Is Interstellar Travel Really Possible?
The very aspect of space that makes it so interesting—its unknown vastness—is also the biggest challenge we face when attempting to explore it. Is interstellar space exploration, even to the nearest stars, really feasible?
The very aspect of space that makes it so interesting—its unknown vastness—is also the biggest challenge we face when attempting to explore it. Our probes can only travel so fast and so it takes a significant amount of time to traverse those extremely large distances.
The farthest humanity has ever been able to send probes is to the outer solar system. At ~12.5 billion miles from the Sun, the most distant satellite is Voyager 1 which was launched in 1977 to study the weather, magnetic fields, and rings of Jupiter and Saturn. Even as the spacecraft hurtles through space at ~38,000 miles per hour to escape our solar system (that’s roughly 0.0057% of the speed of light), Voyager 1 continues to communicate with the Deep Space Network, and will do so until it runs out of nuclear power sometime around 2025. The Pioneer 10 and Voyager 2 spacecraft are not far behind on their own escape trajectories.
We continue to send probes to bring us information on our distant planetary neighbors with New Horizons returning the first detailed images of Pluto in July of 2015. Check back here in July when the Juno spacecraft arrives at Jupiter after five years of travel to learn more about the planet’s origin and evolution. Although reaching Jupiter which is at its closest still a whopping 365 million miles away is an impressive feat, the distances in our solar system are a small fraction of the distance to even the nearest stars beyond our Sun.
Alpha Centauri, the closest star system, resides nearly 4.4 lightyears away which is more than 25 trillion miles or 70,000 times farther than Jupiter. So even traveling at the speed of light, which is significantly faster than our satellites can, a probe would require four years to reach the triple star system of Alpha Centauri. Moving at the typical speed of our space shuttles, or about 17,600 miles per hour, you would need 162,000 years to reach our nearest stellar neighbors. Even at the high speeds reached by New Horizons, the craft (which took 9.5 years to get to Pluto) would need 75,000 years to make the trip. So can we ever hope to send a spacecraft there?
A new initiative announced last month called Breakthrough Starshot is planning to do just that.
Breakthrough Starshot
You may remember the Russian billionaire Yuri Milner from his generous support of the Breakthrough Listen project’s search for extraterrestrial intelligence or for his investment in other Breakthrough prizes like the one awarded for the gene editing technology known as CRISPR-Cas9. Milner has once again pledged funding to space exploration via a program called Breakthrough Starshot.
The ultimate goal is to send on the order of 1,000 nanocraft (think tiny, lightweight spacecraft only about a gram in scale) on a high speed fly by mission through the Alpha Centauri system. The team plans to test the feasibility of using a ground-based array of lasers to produce a 100 gigawatt light beam to propel the tiny ships across the 4.4-lightyear distance in only 20 years. Effectively, the incident light (or photons) from the laser emission transfer their momentum to the sail as they are reflected off of it. Since the craft is so light (and the laser beam so strong) this momentum can then give the nanocraft the push it needs to make its journey.
To make the trip to Alpha Centauri that fast, the nanocraft will have to travel at 20% the speed of light (that’s nearly 100 million miles per hour). You can see a video animation of what the lasers would look like in action on youtube.
To start the mission, a larger rocket would launch the probes into a high altitude orbit. After that, however, each tiny probe would operate as a stand alone, individual spacecraft with its own cameras (the plan for the prototype is for four cameras, each with two megapixels, on a chip) for basic imaging, thrusters, power supply, and navigation and communication equipment including a retractable meter-long antenna to transmit information back to Earth. Of course, since that information cannot reach us faster than the speed of light, we will have to wait another 4.4 years to hear back on the results of the mission.
Is Breakthrough Starshot really possible?
But can we really build not just one but thousands of spacecraft that are so tiny as to not require a significant amount of radiation pressure to send them over such a large distance but that can also survive the high energy laser beams for several minutes? Can we really create laser beams that can be used in unison at such high powers while focused on such tiny targets that are tens of thousands of miles away?
The feasibility of such an effort is exactly what the funding announced last week hopes to address. The $100 million pledged by the team led by Yuri Milner will serve as an investment to explore the production of prototypes for both the laser array and the nanocraft themselves. Also on the Breakthrough board along side Milner are renowned theoretical physicist Stephen Hawking and Mark Zuckerberg, the man who brought us Facebook. The research will be led by the former director of the NASA AMES Research Center, Pete Worden, with the support of an advisory committee which includes Ann Druyan, an Emmy and Peabody award winning author and producer who co-wrote Cosmos with Carl Sagan who later became her husband, and Mae Jemison, the first woman of color in space and a leader in efforts to explore beyond our solar system.
However, this initial $100 million will only buy a proof of concept. Worden has already estimated that the price tag on the full project, should the initial investment prove successful, would be closer to $10 billion. Such a cost is more in line with current large scale astrophysical research endeavors like the Large Hadron Collider in Geneva.
And even though the whole idea may sound far fetched, the details of Breakthrough Starshot are based in several currently cutting edge technologies where scientists and engineers are making significant recent progress. The industry surrounding the development and manufacturing of thin, light weight materials on nanoscales, like graphene, is currently exploding thanks to their many, very practical uses including desalination.
The Planetary Society is also testing the feasibility of the light sail technology via their citizen-funded LightSail project. The nonprofit group conducted a successful test flight in June 2015 with the goal of moving toward the launch of a small spacecraft carrying large, reflective sails into orbit around the Earth. Sometime in 2016 they plan to launch a demonstration of the craft’s solar sailing capabilities, a launch that will involve the help of the Falcon Heavy rocket from the private spaceflight company SpaceX.
What can we learn from visiting Alpha Centauri?
So what can we learn from visiting Alpha Centauri? For starters, knowledge of our nearest stellar neighbors will give us insight into how alone our human-inhabitable world is in the vastness of space. One planet is already known to exist in the triple star system, and, should the larger vision of Breakthrough Starshot become a reality, Alpha Centauri is sure to become the target of extensive investigations into other possible exo-worlds.
The mission will also fundamentally alter our relationship with space travel and ultimately the universe. Given all that we already know about the cosmos, it can be easy to forget that the farthest we have ever sent probes, the extent of our solar system, is almost insignificant when placed into context of the entire observable universe. Not to mention the fact that we humans have never made it past the Moon, our nearest neighbor at 230,000 miles. Space exploration is extremely challenging, but that challenge inspires people to learn more about our relation to the cosmos and even to become scientists or engineers themselves. It’s hard to put a price tag on that.
Until next time, this is Sabrina Stierwalt with Ask Science’s Quick and Dirty Tips for helping you make sense of science. You can become a fan of Ask Science on Facebook or follow me on Twitter, where I’m @QDTeinstein. If you have a question that you’d like to see on a future episode, send me an email at everydayeinstein@quickanddirtytips.comcreate new email.
Image courtesy of the Planetary Society and NASA.
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About the Author
Dr Sabrina Stierwalt earned a Ph.D. in Astronomy & Astrophysics from Cornell University and is now a Professor of Physics at Occidental College.
