In article ,
says...

On 2020-01-03 09:58, David Spain wrote:

The original plan for Dragon V2 called for propulsive landing using the
same Super Dracos used for the launch escape system that proved
problematical last year.

I had wondered about how SpaceX had planned its propulsion for it. So
they would have been thottleable with wide range of thrust?

Yes. Super Dracos can throttle over a wide range. Each of the four
propulsion pods on the side of Dragon 2 has two Super Draco thrusters.
So there is also a lot of redundancy built into the system.

Does the removal of powered landing allow SpaceX to put significantly
less fuel in it? or would propuslive landing take about as much as
launch abort?

No, because that propellant is needed in case of a launch abort. Only
in the case of a nominal launch would that propellant have been used for
a propulsive landing. In the event of a launch abort, Dragon 2 would
have used parachutes to splash down in the ocean. So, in a nominal
launch, the landing propellant is essentially "free" since it had to be
there anyway in case of an abort.

On a nominal launch, Starliner uses its abort propellant as orbital
insertion propellant. And in the case of a complete failure of
Starliner to perform that orbital insertion burn, it will simply reenter
as Atlas V puts it into an orbit whose low point is within the earth's
atmosphere.

With regards to the failure, it would have happened in the same way,
with SpaceX finding out about the not-so-one-way valve and fixing it.
And testing it again until it was considered as trustable.

This is why SpaceX performs a lot of tests. Test as you fly; fly as you
test. This enables both rapid development and increases safety in the
long run.

With regards to the landing legs, I assume they folded back up onto the
side of the capsule?

No. They would have been driven by linear actuators through the base of
the heat shield. Much in the same way that the shuttle orbiter's
landing gear doors were on the underside of the space shuttle.

Could one conceive of a system where there are "mattresses" on the
ground at the landing site and the capsule lands on them instead of
having legs? (and in case of emergencies where de-orbit can't wait for
proper alignment, then they would have to land on a lake/ocean).

So airbags you have to hit precisely instead of incorporating them into
the spacecraft? Not a good idea. In a contingency landing, you would
not have the ability to hit the "mattress". Better to put the airbags
on the spacecraft as Starliner does.

I suspect the other issue for NASA was the potential of compromise to
the heat shield due to the landing legs.

Doesn't Starliner have to compromise heat shield too in order for it to
open up and let the giant balloons inflate?

No more so than Mercury did or any of the Mars probes that dropped their
heat shields before landing (pretty much all of them did this, from what
I remember).

Why was the Friendship 7 Mercury heat shield detachable?
https://space.stackexchange.com/ques...he-friendship-
7-mercury-heat-shield-detachable

Jeff
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