Despite the $100 million Breakthrough Starshot pledge, public accounting shows less than $10 million spending. Philip Lubin (UC Santa Barbara, laser propulsion) received ~$200,000 over eight years. This was less than his NASA grants for similar work. There is an estimate of 30 contracts totaling $4.5 million. Scientists viewed this as a kickstart. Breakthrough’s name lent legitimacy to fringe ideas, attracting matching funds.
Activity peaked in the first 4–5 years (2020–2021). Large/small group meetings identified hurdles (gigawatt-scale lasers) and issued small grants. In the last 2–3 years, funding dried up, meetings ceased, and communications quietly went away leaving.
It normalized interstellar travel as feasible goal. There was also a recognition that the cost would be far more than $100 million.
Scoles pieced together nine years of patchy progress for Breakthrough Starsot.
Lightsail Materials: At Caltech, Harry Atwater’s team explored silicon nitride for ultra-thin (gram-scale, 4m-wide) sails enduring 40,000 Gs and 100 gigawatts of laser power—a novel materials challenge. They made small-scale prototypes showing promise but hadn’t built a full sail.
Spacecraft Design: Zach Manchester at Carnegie Mellon discussed his chip-sats—tiny satellites launched to Earth orbit—as a prototype for Starshot’s nanocraft.
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This was always dumb. Just build bigger space telescopes if you want to image nearby exosolar planets more clearly.
Agree
Sending a gram of matter to another star system at great cost….
No wonder nothing happens. It has no use.
It would be breakthrough enough just to be able to manipulate orbits of satellites, deorbit junk or beam energy. Start with a minimally viable product.
And it was a shame that they didn’t see it all the way through.
Beam powered systems are scalable in ways that other interstellar propulsion systems aren’t. Even if the system only start off with 100 GW, over time it can be built up to 1 TW, then 10 TW, and so on. Which leads to my next point: the end of the interstellar mission dilemma.
It goes like this: If someone launches an interstellar mission to Proxima Centauri with the most advanced propulsion system that is possible, the lithium gridded ion thruster, which works similar to a regular ion thruster only it’s using the much lighter element lithium to propellant rather than xenon. With an exhaust velocity of ~500 km/s or 0.17% the speed of light and assuming a total mass to empty mass ratio of 7.3 to 1 (which means a total delta-v 2× the exhaust velocity), an interstellar colony ship would cover 1 light-year per 600 years or about 2500 years to reach Proxima Centauri (acceleration time not included).
Two hundred years after the trip starts, someone develops a fission-fragment rocket that can travel 1% c or one hundred years per light year or 6 times faster. Despite the 200 year head start, the fission-fragment rocket catches up with the lithium ion rocket in 40 years. But then, a century later after that, someone develops a D-He3 rocket that can travel at 8% c. It will take a century for the fission-fragment rocket to cover what the D-He3 rocket can cover in less than 13 years and the D-He3 will reach Proxima in less than 60 years….assuming that such a rocket is ever built.
That is the dilemma of leaving Earth for another star system. The technology to reach that star could be there in a century…or a millennia…or even never. Just as an example, the interstellar medium could have so much material in it that going too fast will result in massive erosion from interstellar dusk or even a catastrophic collision.
A beam propulsion system that can push objects to the maximum limit allowable by physics that starts off pushing small objects and then those objects increase in size as the system scales up makes this dilemma a non-issue. Start off without small probes. Maybe they solve the problem of gram-size probes transmitting useful information or maybe they decide that the useful information is not images of another star system but data on the interstellar medium and erosion rates of low relativistic objects. Then they move up to 10 grams, then 100, then in the kilogram range. Then to the range of metric tons. By the time the system can handle colony ships, there is no fear that the next big breakthrough will make the up and coming mission pointless. And if the interstellar medium is too cluttered by debris to travel at speeds faster than 1% c, then the mission duration is better understood and there can be no high-risk of there being a faster mission overtaking any in the near term.
Even if Breakthrough Starshot couldn’t provide useful data from all the way to the nearest star system, it would be a great precursor and a way to determining spacecraft survivability in interstellar space traveling at low relativistic speeds.
You’ve correctly identified what interstellar colonization enthusiasts call the “Far Centaurus” problem, after the SF story of that name: If you leave on the slow boat, the fast boat leaving later beats you there.
There isn’t a lot of sense to launching interstellar missions until you can go fast enough to be reasonably confident that won’t happen. Or simply don’t care, because your actual destination is “not here”, you’re flying a generation ship just to get some privacy.
I think the interstellar erosion problem is better characterized than you believe: We can put a ceiling on the density of the interstellar medium simply by the fact that we can see distant stars, and the medium between us and them isn’t undergoing gravitational collapse.
This doesn’t rule out having really bad luck, and hitting a rare pebble in interstellar space, but we can be pretty confident that the average interstellar trip is only going to encounter gas molecules and small dust particles, and a very low density of those.
Of course, at the necessary speeds, you encounter those as high energy particle radiation, even the dust particles are just very tiny and intense radiation bursts, they’re traveling too fast to interact with as solid objects.
I don’t think the precursor missions need to characterize the interstellar medium, so much as test defense strategies.
Incidentally, there’s a reason you use Xenon instead of Lithium. Aside from the fact that Lithium, being chemically active, would attack your grid.
In order to accelerate the ions, you have to ionize the neutral atoms first. The energy that goes into ionizing them doesn’t contribute anything to the thrust, it’s wasted. Neutral atoms launched at the same speed would provide just as much thrust, it’s simply that you don’t have a convenient ‘handle’ to accelerate them by, so you ionize them to provide that “handle”.
Lithium requires 520 kj/mole to ionize, Xenon 1170, but a mole of Li is only 7 grams, a mole of Xenon is 131 grams. So it takes 12% as much energy to ionize a kg of Xenon.
Mind you, if you were using ion engines for interstellar purposes, you’d be dumping so much energy into accelerating the ions that the actual ionization energy would be an afterthought, but that’s the reason. For interstellar purposes you’d probably use neither Lithium nor Xenon, but instead an ionic salt; The ionization cost is trivial, they’re conveniently liquid with negligible vapor pressure over a huge temperature range. Not an ion engine but a hyped up electrospray engine. Powered, I assume, by beamed energy.
But, realistically, using current tech, you’d use an Orion drive for anything that big. Trying to accelerate a manned interstellar craft using any sort of ion engine would be just too awkward.
And an Orion is potentially capable of enough speed to escape the Far Centaurus problem, too!
I guess we’re really due for another discussion of real world propulsion systems for interstellar craft.
Technologically premature, but the primary problem is that nobody saw a plausible way that a probe that small could ever send any data back.