Author Topic: Mars EDL technologies  (Read 175814 times)

Offline rklaehn

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Re: Mars EDL technologies
« Reply #60 on: 09/02/2009 12:56 pm »
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.

They are going to be a secondary payload on the AMSAT P5A mission, which is going to be a secondary payload on an ariane V launch.

I am not sure if they are going to make the launch window this year. But this is not just another powerpoint project: they have built working models and even flown a suborbital test flight.

Offline Xentry

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Re: Mars EDL technologies
« Reply #61 on: 09/02/2009 01:11 pm »
But then you still need HLVs with 10m fairings ... unless you go for some sort of lifting body design, which may be a bit tricky ... since you would enter the atmosphere "head first", slow down, deploy your chute, turn around, fire your engines. With blunt decelerators the vehicle always faces in the "correct" direction for reentry, parachute deployment as well as rocket motor deceleration.
The need for 10m (and bigger) fairings is also driven by the lander stage and the habitat module dimensions, among others. And to be honest, HLVs with 10m fairings sound like a pretty standard configuration to me.
As for lifting bodies, the parachute attachment point could also be located near the nose of the vehicle so it rotated the vehicle to the proper position for thruster firing right from the chute deployment moment. Not that I would advocate a lifting body for a manned Mars mission...

Offline Xentry

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Re: Mars EDL technologies
« Reply #62 on: 09/02/2009 01:13 pm »
Whatever works is good enough. We don't need to go "exotic" just for the sake of doing it. If conventional, proven technology works, then we should use it. However, absent technology development of a folding technique (or inflatable heat shield add-ons) for Viking-shaped heatshields and parachute technique, we ain't going to see >30mt to the Martian surface.

There's still powered descent or a hybrid approach.
There is no other way than a hybrid approach. The chutes would have to be too big and heavy to allow a soft landing under a parachute.

Offline mmeijeri

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Re: Mars EDL technologies
« Reply #63 on: 09/02/2009 01:22 pm »
The need for 10m (and bigger) fairings is also driven by the lander stage and the habitat module dimensions, among others.

Horizontal landers don't need large fairings. Habitats don't strictly need them either, look at the ISS. Inflatable habs sound more practical though.

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And to be honest, HLVs with 10m fairings sound like a pretty standard configuration to me.

Could EELV Phase 1 have 10m fairings? Current EELVs could support 6.5m, but I vaguely remember Crawley saying something about even Atlas Phase 3 having smaller fairings than an SDLV.
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Offline Xentry

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Re: Mars EDL technologies
« Reply #64 on: 09/02/2009 01:39 pm »
The need for 10m (and bigger) fairings is also driven by the lander stage and the habitat module dimensions, among others.

Horizontal landers don't need large fairings. Habitats don't strictly need them either, look at the ISS. Inflatable habs sound more practical though.

Well, then you'd have to build a new type of lander which you haven't done before. Hey I'm all for it, in fact I think it's the most practical solution, but it would sure add to the development costs. As a lifting body would.


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And to be honest, HLVs with 10m fairings sound like a pretty standard configuration to me.

Could EELV Phase 1 have 10m fairings? Current EELVs could support 6.5m, but I vaguely remember Crawley saying something about even Atlas Phase 3 having smaller fairings than an SDLV.

My view is that you'll either have HLV or you can forget about Mars. Also I think that despite the problems NASA is facing right now there will be an HLV.
I respect your point of view, but I think that it greatly complicates an already technically difficult mission to make (meaning, you'd need to add technology development costs that you wouldn't need in case you had an HLV, to the point where avoiding to build an HLV would be unreasonable).
In any case the Atlas Phase 3 would apparently have a cryogenic upper stage 7m in diameter, on top of which one could eventually imagine a ~10m fairing could be placed.

