Artist's concept of LISA spacecraft stacked on the launch vehicle.

The Laser Interferometer Space Antenna's (LISA) spacecraft will be launched from a single Delta-IV rocket and injected into an Earth-escape trajectory. The three spacecraft will then separate from the rocket and from each other. Once separated, each spacecraft will be guided by an individual propulsion module to its own independent orbit around our Sun.

After reaching the final orbits, about 13 months after launch, the propulsion modules will separate from the spacecraft. Each spacecraft's orbit will then evolve under gravitational forces only——not maintained by any onboard propulsion system—— for the expected mission duration of five years. View an animation, courtesy of Mike Sandford of Rutherford Appleton Laboratory, to see how it all happens. (Download free RealPlayer for Windows or Quicktime for PCs or Mac. Click your browser's BACK button to return to the LISA website.)

Spacecraft orbit tilt. See a simple animation of the changing orientation of the spacecraft configuration as it orbits the Sun.

In their orbits, the three spacecraft will form an equilateral triangle with a distance of five million kilometers (about three million miles) between any two spacecraft. Each spacecraft orbit, slightly elliptical and slightly tilted with respect to the other individual orbits and to the plane of the Earth's orbit, will maintain the triangle formation of LISA. The selected orbits will minimize the changes in the distances between spacecraft. This is important because laser interferometry measurements are more difficult to make if the distances between pairs of spacecraft are not nearly equal. Additionally, the distance between spacecraft was carefully chosen to allow LISA to observe in the frequency band of the most interesting sources. The center of LISA's triangle will follow Earth's orbit around the Sun, trailing 20 degrees behind, maintaining——like the Earth——an average distance of 1 AU from the Sun. An AU (one astronomical unit) is the average distance between the Earth and the Sun.

A diagram of LISA following behind Earth's orbit of the Sun. View an animation to see how the LISA spacecraft will travel in orbit. Note that the spacecraft are not drawn in scale with Earth. Still and animation courtesy Jet Propulsion Laboratory.

LISA's operational position was chosen as a compromise between the need to minimize the effects on the spacecraft of changes in the Earth's gravitational field and the need to be close enough to the Earth for easy communication. In addition, it is less costly to design the spacecraft and science instruments needed to operate under the temperature found at 1 AU. The triangle will rotate as the spacecraft orbit the Sun. This rotation is helpful in determining the direction of the sources of observed gravitational waves.

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