Saturday, August 14, 2010

Mission To Asteroid Using SpaceX Hardware - NASA's Target

As a target of study, NASA has identified the asteroid 1999AO10 as the 2025 destination for human exploration. We've heard that NASA plans to build a giant heavy lift vehicle to make the trip, but is it really necessary?

I previously described a human asteroid mission, but I assumed the logical choice of asteroid with the lowest known delta-v (and included analysis for the second lowest too), but for some reason this isn't as interesting to NASA, so let's consider how one might do the trip to their preferred target, using existing SpaceX hardware.


The reference numbers are: Earth departure stage 3291m/s, and storable propellant 3939m/s of total delta-v. We could improve this by carefully measuring the boiloff of LOX in Falcon 9 upper stages and analyzing the required insulation to do the arrival rendezvous using non-storable propellants, but I don't really have that information handy, so I'll just go with the storables.

Like last time, we'll use the Dragon spacecraft as our crew vehicle. Unlike last time we'll actually have a look at the thrusters, it uses 18 Draco thrusters which are similar to the Aerojet 445 in performance with 309s of ISP. The Dragon is carried to orbit on a Falcon 9 with 3000kg of payload in the "trunk", 3000kg of payload pressurized (that includes the astronauts), and 1290kg of storable propellant, giving a dry mass of around 1710kg. To provide 4710kg (dry mass + pressurized payload) with a total of 3939m/s of delta-v requires a gross mass of 19544kg, which means the external tank will be 13544kg when filled.

The Earth departure stage will be the Falcon 9 upper stage, with the Merlin 1C vacuum performance of 342s ISP. The total initial mass in low Earth orbit is therefore 56710kg. Meaning 37166kg of that is LOX/RP-1. With a mixture ratio of 2.56, that means 10440kg of RP-1 and 26726kg of LOX. (btw, if we had a Raptor stage the IMLEO would be 46328kg, and presumably mass-to-LEO of each flight would be bigger, but the boil-off analysis would be completely different, as you'll see).

Ok, so we have all the numbers we need, now we just have to decide what order to launch it all in to reduce the total mission risk. Storable propellants are called that because they can sit without being used for long periods of time and be ready to go when needed. Also, they don't suffer from boil-off when stored on-orbit, or at least not so much as we need to care in this kind of analysis when compared to cryogenics like LOX. As such, I'm of the opinion that the best strategy is to launch the storable propellants in the external tank, and the RP-1, first.

This is a total of 23984kg and includes some of the mass for the tanks to contain the propellants. So we're looking at two Falcon-9 flights with a shortfall of 3084kg. If an initial parking orbit is chosen well, these first two flights can be spread out over as long a time period as desired, limited only by orbital decay.

We now need to deliver 26726kg of LOX, along with the remaining 3084kg of non-cryogenic propellants, for a total of 29810kg. These three Falcon-9 flights will deliver 1540kg of excess LOX which should account for boil-off if the flights are launched without delays. At 0.1% per day boiloff, the launch campaign must be complete in 50 days. But we have an ace up our sleeve.

The final flight of the launch campaign is the manned Dragon. It will be carrying the crew, with all their provisions, on-board propellant, some of which will be used for rendezvous and orbital assembly activities, and 3000kg of LOX in the trunk. Carrying cryogenics in the trunk may seem risky, but it has such an awesome payoff on cryogenic boil-off that it's worth it.

As described in the NASA concept, the mission departs the low Earth parking orbit, and arrives at the asteroid 3.5 months later. The astronauts stay on the rock for 2 weeks, then return to Earth a month later. The entire trip is 5 months. Radiation exposure is similar to a year long stay on the ISS, about half of an astronaut's lifetime limit.

Because of the suboptimal choice of destination, the new mission has five tanking flights at $56M each, and the manned Dragon flight which I estimate at $150M, for a grand total of $430M. This is about 100 times less than what I expect NASA will spend trying to do the same thing.

8 comments:

  1. Maybe think of this as a business opportunity.

    If NASA/Congress formally declare an intention to go to 1999AO10 in 2025, and if the private sector can get to 1999AO10 for say 10% of NASA's budget, then what would the marketing rights be worth for a private company to have its private astronauts arrive at 1999AO10 shortly before NASA arrives?

    Think of the product placement opportunities if these private sector astros could offer the NASA astros a branded cold drink while at 1999AO10.

    Hmmmm . . .

    This is a nice scenario for a novel ;-)

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  2. You're expecting the astronauts to spend five months in a Dragon capsule? That isn't optimal. The Dragon is for getting people up and bringing them down through earth's atmosphere. Trying to force it to also be a habitat capable of a five month journey is bad mission creep.

    Better to take advantage of something that is designed to hold people for longer periods - the Bigelow inflatable modules. Use an orbit trailing your propellant depot by a few kilometers as a staging area for assembling your manned asteroid mission. Send up a Bigelow module on Atlas or Delta or Falcon or Taurus or whatever, send up a Dragon full of paraffin bricks for lining the inner walls of the Bigelow ... you could double or even triple the total number of flights and have a much more capable asteroid mission (while bringing multiple technologies up to TRL9), and still probably spend an order of magnitude less than NASA spent on Ares in the last five yeas.

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  3. Sound good Ed, what's the mass of a Bigelow module?

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  4. I think Ed's statement about the capsule matters with how many astronauts its going to carry. I would not expect to need more than two astronauts on this sort of mission. Maybe even one. You need some spare mass for all the billboards you are going to plant on the asteroid before NASA gets there. And spraypaint to put a big company logo on the face of the asteroid. Maybe send Banksy the graffiti artist as the second seat.

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  7. Quantum G, can you run this analysis with a Falcon Heavy rather than a Falcon 9. If so, what does it buy you? Fewer flights?

    I agree with Ed. Five months in a Dragon is a no-go. It does not have the radiation protection or the room for even one person to survive in good physical and mental health.

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  8. The long stay in Dragon capsile can be made tolerable the same way the Russians do it with Soyuz. Use a light weight habitablility module on the front of the Dragon that's discarded on reentery (Bigelow?). The fuel in the trunk could be used as directional solar shielding.

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