Responding to questions:

>Ok assume the Mars crew have used
>centrifugal gravity to stay healthy,
>and wear counter-gravity suits to take
>up to 9 gees like Apollo.

I don't think Apollo took 9 gravities (might be wrong on this).

>Assume a throw-away ablative shield.
>What would it be then?

We ***always*** assume a throw-away ablative shield. They're cheaper, lighter and after they get loaded up with heat then they're dumped along with the heat.

>I was wondering if you could aerobrake
>from 'fast' 100 day transfer orbits >into elliptical parking orbits.

The 11 km/sec entry that I quoted before was for a fast trajectory (Aldrin escalator orbit).

>On another issue I read an old SF story
>years ago that had ships aerobraking at
>Uranus, deccelerating from ~ 160 km/s
>to ~ 20 km/s - a bit much to believe,
>but any ideas as to what kind of
>aerobraking could be achieved at Uranus?

A 160 km/sec entry is impossible to shield for. The very rough rule-of-thumb is entry speed in km/sec times 1000 gives peak shock layer temperature in degrees Kelvin, i.e. 160 km/sec gives 160,000 deg.Kelvin.

Uranus is not very interesting in terms of planetary science. However Neptune is very interesting because of it's moon Triton.

>Does your code go that far, or does it bust?

I am currenty doing feasibility studies for Neptune aerocapture to Triton.

>Galileo fell into Jupiter with a relative
>velocity of 47.5 km/s and survived...

The ancestor of the branch that I work at designed the Galileo probe (the original designers are all retired from NASA). I'm using Galileo probe flight data to validate my software. The Galileo probe was actually going 47.3691 km/sec [atmosphere relative] at 450.0 km altitude [zero altitude is referenced to 1 bar pressure]. The inertial entry speed was 59.92 km/sec [Jupiter rotates fast]. The success of the Galileo Probe was one of NASA's greatest triumphs. However the Galileo Probe was able to enter Jupiter's atmosphere at such high speed because that atmosphere was mostly hydrogen which has enormous heat capacity. Had the probe entered the Earth's (or Titan's) mostly nitrogen atmosphere at that speed then it would have vaporized.

Gary