Offline mmeijeri

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Re: Mars EDL technologies
« Reply #65 on: 09/02/2009 01:47 pm »
Well, then you'd have to build a new type of lander which you haven't done before. Hey I'm all for it, in fact I think it's the most practical solution, but it would sure add to the development costs. As a lifting body would.

I wonder if that's true. Such a lander could be single stage, which would be a simplification. And initially it wouldn't have to do true landings, assuming the Deep Space option is chosen. What would make a horizontal lander difficult to design?

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My view is that you'll either have HLV or you can forget about Mars.

Why is that?

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Also I think that despite the problems NASA is facing right now there will be an HLV.
I respect your point of view, but I think that it greatly complicates an already technically difficult mission to make (meaning, you'd need to add technology development costs that you wouldn't need in case you had an HLV, to the point where avoiding to build an HLV would be unreasonable).

Well, I certainly respect your point of view too, but I don't see how not having HLV complicates things very much. Propulsive braking might be expensive (much less so if rklaehn is right it's the last 2 km/s that is the problem), but not complicated. Hypergolic in-flight refueling is a proven technology and it's good enough for the foreseeable future.

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In any case the Atlas Phase 3 would apparently have a cryogenic upper stage 7m in diameter, on top of which one could eventually imagine a ~10m fairing could be placed.

To be honest I'm not at all enthusiastic about anything bigger than EELV Phase 1, since it is hard to imagine how that could lead to a high flight-rate.
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Offline rklaehn

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Re: Mars EDL technologies
« Reply #66 on: 09/02/2009 02:09 pm »
Well, I certainly respect your point of view too, but I don't see how not having HLV complicates things very much. Propulsive braking might be expensive (much less so if rklaehn is right it's the last 2 km/s that is the problem), but not complicated.

At least according to the paper you linked, this is the case. From the concluding remarks:

These conditions generally imply SRP initiation at the minimum altitude boundary defined by the timeline considerations of the subsequent EDL events.
You want to fire your supersonic retro propulsion as late as possible.

For the same ΔV, lower thrust coefficients are preferable as they preserve more aerodynamic drag. Overall, however, a lower initiation velocity is preferable over a lower CT.
If I read it correctly, CT is the ratio of propulsive force and aerodynamic force during the propulsive phase of reentry. So the conclusion is that you want your vehicle to have a large T/W and to do the propulsive braking as late as possible.

This can also be seen from the table on page 9, where the "delayed initiation" case with the highest T/W has by far the lowest PMF of 0.202.

Offline simcosmos

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Re: Mars EDL technologies
« Reply #67 on: 09/02/2009 02:11 pm »

You don't need 50m diameter heatshields (I am not even talking about the structural problems you get into by using a 50m heat-shield...). 15-25m does perfectly well. And even for the unreasonably-sized 50m inflatable (or foldable) heath-shield, you don't require a 10m PLF. A 20m heat-shield folded up fits perfectly well into a 6m PLF.

simon-th, do you have a reference or a visual representation about such 20m diameter heat shield properly folded to fit inside a 6m diameter envelope?


I have made some very rough 'studies' about how to integrate a conceptual heat shield that could be folded in two main parts and the very preliminary results - under constraints also dependent of specific heat shield shape, while taking in account PLF width plus some free distance between payload and internal PLF walls - was  something more or less like:

a)   7.6m (external) diameter PLF: ~11.76m heat shield diameter
b) 10.0m (external) diameter PLF: ~15.56m heat shield diameter

There could exist better ways of folding the shield (again, dependent of its geometry): on the examples above was only trying to study something with the minimum of possible of parts for a rigid heat shield (which would have to be unfolded and integrated with payload + departure stage at LEO).

António
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Offline mmeijeri

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Re: Mars EDL technologies
« Reply #68 on: 09/02/2009 02:20 pm »
So the conclusion is that you want your vehicle to have a large T/W and to do the propulsive braking as late as possible.

