New Mars Forums

My congratulations to Spacex.  A feat very well done.  From one old rocket man to the entire Spacex team:  you are indeed "steely-eyed missile men" now,  for sure. 

Automatic launch abort,  quick repair,  launch,  all systems working, automatic flyby,  remote guided approach,  capture/dock,  and cargo delivery.  That's more than one "first" for the history books. 

All with a re-usable capsule that can carry astronauts.  There's more history that will be made. 

GW

I'd use a piece of well-proven ISRU equipment as part of my mission design,  as long as there was a back-up or "way out" designed into the mission.  You have to do that with everything,  anyway.  Once out of Earth orbit,  there is no practical possibility of rescue.  And I think we can all agree that there is nothing in this world as expensive as a dead crew.  Especially in government work. 

That being said,  what I see being discussed and referenced in the forums is beginning to convince me that effective and reliable ISRU for propellants might be something we actually can get "well-proven" in time to make the first trip.  Purity issues can be addressed,  yes,  but you have to find them first. 

Since the adsorption compressor principle we are talking about for Mars ISRU seems to be the same one as is in an oxygen system on the F-22 that is having problems,  well,  I think we just might have found one of the "gotchas".  If we get that fixed,  that's one less "gotcha" with the different hardware/same principle we'd use on Mars. 

It all gets down to doing the development phase correctly,  that much larger effort that goes in between the laboratory demonstrations and the actual application.  Development work is much more art than science.  None of the "gotchas" you are trying to find were ever seen before,  much less written about.  That's detailed,  frustrating,  dirty-fingernails work.  And there's a whopping lot of it to do,  before you ever consider your new product "well-proven". 

That's what the ISRU equipment needs to go through before we bet lives on it.  But it seems to me this could be done.  In time to go,  maybe even within the decade,  if need be.  That's just my experience-based hunch.  I do like what I'm reading about this stuff. 

GW

Rune - that's amazing.  I've never run numbers for a thing that large.  But I suspect the need for a shock absorber system "goes away" if the ship mass is large enough.  That actually helps.  Same ship would make a good colony-planting ship right here in the solar system,  too.  One whopping big transport.  Fast,  too.  That's cool. 

Everybody:

Isn't there some kind of "cryocooler" design floating around somewhere?  I keep hearing that word now and then.  Seems like a module with a solar electrolysis rig could be docked with another module (or modules) with solar powered cryocoolers.  Dock these with a bunch of water tanks,  and a couple of hydrogen and oxygen tanks.  Make water into LH2 and LOX slowly over time,  planning ahead to have the product tanks full at the time of need. 

I think this kind of thing would work for a fuel depot anywhere in the inner solar system where the sun is bright enough for solar power to work,  and also for a ship plying those same regions.  As long as your ship is modular,  that is.  You just need standardized modules for holding water,  LH2,  and LOX,  and for the two conversion equipment sets.  Standardize the design and hookup,  the same way we standardized shipping containers. 

Combine that with standardized engine and hab modules,  and a standardized docking interface for landers and crew return capsules,  and you have the "tinkertoys" to quickly and inexpensively go anywhere in the inner solar system with men.  Reuse the stuff,  re-tailor the stack-up for each mission.  Etc. 

As better engines become available,  you just fit them into that standard module envelope.  Chemical,  nuke,  doesn't matter.

The only trick is sizing the standardized modules.  Do that to support ships anywhere in the inner solar system,  not just Mars or an NEO.  Do it as reusable hardware,  so you launch the modules once,  then just resupply the water.  As money and interest becomes available,  use the same tinkertoys to go and do whatever is at hand. 

This is planning on 50 to 100 year timescales,  not just one-mission-at-a-time,  something the navies of the world have done (more or less) for multiple millenniums now.  Some do it better than others.  Technologies change,  but the approach is what matters.

