We seem to be quite happy with waiting 15 years for the Pluto probe to get there, but how long would we be prepared to wait for a probe that we send to another star?
Or, how fast do we have to make them?
Would you be happy to launch a probe to the Centaurus system that would return results in 50 years? 100 years?
We don’t have any that are nearly that fast.
According to Wikipedia, the current speed record holder among space probes would take about 18,000 years to get there (if it were headed in the right direction).
The problem is that interstellar distances are huge compared to interplanetary ones. A light year is more than 63,000 times the distance from the earth to the sun, and the nearest star is a little over four light years away.
It gets worse if you want to send probes to other galaxies. Then you’re talking millions of years of travel at the speed of light or something close to it, or billions of years of travel for one of our current space probes (from a quick and dirty calculation). The sun would be burned out and gone by the time it got there.
Well, yes. But answering my question solves the issue of how much faster we have to go.
It would have to be a fairly significant percentage of the speed of light. At the speed of light, it would take 4.3 years. At 10% of the speed of light, it would take 43 years. I don’t think we currently have the technology to build a space probe that would go at speeds on the order of 1% or 10% of the speed of light.
In the 1970s, the British Interplanetary Society did an engineering design study on the possibility of building an unmanned spacecraft called Project Daedalus.
The design goal was a probe that could reach Barnard’s Star, which is six light years away, in fifty years. This was a specific design goal because they wanted the probe to reach its destination within the lifetime of the people involved in the project. This would require accelerating the craft to 12% of the speed of light. It would have an initial mass of 54,000 tons and would be assembled in earth orbit. Note that if the Apollo Saturn V rocket were used to launch the components of Daedalus, it would take about 415 launches!
But a 54,000 ton ship is exactly the wrong approach. What we need is Robert Foreward’s Starwisp. An extremely light probe, powered by light pressure from a stationary laser or maser.
So, ‘within our lifetime’ is a reasonable start. This means averaging roughly 0.1c. So how can we reasonably accellerate something to that speed?
The real problem is that anything going at 0.1c or faster is going to be destroyed as soon as it collides with anything large enough to be seen without a microscope. The chances of a probe going that fast and reaching Alpha Centauri without being smashed is essentially zero.
Yeah, that’s the biggest challenge. The other is a sustainable source of fusion (even if you have a hydrogen scoop, you’ll decelerate when you pick the hydrogen up if it’s going .1c slower than you!)
But if we had a probe that could constantly accelerate at g, we’d reach Alpha Centauri in a reasonable amount of time (around 10 years IIRC.) And that would make manned spaceflight a lot easier since we wouldn’t have to worry about artifical gravity or muscular atrophy.
Why would you think this? Space is really, really empty; the probe has a very good chance indeed of getting there without hitting anything.
Obligatory “Hitchhikers” reference:
A way to think of the distances in relative terms:
If our solar system could fit inside a teacup (Sun at the center, Neptune/Pluto at the outer edge) the next closest star would be about 3,000 miles away. Does that give you idea of the distance? There’s a lot of space out there.
Not really. While it’s really empty out there you’re going massive distances.
The value people throw around for interstellar density is 0.1 to 1 hydrogen atom per cubic cm. Let’s take the lower bound of 0.1 protons per cubic cm.
For every cubic meter you move through you’ll run into 10[sup]5[/sup] protons. Not a lot, but from the Earth to Alpha Centauri you have to move through 4.1x10[sup]16[/sup] meters. For a 1 m[sup]2[/sup] tunnel 4.35 lyrs long you’ll have encountered 4.1x10[sup]21[/sup] protons. That wouldn’t be a problem, except that you’re blasting along a 0.1c.
Even worse, at the far end you’ll likely pass through something like an Oort cloud filled with dust or “snow flake” like particles. Since our initial probes likely won’t have brakes, those could definitely ruin your day.
A probe launched toward Bernard’s Star circa 1980 will be the last Earth spacecraft to arrive in the next, say, 50,000 years.
As propulsion systems grow more sophisticated, waiting just two centuries will allow cutting off millennia from the expected space flight. Wait another two centuries and the savings might be tens of thousands of years.
In all likelihood, our 20th century deep space probes will be racaptured and relocated to the Smithsonian’s successor.
Um. Even granting “more sophisticated” propulsion systems (sophisticated enough for interstellar travel, as you imply), how exactly do you envision these deep space probes will be found? Space is very, very big. The probes are very, very small.
Even with a submarine with a really good propulsion system, it would be difficult to locate an object the size of a pinhead floating somewhere in the Pacific ocean.
No. Not really. Any probe launched from Earth will have to go through the asteroid belt, the Kuiper belt and the Oort cloud just to escape from the solar system; then presumably it will have to traverse the equivalent belts of rubble around Alpha Centauri. The chances of it finding nothing in its path are not that great.
This is the damage done to the Space Shuttle’s windscreen by a single flake of paint hitting it at 7.6 kilometres per second - which sounds fast until you realise that that’s only one forty-thousandth of the speed of light. Kinetic energy varies as the square of velocity - the same paint flake travelling at 0.1c would carry *sixteen million *times as much energy. Had it been going that fast it would have destroyed the Shuttle as surely as if a bomb had been detonated inside it. That’s the sort of energy we’re talking about here.
And motion is very, very predictable. Presuming that we still have the trajectory data on each probe available in the year 50,000 or whatever, it should be fairly straightforward to calculate the position to a fair degree of accuracy. Naturally in space, as on Earth, shit happens and a random passing asteroid or comet could throw it far off course but barring that, I don’t see why we couldn’t find at least some of them.
What Q.E.D. said.
Re: your submarine analogy: Technology changes, faster than a 16th century astronomer could imagine. Back in 1506, Copernicus would have been hard pressed to describe the volcanic plumes of Io. Today we have recorded footage of it–along with technologies that would render the genius astronomer silent. Flash forward 500 years from now and the challenge of pinpointing a (historically significant) spacecraft launched from Earth will be child’s play.
Providing, of course, it doesn’t first collide with NCC-1701-D.
Plus, for a probe to do anything useful, it would presumably be transmitting some sort of data back to Earth. It could be tracked down by it’s signal. Now we just have to figure out how to build a probe that will still be operational in 50,000 years…
Actually, no it doesn’t. It goes in fits and spurts, and in different areas at different times. We’re currently in a prolonged spurt, but who’s to say that we won’t shortly plateau? Take PCs for instance: the rate of progress is already slowing down - CPUs have plateaued at about 4 GHz, operating systems are taking longer and longer to develop, adoption cycles are even more extended etc. In medicine, we still can’t cure the common cold. How much did technology change from BC 1 to AD 300?
