Alumni Profile

Two years ago Keith Comeaux (MS 1991, PhD 1995 AA) got a call from NASA’s Jet Propulsion Laboratory (JPL) with an offer he couldn’t refuse: come work on the Mars Science Laboratory (MSL), a next-generation rover headed to the “Red Planet” in 2010.

Comeaux is lead verification and validation engineer for Entry, Descent, Landing, which means he is responsible for making sure that the MSL team has a good plan to ensure a high probability of a successful landing on Mars.

It’s a tall order. The craft’s method of landing hasn’t been tried before in space and two-thirds of all vehicles sent to Mars have never been heard from again. But nobody has had more success than JPL engineers.

Describe the Mars Science Lab generally.

We’ve got a suite of instruments on the Mars Science Lab rover that will help us look for evidence of habitability—evidence that the climate on Mars was adequate to support life sometime in its past. Some of the instruments will be able to drill into rocks, extract samples from their interior, and crush them into small bits to bring them inside the rover to analyze. Other instruments can then look to see what kind of chemicals are in the rocks, which might give us a clue as to whether the interiors of the rocks are suitable for microorganisms to live. And there’s also a laser on board which can vaporize rocks from a distance that the rover cannot actually reach. Using a telescope on the rover we will be able to look at the vaporized material that comes off the rocks, so we can determine what kind of chemicals are present.

That was a much easier way to arrive at the surface.  We didn’t have to have a control system which precisely guided the craft all the way to a soft landing. With the airbags we can release the rover from the parachute and let it bounce on the ground until it stops.  In our case, MSL rover is effectively the size of a small car. When you scale the landed mass to that size, the airbags don’t scale very well with it. It just becomes untenable to try to land a system that big with air bags. So we’ve gone back to powered flight, which was done previously on the Viking missions in the 70s, and of course, on the Moon, with Apollo, and the Surveyor landings in the Sixties. We are using descent engines to slow our speed after we drop off the parachute.
 
The large Rover also requires the largest capsule that has ever gone to Mars: four-and-a-half meters across. This time we are automatically guided during the entry. We swing the vehicle back and forth to steer ourselves during the hypersonic entry to Mars, to land precisely at a selected target on the surface of Mars. Once we reach about Mach 2, we deploy the parachute, and that slows us down to subsonic speeds, at which point we drop the heat shield and acquire the surface with radar. So that sequence is pretty conventional with regards to the past, except that we are a guided entry this time, for a precise pinpoint landing. 

That part of it is completely new. There is precedent, however, for this kind of approach. You see helicopters typically carrying loads flying underneath them. In fact we use the name, Sky Crane, as an homage to the Sky Crane Helicopter, which has been a workhorse of the military for carrying very large loads underneath it. After the rover separates, and you are in Sky Crane mode, the rover is hanging on a seven-and-a-half meter bridle. So that allows the control system to not work as hard in the landing phase of the mission. In addition, the rockets don’t have to get as close to the ground and disrupt the soil and kick up a lot of rocks and dust that might damage the hardware. At the Sky Crane point in the mission we are descending at about three-quarters of a meter per second. And that’s our touchdown speed. We’ll simply place the rover onto the surface at that speed.

We can look at all the pieces, and we test the pieces extensively. We don’t have the luxury of being able to test the full systems here on Earth, because, number one, the gravity is different and, number two, the atmosphere is a hundred times thicker than it is on Mars. So we break apart the system into pieces and we test the functionality of each one of those pieces. For example with the heat shield, we test samples of it in high velocity wind tunnels at NASA Ames and we test the Sky Crane bridle as an individual unit in a test facility here at JPL.

I’ve been here for two years. Previous to JPL, when I left Stanford, I went to work for Hughes Space and Communications (now part of Boeing) in El Segundo, building communications satellites for companies like DirecTV and XM Radio. And it was there I learned what space systems engineering was all about. I worked on the development of the 702 spacecraft product line. It is a commercial satellite platform. That was one of the first commercial applications of ion propulsion technology in the space industry.

Back in the ‘60s, ion propulsion became a new-fangled technique for creating velocity changes for spacecraft. And it was based on accelerating heavy molecules of gas using an electrostatic field instead of chemical propulsion. It gets you much more efficient miles per gallon, if you will. It was featured in Star Trek and other science fiction movies but it became a reality in the ‘90s for commercial space applications, and we were among the first to actually deploy it. The spacecraft is designed to last for fifteen years in geo-stationary orbit, using ion propulsion as its sole means of control.

Two years ago I got a call from JPL. They had an opening and asked me to come join the MSL team and that was just an opportunity that was too good to pass up. Having seen their past successes —Pathfinder, and the Mars Exploration Rovers—and, getting back to my background at Stanford, where I studied hypersonic vehicles, together with my system engineering and integration and test experience at Hughes and Boeing, it was a really good fit for me to work on this project.

I was enjoying the work I was doing but the pull was the opportunity to put hardware on Mars. There are few places in the world like JPL where you can go to do that. And to be able to work in this environment with extremely talented people who have done it before, you know, that was just an opportunity for me to broaden myself and learn about doing things that are almost unimaginable.

I studied computational fluid analysis, particularly as applied to hypersonic problems. My advisors were Dean Chapman and Bob MacCormack, two giants in the field. They were doing computational fluid dynamics before most people even knew what it meant, back in the ‘60s. For me, that was a real honor, to be working with them, as well as my fellow students, who were among the smartest in the country. I try to continue doing that in my career—to surround myself with good people to challenge myself to become a better engineer.