Dead terran spacecraft find new life in moon orbit

From Science @NASA: A pair of NASA spacecraft that were supposed to be dead last year are instead flying to the Moon for a breakthrough mission in lunar orbit.

“Their real names are THEMIS P1 and P2, but I call them ‘dead spacecraft walking,'” says Vassilis Angelopoulos of UCLA, principal investigator of the THEMIS mission. “Not long ago they appeared to be doomed, but now they are beginning an incredible new adventure.”

Artemis (artemis, 550px)

An artist’s concept of THEMIS-P1 and P2 (since renamed ARTEMIS-P1 and P2) in lunar orbit. [larger image]

The story begins in 2007 when NASA launched a fleet of five spacecraft into Earth’s magnetosphere to study the physics of geomagnetic storms. Collectively, they were called THEMIS, short for “Time History of Events and Macroscale Interactions during Substorms.” P1 and P2 were the outermost members of the quintet.

Working together, the probes quickly discovered a cornucopia of previously unknown phenomena such as colliding auroras, magnetic spacequakes, and plasma bullets shooting up and down Earth’s magnetic tail. This has allowed researchers to solve several longstanding mysteries of the Northern Lights.

Artemis (Northern Lights, 200px)

In their previous life, THEMIS-P1 and P2 were on a mission to study Northern Lights. [more]

The mission was going splendidly, except for one thing: Occasionally, P1 and P2 would pass through the shadow of Earth. The solar powered spacecraft were designed to go without sunlight for as much as three hours at a time, so a small amount of shadowing was no problem. But as the mission wore on, their orbits evolved and by 2009 the pair was spending as much as 8 hours a day in the dark.

“The two spacecraft were running out of power and freezing to death,” says Angelopoulos. “We had to do something to save them.”

The team brainstormed a solution. Because the mission had gone so well, the spacecraft still had an ample supply of fuel–enough to go to the Moon. “We could do some great science from lunar orbit,” he says. NASA approved the trip and in late 2009, P1 and P2 headed away from the shadows of Earth.

With a new destination, the mission needed a new name. The team selected ARTEMIS, the Greek goddess of the Moon. It also stands for “Acceleration, Reconnection, Turbulence and Electrodynamics of the Moon’s Interaction with the Sun.”

The first big events of the ARTEMIS mission are underway now. On August 25, 2010, ARTEMIS-P1 reached the L2 Lagrange point on the far side of the Moon. Following close behind, ARTEMIS-P2 entered the opposite L1 Lagrange point on Oct. 22nd. Lagrange points are places where the gravity of Earth and Moon balance, creating a sort of gravitational parking spot for spacecraft.

Artemis (Lagrange Points, 550px)

The ARTEMIS spacecraft are currently located at the L1 and L2 Earth-Moon Lagrange points. [more]

“We’re exploring the Earth-Moon Lagrange points for the first time,” says Manfred Bester, Mission Operations Manager from the University of California at Berkeley, where the mission is operated. “No other spacecraft have orbited there.”

Because they lie just outside Earth’s magnetosphere, Lagrange points are excellent places to study the solar wind. Sensors onboard the ARTEMIS probes will have in situ access to solar wind streams and storm clouds as they approach our planet—a possible boon to space weather forecasters. Moreover, working from opposite Lagrange points, the two spacecraft will be able to measure solar wind turbulence on scales never sampled by previous missions.

“ARTEMIS is going to give us a fundamental new understanding of the solar wind,” predicts David Sibeck, ARTEMIS project scientist at the Goddard Space Flight Center. “And that’s just for starters.”

ARTEMIS will also explore the Moon’s plasma wake—a turbulent cavity carved out of the solar wind by the Moon itself, akin to the wake just behind a speedboat. Sibeck says “this is a giant natural laboratory filled with a whole zoo of plasma waves waiting to be discovered and studied.”

Artemis (orbits, 200px)

A Youtube video describes the complex orbits of the two Artemis spacecraft.

Another target of the ARTEMIS mission is Earth’s magnetotail. Like a wind sock at a breezy airport, Earth’s magnetic field is elongated by the action of the solar wind, forming a tail that stretches to the orbit of the Moon and beyond. Once a month around the time of the full Moon, the ARTEMIS probes will follow the Moon through the magnetotail for in situ observations.

“We are particularly hoping to catch some magnetic reconnection events,” says Sibeck. “These are explosions in Earth’s magnetotail that mimic solar flares–albeit on a much smaller scale.” ARTEMIS might even see giant ‘plasmoids’ accelerated by the explosions hitting the Moon during magnetic storms.

These far-out explorations may have down-to-Earth applications. Plasma waves and reconnection events pop up on Earth, e.g., in experimental fusion chambers. Fundamental discoveries by ARTEMIS could help advance research in the area of clean renewable energy.

