What are the longevity limits to a space probe’s power supply for continuous operation and also what are the limits for a system that can be hibernated to be reactivated?
The Voyager probes launched in the later 70’s are expected to have some power to operate till about 2025 after which Wiki states that they won’t have enough to power ‘any single instrument’. So by using radioactive decay we get 40-50 years of decreasing but still usable power.
I assume because of the way the radioactive decay works we would have to increase the mass significantly to get just a little more time out of that type of system, which increased mass is not all that good for space travel.
So what do we have that can work longer if anything? Are there longer lasting nuclear decay batteries? Can solar compete in longevity if the probe is sticking around the inner solar system?
If this is for a intersteller probe: Can solar power from the arriving star be expected to re-awaken the probe, can solar technology survive frozen hibernation? Can chemical batteries be used, just frozen for the trip until the new star defrosts them? How about mechanical systems to actually put a chemical battery together triggered by the heat of the new star, or even to directly generate power (though it would be very short lived)?
We don’t really have any clue for a true interstellar probe, which would reach the vicinity of another star: The timespans involved are so far beyond what we’ve had any ability to test, that we wouldn’t really be able to trust any material or part to work.
You could make nuclear power supplies to last an arbitrarily long time, but they’ll all have about the same energy density, so the mass of the power supply will be roughly proportional to the amount of time you need it to be operational for. And it’d add extra complication, including extra moving parts (which you want to avoid as far as possible) to make a nuclear power supply that could go dormant and then revive, so you’d need to power the entire voyage, not just the interesting bit at the end.
I don’t know how long solar panels last in the inner solar system. I imagine that the limiting factor is probably degradation by micrometeorites and space dust. Usually, though, the longevity of inner-system missions is limited by other factors, such as orbital degradation, consumable cryogens, or just loss of funding/time for the ground stations on Earth to listen to them.
I assume this is about the same total energy output? With a longer half-life, you could trade less energy at the start of the mission for a longer time until until you can’t power that ‘any single instrument’ any more.
So you should be able to get a longer life if you *really *need it, but you’d be hobbled in what you could do while you’re near the other planets for your sling shot maneuvers.
There’s a fascinating website called In the Public Domain, which appears to be written by one man, Greg Geobel, who is a fount of information. I spent a couple of days just poring through his primer on space flight propulsion, here: http://www.vectorsite.net/tarokt.html
And it was a fascinating read. On a tangent, there’s a bit about the nuclear “radioisotope thermoelectric generators” (RTGs) used in Voyager, and I’ll quote a bit:
(omit description of two accidents involving RTGs)
The third and last US RTG accident took place in 1970, as a consequence of the near-disastrous Apollo 13 mission. The Apollo Lunar Module (LM), used by Apollo crews to shuttle themselves to and from the Moon, carried an RTG as part of a lunar science package that the astronauts would set up and leave in operation. However, the Apollo 13 crew used the LM as a “lifeboat” to help get them back to Earth and the science package remained on board. The spacecraft was guided to a reentry over the Tonga Trench in the Pacific, one of the deepest oceanic canyons in the world, and no radioactivity was released before impact.
The United States gradually lost enthusiasm for nuclear power in space, due to environmental issues and the cost of building an RTG that could meet stringent safety requirements. RTGs were only used on US deep-space probes, such as the Viking Mars landers, the Pioneer 10 and 11 probes, the Voyager 1 and 2 probes, and the Galileo and Cassini probes. In the deep reaches of space beyond Mars solar power wasn’t generally seen as strong enough to power a sophisticated spacecraft and an RTG was the only practical option.
In summary the impression I have is that larger RTGs would be practical but politically dubious. Solar seems to have a problem with scale - the power output is enough to run ion and magnetic drives enough to keep a satellite on station, but not to power it through the solar system. A nuclear engine could power ion drives to do that, but the political obstacles would be just as great.
As for long-duration space probes, as I understand it the Voyager probes are being very gradually degraded by micrometerorite impacts, although presumably the space outside the solar system is relatively clear. But the time scale means that the the effort would be futile. By the time such a probe reached the target star, what would it do? Where would it transmit the data, and how? The Voyager probes are speed demons, but would apparently take more than 70,000 years to reach Proxima Centauri. Plus four years to transmit the data back. We’ll have little withered bodies and giant brainy heads by then.
Went to your intended link, wondering if they mentioned another RTG accident. It’s not there, but it is here. Basically, the CIA/NSA/what-have-you, wanted to listen in on Chinese telemetry. Satellites weren’t all that, at least in 1965-66, so TPTB decided to try and emplace a listening post atop Nanda Devi, a 25,643 ft tall peak in India. The post would be powered by a RTG. Well, they emplaced it, waited a season, went back to retrieve the data, and ‘whoops’, discovered the post and RTG had been knocked off the mountain crest by an avalanche/landslide. The RTG and post were buried beneath several hundred tons of rock, where they remain today. It’s just one of the headwaters of the Ganges, no biggie.
One of the more interesting stories from the Cold War. I can’t imagine the difficulty in climbing a 7400m peak, much less while having to portage up a listening post and emplace it.
You could use an actual controlled nuclear reactor rather than a radiothermal generator. Uranium-235 has a half-life of 700 million years. It will remain inert (more or less) until a critical mass of it is put together.
It’s certainly possible to design solar panels that can survive extremely low temperatures. A solar cell is just a semiconductor; if it’s properly packaged (e.g. using materials that don’t become brittle or warped when cooled down), it should survive low temperature just fine.
It depends on how you would define “space probe” I think. We have working electronics from the dawn of the transister. Capacitors have a limited shelf life depending on heat, even when not in use they are undergoing slow chemical breakdown.
I’ve asked a similar question about how long we can store data, and really the question is that there can’t be a real hard answer. We don’t know because we can’t test it. Voyager 1 is still working 34 years later transmitting data to us and is expected to work until at least 2025. I wonder how much of Voyager 1’s longetivity was intentional, anyone know?