Discovery: Solar Probes Dispatched to Moon

[bystander]

Solar Probes Dispatched to Moon
Discovery News | Space | 27 July 2010

Two space probes are given a new lease on life after being rerouted for a mission to unravel the composition of the moon.

• Two of NASA's five THEMIS satellites, a network that studies the sun, will now set their sights on the moon.
• The perfect vacuum of the moon's far side is a key area for study.
• The probes would have frozen if they weren't relocated, though funding for their new mission is still pending.

A pair of NASA science satellites that have been studying how solar geomagnetic storms impact Earth are being dispatched to the moon for a new mission.

The probes are part of a constellation of five satellites collectively known as THEMIS, an acronym for Time History of Events and Macroscale Interactions during Substorms, which was launched in February 2007.

The spacecraft, which were carefully positioned in orbit for coordinated measurements downstream of Earth, surpassed their two-year design life and remain operational. But over time, the two outer satellites' orbits would have been in Earth's shadow for prolonged periods, leading to cold temperatures that likely would have been fatal.
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Funding for the new mission is still pending NASA's approval, but the satellites already are on their way. The first probe is slated to slip into a preliminary orbit around the moon in August; the second one is due to follow in October.

The orbits will be tweaked until April when the recycled spacecraft would be properly positioned for their new mission, called ARTEMIS for Acceleration Reconnection and Turbulence and Electrodynamics of the Moon's Interaction with the Sun.
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Scientists want to put the spacecraft as close as about 100 kilometers (62 miles) in front of and behind the moon. From that vantage point, the probes could see what's coming toward the moon from the sun, what's coming out the other side and how the environment of the moon varies in response.
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From a heliophysics perspective, scientists want to see what happens to the solar wind as it wraps around the moon. The far side of the moon is considered to be the most perfect vacuum in the solar system.

The probes could also serve as solar wind monitors, providing real-time data about geomagnetic disturbances that could threaten satellites, power grids and radio communications on Earth.

[bystander]

ARTEMIS - The First Earth-Moon Libration Orbiter
NASA GSFC | 14 Sept 2010

Artemis-P1 libration orbits (top view). [i](Credit: NASA/GSFC)[/i]

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Artemis-P1 libration orbits (side view). [i](Credit: NASA/GSFC)[/i]

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In August 1960, NASA launched its first communications satellite, Echo 1. Fifty years later, NASA has achieved another first by placing the ARTEMIS-P1 spacecraft into a unique orbit behind the moon, but not actually orbiting the moon itself. This type of orbit, called an Earth-Moon libration orbit, relies on a precise balancing of the Sun, Earth, and Moon gravity so that a spacecraft can orbit about a virtual location rather than about a planet or moon. The diagrams right show the full ARTEMIS-P1 orbit as it flies in proximity to the moon.

ARTEMIS-P1 is the first spacecraft to navigate to and perform stationkeeping operations around the Earth-Moon L1 and L2 Lagrangian points. There are five Lagrangian points associated with the Earth-Moon system. The two points nearest the moon are of great interest for lunar exploration. These points are called L1 (located between the Earth and Moon) and L2 (located on the far side of the Moon from Earth), each about 61,300 km (38,100 miles) above the lunar surface. It takes about 14 to 15 days to complete one revolution about either the L1 or L2 point. These distinctive kidney-shaped orbits are dynamically unstable and require weekly monitoring from ground personnel. Orbit corrections to maintain stability are regularly performed using onboard thrusters.

After the ARTEMIS-P1 spacecraft has completed its first four revolutions in the L2 orbit, the ARTEMIS-P2 spacecraft will enter the L1 orbit. The two sister spacecraft will take magnetospheric observations from opposite sides of the moon for three months, then ARTEMIS-P1 will move to the L1 side where they will both remain in orbit for an additional three months. Flying the two spacecraft on opposite sides, then the same side, of the moon provides for collection of new science data in the Sun-Earth-Moon environment. ARTEMIS will use simultaneous measurements of particles and electric and magnetic fields from two locations to provide the first three-dimensional perspective of how energetic particle acceleration occurs near the Moon's orbit, in the distant magnetosphere, and in the solar wind. ARTEMIS will also collect unprecedented observations of the space environment behind the dark side of the Moon – the greatest known vacuum in the solar system – by the solar wind. In late March 2011, both spacecraft will be maneuvered into elliptical lunar orbits where they will continue to observe magnetospheric dynamics, solar wind and the space environment over the course of several years.

[bystander]

Dead Spacecraft Walking
NASA Science News | 27 Oct 2010

A pair of NASA spacecraft that were supposed to be dead a year ago 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 so long ago, we thought they were goners. Now they are beginning a whole new adventure."
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"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.

Out of THEMIS, ARTEMIS: Earth's loss is moon's gain
University of California, Berkeley | 27 Oct 2010

Two micro-satellites originally launched into Earth's orbit in 2007 by NASA have been redirected by University of California, Berkeley, scientists toward new orbits around the moon, extending study of the earth and moon's interactions with the solar wind.

The second of the two probes settled into a temporary "Lagrange-point" orbit on Friday, Oct. 22, inaugurating science operations for a new mission dubbed ARTEMIS — Acceleration, Reconnection, Turbulence, and Electrodynamics of the Moon’s Interaction with the Sun.

Lagrange points are places where the gravity of Earth and the moon balance, creating a sort of gravitational parking lot for spacecraft. The two probes will remain there for six months before transitioning to their final, lunar orbits.

Over the next several years, ARTEMIS will help space scientists understand how the earth's magnetosphere is shaped by the strong solar wind at the distance of the moon and also how the moon's own tiny magnetic field interacts with the solar wind. Using simultaneous measurements of particles and electric and magnetic fields from two locations, ARTEMIS will provide the first three-dimensional perspective of how energetic particle acceleration occurs near the moon's orbit, in the distant magnetosphere, and in the solar wind.

Two NASA Spacecraft Begin New Exploration Assignments
NASA | 10-282 | 27 Oct 2010

Two NASA spacecraft have been assigned a new mission after successfully completing their original science objectives earlier this year. The duo began making observations this week to study how solar wind electrifies, alters and erodes the moon's surface. Data could reveal valuable information for future explorers and give planetary scientists a hint of what's happening on other worlds around the solar system.

The new mission is called ARTEMIS, or Acceleration, Reconnection, Turbulence and Electrodynamics of Moon's Interaction with the Sun. ARTEMIS uses two of five in-orbit spacecraft from NASA's THEMIS, or Time History of Events and Macroscale Interactions during Substorms, mission.

"Using two repurposed satellites for the ARTEMIS mission highlights NASA's efficient use of the nation's space assets," said Dick Fisher, director of the Heliophysics Division in NASA's Science Mission Directorate at the agency's headquarters in Washington.

ARTEMIS will measure solar wind turbulence on scales never sampled by previous missions. Solar wind is a stream of charged particles emitted from the upper atmosphere of the sun.
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http://www.nasa.gov/mission_pages/artemis
http://www.nasa.gov/themis

[owlice]

I remember Lagrange points.