Nukes In Space....

phongn · Post by **phongn** » 2003-06-16 07:31pm

SirNitram wrote:Quite. It's about the one situation where I'd advocate Orion.. Let's face it, it's been overhyped to hell.

Yep. If you have to move something big and move it fast, then Orion is good. Otherwise, there's no real point to it.

kojikun · Post by **kojikun** » 2003-06-16 07:32pm

phongn, i dont know the maths, maybe you do. whats the speed of a 100kg probe accelerated by a force of 0.05 Newtons after travelling 20 million km say, and how long will it take to get there?

SirNitram wrote:That's what I've always heard, so I've been wondering if Koji went back for more of whatever he smoked during hte fighters-in-space and Singularity threads.

Don't think I ever participated in any fighters-in-space thread.

kojikun · Post by **kojikun** » 2003-06-16 07:35pm

phongn wrote:Yep. If you have to move something big and move it fast, then Orion is good. Otherwise, there's no real point to it.

That was my point about NERVA tho, the you can move some serious shit, and get it going to high speeds quickly. Putting a man on Mars? Thats a job for NERVA not ion rockets. Mining the asteroid belt? NERVA. Extracting He-3 from Uranus? NERVA or preferably fusion rockets.

SirNitram · Post by **SirNitram** » 2003-06-16 07:37pm

kojikun wrote:
phongn wrote:Yep. If you have to move something big and move it fast, then Orion is good. Otherwise, there's no real point to it.
That was my point about NERVA tho, the you can move some serious shit, and get it going to high speeds quickly. Putting a man on Mars? Thats a job for NERVA not ion rockets. Mining the asteroid belt? NERVA. Extracting He-3 from Uranus? NERVA or preferably fusion rockets.

I suggest you examine the G-forces involved in these short little burns. We don't want to laminate our astronaughts to the bottum of the ship.

kojikun · Post by **kojikun** » 2003-06-16 07:44pm

SirNitram wrote:I suggest you examine the G-forces involved in these short little burns. We don't want to laminate our astronaughts to the bottum of the ship.

Aww why not?

kojikun · Post by **kojikun** » 2003-06-16 07:58pm

are there any conceivable limits to thrust produced by an ion drive? im finding that most ion drives put out mere tens of millinewtons.. they may have serious fuel use lengths, a good many times that of, say, NERVA, but theyre also producing much less thrust. MUCH less thrust..

im not sure, but i think a million newtons with an Isp of 1500 is better then 50 millinewtons with an Isp of 3000..

SirNitram · Post by **SirNitram** » 2003-06-16 08:00pm

kojikun wrote:are there any conceivable limits to thrust produced by an ion drive? im finding that most ion drives put out mere tens of millinewtons.. they may have serious fuel use lengths, a good many times that of, say, NERVA, but theyre also producing much less thrust. MUCH less thrust..

im not sure, but i think a million newtons with an Isp of 1500 is better then 50 millinewtons with an Isp of 3000..

Again, you miss the point. Ion thrust is applied constantly. NERVA is a one shot that'll laminate your crew.

phongn · Post by **phongn** » 2003-06-16 08:00pm

If you need to escape a gravity well, go ahead and use the nuclear drive. If you need to get somewhere fast, you can use a nuclear drive, but you're going to need enormous amounts of fuel, or you can use Orion (which still needs a good number of propellant).

For space probes you want efficiency, and that's where ion comes in.

phongn · Post by **phongn** » 2003-06-16 08:02pm

SirNitram wrote:Again, you miss the point. Ion thrust is applied constantly. NERVA is a one shot that'll laminate your crew.

Well, it might not kill your crew if you cut down flow rate, but it's still not the best choice if you aren't willing to use massive amounts of fuel.

kojikun · Post by **kojikun** » 2003-06-16 08:03pm

SirNitram wrote:Again, you miss the point. Ion thrust is applied constantly. NERVA is a one shot that'll laminate your crew.

Lowering the acceleration increases the time you can use the fuel you have, so its not an issue Nitram.

Can someone answer whether or not ion drives have a conceivable topoff to thrust..

Gil Hamilton · Post by **Gil Hamilton** » 2003-06-16 08:06pm

phongn wrote:If you're moving rocks, you might as well install a pusher plate and put an Orion drive on it. It's useful for when you need high thrust and specific impulse.

In that case, you don't even need the pusher plate. You just need a crater and even then you'll make your own perfectly sized crater by itself.

phongn · Post by **phongn** » 2003-06-16 08:10pm

Gil Hamilton wrote:
phongn wrote:If you're moving rocks, you might as well install a pusher plate and put an Orion drive on it. It's useful for when you need high thrust and specific impulse.
In that case, you don't even need the pusher plate. You just need a crater and even then you'll make your own perfectly sized crater by itself.

Well, you might get suface ablation and such - vaporizing precious material - so a pusher plate wouldn't be a bad idea.

