Author Topic: Mars EDL technologies  (Read 109784 times)

Offline Archibald

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Re: Mars EDL technologies
« Reply #40 on: 09/02/2009 10:23 AM »
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It would work even better with additional depots at L1, SEL2 / ISRU and SEP

Yes ! I like this. Ammonia, hydrogen and/or hydrazine (or any other nitrogen - hydrogen coumpound usable as rocket fuel, if someone know another, plesae tell me...) allows to combine these three elements.

To summarize: a EML-1 or -2 ammonia/hydrogen/hydrazine depot refuel an arcjet-tug for Earth departure. The said arcjet-tug is refueled through ISRU at Mars, for the return trip. 
Thus you combine electric propulsion (low IMLEO) with ISRU (low IMLEO) into an ultra-low IMLEO Mars expedition.

Offline mmeijeri

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Re: Mars EDL technologies
« Reply #41 on: 09/02/2009 10:31 AM »
And initially you wouldn't even need cryogenic depots, although you would want to take advantage of them as soon as they become available. ISRU would require new technology (especially on Phobos/Deimos, less so on Mars itself) but everything else is high TRL proven technology.
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Offline mmeijeri

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Re: Mars EDL technologies
« Reply #42 on: 09/02/2009 11:11 AM »
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Offline DLR

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Re: Mars EDL technologies
« Reply #43 on: 09/02/2009 11:36 AM »
May I ask, why would you want to use rocket propulsion for hypersonic/supersonic braking manouevres when you can just resort to larger shroud diameters?

Perhaps that's why we should get a HLV. It certainly makes things a lot easier for Mars. For the Moon it's not necessary, but for Mars, I certainly think so.
"Bei der Eroberung des Weltraums sind zwei Probleme zu lösen: die Schwerkraft und der Papierkrieg." - Wernher von Braun

Offline mmeijeri

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Re: Mars EDL technologies
« Reply #44 on: 09/02/2009 11:43 AM »
Precisely so you don't need an HLV. And apparently Mars EDL is a problem anyway, even with large fairings, hence Braun & co's research into supersonic retropropulsion.
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Offline mmeijeri

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Re: Mars EDL technologies
« Reply #45 on: 09/02/2009 11:47 AM »
How much easier do things become if you 1) enter from orbit instead of directly, 2) slow down more than is necessary to enter the atmosphere, 3) use the biggest possible EELV fairing (6.5m) and 4) use a lifting body? I'm thinking of entering the atmosphere at a mere 2km/s.

And then there's always the brute-force approach of coming to a standstill above the atmosphere and then descending as rapidly as dynamic pressure, Mach number and whatever other parameters are relevant will allow.
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Offline DLR

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Re: Mars EDL technologies
« Reply #46 on: 09/02/2009 12:04 PM »
A problem? I thought flying a 30t lander on a lifting trajectory with a 15m heatshield would get you below Mach 0.8 at sufficient altitude to start retropropulsion.

The last approach is just plain nuts, no offense.  :D ;)

The vehicle would mass hundreds of tonnes and would only be able to land tens of tonnes.
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Offline rklaehn

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Re: Mars EDL technologies
« Reply #47 on: 09/02/2009 12:05 PM »
How much easier do things become if you 1) enter from orbit instead of directly, 2) slow down more than is necessary to enter the atmosphere, 3) use the biggest possible EELV fairing (6.5m) and 4) use a lifting body? I'm thinking of entering the atmosphere at a mere 2km/s.

I think if you want to do some propulsive deceleration it is best to do it as late as possible: let the atmosphere do the work of decelerating you to about 1km/s, and then do the rest propulsively.

Coming in from orbit will reduce the heat load of the heat shield, but it will not significantly reduce the required delta-v. And designing a heat shield for 6km/s hyperbolic entry is not that challenging compared to an earth entry. So if your mission architecture requires hyperbolic entry (e.g. mars direct) you can do it.

A lifting body or any kind of high L/D shape would be very useful to reduce the required propulsive delta-v. But then a non-axially symmetric vehicle might be much harder to design. It might be easier to just accept the 0.2 PMF required for semi-propulsive braking.
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Offline rklaehn

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Re: Mars EDL technologies
« Reply #48 on: 09/02/2009 12:08 PM »
May I ask, why would you want to use rocket propulsion for hypersonic/supersonic braking manouevres when you can just resort to larger shroud diameters?

Perhaps that's why we should get a HLV. It certainly makes things a lot easier for Mars. For the Moon it's not necessary, but for Mars, I certainly think so.

We won't get a HLV. So we can either do lots of idle speculation about what we could do with an HLV, or we can try to deal with reality. I prefer the latter.

Besides, even if sufficient funds were available for a HLV, I would prefer this money to be spent on actual in-space R&D and hardware.
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Offline DLR

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Re: Mars EDL technologies
« Reply #49 on: 09/02/2009 12:13 PM »
Well then deal with the reality of not going to Mars.

