In Situ Measurements
Hubble Space Telescope | WFPC-2
After approximately 16 years in low Earth orbit aboard the Hubble Space Telescope (HST), the Wide Field Planetary Camera 2 (WFPC-2) was returned to Earth in 2009 by Servicing Mission 4 (STS 125). The WFPC-2 radiator was exposed to the micrometeoroid (MM) and orbital debris (OD) environments and provides a unique record of the MMOD environment due to the duration on orbit as well as its relatively large 1.76 m2 surface area.
The radiator’s outermost layer is a 4-mm-thick aluminum, curved plate coated with YB-71 Zinc Ortho-Titanate white thermal paint. Immediately apparent was the presence of large impact features featuring spallation of the surrounding paint as well as craters resident only in the thermal paint layer; similar phenomenology was observed during a prior survey of the WFPC-1 radiator.
Craters were extracted by coring the radiator in the NASA Johnson Space Center’s Space Exposed Hardware cleanroom and were subsequently examined using scanning electron microscopy / energy dispersive X-ray spectroscopy to determine the likely origin, e.g., micrometeoritic or orbital debris, of the impacting projectile.
Recently, a selection of large cores was re-examined using a new technique developed to overcome some limitations of traditional crater imaging and analysis. This technique, motivated by thin section analysis, examines a polished, lateral surface area revealed by cross-sectioning the core sample.
Hubble Space Telescope | MLI
Multi-layer insulation (MLI) blankets covering the HST electronics bays were removed during HST Servicing Mission 4 and returned to Earth for analysis. The NASA Orbital Debris Program Office obtained HST Bays 5 and8 MLI blankets to characterize impact features and develop a flux estimate based on those features. Two imaging campaigns were conducted in 2011 and 2018, concentrating on Bay 5.
Like other returned surfaces, the MLI display both impact craters and penetrations. A relatively complex 'petaling' phenomenon along with multiple-layer penetration features have been observed in both hypervelocity testing and in the Bay 5 MLI. This indicates a more complicated structure for impact features than earlier assumed. A new methodology of characterization techniques was developed and employed during data collection and analysis of the HST MLI and will provide greater understanding and more accurate estimation of impacting particle parameters.
The NASA Orbital Debris Program Office (ODPO) is leading the effort, with full support from the NASA Hypervelocity Impact Technology, the NASA Meteoroid Environment Office, and the NASA Astromaterials Acquisition and Curation Office, to conduct an MMOD impact survey of the WFPC-2 radiator. The goal is to use the data to validate the near-Earth MMOD environment definition and the Orbital Debris Engineering Model (ordem 3.2). This effort is also very well supported by the HST Development Project Office located at the NASA Goddard Space Flight Center.
Space Debris Sensor
The NASA ODPO Space Debris Sensor (SDS) is the first flight demonstration of the Debris Resistive / Acoustic Grid Orbital NASA-Navy Sensor (DRAGONS) technology developed and matured over 10 years by the NASA ODPO, in concert with the DRAGONS consortium, to provide information on the sub-millimeter orbital debris environment.
SDS was developed under the NASA Class 1E program for experimental spaceflight hardware and was robotically installed aboard the International Space Station’s Columbus module in January 2018 as an external payload. During its operational lifetime the mission was hampered by reduced operational uptime associated with loss of low data rate command/telemetry capability. The mission was effectively terminated by the loss of low and medium data rate telemetry. Efforts to recover the payload were ultimately unsuccessful.
The SDS, with a requirement to operate for a minimum of 2 years, collected 25 days of resistance/engineering data and over 1300 acoustic detection files. Despite its relatively short operational lifetime, the mission was a success in demonstrating the technology required to read and record grid resistance data at 1 Hz, grid acoustic data at 500 kHz, and store and downlink these data to the ground. Unfortunately, due to the short duration of 25 days, the mission failed to demonstrate the ability to characterize multi-grid line cuts, time of flight derived from an acknowledged impact on the second grid layer, an acknowledged impact on the third, backstop layer, and the determination of projectile mass density from impulse/impact energy delivered to the backstop.
The Johnson Space Center curates a variety of spacecraft and spacecraft components that have been impacted by natural and human-made microparticulates. These include the Genesis and Stardust sample return capsules and pieces of Surveyor III, the Long Duration Exposure Facility (LDEF), the Solar Maximum satellite, the European Recoverable Carrier (EuReCa), the MIR space station and the Hubble Space Telescope.