New Mars Forums

BTW,  for the crew orbit-to-orbit transport shown in post 420 just above,  I did NOT overtly specify an atmosphere.  I just specified near 1 full gee at the rim of the two centrifuge disks.  There is NOTHING that inherently links atmosphere choice to gee-level choice.  I picked 1 gee to ensure that all aboard would be physically fit to endure entry and landing gee levels in the 3-6 range with impunity,  as can ordinary untrained Earth citizens. 

We have absolutely no experience,  or any evidence,  to suggest that people acclimatized at 0.38 gee can withstand the 3-6 gee exposures that are inherent for the landing on Mars!  In my opinion,  the lower gee level is a totally unjustified risk!  Suspenders,  belt,  and armored codpiece!  Especially where paying passengers are involved!

In point of fact,  I would use about 43%-by-volume oxygen in a two-gas mix with nitrogen,  at a pressure in the neighborhood of 0.43 atm.  That's my "rule of 43" atmosphere proposal.  That atmosphere meets all the long-term and short-term hypoxia-prevention criteria I can identify,  while at the same time allowing no pre-breathe requirement for pure oxygen spacesuits down to 3.0 psia suit pressure!  There would be no pre-breathe needed for any spacesuit designs at or above that 3 psia figure! 

And that's actually lower than the 3.7 psia used in the Mercury/Gemini/Apollo suits very successfully!  It also makes MCP suit design and operation a lot easier!  Dr. Webb designed his at 3.7 psia,  give or take a tad.  They pretty much become infeasible above about 4 psia.

And,  the oxygen concentration (calculated as kg/cu.m) never exceeds that in 77 F air at 1 atm pressure,  so any fires are NOT accelerated above the Earthly rates we have fire-fighting experience with,  by the 43% oxygen!  They would be accelerated at higher pressures with the higher kg/cu.m of oxygen,  but not at 0.43 atm.  You have to worry about this!  It killed the Apollo-1 crew on the pad,  remember?

And yet,  my proposed atmosphere's oxygen partial pressure does not fall short of that in Earthly air at about 2500 m altitude,  above which there are higher incidences of birthing problems and also higher incidences of chronic altitude sickness,  but not below!  Any settlements or cities we build out there in space or on Mars could use the same atmosphere,  and not fear reproductive failures induced by chronic hypoxia!

GW

Here's a quote from the article I quoted in post 726:  "The escaping air originated in a service module transfer tunnel in Russia's Zvezda module that launched in 2000."

I do not know details,  but the words would indicate the transfer tunnel is part of the Zvezda module. 

Yes,  there is a hatch to the Zvezda module that can be closed.  Closing it eliminates access to a docking port that is currently often used.  The kick force happens whether that hatch is open or closed,  if the module is pressurized. 

As I understand it,  the Russians have agreed with NASA to close that hatch,  but only "at night". 

GW

More on the leak in the ISS:

From the Space.com article summarized in AIAA’s “Daily Launch” for 10-17-2024:

ISS leaks among 50 'areas of concern' for astronaut safety: report
News
By Elizabeth Howell
published yesterday

NASA and Russia are working together on addressing the situation in the wake of an Office of the Inspector General report last month.

NASA and its Russian counterpart have identified 50 "areas of concern" related to a long-running leak aboard the space station, a media report states.

The leak has been ongoing since 2019 in the Russian segment of the International Space Station (ISS) and was the focus of a new report from NASA's Office of the Inspector General (OIG) published in September. While NASA and Roscosmos are addressing the leak, it remains a top "safety risk" for astronauts on board, the OIG report stated.

NASA officials, speaking in an exclusive with the Washington Post, said they are tracking four cracks and 50 other "areas of concern" on the ISS. The cracks have "all been covered with a combination of sealant and patches" by Roscosmos, NASA noted in a statement to the newspaper, and fixes are ongoing. Still, the leaking area is the top risk, at a 5 on a scale of 5, in NASA's internal risk assessments, the OIG stated.

