By Tom Risen|June 2018
SIMON “PETE” WORDEN
Pete Worden has long had a reputation for looking far beyond the confines of his career in the U.S. Defense Department and NASA, so it was perhaps not surprising that after a four-decade government career he would find a bold and provocative goal. Worden leads what’s expected to be a decades-long, privately funded endeavor to launch a succession of spacecraft, each weighing just a few grams, toward the next star system over, Alpha Centauri 4.3 lightyears away. Worden’s team is still figuring out exactly how this might be done, but the current concept calls for accelerating small wafers, called StarChips, to incredible speeds by projecting laser light onto a centimeter-scale lightsail attached to each chip. These StarChips would fly by the exoplanet Proxima-b to beam back images and maybe spectral readings to determine whether it could sustain life. I spoke to Worden by phone about the timing of the Breakthrough Starshot and what it will take to achieve it.
IN HIS WORDS
Timetable for launch
If all goes well, 25 years from now we’ll launch our first interstellar probes.
We hope we find evidence of what might be a life-bearing planet. Currently the best approach is to try to send [StarChips] to fly by and get images and maybe other kinds of data, spectrum and so forth, to really characterize this planet. One of the ideas is obviously some spectrometer [readings]. We’d like to get close enough, if there’s something that looks like forest, to get a spectrum of the forest area versus oceans. A few million kilometers will be our flyby distance.
Images from a super-small spacecraft
What you really need is an optical system, probably a few tens of centimeters [across]. The baseline approach is to actually configure the sail itself, so it acts as an optical [element]. Another idea is that when you get close to the target system, you actually deploy a small, lightweight optical system. So, you need basically some sort of telescope-type function.
Funding the Starshot
Yuri Milner has committed $100 million for the next five to seven years to do the technology. Hopefully after five years, we could begin to construct some sort of major field demonstration. That presumably would take five or so years to build and test. Then sometime 10 to 15 years from now we would start building the full-scale system.
A swarm of nano-spacecraft
The mothership would [release] probably hundreds or thousands of [StarChips and sails]. We’re thinking of something that would look about the size of a typical communications satellite, so a few thousand kilograms maybe is the mothership. It would be in a highly elliptical orbit where the apogee would be pointed kind of in the direction of Alpha Centauri.
The notional place [for the laser beam] would be the Atacama Desert in Chile. Another possibility may be southern New Zealand. It has to be in the southern hemisphere because Alpha Centauri is not visible from the northern hemisphere. We would only [propel] one at a time. It takes about 10 minutes to accelerate [each StarChip] to 20 percent the speed of light. Then the next day you would launch another one.
The total mass of the light sail plus chip is a few grams at most. It’s probably going to be folded up in some way. It should have really low absorption [to avoid heat damage]. It’s how much power [the laser] can put on the sail and how long you can focus it. You reflect most of the light. That’s what gives you your [propulsion] pressure.
One of the reasons that we’re going to send hundreds of them is we’re probably going to lose a lot of them. [Collisions with] dust is the most serious issue. You’ll have three or four cameras, so if one of them gets hit by a piece of interstellar dust there’s other ones to take over.
After you’ve flown through the system you turn around, lock a small laser on board back on the Earth then we fire the laser signal back. We’re convinced that the battery technology as it exists is within the power levels we need.
Starshot contracts in 2018
The next five to seven years we’re going to be addressing key technology questions. We’ve narrowed down to three we consider the real deal breakers. The first is, “Can you build this giant laser array [on Earth] for any affordable cost and get the beam through the atmosphere?” We are writing 13 contracts for the first study phase of that. The second key thing is the light sail and how you attach the [StarChip] to it. We’re within a few weeks of releasing our request for proposal on that. The third part is how do we communicate back from Alpha Centauri? Later this year we’ll have the RFP for the communications piece.
Other science targets
We’re funding efforts of ground-based observatories to see if we can find [other] planets around Alpha Centauri A and B. If we’re lucky we’ll have several planets to fly by. Between TESS [the Transiting Exoplanet Survey Satellite], the James Webb Space Telescope and these ELT [Extremely Large Telescopes], we will find out in a decade if there is a potentially life-bearing planet, or at least something that seems to show some evidence of life, around one of the nearest stars.
I think this is a revolution in our ability to explore the solar system and even deeper interstellar space. As we make progress we could send these probes to the Oort Cloud, to the Kuiper Belt. And they’ll be cheap. Once you’ve built the basic system, it’s a few million dollars per mission, not tens of millions. Titan [Saturn’s largest moon], Venus and Ganymede [the largest moon in our solar system] might have no life but they might have some residual organic matter that would be worth investigating.
Willingness to adapt
You’re looking at whatever concept works. There are a number of people who believe that our advances in fusion engines are coming along. If those things mature faster than a light sail, then we’ll switch. Nothing has been presented yet that would suggest that we should change.
On the late Stephen Hawking, a Starshot adviser
He kind of made it clear this was one of his dreams, too. He was very concerned about the interstellar medium and so some of the questions he asked, we investigated those in detail. He [thought] eventually we can even send humans. We’re skeptical of that but he was very forward leaning on this.