Exploring a lightweight Mobile Hab based HTM architecture

[Michael Bloxham]

Okay guys, I just want to make a call-out: We need more people involved with the refinement of these ideas! Clearly I think there is some concensus emerging about the potential merits of small-crew mobile hab architectures over more traditional big fixed-hab architectures (I have noticed that a few people here, including Kaputnik, Ross Tierney, and others, have explored their potential somewhat). And I think there is a great deal to be said about the potential to realistically approach the idea of a humans-to-mars mission without resorting to speculative technology as has been done in the past (i.e. assumptive EDL, zero boiloff, etc.). And this is greatly facilitated by the potential capability of a Jupiter-esque HLV - specifically its large payload volume capacity with the larger 12m diameter PLFs - which would in turn allow the use of large but heritage-derived mars entry vehicles with adequate surface payload for these smaller mobile habs.

So again: Please help us to refine these ideas! Any comment or question or whatever would help a lot! And if you really want to get involved please do not hesitate to offer: Tell us what your skills / interests are and we might be able to fit you in to a role later on. We need more engineer-types specifically so we can reduce the workload on our poor David Gooding .

Here are a few links to mull over if you want to know what we've been up to:

http://groups.yahoo.com/group/marsdrivemission/attachments/folder/0/list

http://tech.groups.yahoo.com/group/marsdrivemission/

My "baseline" architecture (not representative of the concensus at MarsDrive but rather an excercise in integration of some ideas that would benefit from analysis and feedback in any case):

http://forum.nasaspaceflight.com/index.php?topic=22056.msg620189#msg620189

Please get involved if you can!

Thanks,

[JohnFornaro]

I'm not an engineer, yet I've noticed a few technical mistakes in this Mars Drive proposal.  Do you have any engineers on the team?

Which mistakes might those be?

[Robotbeat]

Regarding superconducting magnets: They really only need liquid nitrogen temps, not liquid helium (although you get better performance if you get colder). You could do it with only cryocoolers, too. The highest critical temperature superconductors under certain conditions can reach about -110 degrees Celsius, which isn't too far at all from night temperatures on Mars (~-90 deg C).

Anyways, superconductors don't always need liquid helium or hydrogen, anymore.

EDIT:I am still of the opinion that space radiation, especially on the surface of Mars, is quite tolerable, even for long periods of time: http://www.angelfire.com/mo/radioadaptive/ramsar.html

[Patchouli]

Regarding superconducting magnets: They really only need liquid nitrogen temps, not liquid helium (although you get better performance if you get colder). You could do it with only cryocoolers, too. The highest critical temperature superconductors under certain conditions can reach about -110 degrees Celsius, which isn't too far at all from night temperatures on Mars (~-90 deg C).

Anyways, superconductors don't always need liquid helium or hydrogen, anymore.

EDIT:I am still of the opinion that space radiation, especially on the surface of Mars, is quite tolerable, even for long periods of time: http://www.angelfire.com/mo/radioadaptive/ramsar.html

You probably could keep the superconductors cool with nothing more then a couple of sterling cycle coolers.
The power requirements over all may be just a few KWh a day which would be trivial to supply.
If you're going to do anything serious on Mars you'll probably have a large solar array or a small nuclear reactor supplying 30 to 100KW.
The mag shield's power requirements would be fairly small compared to the fuel plant,rover, and closed loop life support.

[Michael Bloxham]

A post made at MarsDrive that I thought I'd share here:

***

I put a little thought into MP4 today: I was thinking about how such a heritage-derived architecture would best be "sold"; and thinking about the heritage part I played around with a couple of data points in excel (attached) to show how a mars lander big enough to be suitable for a humans-to-mars mission needn't be so far removed from the evolutionary trend. Here I have assumed the same critical ratios (mass/area, parachute mach number, etc.) as MER, MSL, etc. Of course we'd have to crunch the numbers to get the real EDL performance but from the same mass/area assumptions as MSL an 11.5m diameter aeroshell would seem capable of delivering a 14 tonne rover; which would seem adequate for a medium-sized 2-person mobile hab. Note that this is using *exactly* the same critical ratios as the MSL lander which flies next year. (Whereas Rons' EDL assumptions were around 1.5 times more dense than this, I think.) - The 'chutes (probably three of them - each about 30m in diameter; MSL is 20m dia.) open at the same mach number as MSL (2.05), etc.
 
