82
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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 ...
- 9,976
59
votes
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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 ...
- 4,111
58
votes
Accepted
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 ...
- 1,333
58
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 ...
- 7,996
56
votes
Accepted
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 ...
- 148k
55
votes
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What will now happen with Hubble?
Hubble and JWST work with different wavelength ranges, Hubble with UV, visible light and near infrared (200 to 1000 nm and 800 to 1700 nm), JWST with visible red to mid infrared 0.6–28.3 μm.
Only ...
- 48.8k
52
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 ...
- 556
49
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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 ...
- 21.4k
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, ...
- 3,235
43
votes
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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 ...
- 73.2k
42
votes
Accepted
What is that black thing in center of every star in this JWST image?
The stars in the image are so much brighter than any of the other galaxies that their centers ended up grossly overexposed. Remember, stars are small and should show up with one single pixel only (to ...
- 14.9k
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. ...
- 121k
41
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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 ...
- 1,187
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"...
- 7,996
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 ...
- 73.2k
40
votes
Accepted
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 ...
- 1,584
37
votes
Why didn't JWST include any sensors capable of blue and green visible wavelengths
JWST's optical path includes more than just the large primary mirror. In the OTE (the telescope proper, rather than the instrumentation), there are three additional mirrors:
A secondary mirror, ...
- 821
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 (...
- 73.2k
36
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 ...
- 9,572
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 ...
- 11.5k
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 ...
- 126k
32
votes
What was so hard about the washer nuts on the JWST?
That those washer nuts failed to hold during the shake test was a telltale sign that the JWST might well not have been capable of withstanding the incredible shaking that happens during launch. Those ...
- 73.2k
29
votes
Accepted
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 ...
- 148k
29
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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 ...
- 26.9k
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 ...
- 58.5k
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 ...
- 73.2k
28
votes
Why didn't JWST include any sensors capable of blue and green visible wavelengths
It all comes down to cost vs benefit
If you shoot something into space every gram of mass and every little bit of space counts. Also every bit of energy an instrument uses and heat it produces must be ...
- 3,235
27
votes
What will now happen with Hubble?
Since it is not broken, the intention is to keep it operational as long as possible. The most recent estimate I could find is that the HST will likely remain operational until at least 2026:
"...
- 14.1k
27
votes
Why is the hot part of Webb's MIRI cryocooler in the 300K area?
It IS passively cooled, there is no other way to get rid of heat in space (except if you evaporate some coolant, which JWST tries not to do)...
So the cryocooler has a radiator attached to it to ...
- 3,235
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