After six months at the Lagrange points, ARTEMIS will move in closer to the Moon—at first only 100 km from the surface and eventually even less than that. From point-blank range, the spacecraft will look to see what the solar wind does to a rocky world when there’s no magnetic field to protect it.

“Earth is protected from solar wind by the planetary magnetic field,” explains Angelopolous. “The Moon, on the other hand, is utterly exposed. It has no global magnetism.”

Studying how the solar wind electrifies, alters and erodes the Moon’s surface could reveal valuable information for future explorers and give planetary scientists a hint of what’s happening on other unmagnetized worlds around the solar system.

Orbiting the Moon is notoriously tricky, however, because of irregularities in the lunar gravitational field. Enormous concentrations of mass (mascons) hiding just below the surface tug on spacecraft in unexpected ways, causing them over time to veer out of orbit. ARTEMIS will mitigate this problem using highly elongated orbits ranging from tens of km to 18,000 km.

“We’ll only be near the lunar surface for a brief time each orbit (accumulating a sizable dataset over the years),” explains Angelopoulos. “Most of the time we’ll linger 18,000 km away where we can continue our studies of the solar wind at a safe distance.”

The Dead Spacecraft Walking may have a long life ahead, after all.

Author: Dr. Tony Phillips | Credit: Science@NASA

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77 thoughts on “Dead terran spacecraft find new life in moon orbit

  1. This is a true scientific adventure with no pre-determined outcome. These researchers only strive to collect totally new data to advance our understanding of the natural forces that shape this tiny part of the Universe inwhich we live. Maybe this project will provide a tidbit of evidence about what causes Earth to move from one climate era to the next. There are so many unmanned, under reported satellite projects and space probes collecting new types of data, that I find it hard to absorb it all, much less apply the knowledge in my work. Thanks for the update.

  2. WOW real lunar vantage point based studies, who would of thought they would get around to looking at the Solar, Earth, Lunar, solar wind interactions, its about time!
    The Empire brings unity, but the Rebel terrorists continue to foster division and hatred. 2,471,647 Imperial citizens died in the terrorist attack against the Death Star.

  3. Those L1/L2 orbits remind one of the never-repeating Lorenz attractors of chaos theory.
    It’s surprising the craft had enough fuel to make a moon trip, but I guess once you get away from the Earth, the gravitational well isn’t so steep. Bonus points to the engineering crew.

  4. I hate to say this, but anything but “aurorae” in the plural just looks wrong to me.
    This is an exciting project and an informative article. I expect there is still much to learn about the interaction of the Earth’s magnetic field(s) and the solar plasma streams. Solar-wind erosion on the Moon is also very interesting and I got the hint from the article they expect to extrapolate results to Mars.
    Whoever pulled off this end-of-life Moon mission deserves a prize.

  5. Good stuff. Who knows what may be found.
    Not my money, but isn’t this the kind of thing NASA should be doing, not scaring us with climate catastrophe fairy tails? (rhetorical)

  6. Now that is REAL science in action. Great job all involved. I wonder if there are any earth poinging cameras onboard, so they can send us images of earth from the moon in HD, keep up the good work,.
    Ian

  7. Seems like NASA is still doing some pretty cool stuff these days, in spite of the snaggles in the manned space missions.
    These L1 and L2 orbits seem baffling, almost paradoxical. Paradoxical because these objects are also in orbit around the Earth, but they’re not the same distance from the Earth as the Moon. So the L1, closer to the Earth, should be moving in a faster oribit and L2, further away, should be moving slower. But they’re stationary with the Moon, so moving with the same speed as the Moon. How can that be?
    It’s easy to see the reason why, if you understand that objects ‘in orbit’ around the Earth are actually ‘falling’ around the Earth, accelerated by the Earth’s gravitational pull, the ‘falling speed’ (i.e. orbital speed) dependent on the acceration constant g (9.8 m/s/s).
    What if g were smaller? Then orbital (‘falling’) speed would be slower. Likewise a stronger pull would cause the orbital speed to increase.
    So that explains what is going on here.
    L1, in tighter orbit than the Moon, would normally orbit faster, but the Moon’s gravity pulls in the opposite direction, effectively reducing ‘g’ and slowing the spacecraft down. At L1 the speed matches the Lunar orbit speed.
    L2, further away, would normally orbit slower, but now the Moon’s pull is additive, effectively increasing ‘g’ and making the L2 orbit faster. At the L2 point it exactly matches the Lunar speed.
    These are ideal solutions to the ideal ‘3-body’ model. There are many other perturbations present which cause these points to be slightly unstable. But the satellites can be held in ‘halo orbits’ around these L1 and L2 points with only a small amount of ‘stationkeeping’ engine thrusts.
    So NASA has found a good workable approximation to the ideal Lagrangrian points.

