Beam propulsion background and Breakthrough starshot update

Beamed propulsion could achieve single stage to orbit.

It could be 6 to 100 times cheaper.

Most of the rocket becomes payload.

DARPA funded developing a heat exchanger for direct energy.
They tested a microwave beam director for a 100KW microwave source.

The Breakthrough starshot update was the cost and engineering system model. This was covered by Nextbigfuture.