Space Exploration! [to boldly go]

electricitylikesme

Fusion would be a happy occurrence because it would mean we have a fuel abundant, non-radioactive launch vehicle that we can sell to the public - fusion means if it blows up there's very little dangerous fallout (I'm guessing basically none, since a rocket should not fly nearly as long as a power plant operates, so activated radioactivity would not be a problem).

The basic goal is to get as many tons into orbit as possible per launch, the more you can do, the cheaper (and safer - because you can have redundancy) it becomes. With fusion powered launch vehicles, we'd be looking at launching hundreds of tons at a time, rather then 36 or so.

electricitylikesme

Grid System wrote: »

electricitylikesme wrote: »

We need a nanotube 36,000 km long.

Why does it have to be a single, long tube? Why can't it be a bunch of shorter, interlocking tubes or something?

I'm sure there's a reason, I just don't know what it is.

A spun thread, even with todays knowledge, can only give you something like 70% the maximum tensile strength of the material you spin it from.

AFAIK a nanotube would have to support more load then that.

Grid System

And I guess you can't solve that problem by making the cable thicker. At least, not without running into sets of new problems. Hmm.

electricitylikesme

Grid System wrote: »

And I guess you can't solve that problem by making the cable thicker. At least, not without running into sets of new problems. Hmm.

That's the heart of the issue - we need nanotubes so that the mass of the cable itself isn't so great that it collapses. It's a strength to weight ratio problem.

Edwards' proposed design is the technological limits of the tether material. His calculations call for a fiber composed of epoxy-bonded carbon nanotubes with a minimal tensile strength of 130 GPa (including a safety factor of 2); however, tests in 2000 of individual single-walled carbon nanotubes (SWCNTs), which should be notably stronger than an epoxy-bonded rope, indicated the strongest measured as 52 GPa.[16] Multi-walled carbon nanotubes have been measured with tensile strengths up to 63 GPa.[17]

Wiki

nuclearalchemist

I hate to be the naysayer in terms of the space elevator, but it wouldn't work at all. The unfortunate problem is that essentially the weight of the atoms themselves (under gravity) would pull the tether apart if you attempted to put up a space elevator. Since every atom has to support the weight of the atoms "below" it, eventually you can find out that there is a finite length that you can build it; it doesn't matter how "strong" the carbon bonds are, eventually there will be enough potential energy to pull them apart.

At present I am attempting to find the reference for this.

EDIT: Kinda beat to the punch =(.

Grid System

Okay, so if we can't do the elevator, what about a giant rail gun?

Salvation122

electricitylikesme wrote: »

I'd say it's presently a dead heat between fusion and nanotubes, and mostly because greenpeace has killed the chances of anything fission powered ever lifting off from Earth (god I wish the Russians would do it).

We put (very-low power, admittedly) fission powered stuff into orbit all the goddamn time using Pu-238 atomic batteries. Greenpeace is just goddamn retarded.

Darkchampion3d

Salvation122 wrote: »

electricitylikesme wrote: »

I'd say it's presently a dead heat between fusion and nanotubes, and mostly because greenpeace has killed the chances of anything fission powered ever lifting off from Earth (god I wish the Russians would do it).

We put (very-low power, admittedly) fission powered stuff into orbit all the goddamn time using Pu-238 atomic batteries. Greenpeace is just goddamn retarded.

I just wish they were stupid like PETA and would protest by having beautiful women go around naked. There's a protest that I could get a behind. :winky:

JebusUD

Can't we just counterweight the elevator shaft? Couldn't we just put a big weight on the end in such a way as to constantly be orbiting and pulling the spun nanotubes taught? Wouldn't this counteract the force of gravity collapsing it?

Or do I have no idea what is going on?

[Tycho?]

electricitylikesme wrote: »

My money would be on nuclear rockets before space elevators.

Or as a comparison case: the longest nanotube last I checked was about 4cm. And like I said: we need these to be atomically perfect, which means we need the technology to refine them somehow to this structure (I believe, this will eventually be possible, since we do something quite similar with silicon for the semiconductor industry [in terms of perfection - the exact process would need to be different). No one presently has any practical ideas of how to do this (everyone has an idea of how they'd like to do it).

