Landing on Mars

MatthewRRobinson · 2012-04-11 20:04:38

RobS wrote:

No one has tested a ballute yet, so I don't know how much is known about their properties or what will work. Does anyone have references to them?

wikipedia is always a great place to turn
http://en.wikipedia.org/wiki/Ballute

Of course, I say that because you can confirm and look at the sources themselves.
wiki:
"It was used as part of the escape equipment for the Gemini spacecraft.[3]"
3. http://www.hq.nasa.gov/office/pao/Histo … /ch8-4.htm

According to the article, they've been used on bombs, too.

The clouds would seem to show they're being used at trans-sonic or super-sonic speed, correct?

The ballutes in my proposal are used in-tandem with the heat shield, so plasma formation is still okay.
Either
1) The ballute deploys after significant heating has stopped
or
2) The ballute is well-protected from the hypersonic airflow by the spacecraft.

1., only if 2. is impossible or impractical.

Also, I imagine the ballute, unlike the bombs in the picture above, is on the end of a hose/cable that is at least a few meters or tens of meters out from the ERV; so as to catch the maximum amount of undisturbed air, to get the most drag. So most likely 1. is the case.

Then again, a third option might be possible: Deploy the ballute, but hold it close to the spacecraft; it gives the lifting force of the balloon to have some very small effect on the descent rate, and once significant heating is over, extend it. This shouldn't be too hard, since I envision the hose/cable is already retractable by motor. In this case, it's just making it extendable and retractable, instead of just retractable.
(The reason for the retractable ballute is that the ERV is supposed to be reusable. Think it's hard recovering ejected parachutes on Earth? It's bound to be a much harder, and even exceptionally dangerous thing to do on Mars, and it would entail a significant amount of work to be done on the ERV by EVA. The ballute is mounted on the "dragon" portion, so they'd be doing this work high off the ground, too. Overall it's much safer and probably even saves weight to make it retractable, as opposed to all it would take to make these OPS possible.)

Last edited by MatthewRRobinson (2012-04-11 20:16:03)

GW Johnson · 2012-04-12 12:10:18

Standard military weapons-release speed is 485 knots indicated. At sea level, that's about 0.85 Mach. Definitely subsonic at all low altitudes of any interest. Condensation clouds can exist in the intake of a jet parked static on a carrier deck.

I tried ballutes as a stabilizing drogue back in the mid 80's. Ribbon chutes worked better, and were good to 2.5 Mach, if you bagged it properly for control of opening shock. Different application, same decelerators.

These were ram-air inflated devices, though. In space, you are really talking about low to medium-pressure forced inflation of a shaped balloon. Not quite the same thing. It was the ram air inflation I found unreliable, unlike a ribbon chute.

GW

MatthewRRobinson · 2012-04-15 18:08:13

GW Johnson wrote:

Standard military weapons-release speed is 485 knots indicated. At sea level, that's about 0.85 Mach. Definitely subsonic at all low altitudes of any interest. Condensation clouds can exist in the intake of a jet parked static on a carrier deck.
I tried ballutes as a stabilizing drogue back in the mid 80's. Ribbon chutes worked better, and were good to 2.5 Mach, if you bagged it properly for control of opening shock. Different application, same decelerators.
These were ram-air inflated devices, though. In space, you are really talking about low to medium-pressure forced inflation of a shaped balloon. Not quite the same thing. It was the ram air inflation I found unreliable, unlike a ribbon chute.
GW

Okay, that's great input, I had a feeling transonic wasn't required to cause condensation.

As you said, though, we're not working with ram-inflated devices.

I decided to check the source wiki used for saying "It is a parachute braking device that is optimized for use at high altitudes and high supersonic velocities." That sentence had cited this: http://ntrs.nasa.gov/archive/nasa/casi. … 017080.pdf

The page itself details some tests of ram-air inflated ballutes, simulating conditions of a Martian re-entry, according to the summary.
The actual tests occurred at mach 3.15 with a dynamic pressure of 1843.4 N/m^2, and the ballute broke (one of the inlets were torn from the body).

