69 votes
Accepted

Why wasn't an RTG used on the Juno spacecraft?

That is precisely it. Plutonium-238, which is used in the creation of radioisotope thermoelectric generators (RTGs) is very difficult to come by. There are plenty of news articles on this, from ...
Phiteros's user avatar
  • 5,626
37 votes

Why wasn't an RTG used on the Juno spacecraft?

Another interesting note is that this mission more than any other mission to the outer solar system can use solar power. Why? Juno is in a polar orbit, and will continually be in the sun. Solar panels ...
PearsonArtPhoto's user avatar
  • 121k
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
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
28 votes
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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
26 votes
Accepted

WHY did Rosetta have to go into hibernation for 2.5 years?

From ESA's FAQ page: Why was it necessary to keep Rosetta in hibernation for 31 months? To limit its consumption of power and fuel, and to minimise operating costs. During hibernation it was spinning ...
Hobbes's user avatar
  • 128k
25 votes
Accepted

Potential high temperature power sources for a Venus lander

Thanks to @MarkAddler for his search suggestions I've tried to balance length against completeness, and both lost here. However I have included enough material to try to be convincing that RTGs, ...
uhoh's user avatar
  • 149k
24 votes
Accepted

How does electrical safety system work on ISS?

This answer addresses only the US side of the ISS. Like everything else on the ISS, it's complicated. Fuses are not commonly used on the ISS. There are fuses within the battery subassemblies, to ...
Organic Marble's user avatar
22 votes

Why did Apollo spacecraft use both AC and DC equipment? Still used in present and future designs?

There was no single DC voltage useful for the whole electronic system. A lot of different voltages were needed, for very noise sensitive systems dedicated DC sources were used to avoid interference. ...
Uwe's user avatar
  • 49k
20 votes

What is the maximum speed an ion engine can propel a spacecraft at?

The limit isn't due to power, but to engine lifetime and fuel limits. Ion engines produce very little thrust, so in order to reach speeds of 100km/s they must accelerate continuously for months or ...
Russell Borogove's user avatar
15 votes
Accepted

Are cubesats deployed with fully discharged batteries? Even those on Sherpa?

All cubesats that I have personal knowledge of (including the Planet Labs fleet) were launched with partially charged batteries, typically at around the 50% level that minimizes degradation in storage....
pericynthion's user avatar
  • 10.1k
14 votes

Why wasn't an RTG used on the Juno spacecraft?

I had the opportunity to tour JPL a few months ago and asked this exact question to our tour guide. The solar panels on it are enormous and typically, spacecraft going beyond the asteroid belt are ...
C. Spencer's user avatar
13 votes

Potential high temperature power sources for a Venus lander

An RTG certainly can and would work on Venus, since the hot side is about 1200 C. It just wouldn't be as efficient as it would be with a colder cold side. Search for papers by Geoff Landis on this.
Mark Adler's user avatar
  • 58.2k
13 votes

How did the Mir crew recover from the power outage following collision with Progress 34?

Martin's answer offers a great overview and a link to a hidden gem - transcribed interview with Michael Foale, covering the incident and its aftermath in a great detail. I'd like to share the most ...
Pavel's user avatar
  • 413
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
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Why are RTGs so inefficient?

Here's a brief answer since some people are trying to close the question and prevent answers: As @ikrase points out answers to the Physics SE question Why is the Peltier / Seebeck Effect's efficiency ...
uhoh's user avatar
  • 149k
12 votes
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What is the distribution of ∆V amongst different stages of rocket flight?

Considering fuel consumption or energy expenditure may be misleading, because of the huge change in mass over the flight as fuel is expended. 2/3 of the fuel is expended by the first stage, which only ...
Russell Borogove's user avatar
11 votes
Accepted

Would it be possible to power a Venus lander using a temperature differential?

High temperature in itself is useless. You need a temperature differential, just like the RTG exploits the difference between the temperature of the Plutonium and that of outer space. Kinetic energy (...
Hobbes's user avatar
  • 128k
11 votes

WHY did Rosetta have to go into hibernation for 2.5 years?

Solar arrays are pretty much worthless beyond 4 AU or so from the Sun (depending on the size of the arrays of course). The Juno spacecraft will be the first mission to Jupiter (about 5 AU from the Sun)...
David Hammen's user avatar
  • 74.8k
11 votes

Cosmic rays can be new energy source

The problem is with the low energy density of cosmic rays in the universe. Individual cosmic rays are indeed very energetic, but there just aren't enough of them to be a significant power source for ...
Tom Spilker's user avatar
  • 18.3k
10 votes
Accepted

Solar cells in series

No, it doesn't make sense, for two key reasons. First of all, it is a loss of redundancy. If one of the cells fails, then the entire string fails. You really don't want that to happen... If you build ...
PearsonArtPhoto's user avatar
  • 121k
10 votes
Accepted

Can cosmic background be harvested for energy?

I'm guessing you mean cosmic microwave background radiation. A radio tuned to an empty frequency hears "static" noise. A small fraction of the static received by an analog television is in fact the ...
uhoh's user avatar
  • 149k
10 votes

How does a solar eclipse affect satellites?

Orbiting satellites have to deal with darkness all the time when Earth is between the satellite and the sun, and these periods last for much longer than an eclipse does for the satellite. So although ...
Iamsodarncool's user avatar
10 votes
Accepted

How did the Mir crew recover from the power outage following collision with Progress 34?

The best I was able to find is this description of the event by Michael Foale. In short reactive thrusters of the docked Soyuz spacecraft was used to reorient the whole station. And, in the periods of ...
Martin's user avatar
  • 1,831
10 votes
Accepted

What are the ISS's eight "power channels"? How do they work?

Eight solar array wings, eight power channels. My answer to this question shows one power channel: How does electrical safety system work on ISS? You can read about the gory details of each channel ...
Organic Marble's user avatar
10 votes

What is the relationship (if any) between NASA's Kilopower project and its request for 40 kW reactor designs?

Kilopower is designed for at most 10 kW of power. I asked Patrick McClure, who is the engineer in charge of the Kilopower project at Los Alamos (2019 Humans to Mars summit) if they could scale it up ...
PearsonArtPhoto's user avatar
  • 121k
10 votes
Accepted

Lunar nuclear power system - how can hydrogen generated on the Moon be liquefied?

How would you cool and liquefy this hydrogen on the Moon? I guess one would have to do a serious study to find out for sure which way is more suitable in a given scenario, but I think passive cooling ...
uhoh's user avatar
  • 149k
9 votes

Why wasn't an RTG used on the Juno spacecraft?

Phiteros' answer states the fact that plutonium is in scarce supply and PearsonArtPhoto's answer points out that Juno's mission profile allows it to use solar panels. These issues are legitimate and (...
GreenMatt's user avatar
  • 1,431
9 votes
Accepted

What is the relation between the rocket equation and work, energy and power?

If you're in vacuum, the power represented by the kinetic energy of the thrust is the thrust force times the exhaust velocity (g times Isp) over two: $$P={g I_{sp}T\over 2}$$ One SSME in vacuum ...
Mark Adler's user avatar
  • 58.2k

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