ScienceMaster - Aerospace Engineer Aprille Ericsson's Work At NASA


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AEROSPACE ENGINEER - GODDARD SPACE FLIGHT CENTER
Aprille Ericsson, Ph.D.

2/7: Aprille Ericsson

ERICSSON'S WORK AT NASA
Picture a figure skater spinning on ice. When she pulls her arms in close to her body, she spins faster. When she holds her arms away from her body, she slows down. The skater's mass is distributed differently, changing her inertia. Since momentum must be conserved, the skater's rotational speed must change to conserve momentum.

Now, think of holding your hand out a car window while the car is moving. There is a pressure against your hand, forcing it back. This is one of the laws of aerodynamics.

These two examples are exactly what happens to a spacecraft when it is in orbit. Someone has to study these forces and know exactly how they will effect the space craft's orbit. That someone is Dr. Aprille J Ericsson.

Ericsson is an aerospace engineer at NASA Goddard Space Flight Center in the Guidance, Navigation and Control Center. Her current project is a MIDEX project called MAP- Microwave Anisotropy Probe. The Probe is scheduled to launch in 2000.

MAP is "going to a libration point, points of equilibrium in terms of gravitational pull between the planets," said Ericsson. The instrument on board MAP is measuring microwave radiation. Ericsson said scientists are hoping the information obtained about radiation will provide information about the Big Bang theory.

Ericsson's job is to figure out how to keep the spacecraft in orbit burning the thrusters as little as possible. She is an engineer; therefore, she assists the scientists in fulfilling the mission's goals.

"When you burn the thrusters, that causes a vibration. We stop spinning and that means they (the scientists) can't observe during that period and that effects science," she said. "We want to burn the thrusters as few times as possible and for the shortest amount of time."

The spacecraft also uses a 'gravitational assist' to stay on course. "We use the gravitational pull of the moon to help give us the acceleration to get us out to the L2 point," said Ericsson.

Ericsson said there are a lot of things that go into maintaining stability on board the space craft. Among them:

Fuel Slosh:
The tank on board MAP is spherical (like a ball). "It's spinning and the fuel starts to slosh around," said Ericsson. The effect this has on the spacecraft changes over time as more and more fuel is used up and the tank empties.

Ericsson's job is to create equations to determine how this fuel slosh will change the course of the spacecraft. "Its hard to calculate moving motions," said Jackson. "I like to use equations," she said. "I like to look at the dynamics and physics of a problem."

Solar Pressure:
Solar pressure accumulates on the surface of the spacecraft. Although we don't usually think of it that way, radiation from the sun is actually a force that can change the motion of the spacecraft over time.

"If the spacecraft is rotating perfectly, the forces will cancel themselves out over one rotation," said Ericsson. As the spacecraft spins, equal amounts of force are being applied normally and radially on it from all sides, eventually canceling each other out as they are applied over 360 degrees of rotation. However, if there is a wobble in the spacecraft's orbit, the forces applied on one side will be greater than on the other.

Gravitational Forces:
"The gravitational pull from both the earth and the moon can effect the motion of the spacecraft," said Ericsson.

Inertia:
The figure skater example at the beginning of this page is an example of inertia. The skater, by changing the position of her hands, is changing her inertia, which is proportional to the momentum created in the system. One of Ericsson's responsibilities is to determine how often to 'dump' the momentum that is created in order to keep the spacecraft in
equilibrium.

Aerodynamics:
Like our car window example, aerodynamics can also effect the movement of MAP. Aerodynamics is proportional to the density of the medium that you are traveling through. The force will not be as great as the force on your hand when you stick it out the window, because "the higher you go in altitude, the less the density or pressure," said Ericsson.

"I find this mission extremely exciting because it will implement new technologies, as well as, innovative guidance, navigation and control techniques for a Middle Size explorer system, and it is being built right here at GSFC," she said.

Ericsson dreams of becoming a NASA astronaut, and she has applied for the program. She also dreams of becoming a full-time professor and is currently an adjunct professor at Bowie State University.

NASA'S MAP PROJECT
MAP is part of the Explorers Program, selected by NASA in 1996, to probe conditions in the early universe. MAP measures temperature differences ("anisotropy") in the cosmic microwave background radiation.

MAP will help to answer three of the most fundamental questions in cosmology:

What are the values of the cosmological parameters of the Big Bang theory?

How did structures of galaxies form in the universe?

When did the first structures of galaxies form?