Something like Direct's Jupiter or Atlas Phase 2 is certainly necessary for Mars missions.
"Bei der Eroberung des Weltraums sind zwei Probleme zu lösen: die Schwerkraft und der Papierkrieg." - Wernher von Braun

Offline rklaehn

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Re: Mars EDL technologies
« Reply #50 on: 09/02/2009 12:20 PM »
Well then deal with the reality of not going to Mars.

Something like Direct's Jupiter or Atlas Phase 2 is certainly necessary for Mars missions.

Just saying it does not make it so.

A manned mars mission could be done using existing launchers and propellant depots. Take the mars direct mission architecture: the biggest piece is about 30t. There is no need for anything bigger than that.
« Last Edit: 09/02/2009 12:20 PM by rklaehn »
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Offline simon-th

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Re: Mars EDL technologies
« Reply #51 on: 09/02/2009 12:22 PM »
Injecting some "exotic engineering" here, I wonder if anyone ever considered using buoyancy as a way to descent to Mars. The question is of course, whether an airship similar in design as the one proposed by JP Aerospace for Earth, could achieve enough uplift through the Martian atmosphere earlier enough to not crash, but to achieve a slow and controlled descent.

It is possible to climb to up to ~50km with airships in Earth's atmosphere. Considering that the mean atmospheric pressure on Mars is about as much as at ~30km height on Earth, but due to the lower gravity on Mars the atmosphere actually reaches higher up, I think it is worth at least considering.

Of course, this approach requires a. breaking into low Mars orbit first b. extending the airship and filling it up with a gas (probably hydrogen) c. requires some kind of ion engine for slow deceleration until friction from the Martian atmosphere provides said deceleration.

Offline mmeijeri

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Re: Mars EDL technologies
« Reply #52 on: 09/02/2009 12:23 PM »
A problem? I thought flying a 30t lander on a lifting trajectory with a 15m heatshield would get you below Mach 0.8 at sufficient altitude to start retropropulsion.

The last approach is just plain nuts, no offense.  :D ;)

Now, now, no need for strong language. What I described is most certainly not nuts, it is a perfectly feasible approach if you want to exclude HLV, as I do.

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The vehicle would mass hundreds of tonnes and would only be able to land tens of tonnes.

Not hundreds, a bit over one hundred.
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Offline DLR

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Re: Mars EDL technologies
« Reply #53 on: 09/02/2009 12:25 PM »
But when you slow down from orbit and at the sime time attempt to maitain your altitude above the surface you're incurring huge gravity losses.

Not to speak about assembling this massive vehicle in space and launching it towards Mars and then braking into on orbit.

I'd rather put my money on a HLV than that scheme.  ;)
« Last Edit: 09/02/2009 12:33 PM by DLR »
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Offline mmeijeri

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Re: Mars EDL technologies
« Reply #54 on: 09/02/2009 12:26 PM »
I think if you want to do some propulsive deceleration it is best to do it as late as possible: let the atmosphere do the work of decelerating you to about 1km/s, and then do the rest propulsively.

Sure, but the problem is that that is very difficult with EELV fairings, unless you come up with something like foldable or inflatable heatshields. By the time you get to just above the surface you would be going too fast and the atmospheric density would be too high to fire your thrusters.

Quote
Coming in from orbit will reduce the heat load of the heat shield, but it will not significantly reduce the required delta-v. And designing a heat shield for 6km/s hyperbolic entry is not that challenging compared to an earth entry. So if your mission architecture requires hyperbolic entry (e.g. mars direct) you can do it.

From orbit it is something like 3.5 km/s, which is quite a bit less than 6 km/s.

Quote
A lifting body or any kind of high L/D shape would be very useful to reduce the required propulsive delta-v. But then a non-axially symmetric vehicle might be much harder to design. It might be easier to just accept the 0.2 PMF required for semi-propulsive braking.
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Offline simon-th

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Re: Mars EDL technologies
« Reply #55 on: 09/02/2009 12:28 PM »
Well then deal with the reality of not going to Mars.

Something like Direct's Jupiter or Atlas Phase 2 is certainly necessary for Mars missions.

An HLV will very likely be used for a mission to Mars, but from a mission point of view, nothing on the technical side says you can't go with a mission based on Atlas V Phase 1 (40mt) or even with current launchers, both augmented with fuel depots. A 40mt partially dry-launched EDS can be easily filled up with enough propellant on orbit to launch a 40mt payload launched on a second rocket and docked with the EDS to Mars.

Alternatively, you go for the "all-in" variety of doing a Mars mission and assemble your Mars ship in LEO altogether. 1. Launch depots 2. launch fuel to depots 3. launch Mars surface payload 4. launch dry EDS 5. lauch hab module and 6. launch the crew. Join things together, fill up the dry EDS stage(s) and off you go. All with EELVs. That requires a lot of launches (about 40-50 times 25mt launchers or about 25 if you go for Atlas V Phase 1 if you go for chemical propulsion) but it is possible.

