Why use a 70 ton SLS for the 22 ton MPCV???

[dwightlooi]

This is one thing which does not compute.

We can argue about whether a 130~150 ton launch vehicle is necessary for beyond earth orbit manned missions instead of say three Falcon Heavy launches packing 40~53 ton modules doing LEOR.

But the logic behind developing a 70 ton launch vehicle to loft a 22 ton Orion MPCV doesn't make any sense. You can put that on a Delta IV Heavy or a Falcon Heavy. At the very minimum, they should make the MPCV a 70 ton vehicle with a BIG service module and large fuel capacity so it can actually go places. Since the ARES I no longer exists and NASA is not open to launching the MPCV from multiple launch vehicles, there is no longer a reason for the MPCV to be a 22 ton spacecraft. It should make use of the full initial lift capacity of the SLS.

Alternative, they should scrap the SLS and simply work out ways to put the MPCV on other rockets!

[QuantumG]

Hint: it's 70 tons to LEO. The purpose of the MPCV is to go beyond LEO.

I don't think the SLS is "necessary" either, but at least make a coherent argument please.

[dwightlooi]

Hint: it's 70 tons to LEO. The purpose of the MPCV is to go beyond LEO.

I don't think the SLS is "necessary" either, but at least make a coherent argument please.

I understand that. Which is why I was saying that the MPCV should be a 70 ton vehicle with a big fuel load in the service module instead of its current 22 ton guise. This will get you much better performance in BEO injections that a 22 ton vehicle receiving its departure delta Vs largely from a big, heavy shuttle main tank derived core booster because that 8.4m tank, their engines, interstage and the whole nine yards are a good 50 tons at burn out.

That the ARES I no longer exists and the MPCV is not flying on any oter rocket but the SLS means that the MPCV doesn't need to be a 22 ton spacecraft.

[sdsds]

You might want to compare the trajectories that could be reached with an enlarged MPCV service module to those that can be reached by adding e.g. an interim cryogenic propulsion stage (ICPS, aka DIVH upper stage).

[93143]

I was saying that the MPCV should be a 70 ton vehicle with a big fuel load in the service module instead of its current 22 ton guise.

Or, to avoid redesigning the MPCV to be heavier than it needs to be, you could just launch it together with a Delta IV upper stage - the 5-metre one.  The combination isn't as glaring a mismatch with the SLS Block I's payload capacity, and it can send MPCV through most of a TLI, with only a small top-up required from the service module.

Coincidentally, that happens to be the plan...

[Andy USA]

It's lazy to start a new thread when this has all be discussed in length before.

Locked.