A publication of The Orbital Debris Program Office NASA Johnson Space Center Houston, Texas 77058 October 2000 Volume 5, Issue 4. NEWS A Decade of Growth P. Anz-Meador and Globalstar commercial communication of the population. For example, consider the This article will examine changes in the spacecraft constellations, respectively. Given peak between 840-850 km (Figure 1’s peak low Earth orbit (LEO) environment over the the uncertain future of the Iridium constellation, “B”). This volume is populated by the period 1990-2000. Two US Space Surveillance the spike between 770 and 780 km may change Commonwealth of Independent State’s Tselina- Network (SSN) catalogs form the basis of our drastically or even disappear over the next 2 spacecraft constellation, several US Defense comparison. Included are all unclassified several years. Less prominent is the Orbcomm Meteorological Support Program (DMSP) cataloged and uncataloged objects in both data commercial constellation, with a primary spacecraft, and their associated rocket bodies sets, but objects whose epoch times are “older” concentration between 810 and 820 km altitude and debris. While the region is traversed by than 30 days were excluded from further (peak “A” in Figure 1). Smaller series of many other space objects, including debris, consideration. Moreover, the components of satellites may also result in local enhancements these satellites and rocket boosters are in near the Mir orbital station are 3.0E-08 circular orbits. Thus, any “collectivized” into one group of spacecraft whose object so as not to depict a orbits are tightly January 1990 plethora of independently- 2.5E-08 maintained are capable of orbiting objects at Mir’s A January 2000 producing a spike similar altitude; the International B to that observed with the Space Station (ISS) is 2.0E-08 commercial constellations. afforded the same treatment Not coincidentally, the in the year 2000 data set. 1.5E-08 NASA EVOLVE 4.0 long- Figure 1 depicts the spatial term debris evolution density [1/km3] over the computer model predicts altitude range 100-2000 km 1.0E-08 that this region is sensitive and in 10 km altitude bands. [1/km^3] density spatial to the collision hazard. Figure 1 possesses This result appears driven several salient features. 5.0E-09 by the large size and mass Perhaps the most prominent of the spacecraft resident are the “spikes” located there, particularly the 0.0E+00 between 770-780 and 1410- 0 200 400 600 800 1000 1200 1400 1600 1800 2000 Tselina-2 constellation. 1420 km altitude. These altitude [km] correspond to the Iridium (Continued on page 2) Figure 1. The LEO spatial density in 1990 and 2000. Inside... September Breakup is 22nd in Series ....................................................................................... 2 Liquid Mirror Telescope Observations of the 1999 Leonid Meteors ......................................3 New NASA Orbital Debris Engineering Model ORDEM2000 ............................................ 4 GEO_EVOLVE 1.0 ................................................................................................................... 5 1 The Orbital Debris Quarterly News NEWS A Decade of Growth, Continued (Continued from page 1) inclination; hence, collision rates won’t be starting point: the commercial constellations. Note that both data sets presented are at or linearly related to the spatial density at any Because these constellations are maintained in near Solar maximum. One may expect the low given altitude. Indeed, collision rates will vary precise orbital planes, their expected collision altitudes (< 600 km) to increase by up to a not only with the spatial density but also with rate would be versus the “background” factor of two over the next five years, given the inclination-dependent relative velocity. population only. Hence, the spikes representing decreasing Solar activity and assuming the Altitudes dominated by high inclination (70- the Iridium and Globalstar constellations do not historical fragmentation rate. Such behavior is 110°) orbits are expected to yield a significantly present the inordinate collision risk implied by a historically evident when comparing a 1987 higher collision rate as compared to those casual examination. SSN catalog with the 1990 data set. populated by lower inclination orbits. The The spatial density chart averages over exception to this general rule returns us to our September Breakup is 22nd in Series The year 2000’s third fragmentation event This event occurred after approximately 2480 implementation is unknown. Newer versions of occurred in early September with the days on-orbit. the Block DM stage do not eject the SOZ units fragmentation of a Russian Proton rocket’s The SOZ ullage motors consist of following their ullage burn, though some SOZ ullage motor. Naval Space Operations hypergolic propellant (Nitrogen Tetroxide/ Russian domestic launches continue to eject the Center personnel discovered the event on 7 UDMH) spheres, associated support structure, units. September 