  8. Can we elect these guys for presidedunce and congresscritters instead of the cretins that we have in there. These guys have lots of neurons to rub together. The crowd in DC is nothing more than a sea squirt after it has attached itself to its rock.

  9. Lagrange points are places where the gravity of Earth and Moon balance, creating a sort of gravitational parking spot for spacecraft.
    Not quite.
    The Lagrange points mark positions where the combined gravitational pull of the two large masses provides precisely the centripetal force required to rotate with them.
    That centripetal force is quite important. There are 5 Lagrangian points.

  10. Nice diagram of Artemis L1 & L2 orbits near the moon.
    At first I thought it was our old friend Lord Acton.
    I wonder if he’s from those parts?

  11. Let us all hope Obama dont find out.
    After all, there are no muslims to be found on the moon.
    And according to Obama and the NASA big boss, bridging the cultural gap is priority numero uno for NASA.

  12. Could this have been achieved with manned space craft?
    Absolutely. Just need some serious rad sheilding for the humans.

  13. John Day says:
    These L1 and L2 orbits seem baffling, almost paradoxical. Paradoxical because these objects are also in orbit around the Earth, but they’re not the same distance from the Earth as the Moon. So the L1, closer to the Earth, should be moving in a faster oribit and L2, further away, should be moving slower. But they’re stationary with the Moon, so moving with the same speed as the Moon. How can that be?

    They are baffling. In a normal gravity-well orbit, the relationship is somewhat easy to understand. Something is pulling on you in one direction, and if you get enough speed at a right angle to that acceleration, you can avoid ever falling in. LaGrange points operate somewhat differently. The wikipedia article has a nice image that uses “lines” do show local maxima/minima. Now if you look at L1 , for example, you see that if you started “circling” L1, then the combination of the two gravity wells creates a situation where your orbital mass is somewhat consistently being pulled 60-90 degrees from it’s current direction. It’s more like riding a roller-coaster where the track has two dips in it and two hills. One dip is the moons gravity well, which accelerates you just enough to get re-“caught” by the earths gravity well on the other side of the “hill”, and the other dip is the earth’s gravity well, which accelerates you enough to get re-“caught” by the moon’s well. The beauty comes when your forward momentum is never turned enough to get fully caught by either well, and you essentially “hang” in a loose windy “orbit” around a local maxima in gravity wells.

    • [Not fixed-in-one-constant-motion (statically stable) then, but dynamically stable as it oscillates between two (or more) constantly changing energy states, eh? Like the climate perhaps ]

  14. I’m guessing that the spacecraft designers and original mission planners had this secondary mission in mind when they designed the satellites. It is rare for a spacecraft to have large amounts of propellant remaining at the end of its primary mission, let alone 2 such space craft! At a cost of at least $10,000 per pound of payload delivered to the original earth orbit, the on board load of satellite propellant is tailored to meet the primary mission with some small excess margins for unanticipated contingencies. The secondary moon mission required these birds to climb further out of Earths gravity well. That takes propellant… and not just the little puff burns normally needed for ‘station keeping’. Somebody planned ahead!
    Either way, I’m enthused that we will get a wealth of additional data from these 2 sojourners!

  15. ShrNfr says:
    October 28, 2010 at 5:22 am
    “Can we elect these guys for presidedunce and congresscritters instead of the cretins that we have in there. These guys have lots of neurons to rub together. The crowd in DC is nothing more than a sea squirt after it has attached itself to its rock.”
    Not a good idea. Rocket scientists should design rockets. They have far too many brilliant ideas to hold political office.

  16. This is reminiscent of the the change in Pioneer 11’s plan. Originally it was only going to pass Jupiter, but if I recall correctly, during transit someone found it could take a trajectory that would take it past Saturn.
    Space probes that last beyond their design life open up some really neat possibilities.

    Mike McMillan says:
    October 28, 2010 at 3:13 am
    It’s surprising the craft had enough fuel to make a moon trip, but I guess once you get away from the Earth, the gravitational well isn’t so steep. Bonus points to the engineering crew.

    http://themis.ssl.berkeley.edu/overview.shtml says two probes (these?) got 20 and 30 Earth radii out as part of the primary mission. That’s really far out of the Earth’s gravity well, so that and likely good fuel management made this new mission possible.

  17. RACookPE1978 says:
    October 28, 2010 at 6:04 am
    > Have they solved the classic three-body problem yet from first principles? I thought that was still considered too complex.
    First principles? There’s really only one – Newton’s law of gravitation. A long time ago I wrote a program to figure out sunrise/sunset times from the physics, and even in two body problems there’s an issue that can’t be solved. Something like given the time since perigee, the location on the orbit can’t be determined due to an integration that can’t be solved. (Clearly some times and some orbits have solutions, e.g. after time of one half the orbital period you’re at the apogee, and circular orbits are deterministic.)
    [Jean Meeus – feel free to correct me if I have this wrong!]
    The obvious chaos in 3 body dynamics makes it pretty clear there’s no hope of deriving an equation for their orbits.

