41
votes
Finned heatsinks in space
All of the displayed radiators depend more on convection than they do on radiation. There is no convection in space. Finned radiators in space tend to have the fins in the same plane rather than ...
- 73.2k
39
votes
Could a fan be used to prevent overheating on a Venus bound space probe?
Fans work by moving cool air (or other fluid) over a warm surface. If there is no air, like in space, a fan will serve no purpose. Cooling things in space is actually a bit tricky because of this - ...
- 3,687
39
votes
Why aren't the radiators on the ISS straight?
From the horse's (Vought) mouth, the angle created between each panel and its corresponding scissor beam (20°) is to "provide structural stiffness":
The deployment is achieved by rotating ...
- 2,301
37
votes
Is it bad if hydrazine freezes on a spacecraft? Is it always kept as liquid, or can it be safely allowed to freeze and then thawed when needed?
At least for the Space Shuttle, freezing was OK, but thawing out was bad for piping. Hydrazine contracts when it freezes, so it can 'superpack' (more fluid flows in, then freezes, etc.)...then when it ...
- 178k
31
votes
Why aren't the radiators on the ISS straight?
The radiators are jointed because they were launched folded up into a flat stack.
This screenshot from the official NASA visualization tool DOUG shows one of the radiators partially retracted.
This ...
- 178k
31
votes
Why aren't the radiators on the ISS straight?
This is a scissor mechanism, as used in lifts and pantographs. A fundamental property of the scissor mechanism geometry is that it cannot "open completely" (90* rotation of members) due to ...
- 18k
30
votes
Accepted
Are fans ever used in un-crewed spacecraft?
Soviet planetary probes sometimes had pressurized compartments, so I suspected that they might contain fans.
This answer confirms that Venera-8 had a fan. The illustration in the answer has the inner ...
- 178k
29
votes
Accepted
Why did Salyut 7 freeze over, while ISS requires massive cooling system?
Salyut 7 had a active cooling system as well. The heat exchangers are the large white panels, perpendicular to the solar panels, to be seen in photographs of the station. This is necessary on all ...
- 14.9k
26
votes
Accepted
Did Apollo 13 "barbecue roll" under the propulsion of the lunar module?
Was the lunar module also used to perform a barbecue roll?
Yes, although it took them a while to get there, according to the Apollo Flight Journal.
Starting at about 7 and a half hours after the ...
- 167k
26
votes
Accepted
Why do many RTGs have finned heatsinks, when this is considered bad for radiation heat transfer?
With typical active radiators on spacecraft, heat is transferred away from the sources into the radiators through forced convection - as heated coolant. At that point the only concern remaining is to ...
- 54.9k
26
votes
Where exactly are the Apollo space suit sublimators venting steam into space? is there a photo of an astronaut in space that shows the opening?
It can be hard to see because it's on the front of the PLSS behind the astronaut's helmet.
(NASA photo of Irwin on Apollo 15, I cropped it and added the arrow)
Here's an exploded view showing the ...
- 178k
25
votes
Accepted
How are the electronic circuits in interplanetary missions protected from extremely low temperatures?
Space in the vicinity of the Sun is not that cold, perhaps even out to Jupiter. One side of the spacecraft will be receiving sunlight while the side shielded from sunlight radiates into empty space. ...
- 73.2k
21
votes
Why do many RTGs have finned heatsinks, when this is considered bad for radiation heat transfer?
Multi-fin radiators are worse per unit mass.
But for an RTG, it is absolutely vital to provide a very large thermal gradient between the (very small) core and the outer layers. Adding more fins still ...
21
votes
Accepted
Why is the sunny side of JWST's sunshield purple and covered with silicon?
From this presentation James Webb Space Telescope (JWST) Technology Discussion For APPEL Forum, dated August 7, 2008, I see this:
Low $\alpha_S$/$\epsilon_H$ to minimize absorbed solar heat load
...
- 8,001
18
votes
Accepted
Now that Perseverance is "hot" (RTG in place) and before it gets to deep space, how will it stay cool?