2000 when 57 debris penetrated the and a multi-chamber thruster assembly for An analysis of the event, conducted the Navy's electronic fence, which spans the three-axis attitude control and for Proton fourth day the Orbital Debris Program Office was southern United States. Operational debris stage ullage (propellant settling). The Proton notified of the fragmentation, indicates that the from the Gorizont 29 geosynchronous Earth Block DM fourth stage carries two SOZ units. long-term environmental consequences are orbit (GEO) launch on 18 November 1993, the Each unit has a dry mass of approximately 56 minimal, as the parent object was in a unit (Satellite Number 22925, International kg but may contain up to 40 kg of unused catastrophic decay from the original GEO Designator 1993-072E) was in an orbit of 140 propellant (Johnson et al., History of Soviet/ transfer orbit. This lessens the spatial density in km by 11,215 km with an inclination of 46.7 Russian Satellite Fragmentations, October low Earth orbit because of the large eccentricity degrees at the time of the event. This was the 1995, Kaman). Russian officials have made and low perigee of the parent’s orbit. 22nd known breakup of a Proton SOZ ullage design changes to prevent accidental explosions motor since the first one exploded in 1984. of the SOZ unit, although the date of full Reentry Survivability Analysis of Extreme Ultraviolet Explorer (EUVE) R. O’Hara individual objects predicted to survive. The set to 1.0 for all materials available in DAS, A reentry analysis of the Extreme total casualty area calculated for these implying blackbody radiation for each Ultraviolet Explorer (EUVE) spacecraft was surviving objects was 12.41 m2, which exceeds component analyzed. Thus, objects in DAS performed using the Object Reentry Survival the 8 m2 limit set in the NASA safety standard. tend to lose heat faster and are more likely to Analysis Tool (ORSAT) - Version 5.0. The The EUVE spacecraft was not designed with a survive. In ORSAT, however, the emissivity analysis was done in response to a request by propulsion system and therefore cannot can be adjusted based upon what type of NASA Headquarters and Goddard Space Flight perform a controlled reentry. In order to material the object is composed of. ORSAT Center (GSFC) after a preliminary assessment mitigate the potential risk to human safety from also considers heat of oxidation during reentry, had shown that the EUVE reentry may produce an uncontrolled reentry of the EUVE which means that the object gains heat faster a debris area greater than the limit set within spacecraft, a retrieval of the spacecraft using and will demise more readily. Heat of the NASA Safety Standard 1740.14 guidelines. the Space Shuttle was considered. However, oxidation is not considered in DAS. ORSAT NASA's 3243 kilogram EUVE spacecraft since DAS is a lower fidelity model and tends also allows for thermal conductivity. With this was launched on June 7, 1992 from Cape to produce a more conservative result, the enhancement and using a layered approach to Canaveral Air Station on board a Delta II Orbital Debris Program Office at JSC was modeling the fragments, ORSAT can reduce launch vehicle into a 528 kilometer, 28.5 asked to perform a more detailed reentry study the overall debris area by allowing for objects degree inclined orbit. With the spacecraft using the higher fidelity NASA-Lockheed to partially ablate. In contrast to this method, nearing its end of mission and a possible Martin ORSAT model to determine if taking DAS will allow the entire fragment to surive. reentry into the Earth's atmosphere expected as such a measure would be necessary. And finally, ORSAT enables the user to supply early as October 2001, personnel at Goddard Several sophisticated material and thermal a wall thickness for an object, making it easier Space Flight Center performed a reentry properties are included in ORSAT but do not to model hollow objects. DAS treats all objects analysis using the NASA Johnson Space Center exist in the DAS code. These enhancements as solid and therefore requires a workaround to Debris Assessment Software (DAS) - Version tend to result in fewer objects surviving reentry approximate the reentry heating to a hollow 1.0, in accordance with NASA Policy Directive when using ORSAT as opposed to DAS for a object. This workaround has been validated 8710.3. In the GSFC analysis, there were 18 reentry analysis. For example, the emissivity is (Continued on page 9) 2 The Orbital Debris Quarterly News NEWS In Situ Detections of a Satellite Breakup J. Opiela, N. Johnson two days. In late March 2000 the instrument occurred on 11 March with the fragmentation of For the first time, a particle detector in detection rate soared by over an order of a Long March 4B third stage (see Orbital Earth orbit has provided evidence to directly magnitude, suggesting a potential encounter Debris Quarterly News, “The First Satellite link sub-millimeter orbital debris to a specific with a cloud or stream of debris.