Lubin received funding from NASA last year to study the possibility of using photonic laser thrust, a technology that does exist, as a new system to propel spacecraft to relativistic speeds, allowing them to travel farther than ever before. The project is called DEEP IN, or Directed Propulsion for Interstellar Exploration, and the technology could send a 100-kg (220-pound) probe to Mars in just three days, if research models are correct. A much heavier, crewed spacecraft could reach the red planet in a month—about a fifth of the time predicted for the SLS.
Photonic propulsion works by firing lasers at a reflective material like a solar sail. Though the photons in the laser do not have mass, they do have energy and momentum, and they transfer a small amount of kinetic energy to the reflective surface when they bounce off. In the frictionless vacuum of space, the continued acceleration could hypothetically push a spacecraft to around 30 percent of the speed of light, the types of speeds we have achieved in partial accelerators. After launching a spacecraft into orbit with a conventional rocket, the probe could unfurl a light sail to be hit by powerful lasers on Earth.