It will take thousands of years for humanity's fastest spacecraft to reach even the nearest stars. The Breakthrough Initiatives have been exploring the possibility of reducing this to decades, potentially allowing the scientists who launch the mission to live to see the results. A new paper, in the Journal of the Optical Society of America B, shows one of the major obstacles for such a project can be overcome with existing technology, although the authors admit other hurdles remain.
The more massive an object is, the harder it is to accelerate it, particularly as you approach the speed of light, representing a major problem for any spacecraft carrying its own fuel.
Alpha Centauri is the nearest star and planetary system to Earth – it is 4.37 light-years away, but it would take a human about 6,000 years to get there with current technology.
"To cover the vast distances between Alpha Centauri and our own Solar System, we must think outside the box and forge a new way for interstellar space travel," Dr Chathura Bandutunga of the Australian National University said in a statement. Lightweight missions could be given an immensely powerful push and left to voyage on alone.
The idea of using lasers to provide this push has been around for decades but is now being explored more seriously as part of Breakthrough Starshot. There are many challenges to making this work, but Bandutunga argues the atmosphere needn’t be one of them.
The twinkling of the stars reminds us how much the atmosphere affects incoming light. The same distortions affect laser light sent upwards, potentially preventing lasers from applying the force necessary to push a spacecraft on its way. Some proponents of the idea have suggested locating the launch system on the Moon, but the cost would be, well, astronomical.
Bandutunga is the first author of the paper, which argues the adaptive optics used by telescopes to compensate for atmospheric distortion can be used in reverse. A small satellite-mounted laser pointed down to Earth can be used to measure atmospheric effects in real-time, allowing the vastly more powerful lasers located on the ground to adjust, keeping their focus securely on the space probe.
“Vastly more powerful” is no exaggeration. Previous research identified the power requirements for these lasers to transmit to the craft as 100GW. The entire United States uses an average of 450 GW of electricity at any one time.
Bandutunga and co-author Dr Paul Sibley are undaunted. “It only needs to operate for 10 minutes at full power,” they told IFLScience. “So we imagine a battery or super capacitors that can store energy built up over several days and release it suddenly.” The power would be delivered from 100 million lasers distributed over an area of a square kilometer.
All this power would be directed at an object no more than 10 meters (33 feet) across; by the time the lasers switched off, it would be traveling at about 20 percent of the speed of light. Slowed only insignificantly by the Sun's gravity and the interstellar medium, the craft could reach Alpha Centauri in around 22 years, although its transmissions would take another four years to reach us.
Not melting the probe is “Definitely one of the remaining big challenges,” Bandutunga and Sibley acknowledged to IFLScience. To avoid this it needs to be a mirror so nearly perfect it would reflect 99.99 percent of the light falling on it, doubling the momentum transfer and reducing heat.
A probe would zip through the Alpha Centauri system in a few days, probably never getting very close to a planet. However, the beauty of the idea is that, once the launch system is built, sending additional probes becomes relatively cheap. A fleet of probes could flood nearby star systems, maximizing the chance one will get a close, if brief, look at any Earthlike planets.