We need a nanotube 36,000 km long.

I'd say it's presently a dead heat between fusion and nanotubes, and mostly because greenpeace has killed the chances of anything fission powered ever lifting off from Earth (god I wish the Russians would do it).

Why 36 000km long? Shouldn't it be at geosynchronous orbit?

Well I answered my own question while typing that. Orbit isn't measured from sea-level, silly me.

WMain00

JebusUD wrote: »

Can't we just counterweight the elevator shaft? Couldn't we just put a big weight on the end in such a way as to constantly be orbiting and pulling the spun nanotubes taught? Wouldn't this counteract the force of gravity collapsing it?

Or do I have no idea what is going on?

Call me stupid probably but wouldn't the counterweight need to something equal to, or stronger, than the Earth itself? D:

Aegis

WMain00 wrote: »

JebusUD wrote: »

Can't we just counterweight the elevator shaft? Couldn't we just put a big weight on the end in such a way as to constantly be orbiting and pulling the spun nanotubes taught? Wouldn't this counteract the force of gravity collapsing it?

Or do I have no idea what is going on?

Call me stupid probably but wouldn't the counterweight need to something equal to, or stronger, than the Earth itself? D:

The counterweight would be travelling really, really, really fast due to the rotation of the earth. But I left algebra at home when calculating how one would take into account tangential velocity versus gravity in designing the appropriate weight.

JebusUD

WMain00 wrote: »

JebusUD wrote: »

Can't we just counterweight the elevator shaft? Couldn't we just put a big weight on the end in such a way as to constantly be orbiting and pulling the spun nanotubes taught? Wouldn't this counteract the force of gravity collapsing it?

Or do I have no idea what is going on?

Call me stupid probably but wouldn't the counterweight need to something equal to, or stronger, than the Earth itself? D:

Well, you don't need to counterweight the entire earth, just the action of gravity on the tube. I imagine it being something like tying a ball to a string and spinning it around you.

WMain00

But the very action of gravity must be extremely heavy in a physical form?

Aegis

WMain00 wrote: »

But the very action of gravity must be extremely heavy in a physical form?

Eh?

Darkchampion3d

Aegis wrote: »

WMain00 wrote: »

But the very action of gravity must be extremely heavy in a physical form?

Eh?

Yeah I dont know what he's saying either.

A space elevator uses http://en.wikipedia.org/wiki/Centripetal_force

WMain00

GRAVITY DAMMIT! THE MOOOOOOOOOOOOOON!!1

STTTTTTTTTTTTTAAAAAAARRRRRRRRRRRRRSSSSSSSSSS!!1


HAHAHAH


Yeah i'm rambling. Sorry.

Septus

electricitylikesme wrote: »

I'd say it's presently a dead heat between fusion and nanotubes, and mostly because greenpeace has killed the chances of anything fission powered ever lifting off from Earth (god I wish the Russians would do it).

I'm unaware of this. Would fission rocket power be used at all for reentry? If not, who cares if we dump a load of atomic waste in space, on a trajectory away from the Earth?

Edit: Der, of course, launch explosions. Would the nature of a fission rocket be such that despite incredibly low or largely impossible meltdown chances, the chance of an explosion due to the thrust be relatively high?

Darkchampion3d

Septus wrote: »

electricitylikesme wrote: »

I'd say it's presently a dead heat between fusion and nanotubes, and mostly because greenpeace has killed the chances of anything fission powered ever lifting off from Earth (god I wish the Russians would do it).

I'm unaware of this. Would fission rocket power be used at all for reentry? If not, who cares if we dump a load of atomic waste in space, on a trajectory away from the Earth?

Edit: Der, of course, launch explosions. Would the nature of a fission rocket be such that despite incredibly low or largely impossible meltdown chances, the chance of an explosion due to the thrust be relatively high?

