Naked Science Forum
General Science => General Science => Topic started by: Eric A. Taylor on 02/01/2011 05:50:01
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As a welder I know that when metal, especially steel and aluminum become quite fragile when cold.
Now when I say "cold" I mean "Earth cold", depending on the alloy you may need to heat your weldment up to a few hundred degrees to prevent cracking. Even low carbon steel needs to be preheated if it's very cold (say below 35 F.)
I've just heard that Voyager 1 has reached the 10 billion mile mark. This far away it must be extremely cold, just a few degrees above absolute zero. If I were to take a space ship to catch up with one of the Voyager or Pioneer probes to bring it home would I need to take care to warm it up before bringing onto my nice warm ship.
If I hit it with something could it shatter like a rubber ball frozen in liquid nitrogen?
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You may well be right Eric. The craft still has some power which is reckoned to last until 2025 but any heat from this source is likely to be localised. I'm unsure of the characteristics of the materials in Voyager 1 but I expect some alloys of aluminium would have been used. I suppose the stresses in its flight since launch have been relatively very low. What about the bits of crafts left on the moon? They get hugely temperature cycled on a regular basis.
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I would guess you will need to take care, mostly because the vehicle is made up from very thin and light mass sheets, used to provide thermal insulation to the interior ( more to keep the inside warm, rather than cold, so the electronics inside do not get so cold that they become superconductors, or the silicon stops being a semiconductor) that will tend to tear if touched by anything but the lightest touch. Best way to catch the probe would be to attach on the original spacecraft bus attachments, as these were designed to handle the launch stress and are designed to allow the probe to be handled. You would also need to fold in the RTG generator and such items as were deployed on arms, as this will make handling easier. There may be problems doing this, as the joints are most likely stiffened to immobility after multiple years of vacuum exposure.
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I would guess you will need to take care, mostly because the vehicle is made up from very thin and light mass sheets, used to provide thermal insulation to the interior ( more to keep the inside warm, rather than cold, so the electronics inside do not get so cold that they become superconductors, or the silicon stops being a semiconductor) that will tend to tear if touched by anything but the lightest touch. Best way to catch the probe would be to attach on the original spacecraft bus attachments, as these were designed to handle the launch stress and are designed to allow the probe to be handled. You would also need to fold in the RTG generator and such items as were deployed on arms, as this will make handling easier. There may be problems doing this, as the joints are most likely stiffened to immobility after multiple years of vacuum exposure.
Well I understand THAT part of it. I'm speaking (well ok typing) purely of the fragility of the metal. Assuming I've traveled to the Voyager in a smallish space ship, I'm not sure I'd want to bring the RTG aboard. To me it would seem safer to cut the damn thing off. It is after all highly radio active. Though shielded for the benefit of the craft it may still be too hot to be safe. (I'm also assuming this is being done in the far future, maybe more than 100 years from now) Where would the booster/spacecraft interface be by now? Surly Voyager has done some corrections during it's trip. if these corrections even if tiny, were done 30 or more years ago (good God am I rally THAT old?) it would be billions of miles away.
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The matal would be a little brittle, as it has been exposed for a rather long period to heavy radiation ( not from the RTG source, but more the cosmic rays and other ionising radiation emitted from the sun and such, that we are not exposed to as we are protected by the atmosphere and the magnetosphere ) and the actual metallic structure has had a large number of dislocations created in it, exactly as if it has been stressed to near it's fatigue limits. Added to that is the hydrogen embrittlement caused by the slow diffusion of the solar wind impinging on the craft. This would combine to make the material more brittle than a sample kept on the earth in a vacuum at the same temperature. However the probes are still strong enough to fulfill the original specs, as there is no major stress on them aside from very small forces from the attitude control systems keeping the high gain antenna pointed at the sun. The RTG will probably have decayed by 2025 to below the amount of power needed to power the transmitters, not that the spacecraft will stop working, it will still be able to listen to commands and act on them, just not relay the results. There is currently AFAIK not enough power to run certain instruments, but the low power units and the navigation systems are still running fine, the excess power is dissipated in keeping the spacecraft bus warm.
Interesting is that the controller is a CDP1802 made in the early 1970's, and was used because of it's low power consumption and it's ability to tolerate radiation.
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Interesting is that the controller is a CDP1802 made in the early 1970's, and was used because of it's low power consumption and it's ability to tolerate radiation.
Correction: The CDP1802 has erroneously been reported as being used in Voyager, but it was not.
It was used in the Galileo probes.
See: wikipedia.org/wiki/Voyager_program#Computers
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We have plenty of materials suitable for handling liquid hydrogen and helium, so absolute temperature is less of a problem than thermal cycling. But once you get beyond Mars, I guess you can pretty well ignore the solar input compared with the power dissipation from the interior components so the craft should settle to a predictable and stable temperature gradient. The trick from there on is to minimise local stresses by using gravitational acceleration wherever possible, with very slow course corrections in between.