.1930 atm (2.836 psia),  substantially lower than current NASA practice (3.8-4.2 psia).  Lower-pressure suits might require pre-breathe time,  but no higher-pressure suit would require any. 

This lowest compatible-pressure suit (at 146.7 mm Hg) is also substantially reduced from the 1968-vintage experiments of Dr. Paul Webb with his mechanical counterpressure (MCP) designs based on stretchable fabrics.  His experiments back then used about 170-190 mm Hg as the suit pressure. 

Under the conditions proposed here,  such MCP designs are far more feasible.  And,  conventional full pressure suits are far more comfortable,  and easier to design.

Finally,  the habitat atmosphere calculates to have (at 25 C = 77 F) an oxygen concentration of 0.245 kg/cu.m (per Figure 6 above),  which is less that Earthly air at sea level pressure (0.275 kg/c.m).  The fire danger in this habitat atmosphere should be no worse than Earthly sea level air,  and might actually be slightly reduced,  in spite of the high oxygen percentage. 

Figure 7 – Results for Recommended Suit Pressures and Recommended Habitat Synthetic Air

Final Comments

What I propose here is a low-pressure habitat atmosphere enriched in oxygen content,  yet safe enough in terms of fire danger,  while not requiring any pre-breathe time for pure oxygen space suits of suit pressure far lower than current practice.  Both the habitat and the min-pressure suit design maintain the wet in-lung oxygen partial pressure of Earthly air at an elevation of 10,000 feet,  considered by most authorities as quite adequate for pilot-level cognition.  There is no reason that explorer-type astronauts cannot make use of this in vehicles and space stations located anywhere in the solar system. 

Colonist-astronauts are different:  there are decades of exposure,  not just months or years,  and there are the inherent (and so far unknown) risks of pregnancy and child development.  For that situation,  I recommend that we “dance with who brung us”:  we evolved in Earthly-air at elevations from sea level to around 15,000 feet. 

We are genetically adapted to that.  So use it. 

I would recommend real synthetic air (20.946% by volume oxygen,  the rest nitrogen),  at an equivalent pressure altitude not to exceed about 10,000 feet. You will always have pre-breathe time to contend with,  when decompressing down to a relatively low-pressure oxygen suit.  Recognize that,  and just deal with it.

A suggestion for “dealing with it”: 

Those parts of the colony where pregnant women and young children might be,  should have oxygen-nitrogen at 20.946% oxygen,  and no less than the 10.11 psia that is equivalent to 10,000 feet elevation (0.1441 atm partial pressure of oxygen,  0.5437 atm partial pressure of nitrogen).  That’s 0.1311 atm wet in-lung partial pressure of oxygen, same as the min-pressure suit design. 

Other parts of the colony could use the 45.45% oxygen mix at 6.24 psia (0.1930 atm partial pressure of oxygen,  0.2316 atm partial pressure of nitrogen).  People using suits outside could decompress from the 45%/6.24 psia blend without any pre-breathe time.  That’s also 0.1311 atm wet in-lung partial pressure of oxygen,  same as the min-pressure suit. 

Everybody gets the same wet in-lung oxygen partial pressure,  whether in the habitat with synthetic air at 10.11 psia, the enriched blend at 6.24 psia,  or the min-pressure suit design at 2.84 psia.  There’s no pre-breathe time for decompressing to any higher-pressure suit designs,  although there would for yet-lower pressure designs. 

Whether any pre-breathe decompression time is needed going from the higher-pressure portion of the colony to the lower-pressure portion is something still unknown to me.  But the change is rather modest,  so any such decompression time should also be modest.

If any readers actually know that answer,  please weigh in with your comments!

Sunday, March 4, 2018

Forget the Stupid Wall!

The following article appeared in something fairly close to its submitted form,  in the Waco "Tribune-Herald",  on Wednesday,  Feb 28,  2018.  Here is the as-submitted article:


The notion that a border wall will solve our immigration problems is political propaganda deliberately intended to deceive you.  I can defeat a 30 foot high $25B dollar wall in under 5 minutes for under $150.  So can anybody else,  on either side of the border.  All it takes is a 40 foot extension ladder,  a coil of rope to let you down on the other side,  and a pair of leather gloves so you don't burn your hands sliding down the rope.

