When Oumuamua, the first interstellar object ever observed to pass through the solar system, was discovered in 2017, it exhibited some unexpected properties that made astronomers scratch their heads. Its elongated shape, lack of a coma, and the fact that it changed its trajectory were all surprising, leading to several competing theories about its origin: Was it a hydrogen iceberg with outgassing, or maybe an alien solar sail (sorry folks, not probably?)) on a space trip? We may never know the answer because Oumuamua moved too fast and was watched too late to get a good look.
It may be too late for Oumuamua, but we could be ready for the next strange interstellar visitor if we wanted to. A spacecraft could be designed and built to capture such an object in the blink of an eye. The idea of such an interstellar interceptor was developed by various experts, and funding for such a concept was even provided through NASA’s Innovative Advanced Concepts (NIAC) program. But how exactly would such an interceptor work?
A new paper posted on ArXiv on June 27th explores a possible mission design. The proposal derived from the NIAC study suggests combining solar sail technology with the ability to miniaturize space probes to small, lightweight sizes.
Missions such as JAXA’s IKAROS probe to Venus and the Planetary Society’s ongoing LightSail 2 project in Earth orbit have shown that solar sails, which use the sun’s photons to accelerate, are perfectly viable propulsion systems. The successful use of CubeSats in interplanetary missions was also demonstrated by the Jet Propulsion Laboratory in 2018. They sent two CubeSats called Mars Cube One (MarCO-a and MarCO-b) to accompany the InSight lander on its journey to the red planet. The CubeSats worked like a charm.
Combined, Sun Sails and CubeSats could be a powerful tool for exploration.
To intercept an interstellar object, the paper suggests that a solar-powered CubeSat could be prematurely “parked” in orbit around the sun, quietly waiting for the next interesting object to be discovered worth pursuing become. A fast response vehicle like this would allow for various mission designs. A five year mission, for example, could easily catch up and examine an interstellar object and beam back to Earth the kind of data we didn’t get from Oumuamua. On the other hand, a similar spaceship could even go on a trial return mission if given an extended ten-year period.
Artist’s impression of the first interstellar asteroid / comet “Oumuamua”. This unique object was discovered by the Pan-STARRS-1 telescope in Hawaii on October 19, 2017. Photo credit: ESO / M. Grain knife
One of the greatest engineering challenges for such a mission involves the solar sail’s ability to manage heat. The interceptor would have to travel much closer to the sun than any previous solar sailing test that typically used Kapton coated aluminum. The properties of this material could allow it to survive within 0.15 AU from the Sun without melting, but careful consideration must be given to shielding the controls and other spacecraft systems without adding too much to the spacecraft’s mass. Too heavy and the sail cannot catch up with the target.
The value of such an interceptor spacecraft is pretty clear. Although we’ve only seen two interstellar objects so far, they are likely to be constantly passing by. Better telescopes coming online this decade will help us find them, but they move fast and don’t stay long. If we want to examine an interstellar object up close, we need to be prepared, and a quick-reacting intercept spaceship is probably our best chance of success.
Darren Garber, Louis D. Friedman, Artur Davoyan, Slava G. Turyshev, Nahum Melamed, John McVey, and Todd F. Sheerin, “A Quick Response Mission to Rendezvous with an Interstellar Object”. ArXiv form.
Featured image source: John Ballentine.