"We have conveyed the seriousness of the leaks multiple times, including when I was in Russia earlier this year," associate administrator Jim Free added in an interview with the Post. Since the leaks are adjacent to a hatch, Free added that Roscosmos acquiesced to a NASA request to close the hatch as much as possible: “We've come to a compromise that they close it in the evening."

NASA astronauts also remain on the U.S. side of the orbiting complex to be close to their escape vehicles, in case of the need of evacuation, the agency noted in its statement to the news outlet. That said, NASA has stressed repeatedly that the leak poses no immediate threat to astronauts.

"Not an impact right now on the crew safety or vehicle operations, but something for everybody to be aware of," ISS program manager Joel Montalbano said in a news conference in February 2024 when the leak temporarily increased to 2.4 pounds per day, up from a historic low of 0.2 pounds per day.

The leak has been ongoing for five years and patches have been ongoing since it was first uncovered; agency officials noted in a Sept. 27 livestreamed briefing that repair work reduced the high leak observed in April 2024 by roughly a third.

The escaping air originated in a service module transfer tunnel in Russia's Zvezda module that launched in 2000. Zvezda, along with the rest of the ISS, is aging and requires maintenance to keep going in orbit. The ISS is supposed to last until 2030 to serve both NASA's staffing needs, and also to provide commercial low Earth orbit research. In the following decade, NASA hopes to have a set of commercial space stations ready to take over operations.

NASA's OIG is tracking several other risks that could imperil keeping the ISS going that long, ranging from a sudden micrometeoroid strike to supply chain issues.

SpaceX has been tasked to build a large Dragon-type spacecraft to remove the ISS from orbit, in a contract awarded by NASA earlier this year. The OIG stated it will be looking to learn more about the schedule, costs and risks associated with the new vehicle and the deorbiting plan.

My take on it:

The description of treating the 5 cracks says sealant and patches have been applied.  That is NOT the way to fix cracks originating from cyclic loading.  The critical step of crack stress relief presumably got left out,  because there is no mention of it anywhere in the article.  That step is to find and to drill-out the tip ends (plural! there are two ends to every crack!) to relieve the stress.  Then (and only then) do you apply sealants and/or patches.  Otherwise,  the crack just keeps growing longer with time,  right out from under your sealants and patches. 

This "fix" for fatigue cracks has been known in aircraft design since the early 1950's.  It was actually applied (and it worked) to the wing spars of the Lockheed Electra-II airliners,  long before they ever became the Navy's P-3 fleet.  Somebody (a reporter?) ignorant of this "fix" questioned the technician doing it.  The technician replied "did you ever see toilet paper tear on the dotted line?"  And THAT is the true origin of that old tale!

So,  either both NASA and Roscosmos are ignorant of design practices for dealing with fatigue in duralumin alloys that date back almost 7 decades (which I doubt),  or Roscosmos just wants to limp along risking a blowout rather than spending what it takes to fix the trouble.  Which is either drill out the cracks or replace the module.  What's truly disappointing is that NASA is not calling them out over this. 

And y'all already bloody well know I am right about this!  Any pressure vessel with growing holes in it,  will eventually burst suddenly.  Y'all know that,  too.  The risk here is a dead crew from a sudden explosive decompression that sucks all the air out of the station in only several seconds! Close the damned hatch,  and keep it closed!  Or fix the bloody problem,  but do it right!

I hope someone at NASA reads this post!

GW

Update 10-18-2024: 

If you don't believe the Zvezda module cracking apart would depressurize the station suddenly,  killing the entire crew,  then consider this.  Think about the "PA kick load" that happens like an impact force when two sections of a pressure vessel part from each other.  ISS operates at about 1 std atm internal pressure,  which in US units is 2116 lb/sq.ft.  I don't know the diameter in Zvezda where the cracks are located,  but let's just presume it to be about 6 feet.  If circular,  the cross sectional area is near 28.3 sq.ft.  The PA kick load is pressure x area upon which it acts,  or some 59,830 lb = 27.1 metric tons-force.  Bigger diameter,  bigger force,  proportional to diameter squared!  Twice the diameter is a 4 times bigger force!

