Breakthrough Starshot, Moon mining, QB50, Solar Q&A

This week Russian internet billionaire Yuri Milner announced a project to send tiny spaceships to Alpha Centauri. Milner, alongside Stephen Hawking, announced a $100 million project to develop and launch a cloud of spaceships with sails. They'll be powered by giant lasers based on earth, and will fly at one fifth the speed of light. The Breakthrough Starshot project sounds like science fiction - Adam is joined by Professor Andrew Coates from UCL's Mullard Space Science Laboratory to sort the feasible from the fantasy.Space travel is expensive. Scientists and engineers met recently to discuss a way of making it cheaper. Sending men back to the moon to mine it may sound like a hugely costly process, but as reporter Roland Pease discovers, when it comes to future space missions, it might become an essential part of the process.Closer to home than the moon is a section of the atmosphere called the thermosphere that is poorly understood. A European project called QB50 plans to change this, by sending 50 small satellites, known as CubeSats, into orbit this summer. Most of them will sport sensors that can probe the properties of the upper atmosphere. The group building these sensors is led by UCL's Mullard Space Science Laboratory, which will build 14 spectrometers. These will analyse the relative proportions of different types of particles in the thermosphere. Marnie Chesterton finds out how scientists cope with the challenge of building their gadgets smaller and lighter.Many listeners wrote in after a recent piece on solar panels. We had queries about how to store the electricity, and whether PV panels are worth the energetic cost of producing them and what units to use. We put all these questions to Jenny Nelson, Professor of Physics at Imperial College and author of 'The Physics of Solar Cells.'.