Wolverines in Space: Michigan Students Build a Satellite

Icarus, according to Greek legend, was a man who flew too close to the Sun, and ended up drowning in the Aegean Sea when his wax-covered wings melted. A team of engineering students from the University of Michigan is seeking to repeat the legend, but not by donning bird feathers. The team, which has included two chemical engineers over the past year and a half, has designed and built a satellite for an upcoming NASA mission they've dubbed Icarus. If all goes right, the new Icarus will burn up in the Earth's atmosphere a week or two after its mission begins sometime in the fall of 2000.

Weighing in at only 50 pounds and about the size of a small microwave oven, the box-like satellite was "made to function as an autonomous satellite," said student project manager Jane Ohlweiler, a master's degree student in Michigan's Master of Engineering in Space Systems program. The satellite'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."

Genesis of Icarus
The Icarus Project began in September 1998 as an assignment in the University of Michigan's Master of Engineering in Space Systems program. The group behind the first known all-student designed, built, and tested independent satellite for NASA was formed into a project team in January 1999, and received full NASA approval that summer. Since that time, the team has finished design and is working towards delivering the satellite to NASA in the spring of 2000.

The Icarus Satellite is part of the the Propulsive Small Expendable Deployer System (ProSEDS) mission with which project advisor Brian Gilchrist, an associate professor of electrical engineering and computer science, and associate professor of atmospheric, oceanic, and space sciences at Michigan, is affiliated. Sponsored by Marshall Space Flight Center in Huntsville, Alabama, ProSEDS, will fly as a secondary payload on a Delta II launch vehicle and deploy a 5-kilometer conducting tether (15 km in total) to demonstrate electrodynamic tether propulsion. The primary mission of the Delta II rocket launch will be to lift a Global Positioning System satellite into orbit. 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 km 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.

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.

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. The tug would rendezvous with the payload, and launch vehicle, dock/grapple the payload, and maneuver it to a new orbital altitude or inclination without the use of a boost propellant. The tug could then lower its orbit to rendezvous with the next payload and repeat the process. Such a system could conceivably perform several orbital maneuvering assignments without resupply, making it what NASA terms a "low-recurring-cost space asset," or a good deal.

The flight experiment
From theoretical analyses and preliminary plasma chamber tests, bare tethers appear to be very effective anodes for collecting electrons from the ionosphere and, consequently, attain high currents with relatively short tether lengths. A flight experiment to validate the performance of the bare electrodynamic tether in space, and demonstrate its capability to produce thrust is planned by NASA for the year 2000.

Once in orbit, the deployer will reel-out the tether and endmass system to a total length of 25 km. Upward deployment will set the system to operate in the generator mode, thus producing drag thrust and electrical power.

The drag thrust provided by the tether will deorbit the Delta II upper stage in approximately three weeks, versus a nominal 1.5 year lifetime in a 500 km circular orbit. Approximately 100 W electrical power will be extracted from the tether to recharge mission batteries and to allow extended measurements of the system's performance until it reenters.

Powered by students
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. 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. Marshall has provided about $230,000 for the project and Michigan has put in another $70,000.

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 space systems design, said Lennard Fisk, chair of the 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."

ChE contributions
In a project built primarily around an electrical engineering concept, it might surprise some to find not one, but two chemical engineers involved. In addition to Cesul, Jamey Condevaeux, a chemical engineering graduate from Michigan who is now a graduate student in the Aerospace Department, was also involved.

"In this mission it's hard to give a ChemE spin outside of the work that I had to do with the thermal modeling and some analysis of a thermal control switch which relied on phase changes," Cesul recently told ChAPTER One. "However, the two ChEs we've had on this project, myself included, have proven their worth because of the broad training in key engineering fundamentals and the ability to pick up new material fast."

Cesul started work on the project in January, 1999, after finding out about it through a former dorm mate who was the project manager. "I e-mailed him and told him I was very interested in helping, although I didn't quite know how to fit in," he recalled. After a brief consultation with the management team, "they decided to bring me on as a thermal analyst, running computer simulations. Well I didn't have any idea how to do computer modeling and had just completed my heat and mass transfer class. But I eventually taught myself a standard NASA thermal modeling program called Thermal Synthesizer System (TSS)." After working with engineers and scientists from both Boeing and Marshall Space Flight Center, "I found out that the few chemical engineers that work at these two places are mostly involved in thermal modeling and engineering," he added.

Before the '99 school year ended, "I was asked if next year, in the fall, I would accept a promotion to assistant project manager, basically second-in-charge administration wise," Cesul continues. "I accepted and, when the new year started in September, I jumped right in. I found myself able to assimilate most of the work going on with the satellite as a whole because of my broad ChemE training. Additionally, I had taken classes in electronics, space mechanics, and structural mechanics to make myself more valuable to the team."

The satellite experience has had a definite influence on Cesul's future career direction. "I am actively looking for a career in the space industry upon my graduation in May 2001," he said. "I am taking 5 years for my undergraduate degree so I can take more engineering electives from other departments. I am planning on going to graduate school for Space Systems Engineering, a master's level program here at Michigan and three other national universities. I do independent research in the branching of chemical engineering and space exploration with my current emphasis on in-situ propellant production for future Martian missions, based on the work of Dr. Robert Zubrin of Pioneer Astronautics."

Though he feels that he has to "work very hard to prove to both professors and companies that a chemical engineer is very valuable to future space exploration," Cesul added that "I see the future of manned exploration being directly tied to the developments in chemical engineering, as future missions will rely on us to ‘live off the land' so to speak, and that intrinsically entails the use of chemical reaction and separation systems to harness and adapt the materials needed for our survival. I only wish more chemical engineering faculty and leaders across the country would realize this opportunity available to them before it gets gobbled up by another field."

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