Ground Up Rendezvous

The recent success of SpaceX in sending their Dragon capsule to the International Space Station reminded me of the first Space Shuttle ground up rendezvous and the difficulties we had during that mission.  Of course we were planned it on the 13^th shuttle mission rather than the third, like SpaceX, but you would have to have triskaidekaphobia to believe that was the cause of our problems.

Rendezvous in space was not a new subject in 1984; it had been pioneered by the Gemini program nearly 20 years earlier, and practiced by necessity during Apollo.  Skylab and ASTP required ground up rendezvous.  The Russians accomplished ground up rendezvous capability shortly after the US did.  Even during earlier shuttle flights there had been rendezvous with deployed satellites, the successful SPAS deploy and retrieval on STS-7 for example.  But for STS-13 we planned the first ‘ground up rendezvous’ for the shuttle program with a target that was already in orbit; this was a more complex mission than the deploy/retrieve on shuttle flight 7.

Jay Greene, Emerald Flight, was the lead for the mission, a veteran FDO from Apollo who knew a few things about rendezvous in space; Gary Coen, Gray Flight, was to be the ascent flight director on this auspicious mission; John Cox, Granite Flight, was the EVA specialist; I was the lead Propulsion systems officer; the holder of the “bingo” number which would terminate the rendezvous; Ron Dittemore was Prop officer on the Granite team which would monitor the grapple and EVA repair of the ailing Solar Maximum Mission (SMM)-the objective of the flight.

Launching to catch up with an orbiting satellite requires complex mathematics, precise timing, and variable steering from the launch vehicle.  Monitoring the launch from Mission Control requires complex computations; being able to correct errors during the launch loads even more computational requirements on the MCC.  Back in those ancient days, there were 5 IBM 370/65 mainframe computers which drove the MCC.  Those behemoths collected all the telemetry, processed it for display on small black and white monitors, made all the trajectory calculations, basically did everything.  The prime computer was designated the Mission Operations Computer (MOC) and the backup, in lock step with the MOC, was the Dynamic Standby Computer (DSC).  The other three computers were held in a ready state but not active.  In theory, if the MOC crashed (not unheard of) a select over to the DSC could be accomplished in seconds with no loss of monitoring.

Somewhere during the preparation of the mission, senior NASA managers decided that the shuttle mission numbering scheme was . . . troublesome.  The STS-10 mission had been scrubbed out of the manifest, STS-12 greatly delayed, and the STS-13 mission designation apparently gave some people . . . concern.  So a very complex, almost incomprehensible, mission numbering scheme was invented:  two digits and a letter designation.  First digit, the fiscal year the mission was originally planned (1984 became the “4”), second digit, the launch site (1 for KSC, 2 for Vandenberg), the letter was the sequence of the mission as originally planned for that year.  So STS-11 became STS-41B and STS-13 became STS-41C.  Really complex; really bureaucratic, and in my opinion, really dumb.  I still don’t know how that would have worked when we wrapped around the end of the decade.  Later, of course, we resumed the old fashioned numbering scheme and if flights flip-flopped on the manifest we just lived with it.

As usual, for flight STS-41C, we practiced the mission dozens of times with the crew in the simulators and the full flight control team in the MCC.  Sim Sup gave us hundreds of problems to solve to save the mission.  We were ready.  And on April 6, the orbits aligned, the weather was good, and Challenger and her crew launched right on time.  Immediately after liftoff, the MOC promptly died.  Select over and . . . the DSC was dead.  First time in the shuttle history, the MCC was useless during launch.  A common software problem had stopped processing in both machines.  MCC was blind and the crew was on their own.  Gray Flight was not happy.  The Prop console was located just in front of the Flight Director console.  We heard some choice words from the Flight Director that morning as he spoke with the ground computer operators.  On the row behind the Flight Director console was the Mission Operations Director console, and the legendary White Flight, Gene Kranz, added to the discussion in unforgettable terms.

But Challenger was flawless that day, and the climb to orbit went according to plan.  Within an hour, a new MOC was up and running and we tried to forget the helpless feeling we had listening to the crew radio calls during the data-less ascent.  Problem number 1 of the mission appeared not to have any lasting impact. 

The first objective of the mission, deployment of the school-bus-sized Long Duration Exposure Facility, went off without incident.  Then we set our sights on the crippled SMM.  Bob Crippen was the Commander, a veteran of the STS-7 rendezvous, and everything went exactly according to plan.  For the first time in shuttle history, we put a crew out the airlock during a rendezvous to be ready to grab the SMM.  George ‘Pinky’ Nelson would be flying over to the SMM using the Manned Maneuvering Unit backpack; he had a device called the TPAD to lock onto the SMM strapped to the front of his space suit.  Handover between the Emerald Flight and Granite Flight teams occurred while we were stationkeeping with the SMM.  Even though I was technically off shift, I wanted to watch the retrieval so I scooted over to the left seat on the Prop console during Pinky’s short flight to the SMM. 

Then everything went to worms.  The TPAD device would not attach to the SMM.  Worse, when Pinky bumped the SMM, it started tumbling and translating away from Challenger.  On the Prop console was saw lots of thruster firings and the gas gauges heading down toward the “bingo”.  Crip lost sight to Pinky and started to maneuver the shuttle to keep him in view.  We were using propulsion gas at a fantastic rate.  Granite Flight leaned over the console and asked Ron if we could keep this up “overnight” since the sun was about to set for that orbit.  Ron replied he didn’t know (we had never simmed this!), and in an instant that will forever be etched in my memory, Gene Kranz leaned over the console and said “you better figure that out, Prop!”  I wouldn’t say chaos reigned, but it was close.  Calculators in the Prop back room began smoking as new bingos were calculated.  The potential for catastrophe was high:  the orbiter could run out of gas and not be able to safely deorbit; or the orbiter could run into the SMM or into Pinky, still free flying, or the orbiter could get so far away that Pinky’s MMU couldn’t get him back to the shuttle.  Let’s just say that our heart rates were high.  Crip somehow kept Pinky in sight – the definition of cool in a crisis – and moments later Pinky gave up, flew his MMU back to Challenger, and the shuttle backed away. 

In American football, they call it broken field running; when the play doesn’t go as planned, and the team has to improvise while the clock is ticking.  The next 24 hours were a blur.  With little propellant reserve, we had to plan another rendezvous, stationkeep, and Terry Hart had to try to grapple the restabilized SMM with the shuttle arm.  Somehow the team pulled all that off.  SMM was repaired, nobody died, Challenger landed safely, and the flight went into the history books. 

We learned a lot about rendezvous that flight. 

So when a ground up rendezvous goes smoothly, as almost all the shuttle flights to the ISS did decades later, or as the SpaceX flight did last week, I remember how hard it can be.  I smile, and remember how we nearly lost it, on a flight that was originally planned to be #13.

Triskaidekaphobia?  No.  But some days I do wonder.  As my old boss, an Apollo veteran, would often remind us “It’s good to be smart, but it’s better to be lucky.”