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Payload Design

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This concept payload study assumes the use of standard Hitchhiker/GAS hardware and specifications whenever possible. The Hitchhiker canister, with its avionics and adapter ring, possibly mounted on a JEM-EF (Japanese Experiment Module - Exposed Facility) or EXPRESS pallet with an attachment interface for the ISS could conceivably mount at either the JEM, S3 or P3 PAS (Payload Attach System) mounting sites.
The camera system itself is built around a Hitchhiker/GAS five cubic foot canister mated to a motorized door assembly, which is fitted with a fused silica window. Construction is based on four circular plates separated and supported by three equally spaced struts attached on the circumference. The cameras will be mounted behind the first, a 16mm (5/8") 6061-T6 aluminum plate that acts as a containment shield and structural stabilizer, fitted with a thin glass epoxy light baffle to reduce reflected glare in the optical system.
Six digital cameras operating in different portions of the light spectrum from ultraviolet to infrared are aligned and mounted on the second plate located near the containment shield. Below the camera mounting plate is the third of four internal plates. This plate supports the camera electronics and any ancillary electronics packages needed to interface with the ISS Hitchhiker avionics package. Below this is the fourth or bottom structural plate, which provides support and rigidity through the three base bumpers that provide a mechanical interface with the flight hardware.

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Click here to see plan

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Click here to see plan

Each camera optical path is chosen to match its Skylab equivalent in both spectral range and subject footprint size as closely as practical. With improvements in exposure speed allowed by advances in digital technology, the payload will be able to do away with the cumbersome mechanical rotating mechanism used to stabilize the Skylab camera platform, which was necessary to compensate for orbital motion and extended film exposure times. All six cameras will be fired simultaneously, and the pictures transferred to each camera’s four picture buffer memory. The picture data files will then be sequentially transferred to a mass storage unit which will compress and warehouse the data until it can be downloaded through either the ISS MRDL (Medium Rate Data Link) or the HRDL (High Rate Data Link) as may be available. Camera control will be uplinked through the Hitchhiker control uplink, which is at present an RS-422 serial format (1200 baud) channel. While in operation, the computer will continually monitor all cameras, electronics, payload environment, and its own health, and return the system status by way of the Hitchhiker downlink, which also runs at 1200 baud. Operational power will be derived from the ISS through the Hitchhiker avionics package, and further regulated for the payload requirements.

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Experimental Concept

The View from Space

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