http://en.wikipedia.org/wiki/RIM-161_Standard_missile_3
http://en.wikipedia.org/wiki/AGM-48_Skybolt
http://en.wikipedia.org/wiki/MGM-140_ATACMS

There is a large community who've been building vehicles of an approximately similar performance envelope for some time.


Furthermore

http://www.jpl.nasa.gov/releases/2001/release_2001_153.html
http://ieeexplore.ieee.org/Xplore/login.js...5737.pdf?temp=x
http://www.ingentaconnect.com/content/els/...000004/art00148
http://www.esa.int/esaMI/Aurora/SEMRW7A5QCE_0.html - especially http://esamultimedia.esa.int/docs/Aurora/e...AV_complete.pdf
http://citeseer.ist.psu.edu/385428.html

That's from the first page of putting 'mars ascent vehicle' into google.


Doug

AFAIK, your examples are not of "of an approximately similar performance envelope". Go back and read post 90 of this thread, and many of John's subsequent posts. ASATs aren't getting into orbit.

The ASAT missile weighed a ton, more than the lander, MAV, rover, etc. combined (assumed future affordable capability based on the expectation that the 2009 MSL will successfully land almost 1 ton total on Mars).

A popular definition of "space" is expressed in terms of altitude, but achieving orbit is more about velocity. The ASAT missile merely went straight up to about 500-600 km, which needs a very minor fraction of Earth's orbital velocity. Mars orbital velocity is 45 percent of Earth's. The MAV needs to accelerate zero to 9,000 MPH in 5 minutes.

Generally, rocket motors for military missiles have less raw propulsive performance than space motors, because the former have to be cheaper for quantity production, structurally more robust for abuse in the field, etc. We shouldn't pin our hopes on the possibility that something better than existing space propulsion hardware is available from behind the scenes in the military world.

Overall nprev is right that existing technology gives us "only a starting point." The question is when and how and who is going to move forward to develop a MAV? Part of the reason that the aerospace engineering community does not have a cadre of experts who are spooled up to develop a MAV, is that rocket technology development reached diminishing returns circa 1970, and the expertise in the field faded (along with funding cuts). Today's rocket experts implement relatively small evolutionary departures from existing technology.

John

When they get paid to do it, by doing engineering, probably JPL/Ames or similar in colab with industry.

It's a huge challenge - no doubt whatsoever, but I don't really get your point. Where's the cadre of experts for a Titan balloon? Where's the cadre of experts for anything...that we've not actually done yet? The answer.... you get that talent and knowledge by doing it. There's barely the money to build and fly MSL. Given that politics is a banned discussion from this forum - what do you want to talk about.

You didn't say 'There simply is no community of people who have experience building miniature launch vehicles of the exact scope and specification that will be required for MAV'.

We wont have...until we've built an MAV. I'm not going to get into an argument about this ( although it seem you really want one ) - but it's chicken and egg. We didn't have Mars EDL experts till after Viking. We wont have MAV experts till after MSR. Someone needs to write a very big cheque, and the problem will thus be solved. Thats all there is to it.


Doug

Ironically, I'm not even sure that MAV is the long pole in the tent for MSR; there are a bunch of them. For example, the automated Mars orbit rendezvous, capture, and sample transfer process to the Earth return container seems like it might turn out to be fiendishly complex, and will require extremely robust software with autonomy bordering on AI capabilities.

On the happy side, such a technologically challenging project is just what the doctor ordered for NASA & ESA. As John pointed out, there's been some damping down on rocket development over the last few decades, and thatt's probably true for other disciplines as well since the focus is almost uniformly on staying on time and within budget. The sheer amount of R&D and innovation that will be needed to fly MSR would greatly benefit UMSF overall in the long term, and probably produce a number of significant spin-offs for non-space applications.

Don't usually double-post, but just had a wild thought: Why can't MSR be deferred until the Orion/Constellation Mars landing architecture is developed?

Rationale here is that it might make more sense to frame MSR as both a critical science mission and a critical test of the future manned Mars landing effort. At some point, there will need to be a realistic test of the crew descent/ascent vehicle; why not fly one with a rover or two that could pick up several hundred kg of samples while executing a nominal manned mission profile? A shakedown cruise of the system seems very desirable in any case.

Big bucks, yes...but also access to a different and much larger pot of money...

One reason is because Orion may well be dead six months from now. Another is that the engineering problems aren't very similar even if VSE does ultimately end up going to Mars. Think of Apollo compared to Luna 16.

I think the point John is making, and it's an important one which I have little reason to doubt the validity of, is that the MAV will require a great deal more technology development than many in the Mars community seem to be assuming. For this and many other reasons, I am very pessimistic that we will see MSR any time soon.

Add to this the fact that all the military missiles I saw listed here are solid propellant ones. I'm fairly certain that if there ever is a MAV developed, it will be liquid fueled. Solid propellant, while easier to handle and make rocket motors with has an inferior specific impulse. This implies a heavy ascent stage and a correspondingly heavy descent stage. We can be sure mass will be the limiting factor as usual so we can pretty much rule out solid motors as feasible.