If firing into the hypersonic airstream is not the problem I thought it was, then I agree completely. The whole thing about braking outside the atmosphere and descending as quickly as possible was meant to avoid problems with hypersonic airstreams while keeping gravity losses as low as possible. If that's not an issue, then as close to a Hohmann transfer as possible would be best, which would mean high T/W and firing as late as possible. More realistically it would mean a gravity turn at as low an altitude and velocity as you could afford.
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Offline Xentry

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Re: Mars EDL technologies
« Reply #69 on: 09/02/2009 02:23 pm »
Well, then you'd have to build a new type of lander which you haven't done before. Hey I'm all for it, in fact I think it's the most practical solution, but it would sure add to the development costs. As a lifting body would.

I wonder if that's true. Such a lander could be single stage, which would be a simplification. And initially it wouldn't have to do true landings, assuming the Deep Space option is chosen. What would make a horizontal lander difficult to design?
If what's true? That you'd add to the development costs in case you were to develop a horizontal lander w.r.t. a been-there-done-that vertical lander? Ok, sure, you're entitled to that. I don't think it's difficult to design, just that it's a new type of vehicle and that historically speaking, new things cost more than replicas of old things.

My view is that you'll either have HLV or you can forget about Mars.

Why is that?
The reason was explained in the same post, in the very sequence of my claim. Implies the development of additional technologies (lifting body, inflatable heat shield and habitat modules, horizontal lander, etc) w.r.t. to an HLV-based Mars Mission.


Well, I certainly respect your point of view too, but I don't see how not having HLV complicates things very much. Propulsive braking might be expensive (much less so if rklaehn is right it's the last 2 km/s that is the problem), but not complicated. Hypergolic in-flight refueling is a proven technology and it's good enough for the foreseeable future.

Propulsive braking is not a problem, it just has to be accounted for. You also don't need to brake all the way from 2km/s (about Mach 6), just from Mach 0.8 according to Braun.
Heat shield dimensions are a problem, and parachute dimensions are a problem. And the path of least resistance, according to Braun and Co. is re-qualifying the Viking parachutes and assuming an increased heat shield diameter (to 10-15m). It's their point of view.

To be honest I'm not at all enthusiastic about anything bigger than EELV Phase 1, since it is hard to imagine how that could lead to a high flight-rate.
I certainly agree that an HLV will have comparatively higher costs due to the lower flight rate as compared to smaller vehicles. Having a small fairing, however, does impact the technologies you're able to use for Mars EDL, and those you need to develop.

Offline rklaehn

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Re: Mars EDL technologies
« Reply #70 on: 09/02/2009 06:00 pm »
Propulsive braking is not a problem, it just has to be accounted for. You also don't need to brake all the way from 2km/s (about Mach 6), just from Mach 0.8 according to Braun.

In the table 6 "SRP Performance for 5 t Robotic Cases." in the paper linked by mmeijeri, the initiation M∞ is between 2.96 and 1.82.

The M∞ is the mach number at initiation of the supersonic retro propulsion. Even in the case with the highest T/W, the initiation mach number is well above one.

Just for those who do not want to read the paper in detail: the proposed configuration uses a reentry shape similar to the mars science laboratory (MSL) with a diameter of 4.5m and very low-performance (but reliable) hydrazine monopropellant propulsion. It manages to land 5t on mars using between 1.0t and 1.5t of propellant depending on T/W.
« Last Edit: 09/02/2009 06:05 pm by rklaehn »

Offline mmeijeri

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Re: Mars EDL technologies
« Reply #71 on: 09/02/2009 06:05 pm »
I don't understand how a delta-v of 2km/s can lead to a mass fraction of 0.2. That's about what I'd expect with the vertical descent option using hypergolics. Surely it has to be better than that? Or is this comparing landed mass to IMLEO?
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Offline rklaehn

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Re: Mars EDL technologies
« Reply #72 on: 09/02/2009 06:09 pm »
I don't understand how a delta-v of 2km/s can lead to a mass fraction of 0.2. That's about what I'd expect with the vertical descent option using hypergolics.