GW

So,  let's go further than Mars.  Say,  to the asteroid belt.  Somewhere near 2 years one way,  something more like 6+ years round trip.  Don't you want to fly faster and cut that down?  Especially if you could refuel out there from frozen volatiles?  That engineering target ought to be a water-propellant gas core NTR.  Further,  depending on the solar cycle,  something like 2 to 4 years in space will incur a career limit radiation dose from galactic cosmic rays,  for which all known practical shielding techniques are rather ineffective.  Flying faster gets really important beyond Mars. 

When I looked at either gas core NTR or solid core NTR for Mars,  my vehicle accelerations were around .05 gee as I sized them.  That's a very few days burn for the very largest delta-vees,  orbit-to-orbit.  Electrics (and VASIMR is one),  have vehicle accelerations well under .001 gee,  which means you "burn" for much of half the trip there, just to accelerate,  and then you "burn" for much of the other half of the trip to decelerate.  Acceleration times over a very few days start incurring very significant solar gravity losses.  Fact of life. 

BTW,  the final NERVA testing had a rather radiation-free exhaust,  though few today believe (or want to believe) it.  They solved the core erosion problems,  and the daughter products stayed in the core.  900 Isp,  engine T/W about 3,6,  47 minute burn,  and multiple restarts is what they finally demonstrated.  And a large throttle ratio,  too.  In comparison,  there were major core mass losses in the early Phoebus and Kiwi series.  Very radioactive exhausts.  Some of that stuff is still out there on the nuclear test site in Nevada,  and will be dangerous for decades,  even centuries,  to come.  (Yes,  I do understand the dangers.)

Open-cycle gas core does have a radioactive exhaust,  but it's daughter products only,  not uranium or plutonium.  That's a different beast by orders of magnitude in terms of collateral radiation exposures.  (Myself,  I'd use thorium-bred U-233,  and avoid plutonium entirely,  but that's just me.)  The real advantage of open-cycle gas core is that it's an empty steel can when you shut it down.  Secondary-induced radioactivity in the engine structures decay in hours (at most) to safe levels.  No core on board to worry about when flying home,  or in a crash scenario.  The exhaust stream velocity generally exceeds solar system escape,  so if you don't point it at the ground,  you'll never pollute the atmosphere in the orbit-to-orbit application.  A truly abortable,  rather safe,  nuclear rocket.  Wow!  Is that ever at variance with widely-held public perceptions!

A lot of the fears being used even today to justify not doing nuclear propulsion,  are actually just completely irrational,  and at quite a variance with actual facts.  Not all,  but most of these fears.  There's real problems to design around,  of course,  but the advantages are simultaneous high thrust/high Isp,  especially when compared to every electric scheme I ever heard of. 

The only verifiably-doable thing I ever heard of in the last 50 years,  offering even higher thrust and Isp simultaneously than NTR,  is nuclear pulse propulsion. 

GW

I don't have any data regarding electrolysis,  except the knowledge that overall energy efficiencies tend to be low,  even with electrolytes and catalysts.  It really doesn't take very much electrolyte,  that's just a trace.  Many species will do,  even table salt.  Everything but distilled water will conduct electricity at one usable level or another.  The "standard" is platinum catalysts,  but I know lots of scientists are investigating other materials.  For now,  it's platinum,  though. 

If I had to guess,  I'd guess that,  in a well-designed system,  the ratio of water electrolyzed x theoretical enthalpy of product O2 and H2 = around 25-30% of the electric energy required to break the water.  Not-so-well-designed system,  this could easily be under 10%,  maybe way under.  Just a guess.  I could be wrong.

Given the limitations of solar PV,  it just means your rig is smaller,  lower-powered,  and smaller output rate.  That just means you start earlier to meet a given demand.  And that's just a matter of planning ahead,  once your system size is feasible at all for the demand. 

GW

Returning to one spot is a bad thing only if you decide to confine yourself to the one landing during the mission.  Why not make more than one landing?  After all,  unlike the moon,  it's a very long way to Mars and back with men.

GW

NERVA is a 40-year old technology that was a first step toward the upgrade waiting in the wings:  gas core NTR.  Gas core was at the academic lab project stage when NERVA was ready to fly,  and NASA very unwisely cancelled the whole thing.

