# Tag Info

78

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 simply impractical/impossible for many missions. For example, at the time of its launch, there was no launch vehicle in operation capable of lifting Hubble's 11000 ...

59

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 these galaxies are far away, they’re also huge. The (relative) detail that can be seen in any given telescope will be found by the object’s size divided by the ...

40

There are a couple of reasons. The distance from the L2 to Earth is only 1.5 million km away. The L4/L5 are 1 AU, or about 150 million km away. That leads to a reduction in link margin of 40 db, or 1/10000. That is quite significant. In order to compensate for that difference, you either need a bigger radio dish, more power, or a loss in data. As you ...

40

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 their orbits preventing advanced image interpolation techniques combining multiple observations of same side of Pluto at same lighting conditions. Pluto is ...

31

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 if kept cold by our standards, would look like a bright light at those wavelengths. (Google black-body radiation to learn more.) The infrared detectors need to ...

29

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 orbit and their moons. We don't send deep space telescopes to other planets because it's pointless, a few million miles closer to even our closest neighbor ...

29

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 something goes wrong. In fact, GEO is not a particularly special place for a space telescope and several telescopes are placed (or are planned on being ...

29

Kepler The Kepler space telescope uses a bank of 21 rectangular CCD modules - each with two 2200x1024 pixel CCDs). Each module covers 5 square degrees on the sky. https://keplerscience.arc.nasa.gov/the-kepler-space-telescope.html Giving a field of vision of: Hubble For Hubble, the wide field camera CCD sensor is again rectangular/square https://www....

28

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 kilometres from Earth. From this distance the telescope could see Martian features as small as 19 kilometres wide. Theoretically Our resolution is limited by the ...

27

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 tell you, the brightness of an extended, resolved object like a person, or the disk of a planet, does not decrease with distance between you and the object, and ...

26

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 telescopes. However that is the wrong question. The real question is what advantages, as well as disadvantages, does a telescope on the Moon have over a telescope ...

25

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 telescopes are used to look at very dim objects (magnitude 20 stars), so they need far more sensitive detectors, and longer exposure times with accurate tracking. They ...

22

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. Pluto is currently around 3.5 billion miles. That gives a resolution of 850 miles or so. This is limited by the size of the mirror that Hubble has, which is ...

21

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 the Earth that's turning, and you have to turn the telescope mount to keep the legs pointed at the ground. It's the same thing as having to move the antenna to ...

19

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 wavelengths that aren't visible. The spatial resolution is around 70 milli-arc seconds. That means that the Roadster, being about 4m in size (roughly) in it's ...

19

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 Origin (also here, Klebesadel, Strong and Olson, 1973, ApJ 182:L85-L88). The paper indicates: The observations were made by detectors on the four Vela ...

19

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 spectrum of a black body peaks $\approx 5 k_\mathrm B T$. The boiling point of liquid helium is 4.2 K. The peak wavelength for something at that temperature would ...

18

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 any deep space mission". This camera allows it to take extremely detailed pictures of the surface. If you're looking for other large-diameter telescopes which ...

16

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 points, when L4 and L5 are stable. It comes down to what happens if the satellite loses control. In unstable Lagrange points, if the satellite gets fried somehow ...

16

(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 ? It's mostly (c) but that only works if (b) is true. By being in a halo orbit around the Sun-Earth L2 point, the Sun, Earth, and Moon are all in ...

15

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, director of NASA Goddard Space Flight Center, had this to say on the subject: We cannot make the James Webb Space Telescope fully serviceable like the Hubble ...

15

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 shatter on impact It's primary hexagon mirror elements are made out of Beryllium powder pressed into blocks, that were later cut in half to create two mirror ...

13

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 in the form of light that has been reflected off of it. In a bright, well-lit environment where you're taking pictures up-close or have a huge lens, you can ...

13

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 put here: http://i.giphy.com/l2Sq1WUTZeWNXaoEM.gif In order to make extremely precise measurements of positions throughout the sky, GAIA slowly spins and ...

13

A flag would be about five hundred micro arcseconds. (about 1 meter, at around 375 Mm) The Event Horizon Telescope has a resolution of about 20 micro arcseconds. Therefore, EHT could resolve a flag on the surface of the moon if it were a radio source. However, to view it optically would require around a 350 meter aperture. The largest 'single' telescope ...

13

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 × $10^{−18}$W/m$^2$, respectively. At most temperatures, the amount of heat radiated by the spacecraft itself would easily overwhelm the infrared signals it was ...

11

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 enough sensitivity. If we take the question literally, Kepler would qualify with its heliocentric orbit at a distance of 1 AU. It has a 1.4 m primary mirror.

11

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, which will unfold after the telescope is launched. If the primary mirror is too large for launch, the enclosing tube would be too large also. The JWST does ...

11

Silicon wafers are sliced from a giant single crystal of silicon called a boule, which is grown from a seed crystal dipped in and then slowly pulled from molten silicon. Circuits such as CCDs (and everything else) are patterend on silicon wafers aligned to the crystal axes of the wafers indicated by the wafer flat or notch (1, 2 see alignment flat on bottom,...

10

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 capsule (4 man) or Dragon 2 Capsule (7 man); a Dragon 2 atop a Falcon Heavy could easily reach and have delta-V sufficient for return. ② References ① Space....

Only top voted, non community-wiki answers of a minimum length are eligible