You solve the illegal immigration problem by matching immigration policy with the actual facts on the ground.  Policy is out of balance with the facts on the ground by a factor not far from 100.  This has been so for many decades,  and we have had an illegal immigration problem for those same many decades.

The facts no one wants to hear:  the jobs that few Americans want,  because the pay is really crummy (at best) and the work is hard,  are up here.  The work force,  willing to do those hard jobs for really crummy pay,  is down there.  I'm talking about cleaning toilets,  mowing lawns,  and pouring concrete,  among others.  More Americans might actually do those jobs if the pay weren't so crummy,  but as long as the immigrants are illegal,  they can be extorted into doing those jobs for pay that bad.  "Catch 22".

What I'm talking about is the guest worker visa program,  where immigrant workers and their families come over to take those jobs.  The quota is between 100,000 and 150,000 such visas in any given year (look this up online for yourself if you don’t believe me).  The illegal immigrant population of 10 to 12 million tells you what the actual size of this job market and the corresponding labor force really is.  As I said,  about factor 100 out of balance.  And for over 7 decades now.

It is no secret that these people would starve in Mexico.  They come up here to survive.  They WILL come just to survive,  legally or not.  The reason they come illegally is that they cannot get a legal visa,  because the quotas are set factor 100 too low.  

All that being true,  why would anyone be surprised that we have a lot of illegal immigrants?  Anybody actually surprised by this must be of subnormal intelligence,  or hasn't paid attention to reality,  or else has come to believe the lying political propaganda put forth about this problem.  

This is a problem neither party will admit to,  because they get re-elected by putting out lying propaganda about it.  By the way,  people are dying in the desert because of that political perfidy.  How unethical/evil and un-Judeo-Christian is that?

There would be no DACA problem if both parties hadn't let this perfidy go on for many decades. If we fix the guest worker program,  the DACA problem goes away in a single generation.

My advice:  stop electing and re-electing these evildoing idiot politicians.  Find some who will actually fix the guest worker quotas.  Then we will have absolutely no need of that utterly idiotic $25B wall.


Comments regarding this posting:

First:  assuming the average immigrant family size is two working parents with 4 children,  then the actual number of these jobs the immigrants come north to do is around 2/6 of the immigration population,  or something like 3-4 million jobs that are hard and low-paying.  That's still far more than factor-30 out-of-whack with the guest worker visa quotas,  even if you refuse the workers' families entry (which would be inhumane).

Second:  most of the immigration has been Mexican citizens seeking a living until recent years.  Now there are a lot of refugees from violence coming up from Central and South America.  I didn't include that in my submitted article.  It is related,  but generally,  a refugee from violence is a different problem from a guest worker who cannot get a legal visa.  They,  too,  need a way to make a living,  so it also affects the ridiculously out-of-balance quota problem.

Saturday, February 24, 2018

Yet Another School Shooting

A slightly-shortened version of this article appeared in the Waco Tribune-Herald newspaper as a guest column on Wednesday 21 February 2018.  I received one phone call from a reader I did not know,  indicating total agreement with what I wrote.  His only comment was calling a gun's ammunition magazine a "clip" is technically incorrect,  although most of the public does so.

Here is the full-length,  as-submitted form of the article:


The latest school shooting incident in Parkland,  Florida,  exemplifies exactly the two “big-ticket” things demonstrated by the gun violence data,  if one actually goes and looks:  (1) we have a leak in the background check process that allows crazy people to get guns legally,  and (2) we are utterly failing to adequately defend our gun-free zones.  If you wish the lost kids' lives to have any lasting meaning,  then do something about those two problems!

Those same gun violence data (available in mass quantity from also show no significant protections are to be had from “the usual proposals”:  clip size limits,  “assault” rifle bans,  and such like. 

If you want to see exactly how to analyze such data,  visit,  click on year “2016”,  then click on month “June”,  then read the article titled “What the Gun Violence Data Really Say”,  dated June 21,  2016. 

I put quotes around “assault” rifle,  because things like the AR-15 are exactly like any semi-automatic hunting rifle in terms of firing rate.  The cosmetics have nothing to do with lethality. 

That being said,  it would be wise to ban bump stocks and trigger cranks,  those being devices that increase the firing rate of a semi-automatic weapon into the range of a fully-automatic weapon (machine gun).  The ban on civilian machine guns dates to the 1930’s,  with organized crime gangs using them in the streets.  That ban actually has been proven quite effective. 

