Dragon LAS as BEO ascent stage

[docmordrid]

Neat, I had a verbal description of just that ready to go, but there it is!

Found the session PDF's for a water rover and the ISRU plant, but not for the Dragon sample return.

http://www.lpi.usra.edu/meetings/marsconcepts2012/pdf/sess103.pdf

ISRU water rover: http://www.lpi.usra.edu/meetings/marsconcepts2012/pdf/4268.pdf

ISRU plant: http://www.lpi.usra.edu/meetings/marsconcepts2012/pdf/4224.pdf

[dwightlooi]

Another data point: the claim is that the Super Dracos on Red Dragon decelerate it from Mach 2.28 to 0, which I calculate to be about 550 m/s. (Assuming 1 mT delivered to the surface.) This matches up with meekGee's post.

If we knew the mass of the Dragon tanks when full, we could get closer to a definitive calculation, but it's looking like a descent stage is going to be needed if you wish to return to LLO. And the only reason I can think to take a full Dragon down and up again is for a minimal manned mission. Are there others?

Not quite...

Atmospheric drag alone will get you to about Mach 1~1.5 depending on the drag of the vehicle -- actually let's call Mach 1 1200km/h instead of Mach 1 because Mach 1 on Earth is not the same as Mach 1 Mars and Mach 1 in Space is 0! A parachute can get you to about 300~350 km/h, but since the SpaceX video shows no parachute the best case scenario still gives you a need to decelerate and land on propulsion from about 1200 km/h or ~333m/s.

The Dracos are definitely powerful enough for a thrust to weight ratio of > 1 over the Dragon's 4 ton dry mass. It's 6 tons of payload is definitely enough for enough propellant fraction to effect that Delta V. The only question is how much (non-fuel) payload is left!

For a pressure fed MMH/N2O4 engine we can expect at least 250 secs of Isp, probably closer to 265.

* Total Delta V potential of the Dragon Space Craft = 265 x 9.8 x ln (10 / 4) = 2379 m/s

* Propellant needed for a 330 m/s delta V potential = 10 - 10 / e^330/(265 x 9.8 ) = 10 - 8.807 = 1.193 tons

If we carry nothing but fuel, the Dragon can achieve almost 2400 m/s of total delta V. That's way more than the 330 m/s we need to land. That's also way short of the 3700 m/s we need to get from the martian surface to low mars orbit. Hence we can conclude that:-

* The Dragon cannot plausibly land on Mars and get back to orbit on its own

* The Dragon can do a propulsive landing on Mars with a Payload of ~4.8 tons -- not bad!

[QuantumG]

Allow me to channel Jim.. ummm... ummmm.. we call upon the mighty Jim to join us in this thread.. ummm...

Jim voice: no.

Whoosh, I'm back. What'd he say?

Never mind, I can guess.

[adrianwyard]

Interesting. SpaceX are claiming only 1 mT to the Martian surface (and minimum aerobraked velocity of M2.8, i.e. faster than terminal velocity).

Where do you think the discrepancy comes from?

(QuantumG: Regardless of what Jim thinks of this thread, I personally am learning a thing or two.)

[Ben the Space Brit]

Maybe I'm misunderstanding this thread but, to me, what is really being asked here is: Can Superdraco be used as a MPS for a lander/ascender of some kind? Can you use clusters of Superdracos on a vacuum lander hull and sell it to NASA to use for NEO rendezvous or lunar landing?

So: NOT Dragon as a lander, although the pressure vessel tooling might be reused as would elements such as the Dragonrider's rendezvous and landing sensors, the ECLSS, navigation computer and power system.  However, the resulting lander would look very different to Dragon because it would have different requirements and wouldn't need re-entry shielding and aerodynamics for ascent (it would ride in a FH's PLF).  The engines would likely be a bottom-mounted pusher rather than sidemount too.

FWIW, I think that Superdraco would probably need a better expansion nozzle to be more effectively used as an MPS.  Right now, everything is about thrust, both for abort and landing.  An MPS version would need better vacuum Isp.


[edit]
Fixed typos

[adrianwyard]

Agreed. But a highly modified Dragon has taken us into the realm of pre-powerpoint thought experiment.

I don't see SpaceX doing this mod on their own, nor do I see NASA coming to SpaceX if they wanted to get to the Lunar surface.

If (big IF) Red Dragon projects were green-lit, then I could see some minor value in testing components on a moon-bound mission, e.g. long-ish duration, and deep-space comm. If it can land on the moon, then why not have a go. If a sample-return Red Dragon were developed down the road then that could demo returning moon rocks (from a custom sample ascent stage).

I wonder what price you could sell a new batch of lunar samples for. Can you even sell them, legally?