In the paper the proposed propellant is monopropellant hydrazine with an Isp of 225s. And 0.2 means that with an initial mass of 1ton, 200kg have to be propellant (the rest is structure and payload). For such a low-performance propellant that is not that bad.

Edit: I think the term propellant mass fraction is a bit confusing since people often use payload mass fraction and abbreviate it to PMF.
« Last Edit: 09/02/2009 06:11 pm by rklaehn »

Offline mmeijeri

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Re: Mars EDL technologies
« Reply #73 on: 09/02/2009 06:20 pm »
Ah yes, that makes sense.
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Offline mmeijeri

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Re: Mars EDL technologies
« Reply #74 on: 09/03/2009 09:10 am »
Not to speak about assembling this massive vehicle in space and launching it towards Mars and then braking into on orbit.

Nope, it will easily fit inside an EELV fairing.

Quote
I'd rather put my money on a HLV than that scheme.  ;)

You seem to have a love for HLV. Note that it would be mostly other people's money going towards your hobby.
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Offline DLR

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Re: Mars EDL technologies
« Reply #75 on: 09/03/2009 09:46 am »
I have a love for HLVs?  ;D

Remember that I was the guy who said it was perfectly feasible to fly cheap Lunar missions with ELVs, Soyuz and EML-1 staging.

But I'm not dogmatic about it. I think that for Mars missions a HLV is going to be the best solution.

Also I don't why MLVs shouldn't be incrementally updated until they basically become HLVs, for example like the Atlas with its "Phases".
« Last Edit: 09/03/2009 10:01 am by DLR »

Offline Xentry

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Re: Mars EDL technologies
« Reply #76 on: 09/06/2009 01:19 pm »
Propulsive braking is not a problem, it just has to be accounted for. You also don't need to brake all the way from 2km/s (about Mach 6), just from Mach 0.8 according to Braun.

In the table 6 "SRP Performance for 5 t Robotic Cases." in the paper linked by mmeijeri, the initiation M∞ is between 2.96 and 1.82.

The M∞ is the mach number at initiation of the supersonic retro propulsion. Even in the case with the highest T/W, the initiation mach number is well above one.

Just for those who do not want to read the paper in detail: the proposed configuration uses a reentry shape similar to the mars science laboratory (MSL) with a diameter of 4.5m and very low-performance (but reliable) hydrazine monopropellant propulsion. It manages to land 5t on mars using between 1.0t and 1.5t of propellant depending on T/W.

Ok, but is an initiation Mach number over 1 really surprising for a paper which title is "Performance Characterization of Supersonic Retropropulsion for Application to High-Mass Mars EDL"?

I was taking the results from an earlier, less focused paper in which all different Mars EDL technology options were on the table, which is also linked to in this very thread - http://forum.nasaspaceflight.com/index.php?topic=18387.msg460969#msg460969

Here's the link to that paper: http://www.4frontierscorp.com/dev/assets/Braun_Paper_on_Mars_EDL.pdf

Offline rklaehn

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Re: Mars EDL technologies
« Reply #77 on: 09/06/2009 01:56 pm »
Ok, but is an initiation Mach number over 1 really surprising for a paper which title is "Performance Characterization of Supersonic Retropropulsion for Application to High-Mass Mars EDL"?

No, of course not.

I know that the standard approach is to use various aerodynamic devices such as supersonic parachutes to decelerate to subsonic speeds. I just think that the supersonic retropropulsion option is very attractive.

You need rocket propulsion in any case for a soft landing. So why not use it earlier and accept a bit lower mass fraction. You can use much higher ballistic coefficients, and you do not need something like 30m diameter supersonic parachutes.