Down to brass tacks:  Crazies Getting Guns

The current form of the ban on crazy people possessing guns is based on a court decision of insanity.  It’s a go/no-go “gate”:  if there is no court verdict of insanity,  there are no grounds to deny sale of the weapon. 

And that is exactly what was wrong with the Columbine incident,  the Gabby Giffords incident,  the Las Vegas incident,  many others,  and now the Parkland,  Florida incident.  Sandy Hook was different:  that shooter murdered his mother to steal her guns. 

In each case,  there were family,  friends,  and others aware of the mental problems of the shooters,  before their respective incidents.  In this last case (Parkland,  Florida),  many classmates and teachers knew this person was dangerous with a gun,  it appears the local law enforcement might have known “something” was wrong with him,  and the FBI was tipped off but failed to follow up. 

We need a multi-step decision process,  where anyone can voice a concern,  which leads to a real background investigation questioning real people who know or have interacted with the person in question,  not just an on-line records search.  That extra effort costs,  but the benefit is incidents prevented and lives saved. 

It all gets down to whether money trumps lives,  or vice versa.  Simple as that.  I recommend you judge your elected officials accordingly.

But,  the triggering of a deeper investigation must not presume “guilt”,  until and unless actual facts determine there really are mental problems.  We have to be very careful and very fair how we do this.  But it will help,  and very much more significantly than any of the usual gun control proposals. 

Down to Brass Tacks:  Adequately Defend the Gun-Free Zones

This is something we are currently not doing at all.  Accordingly,  the people in these gun-free zones are perceived to be sitting duck targets by both the crazies-with-guns and the terrorists.  And they are sitting-duck targets. 

Don’t get me wrong:  there are perfectly good reasons to have gun-free zones.  Schools,  shopping centers,  and churches are but a few of many such venues.  Everybody understands why this is so.

But,  we learned in the 19th century frontier towns that you have to defend your gun-free zone adequately.  That means a properly qualified guard or guards,  and a response time under 1 minute. 

Properly-qualified means peace officer training,  not just concealed-carry training.  This is because any armed guard will be called upon to respond as a peace officer if there really is trouble to quell.

The 1-minute response is based on the fact that those same 19th century frontier towns were small.  A deputy from the sheriff’s office could be anywhere in town in under a minute at a dog-trot,  at the first sign of trouble.  When towns got bigger (more than a minute to respond),  death tolls went up.  Simple as that. 

So,  defend the gun-free zones,  and the crazies and terrorists will no longer attack those venues,  by and large.  This will reduce deaths quite significantly,  unlike the “usual proposals”.

Again,  does the money trump the lives,  or vice versa?  That’s how you have to judge those charged with making these decisions.


Follow-up comments for this posting:

In the days following the shooting in Parkland,  it has been revealed that a deputy did not go inside and take on the shooter immediately.  Why has not yet been revealed.

But,  one possible reason is being outgunned by the shooter.  Most deputies have a revolver as a sidearm,  something little different from an Old West six-shooter.  Compared to a semi-automatic rifle,  that kind of weapon has less stopping power,  less rate of fire,  a less effective range,  and a much smaller quantity of shots,  before a much slower reload process is required.  A deputy with nothing but a revolver is way-outgunned.  

Such a deputy is properly qualified as a peace officer,  but is not properly equipped to do his job taking on a heavily-armed shooter.  So,  in addition to what I said above about who is qualified to defend a gun-free zone,  such a guard must also be properly equipped.

In this article,  I also didn't take on mental health care in this country.  There is something about modern American life that seems to be both causing mental issues,  and provoking sufferers to act out.  That issue needs to be fixed.  Again,  hold your politicians accountable.

Arming teachers to be the guards is a bad idea because:  (1) it destroys the atmosphere of trust in the classroom,  (2) the teachers have way more than enough to do already without being called upon to act as guards,  (3) no teacher armed with a handgun is adequate against a shooter armed with long guns,  and (4) nobody will pay them to take on the added risk and workload (they are already not paid enough even just to be teachers).  That idea is just insane.  Whether it comes from Wayne LaPierre or Donald Trump,  it is still insane.

One other point:  there is no difference between an AR-15 and a semi-automatic hunting rifle in terms of lethality.  Neither weapon is a proper "assault weapon" in today's military environment,  because neither is a machine gun.  Period.  End of issue.

