SAC Seminar - Philip Lubin: Prospects for Directed Energy Planetary Defense
Oplysninger om arrangementet
Speaker: Philip Lubin, Physics Department, University of California, Santa Barbara, CA, USA
Abstract: Our planet is bombarded daily by about 100 metric tons/ day of asteroid and meteoritic debris which normally burns up harmlessly in the upper atmosphere. Occasionally we are hit by an object large enough to penetrate to low enough altitudes to do significant harm as we saw last year in Russia. Historically such events have played a large role in the evolution and extinction of a number of species. It is inevitable that large scale destruction will occur again if nothing is done to mitigate it. The consequences of doing nothing are extremely dangerous over long periods of time. Yet even over the span of a human lifetime an event with energy deposition comparable to that of strategic nuclear weapons is not atypical. I will discuss the threat as well as possibilities for using directed energy as a possible means of both a medium and long term mitigation strategy. The same type of system is capable of a number of other uses, beyond including planetary defense, such as space debris removal, photon driven propulsion allowing relativistic probes and interstellar and intergalactic communications and beacons. Recent developments in photonics allow such a system whereas even a decade ago it would have been simply science fiction. While a very difficult engineering challenge no technical miracles need be invoked (except for funding). The generic system is called DE-STAR for Directed Energy Solar Targeting of Asteroids and exploRation. DE-STAR is an orbital modular phased array of lasers, powered by the sun. Modular design allows for incremental development, test and initial deployment, lowering cost, minimizing risk and allowing for technological co-development, leading eventually to an orbiting structure that could be erected in stages. Ground based variants are also be possible but atmospheric perturbations severely limit this with currently known adaptive optics techniques. The main objective of DE-STAR would be to use the focused directed energy to raise the surface spot temperature of an asteroid to ~3000K, allowing direct evaporation of all known substances. Targets with volatiles, such as comets, require much lower effective temperatures and hence fluxes. The system is completely scalable and being modular allows for systems from small size (sub meter class) that could be used on a dedicated mission spacecraft that would rendezvous with a threat to a large system that is a completely standoff unit capable of deflecting all known threats with mitigation starting beyond 1 AU. I will discuss both approaches. The system is inherently multi tasking allowing for simultaneous multiple target engagement and multiple use if needed. A large baseline system, suitable for full planetary defense is also capable of propelling a 10,102, 103, 104 kg spacecraft to 1 AU in 1,3,10,30 days with speeds (for a 102 kg robotic craft) of about 0.4% the speed of light when used in a “photon rail gun mode”. Such speeds exceed the galactic escape speed. The same system will propel a 102 kg probe to 2% the speed of light when propelling a spacecraft out to 30 AU after which the spacecraft will coast and will reach 3% c with continued illumination. The same system can also be used for communications out to extremely large distance. For example all the known Kepler planets would see the DE-STAR beacon as the brightest star in the sky (assuming their sky is like ours). The system is also easily visible at intergalactic distances (Andromeda for example) and indeed two such systems could "see each other" across the known universe. This brings up the question of a visible/ IR SETI search that I will discuss along with their implications. Smaller versions of this same system are immediately useful and can be built now. For example, a DE-STAR 1 (10m size array) would be capable of evaporating space debris at distances up to 104 km away (~ diam of Earth) while a DE-STAR 2 could begin diverting volatile-laden asteroids/ comets that are 100m in diameter by initiating engagement at ~0.01-0.5AU. Other applications we have studied include active asteroid illumination searches and remote composition analysis of the ejected plume my molecular absorption spectroscopy and down linking power to the Earth via millimeter or microwave. Most of the core technologies now exist and small systems can be built to test the basic concepts as the technology improves.