I wonder if it could unfurl a light sail when it got most of the way there to slow it down. Is that feasible?

Interesting idea, but I don't think the sail would be nearly enough to counteract the gravitational acceleration caused by getting near the target system, let alone losing enough speed to enter an orbit.

>> Each spacecraft would be the size of a DVD disc

Not much room for a light sail large enough to fully offset the power of the launch lasers.

In short: no. It'd need to slow down enough to counter-act years worth of a laser specifically making it go faster. Without a laser on the other end, really no shot.

Regardless of travel speed, it would take a lot of energy to get matter or even any identifiable bits of data back from Alpha Centauri to here.

I don't see any discussion of how they propose to tackle that problem.

It is never even hinted how any information could ever be communicated back to Earth.

It makes me think the whole project is not serious, like launching Voyager with no Deep Space Network to listen.

Are they hoping that over the 40 years it takes to get there, a solar-system-sized radio telescope would be built to listen? Even with that it is implausible.

IIRC the idea is to send a chain of probes at regular intervals, and the probes would relay signals back along the chain.

So, even less plausible than a solar-system-sized radio telescope.

According to https://en.wikipedia.org/wiki/Breakthrough_Starshot#Laser_da..., the probes should be able to talk to a 30-meter telescope on earth using lasers. The data rates are very low, of course, but that can be handled by making sure the probe has enough storage for its few-hour-long transit of the system and then transmitting that back over the following months.

How do they get the laser out there? What powers it?

From https://arxiv.org/ftp/arxiv/papers/2005/2005.08940.pdf

> The sailcraft transmits 100 Watts, deriving its power from a 700-Watt hydrogen beam that is normally incident on the sailcraft when it faces Earth. This hydrogen beam is simply a manifestation of the interstellar medium, incident on the sailcraft at 0.2 c.

From https://arxiv.org/pdf/1805.01306.pdf

> One way to tap the sailcraft’s kinetic energy could be via the interstellar medium: The Local Interstellar Cloud is primarily composed of 0.3 atoms/cm3 of partially ionized hydrogen. From the sailcraft’s perspective traveling at cruise velocity, this manifests as a monochromatic hydrogen beam that is incident from the direction of travel, having a combined kinetic energy of 55W m−2, or 0.7 kW over the sail’s area if it faces the direction of travel.

The report for Starlight suggests a RTG:

https://www.nasa.gov/sites/default/files/atoms/files/roadmap...

So you are bombarded by a mix of relativistic hydrogen atoms, molecules, nuclei, and electrons. How do you extract energy from such an influx? Will extracting it slow you down much?

Actually it would vaporize any part of the system needed to control or communicate.

I was thinking the same thing. That part seems like an afterthought. The real interesting part is the laser propulsion.

The answer is to send not one probe, but many (thousands).

If every probe manages to capture and transmit a couple dozen pictures while it is within the interesting range, it adds up.

Also these probes could use each other as relays if we send a long string of them towards one destination.

Yeah. What I’d really like is proposals/discussion around intrastellar travel infrastructure like this. Park sources of light and coms at certain key locations around the solar system to enable faster traffic. Maybe hollow out some larger asteroids for habitats.

as far as comms goes - nothing can speed it up - but yes the idea of using relays makes comms more reliable/repairable

Right, it’s not about speed but the message reliably getting there.

If you are able to determine orbital parameters of planets we'll enough, that would be more than enough time to get much better pictures of exoplanets than any telescope.