NASA floats parking at Lagrange Point 2

One of many proposed configurations for the Gateway architecture, shown above the lunar farside "parked" at Lagrange Point 2 [NASA].

Mark K. Matthews

Orlando Sentinel

Top NASA officials have picked a leading candidate for the agency's next major mission: construction of a new outpost that would send astronauts farther from Earth than at any time in history.

The so-called "gateway spacecraft" would hover in orbit on the far side of the moon, support a small astronaut crew and function as a staging area for future missions to the moon and Mars.

At 277,000 miles from Earth, the outpost would be far more remote than the current space station, which orbits a little more than 200 miles above Earth. The distance raises complex questions of how to protect astronauts from the radiation of deep space — and rescue them if something goes wrong.

NASA Chief Charlie Bolden briefed the White House earlier this month on details of the proposal, but it's unclear whether it has the administration's support. Of critical importance is the price tag, which would certainly run into the billions of dollars.

Documents obtained by the Orlando Sentinel show that NASA wants to build a small outpost — likely with parts left over from the $100 billion International Space Station — at what's known as the Earth-Moon Lagrange Point 2, a spot about 38,000 miles from the moon and 277,000 miles from Earth.

At that location, the combined gravities of the Earth and moon reach equilibrium, making it possible to "stick" an outpost there with minimal power required to keep it in place.

To get there, NASA would use the massive rocket and space capsule that it is developing as a successor to the retired space shuttle. A first flight of that rocket is planned for 2017, and construction of the outpost would begin two years later, according to NASA planning documents.

Read the full article HERE.

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Twin ARTEMIS probes to study Moon in 3D

ARTEMIS P1 and P2 were the outermost two THEMIS probes before maneuvers began July 20, 2009, to swap an Earth orbit for a lunar orbit [UC Berkeley].

Robert Sanders
US Berkeley

On Sunday, July 17, the moon will acquire its second new companion in less than a month. That’s when the second of two probes built by the University of California, Berkeley, and part of NASA’s five-satellite THEMIS mission will drop into a permanent lunar orbit after a meandering, two-year journey from its original orbit around Earth.

The first of the two probes settled into a stable orbit around the moon’s equator on June 27. If all goes well, the second probe will assume a similar lunar orbit, though in the opposite direction, sometime Sunday afternoon. The two spacecraft that comprise the ARTEMIS mission will immediately begin the first observations ever conducted by a pair of satellites of the lunar surface, its magnetic field and the surrounding magnetic environment.

“With two spacecraft orbiting in opposite directions, we can acquire a full 3-D view of the structure of the magnetic fields near the moon and on the lunar surface,” said Vassilis Angelopoulos, principal investigator for the THEMIS and ARTEMIS missions and a professor of space physics at UCLA. “ARTEMIS will be doing totally new science, as well as reusing existing spacecraft to save a lot of taxpayer money.”

“These are the most fully equipped spacecraft that have ever gone to the moon,” added David Sibeck, THEMIS and ARTEMIS project scientist at the Goddard Space Flight Center (GSFC) in Maryland. “For the first time we’re getting a unique, two-point perspective of the moon from two spacecraft, and that will be a major component of our overall lunar research program.”

The transition into a lunar orbit will be handled by engineers at UC Berkeley’s Space Sciences Laboratory (SSL), which serves as mission control both for THEMIS (Time History of Events and Macroscale Interactions during Substorms) and ARTEMIS (Acceleration, Reconnection, Turbulence, and Electrodynamics of the Moon’s Interaction with the Sun).

“We are on our way,” said Manfred Bester, SSL director of operations. “We’re committed.”

What makes the auroras dance?

The five THEMIS satellites (or probes) were launched by NASA on Feb. 17, 2007 to explore how the sun’s magnetic field and million-mile-per-hour solar wind interact with Earth’s magnetic field on Earth’s leeward side, opposite the sun. Within a year and a half, they had answered the mission’s primary question: Where and how do substorms in the Earth’s magnetosphere – which make the auroras at the north and south poles dance – originate?

