NRL's Forward Technology Solar Cell Experiment Flies as Part of MISSE5 Aboard Space Shuttle Discovery Mission

9/19/2005 - 43-05r
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The Naval Research Laboratory served as the payload developer, program manager and system integrator for the 5th Materials on the International Space Station Experiment (MISSE5) which was launched aboard the Space Shuttle Discovery (STS-114) on July 26. MISSE5 is part of NASA's ongoing MISSE program.

At NRL, MISSE5 is a collaborative effort between researchers in the Electronics Science and Technology Division and the Spacecraft Engineering Department. Dr. Robert Walters in the Solid State Devices Branch and Mr. Chris Garner in the Space Electronics Systems Development Branch are the principal investigators.

MISSE5 is actually a combination of three experiments. All three experiments are housed in a 2' x 2' metal suitcase called the passive experiment container or PEC. The PEC was stowed in the multi-purpose logistics module for launch on the shuttle. Once the shuttle docked to the International Space Station (ISS), astronauts performed an extra vehicular activity (EVA), more commonly known as a space walk, to transport the PEC to its intended location on the ISS. The PEC was installed on an ISS hand-rail with a special hand-rail clamp pointer mechanism. The astronauts opened the PEC and enabled the experiment. Astronaut Soichi Noguchi performed the EVA deployment of MISSE5. The experiment is expected to remain on the ISS for 12 months.

Inside the PEC, the first experiment is the NRL-developed experiment is the Forward Technology Solar Cell Experiment (FTSCE). The goal of FTSCE is to put current and future solar cell technologies into space. Once in space the solar cell experiments are subjected to the combined effects of vacuum, thermal cycling, charged particle radiation, ultraviolet radiation and atomic oxygen erosion. Within FTSCE, there are 39 solar cell experiments, including state-of-the-art triple junction solar cells from Spectrolab and Emcore. Thirty-six experiments will have a 32 point I-V curve, sampled once per orbit. The remaining 3 experiments will have their short circuit current or open circuit voltage measured.

Data acquisition for FTSCE will be performed by electronics designed and fabricated by the NASA Glenn Research Center (GRC). The NASA GRC electronics represent a significant technological advance in terms of reduction of size and weight. One data acquisition board is only about 4x6 in.2 and is capable of measuring a 32 point I-V curve on four individual solar cells, making two temperature measurements, and taking data from one sun angle sensor. The data is beaconed down once an orbit via an amateur radio frequency system put together by the U.S. Naval Academy (USNA). NRL's Solid State Electronics Branch (Code 6818) was responsible for the characterization of all of the solar cell experiments with a simulated air mass zero, 1 sun intensity solar simulator. The Solid State Electronics Branch is also responsible for the post-flight generation of I-V curves from the on-orbit data.

The second experiment aboard MISSE5 is PCSat 2. The USNA under the direction of CDR Bob Bruninga (USN Retired) assembled a RF subsystem using commercial off-the-shelf components with selective upgrades to electronic parts and housings. The primary transmit/receive frequencies are 435/145.825 MHz. PCSat2 provides the capability to transmit FTSCE data and upload commands to the experiment. PCSat2 also provides a PSK-31 experiment that allows up to 20 users to correspond on a low Doppler single side band to FM transponder.

The third experiment, also called MISSE5, was prepared by the NASA Langley Research Center (LaRC) and GRC with contributions from a number of other laboratories. The NASA LaRC and GRC team has transformed the outer layer of the thermal blanket into a three and one half ounce experiment to evaluate the in-space survivability of 200 advanced materials that are being developed to enable future U.S. space missions. The survivability of these materials will be established by comparing pre- and post-flight characterization test data.

NRL' s Systems Analysis Branch (Code 8222) provided the mechanical design and integration of the experiments into the PEC. NRL's Space Electronics Systems Development Branch (Code 8240) designed and fabricated the electrical power subsystem for FTSCE and PCSat2. Four strings of Emcore ATJM solar cells provide sunlight power. Four 55-ampere-hour Lithium Ion battery cells from Lithion, Inc., provide power while the experiment is shadowed or in an orbital eclipse. Battery charge controls and load distribution functions are carried out in the power control unit designed by NRL's Space Electronics Systems Development Branch (Code 8244). This will be the first use of high capacity, prismatic lithium-ion batteries in a low earth orbit application.

The US Air Force Space Test Program's-DOD payload office at NASA Johnson Space flight center served as the launch vehicle integrator.

In Figure 1, Dr. Walters explains to astronauts Soichi Noguchi (NASDA-Japan) and Steve Robinson (NASA) the operation of the triple junction solar cell experiments.

Figure 2 shows the position of the solar cell experiments on FTSCE.

About the U.S. Naval Research Laboratory

The U.S. Naval Research Laboratory provides the advanced scientific capabilities required to bolster our country's position of global naval leadership. The Laboratory, with a total complement of approximately 2,500 personnel, is located in southwest Washington, D.C., with other major sites at the Stennis Space Center, Miss., and Monterey, Calif. NRL has served the Navy and the nation for over 90 years and continues to advance research further than you can imagine. For more information, visit the NRL website or join the conversation on Twitter, Facebook, and YouTube.

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