I think it would make a real statement to the space community if we were to use such ultra-conservative numbers yet still come up with a workable architecture!
 
Now you might notice I've added a placeholder titled "MSR". I put this in to show where the most logical interem step between MSL and this DRM might be. This will be something to think about once we pick our DRM. This particular vehicle is 6.5m in diameter and capable of delivering 4 tonnes of payload with an IMLEO that should come in under 23 tonnes - making it suitable for delivery via a variety of existing international and in-the-works commercial LVs. I would suggest that something around this size would be suitable for a 2-part sample return precursor, and would also work well as a supplementary vehicle - capable of delivering extra science equipment, spares, fuel, etc. in support of crews on the surface - as per the original orbital caching idea (which is something I would like to re-assess in the future if possible).
 
I would also think that the mobile habs themselves could easily be portrayed as a logical extension of the trend from Sojourner -> MER -> MSL. (MSL is already as big as a small car.) If we choose to pursue anything like MP4, then this is a point that I would really like to drive home: We don't need super-revolutionary tech to go to Mars. We just need to continue to evolve the existing state-of-the-art. IMHO, this could make a very effective statement.
 
- Mike

***

[Michael Bloxham]

Attachment shows a nice evolution from MPF / MER -> MSL -> MP4. This nicely illustrates how a viable humans-to-mars architecture need not be so far removed from the current trend of progression.

14 tonnes surface payload may not seem like a lot (other architectures usually require surface elements above 25 tonnes each); but again, if the traditional big hab is split up into two smaller 2-crew mobile habs, and the ISRU/MAV lander is similarly split, then 14 tonnes at a time becomes a great deal more attractive.

The utilization of such heritage-derived entry vehicles for a humans-to-mars architecture would be a lot more attractive then spending literally tens of billions of dollars in the design and qualification of more exotic EDL systems.

[Michael Bloxham]

2 more

[Michael Bloxham]

A small update to the mission profile overview image:

Notice the previous image of the MPV or "power rover" in the bottom left hand corner has been replaced with an image that better shows the unfurlable flexible solar array coiled up on the back of the remotely-driven hab-less chassis. This is over 5 tonnes of PV array which is plugged into the ISRU/MAV vehicle and then slowly rolled out. Once the array is deployed the MPV rover may be used as a teleoperable logistics / support vehicle for when the crews arrive in their small mobile habs.

The figures have also been revised among other small changes.

Edit: I doodled with the tiny images a bit more for better clarity

- Mike

[Michael Bloxham]

Hi guys. While contemplating how a subset of this hardware could be utilized for a humans-to-phobos mission, I was wondering: For an opposition-class mission, would it be possible to delay aerocapture and / or also the TEI burn so as to decrease the time spent in Mars' orbit (at the expense of slightly longer transit times if need-be). This may seem a little backwards (the name of the game is usually to decrease transit times and increase time spent at Mars), but I think that for a humans-to-phobos mission this is different.

The idea is to use artificial gravity (by either tethering off the TMI and [later] the TEI stage, or having two independent vehicles tethered nose-to-nose) on both the inbound and outbound legs as much as possible; while minimizing time spent in zero-g near Phobos. I'm assuming here that it is not worth the difficulty of employing artificial gravity while the crew is in the vicinity of Phobos. (This assumption is made for a variety of reasons.)

Currently, I can envision the ERV vehicle meeting the role of the primary crew vehicle during all three major stages of the mission. It will already be designed to allow AG on the return leg for the surface missions. Perhaps there would be two of them, with 2 or 3-crew each, for dual-redundancy and to allow extra margin, etc. This would require a total of 4 SDLV launches if the current ERV design closes.

