In actuality, I truly don't think the issue is really designing a MAV -- no offense, John, but it's really not that hard to design a rocket that can do the job. You don't need revolutionary new propulsion technologies to get off Mars and into MEO.

The problem is that with most any existing rocket technology, you have to land a very large mass onto Mars to make MSR work. Not as large a mass (or set of masses) as for a manned landing and exploration, but a very large mass, indeed. And the problem is that we've maxed out the amount of mass we can land on Mars with something roughly the mass of MSL. Much heavier and you run smack into the Mach 5 problem that has been discussed here extensively; the mass required for a MAV is large enough that friction with Mars' thin atmosphere isn't enough to slow it to a speed from which rocket braking can take over and reduce it to a landing velocity before the vehicle crashes.

Let's face it, it's probably just not possible to build a MAV powerful enough to do the job and that is yet light enough that it can be landed (even in pieces) with our current ability to do a successful EDL.

So, the EDL challenge would seem to me to be the limiting factor. If we can beat the Mach 5 problem, then it just becomes a matter of spending the money needed to get that mass to Mars in the first place.

-the other Doug

Yes of course, oDoug. If you define the problem as (1) "accomplish MSR within existing program budgets," then you have to develop a ~100 kg MAV. If you define the proglem as (2) "design MSR around a practical MAV that can be built with existing technology," then you need to develop a bigger EDL system and spend lots more money. To the best of my understanding, such a MAV would mass several tons, i.e. an order of magnitude in mission scale and cost.

Given that mission costs are about 1-2 million dollars per kilogram placed on Mars, it would seem to be worth a hundred million dollars to develop ANY new Mars technology that can make the mission scale 100 kg smaller. However organizations need to grow, so organizations tend to favor the second scenario even when there is very little hope for increasing funding. Is it possible that MSR is caught in a stalemate such that we can't pay for the necessary work to make the mission affordable?

By the way, the Mach 5 problem could be solved by pushing hard on new innovative propulsion technology. Just use better propulsion instead of a parachute from Mach 5 on down.

John W.

John - what you suggest has been reviewed. There's no way to fire the thrusters during the hypersonic descent. Imagine driving your car in the center of a hurricane!

I do understand your point, John. The problem with just inventing better rockets to drop the mass from Mach 5 down to zero is that, as the mass of what you're landing goes up, the total amount of its entry velocity that can be shed solely through atmospheric drag becomes less and less. And the more velocity you need to shed using rockets, the more propellant you need to carry, and the less effective drag slowing becomes. It's a vicious circle.

And besides, if you're going Mach 5 and you're a kilometer above the surface, and you have no more than about 30 seconds to remove the remaining velocity, just how many G's would you have to pull to avoid crashing? A 50-G deceleration would probably be outside the limits for Mission Success in any manned or unmanned mission I can imagine, and I can't imagine the required deceleration being much less than that.

If you use chemical rockets, you're going to keep coming up against the isp limits we've already identified as barriers to growth. We need truly revolutionary advances in propulsion technology, not just engineering tweaks of known technologies, to get the performance-to-mass ratios required for an effective MSR, much less for manned landings. IMHO.

If you look at it as a Venn diagram, I'm just afraid that the set that contains what's possible to do with chemical rockets, and the set of the mass of vehicles required for MSR, are sets which do not overlap...

-the other Doug

p.s. -- please bear in mind that I'm qualifying all of this when I say we need an EDL breakthrough for an *effective* MSR. I do not consider spending 15 billion dollars to bring back less than a kilogram of samples to be effective. That's an awful lot of money to return, frankly, far less material than we already have to analyze from Martian meteorites. -dvd

Has anyone met a propulsion engineer who finds mossbauer spectra interesting?

very funny doug!

My hack at the problem...its just a broad outline...please turn flame throwers to idle
There is probably nothing new here, other than independent parallel invention

To do the Mars SAR mission and to bypass the mach 5 problem (not enough atmosphere for heavy landers to decelerate safely)
then it must be a divide and conquer solution.

the spaceships required are

* earth-to-mars vehicle that carries a single return-to-earth vehicle with return fuel
* earth-to-mars vehicle(s) that carry one or more of the 2 required landers

Assemble the fleet in mars orbit (use a circularizing method, aerobrake or engine) fly in formation

The two landers:

* One with the MAV 1stage and launch platform (2000lb of propellant) -- use a tested EDL & a sky crane
* the other: a beefy rover with the MAV 2ndstage (1000lb of propellant), also the sample return container/nosecone -- use a tested EDL & a sky crane