  18. This is the good thing about NASA. I know an old”Steely Eyed Rocket man” who’ll
    be proud of this . This is what they are supposed to do. Not “Islamic outreach”…

  19. I love these guys. They continuously find ways to do more with less.
    Unlike the bastions of education (where I work), where we seem to do far less with more.

  20. @Jeremy:
    >> … How can that be?
    > In a normal gravity-well orbit, the relationship is somewhat easy to
    > understand.
    > Something is pulling on you in one direction, and if you get enough speed
    > at a right angle to that acceleration, you can avoid ever falling in.
    > LaGrange points operate somewhat differently.
    Actually, these LaGrange L1 and L2 objects operate the same as any other objects in orbit around the Earth. The difference is that the Moon subtracts and adds gravitational pull to L1 and L2 respectively, changing the orbital speeds so that they remain ‘stationary’ with respect to the Moon.
    Reread my post, I wasn’t asking for an explanation. My question was rhetorical. 😐

  21. Great navigation even if the outer 2 satellites were already almost half way to the moon prior to departure. Of course all that fuel was for orbit correction, a possible but likely undesirable option given the redundant nature of the mission instruments. This option was probably in the works as a possibility for a while, by some really clever and optimistic design team. Here is a recitation of the instrumentation;
    “Each satellite carries identical instrumentation, including a fluxgate magnetometer (FGM), an electrostatic analyzer (ESA), a solid state telescope (SST), a search-coil magnetometer (SCM) and an electric field instrument (EFI).”
    As many stated, congratulations NASA. This is real science by real scientists, And this after this team has already solved the prime mission goal with certainty.

  22. John Coleman says:
    October 28, 2010 at 1:11 am
    This is a true scientific adventure with no pre-determined outcome. These researchers only strive to collect totally new data to advance our understanding…
    ~~~~~~~~
    ^This.
    Well said, John. I was going to post something similar, only to see your first post summed up my thoughts exactly. It’s nice to see NASA doing some true, space-based, scientific research. Especially nice to see it done without any preconceived bias as to what they [want to] find.

  23. So Dr Phillips; I constantly marvel at the way some people at NASA are able to react to unplanned “anomalies” and figure some way to rescue an apparently dead mission. This is such an example.
    So I have a question; relating to the drunken sailor orbits of these two ships about L1 and L2. Are they the result of just not doing a perfect job of getting the car in the parking spot; or is it that L1 nd L2 are not exactly stationary points in a multibody orbit system; so they will roam forever ? Or will they eventually settle down pretty much at L1 and L2 ?

  24. “”” Ric Werme says:
    October 28, 2010 at 7:29 am
    RACookPE1978 says:
    October 28, 2010 at 6:04 am
    > Have they solved the classic three-body problem yet from first principles? I thought that was still considered too complex.
    First principles? There’s really only one – Newton’s law of gravitation. A long time ago I wrote a program to figure out sunrise/sunset times from the physics, and even in two body problems there’s an issue that can’t be solved. Something like given the time since perigee, the location on the orbit can’t be determined due to an integration that can’t be solved. (Clearly some times and some orbits have solutions, e.g. after time of one half the orbital period you’re at the apogee, and circular orbits are deterministic.)
    [Jean Meeus – feel free to correct me if I have this wrong!]
    The obvious chaos in 3 body dynamics makes it pretty clear there’s no hope of deriving an equation for their orbits. “””
    I hate to correct trivial arithmetic misteaks; but If I add 1.sun + 2.earth + 3.moon + 4. Lagrange 1or 2, I come up with a count of four bodies not three. (for each of L1/L2)
    A three body orbital problem in the solar system would be the Jupiter Trojans . Yes I know there’s a whole lot of extra perturbatory bodies !
    As I understand it; the “Three Body Problem ” is an (elementary) problem of Newtonian Orbital Physics, that simply has no general case closed form solution. But it has special case solutions; or at least one such, namely an equilateral triangle of three point objects of arbitrary masses. I suspect that depending on the three masses; there is some “noisy” perturbations of the exact (plane) geometry; that are stable; and presumably could return to exactitude; but I have absolutely no idea how extensive such a noisiness is permitted; nor how it might depend on the three masses; but at some level of perturbation the system has to blow up. The point object restriction I believe is necessary; because otherwise the finite moments of inertia of each object would screw things up; but maybe even that isn’t true ?
    The Lagrange point architecture is something that was completely unknown to me until very recently; when it appeared in some weird NASA orbital discussion; which might have been right here at WUWT. Totally blew me away.

