Tag Info

77

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 ...

45

I treated this as a problem of geometry and came up with this: The sun is the large yellow disk. The earth is the largest black disk, obscuring most of the sun The left-hand dark-grey disk is the moon as it transits across the near-side of the earth, with respect to L2. In reality in this position, the disk of the moon would appear completely black. I ...

44

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 ...

30

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 perspective of an Earth-centered inertial frame. That graphic instead uses a synodic frame, a frame that rotates with the Earth's orbit about the Sun. You can tell ...

27

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 ...

26

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 Hammen explains in his (better) answer, the animation is showing a rotating frame of reference centered on the Earth. Because of the rotation, and the fact that ...

25

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 ...

23

The spacecraft that orbit at L2 usually don't just stay at the L2 point, but do what's called a Halo Orbit, or related Lissajous Orbit. Essentially they orbit the L2 point, instead of right at it. As a result, they actually see the Earth and Moon as distinct from the Sun. And they usually orbit the point in such a way that they will not have a direct line ...

23

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 itself is not a predictor of the stability of an orbit associated with ("around") it. Are some Halo Orbits actually Stable? (stable orbits about unstable ...

22

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. L3 does exist for both, but it will be a very small area. L4 and L5 likely exist, and are somewhat larger, but they still won't have a significant effect. ...

21

The Lagrange points L1, L2 and L3 are stable in prograde- and retrograde direction, but unstable on the radial axis. That means any object on these points will drift away in radial direction unless it uses small amounts of thrust to balance on these points, so any concentration of natural mass or debris at these points is impossible. Only the points L4 and ...

20

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.

19

To add to other answers, the L1-L2 Lagrange points are unstable because they need to follow radial velocity of the two parent bodies as they orbit each other, in our case the Earth in a heliocentric orbit around the Sun, but none of them are really at the orbital altitude matching their radial velocity (too slow in L1 and too fast in L2). Since the Earth's ...

19

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 between the integrated state and observations. These errors are used to adjust initial states and the integration is then re-performed. The cycle stops when the ...

19

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 will show that only one of the five Lagrange points are "between (the) two objects". The pulls are not equal, they balance in such a way as to allow for an orbit ...

19

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 theorem, a spherically symmetric mass. It is this situation where any 2-body orbital dynamics can be reduced to the Kepler laws, with periods depending on the ...

18

Here's a pic of the tether proposed by Liftport. Go 160,000 km beyond EML1 and drop a payload from that point. It will follow an elliptical path whose perigee grazes low earth orbit. A 3 km/s burn at perigee would circularize the orbit at LEO. Doing a 3 km/s burn from LEO and you will get the same ellipse. At the apogee of this ellipse, the rocket is ...

16

To the extent of my creativity, L2 is the only location that can satisfy this for a given planet. We would also need to constrain the discussion to planets because, again, my creativity fails me to think of any other option. Thus, we must use the method described in the other answer to ask "does any planetary L2 fall within the planet's umbra?" To start ...

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 ...

15

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 ...

14

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 radiation environment of low Earth orbit. Outside of low Earth orbit, without the protection of the Van Allen radiation belt, crew aboard the station will receive ...

13

The Lagrange points are not some physical objects, just locations where gravity of other bodies coincides to be of specific value/"shape", and as the strength of gravity field changes, so do the point move; obviously whatever affects the gravity does influence these points, like trajectory of given body that generates them, its mass (influenced by capturing ...

13

Lagrange points do exist between stars. In case of single stars, they are too far away from the stars to have any practical effect. However, in case of the binary stars, the Roche Lobe has its apex located at L1. "RochePotential color" by SamuelHon - Own work. Licensed under CC BY-SA 4.0 via Commons. In case a star's surface extends beyond the Roche Lobe, ...

13

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 ...

12

There's a number of missions that have headed to various of the Lagrange points, see Wikipedia for a good list. Let's look at what it takes to stay there: James Webb- Proposed for L1 point, can only take enough fuel for a 10 year mission. Hershel Space Telescope: Was deliberately moved from L2 to a heliocentric because " the spacecraft would be in a slow ...

11

TL;DR No, there are no sats there today, and no declared plans from any of space agencies to do that. Here's why: An Earth-Sun $L_3$ point is an unfortunate place for a satellite to be in. First off, it is unstable (thus without constant station-keeping burns an object placed there will fall out and start roaming about the Solar System). An alternative ...

10

EML1 and EML2 From EML2 and EML1 it is possible to collide with earth or the moon. It is also possible to sail out of earth's Hill Sphere. Here are a range of pellets from EML2 nudged away from the earth and moon: Some sail out of earth's Hill Sphere. Note the orange pellet makes a close approach to earth. Here are some trajectories from EML1: Nudging ...

10

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 is only 7.6 km (from here). That means that anything in the neighborhood of Phobos is acted on more strongly by the gravity of Mars than of Phobos, so orbiting ...

10

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 year based on a very old spacecraft (SOHO) and a future spacecraft (JWST). I'll address the two closest and most used Lagrange points; L1 and L2. Generally ...

9

There's this proposal floated by Boeing: http://en.wikipedia.org/wiki/Exploration_Gateway_Platform And Russia has had some similar plans, although it was for a station in lunar orbit: http://www.russianspaceweb.com/los.html The Boeing proposal would use some structural elements left over from ISS construction, while also including modules similar to those ...

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