Another Scrub for Starliner Crew Flight Test

The second attempt to launch Boeing’s Starliner Crew Flight Test was halted today less than four minutes before liftoff.  A computer called an automated ground launch sequencer that controls the launch in those last four minutes triggered the hold. The cause is still being determined and a new launch date is pending. NASA said late this afternoon they will not try tomorrow. The next opportunity is June 5.

The ground launch sequencer (GLS) takes over at T-4 minutes. Ten seconds later it stopped the launch of the United Launch Alliance (ULA) Atlas V-Centaur rocket.

The launch window for spacecraft headed to the International Space Station from Florida is very brief and a second try today wasn’t possible. NASA astronauts Butch Wilmore and Suni Williams returned to crew quarters at Kennedy Space Center to await word on when the next attempt will take place.

Their first launch attempt was scrubbed on May 6 about two hours before liftoff due to a faulty valve in the Centaur upper stage. That was fixed relatively quickly, but the launch was further delayed because of issues with the Starliner spacecraft. Everything seemed to be progressing well today, but it was not to be.

A backup launch opportunity is available tomorrow at 12:03 pm ET, but NASA said late this afternoon they will not use it in order to give the team time to fully assess the situation. The next two chances are June 5 at 10:52 am ET and June 6 at 10:29 am ET.

During a news conference after the scrub, ULA President Tory Bruno explained that there are three redundant computers, or racks, housed in a building adjacent to the rocket. All three must be operating in sync with each other — triple redundancy — for the launch to take place.

Today, one of the three was six seconds slow in responding, which triggered the hold.

They don’t know why it was slow and can only find out by physically accessing the building to inspect the computers. The rocket has to be emptied of fuel and the building cleared of any residual hydrogen before that can happen, which will take three to four hours.

When they will be ready to try again depends on whether it’s a simple problem of replacing a computer card or more complicated — a power supply problem or a network communications problem, for example. They simply won’t know until they can access the area.

While stressing they do not know if it was a computer card, Bruno said the cards have been very reliable in the past and all of these were tested prior to launch.

He also emphasized that the rocket itself performed “beautifully.” This was an issue with the ground system, not Atlas or Centaur.

It was the second ground system problem to crop up today. Earlier in the countdown, data from sensors associated with liquid hydrogen and liquid oxygen valves used to top off the propellant in the rocket was interrupted. ULA was confident it was a problem with a sensor, not the valves, because the data stopped for both at the same time. They switched to redundant control circuitry, which solved the problem.

That data interruption was in the same computer rack as the slow GLS card, but ULA does not know if the problems are related. They are two different cards, but in the same rack. The cards are integrated through a network so it’s possible, but Bruno said they won’t know until they have access to the system.

Another small hiccup was that the fans in Butch and Suni’s Boeing flight suits stopped working after they were in their seats. Boeing Vice President and Program Manager for Commercial Crew Mark Nappi explained it was due to a voltage spike when the fans switched from ground power to spacecraft power and the fault detection system turned them off. A simple reset fixed it.

NASA, Boeing and ULA insist they will not launch until they are ready, but they are hoping to launch by June 6. After that, life-limited items on the rocket and spacecraft, like batteries, will have to be replaced. That means rolling the rocket back to the Vertical Assembly Facility. It takes 10 days to replace the batteries and then they have to get back in the queue for launch.

This article has been updated.