Mars Rover + Rocket + Trajectory = My Job
I work for NASA with the Launch Services Program (LSP) at Kennedy Space Center. So what does LSP do?
LSP interfaces between the rocket and NASA unmanned spacecraft. The rockets, or launch vehicles, are actually owned by companies, not NASA. So LSP has to be the rocket experts for NASA, making sure that what happens on the launch vehicle side is best for the spacecraft. LSP selects the rocket that is the best value for the spacecraft, manages the schedule/ budget/ contracts, observes testing, performs analyses, and arranges for the spacecraft to be integrated with the rocket. We work launches here in Florida, but also California, Alaska, Virginia, and even Kwajalein Atoll in the middle of the Pacific Ocean. Our nickname is Earth’s Bridge to Space.
I often think of the spacecraft as an egg, and LSP is working to make sure that egg doesn’t get damaged during launch: the shell doesn’t crack, the yolk and the whites don’t mix, the egg doesn’t end up frozen on one side and cooked on the other. I work as a guidance, navigation, and controls flight analyst, who makes sure the egg is pointing where it needs to, spinning if it needs to, and doesn’t hit the carton on the way out. I also work as a trajectory analyst, who makes sure the egg ends up unbroken in the right place, at the right time. Because if something goes wrong during launch, these amazing spacecraft can’t collect the data and images they were made for.
Mars Science Laboratory (MSL) was actually my first mission as a trajectory analyst. For those of you going “What! They assigned a newbie to a flagship mission?”, let me reassure you. An experienced analyst worked on the mission for the first four years, and I worked as his backup for over a year. He moved to a systems engineering program and I took over the mission at that point. However, I worked closely with my flight design lead on the mission; the rest of the flight design group lent me their expertise throughout the process too. My counterparts at the Jet Propulsion Lab (JPL: MSL spacecraft provider) and United Launch Alliance (ULA: Atlas V launch vehicle provider) also had lots of experience; I was most definitely not out there on my own.
When working on the trajectories, you have to work backwards. You figure out where on Mars and at what time you want to land. For more on planning the spacecraft’s trajectory, see my post “Taking a Road Trip to Mars vs. NYC: Tradeoffs and Margin.” The spacecraft lets the launch vehicle know where and when it wants to be dropped off, along with how fast it wants to be going in which direction. Using that information along with the mass of the spacecraft, the configuration of the launch vehicle, and the requirements of the spacecraft, the launch vehicle trajectory can be planned.
The configuration of the launch vehicle indicates things like how big the fairing is (the shell that protects the spacecraft at the top of the rocket while going through the atmosphere) and how many solid rocket boosters are attached to the rocket (Atlas V can have anywhere from zero to five). The launch vehicle has different rules it has to follow, based on the configuration. These rules are things like how long after liftoff the rocket has to pitch over and the maximum dynamic pressure allowed (if the rocket goes too fast while there is still atmosphere, the pressure could break the rocket).
The spacecraft requirements are different for each spacecraft. Some spacecraft have instruments that are light sensitive and, once the fairing comes off, they can’t be pointed too close to the sun. Just like, as humans, we can’t stare directly at the sun without risking damaging our eyes. Some spacecraft have to be rolled if the launch takes longer than a set amount of time; otherwise, one side of the spacecraft will get too hot from the sun and the other side will get too cold. Some spacecraft have to be spinning at a certain speed at separation; others may want a little spin as possible. These are just a few rules spacecraft may want to have during launch.
In planning the trajectory of the launch vehicle, you make sure the trajectory obeys all the “rules” of the launch vehicle and spacecraft. Then you try to optimize the trajectory, usually for having the most propellant leftover. This way, in case something doesn’t perform as expected, you have extra gas to get the rocket on the correct course. This is called margin. And it takes lots of number crunching to get that margin as high as possible.
In addition to being a trajectory analyst for MSL, I was also on console as the NASA Winds trainee. In the last few hours prior to launch, we send up several high altitude balloons anywhere from 11 to 19 miles up. We look for too high velocities or wind shears; wind shears are when the wind at different altitudes are opposing or very different speeds. These conditions can be too extreme to control the trajectory or could even break the vehicle, so we make sure we don’t launch during those dangerous times. The launch vehicle provider can also use the wind profile to optimize the trajectory for that particular time.
As much as I love to watch rockets launch, it’s quite a different experience to hear the countdown on the headset, see the altitude on the screen increase, and then a minute later feel the launch move through you. It’s very emotional, and unbelievable when you realize the trajectory hits its target dead on. My counterpart at JPL said “This was among the most accurate interplanetary injections ever.” That’s the proudest statement of my career so far.