Tuesday, May 14, 2013

Reentry a big problem?

Since I can't respond there I will respond here. Jim Hillhouse said with regard to an earlier post:
Reentry is going to be a big problem.
Not really, which requires me to explain.

Jim's assertion is only true for a very narrow restrictive mission. For a more realistic mission it falls apart. Orion is a reentry vehicle. Sundancer is not. For long duration missions beyond the moon, Orion simply isn't up to it while costing more than the Sundancer even if you add the cost of retrieving a Sundancer crew from orbit using a Dragon. Orion, by trying to be both a transit and reentry vehicle fails at both except for certain minor, mostly unimportant and wasteful, missions.

Everybody seems to be realizing this which is why you see the addition of expansion modules in many mission designs. They do that because they are starting with the wrong craft to begin with.

Elon realizes this, which is where the MCT comes in. I hope he's successful with it, but it too may be based on a flawed premise. Vehicles should be designed for the environment they will operate in.
  1. To and from orbit.
  2. From orbit to orbit.
Vehicle 2 should be a different vehicle from vehicle 1. Vehicle 1 will be a different vehicle for most planetary bodies except those small vacuum moons which may all be able to use the same vehicle.

One day we may have ships that include their own landing craft. We aren't there yet. The way to do things now depends on if you are talking about the earth or someplace else. For the earth we have options now and soon from now all of which are better than the Orion for just getting to and from orbit. For other destinations, the Orion fails because it can't land there anymore than a Sundancer can. For those situations, the least cost method would be to send a specific lander or lander/accent vehicle ahead on a low cost trajectory.

The Orion, while designed for up to six can only take two at most for longer missions. Even those longer missions fall short of the need because they simply do not have the storage space for longer which most mission would be.

Getting a vehicle to orbit is costly. You reduce that cost for type 2 vehicles by doing it only once. You then reuse that vehicle for multiple missions significantly reducing costs. The only way you could possibly argue with this is with a wasteful strawman mission of no significance. Without a bogus mission of no importance, Orion has no mission at all.

Update: related.

SpaceX poised on the edge.

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