The best-informed design calculations of the time indicated gas core open cycle had Isp's in the 1000-2500 sec range at engine T/W in the 10-30 range without need for a waste heat radiator.  It appeared regenerative cooling was adequate.  They had bench tested a flow scheme as good as perfect containment,  and they had demonstrated controlled gas-phase fission.  The rest was just technology development in a company lab,  because this was way beyond what academic institutions could handle. 

You look at 2000 sec and you find out that a Buck Rogers-type single stage ship could fly to the moon and back,  at both high payload and high structural fractions.  That was LH2.  Nobody had yet really done a water NERVA,  much less a gas core of any kind.  Water is the really attractive propellant,  because it's "everywhere" and you can refuel to come home.  That ups payload massively. 

Operated above 2500 sec Isp,  a very large waste heat radiator was required.  There was an ill-defined "transparency limit" to reactor power levels somewhere around 10,000 sec.  The design target was a spherical injection scheme operated at 6000 sec,  with an engine system (including radiator) T/W was thought to be near 0.01 to maybe 0.1.  This would have made a very good orbit-to-orbit engine,  with enough vehicle acceleration to be "impulsive" and avoid the long-burn delta-vee losses associated with electric propulsion.  (I don't know,  but I suspect SEP will suffer the same low-acceleration long burn losses. It happens when vehicle acceleration falls below crudely about 0.02 gee.)

That 6000 sec gas core engine was one of three candidates being considered in 1969 for the manned Mars mission actually on-the-books at NASA for 1983.  By the the time the whole thing was cancelled in 1973,  that Mars shot had been pushed back to 1987.  The other two were NERVA and chemical. 

You look at 6000 sec,  and you can go to Mars single stage,  two-way,  at very,  very reasonable mass ratios.  You can even fly very fast:  how about 75 days one-way?  There is enough mass ratio for nice payload and structural fractions.  The structural fractions can cover both the equipment required for cry-storage of propellants long-term,  and for far more structural durability than we have ever used before in a rocket vehicle (except the X-15).  The prospect of a fully reusable ship that could serve for decades,  even centuries,  in space,  thus becomes real. 

These are the "small" applications:  vehicles between a few dozen to a few thousand tons.  Mars,  Venus,  Mercury,  the NEO's,  and maybe,  just maybe the Main Belt could be reached with men using tinkertoys like these. 

For the biggies (which would be needed for planting real colonies anywhere later on) there is nuclear pulse propulsion,  which we already knew in 1959 would actually work.  That set of physics is quite peculiar:  it works better and easier at launch weights above 10,000 tons. 

That kind of ship is not built like anything we have ever seen before.  You build it like a warship,  of heavy steel.  In something resembling a real marine shipyard.  Isp potential is in the 10,000 to 20,000 sec range (at least),  and it is difficult to hold vehicle accelerations under 2 gees.  There are side effects:  fallout and EMP effects.  But it would be worth it to launch maybe half a dozen of these things over about 50 years,  sometime in the not very distant future. 

Propulsion advancement is the real key to just about anything we would ever want to do out there.  The best place to test/develop and maybe base the launch of stuff like that is the moon.  No air and water to pollute,  no neighbors to annoy.  Close enough to reach with what we have right now. 

More wild ideas offered to spark out-of-the-box thinking.  But,  these ideas really are/were supported by the numbers.  These could actually be turned to reality,  if we as a people decided to do it. 

Enjoy!!

GW

Yep.  Sure ain't all science,  either. 

For most outfits,  it's 40% science (written down somewhere),  50% art (learned one-on-one on the job),  and 10% blind dumb luck.  The better outfits (like Spacex now) have higher art %'s to skinny down the blind dumb luck %. 

They didn't start out with enough old hands to have enough art.  That's why Falcon-1 had flight test issues at first.  But they did learn,  and they did fix the art problem.  I'm proud of 'em.  "They done good."

GW

Depots or stacked vehicles,  no difference.  With propellants,  there are storables (like hydrazine and nitrogen tetroxide,  and kerosene),  there are cryogenics (like LOX and liquid methane),  and there are more difficult cryogenics that leak really easily (LH2). 

