One way to get around shroud volume issues would be to use an expandable aerodynamic decelerator, like the inflatable heatshield NASA just recently tested. Imagine a circular heatshield launched on a rocket with a 10m fairing expanding to 25m ... such a thing could conceivably bring down cargo in the range from 50t to 60t, just what you need for Semi-Direct missions.
Quote from: mmeijeri on 09/02/2009 12:26 pmQuote from: rklaehn on 09/02/2009 12:05 pmI 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.QuoteQuoteComing 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.
Quote from: rklaehn on 09/02/2009 12:05 pmI 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.
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.
QuoteComing 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.
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.
Hey guys.I was wondering whether anyone has thought about putting some degree of abort-to-surface capability in the mars ascent capsule?
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
You've actually brought up quite an interesting question. Perhaps the case can be made for a small ISRU plant and recyling onboard the orbitally cached 'rescue pack'? But keeping in mind that this thing would be in orbit for at least a few years before being used and therefore cant really store hydrogen onboard, then what sort of ISRU could you use?
Mick,I'm surprised you caught that in there As I imagine them, no. Just a couple of tonnes worth of general supplies, and maybe an inflatable shelter or something (although the capsule would be low-density to be useful for reentry, so the capsule by itself should be quite spacious). Over at MarsDrive we're looking at an architecture which uses long-range mobile habs. In addition to the 'standard' array of safety advantages that they provide to the architecture (crew are always within stones-throw of their base, bring their radiation protection with them, no need to commute in dinky rovers, etc.) I would imagine that they could also be remotely driven. So as long as the aborted capsule lands within say a few hundred kilometers of the launch area, then it should take only a few days for the mobile habs to reach the crew for rescue. A few tonnes of supplies should last the crew a few weeks, even without recycling. So there should be ample opportunity for rescue. Our current baseline actually uses two mobile habs (as this divides their mass in half, and also allows a fully-paired approach thus further increasing mission safety). Perhaps one of them could be pre-staged downrange before the crew even attempts the ascent? Just musings at this stage of course.You've actually brought up quite an interesting question. Perhaps the case can be made for a small ISRU plant and recyling onboard the orbitally cached 'rescue pack'? But keeping in mind that this thing would be in orbit for at least a few years before being used and therefore cant really store hydrogen onboard, then what sort of ISRU could you use?Other options which might fit within the ~2 tonne payload envelope might include a small open rover with supplies, or perhaps even something like the Apollo LRF/LESS?Interesting topic. Is there a spereate thread for 'mars rescue options' and such? I'll have a look...- Mike
Quote from: Michael Bloxham on 09/16/2009 08:53 amMick,I'm surprised you caught that in there As I imagine them, no. Just a couple of tonnes worth of general supplies, and maybe an inflatable shelter or something (although the capsule would be low-density to be useful for reentry, so the capsule by itself should be quite spacious). Over at MarsDrive we're looking at an architecture which uses long-range mobile habs. In addition to the 'standard' array of safety advantages that they provide to the architecture (crew are always within stones-throw of their base, bring their radiation protection with them, no need to commute in dinky rovers, etc.) I would imagine that they could also be remotely driven. So as long as the aborted capsule lands within say a few hundred kilometers of the launch area, then it should take only a few days for the mobile habs to reach the crew for rescue. A few tonnes of supplies should last the crew a few weeks, even without recycling. So there should be ample opportunity for rescue. Our current baseline actually uses two mobile habs (as this divides their mass in half, and also allows a fully-paired approach thus further increasing mission safety). Perhaps one of them could be pre-staged downrange before the crew even attempts the ascent? Just musings at this stage of course.You've actually brought up quite an interesting question. Perhaps the case can be made for a small ISRU plant and recyling onboard the orbitally cached 'rescue pack'? But keeping in mind that this thing would be in orbit for at least a few years before being used and therefore cant really store hydrogen onboard, then what sort of ISRU could you use?Other options which might fit within the ~2 tonne payload envelope might include a small open rover with supplies, or perhaps even something like the Apollo LRF/LESS?Interesting topic. Is there a spereate thread for 'mars rescue options' and such? I'll have a look...- MikeHey Mike.I was thinking along the lines of if the capsule came down somewhere not easily accessable for a rescue, say down in Marineris or on Olympus as extreme examples, then it could be quite a while before they hook up with a Hab/rover. Water and oxygen may run short especially if one or more of the crew are injured or are actively trying to find a way out.Mick
Has anyone done any work on parachute/parafoil landing systems recently for Mars Is there a formula for area vs landing mass
Quote from: MickQ on 11/06/2009 01:02 amHas anyone done any work on parachute/parafoil landing systems recently for Mars Is there a formula for area vs landing mass Parachutes can't be use for landing, only deceleration. Rockets or airbags are needed for final descent
Some time ago I read something about the shape of a "Shuttlecock" being investigated for use in aero-braking.Anyone heard this Mick.
Quote from: MickQ on 11/12/2009 02:02 amSome time ago I read something about the shape of a "Shuttlecock" being investigated for use in aero-braking.Anyone heard this Mick.You mean like Burt Rutan's SS1?
Is there a formula for area vs landing mass Mick.