More interestingly, though, the paper references earlier tests that had been done on smaller ballutes;

"Usry, J . W.: Performance of a Towed, 48-Inch-Diameter (121.92-cm) Ballute
Decelerator Tested in Free Flight at Mach Numbers From 4.2 to 0.4. NASA
TN D-4943, 1969."

Starting at mach 4.2.

Here's the actual paper;
http://ntrs.nasa.gov/archive/nasa/casi. … 008066.pdf

And that paper references another one, some goodyear tests, where ballutes and ribbon chutes were wind-tunnel tested at even higher mach numbers, up to mach 10.
http://ntrs.nasa.gov/archive/nasa/casi. … 027566.pdf

To be honest, I've only skimmed through it, and one thing that stands out to me is the part on page 67 that notes that ribbon chutes were experiencing "breathing" and coning at mach 2.5 +, while the ballutes faired better at the very high mach numbers.

NASA's decision to use Ribbon chutes makes sense, since they work in the mach range of the systems they're used for; the Shuttle's SRB's, or the smaller space probes that can decelerate to those lower mach numbers.

Now, quoting the OP:

RobS wrote:

Have you all seen this?
http://www.universetoday.com/7024/the-m … ed-planet/
It basically says that you can't land a large manned vehicle on Mars with the standard heat shield-parachute-thruster combination because the heat shield can't be large enough to slow the vehicle down to Mach 2 (when you can deploy parachutes) before you hit the ground. The atmosphere is too thin. But it's too thick to fire thrusters straight ahead of you at Mach 2+ because the exhaust plume is too dynamic and the resulting shaking could shake your vehicle apart. It advocates a "hypercone," a big inflatable structure, at Mach 5, to slow down the ship. I suppose a super-large heat shield, assembled in Earth orbit, would do it as well; that possibility is hinted at.

If ballutes can work at much higher mach numbers, then you've entirely circumvented the issue stated in the OP, and the issue the last pages have been dealing with (new heat shield tech.) ; you don't have to slow the vehicle to mach 2 at all, you just have to slow it to something like Mach 4.

Even better if we could re-create those wind tunnel tests from the goodyear paper, but scaled up and in atmosphere for mach 6+.

GW Johnson · 2012-04-16 11:56:21

My engineering intuition suggests the instability of the rocket plume fired into an oncoming supersonic/hypersonic stream derives from it's being fired straight ahead into the stream: the shock layer doesn't know which way to jump, so it buzzes around.

What if you have multiple thrusters and cant them all, at least a little. Now the shock layers know exactly which way to bend things. My intuition suggests this will be fluid dynamically stable. It would make rocket braking feasible during re-entry.

Guess what! The super Draco's on the Spacex Dragon are canted about 45 degrees. It's supposed to be rated for trips to Mars.

Others seem to have the same intuition regarding rocket braking in re-entry. I bet Spacex has already tested this, too.

GW

Russel · 2012-05-04 00:01:59

Probably the quickest and most useful test you could do is to simply launch a dragon and then test fire the thrusters from different altitudes/speeds. I'd imagine SpaceX would have to do something like that anyhow to verify their abort system actually works.

On Mars you've got more latitude. Since I've been considering using a "tail" of sorts to create more drag to weight, I've also considered adding thrusters into the structure. This raises two possibilities. One is you gradually move your thrusters (horizontally) into the slipstream. Another is you gradually pivot your thrusters into the slipstream so that towards the end they're basically pointing vertically down. Remember that if you provide drag above your craft you don't need a classical "capsule" shape to provide stability. Indeed the taller and wider you make it, the less the instabilities under the thrusters matter (or rather you've got longer time constants to play with).

GW Johnson · 2012-05-04 09:02:13

I looked closely at the video of the Armadillo Stiga-2 test with the ballute. It was a powered-inflation balloon deployed in vacuum just after apogee. Before the strap failed, it seemed to be stabilizing the tumble of the rocket, once it hit the thin air high up. I could see the air pressures ripple the surface of the ballute just a bit. This thing was indeed working.

I suspect without proof that the strap failed because of the heavy point mass of the nose cone bouncing around in the middle of the strap. Separate recoveries for rocket body and nose cone might have worked better. Very interesting test, though.

