81 votes
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Why are so many space telescopes placed in LEO instead of at Lagrange Points? And why do we hear about Hubble more than any Langrange-orbit telescope?

The reason there are so few spacecraft placed at Lagrange points is that it's much harder to get there. Launching sizeable payloads to Earth escape velocities requires a very large vehicle and is ...
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  • 9,844
58 votes
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Why is the James Webb Space Telescope's data storage space so small?

Best Technology Available By late 2002, SSDs had just reached ~80 GB capacities. Of course, JWST is not going to take a product which has never seen enterprise deployment, and plonk it into \$2 ...
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58 votes
Accepted

Why did the JWST solar array deploy early?

JWST solar panels have limits on what angular rate of rotation they can be deployed at. After separation, there is rotation introduced into the spacecraft, which it has to dampen with thrusters until ...
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55 votes

If we can get people to the moon and back, why are we so adamant that it's impossible to service James Webb at 4x that with a one way robotic vehicle?

JWST is not designed to be serviceable Sending a robot to JWST is moot, it is not designed to be serviceable by human or robot. In the early days of the Webb project, studies were conducted to ...
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  • 7,376
55 votes
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Why is JWST parked in sunlight, rather than using a nuclear battery?

There's no place to hide! That would be great, but the problem is that there aren't any orbits like that. The only way to keep the temperature of the telescope rock-solid steady is to keep it in ...
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  • 148k
50 votes
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Is there any point in space that the James Webb Space Telescope would be unable to image?

Here's a really great article with pictures that explains it better than I can. But to summarize: If you draw a line between the JWST and the Sun, it can point up to 5° towards the sun or 45° away ...
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45 votes
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If we can get people to the moon and back, why are we so adamant that it's impossible to service James Webb at 4x that with a one way robotic vehicle?

Looking at some of the repair missions to date may be informative. Hubble was repaired from the space shuttle. It was originally flown in the shuttle so size and fixtures were known. It was also due ...
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45 votes
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JWST - Why unfurl before reaching L2?

Some deployments (solar panel and antenna) had to be made shortly after start. For the rest of the deployments the answer is:"why not?" It's not like this is powered flight to L2. Sure, ...
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  • 1,143
41 votes

Will the James Webb Space Telescope be insured against launch failure?

NASA tends not to insure its missions, nor do any government missions. These missions are one-of-a-kind, and so expensive that the satellite insurance market would have a hard time making it work. ...
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  • 118k
41 votes

Why are eclipses of the James Webb by the Earth or Moon not permitted during the mission?

From the JWST Mission Operations Concept Document Some families of Lissajous orbits can result in the spacecraft crossing the line connecting the two bodies. In the Sun-Earth orbit, this can result ...
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  • 63.1k
41 votes

If the James Webb Space Telescope explodes, is there a backup?

I want to clarify something about that "twin" of the Perseverance rover that you've mentioned, something that won't easily fit in a comment. NASA built a twin of the rover not to have one as ...
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  • 1,167
41 votes
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Why is the speed of James Webb Space Telescope decreasing?

JWST is like rolling a ball up a hill to have it coast to a stop at the top. Low Earth orbit is the "bottom" and the Sun-Earth L2 Lagrange point is the "peak" at the "top"...
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  • 7,376
41 votes

Since L2 has no visible marker, how will James Webb's ground control determine its relative position and velocity for station keeping?

So how does JWST identify station keeping corrections? It doesn't. While the JWST does know where it is pointing, it does not know where it is in space. It doesn't need to. The JWST Flight Dynamics ...
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  • 63.1k
37 votes
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Can James Webb take pictures of our solar system? In what ways will they differ from/compliment those from Hubble?

JWST must forever be oriented to remain in the shadow of its own sun shield, so that it remains cool and sensitive to the low temperatures of deep space, limiting what can be observed. Notably, it ...
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  • 1,094
36 votes

Why doesn't JWST use ion thrusters?

Since the L2 point is unstable, JWST needs engines to maintain it's orbit. It uses mono-propellant engines which have given it a 10 year (maximum) lifespan. The JWST uses bi-propellant engines (...
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  • 63.1k
35 votes

James Webb orbit insertion

How can JWST brake without turning around? Answer: JWST does not. From More Than You Wanted to Know About Webb’s Mid-Course Corrections!: One interesting aspect of the Webb launch and the Mid-Course ...
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33 votes

Why is the James Webb Space Telescope's data storage space so small?

Space hardware almost always is pretty archaic technology. The problem is the long lead time coupled with the need to certify it for flight. It wasn't archaic when it was engineered. The JWT was ...
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32 votes

How can electronics on board JWST survive the low operating temperature while it's difficult to survive lunar nights?

If surviving lunar nights are difficult to ensure the survival of the electronics, say on lunar rovers, in the low temperatures, The temperature itself is not the primary reason. Lunar nights are ...
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  • 121k
30 votes

Aren't the mirrors of the James Webb Space Telescope too unprotected?

No. Not too unprotected, as you put it. There are several misconceptions that I find common about the JWST, that need to be addressed: JWST primary mirror elements are not made of glass and do not ...
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29 votes
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How can electronics on board JWST survive the low operating temperature while it's difficult to survive lunar nights?

From Status of the JWST Sunshield and Spacecraft found in @Antzi 's answer: Most of the electronics is on the "hot side" but there needs to be some conventional electronics on the cold ...
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  • 148k
28 votes

Why won't JWST deploy in LEO where it is potentially serviceable?

JWST is being launched on an Ariane V with a cryogenic upper stage. That upper stage has to be used immediately to launch it on a trajectory to the Sun-Earth L2. The stage operates on batteries, and ...
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  • 57.5k
28 votes

How do we know the precise position of the JWST?

How does NASA know the exact position of James Webb Space Telescope at a given time? Now that it has launched, NASA doesn't know the exact position of the JWST at any point in time. The three sigma ...
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  • 63.1k
27 votes

Can James Webb take pictures of our solar system? In what ways will they differ from/compliment those from Hubble?

Here's NASA's site with an overview of already approved Solar System science missions for JWST: https://www.stsci.edu/jwst/science-execution/approved-programs/cycle-1-go If you click on the red number ...
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26 votes

How can electronics on board JWST survive the low operating temperature while it's difficult to survive lunar nights?

Source: Me. I currently work as a systems engineer on JWST. JWST will operating from the 2nd Lagrange Point (aka L2), which is approximately 1.5 million km (or 930,000 miles) past the Earth in Sun-...
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26 votes
Accepted

Why is the James Webb Space Telescope temperature not shown?

According to the NASA blog on Dec 26: Separately, overnight, the temperature sensors and strain gauges on the telescope were activated for the first time. Temperature and strain data are now ...
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  • 376
26 votes

JWST - Why unfurl before reaching L2?

It's a bit of a wrong picture to consider L2 as a destination. This is not some kind mountaintop on which we need to set up the telescope. In fact, JWST will never even reach L2 itself (only halo-...
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25 votes

If the James Webb Space Telescope explodes, is there a backup?

There is no backup telescope. There’s no room for error with the Webb, no backup telescope in a warehouse, and no chance of repairing it once it launches. https://www.inverse.com/science/james-webb-...
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24 votes
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James Webb telescope; limits to propellant lifetime?

For some background see this answer to Could JWST stay at L2 "forever"? this answer to What happens to JWST after it runs out of propellant?. From the 2nd linked answer (slightly edited): ...
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  • 148k
23 votes
Accepted

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 ...
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