  25. Dang, I had found a cute paper calculating the stability of L1 and L2 last month from a link off a NASA page, but I cant find it now. I thought I had book marked it. It was a very nice presentation using rotating reference frames.

    • [A reason why I use “Bookmark -> Science -> NASA -> Orbits;
      Bookmark -> Science -> MWP;
      Bookmark -> Science -> Hurricanes, etc.
      I’m not smart enough any more to remember where I put stuff otherwise. 8<)

  26. George E. Smith says:
    October 28, 2010 at 9:29 am
    namely an equilateral triangle of three point objects of arbitrary masses. […] The point object restriction I believe is necessary
    This is a common misconception. It is enough that the objects are spherically symmetric. Also, L4 and L5 are ‘stable’ against small perturbations [for large enough mass ratios]. L1, L2, and L3 require slight ‘station keeping’ [small corrections to the spacecraft position].

  27. George E. Smith
    October 28, 2010 at 9:29 am
    A solution to the three body problem in classic euclidean space is impossible because the number of unknown constants is greater the the number of known parameters. However a solution might be possible assuming curved space but the derivation could be a nightmare. In any rate, as can be seen from the mess that is depicted in the L1 to L2 transfer, a general solution would end up being a nasty parametrized system of equations. BTW, that diagram only shows what is happening in the orbital plane. It does not show what is going on in the “z” axis!

  28. Leif Svalgaard says:
    October 28, 2010 at 7:54 am
    You will have to revisit Pythagoras. From thousand of years ago knowledge was transmitted by simple, very simple symbols, as the Pythagorean Tetraktis. The fundamental laws of the cosmos are as simple. This was so until the church invented the concept of “inmateriality”, which of course it does not have any reality whatsoever, that took us to irrational extremes as to belief in black holes and multi dimensional realities. Sorry but the universe is material and eternal and it works by the action of just two forces: call it whatsoever, oriental people call them ying and yang, we, occidentals call it, electricity, positive and negative charges. Revisit Pythagoras and you will learn that he just have a simple Monochord and his known theorem for exactly describing nature.
    The origin of error can be traced to the phylosophy of agnosticism, where we humans were told by the then politicians of the church, that we were supposed to believe in Dogmas, inmaterial truths to believe in. The contrary philosophy, since then prohibited was that of gnosticism, which taught that knowledge of the laws of the universe was possible for man.

  29. Very cool!
    You run into a problem, take a look at available resources, and engineer a classy solution that yields some additional benefit from the machines already in space. Great example of good applied engineering and science at work.

  30. @George
    > Are they the result of just not doing a perfect job of getting the car in the
    > parking spot; or is it that L1 nd L2 are not exactly stationary points
    > in a multibody orbit system; so they will roam forever ?
    Here’s a Java simulator where you can get some answers to these questions:
    http://www.princeton.edu/~rvdb/JAVA/astro/galaxy/Galaxy0.html
    You’ll learn that there are no exact solutions to this problem (even in this toy simulation). There many numerical approaches to solution. None perfect, all with varying degrees of instability. That’s why they have to fire those station-keeping engines once in a while, to keep the spacecraft in their halo orbits.

  31. John Day says: “Reread my post, I wasn’t asking for an explanation. My question was rhetorical. :-|”
    Who would bother answering a rhetorical question?

  32. George E. Smith
    October 28, 2010 at 9:06 am
    #
    To add to what
    Leif Svalgaard
    October 28, 2010 at 9:52 am
    said:
    The force vector field about the unstable point accelerates objects away. About the stable point, objects are accelerated towards the point. Think of L1 and L2 as being on a hill, push to far and objects fall off, and L4 and L5 as being in a valley.

  33. > Who would bother answering a rhetorical question?
    I would. Oops, sorry, didn’t realize that was a rhetorical question.
    :-]

  34. Jeez,…everyone is commenting on the Langrangian orbits. I’m more fascinated by the fact that they are going to use a variation of a Molniya orbit about the moon to get the apogee dwell time up for battery charging.

