Watching the Atlantis STS-125 launch

It’s been several weeks since NASA launched Atlantis to service the Hubble Space Telescope. Watching the launch, I heard several calls that made me sit up in my seat. You probably didn’t hear them. Watch it with me here:

Listen to the audio …

At 0:49 into the video, about 15 seconds into the launch, CAPCOM says “Bypass across the board Scooter, no action!”

Wow! I was just imagining what the flight controllers must have been seeing. This is what I heard in my mind as he said that, “Yes we see that you have multiple warning lights and alarms going off, but don’t do anything!” Holy crap!

Listen again at 1:20 into the video, “Atlantis, Houston, No action on the MPS H2 Out key.” In other words, “Yes, we see that additional warning, but don’t do anything about it.” Scooter called back, “Houston, we copy, no action.”

(I can’t believe at 3:20 in the video the public affairs guy (“Mission Control Houston”) says “No issues heading to orbit.”)

At 3:40 into the video, Houston calls up with some explanations for the earlier calls, “Atlantis, Houston, H2 out key is a ducer only, and the ASA-1 is a power only.”

“Copy ASA-1 is power only, and the H2 is ducer,” called back Scooter.

Later on in the post-launch press conference, we got to find out what was going on, and this article on nasaspaceflight.com had a lot more detail:

“A post launch review of the data showed that the failure seemed to have occurred two to four seconds prior to liftoff after main engine ignition and the resulting shake and bake. An EPD (Electrical Power Distribution) review of their BMU data of Main Bus A shows that Main A bus saw a 400 hz signal with a peak to peak of 100 amps. EPD is going to look at the Main B data next.

Wow! I had to wonder if that was a typo. 100 amps of current at 400 hz shorting into an avionics bus! No wonder several warnings and alarms went off.

Later the Flight Director had the commander turn off the power to ASA-1, which is one of four Aerosurface Servo Amplifiers on the orbiter. These are critical components that actually power the rudder and elevons during aerodynamic operations (flying in the atmosphere). With three remaining, they could continue the mission, but another failure would call for an immediate de-orbit.

The other interesting call was related to a transducer (“Ducer” in NASA-speak) that monitors the pressure of the hydrogen being fed to the main shuttle engines. That’s the “H2 out key.” If that warning lights, it could mean that one of the three engines is suddenly not getting enough fuel pressure.

So why did the controllers call “No action!”?

I can almost feel the heart pounding of a “steely-eyed missle man” monitoring all of the systems. One warning by itself is not a drastic call to action. They could see that all of the other systems were functioning correctly, and most importantly, the flight dynamics and performance of the craft as a whole were safe and correct. Doing something could have been a bigger disaster than doing nothing.

The H2 out key warning was a simple call. The controller can see immediately that all three engines are still producing their normal thrust. In the press conference someone pointed out that if there were a real problem, Scooter would have felt it in the seat of his pants, big time. The problem there wasn’t with the H2 pressure, it was with the transducer. “H2 out key is a ducer only.”

But that ASA-1 problem is still a concern, and even today, while Atlantis is in California being mated to a 747 for ferry operations back to Kennedy, technicians are crawling through the orbiter trying  to diagnose the problem. They suggest that a power wire shorted to ground, which fed all that current directly into the bus ground. That would make a lot of systems go a bit funny.

Hats off to the guys behind the screens in Houston. I know hardly anyone shared in those few moments of heart-pounding pressure, but a few of us heard what you were dealing with. Because of your heads-up attention, we can today look back and call it a nearly flawless mission.

If nothing else, for me it was an interesting foreshadow to a mission that would be as dramatic in its problems and solutions as any I’ve seen.

[Edit: The video I was linked to was made private by the uploader, so I found another copy and updated the time notes in the post.]