Shouldn't there be more focus on surface mobility?

Michael Bloxham · 2007-01-11 03:50:04

I think both the Nasa DRM and Mars Direct share a common oversight: That there simply won't be enough geological science to do near the hab; (even with a long range rover) not enough to keep the astronauts, and the politicians, happy over the 1.5 year or so stay.

Whats really preferable is a fully mobile hab.

The retrofit parts (tires, suspension, motors) can be delivered seperately on a cargo vehicle, then later fitted to the hab. Perhaps some of the first missions can omit this ability, but I think the added science and stimulation would be worth adding this ability to later missions.

What do you think?

cIclops · 2007-01-11 04:05:34

It's way too early to be judging this. The DRM will be updated this year, we'll see how much detail they outline in the new version for surface mobility. Note that the Lunar architecture, which is far more advanced, had little to say about mobility at this stage. First things first. Clearly mobility needs to be maximized within mission constraints, how much should be robotic and how much human is probably one of the first decisions.

Michael Bloxham · 2007-01-11 04:43:31

You make a good point about the new lunar missions, which I haven't really considered. I guess you could apply the same concerns here though. The poll can reflect this (luckily the poll is ambiguous, then).

C M Edwards · 2007-01-11 06:46:36

This topic is also related to this thread. Abandoning the idea of a permanent base is the ultimate in emphasizing mobility.

However, I'm beginning to believe that the ability to stay at a central base and work there will prove just as important for the first missions. In that case, the current level of mobility - able to send a small fraction of the crew long distances in a pressurized rover or a large fraction very short distances using unpressurized rovers - is perfectly adequate.

SpaceNut · 2007-01-11 07:47:02

You can also make use of this item:

ROBOTS THAT MOONWALK

060909_coslog_hmed10p.standard.jpg

All-Terrain, Hex-Legged Extra-Terrestrial Explorer, or Athlete for short, It's supposed to be capable of carrying payloads of up to 1,000 pounds (450 kilograms), and even more when multiple Athletes are joined together.

The poll for mobility is being addressed but I think that the scale may need some time to catch up to the need.

GCNRevenger · 2007-01-11 08:24:49

This topic is also related to this thread. Abandoning the idea of a permanent base is the ultimate in emphasizing mobility.
However, I'm beginning to believe that the ability to stay at a central base and work there will prove just as important for the first missions. In that case, the current level of mobility - able to send a small fraction of the crew long distances in a pressurized rover or a large fraction very short distances using unpressurized rovers - is perfectly adequate.

I agree. With ISRU+exhaust collection or a DIPS power plant for the rovers, they will be able to drive around the whole 500 days probably. A mobile HAB introduces far too many problems and mass penalties. With a modified DRM, we are still on a pretty tight mass budget.

The HAB is not an RV, its a small apartment building. Throw in a pair of 100kg class robot rovers and the two crew that stay at the stationary HAB will have enough to do via teleopertion and maintenance.

Commodore · 2007-01-11 16:38:19

Surface mobility is very important, but only once a solid, self-suffient base is built.

GCNRevenger · 2007-01-11 17:34:42

Well, I foresee a number of missions (say, 4-5?) being sent over the whole surface of Mars, and they should each have pressurized rovers that seat at least three (or six for short periods). After these missions have flown, and we have decided on where to build the base, then the manned missions will transition mainly to cargo flights of base hardware for one or two biannual launch windows. Then maybe we can talk about a reusable suborbital rocket vehicle.

C M Edwards · 2007-01-11 21:21:33

Well, I foresee a number of missions (say, 4-5?) being sent over the whole surface of Mars, and they should each have pressurized rovers that seat at least three (or six for short periods). After these missions have flown, and we have decided on where to build the base, then the manned missions will transition mainly to cargo flights of base hardware for one or two biannual launch windows. Then maybe we can talk about a reusable suborbital rocket vehicle.

I foresee a shorter seguey. We almost have enough data already to pick potential sites for a manned base. Start with probes directly to those sites to prospect for water and resources (say, 4-5?), then send some base hardware first (don't wait - it's better to risk losing it before the crew leaves Earth than after, and you don't have to send all your caches to one spot), then send a single manned expedition once everything is soaking on the surface, waiting for them.

One expedition is enough to find a location suitable for a base - even if its not the first landing site. Of course, if they have to practically land blind, with no prior reconnaissance, then four to five missions to locate a good place becomes a rather optimistic estimate.

