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How to maintain operating temperature for outer space electronics ?
Posted by
BravoV
on 25 Jan, 2014 19:22
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How those satellite engineers design the system that can maintain the electronic components within their safe operating temperature while at outer space ? Satellites for example, they work in both extreme temperatures, super hot when there is a sun or super cold when in the dark. Or the outer space objects or probes that are constantly exposed to the sun ?
Are there other special techniques or something that is not commonly used ?
To be honest, its getting dizzier when it comes to think about temp co or the risk of too many extreme temperature cycling that may affect the temperature hysteresis and etc.
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#1 Reply
Posted by
Simon
on 25 Jan, 2014 19:26
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hm thats interesting, never really thought about it. They could have put the electronics in a well insulated case and heat it to the right temperature
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#2 Reply
Posted by
BravoV
on 25 Jan, 2014 19:32
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They could have put the electronics in a well insulated case and heat it to the right temperature
Ok, what if its constantly exposed to the sun ? How to dissipate the heat or the "accumulated" heat ? Its not like on earth where we can use convective heat transfer like through the air in the atmosphere.
Remember, its vacuum out there, an almost perfect heat insulator.
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#3 Reply
Posted by
Simon
on 25 Jan, 2014 19:35
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what about reflectors ? put the electronics behind the solar panel that is powering it, after all a vacuum is an insulator so as long as the suns rays do not beat on it all is well ?
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#4 Reply
Posted by
BravoV
on 25 Jan, 2014 19:39
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what about reflectors ? put the electronics behind the solar panel that is powering it, after all a vacuum is an insulator so as long as the suns rays do not beat on it all is well ?
Ok, lets say you have a 100% reflection (which I doubt it), but still, the electronics components still dissipate heat no matter how efficient it is (never 100% right ?), so how to "move the heat" out of the components so they stay within safe range ?
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#5 Reply
Posted by
IanB
on 25 Jan, 2014 19:40
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Thermal management in space is all about radiation. You point the things you want to cool down towards outer space, which is at a temperature of just a few Kelvin, and you protect the hot sun-facing side with reflective foil and insulation.
For a thought experiment: place the side with good insulating tiles towards the sun. Place the side with good heat conduction and radiation properties away from the sun. If you now look at the thermal profile, the side of the insulating tiles away from the sun will be quite cool.
Objects like satellites in space do not rotate and spin randomly. They always have their orientation precisely controlled, and they always have exactly the right side pointing towards the sun.
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This documentary has some information on the subject.
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#7 Reply
Posted by
dfmischler
on 25 Jan, 2014 23:03
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#8 Reply
Posted by
Rerouter
on 25 Jan, 2014 23:10
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equally and they found this out with the voyager probes, the heat from the electronics does generate an incredibly tiny amount of thrust, causing the probes path to curve if more heat it expelled out one side than the other, it also means that by constantly cooling away from the sun you would eventually decelerate and start accelerating back towards the point of origin if the power source lasted a few centuries.
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#9 Reply
Posted by
Skimask
on 25 Jan, 2014 23:33
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equally and they found this out with the voyager probes, the heat from the electronics does generate an incredibly tiny amount of thrust, causing the probes path to curve if more heat it expelled out one side than the other, it also means that by constantly cooling away from the sun you would eventually decelerate and start accelerating back towards the point of origin if the power source lasted a few centuries.
Pioneer Anomaly?
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#10 Reply
Posted by
IanB
on 25 Jan, 2014 23:52
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equally and they found this out with the voyager probes, the heat from the electronics does generate an incredibly tiny amount of thrust, causing the probes path to curve if more heat it expelled out one side than the other, it also means that by constantly cooling away from the sun you would eventually decelerate and start accelerating back towards the point of origin if the power source lasted a few centuries.
Conversely, the radiation from the sun hitting the space craft can impart a tiny amount of momentum in the other direction. This is the origin of the solar sails concept.
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#11 Reply
Posted by
Rerouter
on 26 Jan, 2014 00:02
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If you really wanted to get scifi, the concept of a neutrino sail would magnitudes more effective, just need to find out how to force them to react with matter at a much higher rate,
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#12 Reply
Posted by
tszaboo
on 26 Jan, 2014 00:51
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If you want well documented essays about the topic, read some "cubesat" documentation. It is a platform for universities to send a satellite not bigger than 100mm into orbit. Some of them are there for years. Since it is uni, it is well documented.
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#13 Reply
Posted by
Kohanbash
on 26 Jan, 2014 00:52
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Hi
As IanB said one of the primary ways to control temperature is by controlling which surface is pointing to the sun and which surface is pointing to space (radiator panel). All of the thermally sensitive devices are directly heat piped (metal/carbon connections) to the radiator panel
On a past project we spent awhile working on a project that had solar panels on four sides. We loved the design since we could always get power from the sun and we could be in any orientation. Unfortunately one of our thermal engineers said it would not work since we would not be able to cool the system since the black (dark blue) solar cells would not radiate enough heat away. So we ended up making two sides (approximately) with solar panels and the other two sides white to help radiate the heat into space.
For the opposite extreme when it gets cold we also put heaters on certain (typically external) components such as the cameras, motors, and science payloads). We also use MLI (its the gold foil you see on satellites) to prevent heat loss via radiation.
Some systems that use a radioisotpes with an RTG can use the power produced to charge the batteries and then use the heat produced to keep the system warm. Depending on the RTG you can heat-pipe the heat to specific regions that need to be cool. The early lunokhod moon rovers had a lid that they would close at lunar night to stay warm and then open during the lunar day in order to not overheat.
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#14 Reply
Posted by
G7PSK
on 26 Jan, 2014 15:35
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There ought to be an EEVblog satellite It seems that they are very cheap to make now.
http://www.50dollarsat.info/under $250 to make but they don't say what the launch cost is.
