Wrong Way Round

I’ve just noticed something odd about the configuration of the Earth Departure Stage (EDS) and Orion, with the Lunar Surface Access Module (LSAM – which I’m now reading is to be called Altair).

After Earth Orbital Rendezvous the stack will then depart for the Moon, with the EDS (effectively the Ares V 3rd stage) providing the thrust. It’s just that the thrust is the wrong way. The astronauts will be accelerating in the opposite direction to that in which they left Earth. They will accelerate in the -x direction, rather than +x. The cone of the CEV will be accelerating blunt end first rather than sharp end first as they will for the other main acceleration phases of any mission, including transEarth injection (TEI) and reentry/landing.

I can imagine astronauts basically suspended in their harnesses as the up they were familiar with on take off becomes down. I can’t imagine it is easy to design couches that are reversible in this way.
This just doesn’t seem right. The acceleration of the EDS stack must be significant, and will be several minutes in length if it is anything like Apollo/Saturn. You’ll recall that the Apollo/Saturn TLI stack, with the SIVB pushing it, was in the same +x axis as at launch, TEI and reentry. How will astronauts cope?

So, have I just ruined a whole vehicle development programme, or am I missing something, or is the problem just not as serious as I think it must be?

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One Response to “Wrong Way Round”

  1. Reid Penner Says:

    I think its a very interesting observation, but i don’t think its as big of an issue as you think it is.

    Granted, my math shows a peak acceleration of 8.7 g of the S IVB, which is of similar design, and uses the earlier J-2 engine, according to wikipedia (i know, it can be unreliable, but i think it can still hold valid info), the EDS will only be throttled up to 80% for TLI. By my math, that still puts it at 7 g, at maximum acceleration. ( assuming the tanks are burnt dry)

    http://en.wikipedia.org/wiki/Earth_Departure_Stage#Mission

    I’m no expert on the matter either, but remember that these accelerations are maximums, and should be expected only near the end of the burn. Therefore, in my humble opinion, i think that the reverse seating is not a major issue. (The burn time of the S IVB was also only around 8 minutes, as well)

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