Center Snapshot: Jody Davis
Image above: Jody Davis has joined a long list of NASA Langley engineers who have worked on Mars entry, descent and landing, a center specialty for more than three decades. Credit: NASA/Sean Smith
By: Jim Hodges
Next summer, a softball team at NASA Langley will be without a second baseman, because she will be with another team at the Jet Propulsion Lab in California, helping land a laboratory on Mars.
On two walls in Jody Davis' office in Building 1209, esoteric-looking formulae offer testimony to the hours and days and weeks and months of work it has taken a team from NASA Langley to determine how to handle the seven minutes it will take to land the Mars Science Laboratory from the point at which it enters the planet's atmosphere.
It's called "seven minutes of hell," because the distance from Earth to Mars proscribes any last-minute manipulation of the craft that will go from 13,000 mph to 2 mph through a series of maneuvers, including parachute slowdown, to rockets that will gentle that last few feet of descent.
"It's seven minutes of fun," Davis insisted, then explained why.
"I have wanted to do this ever since I was 13 years old. I guess I was odd. In my high school yearbook, they had me as 'most likely to go to the moon.' I don't think it will happen in my lifetime, but I think I'm getting close."
In a way, she's getting much farther in working on a spacecraft that will contribute mightily to an eventual human landing on Mars.
Langley claims the "entry, descent and landing" series as a specialty, and others have preceded her in staking that claim, beginning with Mars Viking in 1976.
This time, though, it's different.
"This mission is the first guided entry at Mars," Davis said. "There is entry guidance on board. That enables more of a precision landing than we have ever done before, such as with Mars Phoenix."
To accomplish all of that, the EDL team has loaded the spacecraft with a set of parameters that allows it to adjust for variations in the atmosphere through a series of rolls. And the variables involve more than just the density of the Martian atmosphere and the wind. Davis asks that you consider all of the things that inhibit your driving your car to work, then subtract only traffic.
The team has tested. And tested. And tested in a process called "Monte Carlo," which has some of the characteristics you might imagine from the name, using a set of variables between delineated parameters. Then another set of variables with another set of parameters until a solution becomes apparent.
"We have run up to 100,000 cases in one simulation," Davis said. "It's a roll of the dice. On any given day at Mars, you'll have a set of dispersed inputs, and you see how the simulation reacts to those dispersed inputs to see if your design is robust."
The tests run into the millions with one overriding bit of knowledge: You only get one shot at landing the lab on Mars. There is no tolerance for almost.
The pressure is incredible, but it's what Davis bought into when she left her Minneapolis home for Embry-Riddle University in Prescott, Ariz.
"I've always loved space. When I was little, anything about the solar system interested me," she said. "When I was young, I was really interested in architecture. When I was 3, I drew a house. I kept drawing triangles, and my uncle said 'Jody, you're going to need walls and he showed my how to draw a square.' For some reason, that just stuck with me."
A few years later, architecture and space co-mingled in her young mind. "Then somebody told me about aerospace engineering and I was hooked," Davis said. "I wanted to do that ever since."
She also wanted to fly – enough to earn a pilot's license when she was 17. Enough to spend her weekends now flying renting planes. And enough to covet an SR-22 Turbo of her own, the next time she has a spare half-million dollars or so.
Ahead are more simulations with the EDL team, more tests, more Monte Carlos, for about 8 ½ months beyond launch of the Mars Science Laboratory – all aimed at August 6, when it's time for seven minutes of hell, er, fun.
And then more fun: a trip to Europe with husband Brian – whom she met when they were part of the first graduate class at the National Institute of Aerospace -- to unwind and ponder work that has taken years to fruition, along with another project on which she has just embarked: the Supersonic Flight Dynamics Test of inflatable aerodynamic decelerators.
She might even make it back for the Langley softball playoffs.
The Researcher News
NASA Langley Research Center
Editor & Curator: Denise Lineberry
Managing Editor: Jim Hodges
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