Portland State Aerospace Society hosted a free event featuring Les Johnson, a world-renowned author, physicist and self-described “space nerd” on April 18 at PSU in conjunction with Rose City Astronomers. Johnson’s presentation focused on small spacecraft propulsion without liquid fuel.
“I am a space cadet,” Johnson said, whose interest in space was awakened at the age of seven when he watched Neil Armstrong walk on the moon. Johnson, author of science nonfiction and fiction literature, is also a deputy manager for the United States National Aeronautics and Space Administration at the Science Programs and Projects Office of Marshall Space Flight Center in Huntsville, Alabama.
Johnson’s presentation is especially relevant now for PSU’s space enthusiasts, thanks to NASA’s recent approval of the PSAS “OreSat,” Oregon’s first nanosatellite. In addition, PSAS has begun planning a mission to Jupiter with their next satellite project “OreSat2.”
“I think we need to be starting to work on 21st century propulsion,” Johnson explained. “To build on some of the work I’m doing in solar sails and other technologies, which are not yet flown, that are doable and can be done. We need some innovative thinkers to go out and try to make those happen.”
Rocket propulsion has continued to be a major limitation to space exploration. “It’s that darn rocket equation,” said Johnson, who explained the scale between the size and weight of a rocket, and the bulk and weight of fuel needed to thrust it out of Earth’s gravity. Once the spacecraft escapes Earth’s gravity, the next concern involves maintaining spacecraft functionality for the duration of its mission.
“You can’t load enough propellant on there to make it worthwhile, and if you do then you start losing payload mass,” Johnson said. “If you look at most of the deep space missions that we’ve flown, over half to two-thirds of the launch mass is propellant. That’s a crime.”
Johnson brought up the risk of explosion as an additional concern.
An alternative propulsion method currently in use utilizes electric ion thrusters. Although electric ion thrusters are more efficient than liquid fuel, there are still certain limitations and dangers involving combustion. Iodine propulsion, which theoretically provides a reduced risk of explosion, is currently being tested but has yet to be observed in space.
Johnson wants to challenge and push students in the field of aeronautics. “There’s a lot we can do if we leave rockets behind,” Johnson said.
Some of Johnson’s ideas for delivering small spacecrafts to distant destinations such as Jupiter involve momentum exchange, current collection, electric sails and solar sails. “I think solar sail propulsion is something very viable for CubeSats,” he said. In fact, Johnson has written a book on the very subject.
Johnson’s website features a photograph of him holding a piece of graphene, a candidate material for solar sails. Johnson brought a graphene sample to the presentation for audience attendees to pass around.
During the question and answer session Johnson was asked to describe the process for having his ideas heard and accepted. Johnson’s first point of advice was to make sure that the idea was actually “good” and to then gain credibility and learn to be the “best communicator possible.”
“I think it’s a shame if somebody has an idea and they’re too shy to share,” Johnson said. “A lot of problems could be solved if people had the freedom to think they could pose their crazy idea, because it may not be crazy.”
