Human Exploration of Mars Design Reference Architecture 5.0

[William Barton]

Am I correct in reading that the "surface habitat" lander (transfers crew from orbit to ground) lacks a landing abort capability?

[William Barton]

It seems to me that manned exploratory missions to the Moon and Mars come in two natural "flavors," excursions (single lander, up to 2wks Moon, 30da Mars) and expeditions (multiple lander/rover, 30da+ Moon, typically 18mo Mars). This seems like an attempt to create a hybrid between the two that may not be such a good idea. It's tied to a single landing site, like an excursion, but requires a large at-Mars infrastructure, like an expedition.

Mars Direct originally took advantage of the excursion requirements to Mars to tie excursion together into an expedition-equivalent, but could be used in a purely excursionary format, if necessary. That's probably a better idea.

If I were going to plan an expeditionary exploration of Mars, I'd want an orbital manned infrastructure (my personal favorite uses the martian moons, but that's largely due to my science-fictional antecedents), supporting reusable landers to acquire multiple landing sites. In other words, I'd put an expedition in orbit, and run excursion-like missions to the surface. I know reusable Mars manned landers would be difficult to design (I imagine expendable entry shells, possibly inflatable) delivering crews to prepped ISRU/Hab landers, allowing open-ended exploratory landings whose length would depend on the nature of the landing site, and maybe even on what turned up post landing. The "expedition" would keep on receiving new hardware and crew-rotation at each flight opportunity. It's possible that surface exploration crew members would stay at Mars (some time on the ground, some time in orbit) for a very long time. If 18months is feasible, so might 20 years be. Of course, the political commitment to really explore Mars is fantasy at this point in history.

[William Barton]

One comment about interplanetary radiation. My understanding is, for interplanetary flight, the risks come from solar and cosmic radiation. If the expected Maunder Minimum really shows up  (unknown, because the last one happened before the invention of scientific instruments), there will be less solar radiation, and more cosmic. I expect, either way, interplanetary travel is going to require both shielding and sophisticated medical intervention.

[kfsorensen]

I think this is a step backwards from DRM III, too many rendezvous events, too much mass to launch.

I think it's a step backward from the NEP-AG studies that almost became a DRM IV...

For one thing, a 20 MWt NEP reactor is going to be a whole lot easier to develop than a 500 MWt nuclear thermal reactor.  More sustainable too.

Isn't it kind of silly to have a 500 MW nuclear reactor send you to Mars and then fly there on diddly little solar panels?

Maybe.

A NTR needs turbomachinery to pump the hydrogen through the reactor.  I think that 25 klb thrust, 900 second Isp, and 1000 psi pump exit pressure work out to 1MW of mechanical power.  This can be extracted under comparatively benign conditions via an expander cycle - the heat required gets transfered across a huge surface area (tiny metal tubes) between two liquids at a huge temperature differential.  It has to run a few times during the mission, for a few minutes at a time.

A 20 MWe nuclear reactor needs to handle at least 20 MW of mechanical power (using a Rankine cycle) and possibly much more (Brayton).  It has to reject many MW of waste heat via radiation into vacuum.  It has to work continuously for years with no maintenance.

Not clear which is easier, without doing the math.

ISRU using solar panels does get a bit tricky, for sure.

The turbomachinery is the least of your problems in developing a nuclear thermal engine.

[kfsorensen]

Maybe it's about justifying the enormous payload capability of Ares-V?

That would be my bet too.

Ross.

The NEP-AG study was done to show how to do Mars without heavy-lift.  It's no wonder that in an attempt to justify the Ares V they would move towards a superheavy architecture.

[libs0n]

The political barriers remain significant too.

I have a concept in relation to this: a joint Russian-American Mars expedition where the Russians construct and launch the nuclear components to bypass said domestic political opposition to things nuclear.  I think the Soviets built in space nuclear components, but I would not know what capability they have retained in this area.  They do have an extensive nuclear industry from which to draw on in the future.  Would NASA or would some American nuclear laboratory design such nuclear components?  Perhaps if need be the design portion could remain in America, while the construction and launch take place elsewhere.

[libs0n]

Something I've been wondering.  What happens when you couple an Earth orbiting momentum exchange tether for Trans Martian Injection with one of these high ISP technologies, like NEP SEP or Vasimr to reduce transit times?  I understand from a comment here once that at least for VASIMR that much of the time is spent circling out of Earth's gravity well, or something.  I also have in mind a tether orbiting Mars for the return trip.  I apologize for my lack of actual understanding of space mechanics.

