Домашнее чтение, перевод №2, страницы 1-3. (Некоторые готовые переводы и другие ДЗ), страница 3

The resistive grid with the Ticer material proved tobe stable at room temperature over a one week period. The test was conducted with the panel in a thermal chamberto prevent the resistive grid from being exposed to uncertain room temperature and humidity changes.

The resistanceof the grid was sampled at one minute intervals over the course of a week. This test was carried out multiple timeswith the same results. A Duroid board with Ticer resistive material was then coated with parylene to see if roomhumidity was causing small jumps in resistance that had been observed at constant temperature but it did not help.At the same time it was determined that the Duroid 6002 board and several other candidate materials failed in thehypervelocity impact testing.

If the boards contained any fibrous material, such as in the FR4 board material, theywould shred upon impact at near orbital speeds causing an inconsistent breakage of resistive lines. Tearing of the6American Institute of Aeronautics and AstronauticsTicer resistive layer would occur any time that an adhesive layer was used to bond it to any additional substratewhen it was impacted by a hypervelocity particle at the UoK.The Ticer resistive material without parylene coatingproved to maintain constant resistance at a constanttemperature. However, the material did not meet its 0.25 ohmobjective over the anticipated 140°C orbital variation oftemperature. The differential resistance measurement willminimize the effects of temperature changes, giving the usersthe capability to verify an impact from the acoustic sensors.To eliminate temperature effects, there will need to be atemperature sensor on the resistive grid on DRAGONS.A unique finding in the hypervelocity facility test chamberin the UK has shown that debris traveling at 5 km/s will createa nearly perfect circle in the Duroid 6002 resistive board, witha diameter proportional to the velocity of the debris, as well asthe material and size of the particle.

At low speeds (30 m/s)we have determined that the signal amplitude is directlyFigure 9. Hyper-velocity impact.proportional to particle momentum. At high speeds (5 km/s)the relationship is more complex and depends on particle size rather than mass. Figure 9 shows an impact from a1mm stainless steel sphere at 5.02 km/s. Particles of different size and materials will provide the data needed todetermine the dependence of signal waveform on particle size/mass in the speed range near 300 m/s. The USNA isproviding additional data using air rifle speeds to fill in the data gap.VII. ConclusionOrbital Debris is an ever increasing problem and the increased deployment of spacecraft makes thedetermination of the debris environment an increasing important issue.

President Obama’s space policy issued inMay of 2010 addressed orbital debris and included a call for international cooperation to eliminate space debris. TheDRAGONS mission is to prototype a debris assessment instrument that would help determine the population ofparticles too small to be assessed by ground-based radars. Placing the unobtrusive acoustic system on selectedspacecraft would provide a global assessment of the debris environment. This would result in improved debrismodels that would provide a more accurate assessment of the risk from debris and provide spacecraft controllers,when possible, the opportunity to change a spacecraft’s trajectory to minimize risk from debris.

The DRAGONSinstrument is undergoing system level test that should be completed in the summer of 2011. Subsequent to this, it isanticipated that it will be manifested on a spacecraft by the Department of Defense Space Experiments ReviewBoard as a proof of concept mission.References1. United States Space Command http://www.au.af.mil/au/awc/awcgate/usspc-fs/space.htm2. NASA Orbital Debris Quarterly News. Volume 12, Issue 1, January 2008.http://www.orbitaldebris.jsc.nasa.gov/newsletter/pdfs/ODQNv12i1.pdf3. NASA Orbital Debris Office http://orbitaldebris.jsc.nasa.gov/faqs.html#37American Institute of Aeronautics and Astronautics.