The MAV 1stage lands first.

a few days later the Rover/MAV 2nd-stage lands-- very near the first (2 km?) -- precision landing required

The rover loads a contingency sample into the return container
The rover & second stage set out and find The MAV 1st stage. The MAV stages are mated (both stowed horizontally)
Rover still has access to the sample container (which has the contingency sample locked and loaded)

The rover (sans 2nd stage) goes on a science mission to find the best samples (2-6 week mission, 2-20km )

The Rover comes back and loads the samples

MAV is erected vertically - checkout - launch

Rendevouz with Earth return vehicle - sample container stowed

Leave orbit and head back to earth

Rover continues science studies until it dies

I don't think there is any new or breakthrough science needed here
Just alot of complicated machinery that needs to be robust and elegant.

ok...flame throwers set to stun....


Cheers

I think that the biggest problem won't be the anything concerning the landing phase, but the MAV itself. We all know how complex launching a single rocket is with all problems, delays and so on. A MAV (or a mars rocket) has to be fully autonomous and, of course it has to work flawlessly. That's why I suppose that it will be solid-fueled because it's the simplest design and there aren't many options for failure.

I think that the two-launch scenario (an orbiter plus lander) is the best. The orbiter, while waiting for the MAV to arrive may be busy collecting atmospheric samples using aerogell (already tested on Stardust and Genesis). The MAV may be delivered on the surface using a skycrane technique, specially redesigned for this purpose. I can't think of a better idea. Though I know how difficult fully automated docking may be.

I suspect that when the failure modes are analyzed that the lander/rover/launchers combination contains the overwhelming portion of the MSR risk. I think that having two sets of lander/rover/launcher should be baseline. If both deliver samples, great. However, if you send one and it fails, then the entire $5-8B is gone.

Why don't we just land a tank on Mars? It can rove around, picking up interesting samples and loading them into rocket-assisted shells. Once it is ready to launch, it can use a compressed air gun (remember the post-Columbia tests? ) to fire the shells upwards, one at a time. Fill the tank with CO2, heat it up nice and hot, and BLAMMO! Rifling on the barrel handles the guidance task for the first "stage". That's got to be good enough for a dozen or two km of altitude on Mars. Ignoring drag, 300m/s gives you 12km; 500m/s gives you 34km, enough to reduce the atmospheric pressure by 95%. Then, WOOOSH, your rocket boosts you to orbit!

Problem solved!

I CAN HAZ 8BIZZILLION DALLARS NOW?
K TNX

(Sorry, in a goofy mood)

The rocket guru didn't cower
When confronted with data Mossbauer
She studied for weeks
Spirit's olivine peaks
But who else grooves on MAVs for an hour?

They'd pay for a tiny launch tower
And order propellants for power
But they sought a cheap rocket
Plucked from someone's hip pocket
Their grasp of the MAV didn't wow 'er

Seriously folks, it is too easy for all of us to take the other person's work for granted. But I thought that scientists and mission planners have a strong direct influence on budet decisions that could lead to funding technology for launching off of Mars, while rocket engineers have little or no direct influence on the budget planning process for science. Ideally rocket engineers would have an indirect influence, by creating a 100-kg MAV to leave room on MSR for more science. Yes there are technically valid solutions that permit a heavy MAV, but they all cost more.

Another recent news article:
www.guardian.co.uk/science/2008/jul/14/mars.spaceexploration

Re the latest comment from hendric, the MAV has to be relatively fragile in order to obtain the high ratio of propellant to inert mass, so it would not help to shoot it out of a cannon just to reduce the MAV velocity requirement by 10 percent or so.

John W.

[...]

[...]

Just exactly how much sample do you expect to return to Earth with a MAV that weighs, grand total with sample container and fuel, 100 kg?

No more than a gram, I would imagine -- and that would be pushing it.

Can I ask exactly what you think we can do with a gram or less of Martian surface materials? And why we would spend a billion dollars (or multiples thereof) for such a miniscule amount?

Just... curious.

-the other Doug

Typical figures quoted are about 1kg

The MSR mission is very pricely. Why so much difference?

As an example, the most expensive mission to Mars would be for MSL by between 1-2 thousand millions dollars (I don't say billons -> millions millions). And the MSR would be between 3 to 5 times more expensive than MSL with just adding a few hundred of kilograms of weight to the spacecraft in order to return a 1 kg of sample. Well, I too agree that by sending as many in-situ spacecrafts to Mars would yield a better cost-benefit to science. Just a thought