3ks Specific Impulse with a ns-pulse Laser Microthruster
Abstract
Photonics developed a prototype device which demonstrated the feasibility of using ns-duration laser pulses in a laser microthruster. Using several metallic targets driven by a "microchip" laser, thrust, specific impulse Isp, specific ablation energy Q* and ablation efficiency were measured. Specific impulse was adjusted by varying laser intensity on target. In this way, researchers were able to vary specific impulse from 200s to 3,800s on gold, with corresponding momentum coupling coefficient Cm varying from 70 to 7 micro-N/optical watt and ablation efficiency near 100% at a 1 MJK/sq m optimum pulse fluence. Simulations of the laser-target interaction are discussed, which agreed well with the results obtained on metallic fuel systems. A Concepts Research, Inc., microchip laser was used with 170mW average optical power, 8kHz repetition rate and 20 micro-J pulse energy for many of the measurements. Thrust was in the 100nN - 1 micro-N range for all the work, requiring development of an extremely sensitive, low-noise thrust stand, which is discussed in a companion paper. The design of realistic metallic fuel delivery systems is discussed. Also reported are time-of-flight measurements on ejected metal ions, which gave velocities up to 80km/s. Near the optimum fluence, good agreement was found between Isp deduced from the CmQ* product and from ion velocity v(sub-i). Strong divergence was observed between these two parameters at higher intensity. Relative to the ms-duration thrusters which have been demonstrated in the past, this change offers the use of any target material, the use of more-efficient reflection-mode target illumination, and specific impulse adjustable to match the mission.
Document Details
- Document Type
- Technical Report
- Publication Date
- Aug 23, 2005
- Accession Number
- ADA444975
Entities
People
- Claude Phipps
- James R. Luke
- Wesley D. Helgeson