The effect that load has upon adjacent structures is a sudden impact,  not a gently-applied steady load,  so you must at least double that value for estimating stresses in related structures,  to around 120,000 lb or 54.3 metric tons-force!  A sudden impact that large will break up much of the station,  tearing module from module,  and letting all the air out of them,  pretty much all at once!  No one in the crew will have time to shelter anywhere!

And THAT is why I think the risk of these propagating cracks is so severe!  And so urgent to address!

For "Starship" to land on Earth,  it either needs landing legs or to be caught by the tower,  or else wings to land aerodynamically on a runway.  I've seen things indicating SpaceX wants to catch it with the tower.

For "Starship" to land on the moon,  it has to have landing legs,  and they cannot be the little "peg legs" the early single-stage flight tests used.  Landing on the moon is a soft field,  rough field problem.  The max allowable static bearing pressure is about 0.1 MPa.  And the cg height is way too high for anything resembling the "peg legs" to be stable against overturn.  There are no towers or hard landing pads on the moon.  There won't be for a long time yet.

For "Starship" to land on Mars,  it has to have landing legs rather similar to those it has to have on the moon.  That atmosphere is way too thin for wings to be of any use at all.   There are no towers or hard landing pads on Mars.  There won't be for a long time yet.

All that being said,  I think there might be a solution to the hinge line burn through problem.  That would be a flap of flexible heat shield material (perhaps a ceramic blanket?) extending from inboard across the hinge line to a bit outboard,  on the windward side of the fin.  The pressure is dropping in that direction,  so there cannot be backflow under this flap of material toward the hinge line.  But it does need to be impermeable.

Combine that with the right legs,  and you have a solution for the moon,  Mars,  and for off-site abort landings on Earth.

GW

I retrieved the Wikipedia article about Mars cyclers using the posted link.  Thanks.  I cannot yet say I understand how this works.  It does not look like much of a dV savings,  except that you don't have to launch the large cycler hab but once. The dV's to get on at Earth,  and particularly off at Mars,  look to be rather large,  but the vehicles for those functions can be much smaller. 

GW

Bob:

If you look up old issues of Aviation Week from the 50's and 60's,  whatever the magazine's name was back then,  bear in mind that this was a sort of industry trade journal.  You sort of have to read between the lines to figure out what was really going on.  This sort of "reporting" was as much about chest-puffing and advertising as it was actually reporting facts.  It's all mixed together in trade journals like that.

But you can see in the early 1960's illustrations what the Apollo plan was up until about 1965:  two Saturn 5 launches per mission to the moon,  with one a tanker to refill the other in LEO.  The entire Apollo capsule and a huge service module were to be landed direct upon the moon. After about 1965 that shifted to cluster we actually used,  which had the separate lander,  and one launch per mission. Somewhere about 1964-1965 there was even a notion to send a man one-way to the moon in a Gemini capsule (fortunately that went nowhere).

If you look at issues from the late 1950's,  there were occasional illustrations showing the one-way-to-Russia troop transport that was the original paper design for the Saturn-5. There's a lot of aviation and space concept proposals illustrated in that magazine that never came to fruition as proposed.  Things almost always turn out quite different than the original proposals.

GW

Itokawa as a Cycler?                               

I have not computed the orbital ellipses,  and investigated the crossings with Earth’s orbit and Mars’s orbit.  But multiple big questions come to mind.  The first is:  how could Itokawa (or any other object) function as a “cycler”,  when the differing orbital periods of 3 (not 2) bodies are involved?  (That is actually a fundamental question that I have about all cycler proposals.)   Bear in mind that unless the cycler is very close to the departure planet at one end,  and the arrival planet at the other,  there is little point in trying to effect the transfer via a cycler.  Failing that proximity at both ends,  you are better off just flying direct to your destination,  in terms of both velocity requirements and time spent in space.