Those calling AR-15's "assault weapons" display their ignorance for all to see.  Semi-automatic weapons were actually obsolete before Vietnam,  and proved in combat to be a real loser of an idea for battle in Vietnam.  (That does not address the comparison of the fully-automatic machine gun form M-16 versus the machine gun AK-47,  or the decades it took to correct the reliability problems experienced with the M-16 that the AK-47 did not suffer.)

But,  there is the issue of law enforcement being able to visually determine what they are up againstNo one adds a bump stock or a trigger crank to a hunting rifle.  Protecting our law enforcement people from semi-automatic weapons modified to be effective machine guns (as in Las Vegas) might actually be a good reason not to sell AR-15's and similar to the public.  That idea does deserve some thought and discussion,  even though we already know in general that most prohibitions don't work. 

In conclusion:  "something" needs to be done,  that's for sure.  My take on it is:  why not try those things that might actually confer significant benefit,  instead of the same,  lame old "knee-jerk" things that we already know won't help?

Find a way to stop selling guns legally to crazy people.

Defend the gun-free zones properly.

Friday, February 9, 2018

Launch Costs Comparison 2018

This article compares and correlates unit costs for launchers,  mostly those used commercially.  These data are based upon reported payload capacities and launch costs found in the literature.  The format is cost per unit delivered payload mass,  on the very important assumption that the launcher flies fully loaded.  All figures are at the end of this article.  Click on any figure to see any or all of them enlarged.  You can close that view box and be right back to viewing this article.  

Results are reported in millions of dollars per delivered metric ton,  and in dollars per delivered pound.  To estimate the unit cost when flying at less than full load,  simply divide these unit costs by the fraction of fully-loaded that you intend to fly. 

Scope includes the launchers used in the competitive satellite launch business,  plus a few launchers that were used,  but not competitively,  and the US Space Shuttle as representative of a large spaceplane.  Some of these launchers are no longer in service.  However,  the correlation results are used to predict unit costs for the NASA SLS block 1,  just for comparison.

Data,  Sources,  and Results for “Standard Low Earth Orbit”

“Standard Low Earth Orbit” is 23 degree inclination out of Cape Canaveral,  Florida,  to a 200 km orbit altitude.  This is what the reported payload delivery capabilities in the literature refer to.  These data are for one-way delivery of payload using a simple payload shroud,  not a recoverable capsule,  except for the Space Shuttle.  As researched,  those data are:

Of these,  the US Space Shuttle,  the Titan IVB,  and Falcon-1 are no longer in service.  There is a demonstrated history of reliability problems with Proton-M.  The Titan-IVB was retired in 2005.  The Falcon-1 retired no later than 2012.  The Space Shuttle retired in 2011.  The prices shown are for fully-expendable flights in the case of Falcon-9 and Falcon-Heavy.  There should be some small price break for flying reusably at reduced payload with these two launchers,  although how much is but speculation. 

The trends of unit cost per delivered metric ton (flying fully-loaded) are given in Figure 1.  Figure 2 shows unit cost per delivered pound.  Data are grouped and correlated as “competitive”,  “non-competitive”,  and “spaceplane.  The “competitive” launchers correlate flying fully loaded as:

                Unit cost $M/metric ton = 10.557 e^(-0.033 Wp)  where Wp = delivered payload, metric tons

                Unit cost $/delivered lb  =   4787 e^(-0.033 Wp)   where Wp = delivered payload, metric tons

The launchers marked “competitive” all compete in the commercial (and military) satellite launch businesses,  with market share in part depending upon price.  The launchers marked “non-competitive” never competed commercially,  and thus were not subjected to severe pressure on price.  The model for these assumes the same -0.033 Wp factor,  and uses a coefficient that forces the curve through the average of the Titan IVB and Delta IV Heavy data points: 

                Unit cost $M/metric ton  =   39.1 e^(-0.033 Wp)  where Wp = delivered payload,  metric tons

                Unit cost $/delivered lb = 17,720 e^(-0.033 Wp)  where Wp = delivered payload,  metric tons

This model was extended to 70 metric tons payload to estimate what should be expected for NASA’s SLS block 1 as shown in the figures ($3.878M/m.ton and $1759/lb).  That calculation corresponds to an expected launch cost of $271M,  when NASA’s actual launch cost estimate is $500M,  and its critics estimate twice that.  So instead of only 3 times more expensive than Falcon-Heavy (otherwise comparable in payload) as predicted by the correlation,  SLS block 1 is likely to be at least 6 times more expensive,  and it might even be 12 times more expensive.

