It turns out that 1g is almost exactly 1 light-year per year squared (actually about 1.03). So it would take about six months to accelerate to 0.5c at 1g, or one month at 6g (discounting relativistic effects, which would still be fairly minor at that speed).
Trying to reach speeds like that with chemical fuels is pretty much out of the question – the amount of fuel needed turns out to be an exponential function of delta v (because you need fuel to accelerate the fuel that hasn’t been used yet, so each increment of velocity multiplies the mass of fuel needed for each mass of payload).
Heck, trying to reach speeds like that with* fusion* is pretty much out of the question. Even with an antimatter/ total conversion drive you’d need more fuel than dry mass; and to reach high (>80% lightspeed) velocities you’d need something other than a pure rocket, like a ramjet, etc.
Right. The problem isn’t energy. We can just use matter-antimatter annihilation, all we need to do is create antiprotons one at a time in a reactor and figure out some way to store them. This is just an engineering problem and all it would take is trillions of dollars. And then we load up the antimatter into our rocket and blast off to Gliese 581 at 1g, or heck, 1.4g to get the astronauts used to the gravity and get their faster. No problemo. Except you’re going to run out of fuel if you use a rocket.
All the science fiction rockets of the first half of the 20th century violated the laws of physics, they assumed you just needed energy and you could blast off to Alpha Centauri at whatever speed you wanted. Except even with total conversion of matter to energy a rocketship can only carry so much fuel. And carrying more fuel makes things worse, because you need to burn fuel to move your giant fuel tanks around.
So blasting off at 1g for 20 years in your atomic rocket violates the laws of physics, because you’ll run out of reaction mass. And don’t think in terms of “adding more fuel”, because what that really means is “making your payload smaller”.
Invent a method of travel that isn’t a rocket, and none of this applies. Except of course, nothing like this is even on the horizon, even in theory. It’s possible a physicist will invent a reactionless drive tomorrow, but we have no reason to think anyone will, because it would require a breakthrough in our understanding of the laws of physics. And even if we have a breakthrough in our understanding of quantum gravity that doesn’t mean we’ll ever create such a thing as a reactionless drive, let alone the more exotic stuff.
I wouldn’t be worried about the CO2 and whatever freezing out so much as the water, though. I can’t really see any way that won’t all end up frozen onto the night side.
According to this (PDF…bottom of page 4) 100 milligrams of antimatter is equivalent to the Space Shuttle in terms of propulsive force.
So, there are 259,200 minutes in 6 months. The Space Shuttle burns its load in 2 minutes so we need half that number…but then we need the equivalent at the other end to slow down so will stick with it.
100 milligrams is 0.00022 pounds which means we need about 57 pounds of antimatter to do the trick. Call it an even 60 pounds for a little extra maneuvering fuel and whatnot. Easy.
Currently though CERN has produced about 1 billionth of a gram of antimatter over the last ten years at a cost of hundreds of millions of dollars.
Sooo…if someone can figure out how to mass produce and store large quantities of antimatter cheaply the rest should be relatively easy.
What if we had an orbital tower that were hollow? Could it be used as a maglev? Mechanically accelerate the probe at the start, then let EM take over. There’d be no atmosphere inside to fight. Obviously this would be a one-way trip.
Or, how about an EM launcher going through the moon? To what speed could you accelerate a 1 tonne probe? How about a 100 Kg probe?
Or, to put the question in reverse, how long a launcher in space would you need to accelerate a 1 tonne - or 100Kg - probe to 0.1c?
And what use is a probe that whips through the Gliese 581 system at 29,979 kilometers per second? You have to have some method of slowing the probe down. I suppose a probe that spends the whole trip decelerating from it’s initial .1c speed is an improvement to one that spends the first half accelerating and the second half decelerating.
Ending in either a crash landing or a very quick flyby, without some self-contained means to perform a braking/deceleration maneuver of comparable energy cost.
Remember how on Star Trek (various generations) they never had just “beer” but “Kardassian beer” or not just “prawns” but “Gorvenian prawns” etc. etc.?