With further regard to that first big question,  while there will be a repeating point in time (two of them actually) where the asteroid is at minimum distance from Earth,  when it crosses Mars’s orbit (and there would be two opportunities for that as well) it would seem unlikely in the extreme (!!!) that Mars would be located anywhere near the correct vicinity for an effective transfer of anything.  However,   at least the plane of Itokawa’s orbit is close to the ecliptic,  so crude coplanar estimates would be reasonably close.  The cycler would have to have exactly the right period in order to line up with Earth while Earth is there,  and to line up with Mars while Mars is there.  The periods pf Earth and Mars are what they are.  The period of the cycler is your only variable available by which to address the double-line-up. 

I know very little about Aldrin’s cycler concept.  But whatever period it has is the period any other cycler absolutely must have.  I do not know how to figure that,  but maybe Aldrin did.  Whatever perihelion and apohelion distances go with that period,  that’s the orbit the cycler must be on!

Second big question:  while there is measured “water” content,  bear in mind that it is coming from a combination of hydrated minerals plus a little bit of surface-implanted solar wind molecules,  and it is down around 1% by mass.  That’s what the Hayabusa results indicate.  That is a sparse resource that (1) requires processing a huge bulk to get a small return,  and (2) requires a high energy in the form of concentrated heat for that processing,  that is proportional to that large bulk and not so much to the small resource recovered.  You must heat (all the bulk) the minerals to un-hydrate them,  releasing a small amount of steam.  The required temperature is usually close to the incandescence point (near 1200 F = 650 C).  Given those facts,  why would such a resource be in the least attractive for recovery?

Third big question:  this body is rather certainly a loose rubble-pile of small particles (boulders,  cobbles,  gravel,  etc.),  with no binding but mutual gravity between them.  Because it is so small,  that binding gravity is vanishingly-weak!  Indeed,  the best interpretation of the Hayabusa findings is that Itokawa is a contact binary,  accounting for its bent peanut shape.  Under those circumstances,  I have to wonder exactly how you would implant any sort of habitation upon or within it,  and expect it to stay there?  Our seemingly-unexpected experience at “Didymoon” (although I expected it) would seem to confirm my interpretation of the disruption risks at Itokawa.

Fourth big question:  given its rubble-pile nature,  how do you dock with any sort of habitation upon or within Itokawa,  when the slightest applied force could well disrupt the asteroid into a free-flying cloud of particles?  Or at least detach or excavate the habitat from the rubble pile?  The typical language of “space rocks” used up to now about asteroids and comets is actually very self-deceiving:  these “rubble-pile” things are completely outside any Earthly experiences we humans have ever had.  They are not “rocks” in any prior sense of that word. 

(And these same two big questions apply to asteroid mining proposals as well.)

I posed these comments as questions to emphasize the fact that they demand answers before we can effectively plan missions that attempt utilization of these objects.  Those are answers that no one anywhere yet has!

Given the unanswered nature of these big fundamental questions,  I pose a 5th question:  why is it prudent to explore the “cycler orbital” question (my first big question) by doing calculational work,  when there would seem to be little advantage to be gained trying to use a rubble pile body as a site for a habitation of some kind (questions 3 and 4)? 

Here’s a 6th question that I pose:  given the unknown difficulties cited in “big questions” 3 and 4,  why bother trying to put your cycler habitat upon or inside one of these celestial bodies (assuming one even exists with the right orbit)?  Why not just build the habitat as a free-flying item?  And give it course-correction capabilities,  because close planetary fly-bys will disturb its orbit. 

7th question:  for radiation protection,  how thick a layer of fiberglass batts and Kevlar cloth do you need,  to get to 20 g/sq.cm of low molecular weight materials?  A meter?  So what? 