Michael Bloxham · 2007-01-12 05:26:20

I'm not so sure. I think what needs to be remembered here is that Mars is, for the most part, one big huge flat rocky desert. I imagine that if the tires are big enough, and the rocks small enough, that slowly roving across it in a Hab wouldn't be too uncomfortable (although I admit it won't be quite the same as not roving altogether). Perhaps more importantly though, the fact that mars is basically a huge expansive rocky desert has more implications with the relative concentration of geologically interesting sites. I'm afraid that any geologically interesting pockets might be too quickly explored, and they'll be too far apart.

Michael Bloxham · 2007-01-12 05:53:57

You know what? Honestly, I feel more stongly on this issue than I let on... I was going to write some rant on the inherently mobile nature of historical explorations, but I think Mars suffers enough from wishful parallels already. Instead, we need to consider the uniqueness of mars, and the uniqueness of modern technology. We have the technology, we can build it.

Lets look at some potential pros and cons unique to the situation:

Cons:

- Requires more mass to be delivered to the surface.

- Requires external assembly by the crew.

- Increased stress on components and hab systems, potentially decreasing reliability.

Pros:

- The reduced martian gravity might reduce stress on the suspension, frame, etc.

- The hab will already be extremely lightweight for its size anyway, due to the obvious space launch requirements.

- Mars is extremely flat and deserted: easily navigable by a large rover.

- Having a mobile hab will relieve boredom, increase science return.

- Mobile habs can move themselves next to other vehicles, strategic resources, science hot-spots, etc.

- They can also link up with other habs to fulfill the promise of martian bases. Perhaps they could be remotely driven once the crew has deserted them?

Can you think of any others?

Michael Bloxham · 2007-01-12 06:22:44

Here's another thought: We don't know if the landing site is going to be scientifically interesting enough in advance (even if scouted by robotic rovers). A mobile hab might be a good contingency incase the site turns out dull. I think the truth is is that the science capabilities of the exploration team are a magnitude greater than what might be knowingly available, or even in a best-case scenario guess, of what might be waiting under the surface. At this point at least, we really just don't know. Perhaps even the best mars has to offer will remain comparatively geologically simple to 'probe', which is I guess what these explorers will primarily be doing; probing: taking samples, taking pictures, performing chemical analysis, etc. I guess if the site turned out to be less geologically interesting than needed, the crew could just keep taking samples; measuring the standard variation within specific areas, convincing them and ourselves that this is still good science, but really its just to keep everyone busy. But honestly, to me, thats just not good enough. I mean, if we go through all the trouble of spending billions of dollars getting them there, we ought to expect the best damn science return that we could possibly get in return.

Bang for buck, guys. Bang for buck.

Michael Bloxham · 2007-01-12 06:37:34

Whats the equivalent weight of a Mars Direct style hab under martian gravity? Could be lower than one might expect...

GCNRevenger · 2007-01-12 09:22:02

Here's another thought: We don't know if the landing site is going to be scientifically interesting enough in advance (even if scouted by robotic rovers). A mobile hab might be a good contingency incase the site turns out dull. I think the truth is is that the science capabilities of the exploration team are a magnitude greater than what might be knowingly available, or even in a best-case scenario guess, of what might be waiting under the surface. At this point at least, we really just don't know. Perhaps even the best mars has to offer will remain comparatively geologically simple to 'probe', which is I guess what these explorers will primarily be doing; probing: taking samples, taking pictures, performing chemical analysis, etc. I guess if the site turned out to be less geologically interesting than needed, the crew could just keep taking samples; measuring the standard variation within specific areas, convincing them and ourselves that this is still good science, but really its just to keep everyone busy. But honestly, to me, thats just not good enough. I mean, if we go through all the trouble of spending billions of dollars getting them there, we ought to expect the best damn science return that we could possibly get in return.
Bang for buck, guys. Bang for buck.

Nonsense, robots and satellite observations are very much capable of scouting a site that will be worth our while. The pressurized rover will be capable of long trips from the HAB too.

The fact remains that making the HAB mobile is a huge amount of trouble and will greatly increase the mass. You are talking about a structure 30ft wide and 50ft+ tall with a mass of ~30-40MT. Also consider that even if we could get it to move, it could never move fast enough to justify mobility!

Plus if we are going to use any variation of MarsDirect or DRM, what of the ERV/MAV vehicle? You would ideally have the HAB stay within a suited walk of it during the surface stay, which either chains you to a small area that the pressurized rover could traverse, or else you'd have to make that mobile too!

For all the mass of making the HAB mobile, you could easily just build a bigger superlong range rover too for less probably, and leave the HAB stationary.

