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Launches Test Flight Design Teams
03.21.12
 
The antenna on North Kennedy Space Center Image above: Ground tracking stations around the world are equipped with different kinds and sizes of antennas such as this dish at NASA's Kennedy Space Center in Florida. Other antennas can be put together and mounted in different locations. Still others can be mounted on aircraft or on a ship to follow a rocket. Photo credit: NASA
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An Atlas V lifts off to start the Juno mission to Jupiter. Image above: An Atlas V rocket heads into space carrying the Juno spacecraft on a mission to study Jupiter. Photo credit: NASA/George Roberts and Rusty Backer
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Rocket science is perhaps at its most demanding for the men and women who determine where a rocket needs to go and then track it to make sure it gets there.

They work in what is called "Flight Design" and they are one of the groups most tested on launch day, when the rocket engines are burning and a spacecraft is being lofted into orbit or to a distant world.

On a good day the rocket follows its predicted course and transmits a nearly constant stream of information to a series of antennas arrayed around the planet. The information the rocket sends is generally known as telemetry and it tells the launch team how the vehicle is doing, whether it is healthy and the conditions onboard.

On a bad day, well, the path reads differently, the numbers don't match what was expected and those antennas so carefully laid out months in advance are quickly reset to track a new course.

Either way, there's a lot of work for the trajectory folks starting about a year before a launch and not winding up until weeks afterward. But they wouldn't have it any other way.

After all, not many people get to enter a Facebook status like that of Samantha "Sam" Harris, a Flight Operations Integration Engineer with NASA's Launch Services Program. It read, "Chasing down a rocket in an airplane."

For many on the trajectory team, working so closely with rockets is fulfilling a dream.

"When I was a real little kid, I wanted to be an astronaut," said William "Bill" Benson, a flight design engineer for NASA's Launch Services Program, or LSP. "But this is what I always wanted to do. I always wondered, 'How does the rocket know to go where it wants to go?' "

Benson is part of the team that analyzes the programming that goes into a rocket's flight control computer to make sure the launch will follow its intended course, or trajectory. That means more than simply telling the rocket to start at the launch site and then stop when it reaches orbit.

The programming lays out how much thrust the engines will use at different points throughout the climb to space, when the rocket will need to point its nose toward the horizon instead of straight up and when to fire the bolts that separate stages and discard the payload fairing that protects a spacecraft during the early portion of launch.

Aligning the launch profile for a spacecraft going into Earth orbit is tricky, but arranging the ascent for a mission to the moon or one of the planets adds more levels of difficulty since the rotation of the Earth has to be matched so that the spacecraft’s trajectory will result in a rendezvous with the distant world.

"It is quite a bit more work to do interplanetary," Benson said. "The targets change at least on a daily basis, sometimes on a minute-by-minute basis."

The team has to make sure that as long as one of the engines on the launcher is firing, the rocket is being tracked and relaying data back to the team. Also, antennas have to be in position to pick up the point when the spacecraft separates from the booster and begins its mission.

When the projected course is ready, the engineers use analytical tools of all sorts from computer models to their own intellects to see if the programming will work.

"It doesn't get any deeper into rocket science than that," Benson said. "Being a detective is very much a part of this job."

Once the rocket and its spacecraft are flying, the trajectory team tracks the data and compares it to what was expected to determine whether everything is going well. The numbers sent back from the rocket tell a big picture story of power, speed and altitude, but also include a host of other data that get down into the details of how the rocket is functioning. They are often simple yes or no signals to indicate whether bolts fired as planned and can also relay data such as vibration and temperature aboard the launcher.

Having the various tracking stations from around the world identified for the launch is the province of a team of specialists including Harris.

"About a year before the mission is when we will start looking at which antennas will be used," Harris said. "We have to have strategically placed antennas all over the world."

It's a lot of work, but the payoff is that the controllers know exactly what occurred during a launch and can duplicate it for the next mission. If something goes wrong, then the telemetry is virtually the only source of information investigators have to search for the problem so it doesn't get repeated.

"We like data, we like to know what's going on," Harris said.

The antennas chosen range from the powerful arrays permanently in place at and around the launch site such as those at Cape Canaveral Air Force Station in Florida, to facilities at bases in the Caribbean Sea, South Atlantic, Africa and Australia. There are more options all over the world including at bases in Hawaii, California, New Mexico, Europe and even Antarctica.

For areas in between, NASA can call on mobile antennas mounted in airplanes or on ships and even portable arrays that can be erected by a few people who take them to a mountain or coastline in the flight path and then broken down to a couple suitcase-sized carriers when the launch is complete.

NASA's orbiting Tracking and Data Relay Satellite System, called TDRSS, is also available for some launches to receive telemetry from rockets including United Launch Alliance's Atlas V, Delta II and Delta IV. Other rockets currently rely on ground tracking stations.

Which ones are chosen to track a mission depends on the rocket's planned course, and it can change, too, during the months of preparation and as launch times and events are refined.

"The trajectory is what drives us," Harris said. "It's never really done."

Even the time of day for a launch can change which antennas get called up, Harris said. For instance, NASA's Mars Science Laboratory launch had courses that took it over the Indian Ocean, Africa or Australia depending on when it lifted off from Florida. Therefore, NASA had to have antennas at all the locations ready to go to work.

For each adjustment, engineers have to calculate how that will affect the rocket's performance. In other words, if the launcher is told to fly another degree farther south to take it over a particular tracking station, will it still have enough energy to reach orbit?

"There's always a trade-off," Benson said. "Sometimes it's easier to get a mobile antenna in place."

The detailed work, including all the changes along the way, are important because the researchers relying on the spacecraft have worked so hard for years and years to get everything right, Harris said.

Harris began her trajectory career when she was 24, a choice she made so she could be in a job that was not the same thing, day-in and day-out.

"I would say I scored my dream job right out of college," she said. "It's a lot more hands-on than I expected and it's a lot more work than I expected and I love it for that."

Harris was flying inside an airplane assigned to track the Glory spacecraft's launch into orbit from Vandenberg Air Force Base, Calif. When the fairing on the Orbital Sciences Taurus rocket failed to separate as planned, the rocket changed its course because it was heavier than it expected to be.

Suddenly, the airplane's crew had to adjust its own course to keep the antenna pointed at the rocket as long as it could to retrieve the critical data that would allow engineers to pinpoint what went wrong.

Benson was part of the launch team looking at the data from the Glory mission as it came in. He said it was apparent quickly that the launch was failing.

"There were discretes," Benson said. "The switches that would show the payload fairing separated, they didn't change status when the separation command was issued. The temperature data inside the fairing didn't change."

There have been many successful launches, too, with a number of notable achievements coming in the past year such as the GRAIL mission to the moon, the Curiosity rover also known as the Mars Science Laboratory and the Juno mission to study Jupiter and its magnetic field in detail.

The teams of engineers are working now with the upcoming NuSTAR mission to launch an observatory into Earth orbit that will survey the cosmos for black holes and the remnants of stars that recently exploded.

The conclusion of every mission leads to an intense data review during which engineers pore over all the telemetry the rocket and spacecraft sent during the time it took to get into space. The returns are crucial, Benson said.

"If we didn't have telemetry, we'd never be able to improve," Benson said.

 
 
Steven Siceloff
NASA's John F. Kennedy Space Center