NEWS | June 23, 2011

NRL's Digital Imaging Star Camera Travels to International Space Station

By Donna McKinney

The Naval Research Laboratory's Digital Imaging Star Camera (DISC) launched aboard NASA's Space Shuttle Endeavour (STS-134) on May 18 to travel to the International Space Station. DISC is part of a suite of four experiments that will test concepts in low earth orbit for long duration.

DISC is a low-size, -weight, and -power sensor used for pointing knowledge. The purpose of the DISC mission is to demonstrate the functionality and quality of a low cost small star camera using commercial components for small low budget satellites (cubesats). Accurate precision pointing knowledge is a critical mission requirement for many scientific and operational payloads in space. A low Size Weight And Power (SWAP) pointing sensor like DISC will provide a science-enabling technology on pico- and nano-satellite platforms for payloads with stringent pointing requirements.

DISC was mounted on the International Space Station and the next day following installation, it was powered and all payloads were verified to be operational.

NRL researchers will use the DISC experiment to successfully acquire, downlink and calculate an accurate aspect solution from the DISC image. Performance characterization of the DISC camera including a determination of the limiting magnitude, optimal integration times, and susceptibility to scattered light are of particular interest to the research team.

NRL designed the final payload consisting of the structure and electronics. The data interface and downlink software to support the camera was developed by a NRL two person team. The electronics used a commercial 32-bit ARM processor, FLASH storage memory and a commercial grade FPGA implementing a spacewire interface to communicate with the camera. The software uses an open source real time kernel, which simplified programming significantly since various operations could be broken down into separate tasks. Since all operation sequences could not be determine at the time of the software development, a script capability was implemented to allow flexibility in how the camera operates. The structure was designed to use volume expected in a typical cubesat, but include features required for mounting on the palette and accommodate heaters.

The DISC can be programmed to generate images from 256x256 pixels to 1024x1024 pixels with each pixels having 12-bit resolution. It was extensively tested on the ground by imaging the night sky numerous times.

The goals for NRL's DISC are:
  • to develop concepts and a prototype for a low SWAP pointing system with 0.02 degrees resolution or better;
  • to develop processing algorithms to identify and register stellar sources. The coarse attitude solutions identify the specific region of the sky of the star image. The data from the set of star images will then be used to identify and reduce the error in the star camera vector measurements; and
  • to space-qualify the prototype unit and demonstrate performance capabilities.
The other three experiments on the STP-H3 suite are the Massive Heat Transfer Experiment (MHTEX), the Variable Emissivity Radiator Aerogel Insulation Blanket Dual Zone Thermal Control Experiment Suite for Responsive Space (VADER), and Canary.

The STP-H3 flight provides a proof of concept for a new low-cost, cutting-edge technology, sensing platform that will provide an enhanced pointing capability for nano- and pico-satellite busses. The potential benefit to the space community is the ability to provide operational data from small, low-cost platforms versus traditional large integrated platforms such as Defense Meteorological Satellite Program (DMSP) and National Polar-orbiting Operational Environmental Satellite System (NPOESS) is significant. This technology represents a key transition from large, high-cost, long-timescale programs to small, low-cost rapid response science enabling sensing platforms, explains NRL's Mr. Andrew Nicholas, principal investigator for DISC.

The NRL work was performed as a collaboration effort between the Space Systems Development Department's Space Applications Branch and the Space Science Division's Solar Physics Branch. NRL also collaborated with Space Dynamics Lab at Utah State University in the DISC project.