Evacuate Earth

[RedDwarfIV]

I was reading the WIP Discussion thread's talk about interstellar spacecraft, and it reminded me of a TV show I'd once seen about an effort to evacuate as many people as possible from Earth with a deadline of 70 years or so. Rather than derail that thread by talking about it, I decided to make a new one.

https://www.youtube.com/watch?v=ZpNO_HngUcI

How would you improve in their evac plan?

Personally, rather than building spaceplanes and wasting huge amounts of money on rockets that can only get small pieces to orbit, Ii'd have built as many ORION drive surface-to-orbit shuttles as possible. Perhaps even build entire sections of the final vessel on the ground and launch them on ORIONs before assembling them. This alone might have allowed a much larger, or even a veritable fleet of interstellar escape craft to be built, vastly improving humanity's chances of A) reaching a usable planet and B) actually finishing before the deadline, plus vastly increasing the number of individual humans to be evacuated. Some of these shuttles might even be taken with the interstellar vessels to provide en-mass landing craft, with all the facilities for starting up a colony.

[Mr.Tucker]

What's the timetable for evacuation? Where do they go? etc. Many more things to know. But I digress.

I don't like Orion. Launch enough of them and you slowly poison your planet. Guess it's not a problem if you're evacuating everyone, but still. I'd use some startram systems for the trip to LEO, then a electrodynamic tether in orbit powered by solar\nuclear to hurl the people wherever they need to go. The EDT can use mass driver tech to do that, and then regain its' orbital energy by impinging on the magnetic field of the Earth. High volume transport indeed.

[RedDwarfIV]

What's the timetable for evacuation? Where do they go? etc. Many more things to know. But I digress.

In the show? They pretty much left it until the last minute to actually leave. Earth was still in sight of the evac craft when it was going. They went to a nearby star system that seemed likely to have Earth-like planets, even if the habitability might have to be worked on. But yeah, this is why I linked to the video.

I don't like Orion. Launch enough of them and you slowly poison your planet. Guess it's not a problem if you're evacuating everyone, but still.

This is exactly why I felt ORION would be great in this situation. None of its side-effects matter, because the short-term problem will render the drive's long term issues irrelevant. The only thing that matters in this situation is getting as many people as possible to another star system.

[fredgiblet]

Does ORION even WORK from the surface?

[Siber]

I should hope so, I believe it was originally conceived of as a launch system. I imagine the propulsion units used in the atmosphere might even be simpler than the ones used in vacuum, no special design work needed for shaped charges and whatnot when you've got the fireball provided by atmosphere.

[fredgiblet]

I doubt it was designed as a launch system due to the obvious issues with massive radiological pollution, especially given the extra power needed for launch.

[Siber]

Well, that seems to have given them cold feet eventually, but initial, it was to be for ground launch.

Taylor originally called for a ground launch, probably from the U.S. nuclear test site at Jackass Flats, Nevada (25). The vehicle has been described as looking like a bishop's miter or the tip of a bullet, sixteen stories high and with a pusher plate 135 feet in diameter (26). Intuitively it seems that the bigger the pusher plate, the more efficiently the system would perform. For a derivation of a formula for the effective specific impulse of a nuclear-pulse rocket and for the relations between pusher plate diameter, pulse energy, and Isp, the reader should consult Reynolds (27). The launch pad would have been composed of eight towers, each 250 feet high. The mass of the vehicle on takeoff would have been on the order of 10,000 TONS (28); most of this mass would have gone into orbit. The bomb units ejected on takeoff would have yielded 0.1 kiloton; initially the ejection rate would have been one per second. As the vehicle accelerated the rate would slow down and the yield would increase until 20-kiloton bombs would have been going off every ten seconds (29). The idea seems to have been for the vehicle to fly straight up until it cleared the atmosphere so as to minimize radioactive contamination.

[Nathan_]

nuclear propulsion would be the best for that scenario, but whether orion based or an open core drive, the launch pad is going to get irradiated.

[GeoModder]

It does sound like a one-time solution to orbital ascend, yes.

[Eluvatar]

I would suggest also considering Nuclear salt-water rocketry. (Also here).