Offline Xentry

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Re: Mars EDL technologies
« Reply #78 on: 09/07/2009 11:44 am »
Ok, but is an initiation Mach number over 1 really surprising for a paper which title is "Performance Characterization of Supersonic Retropropulsion for Application to High-Mass Mars EDL"?

No, of course not.

I know that the standard approach is to use various aerodynamic devices such as supersonic parachutes to decelerate to subsonic speeds. I just think that the supersonic retropropulsion option is very attractive.

You need rocket propulsion in any case for a soft landing. So why not use it earlier and accept a bit lower mass fraction. You can use much higher ballistic coefficients, and you do not need something like 30m diameter supersonic parachutes.

I agree - since you already have to have a propulsive landing, it makes every sense to explore supersonic retropropulsion. I was merely pointing out the perspective of the experts on the shortest path to making a manned Mars EDL possible.

Actually, in general I really don't care about which technology or strategy one uses, as long as it makes sense and makes things possible, as opposed to elaborating some grand scheme involving either a huge, multi-decadal development which will never happen and/or radical new technology (and launchers) which will almost surely cost billions which space agencies do not have (or, better yet, billions that the governments behind those agencies will never provide - not that they shouldn't, but as things are today, they just won't).

What strikes me the most as somewhat of a nonsense nowadays, is it seems as if it's the private companies led by space enthusiasts (Bigelow,SpaceX,Scaled Composites) which are developing the kind of new technology (inflatable modules for space stations and surface habitats, reusable launchers, cheap + frequent access to space) that's going to be needed to move any of those grand plans forward. It's pretty weird to think that space agencies, and NASA in particular, have failed miserably at what they should do best, which is developing the kind of enabling technologies that enable space exploration at an affordable cost.

Offline Michael Bloxham

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Re: Mars EDL technologies
« Reply #79 on: 09/09/2009 04:18 am »
Hey guys.

I was wondering whether anyone has thought about putting some degree of abort-to-surface capability in the mars ascent capsule?

Because this is Mars, and the atmosphere is thin, I was thinking you could make the ascent capsule reallly wide and fat, but bare-boned and lightweight: Essentially extremely low-density. That way you might be able to get away with just a thin coating of PICA, and less descent propellant but huge parachutes instead. Land the thing on some giant air-bags or something. You could also use the ascent capsule as your earth-reentry capsule. That way you don't have to lug your reentry capsule all the way from earth to mars and then back again with your ERV (or MDS or transhab or whatever you want to call it).

Okay, full abort-to-surface capability might be a bit much. And you have the problem of saving the crews once they land hundreds of kilometers down-range (although this is where orbital caching of emergency supply packs can really help). So how about just a partial abort-to-surface capability: Fly a dog-leg ascent profile, and keeping the low-density capsule idea, allow an abort-to-surface during the vertical part of the ascent only. The capsule should fall nearer where they lifted off, and the sub-orbital reentry environment should be benign enough that you can keep the capsule really lightweight.

So there are two ideas here: 1) Put full EDL systems on your ascent capsule so you can use it as your earth-reentry capsule too. That way you have full abort-to-surface capability, and you don't have to lug your reentry capsule all the way from earth to mars and then back again.

And 2) Using a dog-leg ascent profile, and just putting a minimal abort-to-surface capability in the capsule to allow aborts during the vertical part of the descent only.

Both using extremely low-density capsule designs with big parachutes and minimal-mass landing systems.

Your thoughts guys?

I guess the question for (1) is: Can mars-optimized EDL systems be made to work adequately during earth-reentry (or vice-versa, whichever way you want to look at it). In other words, can you design an EDL system which can accomplish both tasks reasonably well, without resorting to complete duplication of systems?

And for (2): How lightweight can you make the capsule if you only design in abort-to-surface capability during the vertical part of ascent? And would the vertical flight phase last long enough to make a minimal abort-to-surface capability worthwhile?

- Mike
« Last Edit: 09/09/2009 04:24 am by Michael Bloxham »

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