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written by Thomas Burghardt
December 21, 2019
After a maiden flight that was shortened by an off-nominal orbit insertion, Boeing’s CST-100 Starliner conducted its first landing from orbit. Touchdown at the White Sands Missile Range in New Mexico occurred at 5:58 AM MST (12:58 UTC) on December 22.
The spacecraft approached from the southwest, overflying the Pacific Ocean and Baja California.
If, at any point leading up to the deorbit burn, NASA or Boeing teams felt the need to reevaluate landing options, there was a backup landing opportunity at 1:48 PM MST (20:48 UTC). Had this backup attempt is utilized, the spacecraft would have approached from the northwest. However, the first opportunity was taken.
Sunday’s landing attempt came six days earlier than originally intended. The Orbital Flight Test (OFT) mission to demonstrate end-to-end performance of the uncrewed spacecraft was cut short by an error with Starliner’s Mission Elapsed Timer (MET).
During launch, Starliner sets its MET based on data retrieved from its Atlas V launch vehicle. During Friday’s nominal launch, Starliner retrieved the wrong data, resulting in an incorrectly set MET.
After nominally separating from the rocket, Starliner’s MET indicated that the spacecraft was at a point in the mission profile different than its actual location. This disagreement resulted in the orbit insertion (OI) burn, which moves Starliner into a stable orbit, not occurring on time.
Additionally, Starliner and its antennae were not oriented properly, again due to the MET error. This created a challenge for ground controllers attempting to command the OI burn, as establishing a data link between NASA’s Tracking and Data Relay Satellites (TDRS) and Starliner was delayed.
Once a positive command link was established, ground controllers commanded the spacecraft to conduct two burns in order to reach a circular 250 kilometer orbit.
While this orbit was stable, it was lower than the International Space Station’s altitude. After reaching a stable orbit, NASA and Boeing evaluated the possibility of maneuvering to the station, but concluded that an insufficient amount of fuel remained on board Starliner to conduct an approach. Starliner burned a significant amount of propellant while maneuvering to a stable orbit and maintaining the incorrect orientation after launch. //
In addition to the two burns conducted to reach Starliner’s 250 km orbit, several small checkout burns of Starliner’s propulsion systems have been successfully conducted. Station keeping and attitude control demonstrations were also completed.
Another major milestone was testing of Starliner’s Guidance, Navigation, and Control (GNC) systems. This included successfully using the VESTA star tracking system for navigation. Also successfully established was a command link from ground controllers through the International Space Station to the Starliner spacecraft.