I haven't done much thinking about a NASA Mars mission, but I have also thought that beginning with the moons and exploiting their resources and location for infrastructure was a good strategy.

Random thoughts I might as well include:
-VASIMR, maybe EP, apparently needs lots of energy: what of "beaming" power to the transit vehicle from a stationary power array?
-Getting the long transit times to Mars down would seem to be a priority for manned missions, or at least a priority I favour.  What are all the various "short transit times" options? edit: This may be asking too much so feel free to disregard the question.  On the other hand, I wouldn't be too disinclined to missions of longer duration transit, although as mentioned I would probably favour some 90 days to Mars or less option depending upon what's entailed.

[Kaputnik]

Am I correct in reading that the "surface habitat" lander (transfers crew from orbit to ground) lacks a landing abort capability?

It's designed to make a one-way trip to the surface. So, any 'abort' would just be reinforcing this capability. Unless you mean some sort of crew capsule that could be jettisoned separately? But it might well prove better to have a single reliable system- KISS.

[Kaputnik]

Something I've been wondering.  What happens when you couple an Earth orbiting momentum exchange tether for Trans Martian Injection with one of these high ISP technologies, like NEP SEP or Vasimr to reduce transit times?  I understand from a comment here once that at least for VASIMR that much of the time is spent circling out of Earth's gravity well, or something.  I also have in mind a tether orbiting Mars for the return trip.  I apologize for my lack of actual understanding of space mechanics.

I haven't done much thinking about a NASA Mars mission, but I have also thought that beginning with the moons and exploiting their resources and location for infrastructure was a good strategy.

Random thoughts I might as well include:
-VASIMR, maybe EP, apparently needs lots of energy: what of "beaming" power to the transit vehicle from a stationary power array?
-Getting the long transit times to Mars down would seem to be a priority for manned missions, or at least a priority I favour.  What are all the various "short transit times" options? edit: This may be asking too much so feel free to disregard the question.  On the other hand, I wouldn't be too disinclined to missions of longer duration transit, although as mentioned I would probably favour some 90 days to Mars or less option depending upon what's entailed.

A long transit from LEO to escape velocity is not all that bad, since the crew can join the craft just before it leaves Earth orbit altogether, using a small 'taxi' flight- e.g. an Orion coupled to a DHCSS or similar.

[kfsorensen]

like NEP SEP or Vasimr

It's not NEP, SEP, or Vasimr.

Vasimr is a thruster.  It might solar powered or nuclear powered.  It's like saying "should we drive there in a car, truck, or tire?"

[William Barton]

Am I correct in reading that the "surface habitat" lander (transfers crew from orbit to ground) lacks a landing abort capability?

It's designed to make a one-way trip to the surface. So, any 'abort' would just be reinforcing this capability. Unless you mean some sort of crew capsule that could be jettisoned separately? But it might well prove better to have a single reliable system- KISS.

Wasn't that the theory behind not have LAS for Shuttle? The crew riding down in a one-way vehicle sounds like an invitation to not survive a hard landing. There's a point where KISS = Keep It Simply Stupid. I can't be the only one who thinks having your ride home waiting for you to land successfully is not a good idea. Although, if you crash next to it, I guess you won't be needing it...

[libs0n]

like NEP SEP or Vasimr

It's not NEP, SEP, or Vasimr.

Vasimr is a thruster.  It might solar powered or nuclear powered.  It's like saying "should we drive there in a car, truck, or tire?"

I apologize for my callous use of acronyms.  My question should be refined to what does MX tether boosting offer to the various propulsion options in a Martian architecture and to an overall architecture that includes it.  Although, put that way, the answer would likely be less mission mass of some degree, and less time undertaken for low thrust vehicles to get up to the speed the tether offers.

Crewing through rendezvous of a low thrust vessel already underway is an interesting solution to the time problem, Kaputnik.

[kfsorensen]

My question should be refined to what does MX tether boosting offer to the various propulsion options in a Martian architecture and to an overall architecture that includes it.  Although, put that way, the answer would likely be less mission mass of some degree, and less time undertaken for low thrust vehicles to get up to the speed the tether offers.

If you broke the vehicle into pieces and assembled it at some high-energy location like EML2, the tether could be quite advantageous.  If you want to do it all in one throw, the tether will be super-sized for that payload and will not be advantageous.

