Tuesday, June 24, 2014

Orion Discovery

Very neat. I love the 2001 style and Orion drive ships. I didn't know the original sketches were to have Discovery be an Orion. Neat. Emphasis added. [Link]
The firing rate here is about 1 bomb per second, which is about the typical design spec for a ground-launched Orion. It doesn't need to be so fast for obrital manoeuvres because it's not trying to avoid crashing, but it's an aesthetically nice rate to depict. Interestingly, early on in the real-life Orion project a much higher firing rate was considered : 4 (smaller) bombs per second. Since the detonation point is something like 50-100m behind the ship, you need a powerful gas gun to shoot the 1-tonne bombs out the back. But you can't reload a gun like that four times per second. There are two solutions, both of which ought to worry even the most steely-eyed of astronauts.

Option 1 was not to shoot the bombs through the pusher plate at all. Instead, the bombs would be ejected through the side of the hull, guided along rails, and then either shot by a catapult system or propelled by rockets to their detonation point. Presumably the rockets would also adjust the orientation of the bombs to ensure they were pointed toward the pusher plate - in some designs this meant the bomb would do a full 180-degree flip. Well, what could possibly go wrong ?

Option 1 being rejected on grounds of sanity, option 2 was scarcely less dramatic. From Dyson's book again :

"... a gun a metre in diameter... 10 metres long, weighing 2.5 tonnes to project a 1.5 tonne projectile at 200g's. Obviously this can't be reloaded every quarter of a second so you need maybe 10 of them... this will probably wind up as a battery of Gatling gun-type gadgets."

That's right - they wanted a Gatling cannon that fired nukes, because science. Whether you'd need such a gobsmackingly terrifying contraption for the more leisurely rate of one bomb per second, I don't know.


Before I shut the hell up and let you watch the video, Orion always begs the question : "would it have worked ?" The answer, I think, is probably yes - with a catch. Experiments like Operation Plumbob do seem to indicate that a pusher plate (and therefore the ship) could survive the explosions, but there are plenty of unanswered questions. 

For instance, could a system be engineered to reliably eject one-tonne nukes at 200 mph, with an absolute guarantee that they wouldn't detonate too close to the ship ? What would happen if the ship veered off course and had to be destroyed ? What about if a bomb did detonate early - would it risk the others detonating too ? Even if everything worked perfectly, would the fallout from the bombs be anything to worry about ? Well, the answer to that last one is no, but - and this is the catch of course - it doesn't matter.

Orion is a scheme so monumentally audacious that barring the threat of an asteroid stike, it isn't ever going to fly, assuming it would work at all. The total explosive yield for a 10,000 tonne ship for a Mars-bound mission is something like half a megaton of TNT - enough to destroy Hiroshima thirty times over. Does anyone really believe, deep down, that it would be perfectly safe to launch that kind of devastating firepower, or that doing so wouldn't cause massive public outrage, however misguided that outrage might be ?




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