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 ...
  • 5,571
38 votes
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Function of the separated, individual solar cells on Telstar 1 and 2? Why were they "special"?

The small separated cells had several functions. Six individual units, the "solar aspect cells", were each oriented and attached as if they were on the sides of a cube to identify the spacecraft's ...
  • 12.4k
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 ...
  • 119k
28 votes
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Can the Mars lander's/rover's solar panels be cleaned?

Reasons not to provide mechanical means to clean solar panels on Mars: and this is the primary reason: Wind on Mars occasionally blows the dust away. This means dust is not a major issue, but a minor ...
  • 122k
24 votes
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Can ISS fold its solar panels?

The long boom holding the panels can be retracted (the term used instead of "folding"). It is not done lightly, for fear of not being able to reverse it. It has only been done a few times, once ...
23 votes
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What are the sources of light at L2? How will the James Webb telescope be powered?

The planned orbit for the JWST is quite a large halo orbit around Sun-Earth L2. It's very roughly elliptical, with dimensions of about +/- 350,000 km "vertically" (perpendicular to the Earth's orbital ...
  • 148k
23 votes
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Mars versus the poles of Mercury WRT colonization

Your delta-v analysis doesn't account for the landing delta-v. On Mars, only a fraction of a km/s has to be done propulsively, on Mercury the entire landing will be propulsive. You also don't account ...
22 votes
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Why didn't Gemini, Apollo or STS use solar panels?

The high power levels of Shuttle and its need to return to an aerodynamic configuration would have necessitated a very large array that would need to be deployed and retracted each mission. This ...
20 votes

Why latest Landsat satellites have solar panel on only one side?

Solar panel technology seems to have caught up with power requirements on the satellite. Since price of components is really no object when building a system like this, super expensive panels with ...
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19 votes
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What inspired the circular panels on the Phoenix Lander and InSight rover?

Good catch noting that Cygnus has the same solar panel design! Orbital ATK, developer of Cygnus, builds these panels under the "Ultraflex" and "Megaflex" brands, and did indeed ...
  • 8,715
18 votes
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If we pick any point on the moon (except possibly the poles), is the sun visible for 13.66 days, and then not visible for 13.66 days?

Yes, the light cycle is about one month. 29.53 Earth days, to be precise. (the difference with your figure is because the moon is also orbiting the sun along with the Earth, and after a month the sun'...
16 votes
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Why aren't landers designed to point their solar panels and radio antennas to Sun and Earth?

The Opportunity, Spirit (RIP), and Curiosity rovers all have high-gain antennas that point at Earth when in use, using a two-axis gimbal. They are used mostly to receive the command loads every sol ...
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16 votes
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Curiosity is still dirty! How will the ExoMARS Rover keep its solar panels dust-free and collecting sufficient power?

They will likely be relying on two things: Since the rate at which dust will accumulate on the solar panels is pretty well known, they can estimate a lifespan of the rover. All space probes have ...
  • 5,571
16 votes

How much light is there on the way from Earth to Proxima Centauri?

No, the power collected by solar panels is reduced by the square of the distance from the light source. At the Earth's distance from the sun, the energy of sunlight is about 1300 watts per square ...
15 votes

Do solar panels on satellites gather dust and need cleaning?

Settling dust is not a problem. Keep in mind that dust in space does not settle on surfaces like it does on Earth--it's not slowly sinking, it hits the surface at relative speeds measured in km/s. It'...
  • 1,676
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 ...
14 votes

Can a satellite work like a radiometer?

The Mariner 3 and 4 Mars flyby probes had angled vanes at the ends of their solar panel arms which provided passive stabilization of the spacecraft from solar radiation pressure:
14 votes
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Could Stirling Engines work on sunlight alone?

Could Stirling Engines work on sunlight alone? With the heated side facing the sun and the rest in its own shade, could two contra-rotating Vacuum Stirling Engines and flywheels, in tandem, accumulate ...
  • 148k
13 votes
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Making propellants on Mars: Why not just LH2/LOX instead of methane?

Liquid Hydrogen is difficult to deal with. The temperature must be 33 K or lower. Liquid Oxygen requires 90K, and Liquid Methane is similar. The temperature requirements are far less as such. The ...
  • 119k
13 votes
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Could the International Space Station be fitted with solar sails?

Ignoring the ISS, the question is simply whether light pressure on the sail can counteract the drag on the sail from atmosphere. Light pressure near Earth is about $10 \mu Pa$ (with optimum geometry ...
13 votes
Accepted

How long is a day on the Moon?

This may belong to Astronomy SE, but the $29.5$ Earth day figure, or more accurately the time in the third reference, is what you should be planning on when you or at least your instruments go to the ...
  • 7,950
13 votes

Mining Helium-3 on the Moon and sending it to Earth?

On Earth, before a mineral or petroleum resource is mined/extracted, the deposit is delineated and evaluated. Briefly, the process involves sending a some geologists and some drill rigs and their ...
  • 11.2k
13 votes

Why don't rockets recharge in space using solar panels while orbiting similar to ISS for deeper space travel?

The ISS does not have any sort of electric propulsion system. It uses ordinary chemical rockets, either on visiting vehicles or its own rockets which are refueled by such vehicles. (https://en....
12 votes

Do solar panels on satellites gather dust and need cleaning?

Satellites do not have any capacity to clean the solar arrays. The solar arrays degrade over life due to many factors: radiation damage, UV darkening, micrometeroids, etc. The manufacturers have ...
12 votes

Why didn't Gemini, Apollo or STS use solar panels?

Fuel cells produce water. The output of the Apollo fuel cells (PDF on Apollo power supply system design) was used as drinking water and as a coolant in the environmental control system. If you use ...
  • 122k
12 votes
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Solar panels on Mars?

Well, we don't really know how much energy a Mars base would need, but we can make some rough estimates. Bases like McMurdo and Mawson have power capacities of several hundred to several thousand ...
  • 5,571
12 votes

Largest solar panel (by area) deployed in space? Largest below/at/above GEO?

One solar array wing on the ISS, consisting of two blankets stretched out by a supporting mast, contains 32,800 cells that are approximately 8 cm by 8 cm, giving a total active area of approximately ...
  • 16.9k
11 votes
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Why does the ISS not use the most efficient solar panels available?

As 2012rcampion noted you are using the wrong metric of cost in your efficiency figures. Triple junction solar panels are extremely inefficient wrt weight when compared to single junction. To ...
  • 848
11 votes
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Are the ISS US Segment solar arrays double-sided?

Having worked extensively on the solar arrays over the last five years, I can say they do receive about a third of their power from albedo exposure to the back side. This is further confirmed from a "...
  • 16.9k
11 votes
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The Orbital Mass Accelerator Engine Theory

In theory, yes, if the accelerator and the spacecraft are of the same mass, they'll gain the same amount of velocity when they pass, and so they'll meet at a higher altitude on the opposite side. If ...

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