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National Aeronautics and Space Administration

Goddard Space Flight Center

Office of the Chief Technologist

Office of the Chief Technologist

Two Columns

Feature

NASA Achieves an Orbital First: Goddard Engineers Fly Spacecraft in Unusual Lunar Orbit

NASA’s decision to repurpose two of five spacecraft originally designed to study auroras in Earth’s atmosphere offered a once-in-a lifetime opportunity for Goddard engineers Dave Folta and Mark Woodard. The pair was given a chance to demonstrate for the first time that spacecraft could fly in a unique orbit behind the Moon, but not actually orbit the Moon itself, answering a question that engineers had pondered for half a century.

Working with the Space Sciences Laboratory at the University of California-Berkeley and the Jet Propulsion Laboratory, the Goddard team formulated the orbit design and propulsion maneuvers to send ARTEMIS P1 to Earth-Moon Lagrangian Point 2 (L2), located on the far side of the Moon about 61,300 kilometers (38,100 miles) above the Moon’s surface. At the end of October, the team will send a different set of commands to sister spacecraft, ARTEMIS P2, to maneuver that satellite into orbit around the Earth-Moon L1, located between Earth and the Moon.

“In a nutshell, we had this theory but we never had a chance to prove it,” Folta said. “No one has ever placed spacecraft at these libration points before.”

The refocused ARTEMIS spacecraft also will collect unprecedented observations of the space environment behind the dark side of the Moon — home to the greatest known vacuum in the solar system. In late March, the Space Sciences Laboratory will send commands maneuvering both spacecraft into elliptical lunar orbits where they will continue to observe magnetospheric dynamics, solar wind, and the space environment over several years. “The point of this is science and extending the useful life of spacecraft, but at the same time we were able to validate theoretical work that had been done over the past 50 years,” Folta said. “I’m hopeful that NASA can use the ARTEMIS paradigm to find creative ways to extend the useful lives of its other space assets,” Woodard added. This image shows the kidney-shaped orbits that two repurposed spacecraft are flying. NASA has never before flown spacecraft at these Earth-Moon libration points.

Kidney-Shaped Orbits

Both distinctive kidney-shaped orbits rely on a precise balancing of the Sun, Earth, and Moon’s gravity to allow spacecraft to orbit about a virtual location rather than about a planet or moon. Five Lagrangian points are associated with the Earth-Moon system, but two points nearest the Moon are of particular interest for lunar exploration.

From these locations, NASA will be able to investigate possible regions where it could stage the assembly of telescopes or the human exploration of planets and asteroids. Navigating and controlling the pair of satellites also will supply NASA engineers with important information about propellant usage, required ground station resources, and how to maintain these unique orbits, which are difficult to preserve, Folta said.
This image shows the kidney-shaped orbits that two repurposed spacecraft are flying. NASA has never before flown spacecraft at these Earth-Moon libration points.

The two sister spacecraft, whose name stands for “Acceleration, Reconnection, Turbulence, and Electrodynamics of the Moon’s Interaction with the Sun,” originally were built for the THEMIS (Time History of Events and Macroscale Interactions during Substorms) mission, which completed its studies of auroras earlier this year.

NASA decided before the mission’s conclusion to repurpose two of the five spacecraft to gather additional scientific measurements from a different orbital perspective, giving the Goddard engineers an unprecedented opportunity to navigate in these unusual orbits.

“Maneuvering the two ARTEMIS spacecraft from their original orbits into the lunar Lagrangian orbits was very challenging, but we had an excellent team in place,” Woodard said. “The JPL engineers had to design low-energy transfer trajectories using what little propellant was left in the tanks. On paper the design was feasible, but implementing that design took many long hours and lots of analysis to get it just right.”

For three months, the two spacecraft will take magnetospheric observations from opposite sides of the Moon. ARTEMIS-P1 then will move to the L1 side, where both will remain in orbit for an additional three months. In particular, the two will provide simultaneous measurements of particles and electric and magnetic fields to produce the first three-dimensional perspective of how energetic particles accelerate near the Moon’s orbit, in the distant magnetosphere, and in the solar wind.

Technologies

The Office of the Chief Technologist is involved in a variety of projects, missions, and technologies.