Author Topic: Red Dragon Discussion Thread (1)  (Read 559315 times)

Offline Ben the Space Brit

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Re: Red Dragon
« Reply #180 on: 11/08/2011 08:48 am »
My gut tells me that, even if this is a SpaceX-originated mission concept, it could just as easily fly on a different launcher and in a radically different spaceframe.  Only if SpaceX gets the contract will we see it fly in a 'Red Dragon' modified Dragon EDLV.
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Offline yamato

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Re: Red Dragon
« Reply #181 on: 11/08/2011 09:04 am »
is there any new information on how they plan to decelerate the red dragon? Some chutes, or pure rocket engines?

I realised that conceptual drawings show payload to be placed above the engines section. But standard Dragon has significant part of its pressure vessel in central part of engines section (engines and tanks are around the pressure vessel). So there is some free space, which could bi fitted by additional fuel tanks, so the overall dV would be much higher. Maybe high enough to decelerate from supersonic speed to zero.

Offline MikeAtkinson

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Re: Red Dragon
« Reply #182 on: 11/08/2011 10:18 am »
My gut tells me that, even if this is a SpaceX-originated mission concept, it could just as easily fly on a different launcher and in a radically different spaceframe.  Only if SpaceX gets the contract will we see it fly in a 'Red Dragon' modified Dragon EDLV.

There does not seem to be any other launcher that could enable such a mission for $500M, nor would developing a lander from scratch be likely to fit into that budget, even if MSL EDL were reused.

Offline MikeAtkinson

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Re: Red Dragon
« Reply #183 on: 11/08/2011 10:25 am »
is there any new information on how they plan to decelerate the red dragon? Some chutes, or pure rocket engines?

I realised that conceptual drawings show payload to be placed above the engines section. But standard Dragon has significant part of its pressure vessel in central part of engines section (engines and tanks are around the pressure vessel). So there is some free space, which could bi fitted by additional fuel tanks, so the overall dV would be much higher. Maybe high enough to decelerate from supersonic speed to zero.

There is as yet no information about how they plan to do Mars EDL. The easiest step would be to replace the current parachutes with supersonic ones. My gut feeling is that this step would not be quite enough and the standard Dragon would not have enough fuel for a landing. One option would be to add fuel, another would be to lighten the structure, the pressure vessel probably no longer needs to hold pressure, so there could be some savings there.

Offline apace

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Re: Red Dragon
« Reply #184 on: 11/08/2011 10:29 am »
Why not using areobreaking, going into a circular orbit and then to ground. Should save a lot of fuel.

Offline yamato

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Re: Red Dragon
« Reply #185 on: 11/08/2011 10:41 am »
I donīt think so. You can use lift of the capsule to dissipate enough speed from direct entry (like Apollo did), but at some point you get into situation, where the capsule has not enough lift to brake more, but it has still too much speed. And that does not depend on the initial entry velocity.

I like the idea of supersonic chutes combined with final rocket descend. However Dragon would propably still need more fuel than it currently has. The construction would be propably significantly lightened, the pressure vessel does not need to hold pressure.


Offline Ben the Space Brit

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Re: Red Dragon
« Reply #186 on: 11/08/2011 10:42 am »
Why not using areobreaking, going into a circular orbit and then to ground. Should save a lot of fuel.

That's an issue of the life of the Red Dragon's batteries.  Remember, after trunk/SM jettison, the spacecraft would be limited to its on-board stored power.  I suspect that any solar arrays for surface ops wouldn't be deployed until after landing so there will be no way to recharge until then.  You want the battery to last from trunk jettison to landing with comfortable margin in case of problems with the power system.

A lot depends on how critical is hitting a particular landing site.  Direct descent from transfer orbit is at least hypothetically possible using a Dragon-derived EDLV.
"Oops! I left the silly thing in reverse!" - Duck Dodgers

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Offline MikeAtkinson

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Re: Red Dragon
« Reply #187 on: 11/08/2011 10:50 am »
Why not using areobreaking, going into a circular orbit and then to ground. Should save a lot of fuel.

Aerobraking, whether first into a circular orbit and then for entry or as a direct entry is a given. Just aerobraking will lead to the capsule hitting the martian surface at supersonic speeds. Adding supersonic parachutes will lead to it hitting the surface at high sub-sonic speeds, slowing down using just engines is likely to use more fuel than can be carried on a Dragon. A combination of parachutes and engines is likely to be required, the question then becomes "is the current tankage sufficient to hold the fuel?"

SpaceX has probably done the simulations by now and seem to have a solution they think will work, otherwise we would not be continuing to hear about Red Dragon, but what that solution is we probably won't hear for some time.

Offline Comga

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Re: Red Dragon
« Reply #188 on: 11/08/2011 06:46 pm »
Puh-Leze!  Back to the OP! 