As I read the descriptions of the flight, peak velocity before leaving the air was about Mach 3.8. So, "re-entry" would have been in that same speed class. That's high enough to worry a little about aeroheating, but short enough to heat-sink your way through (the way the other suborbital tourist plane guys do). From a heating standpoint, I would choose Kevlar for the exposed fabrics, as it's good to about 290 F. But, you can't use it for shock-absorbing "structures", as it has almost no "give", at 1-2% elongation-to-failure. The stuff is very, very stiff/brittle under shock loads, that's why it's not used for parachutes. The other materials all fail under 210 F, some under 190 F.

Extending this type of decelerator for use during hypersonic entry is an intriguing idea. But heat protection will drive the issue. Perhaps a layered structure for both ballute and towline? The inner heat-protected part being something with a lot of elongation, like a nylon, sleeved in some way with tough Kevlar that holds a layer of some suitable ablating but hard char-forming rubber (Dow Corning 93-104 perhaps?). The inflation pressure for the ballute will have to be very high as well: re-entry dynamic pressures here on Earth are typically in the 5000 psf class. How one stands-off the tough ablative sleeving from the load-bearing but heat-vulnerable pieces thermally, I don't have a clue.

But it's a very interesting idea. I do smell a solution there. If it can work here on Earth, for sure it can be made to work on Mars.

GW

Russel · 2012-05-05 06:58:49

I'm not entirely convinced that an entirely "spineless" (for want of a better word) ballute is the way to go.

Lets consider the opposite alternative - a rigid structure, or at least one that would be under load. Here's a simple example. Build yourself a very big "racket" structure. Basically a stiffening ring supporting a mesh structure. Now attach support cables. You've now got something that will create drag and be relatively light. The nice thing about mesh is you can fiddle to your hearts content with the porosity, which lets you optimise the stability. You could even string these together in a sequence. Now, that's one extreme.

Somewhere in the middle is structures that have some backbone to them but attached to that is inflatable components.

I'm just tossing this in to point out that there's endless possibilities out there and only a few have even begun to be tested.

Russel · 2012-05-05 07:05:29

This might be interesting..

http://www.mrc.uidaho.edu/~atkinson/IPP … er.ppt.pdf

GW Johnson · 2012-05-05 10:17:31

Very interesting stuff about ballutes. I'm glad somebody's really working this problem, there's great potential there.

Radiative heating is the dominant heating effect by far for high-ballistic coefficient items like capsules, warheads, and the shuttle. I dunno about the low-ballistic coefficient regime, but I suspect it may still be dominant, or at least very important. However, at 2 watts/sq.cm, you might just actively-cool your way through, by maintaining gas flow through the ballute somehow. Just an odd thought.

I never used them in hypersonics. My experience was subsonic to about Mach 2.5. In that regime, ribbon chutes flew more stably than the conical towed ballute we tried. But the real bugaboo for us was inflation. We were trying ram air inflation, and it failed about half the time for us. Powered positive gas inflation eliminates that problem, and allows inflation in vacuum, too.

GW

Russel · 2012-05-05 19:57:03

I suspect that if what you tow has graded porosity then it will behave quite well stability wise.

Its forcing air around the edges that buys you instability.

GW Johnson · 2012-05-06 18:06:55

Oh, yes, porosity has an effect. Too little and the decelerator blows itself to pieces. Too much and it never opens. Doesn't matter what kind, either. Closer to "just right", and stability of the flow field is affected. Of course.

I believe real test data long before I believe computer codes, no matter their pedigree. But, then, I'm an old guy. Over 60 years old.

GW

Impaler · 2012-05-19 17:48:11

Perhaps your heat sinking and internal pressure needs could be satisfied by inflating the thin outer shell of the ballute with water, as it boils off the steam can be released by using a breathable weave. The water won't compress under the aerodynamic load and boil off water can be replenished by pumping in more water, when the point comes ware you want to eject the ballute pump out the water as you will want it for further use in the mission essentially recycling the mass.

With regards to EDL, I certainly see how it's a critical mission stage and something that will need to be validated before we start throwing multiple ton loads at Mars even unmanned ones. I think a progressive enlargement of our current Rovers (they have been growing steadily) up to the payload mass desired for a manned mission would be the most obvious validation program as we will be getting scientific data as well as a grasp of EDL.

