Megawatt beam propulsion by 2023 and Gigawatts by 2030

Billionaire Yuri Milner is spending $100 million to work out the technology for ground based laser based beam propulsion for interstellar travel.

California Polytechnic State University researchers propose a 100 kilowatt space based laser system capable of probing the molecular composition of cold solar system targets such as asteroids, comets, planets and moons from a distant vantage. This system uses existing technology and only some needs refinement. All of it looks achievable in the next 3 to 5 years. They have NASA NIAC funding. They have detailed designs for a 900 kilowatt system that would use two Falcon heavy launches.

The military laser segment will be about a $5 billion per year market by 2020. There is a large multi-billion commercial laser market. Those markets will drive improvements in laser efficiency and technological improvements which will be leveraged for space based systems or ground based lasers for space beam propulsion applications.

University California Santa Barbara looked at sail mass and speed pushed by a 100 GW laser

UCSB has looked closely at issues for what Milner is proposing and have produced a roadmap for interstellar beam propulsion.

1 gram     24% of lightspeed
10 grams   14% of lightspeed
100 grams   7.8% of lightspeed
1 kg        4.3% of lightspeed 
10kg        2.4% of lightspeed
100kg       1.4% of lightspeed
1000kg      0.77% of lightspeed
10 tons     0.43% of lightspeed
100 tons    0.24% of lightspeed

Milner is probably looking at less than 10 grams and about 2-4 GW ground based laser array.

UCSB Operational Maturation and Steps from their laser pushed sail roadmap:

Step 1 – Ground based – Small phased array, beam targeting and stability tests – 10 kw
Step II – Ground based – Target levitation and lab scale beam line acceleration tests – 10 kw
Step III – Ground based – Beam formation at large array spacing –
Step IV – Ground based – Scale to 100 kW with arrays sizes in the 1-3 m size –
Step V – Ground based – Scale to 1 MW with 10 m optics –
Step VI – Orbital testing with small 1-3 class arrays and 10-100kw power – ISS possibility
Step VII – Orbital array assembly tests in 10 m class array
Step VIII – Orbital assembly with sparse array at 100 m level –
Step IX – Orbital filled 100 m array
Step X – Orbital sparse 1km array
Step XI – Orbital filled 1 km array
Step XII – Orbital sparse 10 km array
Step XIII – Orbital filled 10 km array

Spiderfab is application of robotics technology in orbit for assembly of lightweight but large in area structures.

Going from the 30 meter solar array pairs that generate 450 kilowatts to one kilometer across solar arrays where a pair generates a gigawatt is what Spiderfab will enable.

Spacex rocket reusability has emerged in prototypical form now with safe landing of rocket stages. Fully reusable rockets will drive down the cost of space launches by ten to one hundred times.

Improving and testing reliability and a lot of engineering would be needed to get to 100 kilometer structures.

The lasers do not need to become giant death ray lasers ala the Star Wars Deathstar. All that is needed is continuing improvement in laser efficiency (to reduce or control heat radiation requirements) and assembling laser elements into larger and larger arrays which all can be targeted with precision.

Making 6U cubesat trusselator to put out 50 meter trusses and make truss of trusses from several

They are using Baxter robot to work with trusselators.