Red Dragon Discussion Thread (1)

[simonbp]

Roughly speaking, the magnitude will be the planetary escape velocity at the top of the atmosphere minus the difference in orbital velocities (approximately the second delta v in a simple Hohmann transfer). This assumes an entry point precisely on the sunward side of the planet. To maximize aerodynamic braking in the thin Martian atmosphere, Mars entries are always initially horizontal.

Most entries (MSL included) fall slowly until the air builds up enough to allow them to pull up to the top of the atmosphere and effectively begin entry again. The earlier slides on this thread showed Red Dragon doing exactly that.

[Joris]

I'm doing some modeling in MATLAB. What is a typical velocity vector (speed and direction) for Mars entry at, say, 200km?

Do you have a model that describes atmospheric density for Mars?

[Robotbeat]

I'm doing some modeling in MATLAB. What is a typical velocity vector (speed and direction) for Mars entry at, say, 200km?

Do you have a model that describes atmospheric density for Mars?

Yeah, an exponential model works well enough for what I'm doing. The scale height of Mars's atmosphere is 10.8km and the density at "zero" altitude is .02kg/m^3 (does anyone have a better figure?). The atmosphere gets exponentially thinner (assuming temperature is ROUGHLY constant) as you go up because of PV=nRT. A more detailed model would obviously be needed for mission planning, but this works for figuring out the EDL needs.

[Robotbeat]

Roughly speaking, the magnitude will be the planetary escape velocity at the top of the atmosphere minus the difference in orbital velocities (approximately the second delta v in a simple Hohmann transfer). This assumes an entry point precisely on the sunward side of the planet. To maximize aerodynamic braking in the thin Martian atmosphere, Mars entries are always initially horizontal.

Most entries (MSL included) fall slowly until the air builds up enough to allow them to pull up to the top of the atmosphere and effectively begin entry again. The earlier slides on this thread showed Red Dragon doing exactly that.

I'm going to (pessimistically) assume no lifting reentry for my simple modeling. Obviously, "Red Dragon" will be able to get significantly better performance with a lifting reentry.

(Many Mars landing missions have used non-lifting EDL, which is simpler.)

[simonbp]

Prototype hardware!

Honeybee Robotics is already working on the drills for Red Dragon: http://www.flickr.com/photos/planetaryblog/6985258587/

More Honeybee goodies: http://www.planetary.org/blog/article/00003421/

[Robotbeat]

Prototype hardware!

Honeybee Robotics is already working on the drills for Red Dragon: http://www.flickr.com/photos/planetaryblog/6985258587/

More Honeybee goodies: http://www.planetary.org/blog/article/00003421/

I thought this was interesting:

Moving on to new ideas, here's VP Kris Zacny showing off a huge drill for Mars subsurface sample acquisition. They have field-tested it in Antarctica (working with Chris McKay), and they have tricky ways of delivering samples from different depths below the surface to waiting science instruments. He also talked about how they've worked with SpaceX to figure out how the "Red Dragon" -- a Mars lander based on SpaceX's Dragon capsule -- might take not one, but two of these beasts down to land on Mars. They'd sit inside the capsule, and drill right through Dragon's heat shield to get to Martian soil, delivering the samples back inside the capsule to instruments.

Ha! I didn't see that one coming.

[deltaV]

Drilling through the heat shield sounds like a great way to find organic residues on Mars. Residues that are signs of life so advanced that it has conquered orbital reentry. That said I could see drilling through the heat shield cutting cost enough to be worth the risk of contaminated data.

[go4mars]

Yes!!  I love guessing right.  Though some might argue that my guessing is voluminous enough that I had to get one sooner or later. 

A drill that only has to penetrate the dragons hull then 1 m of ice could be pretty simple and light. 

Idea:
Inside dragon ... a drill with a diamond coring-bit descends, cuts through the dragons hull, and 1 meter into the surface.  The core is retracted, and passes vertically up through a gauntlet of active and passive tests and imagers (with the more destructive tests near the top).  Then the data/results get transmitted back (via MRO?) before the dragon expires. 

I hope I guess right that they could pack in a tiny ISRU methane rocket test with the excess downmass capability. 


