Monday, December 10, 2012

Dragon-LP



Sending humans in a SpaceX Dragon v2 capsule to EML-1 or 2 is a worthwhile possible step in a 100% commercial return to the Moon. The SuperDraco thrusters to be included in the sidewalls of the crew Dragon capsule are more than capable of performing the trans-lunar injection burn, as well as station keeping at the Lagrange point, rendezvous with any preemplaced assets - such as a lander - and returning the crew to Earth.

The total delta-v for such a bare bones mission to EML-2 is a mere 4835 m/s. EML-1 is similar. This is a "quick transit" 4-day trip up to EML-2, so the crew spends less time in the radiation belts. A good estimate of the dry mass of the Dragon v2 is 8000 kg. Using an isp of 320s, the initial mass in LEO is just 37344 kg, or 68% of the maximum payload mass of a Falcon Heavy.

Just going to a Lagrange point with a crew on Dragon would be a momentous achievement and could be done for a mere $150M. However, it is just the first step.

If we fill the remaining Falcon Heavy payload mass with fuel, the total delta-v available to the Dragon becomes 6050 m/s. This is sufficient to go from LEO to EML-2 to low lunar orbit and back to Earth, with significant margin for maneuvering and rendezvous, if required.

What might the crew in the Dragon rendezvous with at EML-1, EML-2 or low lunar orbit? Using the same SuperDraco thrusters to take the slower 9-day transit - a delta-v of just 3470 m/s - 18.2 tons of payload can be delivered to EML-2. This payload can loiter for months waiting for the crew to arrive. Up to 14.8 tons can be deployed from EML-2 to low lunar orbit when required. Up to 6.2 tons can be landed on the surface if the lander is taken via low lunar orbit, or up to 8.1 tons if taken directly from EML-1 or 2.

This is all possible because I have avoided two pitfalls of lunar return architectures that have become very common in recent years.

Firstly, I have ignored the possibility of using the second stage of the Falcon Heavy to perform any part of the trans-lunar injection burn. A simple trade study shows that it is not advantageous when you have sufficient thrust on the payload - which you must have to do later maneuvers - so I'm baffled as to why people keep considering it.

Secondly, I have not used any high isp propulsion such as LH2/LOX or CH4/LOX. Although this may become preferable in future lunar architectures (especially if propellant made on the Moon becomes available), it is currently an additional expense which does not provide significant advantage to justify its cost.

7 comments:

  1. What is Dragon v2? Is that just the version with the Superdracos? For the mass you quoted of 8,000 kg should that be the gross mass?
    I like the fact you are arguing in this post and in your prior "humans on the Moon soonest" post that such missions with the Falcon Heavy can be done for a few hundred million dollar cost.
    That is a very important fact in regards to profitability and illustrates why it is key that SpaceX be brought on board. We just have to get Elon interested in Moon missions.


    Bob Clark

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    1. The "Crew Dragon" is Dragon v2, yes.

      I used 8,000 kg as the "dry" mass, fully loaded with crew, supplies, etc, for a lunar mission.. aka, everything but fuel.

      Indeed, a since launch to get to EML-2 is nice and if Falcon Heavy ends up as cheap as SpaceX says it will, it'll be unchallengeable.

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    2. Care in naming is required because you are talking about a 3.7m diam. capsule with superdracos. The Dragon 2 is a 5m. diam. for landing on mars.

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  2. Do you think that somewhere, buried deep inside of NASA, there is someone who has also figured this out, but dares not speak the truth of his/her convictions?

    Or did and got shot down in flames?

    Because your proposal is absolutely top notch.

    Have the folks at Golden Spike reached out to you?

    Can I vote for you as NASA Administrator?

    That would rock.

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  3. Trent as NASA admin? Sounds like an episode of sliders. I'm in.

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    1. Imagine Ron Swanson from Parks And Recreation. (If you've never watched that show, do.)

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    2. Haven't, but will now that you've recommended it.

      Delete