Now that we know the closest star system to us has at least one planet, an Earth-mass and potentially habitable one at that, there is one big question a lot of people are asking: Can we go there? Could we send a probe to Proxima Centauri? The answer is … maybe. There have long been ideas and plans for such a mission, but now that at least one planet has been verified there, interest is at an all-time high. It’s doable, but not necessarily easy.
The newest plan to send a probe to the nearest star system, by Breakthrough Initiatives, is called Breakthrough Starshot. Basically, it would send out tiny probes weighing a little more than a few grams, which would be launched using large arrays of lasers. By using a combination of lightsails and lasers, it is estimated that they could travel up to 20 percent the speed of light, getting to the Alpha Centauri system in only about 20 years. (Proxima Centauri, home of the exoplanet Proxima b, is one of three stars in that system). The miniature spacecraft, called wafersats, would be like tiny circuit boards which could take photos and gather other information. As of now, $100 million has been provided for the research phase.
As described on their website, Breakthrough Starshot “is a $100 million research and engineering program aiming to demonstrate proof of concept for a new technology, enabling ultra-light unmanned space flight at 20% of the speed of light; and to lay the foundations for a flyby mission to Alpha Centauri within a generation.”
It might sound like science fiction, but the technology to do it is available. As noted by New Scientist, around 20 challenges were identified for the mission, according to Yuri Milner, who announced the Breakthrough Starshot project earlier this year, but he is confident they can be overcome. One of the primary concerns is the collision of interstellar dust particles on such tiny spacecraft.
The first studies have now been completed, by Avi Loeb at Harvard University, which focused on the dust problem. “We did a thorough analysis, taking all the relevant physics into consideration,” he said. “We didn’t see any showstoppers.”
For most spacecraft, dust isn’t much of a problem, since they are so much larger and adequately protected. But the Breakthrough Starshot spacecraft would be much smaller, and the speeds of up to 20 percent the speed of light means that the impact from any dust particle would be much more significant, due to kinetic energy. Dust particles could even form craters in the surfaces of the wafersats. A dust grain only slightly larger than a hundredth of a millimeter could theoretically destroy a tiny wafersat. Luckily, most interstellar dust grains are much smaller than that, but it could still happen. According to the studies, up to 30 percent of the wafersats’ surface could be eroded by dust by the time the spacecraft reach Alpha Centauri. To further help compensate, the wafersats would be long and thin, to minimize impact from dust particles. A few millimetres of a “dumb” graphite material could be added to the front of the craft to act as shielding. It would gradually be eroded away and help keep the electronic systems safe.
“Erosion of solid surfaces will be a severe problem at these speeds,” said Ian Crawford at Birkbeck, University of London. “It’s possible that the wafersats won’t be able to complete the journey, but their success or failure will teach us more about the interstellar medium,” he says. “We will learn a tremendous amount that will help us build better starships.”
For the first phase of the mission, the wafersats will be equipped with lightsails. Similar lightsails and solar sails are already being designed and tested for use within the Solar System. Their mirrored surfaces are hit with powerful lasers, propelling them to some fraction of the speed of light. The technology is still fairly new, but has already been shown to work. Similar projects include the LightSail developed by The Planetary Society. For the rest of the journey, the sails will have to be folded up. They could then help further protect the spacecraft, but they also add weight.
“There is a trade-off, always,” Loeb said.
“I don’t think it’s going to be a showstopper, it’s just going to make things more complex,” added Paulo Lozano at the Massachusetts Institute of Technology. “It is pretty clear they are paying a lot of attention to the details, and that’s good.”
As Loeb also noted, “Reality comes back to bite you if you try to ignore it,” he says. “It’s very important to recognise the difficulties and try to find the solution.”
Researchers are, however, quite optimistic. According to Pete Worden, chairman of the Breakthrough Prize Foundation, on Space.com: “We certainly hope that, within a generation, we can launch these nanoprobes. And so perhaps 20, 25 years from now, we could begin to launch them, and then they would travel for 25 years to get there.”
The discovery of the exoplanet Proxima b will now of course have implications for the mission.
“Over the next decade, we will work with experts here at ESO [the European Southern Observatory] and elsewhere to get as much information as possible about the Proxima Centauri planet … even including whether it might bear life, prior to launching mankind’s first probe towards the star,” Worden said.
An excellent listing of research involved in possible interstellar travel projects such as Breakthrough Starshot can be seen here.
Overall, the Breakthrough Starshot program will require:
- Building a ground-based kilometer-scale light beamer at high altitude in dry conditions.
- Generating and storing a few gigawatt hours of energy per launch.
- Launching a “mothership” carrying thousands of nanocrafts to a high-altitude orbit.
- Taking advantage of adaptive optics technology in real time to compensate for atmospheric effects.
- Focusing the light beam on the lightsail to accelerate individual nanocrafts to the target speed within minutes.
- Accounting for interstellar dust collisions en route to the target.
- Capturing images of a planet, and other scientific data, and transmitting them back to Earth using a compact on-board laser communications system.
- Using the same light beamer to receive data from nanocrafts over four years later.
Other possible uses of Breakthrough Starshot include:
- Contribution to Solar System exploration
The Breakthrough Starshot concept could enable rapid solar system missions. At 20 percent of light speed, a nanocraft could reach Mars in an hour (it currently takes around nine months), Pluto in a day (the New Horizons probe took nine years) and interstellar space in about a week. Even at 2 percent of light speed, journey times would be significantly reduced.
- Using the light beamer as a telescope
The light beamer would constitute a kilometer-scale telescope in its own right. No such instrument exists today for optical astronomical observations.
- Asteroid detection
The light beamer could potentially be used to detect Earth-crossing asteroids at large distances.
Another similar concept being studied is the Heliopause Electrostatic Rapid Transit System (HERTS). This electronic sail (E-Sail) could be used to propel a small spacecraft to the outer heliosphere of the Solar System or beyond. It would use a series of 10-20 km-long, ultra-thin slowly rotating tethers that are positively charged. Positively charged protons of the solar wind would collide with the tethers, being repelled, and this exchange of momentum would produce a slight push. Over time, this would add up to considerable acceleration.
HERTS could reach the outer hemisphere in about a decade, while it took Voyager 1 about 35 years to travel the same distance.
One might ask why not just send a regular sized spacecraft like usual? Simply put, to send something that large, at currently attainable speeds, would take thousands of years to get to Alpha Centauri. And sending such spacecraft at faster sub-light speeds isn’t possible yet with current technology. If you want to get there within a couple of decades, then you need to use much smaller spacecraft and more innovative technology. And that’s only for the nearest star system, out of billions in our galaxy. Even the nearest star is much, much farther away than Pluto.
Being able to travel to the nearest star (other than the Sun) has been a long-held dream of many. We may now finally be getting close to realizing that dream. Breakthrough Initiatives also published an eloquent open letter as to why it should be done. A quote, in part:
“There has never been a better moment for a large-scale international effort to find life in the Universe. As a civilization, we owe it to ourselves to commit time, resources, and passion to this quest. But as well as a call to action, this is a call to thought. When we find the nearest exo-Earth, should we send a probe? Do we try to make contact with advanced civilizations? Who decides? Individuals, institutions, corporations, or states? Or can we as species – as a planet – think together? Three years ago, Voyager 1 broke the sun’s embrace and entered interstellar space. The 20th century will be remembered for our travels within the solar system. With cooperation and commitment, the present century will be the time when we graduate to the galactic scale, seek other forms of life, and so know more deeply who we are.”