Richard Fork

Richard Fork

University of Alabama Huntsville

Title: Asteroid redirection using synchronized femtosecond pulse trains


Richard Fork received a PhD in Physics from MIT in 1962, worked as Member of Technical Staff in the Quantum Electronics Department at AT&T Bell Laboratories from 1962 to 1990, was Professor in the Physics Department of Rensselaer Polytechnic Institute from 1990 to 1994 and is currently, 1994 to the present, Professor in the Electrical and Computer Engineering Department at University of Alabama in Huntsville. He has over 150published technical papers listed on Research Gate. These include the original demonstration of laser modelocking as well asa number of the original advances in generation and application of modelocked laserpulses. Inventions include the first optical pulse of 6 femtosecond duration and the colliding pulse laser, which was the first laser operating well into the femtosecond time regime. Grant Bergstue is a PhD student in the Electrical and Computer Engineering Department at University of Alabama in Huntsville.


We examine use ofmultiple synchronized trains of energetic femtosecond duration optical pulses to redirect an asteroid discovered on short notice on collision course with Earth. We find such delivery,entirely in the vacuum and microgravity of space canclosely approach the maximum possible efficiency of redirection. Such efficiency would not be possible, e.g., in the atmosphere of Earth. This optimal application of the redirecting energy is, however, still challenging. One demanding requirement is precision of both location and timing of multiple ablation events usinga minimum of three simultaneous delivered energetic femtosecond optical pulses for each ablation event. Another challenge is undesirable loss in optically absorbing ejecta generated by the focused optical pulses. These ejecta are an inherent complication of the ablative propulsive event.We find this source of loss, however, appearslargely avoidable by use of a combination of sufficiently short duration optical pulses and optimal timingand positioning of deliveryevents.In addition the average number of ablative propulsive events per unit time, which must be precisely timed and positioned, is large. We suggest,while such an engineering task appears extremely demandingit canbe achievedusing currently evolving means of delivering large numbers of femtosecond pulses per unit time. We consider specifically the problem of redirecting a 10,000 metric ton asteroid such as struck Earth near Chelyabinsk, Russia in 2013. We find, e.g.,four months of precisely delivered optical energy at 10 kW average power could, at least in principle, have entirely prevented that collision.

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