28,638 research outputs found
Thermal Control Working Group report
The Thermal Control Working Group limited its evaluation to issues associated with Earth orbiting and planetary spacecraft with power levels up to 50 kW. It was concluded that the space station technology is a necessary precursor but does not meet S/C 2000 needs (life, high heat flux, long term cryogenics, and survivability). Additional basic and applied research are required (fluid/materials compatibility and two phase system modeling). Scaling, the key issue, must define accelerated life test criteria. The two phase systems require 0g to 1 g correlation. Additional ground test beds are required and combined space environment tests of materials
Metal etching composition
The present invention is directed to a chemical etching composition for etching metals or metallic alloys. The composition includes a solution of hydrochloric acid, phosphoric acid, ethylene glycol, and an oxidizing agent. The etching composition is particularly useful for etching metal surfaces in preparation for subsequent fluorescent penetrant inspection
Exceptional covers and bijections on rational points
We show that if f: X --> Y is a finite, separable morphism of smooth curves
defined over a finite field F_q, where q is larger than an explicit constant
depending only on the degree of f and the genus of X, then f maps X(F_q)
surjectively onto Y(F_q) if and only if f maps X(F_q) injectively into Y(F_q).
Surprisingly, the bounds on q for these two implications have different orders
of magnitude. The main tools used in our proof are the Chebotarev density
theorem for covers of curves over finite fields, the Castelnuovo genus
inequality, and ideas from Galois theory.Comment: 19 pages; various minor changes to previous version. To appear in
International Mathematics Research Notice
Design and Performance Estimates of an Ablative Gallium Electromagnetic Thruster
The present study details the high-power condensable propellant research being conducted at NASA Glenn Research Center. The gallium electromagnetic thruster is an ablative coaxial accelerator designed to operate at arc discharge currents in the range of 10-25 kA. The thruster is driven by a four-parallel line pulse forming network capable of producing a 250 microsec pulse with a 60 kA amplitude. A torsional-type thrust stand is used to measure the impulse of a coaxial GEM thruster. Tests are conducted in a vacuum chamber 1.5 m in diameter and 4.5 m long with a background pressure of 2 microtorr. Electromagnetic scaling calculations predict a thruster efficiency of 50% at a specific impulse of 2800 seconds
- …