Continued investigation of LDEF's structural frame and thermal blankets by the Meteoroid and Debris Special Investigation Group

This report focuses on the data acquired by detailed examination of LDEF intercostals, 68 of which are now in possession of the Meteoroid and Debris Special Investigation Group (M&D SIG) at JSC. In addition, limited data will be presented for several small sections from the A0178 thermal control blankets that were examined/counted prior to being shipped to Principal Investigators (PI's) for scientific study. The data presented here are limited to measurements of crater and penetration-hole diameters and their frequency of occurrence which permits, yet also constrains, more model-dependent, interpretative efforts. Such efforts will focus on the conversion of crater and penetration-hole sizes to projectile diameters (and masses), on absolute particle fluxes, and on the distribution of particle-encounter velocities. These are all complex issues that presently cannot be pursued without making various assumptions which relate, in part, to crater-scaling relationships, and to assumed trajectories of natural and man-made particle populations in LEO that control the initial impact conditions

Preliminary analysis of LDEF instrument A0187-1: Chemistry of Micrometeoroids Experiment

The Chemistry of Micrometeoroids Experiment (CME) exposed approximately 0.8 sq. m of gold on the Long Duration Exposure Facility's (LDEF's) trailing edge (location A03) and approximately 1.1 sq. m of aluminum in the forward-facing A11 location. The most significant results to date relate to the discovery of unmelted pyroxene and olivine fragments associated with natural cosmic dust impacts. The latter are sufficiently large for detailed phase studies, and they serve to demonstrate that recovery of unmelted dust fragments is a realistic prospect for further dust experiments that will employ more advanced collector media. We also discovered that man-made debris impacts occur on the LDEF's trailing edge with substantially higher frequency than expected, suggesting that orbital debris in highly elliptical orbits may have been somewhat underestimated

Current activities and results of the Long Duration Exposure Facility Meteoroid and Debris Special Investigation Group

Fiscal Year 1994 will bring to a close the initial investigative activities associated with the Long Duration Exposure Facility (LDEF). LDEF was a 14-faced spacecraft (i.e., 12-sided cylinder and two ends) which housed 54 different experimental packages in low-Earth orbit (LEO) from Apr. 1984 to Jan. 1990 (i.e., for approx. 5.75 years). Since LDEF's return, the Meteoroid & Debris Special Investigation Group (M&D SIG) has been examining various LDEF components in order to better understand and define the LEO particulate environment. Members of the M&D SIG at JSC in Houston, TX have been contributing to these studies by carefully examining and documenting all impact events found on LDEF's 6061-T6 aluminum Intercostals (i.e., one of the spacecraft's structural frame components). Unlike all other hardware on LDEF, the frame exposed significantly large surface areas of a single homogeneous material in all (i.e., 26) possible LDEF pointing directions. To date, 28 of the 68 Intercostals in the possession of the M&D SIG have been documented. This data, as well as similar information from various LDEF investigators, can be accessed through the M&D SIG Database which is maintained at JSC

LDEF meteoroid and debris special investigation group investigations and activities at the Johnson Space Center

Since the return of the Long Duration Exposure Facility (LDEF) in January, 1990, members of the Meteoroid and Debris Special Investigation Group (M&D SIG) at the Johnson Space Center (JSC) in Houston, Texas have been examining LDEF hardware in an effort to expand the knowledge base regarding the low-Earth orbit (LEO) particulate environment. In addition to the various investigative activities, JSC is also the location of the general Meteoroid & Debris database. This publicly accessible database contains information obtained from the various M&D SIG investigations, as well as limited data obtained by individual LDEF Principal Investigators. LDEF exposed approximately 130 m(exp 2) of surface area to the LEO particulate environment, approximately 15.4 m(exp 2) of which was occupied by structural frame components (i.e., longerons and intercoastals) of the spacecraft. The data reported here was obtained as a result of detailed scans of LDEF intercoastals, 68 of which reside at JSC. The limited amount of data presently available on the A0178 thermal control blankets was reported last year and will not be reiterated here. The data presented here are limited to measurements of crater diameters and their frequency of occurrence (i.e., flux)

Seesaw mechanism in the sneutrino sector and its consequences

The seesaw-extended MSSM provides a framework in which the observed light neutrino masses and mixing angles can be generated in the context of a natural theory for the TeV-scale. Sneutrino-mixing phenomena provide valuable tools for connecting the physics of neutrinos and supersymmetry. We examine the theoretical structure of the seesaw-extended MSSM, retaining the full complexity of three generations of neutrinos and sneutrinos. In this general framework, new flavor-changing and CP-violating sneutrino processes are allowed, and are parameterized in terms of two $3\times 3$ matrices that respectively preserve and violate lepton number. The elements of these matrices can be bounded by analyzing the rate for rare flavor-changing decays of charged leptons and the one-loop contribution to neutrino masses. In the former case, new contributions arise in the seesaw extended model which are not present in the ordinary MSSM. In the latter case, sneutrino--antisneutrino mixing generates the leading correction at one-loop to neutrino masses, and could provide the origin of the observed texture of the light neutrino mass matrix. Finally, we derive general formulae for sneutrino--antisneutrino oscillations and sneutrino flavor-oscillations. Unfortunately, neither oscillation phenomena is likely to be observable at future colliders.Comment: 69 pages, 5 figures, uses axodraw.sty. Version accepted for publication in JHEP: some comments and one more Appendix with additional discussion added, references update