Offline rklaehn

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Re: Mars EDL technologies
« Reply #56 on: 09/02/2009 12:30 PM »
Injecting some "exotic engineering" here, I wonder if anyone ever considered using buoyancy as a way to descent to Mars. The question is of course, whether an airship similar in design as the one proposed by JP Aerospace for Earth, could achieve enough uplift through the Martian atmosphere earlier enough to not crash, but to achieve a slow and controlled descent.

I think the airship to orbit idea of JP aerospace is completely unworkable. But the idea of using large inflatable structures for reentry is quite workable.

Here is a very interesting project of the german mars society about mars reentry using a balloon that is inflated in space. It is made from somewhat heat-resistant material, and due to the large surface area per mass unit (low ballistic coefficient), the heating is gentle enough for the balloon to survive reentry.

http://www.archimedes-ballon.de/index.php?id=EN
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Offline rklaehn

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Re: Mars EDL technologies
« Reply #57 on: 09/02/2009 12:39 PM »
I think if you want to do some propulsive deceleration it is best to do it as late as possible: let the atmosphere do the work of decelerating you to about 1km/s, and then do the rest propulsively.

Sure, but the problem is that that is very difficult with EELV fairings, unless you come up with something like foldable or inflatable heatshields. By the time you get to just above the surface you would be going too fast and the atmospheric density would be too high to fire your thrusters.

Rockets work just fine when firing into a supersonic flow. For example the separation rockets of the shuttle SRBs. You just have to make sure that the exit plane pressure of the rocket is significantly higher than the stagnation pressure of the supersonic flow.

Quote
Quote
Coming in from orbit will reduce the heat load of the heat shield, but it will not significantly reduce the required delta-v. And designing a heat shield for 6km/s hyperbolic entry is not that challenging compared to an earth entry. So if your mission architecture requires hyperbolic entry (e.g. mars direct) you can do it.

From orbit it is something like 3.5 km/s, which is quite a bit less than 6 km/s.

Yes. But the part where the thin atmosphere hurts you the most is not the initial part of the deceleration but the last part of the deceleration. Getting from 6km/s to 2km/s is no problem even with a high ballistic coefficient and the thin martian atmosphere. The part from 2km/s to subsonic is where you need the low ballistic coefficient and/or propulsive braking.
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Offline mmeijeri

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Re: Mars EDL technologies
« Reply #58 on: 09/02/2009 12:40 PM »
But when you slow down from orbit and at the sime time attempt to maitain your altitude above the surface you're incurring huge gravity losses.

Sure, the trick would be to descend as quickly as possible. If you descend too quickly you'll get into the velocity/altitude regime where you can no longer start your engine. You also have to take your T/W ratio into account, since you would want to come to a standstill above the surface, not below it... Apparently firing into a Mach 5-6 airstream is possible, but I would think that high up in the atmosphere, where density and dynamic pressure are very low, you might be able to go even faster than that.

So in the all-propulsive scenario you would initially brake to a standstill at an altitude of about 150 km, then plummet down to 20-30 km keeping your velocity below Mach 5-6, then slow down in the increasingly dense atmosphere to keep within the envelope where you can fire your thrusters and then slow down rapidly from around 10 km. I did some simple experiments with the Orbiter space simulator and it looked possible. Not easy but possible. Orbiter doesn't model the interaction between the thruster and an opposing hypersonic airstream, but it does model dynamic pressure. I would love to know what the maximum allowed dynamic pressure/Mach number/whatever envelope is.

My guess is that the all-propulsive approach while possible might be less effective than a hybrid. I'm thinking a hybrid would be best if you exclude HLV.

BTW I'm not denying a large fairing is an advantage for SDLV from the point of view of EDL. I'm just pointing out there appear to be good alternatives (and plenty of problems even with large fairings) so I have no reason to switch away from my preference of smaller launchers.
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Offline simon-th

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Re: Mars EDL technologies
« Reply #59 on: 09/02/2009 12:46 PM »
Injecting some "exotic engineering" here, I wonder if anyone ever considered using buoyancy as a way to descent to Mars. The question is of course, whether an airship similar in design as the one proposed by JP Aerospace for Earth, could achieve enough uplift through the Martian atmosphere earlier enough to not crash, but to achieve a slow and controlled descent.

I think the airship to orbit idea of JP aerospace is completely unworkable. But the idea of using large inflatable structures for reentry is quite workable.

Here is a very interesting project of the german mars society about mars reentry using a balloon that is inflated in space. It is made from somewhat heat-resistant material, and due to the large surface area per mass unit (low ballistic coefficient), the heating is gentle enough for the balloon to survive reentry.

http://www.archimedes-ballon.de/index.php?id=EN

Thanks for the link. Basically this is what I meant - some kind of combination of aero-braking and use of buoyancy. The project website seems to be a bit dated (they speak of a launch this year...) but it quite interesting.

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