If you're trying to do orbital bombardment or deflecting an asteroid, then it hardly matters

phongn · Post by **phongn** » 2003-06-16 08:11pm

kojikun wrote:are there any conceivable limits to thrust produced by an ion drive? im finding that most ion drives put out mere tens of millinewtons.. they may have serious fuel use lengths, a good many times that of, say, NERVA, but theyre also producing much less thrust. MUCH less thrust..

im not sure, but i think a million newtons with an Isp of 1500 is better then 50 millinewtons with an Isp of 3000..

Wikipedia is showing that ion drives top out around 10N of thrust (unknown isp) whereas NTRs are getting around 10000N of thrust with 900 seconds isp or so.

Gil Hamilton · Post by **Gil Hamilton** » 2003-06-16 08:15pm

phongn wrote:Well, you might get suface ablation and such - vaporizing precious material - so a pusher plate wouldn't be a bad idea.

If you're trying to do orbital bombardment or deflecting an asteroid, then it hardly matters

Well, vaporizing part of the asteroid is part of the idea initially, as it will increase the velocity of the asteroid and get where it is going faster, as it's not like a huge percentage of the asteroid's mass is being lost. Once it forms a nice crater that has been nice and baked, you'll have created a natural pusher plate on the asteroid's surface. Besides, the material lost can't possibly be more than the resources used to create a steel plate in the first place.

Post by **Sea Skimmer** » 2003-06-16 08:27pm

Gil Hamilton wrote:Besides, the material lost can't possibly be more than the resources used to create a steel plate in the first place.

But the plate, or at least a good chunk of it should be recoverable.

phongn · Post by **phongn** » 2003-06-16 08:27pm

JIMO QuickTime video

Admiral Valdemar · Post by **Admiral Valdemar** » 2003-06-16 08:55pm

To get rid of a 'roid coming at Earth it would be better to simply produce a reflective surface that nudges the rock away from a collision, most 'roids are collections of smaller rocks flying in tight formation. A nuclear blast could cause the formation to fragment and then you're in the shit with numerous, smaller missiles heading for Earth.

phongn · Post by **phongn** » 2003-06-16 10:05pm

Admiral Valdemar wrote:To get rid of a 'roid coming at Earth it would be better to simply produce a reflective surface that nudges the rock away from a collision, most 'roids are collections of smaller rocks flying in tight formation. A nuclear blast could cause the formation to fragment and then you're in the shit with numerous, smaller missiles heading for Earth.

Proximity detonations are your friend.

kojikun · Post by **kojikun** » 2003-06-16 10:07pm

phong, there are some engines (or enginegroups?) that top out at 1.x million newtons. planned for use in interplanetary missions and stuff. but 10N ion thrusters is.. nothing

phongn · Post by **phongn** » 2003-06-16 10:12pm

kojikun wrote:phong, there are some engines (or enginegroups?) that top out at 1.x million newtons. planned for use in interplanetary missions and stuff. but 10N ion thrusters is.. nothing

And none of those meganewton drives will see the light of day anytime soon. You still haven't brought forth a convincing argument as to why you should mount something as fuel-intensive as a NERVA-style drive on a probe headed to Jupiter.

For manned missions, using high-thrust engines is desireable. But for probes? Not really.

kojikun · Post by **kojikun** » 2003-06-16 10:15pm

Oh! I know why! Because it will be the first step to actually using the real thing in a practical interplanetary mission! :p

in al seriousness tho, youre right, it was foolish to say we should use an NTR for a probe. but who cares, it would look COOL

phongn · Post by **phongn** » 2003-06-16 10:17pm

Bah. NASA is cashed-strapped as it is, no need for them to turn a fission-powered ion-drive probe into this NERVA-powered wundership.

Gil Hamilton · Post by **Gil Hamilton** » 2003-06-16 10:26pm

Sea Skimmer wrote:But the plate, or at least a good chunk of it should be recoverable.

Oh, it undoubtably would be reusable, but you'd need a ship of similar size to push the pusher plate and attach it to the asteroid. You don't need nearly as much resources to just make a natural pusher plate in the asteroid itself.

kojikun · Post by **kojikun** » 2003-06-16 10:37pm

phongn wrote:Bah. NASA is cashed-strapped as it is, no need for them to turn a fission-powered ion-drive probe into this NERVA-powered wundership.

It would be a beautiful end to a no longer beautiful organisation.

SPOOFE · Post by **SPOOFE** » 2003-06-17 03:39am

The beauty of Orion is that you can do it on the cheap. No need to use ultra-lightweight/ultra-strong materials to build your vessel... you can easily make the sucker a mile long and constructed of concrete and rebar and it'll work just fine.

Massive project, though. Too much, in my opinion, for intrastellar missions. I could see it as a crude method of getting to nearby stars with less than a century of travel time (and easier to build than a solar sail).