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.”
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.
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.
“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.”
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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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.
Good stuff. This may reveal some supporting evidence for Ian Wilson’s forthcoming paper on Lunar amplification of the Solar signal in Earth’s climate.
http://tallbloke.wordpress.com/2010/10/20/ian-wilson-forthcoming-paper-2011/
Rock Star spacecraft orbiting a rock craftily to comprehend how our star carves rocks…
Cool!
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.
Could this have been achieved with manned space craft?
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.
Electrifying!
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.
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)
Awesome! Can we get high-res pics of the Moon landings?
Very cool. I wonder how long it took them to back-form the new acronym?
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
Isn’t that wonderful?
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.
Since I studied the ionosphere in grad school, this stuff is crazy cool to me. Nice post.
Any of our solar experts out there?? What do you think of this?
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.
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.
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?
Have they solved the classic three-body problem yet from first principles? I thought that was still considered too complex.
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.
Could this have been achieved with manned space craft?
Absolutely. Just need some serious rad sheilding for the humans.
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 ]
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!
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.