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Use the long-known NASA criterion for no pre-breathe time.  The partial pressure in the habitat,  of the nitrogen,  may not exceed the total pressure of the pure oxygen fed to the suit,  by more than a factor of 1.2. 

If you satisfy that criterion,  there is no "pre-breathe" time associated with donning an oxygen suit and going outside immediately,  without risking the bends from the nitrogen. 

If you do more than about half an atmosphere of 21% O2/ 79% N2 mix in the habitat atmosphere,  at more than around 0.5 atm hab atmosphere pressure,  this is impossible to do. 

But half or a little less than half an atmosphere of oxygen-nitrogen mix in the habitat atmosphere,  meets that criterion for donning a pure O2 suit and just going outside with no pre-breathe.

GW

Propellant manufacture is by far more hungry for high oxygen generation rates.  The equipment to do this will inherently be large,  and power-consumptive.  There is no way around that ugly little fact of life.

I rather think that electrolyzing water purified from mined ice is the better choice for propellant manufacture,  especially if the propellant is LOX-LH2.  Your biggest energy expenditure will be for liquifying the gases.  Although electrolysis might be a fairly close second,  if the ~6% efficiency typical here obtains there. 

It is possible to get LOX-LCH4 propellants by using both water and Martian CO2.  But it's neither electrolysis nor the Moxie process.  Just more big heavy,  power-consumptive machinery to do it on a big scale. 

Purifying water from likely-polluted ice is a thermal process after an initial filtering process.  Either you distill it,  or you freeze it.  Sea water freezes to fresh water ice,  enhancing the brine content in the sea water just below the ice cake.  You could run it through 2 to 4 steps of that,  and get most of the various salts out,  possibly even including the perchlorates.  But all the water you start with will reach the end as product;  there will be significant concentrated brine waste.  You can take advantage of the cold environment to do the freezing.  Distillation would work just like it does here.  You just need to supply a lot of heat energy.  And again,  not all the water you start with arrives as product.  There will always be concentrated brine waste!  It is a Second Law thing.

For the Martian CO2,  the biggest problem is compression.  Compressors there will look (and weigh) more like vacuum pumps,  a lot of power-consumptive machinery for just a very small throughput stream.  The 6 mbar atmospheric pressure is what forces that outcome.  10 mbar,  no difference.  Same problem:  the local "air" is a 1st cousin to vacuum.

If you can slightly cool some sort of duct to a temperature below about -110 F,  the CO2 will preferentially condense out first as a dry ice frost or snow in the duct.  You would have to stop and recover it out of that duct,  making this more of a batch process than any sort of continuous flow process.  Be that as it may,  pack the recovered dry ice tightly into a pressure container,  and warm it above -110 F.  It will be high-pressure CO2 gas in that container in a small amount of time,  and for very little energy input compared to direct compressor-type compression.  Once near 1+ atm pressure,  your ordinary Earthly-type compressors and other machinery will work "right".  But not until you "pre-compress" it to near 1 atm.

GW

A reminder:  the insight mission was very near a polar cap.  All the others have been at "temperate to equatorial" latitudes. 

Subsurface conditions are quite different at polar latitudes here on Earth.

At around 30 deg N latitude here in Texas,  the soil temperature about 6 feet or more down is near 58 F,  with the year-round-day0night average temperature (standard atmosphere model) 59 F.  That's 2 to 3 m down!!!

At the surface,  summer soil temperatures are near the 95-105 F daytime air temperature,  and around 80 F at night.  In the winter,  pipes buried 6 inches or more do not freeze,  if the cold snap is shorter than 2 weeks below freezing.  A foot is better insurance.  But both water systems and fire mains are buried much deeper than that.  Fire mains are 6 feet down,  by code.

GW

You will need doors and airlocks to go into and out of this structure.  Those things have to open and close.  A simple duct through the wall does not have to open and close.  That is an easier thing to do than installing doors and airlocks.  Why not take advantage of the cold heat sink outside to cause the heat you must move to flow spontaneously from warm to cold,  instead of expending power to pump it against an adverse temperature gradient?

Whatever the population is,  that sets how big this dehumidification system must be.  I do NOT have that information!  It is the water vapor in their exhalations that creates the excess humidity in the habitat atmosphere.  You want to condense that out and recover the water to reuse it.  The warm/cold loop is a way to do that with only one moving part:  an axial-flow fan,  and a very low energy cost to run it.  I'm just guessing about a 2 foot diameter duct flowing at something in the 4 to 20 foot/sec range of speed.  Very low friction loss to overcome with the fan.  We are talking a few dozen watts to run the fan.