- 1.5 The manned vs unmanned debate will be never ending, always heated, and it is not allowed on this forum

Three posts deleted.

According to various analyses I've done in the past, the Isp of solids is better than that of monoprop hydrazine and competitive with biprop hydrazine/NTO (in the range of 300 s). Biprop might be a little better, but the advantage is not huge.

More expert opinions welcome. I would love to see a good design for a MAV, but I'm not sure I have seen one yet. The original MiniMAV was very attractive but in hindsight too optimistic.

That's interesting. I was under the impression solid propellants have less than 300 s Isp (the figure for Shuttle SRBs is 285 s in vacuum) while hydrazine/NTO is said to have 340 s in vacuum. I'm using vacuum level Isp because Mars' atmosphere is obviously much closer to a vacuum than Earth sea-level pressure.

Then again, the solid fuels I looked at were optimized for rocket strap-on boosters which could be optimized for high thrust rather than high Isp. Don't know, I'm really not an expert.

Even if the Isps were 285 and 340, that's only a 20% advantage for biprop, which could easily be offset by the mass of tankage, pressurant, plumbing, and thermal control to keep the propellant from freezing. I'd say solids were still viable based on that.

It's true that's only 20% in Isp difference. However, for a given desired delta-V, the fuel mass varies with exp(deltaV/(Isp*9.81)). For low target velocities that's similar to the Isp difference. Say you wanted to reach Mars orbital velocity, 3.52 km/s. That amounts to 22% higher prop mass for solids. If you wanted to reach martian escape velocity, 5 km/s the difference becomes 33% which is starting to look more serious. Add into consideration gravity drag and the delta-V needed to reach orbit exceeds that of orbital velocity by at least a few hundred m/s. Mars has one thing going for it regarding gravity drag - lower gravity and less dense atmosphere allowing a more agressive acceleration profile. Then you come back to the thrust of the ascent stage, in which case solids are better.

A 25% increase in mass doesn't seem that high to justify the complexity of liquid propulsion, agreed, but what about the mass required to land the extra 25% mass in the first place? I have a feeling that doesn't scale linearly either. It's a tricky design to optimize indeed.

I have always wondered...

What about two separate launches from Earth -one for a lander+MAV and one for an orbiter and entry capsule? What about a single-stage MAV plus unmanned docking in Low Martian Orbit?

Hey Doug, hopefully your comments will help me focus better on what I was trying to explain. I think the whole planetary community would agree that a Titan balloon would be entirely about innovation, and I think that planetary scientists and others planning missions do consider Titan balloons to be interesting. My concern is that the MAV rocket problem does not seem to be viewed similarly. Has anyone met a planetary scientist who finds propulsion systems to be interesting?

Innovation is unwelcome in the development of propulsion systems for planetary missions, and the engineering culture is built around the notion of only using what is already proven. Spacecraft organizations treat this sort of work as an automatic process. People working in the space propulsion discipline have been taught by their experience that a new project won't get funded unless they say existing technology will suffice. But the technical problem that exists is not one of obtaining the "exact scope and specification." Launching from Mars to orbit, with a vehicle the size of a person, is far beyond being a variation of previous capability.

I absolutely agree that you get the talent and knowledge by doing it. The Rover Team is a great example of a major technical talent pool being convened and nurtured to do something totally unique to Mars exploration. It took decades to build the team and then create working flight rovers, and my understanding is that it has not been easy to keep the team together. I suspect that building up expertise of a similar magnitude for a similarly specialized purpose is going to be needed for the MAV.

While I too look forward to seeing the big checque written for MSR, the reality is that the Mars Program budget is constrained. If money flowed freely, then robotoc sample return could be a dry run for a human mission, using the full scale hardware. I wouldn't agree that money can solve any defined technical problem, since physical limits do exist. In many engineering endeavors, the primary difficulty is complexity. For the MAV (built small enough for an affordable mission), the primary difficulty is physical limits related to the strength of materials, miniaturization thickness limits, unfavorable cube-square scaling of drag versus mass (similarly heat flux versus mass), and unfavorable scaling for other things like manufacturing precision and the effects of fluid viscosity. Does everyone in the system appreciate that complexity and physical limits present totally different kinds of difficulty?

mcaplinger, thanks for understanding.

John W.

P.S. to ugordan: Despite Mars's thin atmosphere, the ideal acceleration profile starts at about one earth gee, because the effect of drag is greater for tiny vehicles like the MAV needs to be. Solid motors on the scale of interst inherently have ten times the ideal thrust, hence more drag.

P.S. to zvezdichko: Separate launches from Earth as you suggest has been the nominal notion for MSR since the late 1990's, with rendezvous in Mars orbit at 500 km altitude. Even to only reach Mars orbit, a single-state MAV might be more difficult than a 2-stage MAV. I personally think a single-stage MAV is possible with a hard technology push, and desirable for several reasons.