The Space Shuttle (marked “spaceplane”) is quite different,  in that the delivered payload is but a small fraction of the mass of the recovered vehicle.  All the others are one-way trips to space,  with the delivered payload encased in a shroud.  There are no recovered capsules delivered by these launchers. 

The spaceplane model for the Space Shuttle assumes the same -0.033 Wp factor as the “competitive” launchers,  with a coefficient that puts the curve through the data point for the Shuttle:

                Unit cost $M/metric ton  =   131 e^(-0.033 Wp)  where Wp = delivered payload,  metric tons

                Unit cost $/delivered lb = 62,580 e^(-0.033 Wp)  where Wp = delivered payload,  metric tons

Re-Scaling Results for Delivery at the International Space Station (ISS)

I used the payload reduction fraction seen with the Space Shuttle as a constant applied to all the launchers still in service,  for estimating unit cost performance delivering to the ISS.  The ISS is located at a higher inclination and a higher orbit altitude.  For the same launcher technical performance,  a launcher’s max payload capability must be reduced when reaching for the more demanding destination. 

Flying with a 7 person crew,  the Space Shuttle is listed as 24 metric tons to standard low Earth orbit.  It could deliver as much as 27.5 tons,  but only with a smaller crew and less supplies.  Flying with a 7 man crew,  its capability to ISS is reduced to 16 tons.  That is 2/3 of the standard low Earth orbit capability with the same crew and supplies.  Applying this 2/3 factor “across the board” with the same launch prices produces Figures 3 (per ton) and 4 (per pound) below. 

I correlated unit cost estimates to ISS only for the “competitive” launchers that are still in service.  These are (of course) somewhat higher than for “standard low Earth orbit”,  because payload capability is lower,  while launch price is not.  This for one-way payload delivery using a simple payload shroud,  not a recoverable capsule.  That model is:

                Unit cost $M/metric ton = 15.428 e^(-0.048 Wp)  where Wp = delivered payload,  metric tons

                Unit cost $/delivered lb   =    6996 e^(-0.048 Wp)  where Wp = delivered payload,  metric tons

Estimating the Effects of Reusability

I based this estimate on what Falcon-9/Cargo Dragon has demonstrated to ISS with re-use of first stages,  when loaded to max cargo for ISS,  versus what I estimate the fully-expendable deliverable payload is to ISS.  The fully expendable estimate is 15.2 metric tons to ISS.  A fully-loaded (for ISS) Cargo Dragon is 8.8 metric tons.  That ratio is 0.5789,  and I assume it applies to Falcon-Heavy for its payload delivery to ISS with re-use of first stage cores.  The results are given in Figure 5,  for both full price and for an arbitrary modest price break:  80%-of-full-price,  representing savings from re-use. 

Estimating What SLS Block 1 Might Really Do (Standard Low Earth Orbit)

SLS Block 1 is said to deliver 70 metric tons to standard low Earth orbit.  NASA says it expects each launch to cost roughly $500M.  NASA’s critics say each launch might cost nearer $1000M = $1B.  Those data correspond to $7.14-to-14.28M/delivered metric ton or $3239-6478/delivered pound (flying fully loaded). 

The “non-competitive” launcher correlation predicts for SLS Block 1 a unit cost of $3.878/delivered metric ton or $1759/delivered pound (flying fully loaded).  Falcon-Heavy has an almost comparable payload (63.8 vs 70 metric tons),  with unit costs of $1.411M/delivered metric ton or $640/delivered pound (flying fully loaded and fully expendably).  SLS will never be reusable,  as that was never considered as a design requirement. 

SLS is expected to fly only once a year,  and not until 2019 or 2020.  Falcon-Heavy flew its maiden test flight in February 2018.  It is scheduled to fly at least two more times in 2018. 

Other Launchers to Watch For (That Are Not Yet Flying)

There will be an Ariane 6.  Long March 5 may or may not be flying yet.  United Launch Alliance is designing a new heavy lifter to be called Vulcan.  The Jeff Bezos organization Blue Origin is designing a heavy lifter to be called New Glenn.  Spacex is working on a design called BFR which will be a super-heavy-lifter with a fly-back first stage combined with a second stage that is also a reusable spacecraft. 