You do not run the humid atmosphere through that loop,  that risks clogging the duct with frost.  It is a closed-loop system isolated from the atmosphere in a pressure-tight loop of simple sheet metal ducting.  The same gas mixture can be used inside the loop as in the habitation,  but it needs to be zero humidity.  The atmosphere in the habitation you want to run at about 30% relative humidity,  no lower than about 20%.  Risk of drying out nasal tissues if you go too low.

The inherent heat loss to the outside is air flow at maybe 1 to 2 lbm/sec dropping from around 77 F to no colder than 40 F.  That loss would be trivial compared to the heat loss directly through the walls of the dome,  simply because of its enormous exposed surface area.

GW

From AIAA's Daily Launch email newsletter for Wed 12-17-2025:

Space
NASA's MAVEN spacecraft is still silent at Mars — and apparently is spinning, too
NASA still hasn't heard from its MAVEN Mars orbiter, and the spacecraft appears to be spinning in an odd way as well.

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My take:

Odds are the craft was struck by something:  a meteor or a piece of debris.  That event would both alter the orbit and induce a spin,  because it is extremely unlikely the axis of the strike would pass through the center of gravity.  And those literally are the two symptoms seen,  as described in the full space.com article this headline links to.

GW

When you are located in a cold place like most of Mars,  or the lunar night,  take advantage of that cold to condense the moisture out of your air.  You need only a way to collect the frost/ice to use it for water. 

GW

Rob:

I don't know enough to respond fully to what you asked in post #1 above.  But I will say what I do know.

The cold soak up there in Arctic Canada does present some pretty serious problems operating gas turbine engines.  It usually takes a wide-cut fuel to get reliable ignition and operation,  when the plane and fuel are that soaked-out that cold or colder.  Such fuels would be Jet-B/JP-4 (pretty much the same product sold to different customers with different specs).  The JP-8 that most modern military jets burn is not a wide-cut fuel,  but a kerosene,  rather similar to JP-5/Jet-A/Jet-A-1.  Freezepoints vary with the spec a little,  but fall in the -58 to -65 F range (-50 to -54 C).  Wide cut will successfully go colder than that.  Gasoline goes much colder still.  It is not the actual freezepoint,  but the cold vapor pressure which governs the vapor/air ratio in the combustor cans,  that is the real issue.

I am very impressed by the 2 gee maneuver capability at 50,000 ft altitude in that RCAF spec.  Service ceilings for jet fighters usually have been in the 50-60,000 foot range since the Korean War,  right down to the present day,  with exceptions like the U-2 and the SR-71/A-12 family.  Service ceiling is defined in the FAR's to be the altitude at which max power climb rate is down to the almost-imperceptible 200 feet per minute.  Military specs are similar.  There is no maneuver at that service ceiling condition,  the airplane can just barely fly unaccelerated straight and level.  It's easy to stall at high altitude,  and the stall danger is a violent spin,  in air too thin to prevent inertia coupling.  (BTW,  the larger vertical fin on the B-17 from the E model of 1940-onward was a response to this same kind of high-altitude spin risk.)

The "combat ceiling" of 60,000 feet in the spec is not the service ceiling,  not with a spec'd cruise at 70,000 feet!  That would be one impressive high altitude airplane!  I suppose the SR-71/A-12 might be roughly comparable with a Mach 3 to 3.2 max cruise at 85,000 feet.  But those planes burned an early version of thermally-stable jet fuel designated JP-7.  There is no JP-7 any more,  but it would be similar to the kerosenes JP-5,  JP-8,  and Jet-A/jet-A-1.  Wouldn't work well at all in Arctic Canada. 

As for burning-out engines in a fast climb,  there is a time limitation for operation at full power,  because turbine blades,  combustor cans,  and afterburner/nozzle hardware just gets too hot at the max power setting.  You can only do that for a very few minutes.  But,  it takes full power to climb fast.  The "trick" really is being able to handle the heat long enough to get to high altitude at full power,  to meet the time spec.  If the engine was not designed to operate that long at max power,  there is little you can do to meet the tougher short time spec to high altitude. 