Last edited by Impaler (2012-05-19 17:53:16)

GW Johnson · 2012-05-20 13:21:20

One of the re-entry techniques that never got tested on the cancelled X-20 "Dyna-Soar" was a sacrificial phase-change coolant, exactly as you (Impaler) suggested for the ballute.

I really wish they had flown that vehicle way back then (the 1960's). We'd know a whole lot more about practical atmospheric entry than we do now, computer simulations notwithstanding. Real data talks louder than any computer code, and always will.

GW

SpaceNut · 2012-05-20 20:17:24

I found my old post http://www.newmars.com/forums/viewtopic.php?id=5539 on the Mars EDL, Ballutes and more.....

RobS · 2012-06-01 19:27:50

Can someone please ban this guy? The postings are inappropriate and are advertising a website that is probably inappropriate (I don't dare click; I don't click on Russian websites when the French is bad and refers to hardcore lesbians and porno).

GW Johnson · 2012-06-04 09:04:58

I put an illustrated article up over at "exrocketman" that explores aero decelerators on Mars, and their possible combination with simultaneous rocket braking. Also, rocket braking during entry hypersonics is there. Nothing really substantive, just the concepts.

GW

http://exrocketman.blogspot.com

RobS · 2012-06-04 12:49:42

Very nice. Figure 2 isn't opening, though.

SpaceNut · 2012-06-05 06:47:55

RobS wrote:

Can someone please ban this guy? The postings are inappropriate and are advertising a website that is probably inappropriate (I don't dare click; I don't click on Russian websites when the French is bad and refers to hardcore lesbians and porno).

Yes it did take awhile to notify Josh that the spammer was active. In the old days of the moderators having the admin power to remove such creeps it did not result in as much damage to the board as this one might have been causing. The advice to not click on the links is the best action these days and keeping your computers antivirus software updated is another....

Thanks for the round up of the topics of Mars EDL and of the Radiation as well....These are the types of things that I thought the new board was going to do on its main page....

TwinBeam · 2012-06-15 22:20:08

RobS wrote:

Have you all seen this?
http://www.universetoday.com/7024/the-m … ed-planet/
It basically says that you can't land a large manned vehicle on Mars with the standard heat shield-parachute-thruster combination because the heat shield can't be large enough to slow the vehicle down to Mach 2 (when you can deploy parachutes) before you hit the ground. The atmosphere is too thin. But it's too thick to fire thrusters straight ahead of you at Mach 2+ because the exhaust plume is too dynamic and the resulting shaking could shake your vehicle apart. It advocates a "hypercone," a big inflatable structure, at Mach 5, to slow down the ship. I suppose a super-large heat shield, assembled in Earth orbit, would do it as well; that possibility is hinted at.

Rather than use your rockets to slow you down, why not use a rocket pointed DOWN to keep you aloft while aerobraking at 2g or so? Assuming you are coming in nearly horizontally, you only need 0.4g acceleration to maintain a given altitude, so this should still be a net gain.

And you don't need 0.4g of "lift" acceleration for most of it, as you want to keep dropping at a pace that maintains the aerobraking fairly constant as long as possible, and when deceleration falls below about 0.4g, start a controlled descent with parachutes and rockets, from a modest altitude, sufficient to leave time to kill your remaining horizontal component before landing.

louis · 2012-06-16 04:06:45

TwinBeam wrote:

RobS wrote:
Have you all seen this?
http://www.universetoday.com/7024/the-m … ed-planet/
It basically says that you can't land a large manned vehicle on Mars with the standard heat shield-parachute-thruster combination because the heat shield can't be large enough to slow the vehicle down to Mach 2 (when you can deploy parachutes) before you hit the ground. The atmosphere is too thin. But it's too thick to fire thrusters straight ahead of you at Mach 2+ because the exhaust plume is too dynamic and the resulting shaking could shake your vehicle apart. It advocates a "hypercone," a big inflatable structure, at Mach 5, to slow down the ship. I suppose a super-large heat shield, assembled in Earth orbit, would do it as well; that possibility is hinted at.
Rather than use your rockets to slow you down, why not use a rocket pointed DOWN to keep you aloft while aerobraking at 2g or so? Assuming you are coming in nearly horizontally, you only need 0.4g acceleration to maintain a given altitude, so this should still be a net gain.
And you don't need 0.4g of "lift" acceleration for most of it, as you want to keep dropping at a pace that maintains the aerobraking fairly constant as long as possible, and when deceleration falls below about 0.4g, start a controlled descent with parachutes and rockets, from a modest altitude, sufficient to leave time to kill your remaining horizontal component before landing.