Michael Bloxham · 2007-01-12 16:49:26

True, robots are/will be pretty good. But in order to guarantee good science, the robotic exploration phase may risk doing half the work. Anything left might amount to scraps in light of the order of magnitude capability difference between robot and man.

I suspect that in order to maintain a good case for manned exploration, thorough pre-scouting of the sites will be purposely minimized or omitted altogether. Otherwise the robo-fans will cry foul.

The idea of a super-long range rover presents a similar case. I think you get to the point where the rover becomes so big and comfortable that the astronauts compete for time between rover sorties and the hab. Then the leap from large rover to mobile hab (with small rovers) is small enough to step across.

Figuring how much tire contact patch a Mars Direct style hab should have will be a good first step.

GCNRevenger · 2007-01-12 18:08:10

No no, the requirements are so much different!

The HAB needs far more volume for the 6mo trip out to keep the crew sane than they do if they could go for a walk every day. And come on! You are still talking about having a small three-story building move across some of the roughest, least sure-footed terrain in the solar system at tens of kilometers an hour! Have you any clue how much mass that is going to add to it? The mass budget is already tight enough as it is with two heavy-lift rockets per HAB.

And there are practical considerations, if it is to be nuclear powered then it will have to lug the mass of the reactor with the mobile HAB, which is not happening. Already the reactor will weigh about 5MT for just the power plant, the radiation shielding needed to protect the crew will easily run 10MT+ for decent protection.

Plus this small reactor doesn't put out enough power to move the HAB, even at max output, its a stretch to say that 100kW class plant will only give you ~100 horsepower effectively, which is hardly enough to move a ~1MT light truck on Earth much less a 50MT+ HAB, even with the low gravity and low speeds, provided you can even get the thing to Mars cheaply enough. And thats without a single watt left over for other things.

And say that you do get it to move, one of the main reasons for going to Mars is to bring a laboratory with us, where we can find out which samples, locations, etc are important and which ones aren't without having to go all the way back to Earth and come back again. I am telling you that having a laboratory in a moving, swaying, bouncing, vibrating vehicle is not happening! An electron microscope for instance, one of the most valuble instruments that we'll be bringing, is VERY sensitive to vibration. So is the turbo-vacuum pump for a TOF mass spectrometer, and I bet a plain old optical microscope would have problems too.

The HAB is already on a tight enough mass budget, even with Ares-V, and in fact neither DRM plan calls for the pressurized rover to be carried with the HAB at all. It would be too heavy, the HAB would be overweight. Instead it would ride with the MAV and ISRU plant.

Michael Bloxham · 2007-01-12 18:28:42

You make some good points, but I don't think any are real show-stoppers.

The Hab won't need to rove continuously. It'll stop for weeks at a time when it reaches a good science spot. It could even rove only at night, or at least when there's no decent science to do in the lab. (This thing'll be on the surface for 1.5 years, remember.)

As I've advocated before, any Mars Direct or similar plan could benefit a lot from an additional launch to deliver a cargo vehicle to the surface. Not only would this deliver the necessary components to modify the hab, but it could also deliver those large drills we need to, among other bits and bobs.

As for the power requirements: I think I'm as unsure as you are. We definately need to look into this. However, I'd like at least to do this much before dismissing the idea altogether. At the very least, I think this idea deserves to be brainstormed. I don't expect it to be immediately unquestionably adopted.

GCNRevenger · 2007-01-13 09:34:04

If these aren't show stoppers, then there is no such thing

Just how fast is the HAB supposed to go? If it is too slow, then stopping just won't be an option. You'll never get anywhere. If you are going to "stop for weeks at time," then just how many sites are you going to reach? You've got about 70 weeks of time on the surface, so unless you are spending a large chunk of that driving you won't get anywhere.

And please! Please remember! Remember the ERV/MAV! You cannot go driving thousands of kilometers away form it! You cannot, thats just begging to get stranded on the surface until the crew dies of hunger! And the excuse that "oh we'll just hop in the pressurized rover" is silly, first of all you won't have a pressurized rover, since you traded all the mass to make the HAB move (and then some). Second, the whole point of a mobile HAB is to give you more range than a rover, so what good is it if you can't safely travel further than the rovers' range if you did have one?

And please please, you have completely lost grip on the masses involved with trying to make the HAB move, this is just not a rational discussion, this is not happening. Even a very conservative estimate is going to be tens of tonnes most likely, which is just not going to happen, period. The equipment to make the HAB move would weigh almost as much as the HAB itself! This is not just slapping wheels on the end of the landing gear struts, is not.

