Main Engine Controllers

Recent unconfirmed media rumors about engine controller issues brought a long-ago memory to the surface.

About 1991, the Chief of the Flight Director office decided that it would be good to have an exchange program between the Flight Directors and both the NTDs and Convoy Commanders.  At that time, I was a new Shuttle Ascent/Entry Flight Director with just a couple of critical phase flights under my belt.  In turn, each of the Shuttle Convoy Commanders came to JSC to sit with an Entry Flight Director for a landing, and then each Entry FD took a turn sitting with in the Convoy Commander vehicle during a Shuttle landing.  That was where I got to know Tassos Adiabakos, Kelvin Manning, and others.  My turn was for a Shuttle landing at Edwards.  Waiting for the deorbit call with iffy weather, I boldly predicted that Lee Briscoe would delay landing for a day rather than divert to the secondary target of KSC.  When Lee did just the opposite, well, it was a long time before I heard the end of it. 

Similarly, The KSC NTDs (NASA Test Directors) came sequentially to sit with the Ascent Flight Director for a launch, and we returned the favor by going to KSC and observing the action in the Firing Room for a launch countdown.  In July, I followed Al Sofge for STS-43.  We went through the pre-launch planning; Al was a perfectionist making sure the checklists were all in order, the firing room manning was prepared, and even details down to the scheduling of the janitorial crew cleaning the bathrooms – don’t want a delay because the team couldn’t get in and out of those facilities in a hurry! 

I got the opportunity to ride in the Shuttle Training Aircraft as mission commander John Blaha shot approaches to the Shuttle Landing Facility.  It is quite a ride on the jump seat in the cockpit watching the runway rush up at you while the engines scream in full reverse.  With the flaps and dive brakes out, the aircraft still accelerates in a steep approach.  What a rush!

Finally, on launch morning, there was no spot for me to sit on the NTD row of the firing room, so they put me up on the top row, with the legendary Launch Director Bob Sieck.  I felt like a padawan under the tutelage of Obi-Wan.  Bob was as smart as they came, cooler than ice water, never fazed about anything.  He had been a meteorologist in the Air Force before coming to NASA so the toughest call the Launch Director has to make – is the weather good enough – was not problem for him. 

It was to be an early morning launch, so the pre-launch action all took place in the wee hours of the night.  We got a go for tanking and the cryogenics started flowing into the Shuttle, chilling down the propellant systems:  tanks, plumbing, and the engines.  About the same time the smell of cornbread and beans warming upstairs started wafting through the Firing Room ventilation system. Talk about launch pressure!  https://waynehale.wordpress.com/2019/03/03/launch-fever/

Suddenly, the electronic brains of one of the three Space Shuttle Main engines winked off.  Just like that, with no notice.  It was dead, no activity, no signals, no nothing.  It was as if all the redundant power feeds had been switched off at once. 

This was not good.

Clearly this was a violation of the Launch Commit Criteria.  With the SSME Controller failed, the engine could not start.  At T-31 seconds when the onboard Redundant Set General Purpose Computers took control, they would immediately halt the launch sequence. 

The phone rang – it was the Space Shuttle Program Manager Brewster Shaw. 

I learned a lot from Brewster – he had high standards and always ‘encouraged’ the team to lean forward but was always considerate of crew risk.  Al Shepard was called ‘the icy commander’ but he had nothing on Brewster.  I found him was very intimidating.  He wanted to launch anyway.  I was appalled at the time.  Now, I’m not so sure. 

It’s a complex thing to launch a spacecraft, doubly so for the Shuttle.  As Brewster’s successor at the Shuttle Program Manager job, Tom Holloway, frequently told us, ‘the hardest part of a shuttle flight is getting the first foot off the ground.’ 

Later, when it was my turn to hold that position, I frequently about Brewster and Tommy and what it took to get the team to commit to get that first foot off the ground.  But that night I was a rookie and shocked at what Brewster asked.  He wanted to know if there was any way to reset the engine controller and try to launch.  Wise old Bob Sieck shook his head and said probably not, but the team will think about it.  Brewster recommended cycling the power switches to see if the computer would come back on.  But we all knew that even if the computer restarted, it probably couldn’t be trusted to perform properly all the way to orbit. Likely nobody would be comfortable with that possibility in just a few hours.  But Brewster said try, so the team did.

No joy.  SSME controller was still dead, kaput, nonfunctional.  No question about what to do.  Shortly afterward the launch scrub was announced.  John Blaha and his crew hadn’t even had breakfast yet. 

The team at KSC figured out a way to change out the controller on the engine while the shuttle was on the launch pad.  Just over a week later Atlantis launched flawlessly.  But I wasn’t in the firing room.  My travel allowance timed out.  I watched from the assistant flight director seat in the MCC.  I actually liked that better:  better displays there for the flight but the price was less fire and smoke out the window.  And I never got to eat the beans post launch STS-43. 

It is a terrible pressure to be a Program Manager trying to nudge the team into flying all the while making sure that safety is not eroded.  It didn’t hurt anything to power cycle that computer.  I sometimes wonder what we would have done if it had come back on.

Brewster changed the Shuttle paradigm which was often stated of Fly Safely to a slightly different phrase: Safely Fly.  Think about the subtly of the message when put that way.  Brewster put safety first.  But he always challenged the team when he thought there was a way to get off the ground. 

So did I when it was my turn. 

By the way, when they got that Engine Controller into the shop and opened it up, a power cable had broken.  No doubt due to contraction of the device as the engine chilled down.  No way that computer was going to run. 

The new RS-25 Engine Controllers are more reliable and resilient

But it is still hard to get a rocket the first foot off the ground.