Gravity wells could provide 'parking lots' for spaceships

Jul 15, 2009 By Robert S. Boyd
Earth & Moon. Via: NASA Archives

Nature has provided five huge rest stops far out in space for the convenience of spacecraft traveling from Earth. Some NASA folks call them "parking lots" in space.

They're unusual locations where gravity loses its pull and a spaceship can loiter, rather like a marble at the bottom of a cup, without using a lot of fuel. Three of them are 930,000 miles outside Earth's orbit. One is between the Earth and the , and another is hidden on the far side of the sun.

A pair of U.S. unmanned scientific satellites will pass through two of these sites this fall. NASA may eventually park a permanent space weather station at one of them.

Their scientific names are Lagrange points, after the French mathematician Joseph-Louis Lagrange, who predicted their existence more than 200 years ago.

Numbered L1, L2, L3, L4 and L5, they're really just mathematical points marking the centers of "gravity wells" -- places where the gravity of the Earth and the sun cancel each other out. However, the effect of their reduced gravity extends for millions of miles around the points.

The two approaching spaceships belong to NASA's STEREO mission, which was launched in October 2006, to study the sun and its effect on space weather.

One of them, STEREO A, nicknamed "Ahead," will reach L4, 930,000 miles beyond Earth's orbit on the side away from the sun, on Sept. 10. STEREO B, a laggard labeled "Behind," should get to L5, also facing the nightside of Earth, on Oct. 26.

STEREO A and B "are already under the influence of the Lagrange points," said William Thompson, a solar scientist at NASA's Goddard Space Flight Center in Greenbelt, Md. "It takes several months for them to pass through the regions around the L4-L5 points."

There are no plans to slow or halt Ahead or Behind as they enter the gravity wells. "We're moving too fast to get stuck," Michael Kaiser, retired STEREO project scientist, wrote in an e-mail.

Early next year, two European space telescopes, named Herschel and Planck, which were launched on May 14, will reach L2, the Lagrange point between L4 and L5.

Astronomers think L2, which also is 930,000 miles beyond Earth's orbit and far from its shadow, is an ideal setting to observe the universe. It will be the future home of the James Webb , which is to be launched in 2014 to succeed NASA's champion Hubble telescope.

Already parked at L2 is WMAP (the Wilkinson Microwave Anisotropy Probe), a NASA mission that launched in 2001 and has been making detailed observations of the early universe.

L1, a tenth of the way toward the sun, is occupied by SOHO, the U.S.-European Solar and Heliospheric Observatory. SOHO constantly monitors the sun to provide early warning of violent solar storms that can wreak havoc on earthly communications and endanger astronauts.

L3 is permanently hidden on the opposite side of the sun from Earth. Because it's invisible, it's been an ideal spot for science-fiction fantasies about alien spacecraft or a mysterious "Planet X."

After passing through L4 and L5, Ahead and Behind will continue circling the sun indefinitely, or until NASA cuts off their $10 million a year support.

"By early 2011, on Super Bowl Sunday, the two spacecraft will be 180 degrees apart and able, for the first time, to provide a view of the entire sun, front and back simultaneously," Kaiser said.

Meanwhile, Thompson said the STEREO mission will serve as "a test bed for a possible future space weather mission to be parked at L5."

Astronomers also think that L4 and L5 are natural dumps for space dust, debris, small asteroids and perhaps the remains of an ancient planet.

Two Princeton University astrophysicists, Edward Belbruno and Richard Gott, have speculated in books and lectures that a hypothetical planet, which they call Theia, was nudged out of its resting place when the solar system was still forming, 4.5 billion years ago, and plunged toward Earth. The subsequent collision knocked off a huge mass of material that later became the moon.

"These places may hold small asteroids, which could be leftovers from a Mars-sized planet that formed billions of years ago," Kaiser said. "A lot of this stuff could be remnants of Theia."

___

(c) 2009, McClatchy-Tribune Information Services.
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User comments : 22

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noosfractal
4 / 5 (6) Jul 15, 2009
The Earth is at the bottom of a gravity well. The Lagrange points are the local gravity peaks.
Doug_Huffman
4.3 / 5 (6) Jul 15, 2009
Ridges or cusps but not wells.
spacester
2 / 5 (1) Jul 15, 2009
Saddles.

http://tchester.o...ons.html

saddle
A point along a ridge between two peaks where the topography resembles that of the seat used by a horse-rider (the original saddle). Along one direction, the altitude is a local low point (between the two peaks). Along another direction, the altitude is a local high point (between the two drop-offs on either side of the ridge).
Trails frequently go to a saddle since they are:

* low points along a ridge, making for a minimum altitude gain to access the ridge,
* often points of intersection for trails that go in either direction along the ridge, or descend the canyons on both sides, and
* usually places with good views.
N_O_M
3.4 / 5 (7) Jul 16, 2009
Only the L4 and L5 points are stable.

While the Earth-Moon gravity cancels at the L1, L2 and L3 points, a satelite would require constant tiny orbit corrections to remain there. So, unfortunately for Tarl Cabot, you won't ever get a hidden planet at the Earth-Sun L3 point.



The Jupiter L4 and L5 points are known to contain asteroids, named Trojan.
a8ksh4
4.3 / 5 (6) Jul 16, 2009
How can you write an article about this stuff and not include a diagram showing where each spot is? It doesn't even have to be to scale.