Recommendation:  forget trying to use asteroids as cyclers,  just go with a free-flying habitat located in the right orbit for a cycler (whatever Aldrin came up with).  Make it cylindrical 56 m diameter,  spin it in rifle-bullet-mode at about 4 rpm for about 1 gee at the periphery,  and make it long enough to be sure its baton-spin-mode moment of inertia is nowhere near the same as its rifle bullet-spin-mode moment of inertia.  (Why?  Having them the same invites spin instability.)  Then wrap it with that meter-or-so of fiberglass batts and Kevlar cloth,  because you need thermal insulation and meteor protection,  as well as radiation shielding for solar flares and GCR.  Then fit it with some high-Isp propulsion,  with adequate propellant quantities to support course corrections. 

We don’t need any asteroid properties or experience to do this!   But high-Isp propulsion that is also high-thrust,  would be a real boon.

GW

TH:

I honestly do not know.  But I would assume that Blue Origin looked into that,  while designing Vulcan. 

Unlike some on these forums,  I have no prejudice against solids.  Those are just another tool to use,  offering some very specific advantages,  particularly during pre-launch checkout.  But you do have to design them correctly,  and you do have to verify your design is "right" with enough of the right kinds of testing to meet statistical standards. 

Bear in mind that back in 1974 I worked on the Vought "Scout",  which was a 4-stage solid satellite launcher.  It flew 4 times experimentally,  failing once,  then operationally for over 30 years,  without another single failure of the solids.   

Just goes to show what can be done.

GW

TH:

Think of it as a sine wave superposed on a DC level.  The sine wave is the day/night cycle of thermal expansion and contraction,  from the solar illumination or darkness every 90 minutes or thereabouts.  The DC level is the pressure inside the shell,  which is just pretty near 1 std atm.  The DC level makes the basic stress level higher,  while the sine wave is the cyclic part.  It's too late to reduce stress below that for infinite fatigue life: the damage is done,  the crack is there (and leaking). 

These considerations do not depend on whether that is a weld or some shell panel.  Only the specific numbers for cycles-to-failure.  Most of what I read at least implies this is some cracked weld somewhere.  Those fail quicker than the base aluminum,  usually.  But they haven't found it in 5 years of looking,  so nobody really knows what is the true problem. 

Metallurgically speaking,  a sudden increase in crack growth rate occurs right before the fatigue sample actually fails,  in the usual cyclic loading test scenarios.  This is a piece of the module pressure shell,  or there would not be a 5-year leak history.  With the leak rate accelerating by over a factor of 10 very recently,  we "know" that failure is "imminent".   Failure means explosive decompression,  likely fatal for the crew,  unless that door into the leaking module is closed and sealed. 

It really is that simple.  And that dangerous in space.  The biggest problem is that with no details,  there is no definition of "imminent".  Except my gut intuition says it ain't years anymore.  Months?  Weeks?  Days?  Who knows?

GW

From AIAA’s “Daily Launch” email newsletter for October 4,  2024

Space
ULA’s new Vulcan Centaur rocket aces 2nd test launch

United Launch Alliance's (ULA) powerful new Vulcan Centaur rocket is two for two. Vulcan Centaur, the successor to ULA's workhorse Atlas V, launched today (Oct. 4) at 7:25 a.m. EDT (1125 GMT) after a series of holds, from Florida's Cape Canaveral Space Force Station, kicking off a key test flight called Cert-2. The rocket could soon be certified for U.S. national security missions.

My take on it:

If you follow the link to the article from Space,  there is mention and a video showing a serious anomaly with one of the two solid boosters.  The article says there was some sort of problem with the rocket nozzle,  seen as an event creating a shower of glowing pieces.  As near as I can tell,  the exit expansion bell shattered (meaning it suddenly burst from its internal pressure and heating loads) downstream of the throat somewhere. 

Because this failure took place downstream of the throat,  it reduced the thrust from its nominal value to something nearer that of a sonic-only nozzle,  without very much of a “P-A-kick load”.  The sudden loss of thrust on that side was not enough to upset the vehicle’s attitude control,  nor was it enough to prevent the vehicle from flying its intended trajectory anyway.

