We don't need no stinking capsules...

On 05/14/2010 07:48 PM, David Spain wrote:
Jorge R. Frank wrote:
Too expensive to develop for commercial crew to ISS so the commercial
providers won't go for it.

I "get" this idea, but then I also "don't get" this idea.
It may be more expensive to develop but what about the real costs and those
are the recurring costs to operate? Esp. if that capsule requires water
recovery ops? Who's really paying the tab? The providers or NASA?

The basic concept of both COTS and CCDev is that both pay. NASA provides
money for reaching development milestones but deliberately does not pay
the entire development cost of the vehicle. That requires the commercial
provider to seek private investment to cover the rest, ensuring that
they have "skin in the game" and that they will be diligent about
producing a design that is commercially viable.

Designs that are more expensive to develop carry higher risk to capital
and so will be less likely to attract private investment.

Not suitable for evolution to beyond-LEO re-entry so NASA won't go for
it.

Hmm. In the days of Apollo when we didn't have long term presence in LEO
(Salyut notwithstanding) that made sense. But today, with ISS likely to be
around for some time and possibly more return from LEO options on the
way, why is this necessary? Why not "abort to" and "return to" LEO as
suitable options for beyond LEO missions?

Because "abort to" and "return to" LEO require shedding 3+ km/s of
velocity somehow. Doing it propulsively requires lugging all that
propellant with you. Doing it with single-pass aerocapture (required to
prevent subjecting the crew to multiple lengthy passes through the Van
Allen belts) subjects the spacecraft to a high heat load so it will need
a heat shield anyway. It costs very little extra mass to make that heat
shield capable of direct entry (certainly far, far less than the
propellant mass needed to brake into LEO) and that opens up the "abort
to surface" option. At that point you might as well make it the baseline
anyway.

Most designs aren't suitable for brake-into-LEO anyway, since they
usually have a service module covering the heat shield that carries most
of the propulsion and life support. They'd have to jettison the SM prior
to aerocapture, and once that's done, they're pretty much screwed in
terms of actually being able to rendezvous with something within the
remaining lifetime of the crew module.

So direct entry will be the preferred mode of return from beyond-LEO
trajectories for decades to come, I believe.