Any takers?

Thanks,

- Mike

[Michael Bloxham]

ERV general concept. Crossed-box indicates location of tether to TEI stage (hence why the men are upside-down).

This is the biggest hab area I could accomodate while keeping enough room for the return capsule at one end and TEI stage at the other end of the aeroshell. I'm thinking the TEI stage shouldn't need too much space: It is heavy but the methane/LOX fuel is quite dense. But this might not do if we are to minimize boil-off losses (which require fewer more rounded tanks that take up more space but minimize surace area). This hab area is quite big (~200m^3!). For a maximum crew of 4 for 6+ months (for the surface mission return leg) the lower limit may be aroun 80m^3. So there should be plenty of space to work with. I'm not sure about having the crew return capsule hung off the bottom of the hab while using AG though... But I can't seem to think of a better alternative...

[Michael Bloxham]

An 80m^3 hab would probably be fine for 2 or 3 crew each of the dual-ERV Phobos mission. I would say that it is on the small side if the same design is to accomodate all 4-crew during the return journey of the surface mission. But then again, the crew spend only a quarter of the time stuck inside the thing than for the Phobos mission. So maybe this sort of size isn't a bad compromise...

[JohnFornaro]

How'd you get the people to stand on their heads?

GTG.

[e of pi]

An 80m^3 hab would probably be fine for 2 or 3 crew each of the dual-ERV Phobos mission. I would say that it is on the small side if the same design is to accomodate all 4-crew during the return journey of the surface mission. But then again, the crew spend only a quarter of the time stuck inside the thing than for the Phobos mission. So maybe this sort of size isn't a bad compromise...

Have you considered the possibility of leaving off the earth re-entry vehicle, and instead using an EOR with a capsule sent up from the surface to meet the returning vehicle? It seems like if you did so, you'd save a lot of mass and volume on the ERV by leaving at Earth the part that will only be of use at Earth.

[Robotbeat]

An 80m^3 hab would probably be fine for 2 or 3 crew each of the dual-ERV Phobos mission. I would say that it is on the small side if the same design is to accomodate all 4-crew during the return journey of the surface mission. But then again, the crew spend only a quarter of the time stuck inside the thing than for the Phobos mission. So maybe this sort of size isn't a bad compromise...

Have you considered the possibility of leaving off the earth re-entry vehicle, and instead using an EOR with a capsule sent up from the surface to meet the returning vehicle? It seems like if you did so, you'd save a lot of mass and volume on the ERV by leaving at Earth the part that will only be of use at Earth.

Then you'd also have to slow down the whole thing to be captured in orbit, although if you captured at EML1/2, it wouldn't be as much of a delta-v hit as LEO.

[Jorge]

An 80m^3 hab would probably be fine for 2 or 3 crew each of the dual-ERV Phobos mission. I would say that it is on the small side if the same design is to accomodate all 4-crew during the return journey of the surface mission. But then again, the crew spend only a quarter of the time stuck inside the thing than for the Phobos mission. So maybe this sort of size isn't a bad compromise...

Have you considered the possibility of leaving off the earth re-entry vehicle, and instead using an EOR with a capsule sent up from the surface to meet the returning vehicle? It seems like if you did so, you'd save a lot of mass and volume on the ERV by leaving at Earth the part that will only be of use at Earth.

Then you'd also have to slow down the whole thing to be captured in orbit, although if you captured at EML1/2, it wouldn't be as much of a delta-v hit as LEO.

Right. If you try to return to LEO with this thing, you'd need to either provide enough propellant for propulsive capture (which will be heavier than the capsule) or a heat shield on the whole thing for single-pass aerocapture (which will also be heavier than the capsule). So you can't "save a lot of mass and volume on the ERV" by doing EOR in LEO. (I'm not even sure the propellant required for EML1/2 capture of the whole ERV wouldn't also be heavier than the capsule).