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National Aeronautics and Space Administration Orbital Debris Quarterly News Volume 10, Issue 1 January 2006 Collision Avoidance Maneuver Performed by NASA’s Terra Spacecraft Inside... The Terra spacecraft, often referred to as the ignator 1983-063C, U.S. Satellite Number 14222) fl agship of NASA’s Earth Observing System (EOS), would come within 500 m of Terra on 23 October, successfully performed a small collision avoidance GSFC and SSN personnel undertook a more de- Large Area Debris maneuver on 21 October 2005 to ensure safe passage tailed assessment of the coming conjunction. Collector (LAD-C) by a piece of orbital debris two days later. This ac- The Scout debris was in an orbit with an alti- Update ........................2 tion demonstrated the effectiveness of a conjunction tude similar to that of Terra (approximately assessment procedure implemented in 2004 680 km by 710 km), but its posigrade Revision of Space by personnel of the NASA Goddard inclination of 82.4° and different orbit Shuttle Wing Leading Space Flight Center (GSFC) and the plane meant that a collision would have Edge Reinforced U.S. Space Surveillance Network occurred at a high velocity of near- (SSN). The trajectories of Terra ly 12 km/s. By 21 October Carbon-Carbon Failure and its companion EOS space- refi ned analysis of the Criteria Based on craft are frequently com- future close approach Hypervelocity Impact pared with the orbits of indicated that the miss and Arc-Jet Testing ...3 thousands of objects distance was only ap- tracked by the SSN proximately 50 m with Object Reentry to determine if an an uncertainty that Survivability Analysis accidental collision yielded a probability Tool (ORSAT) – is possible. More than of collision on the or- Version 6.0..................4 2600 objects are known to der of 1 in 100. Con- pass through the altitude regime of Terra sequently, a decision was made for Terra to execute Disposal of Globalstar multiple times (sometimes more than two dozen) a collision avoidance maneuver. Satellites .....................5 each day. Terra normally maneuvers a few times each Terra (International Designator 1999-068A, U.S. year to maintain its precision orbit, and the collision Disposal of GPS Satellite Number 25994) was launched on 18 De- avoidance maneuver was designed to serve this same Spacecraft ..................5 cember 1999 on a nominal 6-year mission to moni- function to prevent the waste of precious propel- tor the complex nature of the Earth’s atmosphere lant. A very small maneuver was performed nearly and surface. The nearly fi ve-metric-ton spacecraft two days before the anticipated encounter, ensuring circles the Earth at an altitude of 705 km with an that the Scout debris would pass Terra at a distance orbital inclination of 98.2°. When a conjunction as- of more than 4 km. A post-encounter assessment sessment on 17 October predicted a piece of debris confi rmed that this goal was achieved without dis- from a Scout G-1 upper stage (International Des- ruption to the important Terra mission. ♦ ERBS and UARS Spacecraft Complete Postmission Disposal Activities During October-December 2005, two of Upper Atmosphere Research Satellite (UARS) NASA’s venerable scientific spacecraft were returned valuable environmental data for 21 A publication of decommissioned following the completion of and 14 years, respectively, before their missions The NASA Orbital postmission disposal operations. The Earth were terminated (Orbital Debris Quarterly News, Debris Program Offi ce Radiation Budget Experiment (ERBS) and the continued on page 2 Orbital Debris Quarterly News ERBS and UARS continued from page 1 the atmosphere within 17 years, well in lowered apogee, avoiding any possible im- 9-4, p. 1). compliance with the NASA and U.S. Gov- minent collision threat with ISS. ERBS (International Designator ernment recommendation of not more The final UARS maneuver was per- 1984-108B, U.S. Satellite Number 15354) than 25 years after end of mission. formed on 8 December and was followed had already been placed in a lower altitude UARS (International Designator by vehicle passivation. When UARS even- orbit in 2002, in anticipation of its future 1991-063B, U.S. Satellite Number 21701) tually decays through the orbital regime disposal. This proved to be a fortuitous was still operating in an orbit near 550 km of ISS, routine tracking by the U.S. Space decision because by 2005 the degradation when it began a series of eight maneu- Surveillance Network will help ensure that of ERBS support systems prevented the vers to hasten its fall back to Earth and to any potential collision risk is eliminated, execution of normal maneuvers which passivate the spacecraft as an explosion if necessary via a collision avoidance ma- would further lower the orbit. However, preventive measure. The first six maneu- neuver by ISS. However, such a situation a series