Musk and GW here also have been talking in terms in cantered thrust, which might well make all the difference. Plus a more obvious point: why can't you slow down your craft with reverse thrust way before you hit the atmosphere? And, also, some orbital capture might be part of the solution.

I think NASA has in the past been overstating the difficulties (to excuse its own lack of action and perhaps to put off other space agencies) without actively investing in solutions and lots of commentators have been mesmerised by the negative stuff, taking it at face value. There's no doubt it's a difficult problem, but so was getting people into space and landing on the Moon in 1959. Ten years later people were walking on the Moon.

TwinBeam · 2012-06-16 13:34:02

louis wrote:

Musk and GW here also have been talking in terms in cantered thrust, which might well make all the difference. Plus a more obvious point: why can't you slow down your craft with reverse thrust way before you hit the atmosphere? And, also, some orbital capture might be part of the solution.
I think NASA has in the past been overstating the difficulties (to excuse its own lack of action and perhaps to put off other space agencies) without actively investing in solutions and lots of commentators have been mesmerised by the negative stuff, taking it at face value. There's no doubt it's a difficult problem, but so was getting people into space and landing on the Moon in 1959. Ten years later people were walking on the Moon.

I don't think you quite got the difference of what I was proposing. Musk and GW's plan has been to use rockets fired at an angle to slow the craft, while avoiding turbulence. I presume their thought is to aerobrake AND use rockets to slow down quickly, then use rockets for the rest of the way down. You could do that, but basically the sooner you slow down, the less deceleration due to drag, and the more you need to use rocket power to slow down.

What I proposed is to use rockets only to control descent, keeping the drag at a roughly constant level as long as possible - until it has slowed so much that drag force has become less than 0.4g, while not falling below some safe altitude - perhaps a kilometer up. All the way up to that point, you will have been getting a net benefit from aerobraking, over the cost of using your rocket. This approach maximizes the free deceleration of aerobraking.

As to slowing before entering the atmosphere - yes, of course you could - but again at the expense of relying much more on rocket power. And more rocket power means more mass, more mass to be sent all the way from Earth at higher cost in dollars, or higher cost to other stuff you could otherwise have brought.

louis · 2012-06-16 14:52:34

TwinBeam wrote:

louis wrote:

Musk and GW here also have been talking in terms in cantered thrust, which might well make all the difference. Plus a more obvious point: why can't you slow down your craft with reverse thrust way before you hit the atmosphere? And, also, some orbital capture might be part of the solution.
I think NASA has in the past been overstating the difficulties (to excuse its own lack of action and perhaps to put off other space agencies) without actively investing in solutions and lots of commentators have been mesmerised by the negative stuff, taking it at face value. There's no doubt it's a difficult problem, but so was getting people into space and landing on the Moon in 1959. Ten years later people were walking on the Moon.
I don't think you quite got the difference of what I was proposing. Musk and GW's plan has been to use rockets fired at an angle to slow the craft, while avoiding turbulence. I presume their thought is to aerobrake AND use rockets to slow down quickly, then use rockets for the rest of the way down. You could do that, but basically the sooner you slow down, the less deceleration due to drag, and the more you need to use rocket power to slow down.
What I proposed is to use rockets only to control descent, keeping the drag at a roughly constant level as long as possible - until it has slowed so much that drag force has become less than 0.4g, while not falling below some safe altitude - perhaps a kilometer up. All the way up to that point, you will have been getting a net benefit from aerobraking, over the cost of using your rocket. This approach maximizes the free deceleration of aerobraking.
As to slowing before entering the atmosphere - yes, of course you could - but again at the expense of relying much more on rocket power. And more rocket power means more mass, more mass to be sent all the way from Earth at higher cost in dollars, or higher cost to other stuff you could otherwise have brought.

