Re: Manhole cover beat Sputnik?

Kragen Sitaker (
Fri, 13 Aug 1999 13:04:41 -0400 (EDT)

Robert Thau writes:
> Hmmm... serious people thought Orion (nuclear rockets propelled by
> bombs exploded under their tails) could be made to work; was that
> because the shield itself was expected to liquefy, but to shield the
> rest of the structure from the worst of the effects?

The energy per unit area of the radiation (radio waves, light, etc.)
decreases as the inverse square of the distance from the detonation.
In an unrestricted environment, the same is true of shock waves.
However, underground testing is not such an environment, and it's
entirely possible that the shape of the cavity in which the device was
tested would have channeled a significant amount of the shock-wave
energy to the 'manhole cover', while most of the radiant energy was
absorbed by the walls. (One such structure would be a simple
cylindrical vertical hole.)

So it's entirely possible for the 'manhole cover' to be solid or mostly
solid when launched.

You can decrease the temperature rise at a surface to arbitrarily low
levels by increasing the distance between the detonation and the
surface arbitrarily. Perhaps long distances were envisioned for Orion
-- although Robert Harley's more recent post suggests not.

But as Robert Harley pointed out, simply because the 'manhole cover'
was moving upwards in excess of escape velocity when it was at ground
level doesn't mean it was able to escape Earth's gravity. It would if
the only force acting on it were Earth's gravity, but air resistance
must be taken into account. Even at subsonic speeds, air resistance
grows with the square of the airspeed; I don't know how it grows at
supersonic and hypersonic speeds.

<>       Kragen Sitaker     <>
Fri Aug 13 1999
87 days until the Internet stock bubble bursts on Monday, 1999-11-08.