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Student-built satellite to hang by a thread

ANN ARBOR — A team of engineering students from the University of Michigan has designed and built an entire
satellite for an upcoming NASA mission.

Weighing in at only 50 pounds and about the size of a small microwave oven, the box-like satellite is named
Icarus [http://aoss.engin.umich.edu/icarus/]
after the Greek legend of the man who flew too close to the sun, melted his wax-covered wings, and plunged
into the Aegean sea. If everything goes right, the painstakingly hand-built satellite will meet a similar fate,
burning up in the Earth’s atmosphere a week or two after its mission begins sometime in the fall 2000.

Though student teams at Michigan have flown experiment packages on the space shuttle and participated in
building sub-systems of satellites before, the Icarus project will be the first entirely student-built U-M satellite to
be flown by NASA.

“It was made to function as an autonomous satellite,” said student project manager Jane Ohlweiler, a master’s
degree student in space systems engineering — or satellite-making. The package’s primary function is to act as
a weight to pull a 9-mile-long string called a tether out from a spool on a spent Delta II rocket booster. If
everything works as designed, Icarus will end up sailing along at the end of this tether like an orbital plumb bob.
“First and foremost, we’re a dead weight at the end of the tether,” Ohlweiler acknowledges.

But rather than making the box a mere lump of mass, the students have covered Icarus with solar cells and
crammed it full of instruments that will gather data on the tether’s motion and position and then beam that
information down to listening stations around the Earth. The finished satellite will be a rectangular box about
18 inches long and a foot high, and all of it — the aluminum box, the instruments inside it, the complex network
of wiring, and even the circuit boards that make it work — were designed, built and tested entirely by the
student team.

“Our mission is to prove that we can do this,” said B.T. Cesul, a senior in chemical engineering and assistant
manager of the project. “And we’re helping NASA prove the smaller, faster, cheaper model.”

Icarus is part of a larger mission in which Brian Gilchrist, associate professor of electrical engineering and
computer science and associate professor of atmospheric, oceanic and space sciences, is participating called
ProSEDS, the Propulsive Small Expendable Deployer System. The primary mission of the Delta II rocket launch
will be to lift a Global Positioning System satellite into orbit sometime this fall. Once that is done, ProSEDS will
get to work. Icarus, the spool of tether, and an array of instruments to gauge the experiment’s success will be
mounted on the side of the rocket’s second-stage booster.

Normally, a spent booster like this would take as much as a year and a half to tumble into reentry and burn
up, but ProSEDS aims to bring it down in 21 days or less. Gilchrist and his colleagues who have been studying
varying uses for space tethers think the fuel-free source of thrust created by a 15-kilometer kite string could
be a boon to satellite operators. Though nobody anticipated this problem in the go-go years of the 1960s and
1970s, space has become a fairly hazardous place to fly, with thousands of bits of dead spacecraft and
spare parts zinging around. A cost-effective way to quickly deorbit spent payloads, pull big things like space
stations into higher orbit, or even to do mundane tasks like taking out a space station’s trash, would be a
great improvement. For example, if tethers were used to help keep the new International Space Station aloft
for 10 years, the savings over conventional fuels would be about $2 billion, NASA estimates.

As the ProSEDS project took shape, it was Gilchrist’s idea to hand over the entire “endmass” project to
students. “It’s small enough in scale that students can really handle everything,” Gilchrist said. Icarus started as
a class project in September 1998, and the completed package will be delivered to the Marshall Space Flight
Center in Huntsville, Ala., by March 1, 2000. Marshall has provided about $230,000 for the project and the U-M
has put in another $70,000. NASA officials are visiting the Michigan campus on Jan. 26 to view the finished
product.

Icarus also represents the latest in a new trend in engineering education being pursued at Michigan — student
team projects. Tackling authentic engineering problems and working in an interdisciplinary team helps prepare
students for the way engineering is currently being practiced in the real world. “It’s the kind of thing you don’t
learn in the classroom,” said Ohlweiler, sitting shoulder to shoulder with her teammates in a cramped office
plastered with posters from U.S. and Russian space missions. Nearly 100 students from six different
engineering disciplines have been involved. “We’ve had everybody from freshmen to Ph.D.s participating and
doing things they never thought they’d get a chance to do,” Ohlweiler said.

NASA’s move toward smaller, cheaper missions also opens up a world of new learning experiences for students
interested in learning about space systems design, said Lennard Fisk, chair of U-M Department of Atmospheric,
Oceanic and Space Sciences. “It used to be that rockets were the only option for hardware training, but this
new generation of small satellites opens up all kinds of opportunities.”

* * * * * * * * * * * * * * *

HOW IT WORKS

At 250 miles of altitude, the drag created by the tether isn’t from air resistance, it’s from the Earth’s magnetic
field. The first 5 kilometers of the tether are a conductive wire that captures passing electrons and sends them
streaming toward the Delta II rocket booster. The interaction between that electrical current and the Earth’s
magnetosphere results in a sort of drag that slows the rocket stage down and makes it start to fall. The
tether also generates about 100 watts of electricity that can recharge the experiment’s batteries and keep its
instruments running. Icarus is powered by some space-grade C batteries and solar panels.

WHY USE TETHERS?

Tether propulsion should work near any planet with a magnetic field, including Jupiter. And it wouldn’t be just
for taking things down. This fuel-free source of thrust could also be used to lift satellites and space stations
into a higher orbit. One proposal envisions a fleet of tether-powered tug boats in space that would lift satellites
up to higher orbits after they’ve been carried aloft by rockets. That’s what NASA terms a “low-recurring-cost
space asset” or a good deal.

# # # # #

EDITORS: For further information, contact

* Prof. Brian Gilchrist, (734) 763-6230, gilchrst@umich.edu
* U-M Icarus Project Office, (734) 936-0511, icarus-m@umich.edu
* June Malone, NASA/Marshall Space Flight Center, (256) 544-7061, june.malone@msfc.nasa.gov

Downloadable images are available at
http://www.engin.umich.edu/news/imagebank/