The answer: the storms originate deep in the planet’s shadow, about a third of the way to the moon, where magnetic field lines snap, reconnect and unleash a storm of energy that funnels to the poles and makes the atmosphere glow in reds and greens. Large storms can wreak havoc on satellites, power grids and communications systems.

Mission accomplished, the THEMIS team was eager to divert two of the probes to the moon to extend their magnetic field studies farther into space. One key reason was that the two probes most distant from Earth would soon die because, with too much time spent in Earth’s shadow, their solar-powered batteries would discharge.

Side view of the ARTEMIS P1 probe's orbit in 2010 as it cruised around the two Earth-moon Lagrange points. In 2011 it maneuvered into a permanent orbit around the moon [NASA].

“That was an engineering challenge; this is the first mission where we’ve piloted into a lunar orbit spacecraft not designed to go there,” said Daniel Cosgrove, the UC Berkeley engineer who controls the spacecrafts’ trajectories. The probes’ small thrusters, for example, only push down and sideways. The probes are also spinning, which makes maneuvering even more difficult.

Also, last year probe P1 lost a spherical sensor from the end of one of four long wires that protrude from the spacecraft to measure electrical fields in space. The probable cause was a micrometeorite that cut a 10-foot section off of the 82-foot wire and caused it to retract into its original spherical housing, sending the “little black sphere flying through the solar system,” Bester said.

“All five spacecraft have been built by a very talented team with enormous attention to detail,” he said, predicting that the ARTEMIS probes could survive for another 10 years, longer than the three remaining THEMIS probes, which repeatedly fly in and out of Earth’s dangerous Van Allen radiation belt.

Lunar orbit

Once the second probe, P2, is in orbit, the two ARTEMIS satellites will graze the lunar surface once per orbit – approaching within a few tens of kilometers – in a belt ranging 20 degrees above and below the equator while recording electric and magnetic fields and ion concentrations.

“When the moon traverses the solar wind, the magnetic field embedded in the rocks near the surface interacts with the solar wind magnetic field, while the surface itself absorbs the solar wind particles, creating a cavity behind the moon,” Angelopoulos said. “We can study these complex interactions to learn much about the moon as well as the solar wind itself from a unique two-point vantage that reveals for the first time 3-D structures and dynamics.”

Sibeck noted that NASA’s twin STEREO spacecraft, launched in 2006, already provide a 3-D perspective on the sun’s large-scale magnetic fields. “THEMIS and ARTEMIS study the microscale processes, which we now know run the system,” he said.

One goal of the ARTEMIS mission is to look for plasmoids, which are hot blobs of ionized gas or plasma.

“THEMIS found evidence that magnetic reconnection propels hot blobs of plasma both towards and away from the Earth, and we want to find out how big they are and how much energy they carry,” Angelopoulos said. “Plasmoids could be tens of thousands of kilometers across.”

“THEMIS found the cause and now ARTEMIS will study the consequences, which are likely massive and global,” Sibeck said.

The spacecraft also will study the surface composition of the moon by recording the solar wind particles reflected or scattered from the surface and the ions sputtered out of the surface by the wind.

“These measurements can tell us about the properties of the surface, from which we can infer the formation and evolution of the surface over billions of years,” Angelopoulos said.

The two ARTEMIS probes will join NASA’s Lunar Reconnaissance Orbiter, which has been orbiting the moon since 2009 taking high-resolution photographs and looking for signs of water ice. In September, NASA is scheduled to launch two GRAIL (Gravity Recovery and Interior Laboratory) spacecraft to map the moon’s gravitational field, and in 2013, the agency plans to launch LADEE (Lunar Atmosphere and Dust Environment Explorer) to characterize the lunar atmosphere and dust environment.

“ARTEMIS will provide context for the LADEE mission,” Sibeck said.

Three other non-functioning satellites remain in orbit around the moon: two subsatellites of Japan’s lunar orbiter, Kaguya, which was guided to a crash on the surface in 2009; and India’s Chandrayaan-1, which lost communication with Earth that same year. China’s second lunar orbiter, Chang’e 2, left the moon for interplanetary space on June 8.

