After successfully rendezvousing and docking with the International Space Station (ISS), Boeing’s Starliner is now headed back to Earth after a six-day-long mission in low Earth orbit. The spacecraft autonomously undocked from the forward-facing port at the Harmony module of the ISS at 2:36 p.m. today, wrapping up its stay at the orbiting laboratory.
Boeing and NASA teams are currently targeting 6:49 p.m. Eastern on Thursday, May 26, 2022, for the spacecraft’s return to Earth at White Sands Space Harbor at the US Army’s White Sands Missile Range Facility in New Mexico. If for some reason the teams cannot proceed with the landing on Thursday, a backup opportunity exists on Friday, May 27.
The crew of Expedition 67 said their goodbyes to Starliner as they culminated the Farewell Ceremony at 12:55 p.m. EST yesterday, followed by the closure of the hatch just an hour later.
This is the second flight of Boeing’s Commercial Crew Program Starliner spacecraft which is slated to carry expedition crews regularly to the International Space Station. Named the Orbital Flight Test – 2 (OFT-2), the mission is the company’s second attempt to test the end-to-end capabilities of the Starliner systems, after the first attempt failed to complete several key objectives, including the autonomous rendezvous and docking to the ISS.
An investigation into the original Orbital Flight Test – 1 (OFT-1) mission revealed that the capsule’s Mission Elapsed Timer had polled incorrectly, resulting in the spacecraft not executing its orbital insertion burn at the planned time. The teams on the ground also experienced communication issues with the spacecraft, which affected the command and control of the capsule.
A software issue with the service module separation sequence was also found during the mission which would have resulted in the loss of the vehicle had it not been identified and fixed before Starliner returned to Earth. Boeing teams conducted extensive testing to resolve the problems faced during OFT-1.
The teams were ready to launch the spacecraft on the OFT-2 mission in August of 2021 but faced another issue with the valves in the propulsion systems, causing the launch attempt to scrub and teams to scramble for a fix. The root cause of the valve issue was determined to be corrosion from nitric acid, which had formed as a result of water vapor in the air reacting with the dinitrogen tetroxide that Starliner uses as an oxidizer.
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Ultimately, Boeing decided to swap out the service module for one that had been due to fly the Crew Flight Test (CFT) mission. The new service module incorporates a nitrogen purge system to help mitigate the problem, with spacecraft fueling and pre-launch procedures also amended.
So far, the Starliner is working as expected on OFT-2. The spacecraft launched to space on Thursday, May 19 atop United Launch Alliance Atlas V rocket from Space Launch Complex 41 at Cape Canaveral Space Force Station in Florida.
After separating from the Atlas V’s Centaur second stage, Starliner conducted a series of burns using its onboard propulsion systems — designed and built by Aerojet Rocketdyne — to raise its orbit and align itself to the International Space Station. On Friday, May 20, the capsule successfully docked to the orbiting laboratory, marking a major milestone in Boeing’s demonstration flight for NASA’s Commercial Crew Program.
Once docked, the teams continued to work on flight test objectives for OFT-2. On May 21, astronauts opened the hatch of the CST-100 for the first time and moved inside to become the first people to enter the spacecraft in orbit.
Two days later, the astronauts began unloading the cargo and stowing the materials in their places inside the orbital laboratory. Additional docked flight test objectives completed by the teams include:
Starliner’s Intra Vehicular Activity (IVA) hatch opened
Joint ventilation with ISS established
Docked telemetry paths and file transfers verified
Vision-based Electro-optical Sensor and Tracking Assembly (VESTA) and flight data files transferred from Starliner to ISS for downlink
ISS Portable Computer System connected and checked out
Audio checkouts between Starliner and the ISS, Starliner and Mission Control Center Houston, and Starliner and Boeing’s Mission Control Center in Florida conducted
Starliner Global Positioning Satellite (GPS) and Inertial Navigation System (INS) from ISS state initialized
Recharging spacecraft batteries from the station’s power
Starliner Service Module batteries checked out
Conduct pre-undock Starliner systems activation and checkout
Close Starliner’s IVA hatch
Depressurize the vestibule.
Undocking and Return
Similar to the Russian Soyuz, landing on land is one of the unique features of Starliner spacecraft; however, it can land on water as well in case of emergency. Boeing and NASA teams have designated the US Army’s White Sands Missile Range in New Mexico as the primary landing site for spacecraft. On Monday, May 23, NASA and Boeing teams conducted a mission dress rehearsal at the White Sands Space Harbor to practice the landing and recovery procedures ahead of the landing of the spacecraft.
Today, the NASA and Boeing teams performed a GO/NO-GO poll for the spacecraft to undock from the ISS. Once given a GO, the spacecraft configured itself for undocking. After separating from the orbiting laboratory, the spacecraft executed two short-duration burns to further distance itself from the ISS.
20 minutes later, Starliner will execute a series of 4 burns to exit the Keep Out Sphere and Approach Ellipsoid of the ISS, as it moves over 150 meters away from the orbiting laboratory. These two zones dictate how the vehicles approach and exit the ISS.
The Approach Ellipsoid is over four by two kilometers wide and the keep-out sphere is just 200 meters wide.
Outbound Flyaround Maneuver (OFM)
Departure Initiation Burn (DI)
Departure Resume Burn (DR)
NSR Coelliptic burn
Two hours later, Starliner’s service module will execute a final, de-orbit burn which will put the spacecraft on the trajectory to land at its planned landing site.
Deorbit Burn (DO)
Once completed, the Starliner’s Service Module — which provides thermal control, power, and on-orbit propulsion — will be jettisoned. The Starliner Crew Module will align itself with the heat shield first as it prepares for the atmospheric re-entry, currently scheduled for 16:32 EST (22:32 UTC).
The spacecraft will experience a temporary loss of signal and communication with the ground during the re-entry phase as an envelope of ionized air forms around the spacecraft due to the extreme heat as temperatures can rise to 1,930° C (3,500° F). Approximately four minutes before touchdown, Starliner’s heat shield will be jettisoned, followed by the deployment of the drogue parachutes.
These help to slow the spacecraft down, with the drogues making way for the four main parachutes about one minute and 10 seconds later. Just two minutes and 49 seconds before touchdown, rotation handles will deploy which align the Starliner to land perpendicularly on the land. Shortly after, its base heat shield will be separated, followed by the inflation of airbags which will cushion the spacecraft as it lands at the White Sands Space Harbor in New Mexico.
Once landed, the recovery forces will move towards the spacecraft to secure it. Recovery operations will be assisted by numerous NASA and Boeing personnel, including spacecraft engineers and medical professionals.
(Lead photo: Starliner seen from the ISS during docking on May 20. Credit: NASA)
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