  35. Mac the Knife is the only one who gets it. This mission wasn’t discovered, it was planned from the beginning. Predicting transit of the earth’s shadow for a satellite in high orbit isn’t that difficult; there is no possible way the orbits “evolved” over a mere two years in a way that would surprise anyone competent.
    At best, this is nothing more than NASA shamelessly spinning a moderately clever re-use of hardware into a faux drama of rescuing dying satellites. The 2nd mission was planned long before launch in 2007, but it makes better press to talk about “dead satellites walking.”
    See http://bit.ly/cng3aS (PDF file) “PRELIMINARY TRAJECTORY DESIGN FOR
    THE ARTEMIS LUNAR MISSION”
    “in 2005, the idea of sending P1 “up” instead of “down” was hatched and studied by the THEMIS science team and at JPL.” That’s nearly 2 years before THEMIS was launched.
    The mission designers were unable to get approval and/or funding for the second mission at the time the satellites were being designed and built.
    “proposals for funding were made in 2006 and 2007 to support a detailed low-energy trans-lunar trajectory design study, feasibility studies related to the THEMIS hardware, and optimization of the remaining THEMIS mission for P1 and P2. These proposals were not selected for funding, but concept development continued by the science team as time permitted.”
    So they couldn’t get the mission approved, but they spent their tax-paid salaries developing it anyway.
    The fawning press release states that “The two spacecraft were running out of power and freezing to death,” says Angelopoulos. “We had to do something to save them.”
    Contrast that to the orbit design paper:
    “In the summer of 2007, internal JPL funding became available to support an Explorer progam Mission of Opportunity proposal for the THEMIS mission extension that would become ARTEMIS.”
    The summer of 2007 was less than 6 months after launch. The satellites hadn’t even reached their intial science orbits. The were never “running out of power and freezing to death.”
    This is not a tale of ingenuity and innovation. It could just as easily be presented as a tale of fraud with tax dollars, deliberate misallocation of budgets, and diverting funds to work that did not survive the review and approval process. Then it gets spun as some sort of dramatic rescue mission.
    This is indeed NASA creativity at it’s best. The AGW people could learn some lessons from this abuse of the tax-funded science mission planning process and the use of hyperbolic language to describe the results.
    Had this been presented more honestly, I might be inclined to be more charitable. Lying to the public appears to be an inherent part of government-funded science.

  36. DesertYote says:
    October 28, 2010 at 10:34 am (Edit)
    George E. Smith
    October 28, 2010 at 9:06 am
    #
    To add to what
    Leif Svalgaard
    October 28, 2010 at 9:52 am
    said:

    The force vector field about the unstable point accelerates objects away. About the stable point, objects are accelerated towards the point. Think of L1 and L2 as being on a hill, push to[o] far and objects fall off, and L4 and L5 as being in a valley.

    If so, would not then both L4 and L5 “attract” all randomly moving nearby dust and debris into their regions over the past 3.5 billion years of a stable moon-earth orbit system, thus “filling up” the previously empty L4 and L5 spots with a new moon/asteroid combination? Granted, fast-moving debris might not get trapped, but slow-moving dust should be there in abundance.

  37. -S
    October 28, 2010 at 11:45 am
    That’s not true. I get it, and it has been bothering me for awhile. It is just that some of love math so much, especially cool math like that involved in deriving L point stability and orbits, that it over shadows other issues.
    NASA has always reused mission hardware. I used to work for a organization that built a lot of stuff for NASA. It is an awesome feeling to read articles on the current activities of missions that I was involved with 20 years ago!
    BTW, I saw this yesterday, talk about spin.
    “2. Eco-friendly Spacecraft: Recycle, Reuse, Record – The EPOXI mission is recycling the Deep Impact spacecraft, whose probe intentionally collided with comet Tempel 1 on July 4, 2005, revealing, for the first time, the inner material of a comet. The spacecraft is now approaching a second comet rendezvous, a close encounter with Hartley 2 on Nov. 4. The spacecraft is reusing the same trio of instruments used during Deep Impact: two telescopes with digital imagers to record the encounter, and an infrared spectrometer. ”
    this is from:
    http://www.nasa.gov/mission_pages/epoxi/epoxi20101025.html

  38. racookpe1978 says:
    October 28, 2010 at 12:19 pm
    If so, would not then both L4 and L5 “attract” all randomly moving nearby dust and debris into their regions over the past 3.5 billion years of a stable moon-earth orbit system
    First, the orbit of the Moon has not been stable over billions of years [it is getting larger].
    Second, But there are such debris at Jupiter’s L4 and L5: http://en.wikipedia.org/wiki/Jupiter_Trojan

  39. racookpe1978
    October 28, 2010 at 12:19 pm
    Not to much. Going back to the valley analogy, think of L4 & L5 as a shallow valley on a hill. Past a certain point, the force vector field again accelerates objects away from the L point. The accumulation of perturbations from the other bodies in the solar system will tend to knock objects out of the “dimple”. To get into the dimple is also not a simple matter. Its like trying to roll a ball up a hill to land and stay in within the dimple, to fast and the ball does not stop but rolls out, too slow and the ball does not make it up the hill.

  40. @racookpe1978:
    > … would not then both L4 and L5 “attract” all randomly moving nearby
    > dust and debris into their regions over the past 3.5 billion years of a
    > stable moon-earth orbit system, thus “filling up” the previously
    > empty L4 and L5 spots with a new moon/asteroid combination?
    Yes, that has indeed happened, for example at Jupiter’s L4 an L5 points:
    http://en.wikipedia.org/wiki/Jupiter_Trojan
    Here’s a more complete list of known LaGrangrian objects, man-made and otherwise:
    http://en.wikipedia.org/wiki/List_of_objects_at_Lagrangian_points

  41. Dead satellites walking? Why not make the press release totally B-movie rated and call it “Zombie Robots in Space!” 🙂

  42. L1 & L2 for the win! It has been a long time since I’ve heard of those. Way back in the 70s reading Gerard O’Neill’s book “The High Frontier”.