Final Note:  Falcon-9 Cargo Dragon to ISS

Full price for a Falcon-9 launch is $62M.  This can send to ISS a Cargo Dragon totaling 8.8 metric tons.  Of that,  only 3.310 metric tons is actual deliverable cargo.  Using that 3.31 tons,  the effective unit costs for delivery to the ISS are: 

                $18.73M/delivered metric ton = $8495/delivered pound

Given the same 80% of full price with reusability,  as was used above,  these data reduce to:

                $14.98M/delivered metric ton = $6796/delivered pound

Compare those with what the Space Shuttle costs were,  delivering 16 metric tons to the ISS at $1.5B per launch:

                $93.75M/delivered metric ton = $42,517/delivered pound

These are the best guesses I have for Enhanced Cygnus on Atlas V 551,  and they are not accurate.  The max deliverable mass to ISS is 12.34 metric tons,  which has to be larger than the loaded Cygnus.  Data gleaned from multiple sites on the internet says the max payload to ISS inside the Cygnus is 3.5 metric tons max.  Cygnus cannot return to Earth.  Each launch is $153M.  Those unit costs are thus crudely:

                $46.M/delivered metric ton = $21,000/delivered pound

I have no reliable data on the cargo version of Soyuz,  riding the R-7 rocket.  Best guesses are max 2.4 metric tons of payload in the capsule,  and a launch cost on the order of $65M.  Those unit costs are:

                $27.1M/delivered metric ton = $12,300/delivered pound

Thus,  cargo Dragon on a Falcon-9 appears to be the most cost-effective means to deliver self-maneuvering and self-rendezvousing cargo to the ISS,  of all the vehicles that have done this task.  
Prior Similar Articles

This article replaces earlier postings on this site.  The best of the older postings is “Access to Space:  Commercial vs Government Rockets”,  dated August 7,  2015.  That one compares multiple rockets with the best inflation-corrected costs I could find or devise.  The one prior to that was “Revised Launch Cost Update” dated September 13,  2012.  It refers in turn to “Revised,  Expanded Launch Cost Data” dated May 26,  2012.  That one in turn was a revision to the original “Launch Cost Data” article dated January 9,  2012.  But this current posting is the best,  with the latest versions of the rockets,  and the most current costs I could find.  I did not inflation-correct costs from 2016 to 2018 values.

Figures Follow:

 Figure 1 – Unit Cost Comparison (per ton) to Standard Low Earth Orbit

 Figure 2 – Unit Cost Comparison (per pound) to Standard Low Earth Orbit

Figure 3 – Unit Cost Comparison (per ton) to ISS

 Figure 4 – Unit Cost Comparison (per pound) to ISS

Figure 5 – Unit Costs for Falcon Vehicles as Payload-in-Shroud to ISS with Re-Use

Thursday, January 18, 2018

Weather Versus Climate

This sketch explains why a cold winter does not disprove global warming,  despite what the skeptics so love to claim.

While only an over-simplified  sketch,  the picture speaks for itself.  If you see both harsher winter cold snaps and hotter summer heat waves,  that's one of the tell-tale symptoms of global warming!

As indicated in the sketch,  the extra heat energy goes into powering wider weather swings.

We can always debate as to why the warming might be occurring.  But it is definitely occurring,  despite the harsh winter conditions of January 2018.

If you want to see something about causality,  go see the article titled "Do We Fight Global Warming or Not?",  dated 4-15-17,  on this website.

Wednesday, December 13, 2017

Alabama Special Senate Election Outcome 2017

Well,  the voters of Alabama selected a Democrat rather than an alleged child molester to be their senator in the special election of 12-12-17.  That's a good thing,  but there's a downside.

They only voted that way by around a percent or so margin.  That means very nearly half the voters in Alabama that day actually preferred the child molester to represent them,  just for the political party advantage.

When the voters are so deluded by party propaganda as to effectively have no ethics,  then why is it a surprise that so many politicians are similarly detestable?

Thursday, November 23, 2017

A Better Version of the MCP Space Suit?

This is a concept proposal for a better version of the mechanical counter-pressure (MCP) space suit.  It combines the best features and eliminates the worst disadvantages of the particular two MCP design approaches upon which it is based.  These are the “partial pressure” suit of the 1950’s and the “elastic space leotard” of Dr. Paul Webb.  The result should be a lightweight,  supple (non-restrictive) suit that with suitable unpressurized outerwear,  can be used on pretty much any planetary surface even if totally airless,  or even in space.  It need not use exotically-tailored materials in its construction.  It should be relatively easy to doff and don.