[joestej]

In terms of getting large quantities of individuals and resources into orbit quickly and cheaply, a space elevator is probably our best bet. We don't have the technology to make carbon nanotubes strong enough for one yet, but we don't have the tech for viable extra-solar vehicles either. Considering how the field has advanced in the past decades, I'd say we might be able to get an elevator going quickly if we were faced with a 70-year countdown to extinction.

This way we don't have to waste time worrying about creating vehicles to survive both entry and reentry.

Now, normally I would just suggest we set up some O'Neill cylinder-style space colonies and skip going extra-solar at all. It's a lot of effort and we have no idea if we could anything habitable before we have to get out of town (metaphorically speaking). But assuming the incoming Doomsday will take out the whole system supernova style, then it gets interesting.

Ultimately, HOW we get out of the solar system is less important than how we plan to survive the trip. Even if we whip up a fusion torch to get us really moving, it'll still be decades before we reach any other planet. Likely longer.

Unless anyone has evidence I haven't seen about cryogenics and other suspended animation technologies, those are probably a no-go. The fields don't seem like they're going to produce any usable results in the next 70 years. That means we're stuck with a generation ship.

Getting the ships to be mechanically reliable enough to survive for decades or maybe centuries while simultaneously sustaining hundreds of thousands of humans (and possibly animals, since livestock would be good to bring) is going to be a lot trickier than working out how to build an Orion Drive.

THIS site has some good information about realistic STL travel, as well as hard numbers on lots of different drive methods and how viable each one might be. It also goes into more advanced travel methods/technologies like digital crewmembers and relativistic ships, but I think we can rule those out considering we've only got 70 years until BOOM.

[Grayhome]

Excellent link Joestej, thank you for it.

[Siber]

Personally, I'd rather put my bet on Orion or even just massed chemical launches than an elevator. Yes, we've made good strides lately, but we're still very far from being able to make that cable, and there's no way of knowing how long it'll before we can, if we ever can. Orion was considered feasible,if challenging, with 50s tech, if the money and will were there I'd expect we could get it working very fast. For that matter, if the money and will were there you could get a lot done by simply ramping up existing chemical rocket development and production as fast as possible. Probably not anywhere fast enough to evacuate a significant fraction of living humans, but I'd be shocked if it wasn't enough to preserve the species in 70 years.

Crossing to another solar system is another matter, but it's my personal opinion that if we need to get humans somewhere else in this system then the limiting factors are money and risk aversion. If we were facing extinction we might be willing to take some gambles to test things like radiation shielding schemes that we otherwise wouldn't accept.

Edit: And much as I love NSWR, I definitely wouldn't want to put my eggs in that basket. Most of the info I've read about it includes some allusion to doubt about if the proposed reaction chamber is actually possible or not, while for Orion we've got the whole making bomb thing down pretty well.

[fredgiblet]

Just restarting things like the M1 rocket design would go a long way in a short time. The M1 and F1A were reasonably well developed back in the 70s.

[Absalom]

In terms of getting large quantities of individuals and resources into orbit quickly and cheaply, a space elevator is probably our best bet. We don't have the technology to make carbon nanotubes strong enough for one yet, but we don't have the tech for viable extra-solar vehicles either. Considering how the field has advanced in the past decades, I'd say we might be able to get an elevator going quickly if we were faced with a 70-year countdown to extinction.

Personally, I'd rather put my bet on Orion or even just massed chemical launches than an elevator. Yes, we've made good strides lately, but we're still very far from being able to make that cable, and there's no way of knowing how long it'll before we can, if we ever can.

The 70-year answer to space elevators, I think, is to think differently: instead of a space elevator, use a sky-hook. It wouldn't be quite as convenient, but it would be easier to implement, and quasi- or semi-conventional aircraft could provide the initial launch-bootstrap. If one felt like being thorough, then the lighter-than-air waystation idea could be used in conjunction, thereby allowing a specialized upper-atmosphere aircraft to rondevou with the sky-hook.

For reference, a full elevator can be made with current materials for both Moon and Mars.

