70
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 ...
- 5,626
60
votes
Accepted
Can we power things (like cars or similar rovers) on earth in the same way Perseverance generates power?
RTG technology has been applied on Earth, many times, although not for transportation - they don't produce much power for their weight so any RTG powered vehicle would be very slow. Some pacemakers ...
- 19.9k
53
votes
Why is the supply of RTGs running short?
The Plutonium isotope 238 used in RTGs is highly specialized. It's not produced in large quantities routinely. Not very many radioisotope applications need that much of a highly radioactive isotope, ...
- 8,587
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 ...
- 121k
37
votes
Why was radio contact with Pioneer lost earlier than with Voyager?
Interplanetary communication is mainly dependent on signal strength (for transmission) and antenna size (for reception).
The Pioneers use a 9-foot antenna and an 8-watt transmitter. The Voyagers use ...
- 166k
35
votes
Why did Cassini require so much more power than other probes?
Cassini had a RADAR subsystem
To determine whether oceans exist on Titan, and, if so, to determine their distribution.
To investigate the geologic features and topography of the solid surface of ...
- 48.7k
33
votes
Why are there four RTGs in a row sitting in this room? What are they waiting for? Were they built together and stored for separate launches?
There were seven General Purpose Heat Source - Radioisotope Thermal Generators (GPHS-RTGs) assembled (there were parts for an eighth).
The seven would eventually fly in space on four different ...
- 177k
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 ...
- 48.7k
29
votes
Can we power things (like cars or similar rovers) on earth in the same way Perseverance generates power?
RTGs are expensive to produce, can be politically inconvenient to use, and in the form of a plutonium-bearing device, represent a potential nuclear proliferation hazard (though all RTGs might be used ...
- 7,704
28
votes
Why was radio contact with Pioneer lost earlier than with Voyager?
In addition to a better transmitter, the Voyagers have better power reserves: their RTGs supplied 470 W at launch, while the Pioneer RTGs supplied 160 W at launch. So the Voyager RTGs will take much ...
- 124k
27
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 ...
- 149k
27
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 ...
- 2,331
26
votes
Why is the supply of RTGs running short?
Any isotope used as the basis for a radioisotope thermoelectric generator (RTG) has to have a short but not too short half life. A half life of several decades is ideal. Such isotopes effectively do ...
- 72.5k
25
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 ...
- 54.4k
24
votes
Accepted
Does Curiosity pose a radiation hazard for would be colonists?
At first glance, the RTG does not pose a risk.
It is powered by Pu-238, which is primarily an alpha emitter throughout its decay chain. Alpha particles can be stopped by a sheet of paper. An ...
- 124k
21
votes
Accepted
How an americium-241 RTG would differ from one using plutonium-238?
Power and Mass
From this paper (emphasis mine):
The specific power of an
241Am-fuelled RTG cannot match that of a 238Pu system (except
perhaps at small power output levels); however, the design work ...
- 9,976
21
votes
Accepted
Why are planetary probe RTGs tilted at a jaunty angle?
The Dragonfly cruise stage looks rather similar to Curiosity's cruise stage, so I've looked at Curiosity. Curiosity's backshell contains a hatch. This was used to install the RTG at the last possible ...
- 124k
20
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 ...
19
votes
Accepted
How does the launch risk for a plutonium RTG and a uranium fission reactor compare?
The probability and consequences of a release of Pu-238 from an RTG in a launch accident are very low, due to the protections in place for such an incident. It's not like they never thought of that. ...
- 58.4k
19
votes
Accepted
Why is Perseverance's RTG lifetime only 14 years?
14 years is the design lifetime for the MMRTGs. The thermocouples do degrade over time while exposed to the high temperatures of the hot side and the temperature changes of the cold side. The output ...
- 48.7k
18
votes
Accepted
If Curiosity had lights, could it drive or work in the evening?
TLDR: The rover is power limited not daylight limited
Lights are not sufficient to enable nighttime driving.
The rover is limited by available power. The RTG produced ~114 W at the start of the ...
- 124k
18
votes
Accepted
How (and when) was the RTG in the lunar modules installed?
Partial answer (everything but exactly when in the timeline it was done):
The fuel capsule was installed at the launch pad "through a ten-inch access port in the spacecraft structure". The fabulous ...
- 177k
18
votes
Why is Perseverance's RTG lifetime only 14 years?
This is an addendum to @Uwe's answer. RTG lifetime is a topic of much discussion in the planetary science community, and in particular the MMRTG being currently the only available RTG. MMRTGs decay ...
- 18.2k
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 ...
- 241
14
votes
Why did Cassini require so much more power than other probes?
The power budget, at least what is public, can be seen at https://sci.esa.int/documents/33648/36003/1567254416901-cassini-huygens.pdf . The scientific instruments included are up to 450.9 W, as shown ...
- 121k
13
votes
Why is the supply of RTGs running short?
It's not just the half-life of the material (short enough to make heat, long enough to have a slow changing energy curve) It's also the type of radiation.
For instance Cs137 is plentiful and easy to ...
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.
- 8,587
13
votes
Can we power things (like cars or similar rovers) on earth in the same way Perseverance generates power?
The answers claiming danger/toxicity are chasing something that's irrelevant. The real issue is that they don't produce all that much power*. If you want a car that can only drive a few hundred ...
- 597
13
votes
Accepted
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 ...
- 149k
12
votes
Accepted
Why was radio contact with Pioneer lost earlier than with Voyager?
Pioneers
Several factors lead to the loss of signal.
Radiated power: Pioneer 10's broadcast power is particularly low. 8 W at ~2.2 GHz ①
Very narrow beam; the antenna gain is +65dB, which means 1/(...
- 11.5k
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