New Mars Forums

My opinion/Apollo 8:  They did it to "beat the Russians" even if it wasn't a proper landing.  The big Russian N-1 moon rocket was on the pad being fitted out at the time the Apollo-8 mission decision was made.  Events later proved that the N-1 wasn't ready to fly yet.  Ultimately it never successfully did.  Neither was the US LEM ready.  Apollo-8 flew without one (meaning an Apollo-13-type problem would have killed them - no lifeboat).

My opinion/artificial gravity:  the smartest way to go to Mars with men,  considering the mass that must go,  is with a vehicle assembled in LEO by docking.  Why not make a long stack with the habitat at one end?  Then spin it end-over-end for 1 full gee.  Only takes 4 rpm and a 56 m spin radius.  Forces are fairly low.  No cables,  no trouble de-spinning to maneuver.  Keep the zero-gee intervals short that way. 

My opinion/is Mars gee therapeutic?  No one knows,  those experiments have never been done excepting very questionable surrogates like enforced bed rest.  0.38 gee can't hurt,  it may help.  Is it enough?  Who knows?  I hope it's enough,  but you don't bet lives on it.  Not yet. 

GW

I see Spacex with Falcon-1,  Falcon-9/Dragon,  and very soon Falcon-Heavy/Dragon,  with Dragon able to fly manned not long after -Heavy flies.  Their prices look great.  -9 is about $2500/lb payload to LEO at 10.1 metric tons.  -Heavy is projected around $800-1000/lb payload to LEO at 53 metric tons.  They have no 25-ton vehicle,  but a good guess suggests it would price out around maybe $1600/lb at 25 tons. 

ULA Atlas-5 -551/552 configurations price out pretty close to $2400/lb to LEO at the max 25 ton size.  They appear to be a bit higher than Spacex,  but not all that much.  I don't have the data for Delta-4,  but it's comparable to Atlas-5 in size,  and was around twice as much per lb. 

I rather suspect that if ATK/EADS gets the Liberty flying,  it will be comparable to the Atlas-5 and Delta-4 in payload size and cost.  Similar types of companies.  They'll be competitive at the 25 ton size.  Spacex will have it hands-down in the 10 and 53 ton classes.  The others will have to learn how to launch with a smaller support team to compete.  That's Spacex's real secret.

GW

There no technical reason why the Liberty cannot be made to work.  Most of our ICBM's for half a century have used solid stages topped with a liquid stage for precise burnout control.  Minuteman series and Peacekeeper all work that way. 

On the other hand,  whether ATK/EADS can compete economically with Spacex depends upon a massive change in corporate vision.  It can be done,  but few do it.  The support per launch has to be trimmed from the population of major city to that of a small town.  I include subcontractors and vendors in that assessment. 

With its 3 vehicles,  Spacex has been establishing a trend of payload cost to LEO vs max payload weight to LEO that is lower than all comers except perhaps ULA's Atlas-5 at its 551/552 configuration only.  Maybe.  Depends upon exactly how you plot the data. 

The way I plot it,  ULA Atlas-5 comes off a tad higher than Spacex,  and Delta-4 much higher.  These are built by giant corporations,  used to doing things the NASA way,  or at least the DOD way.  Both customers are a bit bloated,  NASA more so,  these later decades. 

ATK and EADS fall in that same giant corporation category,  used to working on bloated things for government space or defense stuff.  If they make the same paradigm shift that Spacex did,  they can compete in commercial launch.  So could Boeing and Lockheed-Martin,  except I really don't see them making that paradigm change,  unless forced to do so. 

For now,  I'd rather see what Spacex can really do,  as it will drive paradigm change in its competitors,  and break this bloated,  expensive impasse we have suffered since the beginning of manned spaceflight. 

The Russians did the same launch support model,  just within a different economic system:  a huge population supported every single launch.  That can never be cheap.

Dark horses might include the Skylon thing,  or orbital outgrowths of the suborbital spaceplane folks.  As organizations,  they have the right idea:  keep the support team size per launch very small or it'll never be cheap.  We'll see.

GW

Louis:

I crawled around on their website just now.  I saw nothing there to indicate a Mars shot of any kind,  much less a date.  That included looking at their recent press releases.  But,  they do have a habit of springing very unexpected surprises. 

