Workshop on Dust in Planetary Systems 2005 4025.pdf A SEARCH FOR METEOR SHOWER SIGNATURES IN THE LDEF IDE DATA. W. J. Cooke1 and H. A. McNamara2, 1Meteoroid Environment Office, Mail Code EV13, Marshall Space Flight Center, AL 35812 USA, [email protected], 2Meteoroid Environment Office, Mail Code EV13, Marshall Space Flight Center, AL 35812 USA, [email protected] Introduction: For 346 days after the deployment tracted, as this set of detectors should sample the me- of the LDEF satellite on April 7, 1984, the tape re- teorid environment with little contamination from or- corder belonging to the Interplanetary Dust Experi- bital debris. The number of impacts on the tray facing ment (IDE) stored information on over 15,000 impacts radially down, towards Earth, was too small to be use- made by submicron and larger-size particles on its ful, as it was shielded by the Earth. metal oxide silicon (MOS) detectors . These detectors There was no shower signature detected for the were mounted on trays facing in six orthogonal direc- Geminids; no impacts on the space tray occurred while tions - LDEF ram and trailing edge, the poles of the it was exposed to the shower radiant. However, the LDEF orbit (north and south), and radially inward Perseids showed a remarkably strong signature – 18 (towards the Earth) and outward (towards space). The impacts on the 1 µm detectors occurred over the 13.1 second time resolution provided by the IDE elec- shower duration while the tray was exposed to the ra- tronics, combined with the high sensitivity of the MOS diant, with only one occurring when it was not. Figure detectors and large collecting area (~ 1 sq. m) of the 1 shows the impact record, binned in 1 day intervals, experiment, conclusively showed that the small parti- for the 1 µm space-facing detectors from July 17 to cle environment at the LDEF altitude of 480 km was August 24; Note the concentration of impacts about highly time-variable, with particle fluxes spanning day 225 – August 11, near the time of the traditional over four orders of magnitude. Perseid peak. A large number of the 15,000 impacts recorded by IDE occurred in groups, which were of two types - the spikes, single, isolated events of high intensity and the multiple orbit event sequences (MOES), which were series of events separated in time by integer multiples of the LDEF orbital period. Even though the spikes were generally more intense, the MOES could be quite long-lived, some lasting for many days. A previous paper by Cooke et al. [1] attributed the MOES to impacts by man-made debris particles in orbits intersecting that of LDEF. The 20 day longevity of one of these events – termed the May Swarm – led to the suggestion that the debris particles must be con- stantly replenished by their source, as the orbits of micron sized particles will rapidly decay under the influence of radiation pressure and other non- gravitational forces, entering Earth’s atmosphere after only a few revolutions. Figure 1. Impacts on IDE space facing 1 µm de- However, the date of onset of the May Swarm tectors from July 17 to August 24, 1984. (May 22) and the long duration of this event may indi- cate a possible correlation with the annual Arietid me- There is also a strong impact signature during the teor shower, which peaks around June 8. As this daytime Arietids (May 22 – July 8). However, the fact seemed to hold the promise of a less “artificial” expla- that this radiant is close to the Sun, being imbedded in nation than a satellite or rocket body continuously the sporadic Helion source, and also the high likeli- “dribbling” debris , it was decided to take a fresh look hood that IDE observed significant numbers of β at parts of the IDE data set in an attempt to detect meteroids [2], make it difficult, if not impossible, to meteor showers within the impact record. attribute any of these impacts to the Arietids with con- Analysis: Three major annual showers – the day- fidence. time Arietids, the Perseids, and the Geminids were Searches for other showers (Eta Aquarids and Ori- chosen for the initial search. A subset of the data, the onids) were also conducted. The results of these, and impact record for the IDE space facing tray was ex- Workshop on Dust in Planetary Systems 2005 4025.pdf more details of the analyses will be presented, along with an examination of the possible causes for the “May Swarm.” References: [1] Cooke W. J. et al. (1995) LDEF 3rd Post- Retrieval Symposium, 361-371. [2] Cooke W. J. et al. Advances in Space Research, 13, 119-122. .