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#15 Reply
Posted by
SeanB
on 26 Jan, 2014 15:44
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Estimate at $10 000 per kilo, but if you can get space and fit in as a ballast mass on a launch ( they actually do add ballast mass to do compensation for uneven satellites or to trim to a specific launch vehicle charactaristics ) along with having something the launch operator thinks is cool, and are prepared to wait and not care much about orbit then it can be a lot cheaper, or even free. A lot of picosats and microsats go up that way as part of another paid for load. Less steel blocks to machine, and so long as you are not a bother and will not interfere with the main payload you are cheap to add. You might have to pay for the added mounting fixtures, testing and release mechanism to free you from the second stage booster before it is deliberately deorbited.
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#16 Reply
Posted by
Nerull
on 26 Jan, 2014 16:41
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If you really wanted to get scifi, the concept of a neutrino sail would magnitudes more effective, just need to find out how to force them to react with matter at a much higher rate,
Sure, but that's essentially in the realm of 'magic' sci-fi, at least for now. Solar sails could be built today, if we really wanted to.
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#17 Reply
Posted by
BravoV
on 26 Jan, 2014 17:07
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Thanks for all replies guys, much appreciated !
Special thanks to Greg Robinson for that BBC video, it simply answers lots of my questions, and dfmischler for that Sojourner Mars Rover Thermal Performance document.
Just knew that those shiny heat protection golden foils are actually made from Kapton + aluminium foil.
For geostationary orbit satellites, I guess the design and calculation for the ratio for the hot and cold sides area is really critical isn't it ? Apart from the daily routine that it must cycle through day (facing sun) and night (behind the earth) and extra occasions that will last for quite sometime like during total sun eclipse.
I'm imagining if there is a problem at one of those small rocket thrusters that are maintaining the satellite orbital position and the "orientation" went crazy, and ended up turn it up side down that made the cold side facing the sun while hot side facing outer space for long period, magic smoke ?
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#18 Reply
Posted by
SeanB
on 26 Jan, 2014 17:17
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Rocket thrusters are there but are very rarely used, as they have a very finite fuel supply ( and you do not have an easy way to go put more in the tank either) so almost all orbiting satellites have reaction wheels to do orientation changes to point solar panels to the sun or aim antennas at a particular point. They work by storing up momentum in 3 flywheels that rotate the satellite around it's centre of mass to point in the right direction. Eventually you build up enough momentum that you have to dump it by using a series of thruster burns to counteract the change in wheel rotation and then you gradually build up again. Typically they only want to do this less than once a month to conserve fuel. As the fuel consumption is measured in grams per month and there is typically only 100 kg which is there for all manoeuvring including orbit changes and it has to last 15 years minimum and preferably 25 years using 3g a day will lead to a short life.
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#19 Reply
Posted by
BravoV
on 26 Jan, 2014 17:24
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Fly wheel ? Don't see that in the BBC video ?
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#20 Reply
Posted by
SeanB
on 26 Jan, 2014 17:38
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There in the base unit as reaction control, placed pretty close to the middle of the platform. Right next to the 3 accelerometers and the ring gyros.
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#21 Reply
Posted by
DutchGert
on 27 Jan, 2014 10:59
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With CubeSats they use reflective shielding as a main protection against heat.
Another problem is the low-orbit they usually fly in which means there temperature cycles is from -xx to +1xx a few times up to a couple of 10 times a (earth) day.... This means your PCB and components get heavvy stresses due t bending etc.
Therefore they generally don't use BGA's or QFN type packages because the soldering joints would just break. Using quad flat packages with leads and special solder technigues solves a lot of the reliablity problems in this area.
And ofc, do not use an Electrolytic in space...
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#22 Reply
Posted by
SeanB
on 27 Jan, 2014 18:42
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You can use wet slug tantalum with no problems, just derate them a lot. They are the only high value capacitors available in a glass frit hermetic can. Biggest problem is getting heat out, as you only have conduction or direct radiation.
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I worked on a cubesat some time ago, and worked on making a small radar experiment for it with a bunch of local guys. It was a very cool opportunity. I worried a bit about the heat buildup from the power regulation our board needed, characterizing the frequency of the crystal at the range of operating temperatures, and including a temperature monitoring thermistor... but in the end the board was a tiny fraction of the power budget and the remaining electronics, batteries and charging circuits kept the inside of the cube at a fairly limited range of shirtsleeve temperatures. Lucky us!
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#24 Reply
Posted by
Frenchie
on 29 Jan, 2014 02:15
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As others have posted, the aim of the game is to keep as much heat from the Sun out of the satellite as possible. That source is will dominate over any internal generation so if you can handle it, you can generally deal with the rest.
Unless the orbit is highly eccentric, the time in shadow will likely be less than 50% of the orbital period. That combined with the fact that you're relying on radiation to dump heat to space tends to limit the low end of the temperature swing. Your electronics is still going to need a massive working range, but thankfully not down to as low as single digit Kelvin. The more circular the orbit, and the higher it is will further reduce the average time in full shadow.
Of course, when you have a highly eccentric orbit (eg, Moon transfer, planetary transfer), its possible to have very long periods in full sunlight (days, months or years). Eg The Apollo missions spent their entire transfers to the Moon and back in unobstructed daylight. To prevent damage to the spacecraft they had them revolving about once every 3-4 minutes to ensure they were heated evenly (and also dumping heat evenly).
The radiators themselves are pretty damned efficient at what they do. Despite being in full sunlight, the crew of Apollo 13 were freezing because most of their 1960's high heat output electronics was switched off. Instead of having to deal with that heat, the radiators were only dealing with sunlight resulting in a very cold (but still habitable) cabin.