Rendezvous Part 4 – The Early Trajectory

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. 

So, let’s get back to the Rendezvous. You launched from the Kennedy Space Center into the same plane as your target (the ISS, for instance). Typically, we rendezvoused on Flight Day (FD) 3, to allow time to do inspections on FD-2, and make sure that the entire crew was over any space Motion Sickness that might be encountered after launch and into FD-2. If you know WHEN you wanted to rendezvous (FD-3), then you could mathematically determine how much closure was needed and, therefore, how much below the target you wanted to be at the end of Ascent. There are, of course, many ways to skin that cat – you can catch up quickly, then raise the orbit and kind of “par” behind the target. You can do a gradual raise. You can do one big burn, or many small ones. Why the difference? Because you want to catch the target with the right lighting conditions, which is determined by the season, as well as the time of launch – which is sort of determined by the time you are going to be “in plane”. Oh yeah – you want to try and target so that the crew was bright eyed and bushy tailed during the rendezvous as well – not a good thing to do critical flying when you’re sleeping – no matter if you are the target or the chaser! It is all interdependent.

This interdependency is why the planners were some of the busiest folks in Houston coming up on a launch. They eventually realized that launch weather and subtle programmatic changes were always going to affect launch dates, no matter how much we wanted to stick to a plan as laid out on a calendar months (or years) in advance. The trajectory and flight planning folks got to where they came up with launch times for every day where it was possible to go, and we’d roll the plans along until it looked like we were going to really go. Yes, there were many days with no launch solution that worked. Eventually, you’d get off the pad, and it didn’t pay for the Flight Director to fall in love with a particular flight plan or rendezvous sequence – you learned that everything was flexible, and the smart folks would always have a plan to get there.

Flight Days 1 and 2 could include a couple of major burns – we knew they’d be there, but we didn’t know exactly where, or how big they’d be. This was determined by our MECO conditions, and the planners got exceptionally good at putting in placeholders so that we could do whatever was necessary after ascent. Phasing burns were used to set up the closure rate. Planar adjusts could be done separately, but more often than not, you’d add them to a phasing burn, and take care of all the adjustments at once. The goal was to make all Rendezvous days – Flight Day 3 – essentially identical, with the Shuttle at the same height below and distance behind the station every flight. This allowed “grooving in” the procedures and flight techniques for both the cockpit crew and the ground teams, making training easier and more efficient. Generic Rendezvous sims could always be started in essentially the same place, and variations in failures and trajectories could be thrown in beyond that. You’d start the day with a circularization burn that set up the specific parameters to hit what was called the Ti (Terminal Phase initiation) burn essential one orbit before you would get into close proximity of the target. Everything was targeted for Ti – the trajectory and timeline. Ti was important because up to the point where you burned it, you weren’t actually aimed to hit the target – if you didn’t burn Ti, you flew right underneath and past it, harmlessly – a natural collision avoidance maneuver.


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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Christmas is coming!