Well, people often end up saying that to me..."well, yes you could..." To which I respond - well why not? You then reduce the problem to simply getting enough fuel into LEO, which is probably a lot cheaper than developing new landing systems - which might take ten years, and involve hundreds possibly thousands of people being employed on the project. My approach in any case would be to have a pretty small descent craft and rely on supplies pre-landed for life support once you get to the surface. By making the descent craft fairly small, you reduce the problem to a manageable size.

So are you talking about entering the Mars atmosphere at a narrower angle so you pass through more atmosphere? Doesn't that create problems in terms of heat shield protection?

GW Johnson · 2012-06-16 16:55:54

The more I think about it, the more sure I am that landing heavy items on Mars is a thing we can do far easier than we-the-community seem to think currently.

I think it takes low-thrust rocket braking during entry to the end of the hypersonics, followed by low-thrust rocket braking while your chute or ballute takes you subsonic, then high-thrust rocket braking for the final touchdown, probably without the chute, which would be pulling to one side, an instability factor. The idea is to use rocket thrust to make up the deceleration deficit that is inherently due to the extremely-thin Martian atmosphere, in both aero-deceleration phases.

I think the basic solution for rocket braking during entry hypersonics is multiple nozzles canted at around 10 or 15 degrees. That puts enough plume angle into the oncoming stream to make plume trajectory repeatable and steady-state. These engines fire right through open ports in the heat shield near its center, whatever that structure is. The "room" in which these engines are located needs to be sealed gas-tight behind the heat shield, so that there is no flow through that space. That no-throughflow feature is critical. That engine room space will pressurize like a pitot tube to the stagnation pressure during entry, but it will not heat to stagnation temperatures, as long as there is no throughflow. There is no better heat insulator than a static gas column, no matter what NASA says. We in the industry knew better. They didn't (see the segment joint designs in the shuttle SRB’s).

Myself, I'd separate the engines by "blast walls" of some sort, so that an explosion in one engine does not take out adjacent engines. Loss of an engine then means only that the remaining engines throttle up, but differentially, so that the same thrust is maintained, while thrust moments are still zeroed. This would apply to any chemical system, or to any nuclear thermal rocket system.

For the range between Mach 2.5-ish and subsonic, when chutes or ballutes are deployed, as long as the retro thrust remains fairly low, the plume massflow is small compared to the slipstream massflow, so that the aerodecelerators do not see a very-hot mixed flow field oncoming out behind the craft. Kevlar is good to about 290-300 F. Nothing magic there. You shed these aerodecelerators for final touchdown. Chutes or ballutes can be recovered after landing for re-use, by-the-way.

The final touchdown is then just standard rocket braking at throttled-up higher thrust. No different than Viking or the Apollo LEM.

How big a thing do you want to fly, and do you want it to be one-shot or reusable? I think we can do it, regardless.

As for ascent, if it's not reusable, leave the heat shield and any aeroshell surfaces at the landing site. Aeroshell surfaces can double as ramps for unloading content, by the way. The very same engines could serve for ascent, if the separable core has propellant tanks and a payload or crew cabin. Leave the descent tanks on the heat shield.

If it's nuke and reusable, just re-fold the unload ramps into an aeroshell, and just fly the whole thing back up.

I'd recommend a more-or-less conical shape, wider than it is tall, for at least the chemical one-shot version, with a slim core on the central axis for ascent. A fully-reusable nuke vehicle could be roughly as wide as it is tall. These sorts of shapes can prevent tip-over in a rough landing. Suspenders-and-belt.

Wild thoughts way outside the box, from an old rocket and ramjet guy who used to do wild-thoughts-outside-the-box for a living. It was called new product development work. Especially for products others thought impossible.

