Russell P. Cain

Corrosion sensors for concrete bridges

Corrosion of rebar in concrete bridges is a problem for the infrastructure and is difficult to detect. Engineers and scientists at the Johns Hopkins University Applied Physics Laboratory (JHU/APL) have developed a device that is designed to be buried in the concrete when the bridge deck is poured. The device, known as a wireless embeddable sensor platform/smart aggregate (WESP/SA), can provide data about conditions within the bridge deck. This data will assist highway maintenance engineers in determining corrosive actions.

Packaging for a Sensor Platform Embedded in Concrete

The Johns Hopkins University Applied Physics Laboratory is developing packaging for a sensor platform to be embedded in the harsh environment of concrete structures. The sensors will monitor the corrosive environment of the structure over periods of several decades to aid in scheduling maintenance and repair. The United States has recognized the risks associated with its aging infrastructure and is actively replacing deteriorated/high risk structures as well as simultaneously developing the tools and techniques to monitor new infrastructure as it ages. JHU/APL has reviewed the sensing requirements for infrastructure monitoring, especially bridge decks, and developed a concept based on distributed, embedded sensors. The Wireless, Embedded Sensor Platform (WESP) will implement the concept of a low-cost, customizable sensor platform suitable for long-term field measurements. The WESP is designed to be powered and queried remotely as often as required and can be used to measure the evolution of the corrosive environment over time. The objective of this research and development is to design, implement, and demonstrate packaging techniques for embedded sensor suites commensurate with a 50-year lifetime when embedded in concrete having a pH greater than 13, and exposed to harsh environments of salt, and mechanical and thermal stress. To meet this objective, the WESP construction will use a commercial ceramic IC package and unique manufacturing and assembly techniques. The prototype is expected to provide sensor identification, temperature, pressure, and conductivity data within a package volume less than 2.5 cm 3 (0.15 in 3 ). Reliability test results will be reviewed and specialized tests will be performed to evaluate the performance of the packaging design. These include such tests as freeze/thaw cycling, thermal shock, thermal cycling, Highly Accelerated Stress Test (HAST), 85% relative humidity/85°C, and accelerated life testing. Future developments are expected to reduce size and implement additional sensor types to fully characterize the concrete environment.

Update of the midcourse space experiment (MSX) satellite measurements of contaminant films using QCMs

The Midcourse Space Experiment (MSX) satellite was launched on April 24, 1996. This paper provides an update of the quartz crystal microbalance (QCM) data accumulated over these last four years in space. The MSX is the only known experiment that has provided continuous contamination monitoring for such an extended length of time. The five QCMs on board the satellite have provided on-orbit data that have been invaluable in characterizing contamination levels around the spacecraft and inside the cryogenic Spatial Infrared Imaging Telescope (SPIRIT 3). One of the QCMs, the cryogenic QCM (CQCM), located internal to SPIRIT 3, was mounted adjacent to the primary mirror and provided contamination accretion measurements during the 10-month lifetime of SPIRIT 3. Real- time monitoring of contaminant mass deposition on the primary mirror was provided by this CQCM which was cooled to the same temperature as the mirror - approximately 20K. Thermogravimetric analyses (TGAs) on the CQCM provided insight into the amount and species of contaminants condensed on the SPIRIT 3 primary mirror during various spacecraft activities. The four temperature-controlled QCMs (TQCMs) were mounted on external surfaces of the spacecraft for monitoring spacecraft contamination deposition. The TQCMs operated at approximately -50

Advanced QCM controller for NASA's plume impingement contamination-II

DEGC and were positioned strategically to monitor the silicone and organic contaminant flux arriving at specific locations. Updated time histories of contaminant thickness deposition for each of the QCMs are presented. Gradual contaminant thickness increase was observed during the first year in space. During the second year, the QCM frequencies (contaminant film thickness) began to decrease, with the time of onset depending on QCM location. Possible explanationsfor this interesting behavior are discussed.

Particle monitor experiment

Currently, no accurate models or recent data exist for modeling contamination from spacecraft thrusters to meet the stringent requirements of the International Space Station (ISS). Few flight measurements of contaminant deposition from spacecraft thrusters have been made, and no measurements have been made for angles away from the plume centerline. The Plume Impingement Contamination-II (PIC-II)1 experiment is planned to provide such measurements using quartz crystal microbalances placed into the plume of a Shuttle Orbiter RCS thruster. To this end, the Johns Hopkins University Applied Physics Laboratory (APL) has supported NASA in the development of the PIC-II experiment Flight Electronics Unit known as the Remote Arm TQCM System (RATS), which will measure the contamination in the Shuttle Obiter RCS thruster. The development was based on an ongoing effort between the APL and QCM Research to develop an inexpensive, miniature TQCM controller based on a legacy of QCM controllers developed at the APL. PIC-II will provide substantial improvements over previous systems, including higher resolution, greater flexibility, intensive housekeeping, and in-situ operational control. Details of the experiment hardware and measurement technique are given. The importance of the experiment to the ISS and the general plume contamination community is discussed.

Outgassing of optical baffles and primary mirror during cryogen depletion of a space-based infrared instrument

A particle monitor based on the near forward scattering of light from an AlGaAs laser diode was modified for space flight and proved to be robust and reliable during an actual space launch. Near-field particles could result in large extraneous signals from the IR, visible and UV telescopes on board a spacecraft because of their proximity to the sensors. It is therefore desirable to build a particle monitor to go with optical sensors in order to correlate various particulate events with spacecraft operations, so that their effects on the sensors can be corrected. This device, along with the power supply, associated analog and digital electronics, and mechanical mounting will be described. Particulate measurements during ground testing will be presented.

Wireless multi-functional sensor platform, system containing same and method for its use

Outgassing experiments in space were conducted during the critical period in the cryogen lifetime of the large infrared telescope called Spatial Infrared Imager and Telescope (SPIRIT III) on the Midcourse Space Experiment (MSX) spacecraft. This was the period when the solid hydrogen in the dewar was being depleted and the optical components were warming up to evaporate previously condensed volatile materials. The volatile condensable materials were collected on the cryogenically cooled surfaces during the 4 months of prelaunch testing and the 10 months in orbit. The contamination instruments on board the spacecraft were used to monitor the outgassing of these materials. Besides contamination monitoring, it was also desired to control the heating or warm-up process without contaminating the still functioning UV and visible sensors. After considering several scenarios via thermal modeling, it was decided to conduct the warm-up period into two phases, with the first phase intended to approach but not exceed the sublimation point of ice on the primary mirror. Solar radiation was used to heat the SPIRIT III baffle and parts of the +Y face of the spacecraft while the contamination instruments were monitored the outgassing event. Ice redistribution from the baffle to the much colder primary mirror, as well as external pressure bursts and slight film depositions on quartz crystal microbalances were observed. The second phase of warm-up experiments again used solar heating to drive the telescope optics through the 150 K range for final sublimation of any ice remaining as well as condensed hydrocarbons from the cold primary mirror. The results of these end-of-cryo experiments are discussed in terms of the measured film deposits on the cryogenic quartz crystal microbalance and the pressures from the total pressure sensor.