Unless you fuck up massively and have a containment breach with an explosion to generate a nice little cloud of fallout, nuclear rockets don't really "melt down". Even then, the atmospheric nuclear weapons tests done earlier in the century generated more fallout then one of these failing would.

big l

Darkchampion3d wrote: »

Septus wrote: »

electricitylikesme wrote: »

I'd say it's presently a dead heat between fusion and nanotubes, and mostly because greenpeace has killed the chances of anything fission powered ever lifting off from Earth (god I wish the Russians would do it).

I'm unaware of this. Would fission rocket power be used at all for reentry? If not, who cares if we dump a load of atomic waste in space, on a trajectory away from the Earth?

Edit: Der, of course, launch explosions. Would the nature of a fission rocket be such that despite incredibly low or largely impossible meltdown chances, the chance of an explosion due to the thrust be relatively high?

Unless you fuck up massively and have a containment breach with an explosion to generate a nice little cloud of fallout, nuclear rockets don't really "melt down". Even then, the atmospheric nuclear weapons tests done earlier in the century generated more fallout then one of these failing would.

I think it's less a problem of fallout and more "rocket explodes in air ala Challenger/Columbia, plutonium falls to ground, anybody underneath who wants to walks over and picks up some, ZOMG TERRORISTS WITH DIRTY BOMB!!!" which is actually not that unreasonable of a concern.

tbloxham

His Corkiness wrote: »

I'm really looking forward to when launch costs are low enough to make Near-Earth Asteroid mining profitable.

Thats the good thing about doing it with a full system of robot ship miners maintained either by onboard systems or at a large Earth Orbit space station. You don't ever fly anything up. You just drop rocks from space onto the Arizona desert or something, the earths gravity does all your work for you.

You build the station in orbit, and it builds the ships in situ. The ships then fly out to the asteroid belt, grab the asteroid and grind it up and process it on the long journey home. Some of the resources are then given to the station, and others are simply dropped from space onto the earth where we pick them up.

[Tycho?]

Check out http://en.wikipedia.org/wiki/Project_Orion_(nuclear_propulsion) for info on a viable fission drive. The idea of nuclear explosions being used on a rocket makes people a bit wary (for good reason I think). But a lot of probes sent up have radioactive isotopes used for power; an actual fission drive wouldn't be that much more dangerous than a lot of other stuff we've already done.

Septus

tbloxham wrote: »

His Corkiness wrote: »

I'm really looking forward to when launch costs are low enough to make Near-Earth Asteroid mining profitable.

Thats the good thing about doing it with a full system of robot ship miners maintained either by onboard systems or at a large Earth Orbit space station. You don't ever fly anything up. You just drop rocks from space onto the Arizona desert or something, the earths gravity does all your work for you.

You build the station in orbit, and it builds the ships in situ. The ships then fly out to the asteroid belt, grab the asteroid and grind it up and process it on the long journey home. Some of the resources are then given to the station, and others are simply dropped from space onto the earth where we pick them up.

Wouldn't we lose a rather large amount of each rock in the process of entering the atmosphere?

Are the minerals in those asteroids so valuable to counter an inefficiency that large?

ProPatriaMori

Septus wrote: »

tbloxham wrote: »

His Corkiness wrote: »

I'm really looking forward to when launch costs are low enough to make Near-Earth Asteroid mining profitable.

Thats the good thing about doing it with a full system of robot ship miners maintained either by onboard systems or at a large Earth Orbit space station. You don't ever fly anything up. You just drop rocks from space onto the Arizona desert or something, the earths gravity does all your work for you.

You build the station in orbit, and it builds the ships in situ. The ships then fly out to the asteroid belt, grab the asteroid and grind it up and process it on the long journey home. Some of the resources are then given to the station, and others are simply dropped from space onto the earth where we pick them up.

Wouldn't we lose a rather large amount of each rock in the process of entering the atmosphere?

Are the minerals in those asteroids so valuable to counter an inefficiency that large?