For more information:

First ARTEMIS Spacecraft Successfully Enters Lunar Orbit
(NASA press release, June 28, 2011)
Out of THEMIS, ARTEMIS: Earth’s loss is moon’s gain
(UC Berkeley press release, Oct. 27, 2010)
THEMIS mission identifies power behind northern lights
(UC Berkeley press release, July 24, 2008)
Successful launch of UC Berkeley’s THEMIS satellites
(UC Berkeley press release, Jan. 17, 2007)

ARTEMIS P1 successfully enters lunar orbit

The predicted path for ARTEMIS P1 as it enters lunar orbit [NASA/Goddard/D. Folta]. Play/Download Animations HERE.

Karen C. Fox
NASA/Goddard

On June 22, ARTEMIS P1 began firing its thrusters to move out of its kidney-shaped "libration" orbit on one side of the moon, where it has been since January. Three successive maneuvers were used to kick the spacecraft out of its orbit and send it on a trajectory toward the moon.

It continued on that path until June 27 at 10:04 a.m. EDT when the spacecraft was about 2,400 miles from the moon. At that point, flight engineers at UC Berkeley issued the first commands to move it into orbit around the moon. Two more maneuvers helped fine-tune the position, and as of 12:30 p.m. EDT, ARTEMIS P1 is now in lunar orbit.

"ARTEMIS is the first mission ever to orbit the moon's Lagrangian points."

This is the culmination of a complex, two-year journey that relied predominantly on gravity boosts and used minimal fuel. The path from its orbit around Earth to the moon was developed and orchestrated by engineers at the NASA's Goddard Space Flight Center in Greenbelt, Md., NASA's Jet Propulsion Lab in Pasadena, Calif., and University of California at Berkeley.

The engineers will watch the ARTEMIS P1 orbit closely over the next few days in case additional adjustments are required. Engineers are set to move the second spacecraft, ARTEMIS P2, into position on July 17.

ARTEMIS is the first mission ever to orbit the moon's Lagrangian points – points on either side of the moon where the moon and Earth's gravity balance perfectly. It is also the first to attempt to move from the Lagrangian to lunar orbit.

The ARTEMIS mission uses two of the five in-orbit spacecraft from another NASA Heliophysics constellation of satellites called THEMIS that were launched in 2007 and successfully completed their mission in 2010. The ARTEMIS mission allowed NASA to repurpose two in-orbit spacecraft to extend their useful science mission.

Follow the full story, HERE.

"Dead spacecraft walking"

Artist's concept of ARTEMIS A and B (formally THEMIS-P1 and P2), after a circuitous, low-energy orbital transfer resembling a year-long round of pin-ball - back and forth many times between Lagrange points, finally in lunar orbit on a new and important mission. (A full-sized view is available HERE.) Flight Dynamics data from ARTEMIS P2 recently indicated one electric field instrument end-effector may have been struck by a meteoroid [NASA/UCLA].

Tony Phillips
Science@NASA

In 2007 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.

The ARTEMIS spacecraft are currently located at the L1 and L2 Earth-Moon Lagrange points. ARTEMIS-P1 is the first spacecraft to navigate to and perform stationkeeping operations around the Earth-Moon L1 and L2 Lagrangian points. A full-size view is available HERE, and a YouTube demonstration of the route taken to the new mission can be seen HERE [NASA/GSFC/UCLA].

"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.

"Orbiting the Moon is notoriously tricky, however, because of irregularities in the lunar gravitational field."

"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.

Related Posts:
NASA update: ILN Anchor Nodes
and Robotic Lunar Lander Project
August 17, 2010

THEMIS becomes ARTEMIS
Aviation Week
July 30, 2010

Robotic Lunar Landers
for Science and Exploration
41st Lunar and Planetary Science Conference, #2616
March 4, 2010

ARTEMIS, A Two Spacecraft, Planetary
and Heliospheric Lunar Mission
41st Lunar and Planetary Science Conference, #1425
March 4, 2010

Update on the new lunar phase
of THEMIS mission
UC Berkeley Daily Tech
October 30, 2009

ARTEMIS to Lagrange points
to lunar orbit
April 26, 2009