This article updates earlier articles on this subject.  Those are:

Date           title             

2-15-16     Suits and Atmospheres for Space  (supersedes those following)
1-15-16     Astronaut Facing Drowning Points Out Need for Better Space Suit
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

The idea here is to combine the two demonstrated approaches that both apply the fundamental MCP principle:  the body needs pressure applied to its skin to counterbalance the necessary breathing gas pressure.  The body simply does not care whether this counter-pressure is applied as gas pressure inside a gas balloon suit,  or is exerted upon the skin by mechanical means.

The first article cited in the list above (“Suits and Atmospheres for Space” dated 2-15-16) determines that pure oxygen breathing gas pressures from 0.18 atm to 0.25+ atm should be feasible.  How that was calculated is not repeated here.  My preferred range of helmet oxygen pressures is 0.18 to 0.20 atm,  for which wet in-lung oxygen partial pressures range from 0.11 to 0.13 atm,  same as the wet in-lung oxygen partial pressures in Earth’s atmosphere at altitudes between 10,000 and 14,000 feet. 

However,  only 0.26 atm gives you the same wet in-lung oxygen pressure as sea level Earth air.  The 0.33 atm used by NASA is entirely unnecessary,  unless to help overcome the exhaustive efforts necessary to move or perform tasks,  in the extremely stiff and resistive,   heavy,  and bulky “gas balloon” suits they use.

The 1940’s design that operationally met the need for extreme altitude protection for short periods of time was the “partial pressure” suit of Figure 1,  in which compression was achieved with inflated “capstan tubes”.  These suits were widely used into the 1960’s.  The capstans pulled the non-stretchable fabric tight upon the torso and extremities.  This provided the counterpressure necessary for pressure-breathing oxygen during exposures to vacuum or near vacuum,  for durations up to about 10 minutes long.  This was for bailouts from above 70,000 feet,  and would have worked for similar short periods even in hard vacuum.  Hands and feet were left uncompressed,  but for only 10 minutes’ exposure,  these body parts could not begin to swell from vacuum effects. 

The advantages of this design were (1) ease of doff and don,  (2) it was simple enough to be quite reliable,  and (3) it was not very restrictive,  whether the capstan tubes were pressurized or not.  The disadvantages were the achievement of rather-uneven compression,  and leaving the hands and feet completely uncompressed.  This limited the allowable exposure time by (1) uncompressed small body parts begin swelling in about 30 minutes,  and (2) between the uncompressed parts and the uneven compression achieved on the extremities,  blood pooling into the under-compressed parts could lead to fainting within about 10 to 15 minutes. 

Figure 1 – Partial Pressure Suit Design Used From the late 1940’s to the Early 1960’s

In the late 1960’s,  Dr. Paul Webb performed striking experiments with an alternative way to achieve mechanical counterpressure upon the body.  He used multiple layers of elastic fabric (the then-new panty hose material) as a tight-fitting leotard-like garment.  This was not a single-piece garment.  It achieved more-uniform compression on the torso and extremities than did the older partial pressure suit.  Dr. Webb included elastic compression gloves and booties,  so that the entire body was compressed,  removing the time limits.  Breathing difficulties were solved with a tidal volume breathing bag enclosed by an inelastic jacket. 

Breathing gas was pure oxygen at 190 mm Hg pressure (0.25 atm) fed into the helmet from a small backpack with a liquid oxygen Dewar for makeup oxygen.  This type of garment was very unrestrictive of movement,  and was demonstrated quite adequate for near-vacuum exposures equivalent to 87,000 feet,  for durations up to 30 minutes.  It was intended for possible application as an Apollo moon suit,  but could not be made operationally ready in time.  It has been mostly forgotten ever since.

The advantages are very unrestricted movement,  very light weight (85 pounds for suit plus helmet plus oxygen backpack),  and no need for a cooling system:  you just sweat right through the porous garment,  same as ordinary street clothing.   Plus,  the garment’s pieces were quite launderable.  Dr. Webb’s test rig is shown in Figure 2.  6 or 7 layers of the panty hose material provided adequate counter-pressure.

