Comparison of ablation performance in laser lightcraft and standardized mini-thruster

Sean D. Knecht, C. William Larson, Franklin B. Mead

Research output: Chapter in Book/Report/Conference proceedingConference contribution

10 Scopus citations


Experiments on laser ablation of black and white Delrin® with a 10.6-micron laser beam from a CO 2 electric discharge laser are reported. Mass ablation and thrust generation (impulse) were accurately measured as a function of input laser energy in single-shot experiments. The efficiency of conversion of laser energy to jet kinetic energy depended on the geometry of the energy absorption/conversion zone. The standard geometry, an axisymmetric mini-thruster with 13-degree conical half angle and 8:1 expansion ratio, produced ∼65 % conversion efficiency. The extensively-studied 10-cm focal diameter Lightcraft (with inverted paraboloid, plug-nozzle geometry) produced ∼50% conversion efficiency. The upper limit to energy conversion was theoretically computed with a one-dimensional chemical equilibrium code to be 73% for the well-defined mini-thruster geometry. Thus, total losses amount to ∼8% in the mini thruster and ∼23% in the Lightcraft. In these experiments a near-exact match of coupling coefficients, ∼1%, was achieved in a 14-fold scale-down of the 10-cm focal diameter Lightcraft to the mini-thruster. These results helped validate the concept of "momentum calorimetry" in which heats of formation of energetic propellants are obtained by measurement of the momentum of the jets they produce when they are ablated with known laser energy. The performance of chemically-enhanced laser ablation propellants or other solid propellants may be inexpensively measured on a small scale. A matrix of impulse measurements, ablated mass, laser energy and plume absorptivity was carried out with various mini-thruster expansion ratios and chamber geometries.

Original languageEnglish (US)
Title of host publicationBEAMED ENERGY PROPULSION
Subtitle of host publicationFourth International Symposium on Beamed Energy Propulsion
Number of pages13
StatePublished - May 2 2006
EventBEAMED ENERGY PROPULSION: Fourth International Symposium on Beamed Energy Propulsion - Nara, Japan
Duration: Nov 15 2005Nov 18 2005

Publication series

NameAIP Conference Proceedings
ISSN (Print)0094-243X
ISSN (Electronic)1551-7616


OtherBEAMED ENERGY PROPULSION: Fourth International Symposium on Beamed Energy Propulsion

All Science Journal Classification (ASJC) codes

  • General Physics and Astronomy


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