The L2 station keeping plan for the James Webb Space Telescope achieves zero velocity in the x-component at the fourth successive crossing of the XZ plane of the rotating libration point frame. A differential corrector is employed to determine the necessary delta-v. Maneuvering along the position component of the stable eigenvector of the monodromy matrix produces a minimum delta-v solution. The techniques developed to determine the minimum maneuver direction in a full ephemeris model, along with strategies to cope with the attitude constraints imposed by the sunshield that prevents the ability to maneuver along the stable eigenvector, are examined in this study.
The James Webb Space Telescope (JWST) is a flagship mission that launched on December 25, 2021. It is the scientific successor to the Hubble Space Telescope and the Spitzer Space Telescope. The project is an international collaboration between the National Aeronautics and Space Administration (NASA), the European Space Agency (ESA), Canadian Space Agency, and NASA Goddard Space Flight Center (GSFC). The JWST mission will focus on the infrared spectrum to detect the redshifted light from very early in the universe, which will fill a gap in the current range of astrophysical observations and allow the exploration of a whole new set of fundamental scientific questions ranging from the formation of the universe to the origin of planetary systems.
Given the sensitivity of the instruments to stray light, the mission will orbit near the Sun–Earth–Moon barycenter (SEMB) L2 libration point, allowing the optical element to remain pointed away from the Sun, the Earth, and the Moon at all times. The near-constant geometry of the trajectory relative to the Earth as it orbits about the Sun allows the observatory to map large swaths of the celestial sphere while providing long-duration communication links to the Earth. The orbital dynamics in the L2 region also support the observatory mass-budget constraints with minimal transfer and orbit maintenance costs. Thermal constraints on the instruments impose the need for a 161 square-meter sunshield as shown in the image below, the presence of which significantly couples the orbital and attitude dynamics as the Sun’s rays impinge on this surface. In addition to the need for the sunshield, thermal requirements also prevent the placement of thrusters on the instrument side of the observatory; consequently, no direct observatory-to-Sun vector maneuver directions are allowed.
The dynamical region about the SEMB L2 point is inherently unstable. As such, routine station keeping maneuvers are necessary to keep the observatory in a science orbit for the desired 10.5- year mission lifetime. It is well known that maneuvering along the position components of the stable eigenvector of the monodromy matrix provides the minimum station keeping delta-v for libration point orbits (LPO).1-3
The present investigation builds on a maneuver strategy implemented for the WIND mission in 2014, which employed maneuvers along the projection of the position components of the stable eigenvector in the ecliptic plane to reduce WIND’s station keeping costs between 5 and 25 percent relative to the historical method of maneuvering along the spacecraft-to-Sun line.4
The WIND technique will be modified for use by JWST to introduce an out-of-plane component, which will allow for full alignment between the position components of the stable eigenvector and the station keeping thrust vector. In the event that the attitude restrictions of the observatory prevent alignment between the stable eigenvector and the station keeping thrust vector, selecting the observatory attitude that places the station keeping thrust vector as close as possible to the position components of the stable eigenvector will result in the minimum delta-v solution that falls within mission attitude requirements.
To learn more, you can read our white paper “L2 Station Keeping Maneuver Strategy for the James Webb Space Telescope.”
Click the image below to download the white paper.