Figure 2 – Dr. Webb’s “Elastic Leotard” MCP Space Suit Prototype as Demonstrated

The disadvantages were essentially just difficult (time-consuming) efforts to don and to doff the garment’s pieces,  precisely because they were inherently very tight-fitting.  For use on a planetary surface or out in space,  one treats the suit as “vacuum-protective underwear”,  and adds insulating or otherwise protective non-pressurized outerwear over it.  So protection from hazards is not a disadvantage at all,  but only if one uses the vacuum-protective underwear notion. 

The main advantage of Dr. Webb’s “elastic space leotard” over the “partial pressure” suit was the more even (and more complete) compression achievable with the elastic fabrics.  The main advantage of the “partial pressure” suit over the “elastic space leotard” was the ease of donning and doffing the garment,  when the capstan tubes were depressurized,  releasing the fabric tension.  Both approaches offer very significant advantages over the “gas balloon” suits in use since the 1960’s as space suits:  lighter,  launderable,  and far,  far more supple and non-restrictive for the wearer. 

That suggests combining both of the successful MCP design approaches (inflated capstans and elastic fabrics) into a single mechanical counterpressure suit design.  The capstans apply and relax the tension in the fabric which provides the counter-pressure on the body,  and the elastic fabric makes the achievable compression far more uniform.  What is required from a development standpoint is experimental determination of the number of layers of elastic fabric required for each piece of the garment,  in order to achieve the desired compression in every piece. 

If done this way,  there is no need for directionally-tailored stiffness properties in specialty fabrics,  the basis of Dr. Dava Newman’s work with mechanical compression suits (see Figure 3).   Ordinary commercial elastic fabrics and ordinary commercial joining techniques can be used.  In other words,  pretty much anyone can build one of these space suits!

Figure 3 – Dr. Dava Newman’s MCP Suit Based on Directionally-Tailored Fabric Properties

So,  the MCP suit proposed here has certain key features (see list below).  It will resemble the old “partial pressure” suits,  except that protective outerwear (insulated coveralls,  etc.) get worn over the compression suit itself,  and the helmet is likely a clear bubble for visibility.  There is an oxygen backpack with a radio.  There is no need for any sort of cooling system.  Everything is easily cleaned or laundered free of dust,  dirt,  sweat,  and similar contamination.

Key features list:

#1. Pressurized capstan tubes pull the elastic fabric tight whenever the helmet oxygen is “on”,  but depressurize and slack the garment tension when helmet oxygen is “off”.  The capstan tubes are just part of the oxygen pressure breathing system.  Slacking the fabric tension makes doff and don far easier.

#2. The multi-piece garment is composed of multiple layers of elastic fabric to provide the desired level of stiffness that will achieve the desired level of compression in each piece of the garment.  This depends upon both the shape of the piece,  and upon how much circumferential shortening is achieved by inflating the capstan.

#3. The pressure garment is vacuum-protective underwear,  over which whatever protective outerwear garments are worn that are appropriate to the task at hand.  For example,  the wearer might need white insulated coveralls and insulated hiking boots,  plus insulated gloves.  One could even add some sort of simple broad-brimmed hat to the helmet if sunlight were intense. 

#4. The clear bubble helmet is attached to the torso garment piece. This torso garment piece also incorporates an inelastic jacket surrounding a tidal volume breathing bag.  Helmet,  breathing bag,  and capstans all pressurize with oxygen from the supply simultaneously,  and are (in fact) connected.  All are activated by one on/off control.

#5.  The oxygen backpack is just that,  no cooling system required.  It probably uses liquid oxygen from a Dewar as make-up oxygen,  has regeneratable carbon dioxide absorption canisters,  and a battery-powered radio.   It might also contain a drinking water feed connected to the helmet.  Attitude and translation thrusters for free flight in space can be a separate chair-like unit,  and this function is entirely unnecessary on a planetary surface.

#6. For concave body surfaces and complex shapes like genitalia,  the pressure suit can incorporate semi-fluid gel packs that surround these body parts,  making the body effectively convex everywhere.

How all this works together is shown conceptually in Figure 4.

Figure 4 – How the Capstans and Elastic Fabric Work Together for an Improved MCP Suit

About the only caveat might be that the breathing gas pressure could be too small to also serve as the capstan inflation pressure.  If that should prove to be true,  then there need to be two final pressure regulators in the oxygen backpack,  instead of just one.  That problem can be easily solved!