  43. Enneagram says:
    October 28, 2010 at 10:03 am
    “From thousand of years ago knowledge was transmitted by simple, very simple symbols, as the Pythagorean Tetraktis. The fundamental laws of the cosmos are as simple.”
    The Monad is the Father Embracing all that will be.
    The Dyad, the form of Difference, and
    Mother of Multiplicity.
    The Triad, the first actual number,
    With Beginning, End, and Mean,
    The Tetrad completes the arrangement
    Of the Soul and what is seen.
    Ancient Tetraktys, Pythagoras’ vision divine,
    The Decad, a perfect Limit, and Cosmic Paradigm.
    Original poem by Robert Apatow
    The more complex things seem to be becoming, the further we drift from the truth. The position of the observer decides how he views reality. We will only ever be able to understand the universe by looking inwards, rather than looking out.

  44. Tim says:
    October 28, 2010 at 1:46 pm
    L1 & L2 for the win! It has been a long time since I’ve heard of those. Way back in the 70s reading Gerard O’Neill’s book “The High Frontier”.
    ###
    We don’t need no oil, nor a Tokamak coil,
    Solar power supplies us with juice,
    Powerbeams are sublime, so no one will mine,
    If we cook an occasional goose.
    A lost verse from the L5 song.

  45. Ric Werme says:
    October 28, 2010 at 7:21 am
    “http://themis.ssl.berkeley.edu/overview.shtml says two probes (these?) got 20 and 30 Earth radii out as part of the primary mission. That’s really far out of the Earth’s gravity well, so that and likely good fuel management made this new mission possible.”
    However, the article claimed that the probes were spending as much as 8 hours a day in the dark, which is only possible in Low Earth Orbit, at about 1.1547 Earth radii (ie, below 1000km), from which the delta V to L1 & L2 is ~3km/s. Even with good fuel management you wouldn’t get that much left at end of life, unless it had been planned that way from the outset. So something doesn’t add up. Alternatively, had they been in a very high, slow, orbit (>300 Earth radii, 5x the Moon’s orbit) they could have spent up to 8 hours behind the Earth at a time, but then would not have been in full shadow, since the Earth would have eclipsed less than half of the Sun’s disk.

  46. For the L1, L2, and L3 points, a halo orbit or Lissajous orbit has to be used, since those points aren’t dynamically stable. L4 and L5 can be dynamically stable, if there aren’t perturbing factors. In the case of the Earth-Moon system, the eccentricity of the Moons’ orbit and solar perturbations render them dynamically unstable also.
    If you map the space-time curve for the Lagrangian points, L1-L3 are saddle points, while L4 and L5 are dimples.
    L2 and L3 can also be understood as point and the surface of the second body’s Hill sphere.

  47. Leif Svalgaard says:
    October 28, 2010 at 2:54 pm
    ‘Tenuc says:
    October 28, 2010 at 2:18 pm
    …We will only ever be able to understand the universe by looking inwards, rather than looking out.’
    Leif Reply: “nuts…”
    There is a goose trapped in a narrow necked bottle. Poof… in an instant the goose is out.
    Questions:-
    How did the goose get out of the bottle without breaking it?
    How did the goose get into the predicament in the first place?

  48. Tenuc says:
    October 28, 2010 at 3:40 pm
    Questions:-
    How did the goose get out of the bottle without breaking it?
    How did the goose get into the predicament in the first place?

    In four dimensions these questions are non-issues.

  49. I do not know anything about geese.
    The goose in question ….( not exist)
    I see as the greatest concern to attack the correct positions of Dr. Leif.
    The question is. The topic is about the math of 200 years ago.
    Leif, In four dimensions These questions are non-issues.
    Nice read ….
    Amazing how all “barycentric friends” are not present.
    Lukewarmers,
    I do not believe … this position of relative comfort.

  50. Tenuc says:
    October 28, 2010 at 3:40 pm (Edit)
    ….

    There is a goose trapped in a narrow necked bottle. Poof… in an instant the goose is out.
    Questions:-
    How did the goose get out of the bottle without breaking it?
    How did the goose get into the predicament in the first place?