It would be easy to build a depot or a stack-up vehicle,  out of tank modules full of storables,  all plumbed together.  These would store for many months,  even a few years.  But,  Isp is down under 300 seconds.  No practical way around that. 

Cryogenics like LOX and liquid methane have a boiloff problem,  although it can be mitigated a bunch by a simple sunshade.  But,  again,  Isp is limited to the 300-400 sec range.  Really high-pressure engines with big (vulnerable) bells would fall toward the higher end of the Isp range.  With extra propellant to cover boiloff,  you might get a couple of years storage out of that. 

Hydrogen is the toughie!  It leaks extraordinarily easy,  even right through the metal wall of a tank.  Fittings leak all the time.  And the boiloff problem is much worse.  But LOX-LH2 at high pressure could get you shuttle engine performance or a tad higher:  450-470 sec maybe.  Trouble is,  we still have no really good way to store vast quantities of LH2 for a 2 year mission.  That technology needs a hard look before we fly it to Mars for a round trip with men.  Not that it couldn't be done.  But you're going to need some kind of a cryo-cooler,  and some very stringent leak prevention engineering. 

Or,  maybe store it and ship it as water,  and just make enough hydrogen from that water to support the next burn.  Solar electrolysis module,  perhaps?

Solve that storage problem with LH2,  and not only is LH2-LOX possible for Mars,  so also is LH2 solid core NERVA.  That one was cancelled about a year before first flight,  demonstrating 3/4 hour burns,  restarts,  and 900 sec at T/W 3.6.  That could be done "right now" (see below about resurrecting NERVA).

But,  if we resurrected NERVA,  why not try to do what they didn't do back then,  and do a water NERVA.  In fact,  water contaminated with the other volatiles ammonia and methane.  That stuff is present as ice all over the solar system.  Just mine the ice,  melt it,  filter out the solids,  and use it in your reactor.  That's real simple ISRU,  right there. 

There's an Isp penalty, to be sure,  from MW 16-18 instead of 2,  but I'd bet the higher heat capacity of the water might allow higher reactor power at the same mass throughput,  offsetting some of that Isp penalty.  Think 700 Isp and fuel all over the solar system.  That's an exciting prospect. 

Once you get above the 450 sec level with your Isp at high engine T/W,  mass ratios get far more reasonable at lower stage count.  At 900-100 sec for NERVA,  single stage reusable transit vehicles (orbit-to-orbit) and single-stage reusable "landing boat" vehicles start getting really feasible.  These can be assembled from 25 ton modules in LEO,  and sent anywhere desired. 

We did this NERVA thing before.  We could resurrect it and do it again,  pretty quickly,  I.F.F. (if and only if) the right crowd did this.  (Wrong crowd would take forever.)  It sure makes one whopping difference in one's mission designs. 

The shopping list for enabling and continuing technologies for men in deep space appears to me to be (1) modular vehicle designs docked from 25 ton modules,  (2) some sort of cryocooler for long term LH2 storage,  (3) a sunshade that could double as meteoroid armor,  (4) resurrecting NERVA,  and (5) working on a water NERVA for later upgrades. 

So,  why are they instead doing a gigantic 100-ton launcher when we have some 25 ton launchers already,  and a 53-tonner on a short path to readiness?  Bah,  humbug!  Politics plays too big a role in government space programs.  Ridiculous. 

GW

The compression ratio is important because of product density (largely its pressure).  Material strength need be only what is necessary to contain the product you require.  Most of this chemistry stuff takes place at 1 to several atm.  If 1 atm is good enough,  the compression ratio from 7 mbar to 1013 mbar is about 140,  which is doable in any of several ways. 

Since I last corresponded on this thread,  I found out about an absortion (adsorption?) compressor rig.  You absorb CO2 at 7 mbar,  confine the "sponge",  heat it to drive the CO2 out,  which is near 1 atm.  It's an analog to the confined dry ice vaporization I suggested,  except it works straight off atmospheric CO2.  Works anywhere on Mars.  The product comes out near 1 atm pressure,  which is apparently chemically useful for synthesizing methane from CO2 and water.  No super-high pressures there. 

