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The SSDR, developed
by SEAKR, Inc. weighed less than 4.1 kg with a
volume of 2,048 cm3. During standard mapping operations, the
Spacecraft Controller stored data in the SSDR with a total storage of 2.0 Gbit (200
Mb). The SSDR was designed for high reliability by using error detection and correction
with active fault management and built-in test. It had a data throughput greater
than 20 Mb/s with a bit error rate less than one bit per 10 billion. The SSDR used
commercially available four Mb dynamic RAM (DRAM) packaged as multi-chip modules.
Spacecraft telemetry data, sensor images, and experiment data were compressed and
stored on the SSDR until they could be downlinked.Spacecraft Controller
The Spacecraft Controller weighed 7.7 kg with a volume of 7,030 cm3. Each module used a stretched standard electronic module, Type "E" (SEM-E) format and was fabricated using surface mount technologies. The Spacecraft Controller consisted of eight modules, i.e., the housekeeping processor (HKP), the Sensor Image Processor (SIP), the Data Handling Unit (DHU), the Command Module (CMD), the Telemetry Module (TLM), the memory module, the attitude control system/reaction control system (ACS/RCS) module, and a power supply module.
The Spacecraft Controller was a dual processor system that consisted of a Honeywell RH-1750 16 bit HKP module and a R3081 32 bit RISC SIP module. The HKP was an advanced Very High Speed Integrated Circuit (VHSIC) device that used MIL-STD-1750A architecture. It provided the spacecraft command and telemetry, housekeeping, and star tracker camera image processing.
The SIP, developed by Telenetics, Inc., was a commercially available, non-radiation hardened, 32 bit RISC processor. It provided sensor image processing and functioned as a "backup" to the HKP. Communication between the two processors was through a dual port memory.
The Honeywell global memory module provided the processors with 256 kilobytes of radiation hardened and fault tolerant random access memory (RAM).
The DHU module, developed by Innovative Concepts, Inc. controlled the operation of the optical sensor payload. Image data was buffered during lunar mapping at peak aggregate rates of up to 12.4 Mb/s. The DHU controlled the sequencing of the sensor images and used Discrete Cosine Transform, Quantization, and Huffman Encoding to control data compression. The spacecraft also employed the first spaceflight use of an advanced data compression integrated chipset with a compression range of 4x-20x. The compressed image data was formatted and stored to the SSDR. The DHU also controlled the reading of the stored data. It received the low rate telemetry and performed the wide band framing for Radio Frequency (RF) transmission to the terrestrial ground stations at data rates of 128, 64, 8, 2, 1, 0.5, 0.25, and 0.125 kb/s.
The CMD module provided 48 high-level relay commands, 128 matrix relay commands, 32 low-level transistor-transistor commands, 6 serial command channels, and 8 differential commands.
The TLM module provided 48 bi-level telemetry channels, 48 active analog channels, 64 passive analog channels, and 6 serial telemetry channels.
The ACS/RCS interface module provided control of the ten 4.4 N and two 22.2 N thrusters, the 489 N thruster, four pulse valves, and two latch valves. It also provided current drive for four paraffin mechanism actuators.
The Spacecraft Controller power supply module provided regulated output voltages that were short circuit protected with independent overcurrent protection on the switched outputs.
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