Project Starswarm
However:
1. Sending just 1000 probes strikes me as fatally timid. We should be thinking in terms of millions of identical probes. Manufactured in volume, the price each drops to near nothing. Volume makes custom chips practical. The entire probe could have just one chip plus a couple of capacitors and coils.
2. Launching just one swarm would be foolish. Having built the solar-pumped launching laser, we have no reason to turn it off. Keep launching probes throughout the life of the mission. Over the course of 20 years, you could launch 1000 each week, or more: 10,000. 100,000. Each having accelerated to cruising speed, it turns to fly edge-on, minimizing collision risk.
3. There is no value in having probes lined up in a plane as they arrive at the destination. A dispersed cloud of a million probes flying through continuously for 20 years offers enormously greater value.
4. Probes will spend almost all their time close to zero K. This creates design opportunities not available to most projects. A powerful, static magnetic field would help deflect charged cosmic rays, and aid in attitude control, operating against the galactic magnetic field. The reflector might be an atomically thin wafer of superconductor, providing perfect reflection at any long-enough wavelength, stiffened by its own field.
5. Trying to transmit data home via laser would be a monstrous mistake: the star behind the probes interferes with any optical signal. Furthermore, at optical frequency, phased-array transmission by groups of probes is impossible. But at ordinary radio frequency, a swarm may be at random places relative to one another, yet able to transmit as as a phased array with no difficulty, having triangulated their relative positions and synchronized to a pilot signal from home. Similarly, receivers may be situated at thousands of points throughout the asteroid belt, and remain synchronized to operate as a phased array simply using atomic clocks (as was used to image M87).
6. There is no need for probes at the destination to transmit data all the way home. They need only send to the next swarm coming up a light-day behind, which may relay data to the next.
7. Upon approaching the destination, the swarm may orient to concentrate incoming laser light and/or destination starlight on a few, selected probes to slow them down. The rest continue accelerating and diverging from the destination, while the target probes slow enough to enter orbit. Subsequent swarms flying through can help them alter their orbit as needed, with the occasional other probe joining them.
8. The launch laser may be a simple laser cavity pumped with sunlight reflected from an array of monochromatic mirrors ranged around it, with no conversion loss. A 100GW laser needs 2B square meters of such mirrors each reflecting (say) 50W out of 1300W incident. Pumping with monochromatic light minimizes need for cooling. Monochromatic mirrors are easily produced by depositing alternating layers of transparent material with different dielectric constant but identical thickness. But the alternative of launching with an array of masers, instead, should be entertained. Masers are much more easily constructed and operated.
9. Probably the laser/maser should be located on the opposite side of the sun, or beyond the far side of the moon, for security. Being able to point it at Earth from too nearby could be seen as a latent threat.
Can this be improved upon?