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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 ...
David Hammen's user avatar
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23 votes
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James Webb telescope; limits to propellant lifetime?

For some background see this answer to Could JWST stay at L2 "forever"? this answer to What happens to JWST after it runs out of propellant?. From the 2nd linked answer (slightly edited): ...
uhoh's user avatar
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22 votes
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Is this what station keeping maneuvers look like, or just glitches in data? (SOHO via Horizons)

You are most likely seeing an artifact of how JPL represents its ephemerides for fast numerical computation. JPL integrates the equations of motion over time. This inevitably results in mismatches ...
David Hammen's user avatar
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20 votes
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Are any Earth orbits in continual shadow of the Earth?

There is no orbit around the Earth that remains in permanent shadow. Such an orbit would need to have a period of one year, and that orbit would be too large to fit within the Earth's Hill Sphere, ...
notovny's user avatar
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19 votes
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Could JWST stay at L2 "forever"?

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 ...
PearsonArtPhoto's user avatar
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17 votes
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How does a satellite's mass affect its fuel consumption to maintain orbit?

If you re-boost them both at the same time interval, then the lighter satellite's orbit will decay more between re-boosts, it will experience more drag because it falls deeper into the atmosphere, and ...
phil1008's user avatar
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13 votes
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Why are 22N and 440N liquid engines quite common?

As noted by @asdfex, 440N and 22N are convenient round numbers in imperial units: 100 lb-f and 5 lb-f. The exact thrust values for small spacecraft maneuvering thrusters aren't usually critical to ...
Russell Borogove's user avatar
13 votes

James Webb telescope; limits to propellant lifetime?

The telescope trajectory changes direction for halo orbit insertion. Image source: https://jwst-docs.stsci.edu/jwst-observatory-hardware/jwst-orbit Such a large change of direction would require a ...
Uwe's user avatar
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12 votes
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Could a ball of water stay in orbit?

The ball of water in that picture is in orbit; it's just surrounded by (presumably) the ISS. But a ball of water like that definitely cannot survive in the vacuum of space. Below a certain pressure, ...
Mark Foskey's user avatar
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12 votes
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How frequent are (or will be) JWST station keeping burns at L2?

How frequent are (or will be) JWST station keeping burns at L2? 21 or 42 days I've heard mention of 'every 21 days' which at first look seems excessive but on second look may not be nuts if very ...
uhoh's user avatar
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12 votes

How does a satellite's mass affect its fuel consumption to maintain orbit?

If you apply conservation of energy, fuel consumption should be the same since energy loss to air drag is identical.
Woody's user avatar
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11 votes

Are any Earth orbits in continual shadow of the Earth?

One highly reusable observation is the following: For any plane going through the centre of mass, a satellite must spend some part of its orbit on one side of it if it spend some time on the other ...
SE - stop firing the good guys's user avatar
10 votes

Why is the US building a Lunar Orbital Platform-Gateway (LOP-G)?

A zillion years ago I was at a meeting where large projects were discussed and attempted to be justified. A slide was shown listing say five reasons why project such-and-such was absolutely vital and ...
uhoh's user avatar
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9 votes
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Moon orbit station-keeping delta-V budget

Here's a paper on LRO stationkeeping. The fundamental problem is articulated on page 3: LRO will fly in a mean 50 km mission orbit that, for scientific purposes, would ideally be a perfectly ...
Anton Gromov's user avatar
9 votes
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Do operating GPS satellites ever make orbital maneuvers for station-keeping?

Yes, GPS satellites do execute station keeping maneuvers. Primary purpose is to keep them within the desired repeating ground track, which leads to a maneuver every year or so for each satellite. I ...
Carlos N's user avatar
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9 votes
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What orbit would a space station need to stay in orbit for N years?

tl;dr: Park your ISS-like space station above 700 km and there is a good chance it will only lose 100 m/s in 1,000 years due to atmospheric drag at least (and 2000 km for a million years). However, ...
uhoh's user avatar
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9 votes

Since L2 has no visible marker, how will James Webb's ground control determine its relative position and velocity for station keeping?