2kW is not that much on Earth
You've mentioned radiation and convection in your answer (you forgot conduction). Turns out the properties of Earth's atmosphere make conduction and convection way ...
- 975
16
votes
Accepted
Why do some spacecraft have heat radiators? Why not repurpose the energy?
Yes, you would like to conserve the energy, but sadly that is not possible. The problem is: The energy you have is heat.
The second law of thermodynamics states that entropy always increases, and ...
16
votes
Is it bad if hydrazine freezes on a spacecraft? Is it always kept as liquid, or can it be safely allowed to freeze and then thawed when needed?
The Olympus satellite (1989-053A, 20122) lost pointing and power for long enough that all the fuel froze. It was recovered after a couple months and the fuel defrosted. I couldn't easily find what ...
- 2,107
15
votes
Accepted
Is it feasible to paint SpaceX Starlink satellites black so as not to frequently saturate the CCDs of the Large Synoptic Survey Telescope?
In general satellites are not "painted". They are covered in a variety of Multi-Layer Insulation (MLI) blankets with varying optical qualities. I have seen MLI in silver, black, and gold - sometimes ...
- 4,444
15
votes
Are fans ever used in un-crewed spacecraft?
Sputnik-1 was filled with dry nitrogen pressurized to about 1.3 bar and had a fan to control gas temperature between 20° and 30° C.
See Wikipedia in german or english.
A picture of Sputnik-1 design ...
- 48.8k
15
votes
Finned heatsinks in space
As referenced in another post in this SE, energy from the sun, for example, will heat up a craft on the side facing the sun, unless mitigated by reflective material.
The shadow side of the spacecraft ...
- 1,870
13
votes
Accepted
Why does the Alpha Magnetic Spectrometer (AMS) on the ISS use carbon dioxide for coolant?
1) There is no superconducting magnet in AMS-2. This would have required cooling with liquid helium resulting in a limited life time of only 3 years because of helium evaporating. Instead, they used a ...
- 14.9k
12
votes
Accepted
How cold is the Martian sky at night? Or the day for that matter?
You've asked a question that is very difficult to answer accurately without in situ measurements, which apparently we don't have. The short answer: We don't know closer than ~100K!
There was an ...
- 18.2k
11
votes
Accepted
How have space suits dissipated the heat removed from astronauts?
For Apollo, space suits used the Primary/Portable/Personal Life Support System during EVAs.
This is a schematic of the PLSS:
The PLSS used sublimation cooling. Water was run over a heat exchanger, ...
- 126k
10
votes
Accepted
Why are deeper folds better for absorption?
I just saw this and recognized my research, ha ha. I realize this is an older question but I wanted to give my two cents. The published article is a bit deceitful in describing the technology (which ...
- 216
10
votes
Could a fan be used to prevent overheating on a Venus bound space probe?
The effect of a fan in an electronic device is to accelerate the temperature exchange between circuits and atmosphere.
But that temperature exchange works in both directions. When the atmosphere is ...
- 9,346
10
votes
Finned heatsinks in space
I think what other answers have missed or glossed over is solar irradiation. A radiator facing flat edge into the sunlight will be a strong heater, not a radiator. With 1440 watt/m^2 it's about ...
- 54.9k
9
votes
Why did Salyut 7 freeze over, while ISS requires massive cooling system?
A space station must expel the heat from its electronics. This heat can be considerable, which usually requires large radiators. If the station is dead, then the heat is expelled, without having the ...
- 121k
9
votes
Accepted
What were the uses of the RTGs in the Apollo spacecrafts?
The RTGs powered the Apollo Lunar Surface Experiments Package.
This is also the first thing that comes up when you google "Apollo RTG".
- 178k
9
votes
Why does ISS uses liquid ammonia in the Active Thermal Control System?
Ammonia is used because it has excellent heat transfer properties (as you mention) and a low freezing point. Because of its toxicity, the ISS has internal coolant loops which use water as a heat ...
- 178k
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