PDA

View Full Version : Footfall (Spoiler Warning)



David Hall
2002-Apr-01, 11:03 AM
I just finished the book Footfall by Larry Niven and Jerry Pournelle. Overall I thought it was pretty good, but not up to the standards of their other collective works, especially The Mote in God's Eye.

For those of you wanting to read it, you might want to stop now, as I'm about to give away a pretty big plot point.

Now, onto the question. Near the end, the USA launches a VERY large ship (Large enough to carry space shuttles as secondary craft) using atomic bombs as propellant.

Now I know that the theory is well-developed for use in space; build a large shield at the end of your ship, set off an explosion behind it, and watch it go, but I have a hard time believing in using atomic explosions as launching thrusters. Specifically, I would believe the acelleration forces would be too great for the crew to survive or at least function properly.

The only saving grace I see is that it was launched from a track, which might lessen the initial shock, although I really don't know how exactly.

Does anyone have any comments as to the feasability of this kind of launch? Did they get the science correct? How big of a ship do you think could actually be sent up in this manner?

Alan
2002-Apr-01, 01:18 PM
On 2002-04-01 06:03, David Hall wrote:

Does anyone have any comments as to the feasability of this kind of launch? Did they get the science correct? How big of a ship do you think could actually be sent up in this manner?



Try this site:

http://www.rocketry.com/mwade/articles/probirth.htm

Alan

Bob S.
2002-Apr-01, 07:55 PM
Also remember the the comet-intercepting spaceship in (http://us.imdb.com/Title?0120647) "Deep Impact" also used an Orion Drive for its propulsion.

Some of the practical problems (maybe not impossible to overcome in the future) would be the effects of sudden acceleration turning your astronauts to goo, then the intense radiation cooking that goo.

(edited for HTML code, pardons)


<font size=-1>[ This Message was edited by: Bob S. on 2002-04-01 15:00 ]</font>

Chuck
2002-Apr-01, 08:37 PM
I suppose the rear plate would have to be thick enough to block the radiation and would have to have really good shock absorbers. It still sounds like a bumpy ride, though.

Darkwing
2002-Apr-05, 05:45 PM
Now I haven't read the book, so I don't know how they did it there, but for an atomic drive of this short, you wouldn't set off megaton sized bombs or anything... You'd set off many bombs, at a rate of several a second, and they would all be extremely small (compared to megaton weapons). Setting off lots of little bombs in rapid sequence would produce a more smooth thrust, and thus less shock, than larger bombs more spaced out in time, and provide a comparable thrust.

Geo3gh
2002-Apr-05, 08:20 PM
I haven't read it in a while (it's not my favorite of their work), but I do recall Niven and Pournelle going into detail about the engineering involved. Very thick shielding and small to mid-size nukes if I remember right. And yes, very bumpy ride.

David Hall
2002-Apr-06, 09:41 AM
On 2002-04-05 15:20, Geo3gh wrote:

I haven't read it in a while (it's not my favorite of their work), but I do recall Niven and Pournelle going into detail about the engineering involved. Very thick shielding and small to mid-size nukes if I remember right. And yes, very bumpy ride.


I think you're probably right. I may not have been concentrating very well when I reached that passage. I guess it probably was giant shock absorbers that helped the lift-off. And yes, I'm aware the nukes probably weren't that powerful. No need to set off a megaton when a few kilotons will do the trick.

However, in reply to Darkwing's post, they definitely weren't set off that close together. I believe the launch itself was one detination for the initial launch, followed by another a few seconds later to get them to escape velocity. After they were in orbit, the bombs went off at much longer intervals, on the order of minutes usually, although they also used smaller bombs to power nasty gamma-ray lasers as well.

Conrad
2002-Apr-06, 11:15 AM
Apropos Project Orion and spaceships, during the pre-production on "2001", Stanley Kubrick pondered using a pusher-plate spaceship for the [i]Discovery[i/]. There are some design sketches of same in the very excellent "Filming the Future" by Piers Bizony.
And I recall reading the blurb on a sf novel - can't remember the title or author - about a pusher-plate spaceship that suffers a bit of engine failure (i.e. it nukes itself into plasma), leaving only a scout pilot as sole survivor. Which illustrates one of the drawbacks about fission-powered engine plant.

Ad Hominid
2002-Apr-07, 02:51 AM
Orion links (http://www.nuclearspace.net>Nuclearspace.net</a>)). Freeman Dyson was a major participant in the original project. His son, George, has written a new book about the project and how it would have worked. Its technical feasibility is not in serious doubt.

<font size=-1>[ This Message was edited by: Ad Hominid on 2002-04-06 21:54 ]</font>

Silas
2002-Apr-07, 07:24 PM
There were tests, using a scale model and ordinary explosives, and the experiments were filmed. They showed them, not too long ago, on The History Channel. It was quite amusing to watch the failures...and the successes. I think their best effort was a mere three-stage affair, with only three small bangs, but after the third pop, the payload flew a very respectable distance.

Silas

Geo3gh
2002-Apr-08, 01:26 AM
On 2002-04-06 04:41, David Hall wrote:
However, in reply to Darkwing's post, they definitely weren't set off that close together. I believe the launch itself was one detination for the initial launch, followed by another a few seconds later to get them to escape velocity. After they were in orbit, the bombs went off at much longer intervals, on the order of minutes usually, although they also used smaller bombs to power nasty gamma-ray lasers as well.


I just re-read the section where they launch Michael, (that's the name of the Orion ship). The way Niven writes it, it seems to be one a-bomb every two seconds or so. He has two people talking, so you can see how fast they are coming by where the sentences are cut off. Then there's one guy stuggling through the takeoff, and asking himself "how many have there been so far? 20? 30?"

And in describing the design, N and P talk anout the shock absorbers, sandwiched between two layers of reinforced concrete. And thousands of nukes, all identical, for the engines.

We are talking a very bumpy ride, and the bumpiness is extended.