Human Exploration of Mars Design Reference Architecture 5.0

[rdale]

    This document reviews the Design Reference Architecture (DRA) for human exploration of Mars. The DRA represents the current best strategy for human missions. The DRA is not a formal plan, but provides a vision and context to tie current systems and technology developments to potential missions to Mars, and it also serves as a benchmark against which alternative architectures can be measured. The document also reviews the objectives and products of the 2007 study that was to update NASA's human Mars mission reference architecture, assess strategic linkages between lunar and Mars strategies, develop an understanding of methods for reducing cost/risk of human missions through investment in research, technology development and synergy with other exploration plans. There is also a review of the process by which the DRA will continue to be refined. The unique capacities of human exploration is reviewed. The possible goals and objectives of the first three human missions are presented, along with the recommendation that the mission involve a long stay visiting multiple sites.The deployment strategy is outlined and diagrammed including the pre-deployment of the many of the material requirements, and a six crew travel to Mars on a six month trajectory. The predeployment and the Orion crew vehicle are shown. The ground operations requirements are also explained. Also the use of resources found on the surface of Mars is postulated. The Mars surface exploration strategy is reviewed, including the planetary protection processes that are planned. Finally a listing of the key decisions and tenets is posed.

http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20090012109_2009010520.pdf

[Kaputnik]

Thanks for that, very interesting indeed.
A few points though:
- aerocapture for the DAV- why not direct entry?
- DAV seems rather heavy- this may be because it only uses partial ISRU- is CH4 generation seen as too risky?
- I've never been a huge fan of NTR. The benefit over conventional cryo propulsion isn't anything astonishing, when you factor in much lower thrust/weight ratio of the stages. The political barriers remain significant too.
- Drop tank TMI stage seems a bit crude. I wouldn't be surprised if it worked out better to just keep the tank in place, which saves you a rather heavy-looking semi-cylindrical truss structure.

[kfsorensen]

JSC can't seem to give up on NTR.  Too bad.  That alone will sink any hope of this mission ever happening.

[kraisee]

If you can deploy Low Boiloff technology and Cryogenic Propellant Transfer technologies, you don't need any form of nuclear propulsion.

Which is cheaper?   Which is more realistic?   And which would offer benefits beyond just a human mission to Mars?

That isn't to say that I don't ever want to see a nuclear space engine.   I most definitely do.    But I think it would be crazy to include it on the critical path for any human exploration missions.

Ross.

[mike robel]

I still wonder about what my friend Guenter Wendt says about Mars Missions, which is that the crew will be dead within 7 days due to radiation....

[A_M_Swallow]

{snip}
- I've never been a huge fan of NTR. The benefit over conventional cryo propulsion isn't anything astonishing, when you factor in much lower thrust/weight ratio of the stages. The political barriers remain significant too.

Mars is still within the area that STR (Solar Thermal) motors work.  Solar Thermal Propulsion can also be used to the Moon, Asteroids, GEO and inner planets.  The high temperature chamber technology can probably be transferred.

[Jorge]

I still wonder about what my friend Guenter Wendt says about Mars Missions, which is that the crew will be dead within 7 days due to radiation....

Hate to say it, but he was speaking out his ass.

A crew traveling to Mars would get less radiation exposure during their first 7 days than the Apollo crews got during their entire missions. This is because the Mars crew would only get one exposure to the Van Allen belts while the Apollo crews got two.

If Wendt was right, none of the Apollo crews should have survived their missions.

[mike robel]

I still wonder about what my friend Guenter Wendt says about Mars Missions, which is that the crew will be dead within 7 days due to radiation....

Hate to say it, but he was speaking out his ass.

A crew traveling to Mars would get less radiation exposure during their first 7 days than the Apollo crews got during their entire missions. This is because the Mars crew would only get one exposure to the Van Allen belts while the Apollo crews got two.

If Wendt was right, none of the Apollo crews should have survived their missions.

Well, what bugs me is I can't find any hard data about radiation exposure from probes we have sent to Mars.  Zubrin says , FWIW, that the radiation exposure would only add a slight increase in probability of developing cancer.

So I am have anecdotal data on two extremes and no hard data...

[Jorge]

I still wonder about what my friend Guenter Wendt says about Mars Missions, which is that the crew will be dead within 7 days due to radiation....

Hate to say it, but he was speaking out his ass.

A crew traveling to Mars would get less radiation exposure during their first 7 days than the Apollo crews got during their entire missions. This is because the Mars crew would only get one exposure to the Van Allen belts while the Apollo crews got two.

If Wendt was right, none of the Apollo crews should have survived their missions.

Well, what bugs me is I can't find any hard data about radiation exposure from probes we have sent to Mars.  Zubrin says , FWIW, that the radiation exposure would only add a slight increase in probability of developing cancer.

So I am have anecdotal data on two extremes and no hard data...

