In article SwVUg.29045$gF3.15129@trnddc02,
David Spain wrote:

Steve Hix wrote:
In article ,
"Danny Dot" wrote:
On orbit, a nuclear explosion may not even provide a impulse via blast.
Without an atmosphere, I don't think there would be an impulse of force.
Huge amount of heat in the form of radiation, but no blast overpressure.

Which is OK, since the atmosphere isn't needed to produce the thrust.
The thrusters would have been surrounded with a jacket of water or wax
(for example), and the plasma produced provides the thrust.

Well you could certainly embellish the pusher plate with coatings of this
kind to improve overall efficiency, but anything that reflects will work.

"Huge amount of heat in the form of radiation", is the key phrase here.
The light pressure from the emitted radiation alone is enough. Remember
those photo sensitive vanes in a evacuated bulb you may have seen in junior
high? Now scale it up. The trick is too keep the pusher plate cool enough
to maintain its reflectivity.

The physics is no different than solar sailing or using a ground or
space-based
laser to propel a spacecraft. Except the light energy is coming from your own
supplied bombs.

Not hugely efficient, maybe, with plasma being wasted on each pop; but
who cares when the total energy being produced is so much over the top
of your requirements, not to mention any chemical alternatives.


I image only a fraction of the energy released by the bomb is actually
providing
propulsion. IIRC you need some kind of super shock absorber that resonates
with the
explosive pulses connecting the plate to the spacecraft if you want to
provide
a comfortable experience for the occupants. Also IIRC the bomb detonates at a
goodly distance (many, many, many miles) from the spacecraft.

Google around for "Orion nuclear rocket". Lots of stuff, including
proof-of-concept tests.

But a nuclear reactor with hydrogen of even water being boiled and heated
then expelled out a nozzle would make a good rocket engine.

Easy (relatively). The NERVA test engine was running in the 1960s.
Northwind is a more recent notion.

Politics stopped their use; until you can convince the Greenies that it
would be safe enough to put the (cold) engine in orbit before fueling
and lighting it off, we won't see any.

Putting the cold engines in orbit doesn't present a problem. It's putting up
the fuel.

Which is what I said; you don't go hot (critical) until after you're in
orbit. But they even freak out about small radio-thermal power sources.

Since the days of Three Mile Island the words nuclear and
irrational have become synonymous in the English language.

Although it has been interesting, over the past few months, to hear some
long-time green types beginning to argue that nukes might not be so bad
after all.