[jongoff]

The turbomachinery is the least of your problems in developing a nuclear thermal engine.

Fair enough.  But with an NEP system, now you have to build the biggest electric propulsion system ever flown (by at least a few orders of magnitude), the biggest radiator ever flown (by at least two orders of magnitude), the biggest space nuclear reactor ever even ground tested (by what something like an order of magnitude at least?), etc.

At least NTRs in moderate sizes have been built and groundtested in the distant past.  In fact, the highest power reactor even run was the size of a desktop, and was an NTR...

That said, I think that using propellant depots, and just throwing some extra mass at it might actually yield a lower cost overall than trying to build some fancy nuclear propulsion system (NTR or NEP) that's only going to get used a few times over the course of many years.

Most of the cost of a chemical propulsion mars mission (as an aside, I agree that going aggressively on the ISRU on the Mars end does make a lot of sense) is the launch costs.  But with the kind of mass you're talking about, you have high potential for being able to provide flight rates capable of dropping prices substantially...

Of course talking about manned mars missions right now is utterly premature, when our country is no closer to having a sustainable lunar transportation network than it was when I was born.  By the time we're ready as a civilization to even start the engineering on a mars program, enough things will have changed that speculation at this point is probably futile.

~Jon

[JPK]

Re the 3.0 architecture
Could an aries V put both the NTR stage an space craft
up in a single launch ie 3 launchers per mission?

[kfsorensen]

when our country is no closer to having a sustainable lunar transportation network than it was when I was born.

Considering the quality of lunar mission analysis being done around the time you were born, I would say we are quite a bit FURTHER away from a sustainable lunar transportation network than we were when you were born.

Thanks, Mike.

[kfsorensen]

At least NTRs in moderate sizes have been built and groundtested in the distant past.  In fact, the highest power reactor even run was the size of a desktop, and was an NTR...

Correct, but you will never get to replicate the testing setup they used in the 60s.  Forget about it.

The NEP reactor is at least intended for closed-cycle operation, unlike the NTR.  Don't get me wrong, it's challenging, but I'd pick building NEP over trying to build an NTR or launching gigatons of LH2/LOX propellant on HLVs.

[jongoff]

Don't get me wrong, it's challenging, but I'd pick building NEP over trying to build an NTR or launching gigatons of LH2/LOX propellant on HLVs.

Ah come on, aren't we being a *wee* bit hyperbolic here (not that I ever do that myself...)?  Gigatons?  Isn't that like...6 orders of magnitude high?  :-)  The thing I like about doing a propellant depot based architecture is that it allows you to split the mission up into much smaller pieces.  And if for instance ISRU on Mars on on its moons turns out to work, you get a lot more leverage...

But once again, this discussion seems to be really premature.  "Predictions are tough--especially about the future."

~Jon

[Kaputnik]

Am I correct in reading that the "surface habitat" lander (transfers crew from orbit to ground) lacks a landing abort capability?

It's designed to make a one-way trip to the surface. So, any 'abort' would just be reinforcing this capability. Unless you mean some sort of crew capsule that could be jettisoned separately? But it might well prove better to have a single reliable system- KISS.

Wasn't that the theory behind not have LAS for Shuttle? The crew riding down in a one-way vehicle sounds like an invitation to not survive a hard landing. There's a point where KISS = Keep It Simply Stupid. I can't be the only one who thinks having your ride home waiting for you to land successfully is not a good idea. Although, if you crash next to it, I guess you won't be needing it...

Well what would your suggestion be?
Abort to anywhere other than the surface is virtually impossible. If it were otherwise, people wouldn't be swallowing up the cost/risk of ISRU in an attempt to get the ascent vehicle down to a reasonable mass.
The only feasible thing that I can think of is that the nominal cargo+crew landing is done under a combination of propulsion and parachutes, but the abort mode would jettison the cargo element leaving the smaller crew capsule to make a landing using its own descent system.
This would have two issues- firstly, mass on any Mars entry vehicle is going to be a very precious thing indeed. Such an abort system may simply not be possible within the mass limits. Secondly, it is almost certainly better to have a single highly capable landing system rather than two mass-squeezed ones- analogous to Apollo's three parachutes instead of two plus a reserve.

[kfsorensen]

Ah come on, aren't we being a *wee* bit hyperbolic here (not that I ever do that myself...)?  Gigatons?  Isn't that like...6 orders of magnitude high?  :-)

You're right...gigagrams of LH2/LOX propellant.