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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 ...


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 ...


32

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. They simply triple-check everything they can, and expect to lose a few missions, so called "Self-insurance". They have considered insuring things like the ISS ...


25

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 the cryogenic fuel is boiling off. So there would be no time to do anything even if you deployed the telescope before departure. Furthermore, the deployed ...


25

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 difficult to survive because you have 14 days of darkness. If you want to design a solar-powered rover that can store enough energy to stay warm for 14 days, ...


22

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 side (beside the cooled IR sensor chips). Small thermal environments on the cold side are equipped with heaters to provide mini-environments at normal operating temperature ...


19

The JWST is made to fold up, to fit inside the standard fairing. You can sort of see this in your image, 3 mirror segments are visible (the hexagons in the middle), other segments are viewed side-on and aren't visible. Folding animation Time lapse showing the folding during assembly


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 ...


17

No it will not According to this answer, James Webb will require 150 m/s of $\Delta v$ to maintain its orbit for its mission duration (5 year), an overall very small amount See also this question as to why L2 isn't perfectly stable. It looks like a giant kite This is purely a cosmetic remark, and the heat shield is absolutely not designed to produce ...


16

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 ...


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

According to Wikipedia, the delta-v requirements to stay at L1 or L2 are about 30-100 m/s per year. That seems quite high, however, more likely is around 5-16 m/s. The sun shield has an area of about 300 m^2. The thrust possible is about 0.00279664 N, assuming purely reflective. Mass of JWST is about 6200 kg. Putting all of that together, the possible ...


16

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-Earth line. This is approximately 4x the distance from the Earth to the Moon. This distance, in addition to its lissajous orbit, ensure it will not encounter ...


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

Insurance is done when losing a mission would mean an unacceptable financial loss, e.g. when a launch failure would bankrupt your company. The government is large enough to absorb such losses, so no insurance is necessary.


14

The James Webb Space Telescope will not be deployed in Low Earth Orbit because there is too great a risk of the optics being damaged by debris. [T]he environment around the ISS is not suitable for the exposed optics that JWST has and would have had the possibility to damage or contaminate the optics. The deployment of JWST happens far above Low Earth ...


12

According to the James Webb Space Telescope Initial Mid-Course Correction Monte Carlo Implementation using Task Parallelism, J. Petersen et al. (PDF): 3.1 Propulsion System Overview Two sets of thrusters comprise the observatory’s propulsion system. The first is a set of Secondary Combustion Augmented Thrusters (SCATs) that are the main thrusters ...


12

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 plane) and about +/- 750,000 km "horizontally" (in the Ecliptic plane). You can see a drawings in (for example) James Webb Space Telescope Initial Mid-Course ...


11

This Northrop Grumman video (starting at 09:31) illustrates JWST's orbit in a non-rotating (normal) frame. It's really in an orbit around the Sun about 1% farther than Earth's, but the weak tug of Earth pulls it along a bit faster so that it remains in 1:1 resonance with the Earth. The orbit is called a "Halo orbit" because in a rotating frame it looks like ...


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 ...


10

As of now, it does not and that's not likely to change. I asked this question of leaders of the JWST project at Goddard Space Flight Center. It isn't that it wouldn't be useful, the problem is funds and time. Considering the current cost of the project, any new addition would increase the cost and could impact the scheduled launch date of October 2018. ...


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....


9

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 mirrors that will act in unison as one large mirror. These mirrors are packaged together into three sections that fold up - much easier to fit inside a rocket....


9

It will not be serviced. When it runs out of fuel or there's a problem, it's End of Mission. Because Webb, like virtually every satellite ever constructed, will not be serviceable it employs an extensive seven year integration and test program to exercise the system and uncover any issues prior to launch so they might be remedied. Unlike Hubble, which ...


9

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 technology was essentially that of a spy satellite but pointing the other way! As they found out soon after Hubble was launched the satellite vibrated when the solar ...


9

It’s really hard to stop IR radiation. Any surface that the JWST optics can “see” has to be kept very cold to prevent IR from that surface reaching the optics. If you had a tube, you’d have to work hard to keep it cold. Or you could not have a tube at all... Usually tubes are structural (not needed in the JWST case) or to block light. Hubble, as a visible ...


8

None whatsoever. If JWST has issues, it is basically out of luck. Maybe one day, Orion might be able to go visit, but Orion is a lousy repair platform compared to the Shuttle. Shuttle had more crew (7 vs 4), more room for equipment, a place to dock the Hubble as a work platform, an RMS to move heavy equipment around (in and out of the Hubble).


8

James Webb Space Telescope Program Scientist Dr. Eric Smith spoke about this on TMRO recently. The main reason is that the telescope wasn't designed to be serviced so it is not as modular as Hubble and systems are integrated throughout the telescope rather than being discrete units that can be removed and replaced like on Hubble. It was designed like this ...


8

This paper by Heiligers et al. explores Earth-moon libration point orbits with the addition of solar sail thrusting. While it is of course not directly translateable to Sun-Earth L2 (JWST) the dynamics of libration point orbits in both systems are at least comparable. The study shows that an increase in stability can be acquired for some orbits (lunar L2 ...


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