of maneuvers in September and vers, conducted between 4 October and 1 is highly unlikely. Hundreds of cataloged October was able to consume the remain- December, were designed to lower peri- objects pass through the ISS altitude re- ing 80 kg of propellant. These maneuvers gee to an altitude just above the orbit of gion many times a day, but the frequency left the mean altitude of ERBS essentially the International Space Station (ISS), near of ISS collision avoidance maneuvers is unchanged, while reducing its eccentric- 350 km altitude. Since the amount of less than one per year. ity. propellant remaining after these six ma- UARS is now expected to reenter the Passivation of ERBS was completed, neuvers was still uncertain, further near- atmosphere in about 5 years, at least 20 and the spacecraft was officially decom- term, post-maneuver conjunction assess- years earlier than if no maneuvers had missioned on 14 October. From its cur- ments with ISS would have been difficult. been performed. ♦ rent orbit, ERBS is expected to reenter Therefore, the remaining two maneuvers 600 580 Apogee 570 550 Perigee 560 500 550 540 450 530 Altitude (km) Altitude (km) 400 520 Apogee 510 350 Perigee 500 300 490 2005 2005.2 2005.4 2005.6 2005.8 2006 2002 2003 2004 2005 2006 By performing a series of disposal maneuvers, UARS reduced its remaining orbital ERBS operated near 600 km for nearly 18 years before its orbit was lowered to lifetime by more than 20 years. accelerate its decay after end of mission. Large Area Debris Collector (LAD-C) Update The official kickoff meeting for the nizations. The STP Office is responsible for LAD-C mission objectives and requirements; Large Area Debris Collector (LAD-C) was the manifesting, integration, and deployment on the acoustic and electronic components hosted by the U.S. Department of Defense of LAD-C on ISS, and the retrieval of the of the system (see Orbital Debris Quarterly (DoD) Space Test Program (STP) in Hous- system after one to two years. News, 8-2, p. 3); and on the primary science ton, Texas on 27 October 2005. LAD-C is The kickoff meeting included presen- objectives, and the benefits of the science re- a 10 m2 aerogel and acoustic sensor system tations by STP managers and engineers on turn for orbital debris, cosmic dust, and safe- designed to characterize and collect sub-mil- project organizations, roles and responsibili- ty communities. Additional issues regarding limeter micrometeoroids and orbital debris ties; on ISS and Shuttle payload, integration, the mechanical design, power requirements, on the International Space Station (ISS). and safety requirements; and on extravehicu- system location and orientation, and poten- The project is led by the U.S. Naval Research lar activity issues. According to STP’s payload tial ISS environment contamination were also Laboratory (NRL) in Washington D.C. with schedule, LAD-C deployment is tentatively discussed at the meeting. Follow-up biweekly primary collaboration by the NASA Orbital set for mid-2007 with an exposure time of teleconferences will be arranged to continue Debris Program Office at Johnson Space at least one year before retrieval and return the technical information exchange among all Center, and possible contribution by the Eu- to Earth. The LAD-C Principal Investigator team members. ♦ ropean Space Agency and several other orga- and Co-Investigators presented overviews on 2 www.orbitaldebris.jsc.nasa.gov Revision of Space Shuttle Wing Leading Edge Reinforced Carbon-Carbon Failure Criteria Based on Hypervelocity Impact and Arc-Jet Testing E. CHRISTIANSEN, J. HYDE, D. LEAR, to burn-through in some areas of the WLE nose failure criteria maps before and after T. PRIOR, & F. LYONS where burn-through can lead to loss-of-ve- the recent changes for STS-114. The reduc- As part of the Shuttle Return-to-Flight hicle (LOV) during reentry. Figure 1 shows tion in allowable damage results in increased (RTF) effort, the NASA Johnson Space the resulting damage caused by a 0.8 mm calculated MMOD risks for future missions, Center’s Hypervelocity Impact Technology diameter aluminum hypervelocity impactor if all other things remain constant. Facility (JSC/HITF) performed hypervel- and subsequent damage growth due to AJ The Shuttle and International Space ocity impact (HVI) testing and analysis of testing. Station (ISS) Programs decided to decrease Shuttle wing leading-edge (WLE) reinforced For STS-107 and previous missions, MMOD impact risks to STS-114 and sub- carbon-carbon (RCC) test samples to update WLE failure threshold consisted of 1 in. di- sequent flights by reversing the orientation WLE threshold failure criteria. After the ameter allowable hole sizes in RCC on the of the ISS during the ISS docking phase of hypervelocity impact tests, the samples were upper surface and ¼ in. hole size on the the Shuttle mission. The change in orienta- exposed to typical reentry heating conditions lower surface.