This effect was manifested in a different way in the Mig-25 Foxbat.  That airplane,  if carrying no external stores at all,  could fly as fast as Mach 3.5.  Its engines were short-life at only 500 hours.  And you did not overhaul them,  you simply replaced them.  This obtains because of the max power setting for long intervals required to intercept at Mach 3.5,  or to intercept at the redline Mach 2.8 and near-max power with external stores.  At max power,  engine stuff just gets hot.  And at high supersonic,  the inlet air is rather hot,  which makes the whole problem worse.  Carrying stores,  the issue was vibration from the aerodynamics around the stores,  but with the drag of the stores,  it wouldn't have gone much faster,  even without vibrations.

If you really want to fly high altitude with handling practicality,  you must fly well-supersonic.  The U-2 was subsonic,  with a service ceiling altitude somewhere around 70,000 feet.  But subsonic like that,  the difference between stall speed and max speed was only 5 KIAS,  even with that huge wing.  And that huge wing made landings difficult indeed.  The wind can upset you all too easily with a landing speed that low,  in an airplane that big.

I hope that answers your question to me.

GW

I would also add to the previous post that I think the concerns about in-space refueling are overblown.  SpaceX is evolving toward accelerating the docked pair of vehicles at very low gee with thrusters of one type or another,  slowly settling the propellants into the bottoms of the tanks.  That will work. 

Whether this can be done robotically is the real question here,  especially since the AI stuff is already proving to be problematical in self-driving vehicles.  If the programmers actually address all the possible contingencies,  it will work.  If they do not,  sooner or later there will be a catastrophe.  Simple as that.  The track record with self driving cars is not promising,  as regards programmers anticipating all possible contingencies. 

As for the number of tanker flights,  I think it is far too soon to be saying that it will take this or that number of flights.  This thing is still in experimental flight test,  and the final vehicle layout and configuration is still unknown at the detail level required to determine how much propellant payload could be delivered on-orbit.  Even the propellant capacity of the vehicle is still evolving. For a full refill,  could be anywhere from 6+ to 12+ flights.  No one knows for sure yet!  Claims "to know" this number are still BS.

And there is the long-term boil-off problem.  Most anything they are doing will get you days of "stage life",  but not weeks.  They might get to weeks if the propellant tankage has the header tanks nested inside the main tanks,  but only for the small quantities that the header tanks hold.  To make it work,  they will have to empty and vent the outer main tank,  so that the vacuum between makes the tank system into a thermos bottle.  The outer tank shell is also the sun shield that stops solar heating of the header tank,  but only if there is vacuum between them.

One header tank is nested right now in the flight test configuration up to this point,  the other is not.  That will have to be rectified for the real mission.  But as I said,  we are still in experimental flight test with experimental configuration,  and these configurations are still evolving.  Claiming to already know the final "stage life" is also BS at this stage of the game.

But,  what those considerations just discussed prove,  is that this vehicle design is NOWHERE NEAR done with very experimental flight test,  much less any final development prove-out testing!  Precisely because of that,  projecting mission schedules using it are still near-100% BS!  That's the real effect of the factor-3-ish ratio between "Musk time" and real-world time that we have seen,  ever since SpaceX first started flying Falcon-1's expendably out of Kwajalein.

That time ratio is different with each contractor,  but all contractors have always had such time ratios.  Long ago,  that was taken into account by the government when planning military aircraft and space programs,  and also for the civilian space program (same crowd of contractors back then).  The details have shifted some since then,  especially since there are now different pools of contractors for the various military and civil programs that only overlap some now.  But it would seem that nobody at today's version of NASA (or DOD for that matter) remembers anything about evaluating and taking into account these time ratios. 

That lack shows in how slow (and concomittantly expensive) it has become to actually do anything anymore.  The P-51 Mustang went from a sketch on a napkin to a flying prototype in about 100 days.  It took another year to re-engine the plane to make it the success that it finally became.  And another year or three before they went to the bubble canopy on P-51D,  solving the pilot combat visibility issue.  That's about 3.5 years from an idea to a fully-successful combat design truly worthy of mass production. 

Today that's now running about 25+ years (!!!) for airplanes and giant rockets.  I think SpaceX is doing fairly well;  their half-reusable Falcon-9 was ready in about a decade from idea to reality,  which is way better than the industry usual.  I think Starship/Superheavy is going to take them about that same decade to make ready.  They are still a tad less than halfway done doing that.

GW

I dunno what "right wing music" is.  Sounds rather contrived to me.  Typical of what happens as extremists of one type or another take over your government or your political parties. 

But I do know what both far-right and far-left extremism does:  install dictatorships.  Britain almost was destroyed by the far-right dictatorship of Nazi Germany.  We helped them survive and together defeat Hitler.  Everybody knows what Stalin did in his far-left dictatorship.  All dictatorships are the same.  Does not matter what they say or how they got there,  it only matters what they do.