I rather think they could send a Dragon unmanned one-way to Mars rather easily with Falcon-Heavy,  and probably even just Falcon-9.  I'm not sure they could land it there with what hardware and technology they have so far revealed.  The new SuperDraco's have more than enough thrust to make a powered landing,  but I don't see 1290 Kg of on-board propellant being enough,  at hydrazine Isp's and a 45-degree cosine factor,  without some sort of aero-decelerator help.  Spacex lists no Isp's,  but says "deep-throttleable" and "120,000 lb axial thrust" on their website.

One cannot count on the volume in the cylindrical  service module for the fuel supply to do a rocket landing,  because that module has to be jettisoned prior to atmospheric entry.  Sad,  because it would be fairly easy to store several thousand pounds of extra propellant tanks in there. 

I just don't see that much delta-vee from 1.29 tons of propellant in a capsule flown "lightweight" at around maybe 5 or 6 tons,  given Isp in the neighborhood of 300 sec and a 0.71 cosine factor for canting.  On the other hand,  if they use maybe 3 tons of extra propellant from the service module to slow way down before entry,  a one-way landing starts looking better.  Not so very efficient,  but it might work. 

All that being said,  given an entry aero-decelerator,  followed by a powered rocket landing,  I think Dragon might go to Mars very soon.  Falcon-Heavy is listed as flying for the first time from Vandenburg in 1013.  I just don't see the hardware for a sample return,  much less anything manned. 

After all,  if one has gone to all the trouble to send men to Mars,  what is the point of not landing?  Doing an Apollo-8-like flyby or orbit-only trip seems nuts,  given what it takes just to get there. 

There's no telling what folks are working on "in secret".  But,  as of yet,  I have seen nothing that looks like anybody working on a lander for Mars,  other than some tiny sample-return rockets.  I suspect that a two-way lander will drive the design of a manned Mars mission,  more than any other single item.  (That same basic "how-do-we-land-and-take-off-again?" problem drove the Apollo/Saturn designs,  too.) 

GW

If Vesta has subsurface ice,  then self-pressurized ice caves/aquaculture volumes become possible on it.  Nothing more sophisticated than drilling rigs and steam generators are needed to hollow them out.   

Although,  I have yet to figure out how to anchor a drilling rig on a really low-gravity world like Vesta (2.9% of a gee,  is that not what I saw quoted somewhere?)

GW

Oh,  yes,  porosity has an effect.  Too little and the decelerator blows itself to pieces.  Too much and it never opens.  Doesn't matter what kind,  either.  Closer to "just right",  and stability of the flow field is affected.  Of course. 

I believe real test data long before I believe computer codes,  no matter their pedigree.  But,  then,  I'm an old guy.  Over 60 years old. 

GW

Shellfish,  and shrimp,  too.

Red Planet Lobster,  perhaps?

GW

Chemical engines for Mars

I took a look around on the internet for the history of air-independent propulsion in submarines and torpedoes,  specifically high energy-release chemical.   Various sites had different things to say,  but I think what I found matches well with much of what I thought I knew earlier. 

Non-battery submarine ship propulsion (exclusive of air through a schnorkel and nuclear power) seems to have taken two forms,  neither very successful for pushing the ship.  One was running a piston diesel engine with fuel plus pure oxygen from bottles or a LOX supply,  and running almost the entire exhaust stream back through as dilution gas.  The articles didn’t say,  but I’d almost bet there was a sea water cooler to cool the exhaust gas before feedback.  These systems needed bottled argon for a temporary initial dilution gas to start up.  They had serious problems with fires and explosions handling the oxygen,  dangerous on any ship,  really dangerous in a submarine.   The other problem with exhaust gas feedback was the necessary filtering to clean it up of solids (carbon,  etc).

The second was a Walter turbine-based design,  centered on high-purity hydrogen peroxide decomposition,  usually after-burnt with a little diesel fuel.  Peroxide catalytic decomposition produced very superheated steam with oxygen in it.  Some of these systems used alcohols or other lighter liquid fuels for the afterburner fuel.  All were water-cooled combustors,  some featured water injection.  The articles didn’t really get into peroxide stability,  but it takes above-90% strength to work like this,  and the safe storage life at that strength is but a very few days.  Spontaneous decomposition is very violently explosive,  really bad inside a pressure hull.

