In article om,
says...

On 2017-09-24 08:43, Jeff Findley wrote:

itself during descent, even when the Super Dracos aren't firing. This
is quite similar to Falcon 9 first stage landings where the Merlin
engines only fire briefly for boost back, reentry, and landing.


And how many stage 1s were lost before SpaceX got it right?

The aerodynamics of Dragon are easier and well known at this point.
Dragon V2 isn't much different aerodynamically from the current cargo
Dragon.

For the initial test flights for Dragon, NASA should have let SpaceX try
landings on land. SpaceX could have debugged it and gotten something
trustworthy by the time they switched to "production" flights.

Propulsive landings nixed from SpaceX?s Dragon spaceship
July 19, 2017 Stephen Clark
https://spaceflightnow.com/2017/07/1...gs-nixed-from-
spacexs-dragon-spaceship/

From above article:

"The reason we decided not to pursue (powered landings) heavily
is it would have taken a tremendous amount of effort to qualify
that for safety, particularly for crew transport," Musk said.
"And then there was a time when I thought that the Dragon
approach to landing on Mars, where you've got a base heat shield
and side-mounted thrusters, would be the right way to land on
Mars, but now I'm pretty confident that is not the right way,
and that there's a far better approach."

So, since it's not as important to Mars as SpaceX once thought it was,
it's just not worth the effort to qualify it for manned landings. This
was a management/engineering trade-off and appears to be SpaceX's call,
not NASA's.

In terms of landing accuracy, can landing from a full orbit altitude be
as accurate as landing after a 3 minute flight where speed during
re-entry is much lower so minute deviations in angles etc have far
lesser impact?

Yes. Dragon flies a lifting reentry and therefore has some cross-range
capability. This was also true of both Gemini and Apollo (and Russian
Soyuz and Chinese Shenzhou).

I know that guidance can bring a ship over the "X". But running out of
fuel before you land doesn't let guidance do much, and unless you do
like Batman and land on a mattress factory, the landing will be rather
harsh if you run out of fuel.

After the deorbit burn, the fuel remaining in the reaction control
system is only used to maintain the proper attitude. The "lift" of the
craft is provided by aerodynamics and an offset center of gravity.
There would be little worry about "running out of fuel". And if that
were the case (e.g. a launch abort), then the plan was for Dragon V2 to
land using parachutes, not propulsion.

Jeff
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