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To the stars
Astronomers recently announced strong evidence of an Earth-like alien planet around Proxima Centauri, the star closest to our sun, making it the closest exoplanet found to date. Though the star system is our cosmic neighbor, it is still located 4.2 light-years, or 25 trillion miles, away from Earth. At such distances, could we ever visit the newfound planet?
Even the nearest stars would takes tens of thousands of years to reach using conventional spacecraft, such as the robotic probes being used now to explore the solar system. These spacecraft are driven by a combination of chemical rockets, low-thrust ion drives and gravity-assisted trajectories — including so-called "slingshot maneuvers" around the sun or large planets that give them a big burst of speed.
But if we're going to travel beyond our solar system, we're going to need something a little faster than that — perhaps something like the giant Project Daedalus fusion rocket, shown here to scale with NASA’s Saturn V rocket in an illustration by graphical engineer and space artist Adrian Mann, whose work is featured in this countdown of futuristic space technologies. Here are seven ways that robots, or even human explorers, could visit the Proxima Centauri system or other cosmic neighborhoods.
Project DaedalusSlide 2 of 15
Project Daedalus is a concept design for an interstellar probe, developed in the 1970s by a group of technical specialists for the British Interplanetary Society. The target destination was Barnard’s Star — a red dwarf about 6 light-years away, in many ways similar to Proxima Centauri, where astronomers now report they have found signs of a potentially habitable planet. When Project Daedalus was conceived, some astronomers thought a gas giant planet might be in orbit around Barnard's Star, but since then, no planets have been found in the star system.
The result of the five-year project was the design of the Daedalus spacecraft, a two-stage, 54,000-ton nuclear rocket that would boost a 400-ton robotic probe to around 12 percent of the speed of light. This would enable the probe to make the 6-light-year journey to Barnard’s Star in around 50 years.
The rockets of the Daedalus spacecraft would be powered by nuclear fusion, using electron beams to detonate a stream of pellets of fuel such as helium-3, which could be mined from the surface of the moon. Even so, the engines would consume tens of thousands of tons of fuel to get the spacecraft up to its top speed in about 4 years — and because there wouldn’t be any fuel left to slow down, the end result of the 50-year journey would be just a 70-hour flyby of the destination system, before the spacecraft speeds past into interstellar space.
The Daedalus would be much too large to lift off from the Earth’s surface, so it would have to be built in orbit, which means spacecraft like this couldn’t be built without a capacity for construction in space that doesn’t exist today, said space scientist Ian Crawford, a professor of planetary science and astrobiology at Birkbeck College in the United Kingdom.
While Crawford thinks the science behind the Project Daedalus concept is better understood now than when the spacecraft was designed, he said the immense cost and enormous technical challenges likely mean it would be more than 100 years before something like the Daedalus sets out for the stars.Slide 3 of 15
Project IcarusSlide 4 of 15
The Project Daedalus concepts from the 1970s are the inspiration for Project Icarus, an ongoing joint project by the British Interplanetary Society and the Icarus Interstellar organization, an international network of scientists, engineers and enthusiasts who hope to develop the capabilities for interstellar spaceflight by the year 2100.
Project Icarus is designed to reach any star within 22 light-years of Earth that has a potentially habitable exoplanet, meaning if a planet is confirmed around Proxima Centauri, it could become a target destination.
Project Icarus aims to update the Daedalus design with new technologies and ideas. Among the refinements proposed are fusion rocket engines that use a different nuclear fuel, which would be detonated by lasers instead of electron beams — a technology that could draw from recent advances in laser-ignition fusion at the National Ignition Facility at Lawrence Livermore National Laboratory in California, Crawford said.
The Icarus probe could also be smaller than the 400-ton probe envisioned for Project Daedalus, thanks to advances in electronic miniaturization and robotics, and future nanotechnologies — which would mean the spacecraft would need to carry less fuel to reach its full speed.Slide 5 of 15
Light sailSlide 6 of 15
Our best bet for interstellar travel may be to not use a rocket at all, Crawford said. Light sails, which use the pressure of light to propel a payload, are already being considered for interplanetary space probes, and in 2010 Japan’s experimental IKAROS spacecraft successfully used its 60-foot-wide (20 meters) light sail to maneuver during a six-month journey to Venus.
But although light sails driven by sunlight are already an effective way to explore the solar system, they are not fast enough to cover interstellar distances in a reasonable amount of time.
Crawford said the answer may be to use powerful lasers to push the light sail to very high speeds with bursts of light at the start of the journey, until the spacecraft is too far from the laser source to gain more thrust from the light beam.
Since the driving lasers would be built on Earth or in orbit, interstellar light-sail spacecraft would not need to carry fuel for the journey, and so the mass of the spacecraft could be kept small.
Laser-driven light sail spacecraft are the basis of the Breakthrough Starshot project that was announced this year by investor Yuri Milner and physicist Stephen Hawking. The project aims to build a working prototype by 2036 at a final mission cost of around $10 billion dollars.
The project envisages a swarm of around 1,000 stamp-size "StarChip" spacecraft, each weighing a few grams and attached to a light sail measuring 13 feet (4 m) across, which would be deployed from a "mothership" in orbit before being accelerated by ground-based lasers to speeds of around 15 to 20 percent the speed of light.
This would allow the spacecraft to make the 4-light-year journey to the Alpha Centauri system — a triple-star system that includes the star Proxima Centauri and its possible planet — in between 20 and 30 years.
The concepts behind the Breakthrough Starshot project have been studied by Philip Lubin, a professor of cosmology at the University of California, Santa Barbara, who says the biggest challenge remaining is to create sufficiently powerful lasers to drive the light sail spacecraft.Slide 7 of 15
Bussard ramjetSlide 8 of 15