Laser propulsion system performance requirements for single-stage to GEO launch

This paper gives a discussion about the laser propulsion system performance requirements for optimal vertical ascent to the geosynchronous earth orbit (GEO) with both dynamic pressure and thrust acceleration constraints imposed. The performance index is to minimize the final mass. In other words, the propellant consumption is to be minimized. The acceleration due to the thrust is limited to 2,5 times of the gravitational acceleration at the Earth's surface. The dynamic pressure is limited to the maximum allowable level for space shuttle ascending flight. It is found that for the final mass to be 10% or more of the initial mass, the specific impulse must be 1500 s or larger. The total efficiency of the laser propulsion system is the product of three efficiencies: the transmission efficiency which expresses the atmospheric absorption of the laser energy, the diffraction efficiency which expresses the laser beam spreading in the atmosphere, and the thruster efficiency. Under the consideration of the total efficiency, the power requirement of the laser system as a function of the flight time is solved. The initial mass of the launch vehicle is selected to be 10,000 kg. Its 10% is 1 ton and is the mass of a proper payload. The peak laser power required is found to be 4.5 GW.