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?

Sabrina Stierwalt, PhD,
May 9, 2016
Episode #191

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Image courtesy of NASA and the Planetary SocietyThe 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.  


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