That'll work,  we just gotta try it enough to work all the bugs out,  before risking depending on it.  Some of that can be done here,  the final check being maybe an unmanned trial on Mars. 

Purity is an issue to be evaluated.  I'm not sure,  but I think this absorption compression thing is the same basic technology that's in the oxygen system in the F-22.  It seems to be having troubles,  and I'd hazard a guess that's a purity-of-product issue.  Mars's atmosphere is not just pure CO2,  so the same risk applies. 

GW

Impaler said somewhere above:

"But with regard to Marshaling we should really be developing the next generation of technologies that both make Marshaling more flexible such as long-term Cryogenic storage, Cryo-propellent transfer, autonomous rendezvous and docking."

I quite agree.  The next upgrade to NERVA ought to be a version that uses water,  contaminated with variable amounts of methane,  ammonia,  and perhaps other volatiles.  I know the Isp is reduced (square root of molecular weight effect),  but propellant availability expands to every object in the solar system with frozen volatiles,  not a small advantage!  Frozen "dirty" water keeps "forever" as long as it is contained and pressurized with 6+ mbar worth of water vapor pressure.  Ice (and liquid water) is very compact and easy to store. 

Perhaps the really high specific heat of liquid water,  and the really high latent heat-of-evaporation of water,  can be used to offset substantially-higher reactor powers,  in order to maintain Isp in the 700-1000 sec range.  I dunno.  Project Rover never really explored that option. 

I'd consider that a follow-on.  The old LH2 NERVA could be quickly resurrected and used "right now".  And should be.

Anything that might work solid core would be easier to do in gas core.  This is true whether open-cycle or "nuclear light bulb".  There's an even better follow-on for you,  although it would take a tad longer to do than a water NERVA. 

GW

PS - don't forget about nuclear explosion propulsion.  Works better the larger the ship.  10^4 -- 10^5 tons,  that's the proper class for pulsed propulsion.

Impaler: 

I quite agree with you.  Leave the transfer habitat in orbit for return.  That provided a huge payoff in Apollo.  Why sacrifice the benefits of "lunar orbit rendezvous" at Mars? 

The lander could be itself the habitat,  as in Apollo.  Or,  maybe not,  if its engines are solid core nuclear,  as in NERVA.  Who yet knows?  Depends upon what we might get operational in the next 5 years or so. 

It would be handy to have at least a small shirtsleeve environment on the surface in which to eat,  sleep,  and do whatever lab work supports "exploration".  That last item is far more important than it might sound,  and is something we did NOT do on Apollo.  That surface habitat could be nothing more than the inflatable version of a Quonset hut.  That engineering problem is not all that hard to solve.

As for rovers,  it's design depends mostly on the size,  mass,  and endurance of the astronaut's spacesuit,  because that is the "payload" for every astronaut being carried.  Why not consider a mechanical counterpressure suit?  They are 2-4 times lighter,  and unbelievably more supple than the "traditional" gas balloon suits we currently use. 

If we were to back off from the arbitrary NASA requirement of 1/3 atm equivalent body compression,  to about 1/5 to 1/4 of an atm,  we could build one today in the lab that worked (we already did,  way,  way back in 1969),  and we could "develop" it to a usable form in about 5 years,  given the "right" contractors. 

A lightweight astronaut/suit requires FAR LESS of a rover,  maybe even one that is unpressurized (just carry an inflatable Quonset hut with you).  Such a thing might even be able to "fly" on rocket engines to very long ranges,  compared to what we are used to thinking about (surface battery cars).  Liquid propellants really do store more energy per unit mass than any battery ever imagined,  so far.

Gotta think way outside the "traditional boxes" to really solve these problems.  There are a few of us (very few) who did that professionally.  From 1976 until 1994,  I did exactly that,  for aerospace/defense applications.  And I was very good at it.  Space travel stuff is really no different. 

That's why I come up with these wild-seeming ideas.  If you look closely,  they might actually work.  Maybe,  they are not really so wild after all. 

GW