Starliner Ready for Third Try on Wednesday, June 5

NASA, Boeing and the United Launch Alliance said today the ground equipment problem that scrubbed yesterday’s launch of the Starliner Crew Flight Test is remedied. They are ready to try again on Wednesday. This will be the third attempt to launch the first crewed flight of Boeing’s Starliner commercial crew spacecraft since May 6.

Yesterday’s launch attempt stopped 3 minutes and 50 seconds before liftoff when the automated ground launch sequencer (GLS) detected a problem.

The GLS, a computer system, takes over from human operators when the countdown reaches terminal phase at T-4 minutes. Ten seconds later it halted the launch when one of three redundant computers was six seconds late responding. All three must be perfectly in sync for the launch to proceed.

ULA President Tory Bruno explained in a post-scrub news conference that they would not know why it was slow until they could access the building where the computers are located, which is adjacent to the rocket. That meant they had to wait until they defueled (“detanked”) the rocket and vented the building of any residual hydrogen.

Once inside, engineers determined the issue was with a power supply to that computer chassis. The computer cards in that chassis included the one associated with topping off the rocket’s liquid hydrogen and liguid oxygen propellant. Earlier in the countdown, data from sensors associated with those topping valves suddenly stopped and ULA switched to redundant circuitry in order to continue. Only two of the three computers had to be working at that point, but all three were needed once they got into terminal count.

ULA now has replaced the chassis with the faulty power supply. They will inspect it to determine why it failed, but are ready to resume launch preparations.

Technicians and engineers with ULA (United Launch Alliance) worked overnight and on Sunday to assess the ground support equipment at the launch pad that encountered issues during the countdown and scrubbed the June 1 launch attempt. The ULA team identified an issue with a single ground power supply within one of the three redundant chassis that provides power to a subset of computer cards controlling various system functions, including the card responsible for the stable replenishment topping valves for the Centaur upper stage. All three of these chassis are required to enter the terminal phase of the launch countdown to ensure crew safety.

On Sunday, the chassis containing the faulty ground power unit was removed, visually inspected, and replaced with a spare chassis. No signs of physical damage were observed. A full failure analysis of the power unit will be performed to better understand root cause. Meanwhile, ULA has completed functional checkouts of the new chassis and the cards, and all hardware is performing normally.  — NASA

NASA astronauts Butch Wilmore and Suni Williams remain in quarantine at Kennedy Space Center. Their first attempt to fly this test flight of Boeing’s Starliner spacecraft to the International Space Station on May 6 was scrubbed about 2 hours before liftoff due to a faulty valve in the Centaur upper stage of ULA’s Atlas V rocket. The rocket had to be returned to ULA’s Vertical Assembly Facility to replace the valve.

While there, Boeing detected two issues with the Starliner spacecraft itself — a helium leak in one of Starliner’s Reaction Control System thrusters and a “design vulnerability” in ensuring there are three redundant methods for returning Starliner to Earth.

After extensive analysis, NASA and Boeing decided Starliner is safe to fly as is although changes may be made for future flights. They rescheduled the launch for June 1, but the result was another scrub because of the GLS power supply failure.

If anything goes awry on June 5, June 6 is a backup opportunity. NASA, Boeing and ULA are eager to get Starliner into orbit by then. Otherwise life-limited parts on the spacecraft and rocket, like batteries, will have to be replaced, resulting in a longer delay.