Anywho, yah, this is cool stuff ;-)
frajo
3.8 / 5 (4) Jul 16, 2009
How can you write an article about this stuff and not include a diagram showing where each spot is? It doesn't even have to be to scale.

The diagram IS included - at http://en.wikiped...e_points :)
lysdexia
1 / 5 (2) Jul 16, 2009
Ahead and Behind? You mean Before and Behind.. Ahead and Afoot.
yOnsa
1 / 5 (3) Jul 16, 2009
How 'bout Ashmoke and Apancake?
TheBigYin
2.7 / 5 (3) Jul 16, 2009
It's hardly 'news' though, is it?
poi
1 / 5 (2) Jul 16, 2009
Well.. it talks about a maybe dead planet. Obit maybe?
lol!
frajo
1 / 5 (2) Jul 16, 2009
How 'bout Ashmoke and Apancake?

No - because people like me need both the first letters to be different. Otherwise I always end up mixing it up.
getgoa
1 / 5 (4) Jul 16, 2009
I guess earth and why hell and satan exists on this planet is because it is the lowest planet for sustaining life in the universe? The image of sun projected for 2011 is nice, but I would like to see an attempt of a 3d universe chart in the form of a complex hologram.
barakn
3.7 / 5 (9) Jul 16, 2009
L4 and L5 are technically not stable either as they are gravitational potential maxima (not saddle points) in a rotating frame of reference. However, once an object at either of those points deviates away slightly, the Coriolis force takes over and causes the object to orbit around the the Lagrange point, so it is quasi-stable.

The description of Lagrange points has been so dumbed-down for the general reading audience that it is completely wrong, and it's not limited to the issue that has already been described by other commenters, i.e. that Lagrange points are not a "well" or "cup."

Take for example the phrases "They're unusual locations where gravity loses its pull" and "places where the gravity of the Earth and the sun cancel each other out." If gravity lost its pull or canceled out, then there would be no forces acting on the object and it would travel in a straight line, which is obviously not the case. Perhaps they are referring to a rotating frame of reference, but then they've forgotten to mention the centrifugal force in addition to gravity.
GrayMouser
3 / 5 (3) Jul 16, 2009
Didn't we already go over all of this in the 60s and 70s?
Girthy
1 / 5 (2) Jul 17, 2009
How can it be hidden on the far side of the sun? We orbit the sun...

Unless I am completely missing something?
visual
5 / 5 (1) Jul 18, 2009
Girthy, the Lagrange points are also orbiting the sun with us. Look at the wikipedia link that frajo posted.
yyz
not rated yet Jul 18, 2009
barakn makes a good point. None of the Lagrange points is technically stable. Space probes sent to these points enter into Lissajous orbits around the barycenter at all 5 Lagrange points. See the Wiki page for more info here: http://en.wikiped...us_orbit . The Wiki article states "In practice, any orbit around a Lagrangian point is dynamically unstable, meaning small departures from equilibrium grow exponentially over time.[2] As a result, spacecraft in libration point orbits must use their propulsion systems to perform orbital stationkeeping."
smiffy
not rated yet Jul 18, 2009
In the light of the instability of lagrangian orbits, it makes me wonder how some people have theorised that the body that smashed into the Earth, creating the Moon, could have formed at a lagrangian point in the first place.
Girthy
1 / 5 (1) Jul 18, 2009
Girthy, the Lagrange points are also orbiting the sun with us. Look at the wikipedia link that frajo posted.


I realize it orbits with us but I sort of assumed that they meant that it is ALWAYS hidden. They must mean that it is only currently hidden due to the current orbits of the planets.
YawningDog
1 / 5 (1) Jul 19, 2009
Anybody remember the "L5 in 95" movement that fizzled out back in the 70's. Right after the moon landings when anything seemed possible, that we could achieve anything.

But then NASA was taken over by the Peter Principle (In a Hierarchy Every Employee Tends to Rise to His Level of Incompetence and Stay There)and it's been nothing but underachievment and mismanagement ever since.

If you really want to sink into a deep depression over the NASA debacle read "Challenger Revealed". Should be at 363.127 on your library shelf.

The only thing that can save us is a meritocracy in which the competent rule. But the incompetent will never relinquish power - while they're still alive.
Ivan2
5 / 5 (1) Jul 19, 2009
"How 'bout Ashmoke and Apancake?"

Uh, Alice and Bob weren't available for further comment.(;)
Shootist
not rated yet Jul 20, 2009
Anybody remember the "L5 in 95" movement that fizzled out back in the 70's. Right after the moon landings when anything seemed possible, that we could achieve anything.

But then NASA was taken over by the Peter Principle (In a Hierarchy Every Employee Tends to Rise to His Level of Incompetence and Stay There)and it's been nothing but underachievment and mismanagement ever since.


Which is a corollary to Pournelle's Iron Law of Bureaucracy, which states, " that in any bureaucratic organization there will be two kinds of people: those who work to further the actual goals of the organization, and those who work for the organization itself. Examples in education would be teachers who work and sacrifice to teach children, vs. union representative who work to protect any teacher including the most incompetent. The Iron Law states that in all cases, the second type of person will always gain control of the organization, and will always write the rules under which the organization functions."