82 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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59 votes
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Why is it hard to take a high quality image of far away objects (like Pluto) using a high-tech space telescope?

I think a lot of folks see these gorgeous photos of distant galaxies, with fine detail on dust lanes and spiral arms and assume that since they’re so far away, seeing Pluto would be easy. But while ...
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  • 5,772
40 votes

Why is it hard to take a high quality image of far away objects (like Pluto) using a high-tech space telescope?

Distance. Size of the target. Its poor albedo at such distance to its only source of illumination, the Sun, compared to closer celestial bodies. And movement of the target and the vantage point in ...
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  • 75.6k
31 votes
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Why do some space telescopes require cooling (sometimes down to 3K)?

Space telescopes like Spitzer, Herschel, Planck, WISE, and in few years Webb, need to observe in the mid and far infrared wavelengths. The infrared radiation of normal spacecraft temperatures, even ...
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  • 57.7k
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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  • 75.6k
30 votes

Why haven't telescopes been sent to other planets?

We have sent telescopes to other planets, almost all the optical sensors on probes are in fact telescopes so they can focus on a specific area in detail. These sensors are to explore the planets they ...
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30 votes

Why aren't space telescopes put in GEO?

Spacecraft are placed into the orbits that they need to be in, given the objectives of the mission and the constraints during design. Nothing in space is arbitrary, since there is so much at stake if ...
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28 votes
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Would a lunar telescope provide a significant improvement over terrestrial based equipment?

As stated, the answer to the question has to be yes, a telescope on the Moon can have significant advantages over a telescope on Earth, because of Earth's atmosphere. That's why we have space ...
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  • 57.7k
28 votes

Could a spy satellite in orbit be recommissioned to do astronomy?

Surprisingly, yes, in at least a few limited cases. There are aspects of astronomy that could be done by pointing a spy satellite at solar-system objects besides the Earth. As any photographer will ...
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  • 148k
28 votes
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Could we see someone walking on Mars from Earth?

From here, discussing images of Mars taken by Hubble while near to its closest approach to Earth: The telescope snapped these pictures between April 27 and May 6, 1999, when Mars was 87 million ...
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  • 9,854
26 votes

Could a spy satellite in orbit be recommissioned to do astronomy?

Spy satellites are used to look at a really bright object: daytime Earth. This needs short exposure times, detector noise is no problem, and you want a B/W or full-color image. Astronomical ...
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  • 122k
24 votes
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Why aren't space telescopes put in GEO?

It wouldn't need to turn as fast to stay focused, maybe increasing the lifetime of its reaction wheels. On Earth when you "turn" a telescope, you are really keeping it pointed in one direction! It's ...
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  • 148k
22 votes

Why is it hard to take a high quality image of far away objects (like Pluto) using a high-tech space telescope?

For getting really high resolution stuff, you need to get outside of the atmosphere. The best instrument to do this is the Hubble Space Telescope. The resolution of Hubble is about 0.05 arc seconds. ...
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  • 119k
21 votes

Could a spy satellite in orbit be recommissioned to do astronomy?

Yes! Gamma-ray bursts from deep space were actually first discovered by the VELA spy satellites looking for hidden nuclear tests. The original 1973 paper Observations of Gamma-Ray Bursts of Cosmic ...
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20 votes
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Why are JWST optics not enclosed like HST?

(a) it will be observing a different part of the spectrum to HST; (b) it will be in a different location, L2 rather than LEO; (c) its optics will be shielded by a sun shield; (d) some other factor ? ...
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  • 148k
19 votes
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JWST observing cherry red Tesla roadster

First of all, can the color even be seen? James Webb has a spectrum of 600 nm at the lowest end, which means it can just barely see the color red. In addition, it could potentially be seen in other ...
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  • 119k
19 votes
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Why did the Herschel Space Telescope need helium coolant?

Imagine your telescope optics looked like this red-hot glass! Herschel's instruments look at the world in the wavelength range of 55–672 µm. When plotted as a function of wavelength, the thermal ...
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  • 148k
18 votes

The JWST - What happens if/when it breaks?

There is a docking ring on the JWST, so in theory astronauts could visit it. It would be easier to get to JWST than to the Moon, but more difficult than LEO like we have been doing. Edward Weiler, ...
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  • 119k
18 votes

What's the largest aperture telescope sent beyond the Earth-Moon system?

After looking through various mission articles on Wikipedia, the Mars Reconnaissance Orbiter's HiRISE camera has an aperture of 19.7 inches (50 cm), which Wikipedia claims is "the largest so far of ...
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  • 5,571
17 votes

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?

To add to the existing good answer about the practicalities of launching to Lagrange points, it's also worth considering why the missions which have gone that far are using the unstable Lagrange ...
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  • 1,740
17 votes

What caused the JWST Instrument Radiator temperature to start cooling faster on day 34?

That is very likely the day the instrument went to active cooling. For a number of reasons they wanted to cool the instrument slowly, mostly to avoid any ice freezing on it. In fact, there's an ...
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  • 119k
16 votes
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Why does the Gaia space telescope have two main mirrors

above: GAIA's Silicon Carbide Optical Bench, with the two objective mirrors of it's twin telescopes pointing 106.5° apart. From Spaceflight 101, image credit: ESA/Astrium. Cool GIF that is too big to ...
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  • 148k
15 votes
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Why the thermal imaging of Mercury's surface requires a telescope on a jet flying through an eclipse?

Why not a satellite-based telescope to observe Mercury in the thermal infrared? Space-borne satellites that are designed to look at the Sun (e.g., SOHO) aren't instrumented to look in the thermal ...
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  • 65.5k
13 votes

Why is it hard to take a high quality image of far away objects (like Pluto) using a high-tech space telescope?

To add to some already great answers, I'd like to toss in the basic physics of photography that you can experience here on Earth. When you take a picture of something, you're collecting information ...
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  • 283
13 votes

Why did the Herschel Space Telescope need helium coolant?

Herschel was an infrared space telescope. According to this paper, the performance is expected to be not far from background-noise limited, with sensitivities (5σ in 1h) of ∼ 4 mJy or 3 − 20 × $10^...
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12 votes

The JWST - What happens if/when it breaks?

As of 2013, NASA still had a docking ring for the JWST. ① While they have no plans to service JWST, they left the docking capability just in case. The most likely service vehicles are either an Orion ...
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  • 11.5k
12 votes

Why aren't space telescopes put in GEO?

At least one space telescope has been put into a geosynchronous orbit (but not geostationary) due to its unique mission: The Solar Dynamics Observatory (SDO) (Wikipedia)(Official mission site). One ...
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