Mathematics. JWST will use the general techniques of locating itself in space - doppler shift, star trackers etc - same thing deep space probes use. Knowing the Sun position, Earth position and their ...
SF.'s user avatar
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8 votes

Could JWST stay at L2 "forever"?

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 ...
Alexander Vandenberghe's user avatar
7 votes
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How do launch and stationkeeping fuel costs vary with altitude?

Your question is hard to answer because it's the reverse of how things are normally done. Typically satellite missions are driven first by the orbital and lifetime requirements, which determines the ...
Russell Borogove's user avatar
7 votes
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Will the ISS have electric propulsion to maintain altitude? Is there enough power for it?

the VASIMR test planned by Ad Astra has been cancelled: On December 8, 2008, Ad Astra signed an agreement with NASA to arrange the placement and testing of a flight version of the VASIMR, the VF-200, ...
Hobbes's user avatar
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7 votes
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How much Delta-V is needed for Orbital Maintenance?

Good question, I’m also interested if someone has a more specific answer to share! On the following table, you can find the required delta-v per year for different orbits. And about formula, I'm not ...
Astrea's user avatar
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7 votes

The design of the halo orbit of the James Webb Space Telescope

Has the JWST halo orbit been chosen from a stable halo "template", and in "broad terms", what were the trade-offs between JWST's scientific mission requirement, orbital life-time ...
uhoh's user avatar
  • 149k
7 votes

How does a satellite's mass affect its fuel consumption to maintain orbit?

The energy loss due to atmospheric drag is proportional to the frontal area of the satellite. If the 'otherwide identical' clause means they have the same frontal area, then they will lose energy at ...
Neil_UK's user avatar
  • 271
6 votes

Why is the US building a Lunar Orbital Platform-Gateway (LOP-G)?

I can maybe answer these questions, as someone that has worked on NextSTEP studies (HAB, PPE) and HLS Architecture and Lander Studies. In general, I thought a lot of the news articles were mostly ...
mothman's user avatar
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6 votes

Why is the US building a Lunar Orbital Platform-Gateway (LOP-G)?

Let's examine what Jim Bridenstine, current director of NASA and previous member of the Rocket Racing League (1, 2, 3) says. NASA Administrator Jim Bridenstine Explains the Lunar Gateway is a ...
uhoh's user avatar
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6 votes
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Xenon vs Hydrazine, "Should I Stay or Should I go?" Dawn mission decisions

There is one wheel still operable (at least it was operable the last time they operated it), but Dawn no longer uses it. The third wheel failure was in April of this year (2017 for those reading this ...
Mark Adler's user avatar
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6 votes

Could JWST stay at L2 "forever"?

tl;dr: I think there could be room to do this. However, I don't think a conclusive answer can be had through analyses of magnitudes on envelope-backs. A real answer would only come from even more ...
uhoh's user avatar
  • 149k
6 votes

How do stable equilibrium points work in GEO? If all geosynchronous spacecraft suddenly lost stationkeeping, would most "fall into" one or the other?

There is a very nice article about the synchronized variation of the debris motion at GEO, available here. Authors give an example of the 'well-known GEO stable plane, which is a fixed point of ...
prop-a-gator's user avatar
6 votes

The Earth's rotation does change by small amounts; what is done to keep geostationary satellites aligned with ground stations?

The very small changes in the Earth's rotation rate pale in comparison to the much larger perturbations that geosynchronous satellites experience from the Earth's non-uniform gravitational field, ...
David Hammen's user avatar
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5 votes
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Spacecraft remaining at station-keeping with respect to the ISS

The case of failed docking of Soyuz MS-14 may fit to constraints of the question. It was in orbit near ISS for 3 days between failed docking attempt and successful attempt. The linked above Wikipedia ...
Sergiy Lenzion's user avatar

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