Getting the ships to be mechanically reliable enough to survive for decades or maybe centuries while simultaneously sustaining hundreds of thousands of humans (and possibly animals, since livestock would be good to bring) is going to be a lot trickier than working out how to build an Orion Drive.

I haven't done studies on it or anything, but I expect that the first step would be to ensure that the exterior is sufficiently simple that there's little to break. You'll want docking access of course, but if you build your docking structure correctly then both dock and vehicles will be completely shielded from exterior line-of-site, and thus from most impactors. Two slowly rotating and one fixed "gates" might be of utility in this, with the "open" portions only intersecting two at a time, and never three at a time. From there, presumably it would be a matter of dividing and conquer (e.g. the pressure hull should be double-or-more hulled to reduce or eliminate atmospheric losses, and should ideally be filled with inert gasses, to reduce corrosion: non-pressure interior hulls can thus deal with e.g. corrosive atmospheres). Also, it would have to be designed with the assumption that maintenance will be performed: because it wil, and without the benefit of an external docking facility.

[joestej]

Personally, I'd rather put my bet on Orion or even just massed chemical launches than an elevator. Yes, we've made good strides lately, but we're still very far from being able to make that cable, and there's no way of knowing how long it'll before we can, if we ever can. Orion was considered feasible,if challenging, with 50s tech, if the money and will were there I'd expect we could get it working very fast. For that matter, if the money and will were there you could get a lot done by simply ramping up existing chemical rocket development and production as fast as possible. Probably not anywhere fast enough to evacuate a significant fraction of living humans, but I'd be shocked if it wasn't enough to preserve the species in 70 years.

The reason I'm more in favor of a space elevator than Orion or chemical launches is because of how much extra construction they require, especially in the case of Orion. Getting a ship into and out of our atmosphere has historically always been the most dangerous part of spaceflight. Just ask Challenger and Columbia. To perform a terrestrial Orion launch, you need a ship that can not only survive the stress of launch but also survive its own deadly exhaust (it is sitting on a nuke, after all). That's a lot of over-engineering that could be bypassed if we had an elevator. Still, the usefulness of Orion vehicles as heavy-lifters should never be underestimated.

Since we're probably going to want those carbon nanotubes to build our Generation Ships anyway, a feasibility study wouldn't hurt our escape effort much.

The 70-year answer to space elevators, I think, is to think differently: instead of a space elevator, use a sky-hook. It wouldn't be quite as convenient, but it would be easier to implement, and quasi- or semi-conventional aircraft could provide the initial launch-bootstrap. If one felt like being thorough, then the lighter-than-air waystation idea could be used in conjunction, thereby allowing a specialized upper-atmosphere aircraft to rondevou with the sky-hook.

I agree that the Skyhook or a Launch Loop would be a good compromise. Reusable or disposable vehicles could get resources into space without the expense of building a one-way vehicle strong enough to get millions of tons into space and still survive the trip.

Besides, who says we can't use multiple methods simultaneously? A space elevator, Skyhook, or loop could be used for lighter materials, while a smaller number of Orion launch vehicles could take everything that can't be easily hooked into space. We can have multiple chemical launches, Orion launches, and elevator/hook/loops payloads going up all at the same time.

This is Armageddon, I think we'd be trying everything short of flapping our arms and wishing to get as many people and materials into space as possible.

I haven't done studies on it or anything, but I expect that the first step would be to ensure that the exterior is sufficiently simple that there's little to break. You'll want docking access of course, but if you build your docking structure correctly then both dock and vehicles will be completely shielded from exterior line-of-site, and thus from most impactors. Two slowly rotating and one fixed "gates" might be of utility in this, with the "open" portions only intersecting two at a time, and never three at a time. From there, presumably it would be a matter of dividing and conquer (e.g. the pressure hull should be double-or-more hulled to reduce or eliminate atmospheric losses, and should ideally be filled with inert gasses, to reduce corrosion: non-pressure interior hulls can thus deal with e.g. corrosive atmospheres). Also, it would have to be designed with the assumption that maintenance will be performed: because it wil, and without the benefit of an external docking facility.