And you could argue there would be significant PR value in being the first commercial craft on the moon, but is there enough here to justify the cost? I don't think so.

[Ben the Space Brit]

And you could argue there would be significant PR value in being the first commercial craft on the moon, but is there enough here to justify the cost? I don't think so.

Others have rightly pointed out that Elon isn't entirely in it for the money.  What really interests me is the idea that SpaceX would enable exploration from those who can't normally afford it.  "We provide the technology, you provide the astronauts!" Literally kicking down the door of human space exploration and allowing anyone who can afford their prices to have an HSF-X program.

It might be worth it just to watch people of certain opinions point at him and scream "treason" at the top of their voices in impotent rage.

[rst]

Others have rightly pointed out that Elon isn't entirely in it for the money.  What really interests me is the idea that SpaceX would enable exploration from those who can't normally afford it.  "We provide the technology, you provide the astronauts!" Literally kicking down the door of human space exploration and allowing anyone who can afford their prices to have an HSF-X program.

It might be worth it just to watch people of certain opinions point at him and scream "treason" at the top of their voices in impotent rage.

Congressmen of certain opinions are far from impotent.  Rocketry is weapons technology and regulated as such.  Joint operations with, say, ESA probably wouldn't be too controversial, but work with, say, India (let alone China!) would likely attract the wrong kind of attention really quick. 

(Off topic, I know, but the topic is silly to begin with...)

[mikes]

Would you call a Lunar mission Blue Dragon, perhaps? (Or Cheese Dragon?)

Soup Dragon, obviously!

(in memoriam Oliver Postgate)

[QuantumG]

I don't see SpaceX doing this mod on their own, nor do I see NASA coming to SpaceX if they wanted to get to the Lunar surface.

Resupply to a lunar base.. of course NASA doesn't care about the Moon anymore.

[adrianwyard]

Would you call a Lunar mission Blue Dragon, perhaps? (Or Cheese Dragon?)

Soup Dragon, obviously!

(in memoriam Oliver Postgate)

Now you mention it, Soup Dragon is a pretty good name for the SpaceX CRS spacecraft - there has to be some soup sent to the ISS...

[Robotbeat]

Would you call a Lunar mission Blue Dragon, perhaps? (Or Cheese Dragon?)

Soup Dragon, obviously!

(in memoriam Oliver Postgate)

Now you mention it, Soup Dragon is a pretty good name for the SpaceX CRS spacecraft - there has to be some soup sent to the ISS...

And if there's an abort of some kind, you can say... (I think you can figure it out.)

[A_M_Swallow]

Others have rightly pointed out that Elon isn't entirely in it for the money.  What really interests me is the idea that SpaceX would enable exploration from those who can't normally afford it.  "We provide the technology, you provide the astronauts!" Literally kicking down the door of human space exploration and allowing anyone who can afford their prices to have an HSF-X program.

It might be worth it just to watch people of certain opinions point at him and scream "treason" at the top of their voices in impotent rage.

Congressmen of certain opinions are far from impotent.  Rocketry is weapons technology and regulated as such.  Joint operations with, say, ESA probably wouldn't be too controversial, but work with, say, India (let alone China!) would likely attract the wrong kind of attention really quick. 

(Off topic, I know, but the topic is silly to begin with...)

That will depend on the ITAR rules for spacecraft passengers.  These may be different from the ITAR rules for pilots and repairmen.

[dwightlooi]

I don't think the Dragon is suitable for Moon (return mission)...

The Dragon is a heavy, pressurized capsule designed for atmospheric entry. The Dragon weighs 4.2 tons with it's trunk, 3.2 with the re-entry capsule alone. It is rated for 6 tons of payload, of which up to 3.3 tons may be pressurized within the capsule with the rest being external (in the trunk).

Even if we assume that we are able to use all 6 tons for fuel, and the landing legs and tanks weighing nothing -- which won't be the case -- we still don't have enough Delta V to get an empty vehicle on the moon and back up to Lunar Orbit. For that we need about 3.7~4 km/s of total Delta V potential. Starting at 9.2 tons with 6 tons of fuel and about 309 Isp for the thrusters, we end up with a total Delta V of 3.2 km/s. That's not enough to land and get back up. We can however land with 2 tons of payload burning about 4 tons of fuel. We just can't get back up.

Mar's is easier to land on actually, If you can get the capsule to slow down to about 0.5km/s (1800 km/h) via the vehicle's drag through the atmosphere during re-entry and, if necessary, a parachute. All you need is just 1.5 tons of propellant for a powered landing. That leaves 4.5 tons for payload assuming you don't need any additional landing associated hardware.

That heavy structure in pressurized, atmospheric re-etry capable designs really means that the propellant fraction is going to be rather bad. This is why the Lunar Module was built like an like a tin car and leaves half of its structure behind.