More supersonic drag chutes and landing fuel, less cheerleading or mudslinging about SpaceX's prospects for revolutionizing the 21st century or going bankrupt.  Let's stay on the cautious side of the boarder between out-of-the-box and out-of-our-miinds.
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Re: Red Dragon
« Reply #189 on: 11/08/2011 06:53 pm »
As above. Thread needs to be specific. We have an entire SpaceX section for other items of interest. Thread trimmed and reopened.

Ignore the above and I'll get the big stick out ;)
« Last Edit: 11/08/2011 07:54 pm by Chris Bergin »
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Offline go4mars

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Re: Red Dragon
« Reply #190 on: 11/08/2011 08:07 pm »
$500 Megabucks for one Red Dragon.  I wonder if like Spirit and Opportunity, the mission built 2 and selected different locations (perhaps opposite poles), what the savings on the second would be...  Would the potential results justify the incremental expense?  NASA/SpaceX could even launch them in separate temporal windows to reduce risk and keep research staff stream-lined.
« Last Edit: 11/08/2011 08:10 pm by go4mars »
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Offline baldusi

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Re: Red Dragon
« Reply #191 on: 11/08/2011 08:22 pm »
Now that I think of it. Wasn't a problem of aerocapture that they could only land near the equator. But the article said about going to the poles. Wouldn't that mean using the SuperDracos?

Online ugordan

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Re: Red Dragon
« Reply #192 on: 11/08/2011 08:30 pm »
Wasn't a problem of aerocapture that they could only land near the equator. But the article said about going to the poles. Wouldn't that mean using the SuperDracos?

I'm afraid you're not making much sense here. What has aerocapture got to do with landing? The equatorial constraints are mostly solar power and thermal.

Also, any landing with a Dragon would require propulsion.

Offline starsilk

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Re: Red Dragon
« Reply #193 on: 11/08/2011 08:44 pm »
Wasn't a problem of aerocapture that they could only land near the equator. But the article said about going to the poles. Wouldn't that mean using the SuperDracos?

I'm afraid you're not making much sense here. What has aerocapture got to do with landing? The equatorial constraints are mostly solar power and thermal.

denser atmosphere, and more of it (altitude wise) to burn off speed, at the equatorial latitudes.

Online Kaputnik

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Re: Red Dragon
« Reply #194 on: 11/08/2011 09:25 pm »
I would love to know how they are planning to make this work.

Power source? Solar arrays will need new hatches in the OML for deployment; RTGs would cost too much, perhaps not be allowed on such a new LV as FH, and anyway still need hatches for radiators. Either option is far from a trivial modification to the vehicle- it's not necessarily difficult to cut a new hatch, but you need to redesign the pressure vessel to make enough space available.
Similar problems apply with surface sensing and communications arrays .

Thermal and radiation environment beyond LEO is totally different.

And the elephant in the room is EDLS. You just have to compare Dragon to MSL, in terms if heatshield diameter, and then in respective masses.
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Offline Zed_Noir

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Re: Red Dragon
« Reply #195 on: 11/08/2011 09:51 pm »
Solar arrays for a Red Dragon could be partially on the capsule exterior  for minimal usage and a pop out umbrella like array from the top of the capsule. SpaceX can encapsulated a solar array in a sealed canister mounted on the CBM docking mechanism inside the capsule. 

Online Kaputnik

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Re: Red Dragon
« Reply #196 on: 11/09/2011 07:41 am »
External arrays cannot be done in the same way as those on the Trunk, as you need to maintain the shape of the OML; also you need fairly good TPS coverage on the sidewall. You can bet that a Dragon attempting to land on Mars will make the maximum possible use of LD and therefore sidewall heating will be harsh.
The nose cap would indeed make a good place to deploy the other arrays from, though.

Do we know how a spherical-section heatshield works in a CO2 atmosphere? All successful Mars landings to date have used a 70 degree sphere-cone shape.
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Offline Ben the Space Brit

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Re: Red Dragon
« Reply #197 on: 11/09/2011 09:10 am »
I suspect that the surface solar arrays will be an 'umbrella' configured array inside what would be the docking port on an LEO Dragon.  It would remain folded until after landing after which it, and likely the high-gain antenna, would deploy vertically through a pseudo-CBM hatch.
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DON'T PROPAGANDISE, FLY!!!

Offline Zed_Noir

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Re: Red Dragon
« Reply #198 on: 11/09/2011 09:18 am »
Partial exterior solar array on a Red Dragon should be like a 20cm band just below the nose cone. For very minimal  power generation to keep the capsule in standby mode until the main solar array is deploy. Perfectible mechanistically.

Online Kaputnik

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Re: Red Dragon
« Reply #199 on: 11/09/2011 12:48 pm »
Does a standard Dragon have all of its electronics inside the pressure vessel? And is everything vaccum-rated in case of emergency depressurisation?
Just the more that I think about this, the more it becomes apparent that the pressure vessel is going to have to have so many things inside it needing access to the outside that it will almost certainly have to be vented.
"I don't care what anything was DESIGNED to do, I care about what it CAN do"- Gene Kranz

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