I'm less worried about interstellar impacts and more about routine breakdowns. Apollo 13's famous oxygen tank rupture was caused by damaged Teflon insulation. Soyus 11 was lost to a ventilation valve that got knocked open. If one of our extrasolar vehicles has one of those problems (or any of a hundred other mechanical issues that are sure to pop up in a decades/centuries long voyage), we can't order a new part sent or try an emergency landing. We need these things to be as fail-proof as humanly possible.

Excellent link Joestej, thank you for it.

Thank you! Atomic Rockets has been my go-to for any Hard Scifi facts I need in my writing. The tone is casual enough that you don't need a physics degree to understand how something works, but they've got the numbers to prove what they say.

Incidentally they've already taken a look at the problem of moving large payloads to orbit, and have a whole page dedicated to different launch methods.

From what they provide, it seems that the Lofstrom loop I mentioned previously is the cheapest method, per kg. HOWEVER, they agree with Siber in that, if you don't care about the planet you live on (we don't, provided enough people survive to make it on the extra-solar ships), Orion is hands down the best way to get lots of stuff into space fast. A 1080 bomb Super Orion can lift more in one launch than a Lofstrom loop can in a year. It can almost boost an entire L5 colony into orbit BY ITSELF. They couldn't calculate the cost per kg on the Orions because no one has ever figured out how much one of those suckers would cost to build, but with the End of the World coming we only care about cost to figure out how many we can make before Last Call.

[Siber]

The reason I'm more in favor of a space elevator than Orion or chemical launches is because of how much extra construction they require, especially in the case of Orion. Getting a ship into and out of our atmosphere has historically always been the most dangerous part of spaceflight. Just ask Challenger and Columbia. To perform a terrestrial Orion launch, you need a ship that can not only survive the stress of launch but also survive its own deadly exhaust (it is sitting on a nuke, after all). That's a lot of over-engineering that could be bypassed if we had an elevator. Still, the usefulness of Orion vehicles as heavy-lifters should never be underestimated.

Since we're probably going to want those carbon nanotubes to build our Generation Ships anyway, a feasibility study wouldn't hurt our escape effort much.

The durability challenge of an Orion craft is somewhat counterbalanced by the fact that you're at least mostly freed from the need to minimize the mass of every possible thing. I'd expect an Orion's construction to resemble a bunker more than an aircraft. But I definitely agree that doing serious study of nanotube cables would be worth it. Even if it doesn't result in an elevator, the materials would probably get used elsewhere.

[joestej]

The durability challenge of an Orion craft is somewhat counterbalanced by the fact that you're at least mostly freed from the need to minimize the mass of every possible thing. I'd expect an Orion's construction to resemble a bunker more than an aircraft. But I definitely agree that doing serious study of nanotube cables would be worth it. Even if it doesn't result in an elevator, the materials would probably get used elsewhere.

The designs I've seen are basically half-domes with explosions on the bottom, so that's about right. Minimizing would still be a good idea (less ship weight = more cargo weight), but it is definitely less critical for Orions than for other types.

But I definitely agree that doing serious study of nanotube cables would be worth it. Even if it doesn't result in an elevator, the materials would probably get used elsewhere.

That's the good part of this situation: most of the stuff we're talking about is cross-compatible. So even if one design doesn't pan out, we can take what we learned and apply it elsewhere. While Orions are probably our best bet for heavy lifting, that doesn't preclude working on Loops, Hooks, Elevators, or even laser propulsion as well. They'll all help, one way or the other, and we have LOTS of scientists and engineers with lots of different specialties. No sense letting them go to waste!

[Absalom]

The reason I'm more in favor of a space elevator than Orion or chemical launches is because of how much extra construction they require, especially in the case of Orion. Getting a ship into and out of our atmosphere has historically always been the most dangerous part of spaceflight. Just ask Challenger and Columbia. To perform a terrestrial Orion launch, you need a ship that can not only survive the stress of launch but also survive its own deadly exhaust (it is sitting on a nuke, after all). That's a lot of over-engineering that could be bypassed if we had an elevator. Still, the usefulness of Orion vehicles as heavy-lifters should never be underestimated.

Don't forget that you're probably going to use one to boost your ship towards it's destination as well, even if eventually you switch over to something else.

