The Double Lunar Swingby

Today we have been reflecting on an impactful experience that happened on this day, March 14th, in 2008!

After a failure of its Briz-M upper stage shortly after launch on March 14, 2008, the AMC-14 communications satellite was left stranded in an inclined geostationary transfer orbit. John Carrico and Mike Loucks developed a recovery trajectory to deliver the spacecraft to its originally intended orbit.

Changing the angle between a spacecraft’s orbit plane and the equator is expensive in terms of propellant. Since AMC-14 was stranded near an inclination of 52 degrees, propellant could be conserved by boosting the apogee of the spacecraft’s orbit out to lunar distance.

Two lunar encounters (a “double lunar swingby”) reduced the inclination to 0 degrees (an equatorial orbit) and raised perigee to GEO altitude. Perhaps counterintuitively, the propellant required for these large changes in altitude was less than that required to reduce inclination propulsively.

Ultimately, AMC-14 did not utilize a double-lunar swingby trajectory to reach GEO. Instead, a series of low-thrust maneuvers were performed to raise orbit and eventually reach an inclined, geosynchronous orbit.

Learn More

The SEE team has studied the use of double lunar swingby trajectories for other applications, including transferring a satellite from a lunar rideshare to GEO. Stephen West presented this work at last year’s Spaceflight Mechanics Meeting. Read his paper, entitled, “Double Lunar Swingby Trajectories to Near-Geostationary Orbit.”

Double lunar swingbys are one of the “tools” in the astrogator’s toolbox. For resource constrained missions, lunar gravity assists can enable large orbit changes while conserving propellant. Every day, the SEE team applies techniques like this to solve challenging mission design problems!