NASA and Boeing achieved a key commercial space milestone May 25 when they safely returned a second astronaut-transportation system to Earth from a docked mission with the International Space Station.
The path to that milestone was not with some “excruciating” and “nail-biting” moments as the spacecraft docked with the station May 20.
Boeing’s CST-100 Starliner, built under a 2014 $4.2 billion, fixed-price contract, touched down at 4:49 p.m. MDT May 25 at New Mexico’s White Sands Space Harbor four hours after departing the space station. Borne by three parachutes and cushioned by six air bags, the capsule landed at about 18 mph (28.5 km/hr) on White Sands’ gypsum flats.
The Starliner’s only occupant was an anthropomorphic test device fitted with 15 sensors to collect data on what astronauts would experience flying in the new spacecraft. Dubbed Rosie the Rocketeer, the device paid homage women — symbolized by Rosie the Riveter — who during World War II filled American factories to keep the war-production effort running.
The six-day flight was a critical achievement in NASA’s 11-year campaign to develop commercial providers of two separate, redundant systems to transport astronauts to the space station. One such provider, SpaceX, has been flying astronauts to the station on its Crew Dragon for 18 months. It won a $2.6-billion NASA contract in 2014.
“This is a landmark mission,” Joel Montalbano, manager, NASA’s International Space Station (ISS) Program. If post-flight data reviews confirm Starliner’s success and clear it to fly humans, Boeing will become “a second crew provider to the ISS team and the NASA program in general.”
NASA relied on single crewed systems for most of its human spaceflight program, which was hobbled after a system suffered a major failure. Since space shuttle was retired from service in 2011, NASA had relied solely on Russia’s Soyuz spacecraft to carry astronauts aloft until the Crew Dragon was approved for that mission.
The Starliner mission also marked a redemption for Boeing Space. Launched May 19 at 6:54 p.m. on a United Launch Alliance Atlas V rocket from Cape Canaveral Space Force Station, Florida’s Space Launch Complex-41, the mission was designated Orbital Flight Test 2 (OFT-2). Boeing’s first Starliner, in 2019, failed after the spacecraft was unable to dock with the station.
That Orbital Flight Test mission had several problems. One, with Starliner’s onboard clock, caused thrusters to misfire and leave the spacecraft in an orbit from which it could not reach the station. Space-to-ground communications problems interfered with
command and control of the spacecraft. While Starliner was in orbit, controllers found a flaw in software governing the separation of Starliner’s service module. They fixed the flaw, but a later review found the flaw could have destroyed the spacecraft during re-entry.
NASA added OFT-2 to demonstrate those problems had been fixed before it would certify Starliner to carry humans. But during the first OFT-2 launch attempt, on Aug. 3, 2021, the countdown was scrubbed after ground controllers were unable to move 13 propulsion system valves in service module to their correct position. An investigation after the spacecraft was pulled from the launch pad found that moisture had infiltrated the valves. The moisture combined with the propulsion system’s dinitrogen tetroxide oxidizer to form nitric acid that corroded the valves. Boeing replaced the service module and developed a temporary solution to prevent moisture from entering the valves. But that work pushed the launch re-attempt back nine months.
The second Starliner mission went smoothly, for the most part. The countdown was flawless, launch officials said, and the ascent to orbit was “nominal,” despite the failure of a couple of orbital maneuvering thrusters. Once on orbit, Starliner accomplished many demonstration objectives, including proving its ability to accurately establish and maintain its position as it rendezvoused, docked, and departed from the station and execute a precise de-orbit, re-entry, and landing. It also demonstrated a new, common docking system for spacecraft and Boeing’s Vision-based Electro-optical Sensor Tracking Assembly (VESTA), an artificial intelligence-based system to guide the spacecraft during rendezvous operations.
As the spacecraft began the process of docking with the station the day after launch, flight controllers at the Johnson Space Center in Houston confronted some issues, including a glitch with docking graphics and a need to retract and re-extend the new NASA Docking System. Starliner finally docked with the station at 8:28 p.m. EDT, about an hour later than planned. The rendezvous had begun about five hours earlier. Starliner was required to spend the last hour-plus holding its position about 33 feet (10 meters) from the station’s Harmony module docking port before controllers cleared it for the final approach.
Those last hours were “excruciating,” said Kathy Lueders, the associate administrator in charge of NASA’s Space Operations Mission Directorate. “Seeing that beautiful spacecraft sitting right out of range of ISS was pretty tough.” But, she added, “this was a really critical demonstration mission, and it was important for us to put the vehicle through its paces.”
Mark Nappi, the vice president and program manager heading Boeing’s Commercial Crew Program, said, “It was really nail-biting watching that vehicle sit out there for a while until it was time to come in.”