Anyone who grew up on a diet of science fiction — often Star Trek or Star Wars — has at some point felt the longing for real-world interstellar travel. But the reality is we have no remotely plausible technology that could transport humans to planets around other stars.
Richard Linares, the co-director of the Space Systems Lab at MIT, has an idea. We can’t travel to the stars, he says, but the stars are already coming to us; all we have to do is find a way to catch up with them as they pass. And he thinks, it can be done with an hover-and-attack spacecraft that he calls a Dynamic Orbital Slingshot.
And NASA Innovative Advanced Concepts (NIAC) programme gave Linares a Phase I grant to explore the feasibility of the slingshot for a real space mission.
None of this would be happening if not for the mysterious, comet-like object known as ‘Oumuamua, which swung past the Sun in 2017. Its hyperbolic orbital trajectory flagged it as an interstellar object, meaning that it originated from some place far beyond our solar system. Astronomers had long speculated that comets might escape from other planetary systems and pass through our own, but this was the first concrete proof.
And ‘Oumuamua was followed very shortly by a second interstellar visitor, Comet Borisov in 2019. Spotting two interstellar comets in such rapid succession means that they must be extremely common.
Now, it is clear that interstellar visitors (of the inanimate kind) pass through our solar system all the time, which means that there are lots of potential targets to explore.
The upcoming Rubin Obseratory, set to begin operations in 2022, will scour the night sky for anything that moves or changes. By some extrapolations, it could easily identify one new Borisov-like object every year.
Interstellar objects come in fast. Comet Borisov arrived from deep space moving at 32 km per second. Short notice plus high velocity equals a very elusive target.
That’s where Linares and his Dynamic Orbital Slingshot come in. His idea is to have a network of space probes already out, just there lying in wait for an interstellar visitor to arrive. These would be very unusual types of spacecraft that he calls ‘statites,’ or static satellites. Unlike every other object in the solar system, they would not orbit the Sun. Instead, they would hover in place.
Normally, the Sun’s gravitational pull makes such hovering impossible. The statites would compensate by using enormous solar sails, each one attached to a lightweight cubesat-style probe. If the sail is large enough and thin enough, the pressure of solar radiation would be great enough to balance out the pull of gravity, allowing the statite to live up to its name.
As soon as astronomers spot an inbound interstellar object, the statite would change its orientation of its sail so that sunshine no longer holds it in place. It would immediately start falling rapidly toward the Sun, using solar gravity to accelerate it like a slingshot — hence Dynamic Orbital Slingshot. Adjusting the angle of the sail would allow it to steer, setting an intercept course for the interstellar target, all without the need for any onboard propellant.
A slingshot trajectory around the Sun would provide enough velocity that the statite could catch up to its target and match its velocity. Instead of a brief, high-speed flyby, the probe could execute a leisurely encounter, studying the object in depth. The statite could potentially drop a little lander on the comet, studying its surface up close.