This guy points out another cool thing that would be a shame not to send along if there is excess downmass capacity.

An experiment of this type was already developed for the cancelled 2001 Mars Surveyor Lander mission.  When the lander was re-purposed as Phoenix, it was not flown.  I haven't seen any reference as to if the flight hardware still exists.

http://www.lpi.usra.edu/meetings/marsmiss99/pdf/2503.pdf

 

[simonbp]

Drilling through the heat shield sounds like a great way to find organic residues on Mars. Residues that are signs of life so advanced that it has conquered orbital reentry. That said I could see drilling through the heat shield cutting cost enough to be worth the risk of contaminated data.

Actually, I think part of the point is precisely to reduce contamination; a door could release material from inside the lander to the surface. Drilling through the heat shield releases only heat shield material that can be well-characterized on Earth beforehand.

Also, PICA-X doesn't have organics; it's a silicate ceramic.

[deltaV]

Doesn't PICA stand for Phenolic Impregnated Carbon Ablator? Aren't phenols organic?

[Nathan]

Doesn't PICA stand for Phenolic Impregnated Carbon Ablator? Aren't phenols organic?

I think the point is that the heat shield material is known and can be accounted for in any sample analysis.

[dcporter]

What if Martian life is PICA-X based?

[Ben the Space Brit]

What if Martian life is PICA-X based?

They could also be titanium-based and thus be indistinguishable from shavings from the hull; you can't plan for everything, you know!

[baldusi]

I've been thinking. And couldn't they modify the Red Dragon heat shield to be disposed before landing? It would also save fuel for powered landing. If not the whole shield then a couple of tiles through which the drills would pass.

[Chris-A]

If Red Dragon is depressurized, the vessel structure could have holes for the drill bits to pass through.

[Robotbeat]

I've been thinking. And couldn't they modify the Red Dragon heat shield to be disposed before landing? It would also save fuel for powered landing. If not the whole shield then a couple of tiles through which the drills would pass.

That's what Soyuz does, right?

I think, though, is that the whole idea of Red Dragon is to reuse the Dragon capsule with minimal alteration.

[baldusi]

If Red Dragon is depressurized, the vessel structure could have holes for the drill bits to pass through.

We don't know if the require the pressurization for structural purposes. In any case drilling through aluminum is way easier than through rock. And there's lost of experience on doing it. So that shouldn't be a problem. The PICA-X shouldn't be a problem, either. But the drill requirements are very different. And the only issue you might have is the carbon contamination.
On the other hand, they did talk about using a pneumatic system to extract and move around the samples. It might also be used to blow off the PICA-X residues.
I still think that drilling through the hull is genius. It solves most of the problems that I had foreseen for the Dragon. In fact, if they use the pneumatic system, they might want to keep the whole thing airtight, keeping the rest of the Dragon cabin pressurized and thermally controlled. Genius.

[corrodedNut]

The landing legs are already going to protrude though the heat shield, would a drill be any harder? They could locate the drill near one of the legs and share the opening.

[kirghizstan]

If Red Dragon is depressurized, the vessel structure could have holes for the drill bits to pass through.

We don't know if the require the pressurization for structural purposes. In any case drilling through aluminum is way easier than through rock. And there's lost of experience on doing it. So that shouldn't be a problem. The PICA-X shouldn't be a problem, either. But the drill requirements are very different. And the only issue you might have is the carbon contamination.
On the other hand, they did talk about using a pneumatic system to extract and move around the samples. It might also be used to blow off the PICA-X residues.
I still think that drilling through the hull is genius. It solves most of the problems that I had foreseen for the Dragon. In fact, if they use the pneumatic system, they might want to keep the whole thing airtight, keeping the rest of the Dragon cabin pressurized and thermally controlled. Genius.

I wish i could have been at the moment when someone was like, here is an idea, why don't we just drill through the hull. 

[Danderman]

I've been thinking. And couldn't they modify the Red Dragon heat shield to be disposed before landing? It would also save fuel for powered landing. If not the whole shield then a couple of tiles through which the drills would pass.

That's what Soyuz does, right?

No, but the Almaz VA did have a hatch in its heat shield.