82 votes
Accepted

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 ...
Jack's user avatar
  • 9,976
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 ...
GdD's user avatar
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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 ...
Michael Stachowsky's user avatar
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 ...
Mark Adler's user avatar
  • 58.2k
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 ...
uhoh's user avatar
  • 149k
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 ...
Jack's user avatar
  • 9,976
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 ...
Hobbes's user avatar
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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 ...
uhoh's user avatar
  • 149k
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 ...
Nicole Sharp's user avatar
21 votes

Would electrically powered thrusters on JWST have made it last for decades longer?

There are a couple of design choices that might have affected the decision of using chemical thrusters. First, the propulsion systems of the JWST were used to correct the insertion trajectory to the ...
Gabriel Sanchez's user avatar
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 ? ...
uhoh's user avatar
  • 149k
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 ...
PearsonArtPhoto's user avatar
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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 ...
uhoh's user avatar
  • 149k
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 ...
Phiteros's user avatar
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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 ...
Graham's user avatar
  • 1,922
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 ...
PearsonArtPhoto's user avatar
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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 ...
uhoh's user avatar
  • 149k
15 votes
Accepted

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 ...
David Hammen's user avatar
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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^...
DrSheldon's user avatar
  • 48k
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 ...
Ghedipunk's user avatar
  • 1,167
12 votes

Why are JWST optics not enclosed like HST?

The JWST is not enclosed in a tube because it would be too big for launch otherwise. The primary mirror is too large for existing launch vehicles, so the mirror is composed of 18 hexagonal segments, ...
Uwe's user avatar
  • 49k
12 votes
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Is it possible to control the operation of the Hubble Space Telescope from ground stations?

Yes, Hubble is actively controlled from the ground. See this NASA page on Hubble Mission Operations Examples include monitoring and adjusting the spacecraft’s subsystems (e.g., power, thermal, ...
Polygnome's user avatar
  • 6,936
12 votes

Would electrically powered thrusters on JWST have made it last for decades longer?

Electric thrusters really have only one advantage over chemical ones: you need less fuel for the same momentum change. In particular less mass of fuel. The measure that directly expresses this is the ...
leftaroundabout's user avatar
11 votes
Accepted

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

Voyager's Infrared Interferometer Spectrometer (IRIS) has an aperture of 0.5 m (19.685"). This is not an imaging instrument though (resolution=1 pixel). The large aperture was needed to provide ...
Hobbes's user avatar
  • 128k
11 votes
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Why would the James Webb Space Telescope need adaptive optics outside the atmosphere?

The primary and secondary mirrors on JWST can be adjusted: Launching a mirror this large into space isn’t feasible. Instead, Webb engineers and scientists innovated a unique solution – building 18 ...
Hobbes's user avatar
  • 128k
11 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?

The other thing is you need more power to transmit large amounts from the Lagrangian points so that requires bigger solar panels hence more mass. Another reason Hubble is in LOO is that the ...
JohnM's user avatar
  • 131
11 votes

What would be merits of placing space telescope after the asteroid belt or closer to the Kupier belt?

Very little upside, lots of downside. It's colder out there, which means that keeping your IR sensors cool is a bit easier. The orbit is wider, so you get more parallax, but the orbit is slower, so ...
James K's user avatar
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