The 70-year answer to space elevators, I think, is to think differently: instead of a space elevator, use a sky-hook. It wouldn't be quite as convenient, but it would be easier to implement, and quasi- or semi-conventional aircraft could provide the initial launch-bootstrap. If one felt like being thorough, then the lighter-than-air waystation idea could be used in conjunction, thereby allowing a specialized upper-atmosphere aircraft to rondevou with the sky-hook.

I agree that the Skyhook or a Launch Loop would be a good compromise. Reusable or disposable vehicles could get resources into space without the expense of building a one-way vehicle strong enough to get millions of tons into space and still survive the trip.

For a 70 year project, I'd be more inclined to skyhooks than launch loops: the "special" bit is simpler, and aircraft production lines could be converted (or expanded) to build reasonable craft for the "bottom half". Launch loops would probably be a great option for a longer-term space program.

Besides, who says we can't use multiple methods simultaneously? A space elevator, Skyhook, or loop could be used for lighter materials, while a smaller number of Orion launch vehicles could take everything that can't be easily hooked into space. We can have multiple chemical launches, Orion launches, and elevator/hook/loops payloads going up all at the same time.

This is Armageddon, I think we'd be trying everything short of flapping our arms and wishing to get as many people and materials into space as possible.

Hmm, I wonder how well a hybrid Pluto/nuclear rocket using a modification of the Skyhook pilot-rescue system would work for bringing cargo gliders up?

I'm less worried about interstellar impacts and more about routine breakdowns. Apollo 13's famous oxygen tank rupture was caused by damaged Teflon insulation. Soyus 11 was lost to a ventilation valve that got knocked open. If one of our extrasolar vehicles has one of those problems (or any of a hundred other mechanical issues that are sure to pop up in a decades/centuries long voyage), we can't order a new part sent or try an emergency landing. We need these things to be as fail-proof as humanly possible.

One of the points is to keep almost all of the equipment either internal-only or external-only. Anything that you think is prone to causing rapid pressure changes you stick in it's own auxiliary hull(s). Environmental control equipment should be entirely contained within the habitable hulls. If you're worried about terrorist bombings at some point, then reinforce and segment. Almost nothing should cross the pressure hulls: basically just airlocks, since e.g. radiators can just be in contact with the pressure hull walls and still work semi-well. Remember, volume is cheap, and the mass is already going to be unrealistic, so you'll be sticking almost everything inside: any external valves should be highly monitored, and rare. 90%+ of your equipment is never going to be exposed to non-habitable conditions anywhere in it's operational life. Even your industry will largely take place in attached but distinct pressure hulls, with plenty of Whiffle shield between them and your primary hull(s).

HOWEVER, they agree with Siber in that, if you don't care about the planet you live on (we don't, provided enough people survive to make it on the extra-solar ships), Orion is hands down the best way to get lots of stuff into space fast. A 1080 bomb Super Orion can lift more in one launch than a Lofstrom loop can in a year. It can almost boost an entire L5 colony into orbit BY ITSELF. They couldn't calculate the cost per kg on the Orions because no one has ever figured out how much one of those suckers would cost to build, but with the End of the World coming we only care about cost to figure out how many we can make before Last Call.

That's not even quite the limit on surviving population: the real limit is determined by the lesser of:
1) the population that the initial load(s) of mining, processing, & construction equipment and workers sent to the moon can build appropriate habitat capacity for, or
2) the population that the evacuation-stage orions can bus up to the habitats built from lunar materials.

[joestej]

That's not even quite the limit on surviving population: the real limit is determined by the lesser of:
1) the population that the initial load(s) of mining, processing, & construction equipment and workers sent to the moon can build appropriate habitat capacity for, or
2) the population that the evacuation-stage orions can bus up to the habitats built from lunar materials.

Well, that's a bit of a question though. If the coming catastrophe is just going to wipe out Earth, then Lunar/Martian/space colonies are our obvious solution. But if the whole solar system is going to become uninhabitable, our problems are much more dire. I've been assuming that this more extreme threat is the one we'd be dealing with, because it's a more complex problem so there's more to talk about.