Post by J. ClarkePost by William George FergusonPost by J. ClarkePost by William George FergusonI'm not going to argue that it is impossible with 1963 technology, plus
reasonable developments, which we know are reasonable because, duh, they
occurred. However, to give some perspective, to reach the comet, the
Rosetta had to make multiple slingshot orbits, to get its speed up to
40,000 mph relative to Earth. To reach 0.01C would require acheiving a
speed of just under 7,000,000 mph. The difference between 40 thousand and
7 million is rather large.
So is the difference between Orion and anything that we have built.
Given you are referring to thermmonuclear pulse propulsion, the biggest
diffence between it and anything else that we have built is that we haven't
built it.
The "else" is your insertion.
You're absolutely right, and I apologize. I was seeing in my head
something that wasn't there on (virtual) paper.
Post by J. ClarkeIf you know of a technological showstopper to Orion please present it.
Post by William George FergusonPost by J. ClarkeRosetta is a poor example--it isn't even using the most capable
propulsion that we have actually put in service. We have ion and plasma
thrusters that can achieve much higher delta-v than the chemical
thrusters that were the main propulsion for Rosetta.
But there do not appear to be any technological obstacles to Orion, with
its .1c delta-v and multi-million ton payload. People seem to have
forgotten about the old cold-war dinosaur, and NASA's calling their POS
Apollo clone by the same name seems to have been deliberately intended
to further obfuscate.
The biggest drawback to thermonuclear pulse propulsion (ignoring the
radioactive fallout potential if you actually use it near a planet) is that
it is inefficient as a propellant.
Inefficient by the standard of "something else using the same amount of
energy could be more efficient" yes. By the standard of "we know how to
make something that is actually more efficient", what do we know how to
make that is more efficient in turning mass into delta-v?
Post by William George FergusonDespite the best efforts of 'shaped
nuclear bombs', the majority of the force of the explosion is not going to
act on it
You don't seem to be
aware that up until 1963 the government was funding the program at a
level that suggested that there was every intention of building it.
In 1961, the government had every intention of launching Orions from
Antarctica
Post by J. ClarkePost by William George FergusonFreeman Dyson felt that
the only way to truly understand the effects would be to build a propulsion
plate and set off a nuclear bomb behind it
That was then, this is now. Dyson didn't have massive computer power
available. I don't know if anybody has modeled this but there don't
appear to be showstoppers. You're just telling us what the engineers
have to figure out.
Since one of the things is 'is it possible', that's fairly significant.
Post by J. ClarkePost by William George FergusonOne difficulty of testing it is that, before the engineering had caught up,
the Partial Nuclear Test Ban Treaty of 1963 made testing it illegal.
Which was already stipulated so what point do you think you are making
by bringing it into the discussion?
Just explaining why we aren't further along in testing and modeling than we
are.
Post by J. ClarkePost by William George FergusonThe
closest thing to a test was the Pasca-B containment test in 1957, where an
a-bomb was set at the bottom of a deep shaft which was covered by a six
inch thick steel cap. When the bomb was set off (and containment pretty
much completely failed) the estimated upward speed of the steel cap was
somewhere between 22mps and 41mps.
Actually nobody knows the speed, only that it was very high. There was
a camera set to record its movement but it only appeared in one frame--I
don't know if that is because the camera malfunctioned or becaues it was
moving faster than planned.
1. Using the word 'estimated' and giving such a large range (22mps-41mps)
pretty much acknowledges 'nobody knows'. I still like the project
designer's estimate as the most accurate, "going like a bat out of hell".
2. the Pascal-B test was testing containment in case of a 'fizzle
explosion' due to some external factor, rather than a deliberate explosion.
The bomb was supposed to yield about 1.5 kilotons, simulating such a
'fizzle' explosion. In fact, the bomb is estimated to have had a yield of
about 33 kilotons, so yeah, a lot faster than planned.
Let me make a few more comments, since you seem to be taking me as
adversarial, and I'm not (or at least I don't perceive myself to be)
Barring Clarke level Sufficiently Advanced Technology, I do not believe
that it would be a good idea ever to launch a thermonuclear pulse
propulsion ship in the atmosphere of any planet on which we are going to
continue to live..
Launching this type of propulsion sufficiently far from the Earth's surface
would avoid many, possibly most, of the problems of launching from Earth,
but would add the problem of getting the ship (and payload) into that
position
Improving that last 10 (or whatever) percent on carbon nanotube tech, and
building a skyhook/space elevator, would neatly get around that problem,
but the fact is, we can lift that amount of tonnage into high orbit now, if
we really, really want to
All that said, I'm not sure that any modeling done so far stands up to
having an Orion type propulsion ship reaching 0.1C. A lot of the initial
modeling was done back in the 60s, and comes off as blue sky. There has
been modeling done since computer power has ramped up, especially since
computer power reached the point that scientists don't have to depend on
government funding to do the computer modeling.
If an Orion type ship reached 0.01C (which I think is far more likely), it
wouldn't reach Proxima Centauri in 100 years, more like 350 (that's
referring back to the original problem, I think you already pointed this
out somewhere.)
One more thing to consider is that the human race developed under 1.0
gravitation. Any long term deviation from this causes problems. You can
design a vehicle with a significantly lare squirrel cage to get around
this, but you'll have too many problems if you have it spinning while those
bombs are popping at the back. Of course, you also get around this by
having it unmanned, but where's the fun in that?
--
I must not fear. Fear is the mind-killer.
Fear is the little-death that brings total obliteration.
I will face my fear. I will permit it to pass over me and through me.
And when it has gone past I will turn the inner eye to see its path.
Where the fear has gone there will be nothing. Only I will remain.
(Bene Gesserit)