You are such a poor shot that you couldn't throw an AA battery from orbit and have a hope of even hitting the earth.

Jorge R. Frank wrote:
(Mike Miller) wrote in
om:

Ian Stirling wrote in message
...
Mike Miller wrote:

If you had a space station at a 600-mile altitude circular orbit
and wanted to drop cannisters from orbit, what's the minimum
retrograde velocity that needs to be imparted to the cannisters to
have them re-enter fairly quickly [1]? Would 300mph be adequate?

I'd think not, I think the perigee only goes down to around 450
miles.

As a rough guide, you lower the orbit by 1/4 of the velocity.
So, you might need 2000mph or so.

Whoa...the orbital velocity of a 600-mile orbit is 8000mph?

So, could you launch the cannister in any way from the station and
have it deorbit fairly quickly (over several days) with less than
1000mph delta-V?

Nope, see my other post on the subject. Working out all the insane unit
conversions, the delta-V needed to drop from a 600 statute-mile circular
orbit to an elliptical one that just grazes the atmosphere (400,000 ft
perigee, which is what NASA considers "entry interface"), is about 510 mph.

I don't really do miles.
I think I managed to do the conversion from m/s to mph the wrong way round.

"Anonymous" wrote in message . com...

[snip]

Both ideas make use of several feet of compressible carbon such as was on the legs of the lunar
lander modules to cushion the landing on earth -

Pilots who have to make rough landings generally choose parachutes.
That way your own legs soften the laanding, and you get more control
over the landing site as well. So I would remove the soft landing
requirement and replace it with explosive bolts which open the capsule
at 15Km altitude, a small oxygen bottle, and a good parachute with a
reserve and an emergency life raft.

either on land or in the water. The landing area
for the orbital canister would probably have to be largely random on earth - so if you came down in
a volcano or a North Korean military camp you would just be plain out of luck.

Guidance would be a good idea, I think.

But how is this for an idea:

Instead of using a retrorocket to deorbit, you could deploy a large
and very light parachute while still in orbit. I am thinking in terms
of 10000m^2 or so of thin plastic sheet. It could be deployed by a
puff of CO2 gas from a small bottle, and then finally inflated by
aerodynamic drag at altitude. This would be unlikely to work from
600Km but it might be a goer at 200Km. What do you think?

[snip]

I'm guessing that the biggest problems with this idea would be in order:
1 - Time to atmosphere would be too great for the amount of air.

As long as you can recirculate your oxygen and extract excess CO2 this
should not be a great issue. A couple of days on a tank of air sounds
feasible to me.

2 - Danger to people on earth from canister hitting them

Despite our best efforts at filling up the earth this is still not a
major issue. Most of the earth, especially the oceans is quite empty.

3 - Heat build up inside the canister

This might be an issue during the "cruise phase" before re-entry
because the occupant will be generating heat and this can be difficult
to dispose of in vacuum. If you mean heating during re-entry then I
would not be as concerned. Ablative heat shields do a good job of
disposing of frictional heat.

4 - Deceleration forces to great to survive

A badly designed capsule will expose the occupant to 100G or so which
is not fatal unless it goes on for too long. With a good aerodynamic
design it should be possible to maintain altitude during aerobraking
and keep G loads under 100m/s/s or so.

5 - Looking at Earth to fire a re-entry burst is not good enough to hit it.

You only really have to fire roughly backwards to break out of orbit.
This should not be hard. Aiming for a particular landing sight might
be more difficult. I can imagine a simple flight control system which
works out the orbital elements from GPS data and then chooses the
right time for the
de-orbit burn to put the landing close to a designated safe location,
many of which would be pre-programmed into it.