40 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 ...
ymb1's user avatar
  • 2,423
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 - ...
Nuclear Hoagie's user avatar
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 ...
Organic Marble's user avatar
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 ...
Organic Marble's user avatar
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 ...
Woody's user avatar
  • 21.6k
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 ...
Organic Marble's user avatar
30 votes

Why exactly does Curiosity's RTG make more electricity on cold days?

There is Carnot's theorem for the theoretical maximum efficiency of heat engines. It is valid not only for mechanical engines like steam engines or Stirling engines but also for solid state devices ...
Uwe's user avatar
  • 49k
30 votes

Could sheets of stacked graphene be used as part of a heat shield, since its melting point is 3000k to 5000 K

For a non ablative heat shield you need a material with a very high melting point and a very low thermal conductivity. It should not burn in hot air. Unfortunately graphene seems to have a high ...
Uwe's user avatar
  • 49k
28 votes
Accepted

Why are RTGs different colors?

Answer: Thermal radiating coating technology has improved, so they are no longer forced to be sub-optimally black in visible light. They can now be white and reflect incident sunlight to improve ...
uhoh's user avatar
  • 149k
28 votes

Why are RTGs different colors?

The big difference between the two darker RTG fins (Black and Grey) and the white RTG fins, is that the white fins were destined for use in an atmosphere (Mars). The presence of an atmosphere, even ...
Josh King's user avatar
  • 2,429
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 ...
SF.'s user avatar
  • 55k
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 ...
Organic Marble's user avatar
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. ...
David Hammen's user avatar
  • 74.8k
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 ...
SE - stop firing the good guys's user avatar
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 ...
Starfish Prime's user avatar
19 votes

Has any vehicle prior to Starship's IFT3 "taken a selfie" during reentry?

Although it doesn't exactly match your question requirements, in the early days of the Shuttle program Columbia had an instrument mounted on its tail known as the SILTS pod (Shuttle Infrared Leeside ...
Steve Pemberton's user avatar
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 ...
IronEagle's user avatar
  • 965
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 ...
Ross Millikan's user avatar
16 votes

temperatures of metal facing the sun in space

A single number is impossible to give, unless you exactly specify the kind of metal. So I'll answer in the general sense. The first question to answer is "How much energy does the sheet absorb?&...
Polygnome's user avatar
  • 6,926
16 votes

Has any vehicle prior to Starship's IFT3 "taken a selfie" during reentry?

Several of the Apollo missions filmed their reentry using the 16mm film camera, looking out of one of the CM windows. Example: Apollo 15. A few weeks ago, Varda released ...
Hobbes's user avatar
  • 128k
15 votes
Accepted

Why the thermal imaging of Mercury's surface requires a telescope on a jet flying through an eclipse?

Why not a satellite-based telescope to observe Mercury in the thermal infrared? Space-borne satellites that are designed to look at the Sun (e.g., SOHO) aren't instrumented to look in the thermal ...
David Hammen's user avatar
  • 74.8k
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 ...
Carlos N's user avatar
  • 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 ...
Uwe's user avatar
  • 49k
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 ...
asdfex's user avatar
  • 15k
13 votes

Why exactly does Curiosity's RTG make more electricity on cold days?

All heat engines, whether mechanical or solid state, produce work based on heat flow across a temperature difference. The maximum efficiency of a heat engine depends on how large that difference is.
ikrase's user avatar
  • 8,874
13 votes

Is a Raptor 2's thermal output really comparable to that of a nuclear power plant?

On average it isn't wrong as a "close-enough" analogy. All but one of Britain's 10 operating nuclear power stations are scheduled to close by 2023 and two of these are planned to close at ...
Organic Marble's user avatar
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 ...
Tom Spilker's user avatar
  • 18.3k
12 votes

Insulation on rockets--why take it to space?

The insulation's job is also to prevent ice from forming on the rocket's skin (and breaking off during ascent). Shards of ice are more dangerous than chunks of foam. Even if ice were no problem, for ...
Hobbes's user avatar
  • 128k
12 votes
Accepted

Why is the Heat Shield of ESA's Solar Orbiter Black in colour?

Apparently, black was chosen despite its thermal properties. This 2005 paper was written at the end of the assessment phase where technical feasibility of the mission has been demonstrated. It shows ...
Hobbes's user avatar
  • 128k
12 votes
Accepted

Is a Raptor 2's thermal output really comparable to that of a nuclear power plant?

Power is in units of "energy rate," joules per second, and thus it is relatively easy to estimate for a rocket engine: take the "energy rate" of the exhaust gases at the nozzle ...
BrendanLuke15's user avatar

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