    1) The goose did not break the bottle. As a caring engineer, I did, in order to save the goose’s neck.
    2) The goose, like many too careless in their pursuit of life but who think they can learn all that is important from peer-reviewed theoretical research, measured his neck and then measured the bottle’s neck.
    Thus fully informed about the theory of sticking heads in bottles, he chose to stick his head in the bottle. His head, now closed in the bottle, swelled up and prevented removal because the goose forgot about feedback, biology, and the small size of the thermal expansion of glass under under pressure.

  51. “”” Leif Svalgaard says:
    October 28, 2010 at 9:52 am
    George E. Smith says:
    October 28, 2010 at 9:29 am
    namely an equilateral triangle of three point objects of arbitrary masses. […] The point object restriction I believe is necessary
    This is a common misconception. It is enough that the objects are spherically symmetric. Also, L4 and L5 are ‘stable’ against small perturbations [for large enough mass ratios]. L1, L2, and L3 require slight ‘station keeping’ [small corrections to the spacecraft position]. “””
    Thanks Leif; I wasn’t too sure about the “point object” aspect; which is why I had the CYA weasel words. I thought later that maybe non-zero moments of inertia might not be a problem. I gather without looking at pictures that L4 and L5 are the Trojan locations and assumed they were sort of meta-stable, in that for Jupiter; there are already occupants there (apparently).

  52. George E. Smith says:
    October 28, 2010 at 5:22 pm
    I gather without looking at pictures that L4 and L5 are the Trojan locations and assumed they were sort of meta-stable, in that for Jupiter; there are already occupants there (apparently).
    There are currently about 4000 Jupiter trojan asteroids with catalogued orbits, asymmetrically distributed between the planet’s L4 and L5 at a 2:1 ratio. There are no doubt hundreds of thousands of smaller motes hanging around as well.

  53. As I remember, Arthur C Clark was writing about Lagrange points in the ’60’s. Just like he did about geocentric orbits in the ’40’s. Or maybe it was another sci-fi writer like Izamov or Heinlein. I am glad the mathematics have been improved and hats off to the NASA folks who actually did this.

  54. Dr. Leif Svalgaard , What about the science data coming from the P1 and P2? Orbits and geese in bottles, not withstanding.

  55. Paul Birch says:
    October 28, 2010 at 2:32 pm

    Ric Werme says:
    October 28, 2010 at 7:21 am
    “http://themis.ssl.berkeley.edu/overview.shtml says two probes (these?) got 20 and 30 Earth radii out as part of the primary mission. That’s really far out of the Earth’s gravity well, so that and likely good fuel management made this new mission possible.”
    However, the article claimed that the probes were spending as much as 8 hours a day in the dark, which is only possible in Low Earth Orbit,….

    That’s true for circular orbits, but these were in extemely eccentric orbits. I don’t fully understand the arrangement, but I assume that when the major axis of the orbit line up with the sun and the perigee is sunward, then the satellites would whip around the sunward side of the Earth and dawdle on the shady side for the long climb and fall on the other side.
    John Day says:
    October 28, 2010 at 10:15 am

    Here’s a Java simulator where you can get some answers to these questions:
    http://www.princeton.edu/~rvdb/JAVA/astro/galaxy/Galaxy0.html

    Oh good, I was going to post this, it’s nice to know other people know of Vanderbei’s site. I strongly recommend people interested in orbital dynamics spend a little time playing with the simulator, it’s fascinating seeing how what appears to be a stable orbit can quickly fall apart.
    Also, check out his home page for other interests and the photos he’s coaxed out of his Questar telescope and others.

  56. DocWat says:
    October 29, 2010 at 5:32 am
    Dr. Leif Svalgaard , What about the science data coming from the P1 and P2? Orbits and geese in bottles, not withstanding.
    That data will be interesting because we’ll sample the solar wind before it hits the Earth, so space weather forecasting will improve.

  57. Ric Werme says:
    October 29, 2010 at 5:40 am
    “”Paul Birch: … the probes were spending as much as 8 hours a day in the dark … only possible in Low Earth Orbit”
    That’s true for circular orbits, but these were in extemely eccentric orbits. I don’t fully understand the arrangement, but I assume that when the major axis of the orbit line up with the sun and the perigee is sunward, then the satellites would whip around the sunward side of the Earth and dawdle on the shady side for the long climb and fall on the other side.”
    I don’t think that quite works. With a low perigee (1.15R) and a very high apogee (25R) the orbital velocity at apogee is indeed low enough, at 440m/s, to keep the probe in shadow for up to 8 hours at a time. But not 8 hours a day, since the orbital period is then ~3 days. However, if you make the burn at perigee, the delta V to L1 & L2 is then only a few hundred metres per second, which is certainly plausible. Though a much smaller burn would nudge the orbit out of shadow anyway.
    I guess the 8 hours a day could have been a journalistic error.

  58. Yeah, I remember Clark writing about LaGrange points and discussions about having space stations there. To the person who asked if this could have been a manned mission – I guess the costs/risks are considered too great.

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