I have invented a new desert to honour this newly-discovered planet, Gliese 581 g. It is called “Baked Gliese”. One side has a layer of whipped egg whites that are flash-baked to 581 degrees (cute touch huh?) by a laser beam. On the other side it is hard-frozen ice cream.
(Actually, the dish is just baked Alaska turned on its side but don’t tell anyone. )
Even if your probe could survive 100 gees on launch (optimistic, I think, but we’re obviously talking far future tech here), I get that you could only reach about 0.03% of c by launching through the Moon.
Given that we’ve been happy with those sorts of results with probes to the moon and other planets in the past, I don’t think that that’s a problem.
Is 100G a problem for an unmanned probe? And G is rather less on the moon anyway. Further, this isn’t far future tech: it’s a matter of logistics and funding. We have tunnelling machines. We have maglev. We have linear accelerators. We have sufficient power sources. We have launchers. The non-trivial problem is the expense of getting everything to the moon.
Even if 100g isn’t a problem you have the problem of slowing down once you arrive at Gliese else the whole trip will net you a fast flyby at the other end.
If you carry enough fuel on-board to stop in the Gliese system your probe will be HUGE and accelerating that at 100g is probably out of the question.
Antimatter I think is the only thing non-scifi that we know of that will work.
Unfortunately we cannot produce much at all and currently it costs about $62.5 trillion per gram so a wee bit expensive. Solve that problem and a lot of possibilities open up (and pray we do not make antimatter bombs with it).
For an idea of what a team of scientists and engineers think of what it would take to launch an interstellar mission, take a look at Project Daedalus or Project Icarus.
Daedalus was a design study done in the 1970’s by the British Interplanetary Society for an unmanned probe. They believed they could reach Barnard’s Star (about 6 l.y. away) in 50 years using a massive (54,000 ton!) two-stage fusion rocket. Daedalus wouldn’t have stopped at it’s destination, but zip past at 0.12c. The rapid transit through the target system was to be mitigated somewhat by beginning observations while the probe was still years away from arrival, then deploying a number of sub-probes targeting any areas of interest that were identified.
They seemed to think the engineering challenges could be solved (although IMHO the fusion rocket concept still seems far-fetched today), and that the main obstacles were economic and political - the vehicle would be so expensive to construct, it couldn’t be done by any one nation. It would require an unprecedented level of international cooperation for a couple of decades.
Icarus is a modern-day revisiting of the Daedalus design, the main difference being this time they want to allow for some deceleration before reaching the target while possibly trading off a longer time en-route. This project is still ongoing and they don’t have a specific target selected yet, but are considering stars within 15 l.y., which they think they could reach in a century. At 20 l.y., Gliese 581 is a little bit out of range.
That was Earth-gees, not Moon-gees. When you’re running a linear accelerator clear through a planet, the gravity of the planet itself is pretty much irrelevant. In any event, the final speed is proportional to the square root of the acceleration, so even if you could make a probe to survive ten thousand gees, you’re still only increasing the final speed by a factor of ten over what I had said, which is still about a thousand years to get to another star.
Yes. I’ve been plugging the numbers into Newton’s equations and the numbers are not pretty. We’d need a very long accelerator indeed. So we can scratch that idea.
You are forgetting about relativity, we could get to the edges of our galaxy rocket mans lifetime because of realitivity at .1c, although no one on earth would be alive
This just occurred to me: On a tidally-locked planet, there would be no sunrise or sunset. What sort of time-sense, if any, would lifeforms evolve there? If there were sentient beings, would they have no clocks, and no words for time-related concepts more specific than “before” or “after” or “long time” or “short time”? And without that, could they develop enough science to have an industrial civilization?
Depends on how interested in astrology/astronomy they were. Far enough into the darkside to see stars, you’d see the constellations change as the planet orbited it’s star.
In addition to seeing the stars change on the dark side, if there were an axial tilt - and I understand that solid planets without largish moons tend to tumble over the aeons so there could be a large one - they would have seasons.
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