"Blimps in Space", Input/Output, ME Departments, November 2005

input/output

by Jean Thilmany

Blimps in Space

It's neither bird nor plane nor even frog. This may sound strange, but it's a flying blob. Or, rather, blimp.

Three Johns Hopkins undergraduates designed a 17-foot-long, helium-filled blimp that carries sophisticated electronics. The airship is a scale model of a military blimp in development at the university and is intended to serve as a testbed for the engineers who are designing the full-size version, which will conduct surveillance at the outer edge of the Earth's atmosphere.

When complete, the surveillance blimp will send information from an altitude of about 100,000 feet above sea level, according to its developers at Johns Hopkins University's Applied Physics Laboratory in Laurel, Md.

Student engineers at Johns Hopkins University designed a 17-foot blimp to serve as a test model for technology that will control a military surveillance airship on the edge of space.

But because the researchers at the physics lab had never built such a thing, they asked mechanical engineering students to devise a smaller version of the airship. The laboratory's engineers will use lessons learned from the model to refine the guidance, navigation, and control systems for their aircraft.

"We're trying to see how these systems would work, using commercial off-the-shelf equipment," said Vincent Neradka, an Applied Physics Laboratory engineer, who worked with the undergraduates. "The model aircraft works very well. The students met almost all of our objectives."

The student team's airship can fly on its own and follow computer commands to move itself to a predetermined location. The students can steer the craft manually with a wireless remote control. Onboard equipment includes a video camera to transmit real-time images from about 50 feet above the ground.

The full-size blimp is meant to be a relatively inexpensive disposable airship that would hover high over a military location for two to four weeks, sending pictures of activity on the ground and relaying communications, Neradka said.

That military airship, dubbed a High Altitude Reconnaissance Vehicle, or HARVe, will be stuffed inside a missile or reusable rocket, which will carry it to a near-space altitude. After emerging from its carrier, a mammoth balloon will inflate and carry a gondola equipped with sensors and propellers. Unlike most conventional satellites, HARVe could be directed to stay in place above a single location for weeks at a time. Then, the airship would either disintegrate or be destroyed.

The model, built by the students for about $12,500, will help engineers decide which low-cost technology might work in a full-size version.

The student model can carry a 10-pound aluminum gondola. The gondola is equipped with two propellers facing forward and two reversible propellers facing up and down. It also holds the video camera, and the electronic navigation, control, and guidance systems.

The student project was not without setbacks, however.

The motors that the students' computers had predicted would be able to run the vertical propellers turned out not to be powerful enough, according to Nicholas Keim, a mechanical engineering major who was a member of the design team.

"One of the things we learned was that theory doesn't always work out," Keim said. "Sometimes, things just break."