I guess you could have other robots manufacture an aeroshell and thermal protection system of some sort from some of your rock. It wouldn't be easy but neither is the robotic mining.

Salvation122

Septus wrote: »

tbloxham wrote: »

His Corkiness wrote: »

I'm really looking forward to when launch costs are low enough to make Near-Earth Asteroid mining profitable.

Thats the good thing about doing it with a full system of robot ship miners maintained either by onboard systems or at a large Earth Orbit space station. You don't ever fly anything up. You just drop rocks from space onto the Arizona desert or something, the earths gravity does all your work for you.

You build the station in orbit, and it builds the ships in situ. The ships then fly out to the asteroid belt, grab the asteroid and grind it up and process it on the long journey home. Some of the resources are then given to the station, and others are simply dropped from space onto the earth where we pick them up.

Wouldn't we lose a rather large amount of each rock in the process of entering the atmosphere?

Are the minerals in those asteroids so valuable to counter an inefficiency that large?

Depends on what the rock is made of and what the trajectory is.

A bigass chunk of iron isn't going to burn up on reentry. It will, however, kill anything in a ten mile radius when it hits the ground.

electricitylikesme

[Tycho?] wrote: »

Check out http://en.wikipedia.org/wiki/Project_Orion_(nuclear_propulsion) for info on a viable fission drive. The idea of nuclear explosions being used on a rocket makes people a bit wary (for good reason I think). But a lot of probes sent up have radioactive isotopes used for power; an actual fission drive wouldn't be that much more dangerous than a lot of other stuff we've already done.

Yeah, Orion is the insane version of this. The one we're talking about is more like the Pluto, and it's a lot more efficient. It's the same basic concept, just you flow liquid hydrogen over the reactor to generate the thrust (since H2 doesn't suffer from activated radioactivity).

EDIT: For additional reading, look up "nuclear thermal propulsion".

ProPatriaMori

NTP does sound fun. People protest RTGs, though...so we'd have to ignore even more hippies to get NTP going.

I still like Sea Dragon as far as heavy lift goes. Giant pressure-fed engines? Yes please.

Spindizzy

Salvation122 wrote: »

A bigass chunk of iron isn't going to burn up on reentry. It will, however, kill anything in a ten mile radius when it hits the ground.

Peter Hamilton covered this point in his Nights Dawn Trilogy. Essentially you process the asteroids metals into a sponge like consistency (to allow them to float) then cover them in an ablative foam that will burn up on re-entry. Along with Parachutes to slow decent into the ocean for retreaval prevents any risks of asteroids hitting landmass and causing problems.

Any thoughts?

electricitylikesme

Spindizzy wrote: »

Salvation122 wrote: »

A bigass chunk of iron isn't going to burn up on reentry. It will, however, kill anything in a ten mile radius when it hits the ground.

Peter Hamilton covered this point in his Nights Dawn Trilogy. Essentially you process the asteroids metals into a sponge like consistency (to allow them to float) then cover them in an ablative foam that will burn up on re-entry. Along with Parachutes to slow decent into the ocean for retreaval prevents any risks of asteroids hitting landmass and causing problems.

Any thoughts?

All this depends on what the relative expense/pay-off of it is. The big problem is we won't know until launch capability costs go down enough that we can then spend the time we'll need tooling around in space to figure out what those costs are.

DanHibiki

electricitylikesme wrote: »

I'd say it's presently a dead heat between fusion and nanotubes, and mostly because greenpeace has killed the chances of anything fission powered ever lifting off from Earth (god I wish the Russians would do it).

you know, i bet Russia has several working designs ready to go they just don't do it because no one's paying their bill.

Darkchampion3d

DanHibiki wrote: »

electricitylikesme wrote: »

I'd say it's presently a dead heat between fusion and nanotubes, and mostly because greenpeace has killed the chances of anything fission powered ever lifting off from Earth (god I wish the Russians would do it).

you know, i bet Russia has several working designs ready to go they just don't do it because no one's paying their bill.

http://www.novosti-kosmonavtiki.ru/content/numbers/218/58.shtml