The was one experimental USN sub (SS-X-1) that used peroxide decomposition for the oxygen to feed a piston diesel engine.  I do not know how the steam and oxygen were separated,  or what the dilution gas was.  The boat was nearly lost to some sort of explosion,  I presume related to high-strength hydrogen peroxide. 

The non-electric torpedoes pretty much used the same class of systems from WW1-onward.  Most of these by far used compressed air bottles to burn with an alcohol fuel,  feeding through a turbine to drive the torpedo propeller.  The articles today talk about methanol fuel,  while the old salts’ tales I heard talked about ethanol,  which actually has the higher combustion energy.  Some of these were “wet” systems with seawater injection into the combustion stream,  others “dry” without it.  I think I read about peroxide being tried in some of these,  but alcohol-air was,  and is,  by far the most common and most practical. 

There is a reason earth-moving machinery here on Earth is almost invariably diesel-powered,  with some heavy-duty hydraulics.  The torques and forces required are enormous and variable.  A piston diesel engine as a prime mover is the perfect choice to supply them,  having really good low-speed torque.  Gasoline engines also have similar characteristics,  but are not as economical at part load,  due to intake stream throttling.  Diesel is controlled by mixture ratio,  no throttle at all. 

To run a piston engine like that on Mars,  I think I would opt for LOX with liquid CO2 as the dilution gas.  The LOX tanks are fairly low pressure items,  but the liquid CO2 tanks are fairly high pressures (dozens of atm).  LOX from water,  and atmospheric CO2 are common on Mars.  The LOX and liqCO2 tanks will be far larger than the diesel fuel tanks we are used to seeing.  You just cannot aspirate and compress a 7 mbar CO2 atmosphere enough to serve on Mars.  Pre-ignition as-compressed pressures in engines like that are in the neighborhood of 9-10 atm gasoline,  and 15-22 atm diesel.  21/.007 is a compression ratio of 3000:1,  which simply cannot be built into such an engine by any known means. 

I don’t think I would mess with massive exhaust gas recirculation as the dilution gas,  because there are very serious contaminant filtering issues.  It would be easier and more reliable to work the liquid CO2 pressure tank issue. 

I’d recommend liquid methane as the fuel on Mars,  as it can be made from local water and atmospheric CO2.  The engine will likely have to be spark ignition and throttled,  like a gasoline engine,  because methane has a high octane number,  making it unusable as a diesel fuel.  That fuel tank will also be larger than a simple diesel fuel tank. 

The locomotive or truck tractor application is more in line with electric drive.  Running a generator is more of a constant-speed thing,  and that’s really well-matched with a turbine.  LOX-liquid methane with liquid CO2 as the dilution gas source should work pretty well. 

I don’t think I’d mess with hydrogen peroxide unless I had to,  for some other compelling reason.  The spontaneous decomposition difficulty is just too dangerous.  At “safe” strengths,  it’s just not useful as an oxidizer. 

GW

Aww,  Rune,  I was just looking for an excuse to fly. 

All this focus on the bottom line killed full-service gasoline stations,  too.  The dollars ain't everything,  but so many forget that,  these days. 

GW

Oh,  I know the easiest NEO's are not far from LEO,  but the bulk of them are tougher to reach,  having more elongated orbits.  That's why I suggested a pair of Falcon-Heavies,  to reach the more difficult targets,  and perhaps even travel from one to another to another to another ........  Plus,  the spacecraft itself can be bigger,  heavier,  and more capable.  If we're going to go prospect the NEO's,  let's look at a whole bunch of them.  They're all different,  or that's the way it seems,  anyway.  More likely to find what we want by visiting many.  I picked Falcon-Heavy for $800-1000/lb payload at max payload 53 tons.  It's 2.5 to 3 times cheaper than Atlas-V 551/552 at $2400/lb at 25 tons.  Thinking bigger is actually cheaper,  in many ways!!!!

Radiation shielding:  doesn't take very much dirt to shield solar particles.  I was thinking equivalent to 20 cm thickness of water.  At an effective sp.gr about 2 for "dirt",  that's only about 10 cm of said "dirt".  Cosmic rays,  that's also about as good as it gets,  unless you go with meters and meters of thickness,  due to the secondary particle shower.  There's going to be some sort of waste crap that can serve as "dirt" almost anywhere you go. 

