Student Calculates a Cost-Saving Maneuver for Space Station

By Patrick Kurp

In a rare fulfillment of a boyhood fantasy, Sagar Bhatt watched as the International Space Station (ISS) maneuvered in space, for the first time in history, without burning any costly propellant, just as his calculations had predicted.

For 18 months, Bhatt, a third-year graduate student in computational and applied mathematics, worked as a fellow at the Charles Stark Draper Laboratory, collaborating with Yin Zhang, Rice professor of computational and applied mathematics, and Nazareth Bedrossian of Draper Laboratory to perfect the Zero-Propellant Maneuver (ZPM). Zhang describes the ZPM as “similar to the way a sailboat would tack against the wind.” Through a series of commands, the ISS was maneuvered along an optimized trajectory without the use of thrusters and without modification of its flight software. Bhatt calculated the optimized trajectory, which takes advantage of naturally occurring environmental torques to maintain the ISS gyroscopes within operational margins while performing the 90-degree reorientation.

Zhang praised Bhatt’s hard work and ingenuity, but maybe Bhatt’s best reward was seeing his work in action. He was at Johnson Space Center last November as the ZPM was executed successfully. “For two hours, the 450,000-pound space station did exactly what we thought it would do,” he says. “It was unbelievable.”