Abstract
Conducting space experiments with small budgets is a fact of life for many design groups with low-visibility science programs. One major consequence is that specialized space grade electronic components are often too costly to incorporate into the design. Radiation mitigation now becomes more complex as a result of being restricted to the use of commercial off-the-shelf (COTS) parts. Unique hardware and software design techniques are required to succeed in producing a viable instrument suited for use in space. This site highlights some of the design challenges and associated solutions encountered in the production of a highly capable, low cost space experiment package.
Introduction
The Forward Technology Solar Cell Experiment (FTSCE) is a space solar cell experiment built as part of the Fifth Materials on the International Space Station Experiment (MISSE-5). It represents a collaborative effort between NASA Glenn Research Center (GRC), the Naval Research Laboratory (NRL) and the US Naval Academy (USNA). The purpose of this experiment is to place current and future solar cell technologies on orbit where they will be characterized and validated. This is in response to recent on orbit and ground test results which have raised concerns about the in space survivability of new solar cell technologies and about current ground test methodology. The various components of the FTSCE are assembled into a passive experiment container (PEC) which is a 2′ x 2′ x 4" folding metal container which is attached to the outer structure of the International Space Station (ISS). Test data is transmitted to Earth and stored in on-board back-up memory. At the end of a nominal one year mission, the PEC will be removed and returned to Earth. The experiment is designed to remain in orbit for two and a half years if the need arises.
MISSE-5 Hardware Overview
MISSE-5 has 39 advanced technology solar cells positioned on the side of the PEC that faces the sun. The technologies include state-of-the-art and next generation multijunction InGaP/GaAs/Ge, heteroepitaxial GaAs/GeSi/Ge, and amorphous Si and CuIn(Ga)Se2 thin film solar cells. In addition to these cells are a number of other sensors that include two-element position sensitive diodes for sun position sensing, single point solar cells for radiance and sun position sensing and temperature sensors in the form of resistance temperature devices (RTD) and two terminal temperature sensors from Analog Devices (AD590). The electronics assembly to integrate these sensors and to communicate with the second prototype communication satellite system (PCSAT2) has been provided by NASA GRC personnel. The PCSAT2 communication system will be used to telemeter test data to Earth and to telemeter command and control from Earth to the NASA GRC electronics using the International Telecommunication Union (ITU) Amateur Satellite Service. In the event of a communications failure, the NASA GRC electronics will continue to operate in a stand alone mode, taking data according to time, temperature and sun position schedule. Data normally sent to Earth will also be archived in on-board flash memory. The PEC will be recovered in a year or two during an EVA and returned to earth where its data can be downloaded from the flash memory. The NASA GRC electronics are made up of the main microcontroller board (mother board, which is numbered board 0) and nine data acquisition boards (daughter boards, numbered 1 through 9).
