(George William Herbert) wrote in message ...

A circular parachute
will give you less control, so your choice of landing site will be
constrained by a possible off-filed landing in a backup situation.
Thus, you lose some of the advantages of having a ram-air chute in
the
first place.

One of my design assumptions for capsules is that the landing point
will eventually be on the worst possible spot (sharp heavy rock,
solid thick cement, whatever). If your design assumption is that
you have to avoid injury WHEN that happens, then landing on the nice
prepared raked sand at Dugway or wherever is just gravy.

I was thinking of the true worst case -- coming down in the middle of
I-80 at rush hour or in a schoolyard at recess. That's not something
you can design for, it's something you have to factor into selection
of your drop zone. If your backup system is significantly less
accurate than your main system, the backup becomes the limiting
factor.

Vertical touch-down velocities for X-38 were about twice those of
carrier landings. That may not approch physiological limits, but I
wouldn't call it comfortable, either.

X-38 flared at 8 fps; that's nowhere near what carriers land at.

I think you may have mistaken feet and meters. Marti Sarigul-Klijn
reported the average vertical landing velocity as 20 fps (6 m/s) and
the maximum as 27 fps (8.2 m/s). From the videos I've seen of X-38
landings, I can easily believe that. A carrier landing is about 10 fps
(3 m/s), so it's quite a bit harder.

Either one might be a hard sell for certain missions, though. The
ISS
ambulance mission, for example.

If the flight controls lock up on a winged ISS ambulance CEV,
the vehicle is a writeoff,

Perhaps you've forgotten that on the last flight of SpaceShip One, a
flight control did lock up. Mike Melvill simply went to a backup
system. You're assuming a winged vehicle with no more rendundancy than
a model airplane, which isn't likely to be the case.

and the crew either all die or
the evacuee can't survive a parachute hop and dies or the
evacuee gets an unpleasant personal parachute ride but survives.

Or they have an escape capsule. I find rather strange that people who
advocate using capsules as routine transportation always seem to
overlook the possibility of using them as emergency systems.