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Using 1960s engineering (and many, many nuclear bombs), an Orion-powered starship could make it there in less than 150 years, one-way. And no slowing down; it
by randallsquared 14y ago
Using 1960s engineering (and many, many nuclear bombs), an Orion-powered starship could make it there in less than 150 years, one-way. And no slowing down; it would be a flyby.
http://en.wikipedia.org/wiki/Project_Orion_(nuclear_propulsion)#Interstellar_missions http://en.wikipedia.org/wiki/Project_Orion_(nuclear_propulsi...
- rdl 14y agoCan't you just turn around midway and start throwing bombs out in front of your path of travel to slow down?
- jasonkester 14y agoOne of the interesting things in that Wikipedia link is that you only need to run your Orion for 36 days to get it up to speed. Beyond that, detonating more bombs won't accelerate you any further. So yes, you could turn it around. But surprisingly it seems you can wait until a month before arrival to do so. The downside, however, is that your max velocity gets cut in half if you bring enough bombs to slow down. With better explosives, you could get a higher max velocity and therefore closer to the "accelerate halfway, decelerate halfway" ideal case, but at the moment such explosives don't exist.
- rdl 14y agoI'm not sure how that works out. Do 36 days of acceleration at the beginning (or spread it over a year to reduce peak acceleration) -- go from 0 to 0.1c or whatever the cruise speed is. Coast for ~100 years. Spend the last year going from 0.1c to 0. It does mean you have to carry twice as many bombs, and carry half of the bombs for 149 years, but bombs are really lightweight relative to the ship. It also means you can't just jettison the pusher plate, which is probably a bigger deal.
- randallsquared 14y agoIn this case, the weight of the bombs is larger than the rest of the ship: 50K tons for the ship structure, 300K for the weight of the bombs [1]. Twice as many bombs essentially doubles launch mass. Orion is a great concept for tooling around the solar system easily, but what it buys us over interstellar distances is that it makes macroscopic payloads and reasonable travel times possible; they're still not easy. [1] Table 2 in http://galileo.phys.virginia.edu/classes/109.jvn.spring00/nuc_rocket/Dyson.pdf http://galileo.phys.virginia.edu/classes/109.jvn.spring00/nu...
- mikeash 14y agoJust to reinforce: Orion is still a rocket. And not a particularly efficient rocket, either. It uses an incredibly energy-dense fuel, but not so dense to allow you to ignore the rocket equation.
- duopixel 14y agoWhat if instead of braking Orion itself, it just drops off a lighter satellite that is able brake without expending so much energy?
- Tichy 14y agoI'd think it would still have to brake using Orion technology, so it is doubtful if it could be built smaller than Orian itself.
- JoeAltmaier 14y agoIt could use solar wind, or gravity-slingshot (which can slow as well as accelerate a satellite). So yes it could be much smaller.
- rdl 14y agoI wonder if Elon Musk has ever spoken about Orion. I'd love to live in a world in 2030 or so where a private shuttle runs Earth-Mars every few weeks using Orion technology, since it wouldn't then need to operate on energy-conserving orbits.
- randallsquared 14y agoSure, but it raises the number of nukes needed at launch considerably, holding the travel time constant. More than double, even leaving aside considerations like the additional storage size. Also, designing nukes that last for 150 years before being used is non-trivial (can't use tritium in the initiator, for example; it decays too rapidly for that).
- tocomment 14y agoI don't see why it can't use atompsheric braking, or reverse slingshot effect amount the planets to slow down?
- com 14y ago1000km/s on the energy-limited Orion would be hard to slow down using aerobraking without potentially disrupting the planet below, and reverse slingshots would probably occur too fast to do anything more than staying in-system for a few weeks...
- tocomment 14y agoHow about a solar sail for braking? (We've got to be creative, I can't imagine there's no solution for slowing down.)
- polyfractal 14y agoI imagine you would need a ridiculously large solar sail to slow down the mass of an Orion. It's not that slowing down is impossible...you just start throwing bombs the other direction. But by slowing down you increase your travel time, so the 150 year estimate is no longer valid.