Latest Progress Towards Laser Pushed Solar Sails

Philip Lubin has led a team at UCSB to create laser arrays for propulsion and asteroid deflection. He has received NASA and Starshot funding. There have 100 students in his programs. They have created hardware components and performed various experiments.

The DE-STAR (Directed Energy System for Targeting of Asteroids and ExploRation) has several sizes. DE-STAR-1 is 10 meters on a side, DE-STAR-2 is 100 meters on a side, DE-STAR-3 is 1000 meters on a side and DE-STAR-4 is 10,000 meters on a side.

A full-scale DE-STAR 4 (100GW) will propel:

* a wafer-scale spacecraft with a 1 meter laser sail to about 26% of the speed of light in about 10 minutes (20kgoaccel)
* a wafer craft could reach Mars (1AU) in 30 minutes
* a wafer craft pass Voyager I in less than 3 days
* a wafer craft could pass 1,000 AU in 12 days and
* a wafer craft reach Alpha Centauri in about 20 years.

After a few minutes of laser illumination the wafers are launched. This allows hundreds of launches per day or 100,000 missions per year.

The same directed energy driver (DE-STAR 4) can also propel
* a 10 kg payload to 2.5% of light speed
* a 100 kg payload to about 1% of light speed and
a 10,000 kg payload to more than 1,000 km/s.

Systems in Earth orbit, Mars and the moon could accelerate and decelerate solar sail craft.

There are very large economies of scale in such a system in addition to exponential pho-tonics growth. The system has no expendables, is completely solid-state and can run continuously for years. Industrial fiber lasers and amplifiers have a mean time between failures (MTBF) in excess of 50,000 hrs. The revolution in solid-state lighting, including up-coming laser lighting, will only further increase the performance and lower the cost.

They have already achieved 43% wall-plug efficiency in our lab with efficiency limited by the pump diode efficiency. New diode designs promise ever higher efficiencies and allow full system amplifier efficiencies greater than 50% in the near future. The same basic system can also be used as a phased array telescope for the receive side for laser communications, as well as for future kilometer-scale telescopes for specialized applications such as spectroscopy of exoplanet atmospheres and high redshift cosmology studies.

Reducing the reflector thickness from 1 micron to 0.35 nm (single layer graphene) would increase the speed by (1000/0.35) 1/4 ∼7.4 in the non-relativistic limit. Such a reduction in reflector thickness would also allow the product of photon driver power and size (P0d) to be reduced by a factor of (1000/0.35)1/2 ∼53.

Mass Ejection Thrusters

Miniature ion engines are emerging, which may allow a near term option for even wafer-scale systems. For example, single tip electrospray thrusters are compatible with wafer-scale fabrication and could be effectively used for maneuvering during the cruise phase. With Isp in the 2000-4000 s range these would allow significantly more attitude and transverse maneuver controls than the baseline photon thrusters for the same power level. The amount of ejection mass needed is small compared to the system mass, and thus they are an attractive alternative, as they are vastly more energy-efficient for the same momentum transfer (ratio of Isp).

There is a NASA NIAC looking at 50,000 ISP lithium-ion propulsion.

There is a 2020 Path to Interstellar Flight article in the ESA Acta Futura.

There was a recent presentation at the TVIW (Tennessee Valley Interstellar Workshop).