The Voyager 1 probe has been traveling for almost 39 years, covering just over 130 astronomical units, becoming the only human spacecraft to reach interstellar space. Unfortunately, if we reproduce Voyager 1's pace, a mission to Alpha Centauri would take tens of thousands of years... but what if we could reduce the time to two decades? With that in mind, Starshot was announced, a $100 million program that plans to send a fleet of micro-spacecraft using the concept of a "solar sail" to achieve 20 percent of the speed of light.
More than once we have seen the speed of light as the ultimate goal for advanced space exploration, but the truth is that even a fraction of it would represent an extraordinary advance. When we talk about interstellar missions, all eyes point to Alpha Centauri, the closest system to the Sun. According to the latest measurements, the distance separating us from Alpha Centauri is about 4.3 light-years, so with 20 percent of c, a theoretical trip would take just over two decades, a number within our life expectancy. The big question is: What do we intend to send? A crewed ship or a New Horizons-style probe are completely ruled out, since the amount of energy required is staggering, but if we consider a maximum mass of just a few grams, the parameters change completely.
Project Starshot: the initiative
This is how we arrive at Project Starshot, a new initiative funded by Russian physicist and tycoon Yuri Milner, with direct support from names like Stephen Hawking (who was at the official presentation), Freeman Dyson, Ann Druyan (Carl Sagan's widow and responsible for the Cosmos series), astronomer Avi Loeb, astronauts, and former NASA members. Milner will provide the first $100 million for research and development. Each micro-spacecraft will cost about as much as a high-end smartphone, enabling mass production, and will be equipped with photonic thrusters, cameras, navigation/communication systems, and a power source. The key to the overall propulsion of each micro-spacecraft lies in a light sail and a laser array on the order of 100 gigawatts. In the best case, acceleration to 0.2c would take between 20 and 30 minutes.
A one-way trip
Of course, a fundamental problem with this propulsion method is that the ships will not be able to decelerate, and assuming they arrive intact at Alpha Centauri, they will probably have only a few days to collect information and transmit it to Earth, which implies an additional wait of 4.3 years. In other words, the challenge is gigantic, and it may never take shape, but I think it is worth the effort to explore the possibility of sending technology to Alpha Centauri within a quarter century or less.