This notion of sending the equipment to make the HAB mobile in a separate launch, then rebuilding the lower half of the HAB to accommodate it isn't happening either, its too much work for the astronauts to make such a radical modification. It also doesn't make the equipment any lighter, and greatly increases the price of each mission. "Bits and bobs" are expensive, hundreds of millions if not billions of dollars expensive, just what in the heck would these be to justify their transport?

There is already going to be a separate cargo flight too under DRM, which carries the MAV, ISRU plant, and the pressurized rover. Even if you delete the rover, it would not be enough mass to make the HAB move. Speaking of the rover, the rover itself would carry the heavy drill, act as the transporter/base of the drill, and provide the power for it in lieu of the main motors. The drill will be a part of and ride on the pressurized rover, its mass accommodated by the slightly higher payload of Ares-V. This saves a gob of mass since you won't need separate hardware to support the drill.

And under DRM, the aerobrake shield is integral to the structure of the HAB, which makes the HAB quite tall (~50ft) versus its width (~30ft). It will be too top-heavy to drive on slopes and grades safely, unlike a dedicated surface rover. And just where is this reactor supposed to go? If it winds up weighing 20-25MT, which is entirely possible if upgraded to produce enough power to move it, won't that make make the HAB's weight dangerously imbalanced?

Unsure about power? I am not at all unsure, I am sure that a 100kW reactor won't be big enough. If superlong range mobility is so critical, and since no mission of reasonable cost can be packed into one uber-rover (HAB, ERV/MAV), then it simply stands to reason that overland travel is not acceptable at all. In which case, we do what we can overland until we have a base with reusable suborbital rockets.

Not all ideas are worth considering, in fact when you disguard the requirement that ideas be practical, there are an infinite number of ideas that should not be "brainstormed." We do not need to look into this. Case closed.

Michael Bloxham · 2007-01-13 10:17:12

Don't dig too deep, GCNR. Prove to me it won't work. I want to see some numbers.

cIclops · 2007-01-13 10:28:34

There may just be a way to give the HAB mobility. It does have engines and fuel tanks to land in the first place ...

RobS · 2007-01-13 11:06:37

Some early designs for habs did include wheels, but they were meant to move the hab a few hundred feet. You couldn't use such wheels across hundreds of kilometers because they were little wheels (partly because of weight; they were dropped because of weight considerations). If you want to move something really big, you need big wheels. Something very tall would be unstable on slopes, too. You wouldn't want your hab to topple over or get stuck in a ravine 1,000 kilometers from the MAV. Mars isn't as smooth as you think; there are a lot of bouldery areas where a large vehicle could not go without bulldozing.

Asking GCN for numbers is silly. He already gave you some (kilowatts) which are the key bottleneck.

Mobility, like everything else on Mars, will start small and grow over time. Zubrin was very impressed by ATVs when he was at Devon Island. These are little one-person vehicles that can carry two in an emergency. Something like that would help greatly for movement of a kilometer or two or five (in my novel, I called them buggies). Perhaps they will be needed. After that, I'd favor the equivalent of a truck (the size of a four-door pickup truck, but without the flatbed in back) that would have a pressurized cab and could haul either a trailer, a driller, or the equivalent of a camper. It would probably have a bulldozer blade in front that you can raise or lower. It might be helpful, if you have the energy, to do some trail clearing when going out on expeditions, because it would speed up the return and speed up future exploration in the same general direction. And after that I'd favor something the size of a small mobile home; maybe 30 feet/9 meters long and 8 feet/2.5 meters wide. But it wouldn't be the only vehicle on the expedition; it would be accompanied by a truck, maybe a pressurized tent/camper, and a few ATV-like rovers. The truck could always tow the mobile hab or vice versa if there's trouble on the trail.

-- RobS

GCNRevenger · 2007-01-13 11:55:09

You want a showstopper? Fine, I think I found you one:
Inverse square law & calculator
The radiation shield for the 100kW reactor is at least 1MT with 1990's technology, assuming the reactor is 2500m distant. Go ahead and assume fancy light-weight shielding and NASA paranoia gets this down to 100kg.

Then lets say this same reactor is much closer, say 2.5m, you will need proportionately more shielding with intensity.

You do the math

And thats only across a 90deg arc, with 10X more dose across the other 270degrees so you couldn't walk around behind your mobile HAB for long either.

Again, the problem of traveling long distances from the ERV/MAV is insurmountable anyway, unless you made BOTH vehicles mobile.

Using rockets to make the HAB "hop" is not happening without some indigenous supply of Hydrogen and a bigger supply of energy. Even then, again, you cannot travel huge distances from your ride home safely, unless you had a second rocket vehicle that could come pick you up.