"Anecdotal data" is an oxymoron, I'm afraid.

What you have are two anecdotes and no data, and one of the anecdotes (Wendt's) is trivially false. I could excuse him for saying it if he said it before Apollo 8, but it would beg the question of how he could bring himself to strap in the 8 crew if he believed it to be true.

Once you get outside the Van Allen belts, the radiation environment doesn't change much until you get to Mars. Time of exposure then becomes the biggest factor, if the amount of shielding is assumed to be constant.

[kfsorensen]

{snip}
- I've never been a huge fan of NTR. The benefit over conventional cryo propulsion isn't anything astonishing, when you factor in much lower thrust/weight ratio of the stages. The political barriers remain significant too.

Mars is still within the area that STR (Solar Thermal) motors work.  Solar Thermal Propulsion can also be used to the Moon, Asteroids, GEO and inner planets.  The high temperature chamber technology can probably be transferred.

Solar thermal can't provide the high thrust needed to take advantage of the DV reduction that comes about from doing the trans-Mars injection burn deep in the gravity well.  That loss means that whatever Isp advantage of solar thermal is trashed by the nearly doubling of the DV required for trans-mars injection.

[A_M_Swallow]

{snip}
- I've never been a huge fan of NTR. The benefit over conventional cryo propulsion isn't anything astonishing, when you factor in much lower thrust/weight ratio of the stages. The political barriers remain significant too.

Mars is still within the area that STR (Solar Thermal) motors work.  Solar Thermal Propulsion can also be used to the Moon, Asteroids, GEO and inner planets.  The high temperature chamber technology can probably be transferred.

Solar thermal can't provide the high thrust needed to take advantage of the DV reduction that comes about from doing the trans-Mars injection burn deep in the gravity well.  That loss means that whatever Isp advantage of solar thermal is trashed by the nearly doubling of the DV required for trans-mars injection.

Is that low thrust intrinsic to the technology or just that people have only been making small Solar thermal engines?

[yinzer]

{snip}
- I've never been a huge fan of NTR. The benefit over conventional cryo propulsion isn't anything astonishing, when you factor in much lower thrust/weight ratio of the stages. The political barriers remain significant too.

Mars is still within the area that STR (Solar Thermal) motors work.  Solar Thermal Propulsion can also be used to the Moon, Asteroids, GEO and inner planets.  The high temperature chamber technology can probably be transferred.

Solar thermal can't provide the high thrust needed to take advantage of the DV reduction that comes about from doing the trans-Mars injection burn deep in the gravity well.  That loss means that whatever Isp advantage of solar thermal is trashed by the nearly doubling of the DV required for trans-mars injection.

Is that low thrust intrinsic to the technology or just that people have only been making small Solar thermal engines?

Intrinsic to the technology.  A NTR might have 4500 MW thermal power.  Solar flux at the earth's orbit is roughly 1 kW/m^2, so you'd need solar concentrator over 2 km in diameter to capture that much power.  The upper stages in the attached PDF have 3 such engines...

[iamlucky13]

- aerocapture for the DAV- why not direct entry?

First of all, remember this is an early baseline, not a final proposal. I tend to agree with the implications of your other questions.

Regarding the quoted question, for payloads much larger than the MSL, the thin Martian atmosphere makes the required size of heat shield for direct entry generally prohibitive.

[Seer]

Interesting new report.  First thoughts are that they've gone in the other direction to DRM 3.0, which scubbed mass. This plan is DRM 1.0 on steriods.  The aeroshell is massive at 43 tonnes, that's about 40% of aerobraked mass. The Transhab is also huge: it's 40 tonnes, nearly twice as big as the previous one. The orion EERV is more realistic at 10 tonnes, rather than 5 tonnes

Seven Ares V plus nuclear is going to be costly. The mobility options are pretty bold. That Commuter hab looks like something out of Star Wars! 

[Kaputnik]

Maybe it's about justifying the enormous payload capability of Ares-V?
As a side note, if you swallowed the inevitable development costs, could Ares-V be optimised for LEO launches, i.e. cut 40% of the EDS tankage? By my crude calculations you'd get another 10t or more payload.

[PurduesUSAFguy]

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

[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?

[yinzer]

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.

[kraisee]

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

That would be my bet too.

Ross.

[Kaputnik]

It seems to be a case of throwing mass at any problem. Even those that don't really exist. For example, a more comprehensive ISRU plant generating CH4 as well as O2 would allow a significantly lower DAV mass.
The multi-purpose aerodynamic shroud and entry shell could be problematic- it is really heavy, and the TPS is exposed for something like a whole year through launch to entry. The development effort associated with such a design would be immense.
I tend to favour much smaller entry vehicles, even if that means four rather than two to accomplish the mission, because it is less of a scale-up from existing systems and would be much easier to test out.