It's the career limit on cosmic rays you worry about for long-term exposure,  since the thin shield only cuts it down crudely by a factor of 2.  Otherwise,  you have to have a really thick shield.  Solar minimum GCR is 60 REM/year.  Cut that in half to 30 with a thin shield.  If the astronaut is already old enough to take the high career limit of 400 REM,  it'll take over 10 years to accumulate,  as long as he doesn't go outside.  Younger people are allowed less,  and cannot stay as long. 

Refueling is "automated" with Progress,  I know,  but it's sort of a restricted case,  and not everybody is doing it yet.  Besides,  overseeing the tasks,  and making sure everything happens correctly with refueling,  is a good excuse for astronauts to fly.  So,  why not?

.... choir boy's singing again.......

GW

How to reach an NEO with what we have this year or next,  to support prospecting for mining?  Hmmmmm. 

How about launching two Falcon-Heavies?  One has the unmanned spacecraft (whatever it is) that will go to the NEO.  The other payload is nothing but a giant propellant tank made out of a Falcon second stage,  but without engines.  The vehicle with the NEO spacecraft keeps its second stage,  using it to circularize in LEO at near-depletion of propellant.  The second vehicle is just a refuelling tanker. 

Once refueled in LEO,  the spacecraft uses the refueled Falcon second stage as its propulsion for departure and rendevous,  much like we used the Saturn S-IV-B stage decades ago.  Except,  I'd plan to use it for the rendezvous with the NEO,  too,  that's typically a significant delta-vee.  Then the spacecraft itself can prospect the NEO,  collect samples,  and perhaps return. 

I'm thinking we'll need men to oversee the refuelling transfer in LEO.  Certainly to safely dock the two big "spacecraft" and make the fluid hookups.  So,  the tanker probably has a manned Dragon on its nose.  Crew of 2? 

This is not an idea for sending men to an NEO,  just a prospecting robot.  Sending men requires a different kind of vehicle,  one resembling a manned Mars transfer vehicle.  That's a different problem,  but the same basic transfer vehicle assembled in LEO could serve.  The difference is that you don't need a lander to visit NEO's. 

GW

Louis:

You are correct about the possibility thrusted descent.  I have a hunch that the canted thrusters on Dragon will be fluid dynamically stable for thrust during entry.  I suspect that is in part why they are designed that way,  in part just simple geometry without firing directly through a heat shield (although I believe that could be done,  too).  I wouldn't say killing all the velocity before entry was the wisest thing to attempt,  but thrusting during hypersonic reentry could be a wise course,  as long as not too many deceleration gees result. 

The lander problem is less about descent (hard as that is on Mars) than it is the following ascent.  Even with ISRU refueling on the surface,  where would you put it in a Dragon?  There's not enough space inside the heat shield-protected capsule for the fuel for a full thrusted descent,  aerobraking of some kind must assist.  The space where you could stash a lot of fuel would be in the trunk module,  which you have to jettison before entry. 

In fact,  use the rocket equation and the required delta-vee yourself,  at realistic mass fractions,  and you find out that a chemical lander will have to be 3 or even 4 stages.  You could get away with 3 (1 descent,  2 ascent) if you had a really big heat-protected ballute of some kind during a thrusted entry,  with thrusted deceleration to M2.5-ish post-entry big chute deployment,  and a final heavily-thrusted landing.    You'll still need at least 2 stages to return to orbit.  For a given payload of,  say, 2 men and minimal equipment,  the thing is still going to be huge.  Remember,  all such landers are dead-head payload that must be sent to Mars,  even if not fueled for the trip. 

300 sec-class Isp for storables,  structural mass fractions in the 10% range for a throwaway vehicle,  and the problem is very ridiculous,  because each stage is the previous one's dead-head payload.  Even at 450 sec-class Isp for LH2/LOX,  it's still ridiculous,  although you might get away with 2 stages,  1 descent,  1 ascent.   

Compare that with 900 sec-class Isp with NERVA.  1 stage goes down and back up again,  including a 30 degree plane change both ways,  and no aerobraking assist,  just rocket thrust all the way both ways.  I used 20% structure for reusability,  and 10% payload.  6 tons of men and equipment in a 60 ton fully-fueled lander.  6 tons returned,  too.  A real landing boat built tough,  not some fragile throwaway toy like the Apollo LEM.  You could carry a whopping lot more down,  if you ISRU refueled on the surface. 

Just wishing .....

GW