Extra thruster exams for Starliner earlier than return

WASHINGTON — NASA and Boeing will hearth thrusters on the CST-100 Starliner spacecraft docked to the Worldwide Area Station this weekend in what could also be a remaining check earlier than approving the spacecraft’s delayed return to Earth.

At a July 25 briefing, NASA and Boeing managers mentioned they haven’t set a date for the undocking of the Starliner from the station, returning NASA astronauts Butch Wilmore and Suni Williams again to Earth to conclude the Crew Flight Check (CFT) mission. The spacecraft has been on the station since June 6 for what was initially billed as a keep of as brief as eight days.

The main focus of testing has been on the spacecraft’s response management system (RCS) thrusters, a number of of which have been shut down by the spacecraft’s laptop throughout Starliner’s method to the station. NASA and Boeing just lately concluded testing of an RCS thruster on the bottom at NASA’s White Sands Check Facility to try to replicate the degradation within the thruster’s efficiency.

Steve Stich, NASA business crew program supervisor, mentioned the working speculation was that larger temperatures within the “doghouses” that host the thrusters might have triggered oxidizer to vaporize and cut back the thrust produced. He mentioned engineers ran two “uphill” profiles of thruster firings as Starliner approaches the station and 5 “downhill” profiles because it departs the station to return to Earth.

“What we did see within the thruster is similar form of thrust degradation that we’re seeing on orbit in quite a few the thrusters. We’re seeing diminished thrust,” he mentioned. Evaluation of the thruster confirmed a bulge in a Teflon seal on the oxidizer line, decreasing the circulation of oxidizer and maybe explaining the diminished thrust. He mentioned further work is deliberate to verify that the seal can stay intact for the remainder of the flight.

Managers additionally agreed to fireside the RCS thrusters on Starliner whereas nonetheless docked to the station. All however one of many thrusters will hearth a collection of pulses to verify its efficiency. The excluded thruster is one which confirmed very low thrust whereas on method to the station.

“We’re going to fireside all these thrusters for quite a few pulses simply to ensure earlier than we undock that entire system performs the way in which we anticipated and the way in which it did final time we checked it,” Stich mentioned.

“With all these check outcomes, we decided that we might run another set of exams whereas we’re docked, and is de facto icing on the cake for us,” mentioned Mark Nappi, Boeing vice chairman and business crew program supervisor. He added that Boeing will in all probability do such thruster exams on future Starliner missions to the station, stating that he was unaware that different visiting autos carry out comparable thruster exams previous to their departures.

Engineers will even verify the spacecraft’s helium manifolds for any modifications in leak charges throughout the thruster exams. Stich and Nappi mentioned that examination of a Starliner service module, fueled however saved for 3 years at White Sands, exhibits indicators of degradation of seals in helium programs, possible brought on by publicity to nitrogen tetroxide propellant. That might clarify the issues with the seals that triggered the helium leaks.

Solely after the upcoming thruster exams will NASA embark on a remaining collection of evaluations, together with on the company degree, to verify that Starliner is secure to return residence and set a date. “I believe we’re beginning to shut in on these remaining items of the flight rationale to make it possible for we will come residence safely,” Stich mentioned, with that agency-level assessment deliberate for as quickly as late subsequent week.

He added one change within the Starliner mission profile for its return to Earth is to drop plans to carry out a set of guide maneuvers after undocking. “We notice now that a number of the guide maneuvering put some additional stress on the thrusters, and so we’re not going to do this.”

Whereas NASA has not set a date for Starliner’s return, Stich mentioned they’re choices by means of Aug. 19 or 20 for its undocking. That will unlock a docking port for the launch of Crew-9 mission on a SpaceX Crew Dragon, permitting for a “direct” handover, or overlap, with Crew-8 earlier than it departs. He mentioned that handover must be completed by about Sept. 11 to keep away from conflicting with a separate Soyuz spacecraft handover.

NASA, he added, continues to have a look at contingency choices that might contain using Crew Dragon to convey again Williams and Wilmore from the station fairly than Starliner, however that at the moment he expects them to return on Starliner. “There are a number of good causes to finish the mission and produce Butch and Suni residence on Starliner,” he mentioned. “Our prime intent is to return with Butch and Suni.”

“I’m very assured we’ve a very good car to convey the crew again with,” Nappi added.

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