As a result of the first mission, we discovered that IMAPS could indeed observe during the daylight side of an orbit (§6.1.1). With this liberation from the nighttime constraint, we now feel that we can no longer justify the use of time during the orbital day to dump data to the slow, onboard tape recorder. This recorder is a resource shared with the other experiments on the Astro-SPAS platform, and under most circumstances we have access to it only during the time IMAPS is observing.
We considered several methods for outfitting IMAPS with an internal non-volatile image storage capability. Rotating disk media (e.g. hard disk drive) were deemed unsuitable because they would exert a torque on Astro-SPAS, require considerable power, and need a pressurized container for operation in space. Fortunately, flash memory technology has recently evolved to a point where it is dense enough and economically feasible for building a gigabyte sized data storage with nonvolatility, low power and solid-state reliability.
The new, long term IMAPS data storage incorporates the Intel 40 Mbyte capacity linear flash memory PCMCIA cards designed for the laptop computer market. The PCMCIA flash memory card adheres to a documented standard bus and thus provides an off-the-shelf alternative without having to design circuitry for individual memory chips.
Our new data storage system consists of 8 motherboards, each with sockets for 8 PCMCIA flash memory cards, for a total of 2.5Gb of addressable flash memory space. One motherboard serves as a master and is controlled from the parallel port of the IMAPS micro-computer. Seven more identical motherboards are not populated with the micro-computer interface circuitry and are slaved to the master motherboard.
The flash memory system will reduce IMAPS data dump times by a factor of ten, but it still can not operate fast enough to absorb data directly from the frame-integrating memory. This is not a problem because there is 32Mb of fast static RAM in our existing system which stores up to 128 IMAPS exposures (integrated images). The static RAM acts a cache for the flash memory, allowing many of the data dumps to take place during non-observing times e.g. during target slews or when other Astro-SPAS experiments are observing. The internal flash memory storage will double the IMAPS observing efficiency compared to the first mission on Astro-SPAS.