Miguel J. Rodriguez Carrillo/AFP via Getty Images
The first crewed test flight of Boeing’s long-delayed Starliner spacecraft will not take off Saturday as planned, and could face a longer delay as engineers evaluate a persistent leak of helium from the capsule’s propulsion system.
NASA announced the latest delay to the Starliner test flight late Tuesday. Officials will need more time to consider their options on how to proceed with the mission after discovering the small helium leak in the spacecraft’s service module.
The space agency has not described what options are on the table, but sources say they range from flying the spacecraft “as is” with a thorough understanding of the leak and confidence that it will not become more significant during flight, to removing the capsule from space. his Atlas V rocket and takes it back to a hangar for repairs.
Theoretically, the former option could enable a launch attempt as early as next week. This last alternative could delay the launch until at least late summer.
“The team met for two consecutive days to review the flight rationale, system performance and redundancy,” NASA said in a statement Tuesday evening. “Work continues to progress in these areas, and the next possible launch opportunity is still being discussed. NASA will share more details once we have a clearer path forward.”
Delays are nothing new for the Starliner program, but it’s not yet clear how this delay will compare to the spacecraft’s previous setbacks.
Software problems ended an unmanned test flight in 2019, forcing Boeing to fly a second demonstration mission. Starliner was on the launch pad when checkouts before the 2021 flight revealed stuck valves in the spacecraft’s propulsion system. Boeing finally flew Starliner on a return flight to the space station in May 2022. Concerns about Starliner’s parachutes and flammable tape in the spacecraft’s crew cabin postponed the crewed test flight from last summer to this year.
Boeing aims to become the second company to ferry astronauts to the space station under contract to NASA’s commercial crew program, following the launch of SpaceX’s crew transport service in 2020. Assuming a smooth crew test flight, NASA hopes to release the Starliner spacecraft for six months can make. Monthly crewed rotational flights to the space station starting next year.
In the dog house
Engineers first noticed the helium leak during the first launch attempt for the Starliner crewed test flight on May 6, but managers did not consider it significant enough to stop the launch. Ultimately, a separate problem with a pressure control valve on the United Launch Alliance (ULA) Atlas V rocket forced officials to scrap the launch attempt.
NASA astronauts Butch Wilmore and Suni Williams were already strapped into their seats in the Starliner spacecraft on the launch pad at Cape Canaveral Space Force Station, Florida, when officials ordered a halt to the May 6 countdown. Wilmore and Williams returned to their homes in Houston to await Starliner’s next launch opportunity.
ULA returned the Atlas V rocket to its hangar, where technicians replaced the defective valve in time for another launch attempt on May 17. NASA and Boeing pushed back the launch date to May 21 and then to May 25 while engineers assessed the helium leak. The Atlas V rocket and Starliner spacecraft remain at ULA’s Vertical Integration Facility awaiting the next launch opportunity.
Boeing engineers traced the leak to a single-thrust reaction control system flange in one of four doghouse-shaped propulsion pods on the Starliner service module.
There are 28 reaction control system thrusters – essentially small rocket motors – on the Starliner service module. In orbit, these thrusters are used for minor course corrections and to steer the spacecraft in the right direction. The service module has two sets of more powerful engines for greater orbital adjustments and launch abort maneuvers.
The spacecraft’s propulsion system is pressurized using helium, an inert gas. The thrusters burn a mixture of toxic hydrazine and nitrogen tetroxide propellants. Helium is not flammable, so a small leak is unlikely to pose a major safety problem on the ground. However, the system requires enough helium gas to force propellants from their internal storage tanks to Starliner’s thrusters.
In a statement last week, NASA described the helium leak as “stable” and said it would not pose a risk to the Starliner mission if it did not worsen. A Boeing spokesperson declined to provide Ars with details about the helium leak rate.
If NASA and Boeing resolve their concerns about the helium leak without requiring lengthy repairs, the International Space Station could accommodate the Starliner landing through part of July. After docking at the station, Wilmore and Williams will spend at least eight days at the complex before undocking and heading for a parachute and airbag landing in the southwestern United States.
After July the schedule gets messy.
The space station has a busy schedule in August with multiple visiting crew and cargo vehicles, including the arrival of a new team of astronauts on a SpaceX Dragon spacecraft and the departure of an outgoing crew on another Dragon. There may be an additional period during which Starliner can dock with the space station in late August or early September, before the launch of SpaceX’s next cargo mission, which will occupy the docking port Starliner is required to use. The docking port will open again in the autumn.
ULA also has other high-priority missions that it would like to launch from the same platform needed for the Starliner test flight. Later this summer, ULA plans to launch the US Space Force’s final mission, using an Atlas V rocket. ULA then wants to launch the second demonstration flight of its new Vulcan Centaur rocket, the replacement for the Atlas V, in September.