And I have noticed that some Brits and some Canadians (and some French and some Germans) have very most definitely noticed the dictatorship currently still being installed in the US.  They've seen this crap in action before,  we haven't (although the trend toward it was interrupted by the Pear Harbor attack).  Its installation is not complete yet here in the US,  but there is very little time left to oppose it. Unless you want to do armed revolution in the streets.  I'd rather not:  incredible amounts of mess to clean up afterward.  But I will if I have to.

GW

Regarding post 32 above,  more "I-told-you-so" stuff showed up in today's (5 Dec 25) "Daily Launch" from AIAA:

Ars Technica

Congress warned that NASA’s current plan for Artemis “cannot work”

In recent months, it has begun dawning on US lawmakers that, absent significant intervention, China will land humans on the Moon before the United States can return there with the Artemis Program. So far, legislators have yet to take meaningful action on this—a $10 billion infusion into NASA’s budget this summer essentially provided zero funding for efforts needed to land humans on the Moon this decade. But now a subcommittee of the House Committee on Space, Science, and Technology has begun reviewing the space agency’s policy, expressing concerns about Chinese competition in civil spaceflight.

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My take:

Finally,  it is just beginning to dawn on the politicians running NASA's show that they have been seriously miss-running it!  About time!  Actually,  far too late!  Announcing an expected landing date without a lander (and a rover) almost done with development,  was just UTTERLY STUPID!  But that's EXACTLY what you get when you let incompetent politicians be the top managers.  Always has been,  always will be.

This return-to-the-moon thing should not be another space race in the first place.  The US put boots on the moon 56-53 years ago.  It should no longer be about "who does something first".  It should actually be about going there to do something significant and perhaps even useful.

Congress took over managing NASA by the end of Apollo.  We have spent the last half a century puttering around with men in orbit (WITHOUT doing artificial spin gravity work !!!),  while sending probes to other planets from the one part of NASA not so badly micromanaged by Congress until recently.  Before Nixon killed all manned spaceflight outside LEO (not just Apollo!!!),  the plan was US boots on Mars in the 1980's!!! 

EDIT UPDATE same day:  NASA killed NERVA just as it was ready to fly as an alternate 3rd stage on Saturn-5,  when Nixon forbade manned flight outside LEO,  based on the reasoning "who needs the rocket if we aren't going to go?"  They learned that kind of "reasoning" from Congress!

See what Congress micromanaging NASA REALLY did?

GW

There may or may not be large quantities of easily-recoverable ice on the moon near its poles.  We still do not know with real ground truth.  Remote sensing still often lies to you,  precisely because too many inferences have to be made.

But if easily recoverable ice exists,  then LOX-LH2 should be producible powered by a mix of solar and nuclear electricity (remember,  the day/night cycle is a month long!).  All it takes is electricity to do purification,  electrolysis,  and liquifaction.

If you have a single stage,  reusable lander rigged to use LOX-LH2 propellant,  you can use it to ferry some of that same LOX-LH2 propellant to orbit.  You refuel the lander on the surface.  It uses less propellant to launch cargo into lunar orbit and return,  done that way.

That being the case,  what purpose does a lunar space station serve?  Why build 2 propellant production plants?  Just use the one you need on the surface,  and ship product to orbit for transit elsewhere.

That approach makes more sense to me,  because you get the same effect while building less infrastructure. 

Now,  if you intend to use LOX-LCH4 propellants,  you will have to ship carbon from Earth or elsewhere,  and it needs to be pure,  and in powder form.  There is no easily recoverable carbon on the moon. 

Extremely dilute concentrations of anything are not easily-recovered resources.  That is why sea water has never been "mined" for the uranium that is there,  in extremely dilute concentrations.

GW

Just an update on my solar installation.  It's been 16 months since installation.  On average,  my electric bills are around a third to a quarter of what they once were (it varies with season and weather).  The meters run backwards on most bright sunshiny days.  Which means I am selling power back to the electric coop (we have a rural electric coop for service out here in the boondocks).  Our coop has lower prices than the big utilities,  and its service has far fewer outages.  Typical of rural coops vs the big utility companies,  actually.

The installation that can sell power back like that has to meet the technical requirements of the coop.  That's why I cannot be stand-alone on my solar with a battery.  They do not allow that kind of connection.  Their sine wave is what my system detects in order to phase-in correctly.  It does not operate without that signal.

GW