GW

louis · 2012-06-16 20:03:00

GW Johnson wrote:

The more I think about it, the more sure I am that landing heavy items on Mars is a thing we can do far easier than we-the-community seem to think currently.
I think it takes low-thrust rocket braking during entry to the end of the hypersonics, followed by low-thrust rocket braking while your chute or ballute takes you subsonic, then high-thrust rocket braking for the final touchdown, probably without the chute, which would be pulling to one side, an instability factor. The idea is to use rocket thrust to make up the deceleration deficit that is inherently due to the extremely-thin Martian atmosphere, in both aero-deceleration phases.
I think the basic solution for rocket braking during entry hypersonics is multiple nozzles canted at around 10 or 15 degrees. That puts enough plume angle into the oncoming stream to make plume trajectory repeatable and steady-state. These engines fire right through open ports in the heat shield near its center, whatever that structure is. The "room" in which these engines are located needs to be sealed gas-tight behind the heat shield, so that there is no flow through that space. That no-throughflow feature is critical. That engine room space will pressurize like a pitot tube to the stagnation pressure during entry, but it will not heat to stagnation temperatures, as long as there is no throughflow. There is no better heat insulator than a static gas column, no matter what NASA says. We in the industry knew better. They didn't (see the segment joint designs in the shuttle SRB’s).
Myself, I'd separate the engines by "blast walls" of some sort, so that an explosion in one engine does not take out adjacent engines. Loss of an engine then means only that the remaining engines throttle up, but differentially, so that the same thrust is maintained, while thrust moments are still zeroed. This would apply to any chemical system, or to any nuclear thermal rocket system.
For the range between Mach 2.5-ish and subsonic, when chutes or ballutes are deployed, as long as the retro thrust remains fairly low, the plume massflow is small compared to the slipstream massflow, so that the aerodecelerators do not see a very-hot mixed flow field oncoming out behind the craft. Kevlar is good to about 290-300 F. Nothing magic there. You shed these aerodecelerators for final touchdown. Chutes or ballutes can be recovered after landing for re-use, by-the-way.
The final touchdown is then just standard rocket braking at throttled-up higher thrust. No different than Viking or the Apollo LEM.
How big a thing do you want to fly, and do you want it to be one-shot or reusable? I think we can do it, regardless.
As for ascent, if it's not reusable, leave the heat shield and any aeroshell surfaces at the landing site. Aeroshell surfaces can double as ramps for unloading content, by the way. The very same engines could serve for ascent, if the separable core has propellant tanks and a payload or crew cabin. Leave the descent tanks on the heat shield.
If it's nuke and reusable, just re-fold the unload ramps into an aeroshell, and just fly the whole thing back up.
I'd recommend a more-or-less conical shape, wider than it is tall, for at least the chemical one-shot version, with a slim core on the central axis for ascent. A fully-reusable nuke vehicle could be roughly as wide as it is tall. These sorts of shapes can prevent tip-over in a rough landing. Suspenders-and-belt.
Wild thoughts way outside the box, from an old rocket and ramjet guy who used to do wild-thoughts-outside-the-box for a living. It was called new product development work. Especially for products others thought impossible.
GW

Well I hope Space X are reading this and taking benefit of your advice GW!

GW Johnson · 2012-06-17 12:44:40

Hi Louis:

Actually, I rather doubt anybody who really needs any of these ideas is seeing much of this stuff. (Although, that's how one outfit ran across me, so the odds aren't infinite against.) Life in large organizations gets focused inward fairly strongly. The larger, the worse it is. A.K.A. "not invented here".

I have dreamed up a concept for a chemical lander, but I haven't run any numbers to size out the pieces of it, yet. In the next several days, I'll get that done, and post it in illustrated form over at http://exrocketman.blogspot.com. I still haven't a clue how to show illustrations here, although I've seen others do it.

(My slide rule was never this difficult to figure out.)

After a while, I'll do the same thing for a nuke lander, using old NERVA data. And I'll post that as well. I already know one piece of the answer: the chemical lander will be a lot larger and heavier for the same total dead-head payload deliverable to Mars. That's the penalty one pays for chemical vs nuke Isp. More crap to shoot up to LEO and assemble, plus shooting it 1-way to Mars.

PS - does anybody have a decent figure for the altitudes above Mars where hypersonic entry begins and where speed is down to around Mach 2.5-ish? Or does anybody have a good temperature vs altitude "standard" profile for Mars?

GW

"gas core and pulse propulsion !!"

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#76 2012-04-11 20:04:38

Re: Landing on Mars

#77 2012-04-12 12:10:18

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#87 2012-05-19 17:48:11

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#90 2012-06-01 19:27:50

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