In my book “Shuttle, Houston: My Life in the Center Seat of Mission Control”, I bring readers deep into the middle of how Mission Control worked during the Space Shuttle era. I give readers a glimpse of both the technology and the humanity required to put humans in space on a routine basis. There are many parts to this thirty-year story, and only a small portion of the tales fit into the book – so here is an excerpt from an unused chapter on the process of rendezvousing the shuttle with other objects in orbit.
I like to tell people that performing a rendezvous in space is a lot like playing golf. Theoretically, on a golf course, you can stand on the green with the hole about 180 yards away. You can see the hole, you know where it is, and you can choose a club that should drive exactly that distance. You can then (theoretically) line up the shot, take a perfect swing, and if you have allowed for winds, you can put that little white ball directly into the cup for a hole in one. That’s if you did everything perfectly. Theoretically. Rendezvous is just like that. The equations say that you can theoretically lift off of the launch pad with your target vehicle in exactly the right place, and – if you make a perfectly timed and executed launch, you can climb right in to orbit and dock immediately. Theoretically.
Now, as I always add, I don’t know about you – but that perfect golf shot? I don’t’ play golf that way! No…the first swing slices into the woods on the right, so I pull out another ball and take a Mulligan. The second shot is straighter, but not too long, so I play the next one from the lady’s tee, plopping it into the greenside bunker. I can easily get out of the sand in three shots, leaving myself on the green. Then four – maybe five – putts, and I’m in! And that, my friends, is how we plan a Rendezvous. – not assuming that we can make the hole in one, but by putting together a series of burns over a couple of days that will allow us to correct our small mistakes each time and slowly close in on the target. It isn’t showy – but the United States has never blown the rendezvous of a crewed spacecraft using this approach.
The mathematics and physics of Rendezvous are well understood and have been for many years. It would surprise most navigators that the actual positions of the target and chaser vehicles really aren’t that important – it is the relative positions and motions that we compute. The problem with translating the equations to the real world have nothing to do with the difficulty of bringing two spacecraft together – the shortcomings and errors come from the sensors that we use to determine the relative positions – because every measuring device has its own quirks and limitations that allow errors to creep into our knowledge of the positions and relative motions. The real world is, in fact, a bit messy. And learning how messy it can be is the key to becoming a Rendezvous Flight director. I know, not because I started out as a rendezvous expert – but because somehow, I ended up as the most experienced rendezvous flight director in American spaceflight history. And I still can’t write the equations of motion. But then again – I had experts who could….
I remember when I was a front room Maintenance, Mechanical Arm & Crew Systems Engineer (MMACS) flight controller doing sims and flights that required a rendezvous. Sitting in the back row, I’d watch the interaction of the Rendezvous officer, the Propulsion (PROP) and Guidance, Navigation, and Controls Systems (GNC) flight controllers, and the Flight Director, all conspiring over the “goodness” of a series of radar or star tracker marks, looking at the results of targeting to see if they trusted it to do the next burn, or determining how to get out of a crazy trajectory that resulted from a series of failures in navigation and guidance – or jets. I’d watch this all-day exercise while dealing with minor failures in my own systems (put there just to keep us awake and give us a chance to feel like we weren’t wasting our time while the real show was the rendezvous), and thinking “how in the world does a Flight Director ever learn all of this stuff?!?”
Twenty years later, I was the most experienced rendezvous Flight Director in Shuttle history – and I still can’t tell you exactly how that happened – or how I learned all that stuff. But the simple fact is, we learn by doing – and take lots of training along the way.
We’ll bring you the next portion of “Rendezvous” next week right here! If you enjoyed this look inside the Shuttle program, you can find many more details and stories in the book – look for it wherever you buy your paper books, or add it to your favorite E-reader or audio book account.
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