Hi All

The article from "Nature" that the report comes from assumes NEP ion-drive propelled space-probes doing a measly ~ 0.001 c. However if 300 km/s is enough, as they assume, then a nanotube solar-sail on a solar fry-by or a magnetic-sail using the solar-wind should be enough to launch and deccelerate the message vehicle. Either system will do and neither is as heavy or complex as an NEP.

Also the system assumes that guarding against cosmic-rays will require a lot of cladding, but the cosmic-ray exposure is largely due to the excessive trip time they assume. Speeds of 0.01 - 0.1 c are achieveable via laser or particle-beam pushed variations on the propulsion systems I mentioned and are potentially more energy efficient than rockets if the probe mass can be reduced thanks to lower shielding.

Solar-sail probes capable of ~ 300 km/s are easy. Solar sails hitting ~ 3,000 - 30,000 km/s are extreme, but also distinctly possible. If so, then there is NO energy cost to the message-senders since stars squander their energy stores heedless of any "costing"... so why not tap some tiny fraction of that torrent? Messages could be sent to every star in the Galaxy then...

Adam