Michael Bloxham · 2007-01-13 13:30:05

Here's what I'm thinking: During the first couple of missions, we'll use the basic Mars Direct or DRM mission profile. Later, after the first crews have safely returned, as part of each succesive mission, we'll implement an additional heavy-lift launch to deliver an additional supply vehicle to the surface.

The supply vehicle will contain spare parts for the hab, big drills, extra rations, etc. More importantly though, it'll have a small methane engine, or perhaps a fuel cell, and heaps of fuel. And last but not least, it'll have four really big tires around the outside.

This supply vehicle is then remotely driven towards the Hab, partially disassembled, then reassembled around the Hab (sort of like a bolt-on 4-wheeled cradle).

The Hab will keep its original long-range rover, as a contingency, but the roving Hab will likely either trace a path toward or around the ERV, depending on its landing proximity. Or, with the extra rations, you could allow the crew to keep on rovin' until the fuel gets low, setting a later ERV down ahead of them.

No radioactive power plants required. And yeah, it'll be a launch more expensive, but I think it'll be worth it considering the huge increase in science return (both from the mobile hab and the extra science equipment).

Plus, it'll be more fun!

GCNRevenger · 2007-01-13 17:16:32

No no no, the "wheels and engine and stuff" for the HAB is not going to work, sure its possible but its just not practical, its all too big and heavy to be worthwhile. The size of the structure/wheels/etc to push the 30x50ft high 40MT HAB are just too great. The HAB alone weighs as much as a superheavy mining dump truck, and thats not counting the structure (load bearing, shocks, brakes), wheels, motors, or power plant. Such a contraption probably wouldn't fit in a single cargo flight even if it were the only thing aboard.

The real killer though is fuel supply: you don't have any. The fuel requirements to move such a beast are, I'm sure, quite extreme. Remember, you have to carry your Oxygen too, which weighs quite a bit more than the Methane. A mining dump truck needs between 500-1000kW on Earth, and that is going to eat up an awful lot of methane. Where will you get all of that? You just can't carry all that much of it either, which is going to kick the legs out from under your range. It will also add to your mass substantially too, further increasing the size of the HAB-rover, and is fuel requirements. A vicious cycle.

And where will your power come from? If you are rolling around the surface, you can't use nuclear or large stationary solar arrays. So, that power will have to come from the chemical power plant too, which will further tax the fuel supply.

Plus, unless you are going to capture and lug all the water consumed with the burning/reacting Methane, then you are dumping precious Hydrogen overboard. Already most of it budgeted for DRM is slated to go to the MAV fuel supply, with a little left over being used for the smaller rovers and misc. equipment. That too will increase mass, from both the tankage, condenser/scrubbers, and the water itself.

And it gets even more fun, that if you DID bring the water back to the stationary ISRU/MAV plant for conversion back into Methane, that will take quit a while for a large tens of tonnes batch, time which you will be stuck sitting still.

But even say all the above didn't matter. None of it is a problem. All gone away. You still can't drive, for intents, any further then the range of the pressurized rover from the MAV in the first place. If you did, and you had a "breakdown" or otherwise got stuck, you are going to die.

painfully

on national television

...and that won't go over well at congressional hearings

And what is this about "sending another MAV/ERV ahead," the former strongly hinges (probably not possible without) and the latter doesn't work at all without ISRU, so they will be landing with their fuel tanks empty. Bad news if you are too far from the first good ERV/MAV that does have fuel. It also takes approximately two years for the ISRU plant to make enough fuel for the return trip, give or take some months.

And why do you think just because the HAB can visit a site that we will get alot more science done than if the heavy rover does?

GCNRevenger · 2007-01-13 17:34:38

And really, the pressurized rover will have a range of at least 500km, and that is pretty far.

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#1 2007-01-11 03:50:04

Re: Shouldn't there be more focus on surface mobility?

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Re: Shouldn't there be more focus on surface mobility?

#3 2007-01-11 04:43:31

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#4 2007-01-11 06:46:36

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#5 2007-01-11 07:47:02

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#6 2007-01-11 08:24:49

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#7 2007-01-11 16:38:19

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#8 2007-01-11 17:34:42

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#9 2007-01-11 21:21:33

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#10 2007-01-12 05:26:20

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#11 2007-01-12 05:53:57

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#12 2007-01-12 06:22:44

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#13 2007-01-12 06:37:34

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#17 2007-01-12 18:28:42

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#22 2007-01-13 11:55:09

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