The problem of "space junk" – satellites that have reached the end of their lives, discarded rocket stagings and fairings, space rocks trapped in orbit and items that have simply fallen off spacecraft – has been known for some time, but is beginning to approach critical levels. While most pieces of hardware in orbit fall back into the Earth's atmosphere within a couple of years and burn up harmlessly, items in higher orbits can remain circling the planet for more than a century.
David Spencer, a specialist in space robotics at Purdue University in Indiana, explains why this is a problem. "There are a number of high-value orbits that have become so populated with defunct satellites and debris spacecraft that they’re approaching a tipping point,” he says. “Once that tipping point is reached, a cascade of uncontrolled collisions can occur, rendering the orbit unusable. Add into the mix the thousands of satellites that companies plan to launch into orbit in the next several years, and the problem becomes much worse.”
Spencer, an assistant professor of aeronautics and astronautics, has returned to academia after 17 years at NASA's Jet Propulsion Laboratory in Pasadena. One of his previous projects was a device called Light Sail, developed for the Planetary Society, a non-profit organisation originally founded by Carl Sagan to inform the public about space research and its relevance. Light Sail is a deployable structure which uses sunlight to boost and adjust the orbit of satellites, but Spencer reasoned that it would also work in reverse, using the gas particles of the atmosphere – which persist even at very high altitudes – to slow spacecraft down by increasing the drag area of the satellite. and decay their orbits.The sail would be deployed automatically at the end of the satellite's mission, ensuring it does not become part of the hazardous debris cloud.
Spencer is working on this with his students, as part of programme to take them through the entire life-cycle of a spaceflight project with small satellites, from design and fabrication to testing and operation. As well as this being valuable practice, Spencer believes that it is a good opportunity for his students to develop cutting-edge technology to address current issues in the space sector. “Working with students on projects that will advance the aerospace industry and benefit society overall, that’s really rewarding,” Spencer says.
Spencer's overall goal is for Purdue to to lead a planetary mission using Cubesats within the next 10 years. “Small satellites can address key planetary science goals that larger missions don’t address,” he said. “Purdue can make a lasting impact in this area."