Had this bursting taken place ahead of the throat,  the sudden change in thrust would have been much larger (loss of essentially all of the thrust),  aggravated even further by a “P-A-kick” load of very significant size.   That would likely have thrown the vehicle out of control.  Even if it stayed in control,  the vehicle would likely have been unable to fly its mission on thrust from only one of the boosters.

Somebody at Northrup-Grumman’s big solid motor operation (the monopoly that supplied these boosters) screwed up this nozzle design.  That much is for sure!  It is unclear whether that problem is a fundamental design error,  or an undetected material quality defect.  Neither is acceptable.

If I were making decisions for the Air Force,  I would NOT certify this vehicle for launching spy satellites until I knew what actually caused the solid booster nozzle anomaly,  and what must be done to see that it does not recur!  Those payloads are expensive,  and time-critical. 

I would insist that the fix be demonstrated in flight,  before even beginning to contemplate man-rating this vehicle!  Why?  Because I do not trust monopolies to behave ethically and responsibly.  They never did before,  in history.  And big solid motors are now a monopoly in this country.

GW

This is only my opinion,  but I think the distinction between "asteroid" and "comet" in our language was likely a mistake.  These bodies are all rather similar,  with wildly varying amounts of volatile ices.  Some formed with lots of volatiles,  others did not (likely forming closer to the sun).  Over 4.5 billion years,  the ones closer-in have lost their volatiles from sublimation:  a bit higher temperature due to sunlight illumination.  Way further out,  they stay cold enough to retain significant volatiles. 

Recovering a resource is only worthwhile if you can afford the costs of extracting it,  and then the costs of refining it into something you can really use.  There are always refining costs,  particularly to create actually-useful metal alloys.  But don't forget the up-front extraction costs:  this is exactly why fossil fuels were preferred for centuries over anything synthesized.  It's just easier to dig something up than it is to heat something up to high temperatures,  and try to handle that hot stuff,  to obtain what you desire.

Just because you can do something is no reason to believe that you should do that something.  The world around us is not simple. 

GW

I cannot answer most of your questions because those answers are not in any of the reports I have seen. 

All of the ISS is pressurized to about 1 atm of synthetic air (21% O2,  79% N2).  That would include the leaking tunnel module,  except when that hatch is closed.  Then only that module (and presumably the docking adapter it connects to) leaks down,  without leaking down the pressure in the rest of the ISS.  Nobody says,  but I presume they have to equalize by bleeding air (somehow) into the leaky module before they can re-open the hatch and use the docking adapter.

I have seen absolutely nothing describing how they have been searching for the leak. 

Any impactor to an asteroid is a "push",  meaning compression in the material underneath the impact point.  The gravity tractor is actually a "pull",  because the force on the asteroid is directed toward the spacecraft,  and the force on the spacecraft directed toward the asteroid.  The spacecraft thrusts to keep from being pulled onto the asteroid.  That thrust has to be canted at rather strong angles,  so that the expelled mass streams DO NOT strike the asteroid,  but instead just pass it by.  Ion,  other,  makes NO difference.

Most people think you use a nuclear device as a direct surface impact,  or even exploded within the asteroid,  but that IS NOT correct!  There is no blast wave in a vacuum.  You explode the thing alongside very close by,  and use the radiant energy to overheat and vaporize the adjacent asteroid surface materials.  Those vaporized materials "explode" into space quite violently,  causing a big "rocket reaction" force in the opposite direction.  The spalled material from an impactor works exactly the same way.  Neither approach can be used on a dry C-type (excepting the very smallest,  rather inconsequential impactors),  because the asteroid will disrupt into a cloud of debris instead of accelerating in the "push" direction.

And yes,  the larger the mass of the gravity tractor craft,  the more effective it will be.  And the larger your thrust requirement,  the more expensive your construction,  and the more demanding your launch problem.  It's a very complex trade-off.  Nobody yet knows the right answers,  because it has yet to be attempted in any form. 

GW