"Russian venture capitalist Yuri Milner, along with physicist Stephen Hawking, has announced a $100 million initiative for exploring Alpha Centauri, the star system nearest to our own. The new project is called Breakthrough Starshot, and the goal is to explore the technologies needed to create small, light-powered spacecraft capable of reaching Alpha Centauri in just 20 years. The project will be led by Pete Worden, the former director of NASA's AMES Research Center. Facebook founder and CEO Mark Zuckerberg will join Hawking and Milner on the project's board of directors." --Might be nice if we can do some analysis on the back of an envelope showing that this entire fantasy is a total crock with zero hope. Allegedly the spacecraft would mass about 1 gram, consist of a small but amazing instruments and brain ("cameras, photon thrusters, power supply, navigation and communications equipment"), plus a light sail up to a few meters in diameter but only 3-1000 atoms thick. Accelerated by light pressure from huge lasers (located on the moon? some high altitude location on Earth?) to reach speed 0.2c. The lasers would be 1 km diameter. Supposedly that whole acceleration to 0.2c will take only a "few minutes." Flock of several thousand of them launched simultaneously by rocket, but only 1 is accelerated to relativistic speed at a time. How does it communicate back to us after reaches alpha centauri? Little or no idea. http://www.sci-news.com/space/breakthrough-starshot-plan-alpha-centauri-0378... OK, here are a few calculations: Mass of sail 1000 angstrom thick, 10 meter^2 area, density of water: 1 gram. Kinetic energy of 1 gram at 0.2c: 1800 giga joules = 0.5 gigawatt hours. Can that much intelligence and sensory capability be done in 1gram? A large butterfly weighs a fraction of a gram and has eyes, navigation good enough to take it to one particular place in Mexico, brain, senses, thrust. So, maybe. Acceleration needed to reach 0.2c in 3 minutes: 34000 gees = 333000 meter/sec^2 which is about the same as a bullet experiences inside a pistol or rifle. For a 1 gram mass this is a force of 333 newtons. Tensile strengths: kevlar 3*10^8, steel 4*10^8, graphene 10^11 (all in pascals). So a 1000 angstrom thick film 1 meter wide with those strengths could pull 30-10000 newtons without breaking. Light pressure: A pressure of 100 newtons/meter^2 = 100 pascals on a reflective mirror, is achieved with beam power 30 gigawatt/meter^2. Lasers: wikipedia says "The AN/SEQ-3 Laser Weapon System or XN-1 LaWS is a directed-energy weapon developed by the United States Navy. The weapon was installed on USS Ponce for field testing in 2014... it generates (up to) 33 kWatt in testing..." a picture suggests the aperture diameter is about 2 feet, i.e. less than 1 meter. Allegedly the Navy claims it works well enough either as a weapon or in reverse as a telescope, that they want to keep it. So... looks like the laser beam intensity is a major problem for "starshot." Factor of a million short. I also have a hell of a big problem seeing how it could tell us anything from alpha centauri. There is some suspicion there are 1 or more planets orbiting one of the three alpha centauri stars, but so far that is unconfirmed. If we cannot even detect a freaking planet, then hard to detect communications from a tiny spaceprobe. If the power source was solar, then the probe will be within 1 AU of alpha centauri star for a total timespan of about 1.5 hours given its 0.2c speed. Even if it were capable of sending 1 bit per second (which seems to me incredibly optimistic) that'd be under 5 kbits total; I personally doubt (based on extrapolation of known bitrates from known spaceprobes), that it could send us even 1 bit ever. Actually perhaps the best try to send us 1 bit would be, if possible, to intentionally ram the spaceprobe into an asteroid so we could try to detect resulting explosion, which would be about 0.4 kilotons in nuclear weapons terminology. -- Warren D. Smith http://RangeVoting.org <-- add your endorsement (by clicking "endorse" as 1st step)