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 ...
Jack's user avatar
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47 votes
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Delta-v to hit the moon: is reaching Lunar L1 enough?

This is an excellent and fun question, bravo. First, the table is being read incorrectly, here's how to properly read it: For example, to go from LEO-Ken to EML1 is given as 3.77 km/s, not 0.77 km/s. ...
BrendanLuke15's user avatar
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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36 votes

Why doesn't JWST use ion thrusters?

Since the L2 point is unstable, JWST needs engines to maintain it's orbit. It uses mono-propellant engines which have given it a 10 year (maximum) lifespan. The JWST uses bi-propellant engines (...
David Hammen's user avatar
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30 votes
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This orbit looks wrong near a Lagrange point. Is it?

Is the orbit shown in the graphic wrong, or is my understanding of orbital mechanics lacking, having only been influenced by KSP? It's not an either-or question. The graphic is "wrong" from the ...
David Hammen's user avatar
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30 votes
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Does the distance to L2 vary?

Does the distance to L2 vary? Yes, it does. The Earth is in a more or less elliptical orbit about the Sun. I wrote "more or less" because the Moon is a factor, and also because Venus, ...
David Hammen's user avatar
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26 votes

This orbit looks wrong near a Lagrange point. Is it?

As noted by Mys_721tx in comments, this is the trajectory of the object J002E3 -- believed to be the S-IVB upper stage launched with the Apollo 12 mission -- and the animation is accurate. As David ...
Russell Borogove's user avatar
26 votes

Is there something inherently more difficult about servicing satellites in the 2nd Sun-Earth Lagrangian point?

Distance certainly is a key factor. It took JWST a month to go from launch to L2 pseudo-orbit insertion. Another key factor is that to date, the only successful satellite servicing missions have been ...
David Hammen's user avatar
  • 74.8k
25 votes

What is the "mass" of a Lagrange point?

Lagrange points... can be orbited by asteroids, satellites, and any other useful or interesting object. Assuming two-body motion however... First a quick note; the stability of a Lagrange point ...
uhoh's user avatar
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23 votes
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What are the sources of light at L2? How will the James Webb telescope be powered?

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 ...
uhoh's user avatar
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23 votes
Accepted

How Many Martian Lagrange points are there? ...And are they useful for satellites?

The Phobos and Deimos L1 and L2 points are virtually coexistant with the moons themselves. I have seen that the L1 point for Phobos is 10 km above the moon. At that altitude, just build a large tower. ...
PearsonArtPhoto's user avatar
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23 votes

Why doesn't JWST use ion thrusters?

@DavidHammen's answer goes a long way towards answering, especially in that the space telescope's bus was finalized quite a long time ago when ion propulsion was much less a proven long-term reliable ...
uhoh's user avatar
  • 149k
23 votes

Does the distance to L2 vary?

JPL Horizons has data for 8 Lagrange points: ID# Name Designation IAU/aliases/other 31 SEMB-L1 Lagrange 32 SEMB-L2 Lagrange 34 SEMB-L4 Lagrange 35 SEMB-L5 Lagrange 3011 EM-L1 Lagrange 3012 ...
PM 2Ring'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

Ordering of the Lagrange points

According to Wikipedia, L1-L2-L3 were discovered first, by Euler, prior to Lagrange's work, and L1 is "the most intuitively understood" of them.
Russell Borogove's user avatar
20 votes

Is there something inherently more difficult about servicing satellites in the 2nd Sun-Earth Lagrangian point?

Getting to L2 in a timely fashion is more challenging than going to the Moon. The Apollo missions took about 3 days to get to the Moon. 4.5 days is how long the LRO took to orbit the Moon when ...
PearsonArtPhoto's user avatar
  • 121k
19 votes

How many satellites can stay in a Lagrange point?

Lagrange points as I understand it are points in space between 2 objects where the gravitational pull between them is effectively equal. A quick check of Wikipedia's Lagrangian point or any article ...
uhoh's user avatar
  • 149k
19 votes

What is the "mass" of a Lagrange point?

When we consider the mass something is orbiting about, we assume a gravitational potential corresponding to an inverse-square force, which corresponds to either a point mass or, by Newton's shell ...
leftaroundabout's user avatar
17 votes

What does the Sun-Earth-Moon system look like from the Sun-Earth L-2 point?

A reasonably accurate1 rendering can be made with Celestia. Here we are at 1,500,000 km from Earth's center, on August 26, 2018 (the next full moon as I write this), at approximately the Earth-Sun L2 ...
Phil Frost'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
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15 votes
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Would it be possible to Boost ISS to L1 or Lunar Orbit?

Before getting to the technical feasibility of moving the ISS, I feel obligated to point out that operating it at L1 or lunar orbit is impractical for a few reasons: The ISS is designed for the ...
Russell Borogove's user avatar
14 votes

Is L2 at a distance where the Earth totally eclipses the Sun?

No. The Earth's umbra extends 1.4 million km. The L2 point is at 1.5 million km. Even if perfectly aligned, the Earth will only show as an annular eclipse, shading about 70% of the sun's disk. However,...
CuteKItty_pleaseStopBArking's user avatar
13 votes

Are large halo orbits around L₁'s and L₂'s preferred over small orbits for reasons other than geometry?

There are several reasons why spacecraft are sent into pseudo-orbits (they aren't actually "orbits") about the unstable Lagrange points. The least important reason is that only one spacecraft can be ...
David Hammen's user avatar
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13 votes
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Gravitational field of the Moon and Earth

Because the gravitational field is a field, there's a couple ways this question could be interpreted: The magnitude of the gravitational accelerations due to the Earth and Moon are equal The ...
Anton Hengst's user avatar
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12 votes
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What is the required burn to keep a satellite at a Lagrangian point?

What is the required burn to keep a satellite at a Lagrangian point? tl;dr: typical station keeping delta-v for a halo orbit around Sun-Earth L1 or L2 points are of the order of 2 to 4 meters/sec per ...
uhoh's user avatar
  • 149k
12 votes
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How do the Moon and other planets affect Earth-Sun Lagrange points' locations?

Lagrangian points are mathematical entities, and unless a specific list of criteria are met, they simply don't exist. The constraints are those of the circularly restricted three body problem (CR3BP), ...
SE - stop firing the good guys's user avatar
11 votes

Is there a synchronous orbital height for Phobos?

No, or at least there isn't a useful synchronous orbital height. As you pointed out in your question, the mean radius of Phobos is 11.26 km, but if you look closer the sphere of influence of Phobos ...
1337joe's user avatar
  • 7,206
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

Why are Jupiter's trojans even remotely stable?

I'm answering my own question here based largely on the comment from @CuteKItty_pleaseStopBArking Saturn's influence can be separated into a radial component (near Saturn's conjunction with the ...
Roger Wood's user avatar
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11 votes
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What are the characteristics of JWST's orbit around L2?

The orbit is more oval than elliptic since it is centered on... well, the center, rather than one focus. It is roughly perpendicular to the Sun-Earth axis. The orbital period 6 months. Radius of the ...
Woody's user avatar
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