Breakthrough Starshot is the Initative to send a probe at 20% light speed (0.2c) to the nearest neighbouring star Proxima Centauri.
But how do we achieve such a high speed?
It turns out that if we have an extremely powerful laser (and exponential advances in tech over the next decades will mean that they will inevitably happen) and project the laser beam onto a space sail, then the momentum of light reflected off the sail will result in thrust.
Note there is NO on-board propellant on the space sail, all the energy for propulsion is stored at the location of the laser itself, which might be at a suitable location on Earth for example.
Such would be the intensity of the beam that a 10 minute 'firing' of the beam would accelerate a 1 gram-scale space sail (or you might call it a laser sail) to the required speed of 0.2c.
I have been working for Breakthrough Starshot on behalf of i4is (the Institute/Initiative for Interstellar Studies) and Robert G. Kennedy III, Marshall Eubanks, Paul Blase, Andreas Hein and I have derived several new innovations and technological advancements which we think will make the Initiative a reality.
1) We use a SWARM of laser sails to accommodate attrition due to any members striking interstellar dust particles. Although these particles are small, nonetheless at 0.2c, the kinetic energy of the particle is enormous and would immediately destroy the laser sail.
2) Our laser sail (pizza plate) will, once accelerated, fly edge-on to the interstellar medium (ISM), thus reducing the surface area presented by the laser sail and minimising the chances of a collision with a dust particle.
3) Flotillas of laser sails will be shot off from Earth at intervals of 10 mins, allowing say 10 sails per flotilla. After an Earth day has ellapsed, alignment with the target - Proxima Centauri - will return at which point we shoot off another flotilla, with SLIGHTLY MORE VELOCITY than the first flotilla. This so-called 'gross modulation' of the laser sail velocities will allow sail members at the back of the swarm to eventually catch up with those at the front, this is known as T o T = Time on Target.
4) There is the further issue of ensuring that the swarm eventually coallesce, in other words present a concerted front to the target which will be Proxima b (an exoplanet known to orbit Proxima Centauri). For this we need them to have an identical velocity (V o T = Velocity on Target). We have devised a clever scheme to achieve this and that is to exploit the ISM (which is largely composed of hydrogen, hydrogen ions and electrons) and use it as a device to slow down laser sails travelling faster so that they match speeds with the slower ones. You see the ISM, is actually acting as DRAG on the laser sails, so by pitching the edge-on laser sails, they will present more cross-section to the ISM and slow down more. This is similar to tacking with boat sails on Earth.
5) A power source has been identified which would be IDEAL for supplying our little interstellar probes, and that is the isotope Strontium 90 in a betavoltaic power supply.
6) To send results back to Earth from the huge distance of Proxima requires an accuracy and operational power which would ostensibily seem beyond the scope of a single laser sail. However we have discovered that with a SWARM of laser sails, they can send a stream of individual photons back to Earth which are coherent across the SWARM, thus with precise atomic clocks, the photons from each sail will arrive at Earth at the same time and can then be more readily detected by a suitable sensor array.
There are other innovations which I shan't go into, but there is one problem which needs to be addressed and the paper articulates - that is the problem of predicting the precise location of the exoplanet PROXIMA B, 20 years (the flight duration) ahead of time to within sufficient accuracy.
Go to an animation of the 2D trajectory here: