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.
The lasers would be positioned in
vast banks of lasers arrayed in pods of ten. Image Credit Breakthroughs
Institute
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.
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