Technical Sessions

Session V: Advanced Technologies 1

Chair: Charles Scott MacGillivray, The Boeing Company

Tuesday, August 11, 2009

2:30 p.m. Exploiting Link Dynamics in LEO‐to‐Ground Communications

Joseph Palmer, Michael Caffrey – Los Alamos National Laboratory

ABSTRACT: The high dynamics of the LEO‐to‐ground radio channel are described. An analysis shows how current satellite radio systems largely underutilize the available radio link, and that a radio that can adaptively vary the bit rate can more fully exploit it, resulting in increased data throughput and improved power efficiency. We propose one method for implementing the adaptivity, and present simulation results.

2:45 p.m. Electrochromic Thermal Manager for Mini, Micro and Nano Satellites

Hulya Demiryont, Kenneth Shannon – Eclipse Energy Systems, Inc.; Elwood Agasid – NASA Ames Research Center

ABSTRACT: The thermal environments of satellites, in general, and futuristic mini, micro, nano and pico satellites, in particular, are in a constant state of flux. Each satellite houses valuable equipment having specified temperature limits and a range of heat generation rates. In order to maintain all equipment within operational temperature in this continuously temperature changing environment, an active thermal control system is required. Weight, size and energy requirements of the thermal controller of a satellite are a major challenge especially in light of the trend toward diminishing satellite size. In this paper, we present an active thermal manager capable of controlling the thermal conditions within a satellite and maintain a near room‐temperature environment. The thermal manager is an electrochromic device (ECD) that changes the reflectance/emittance properties of the attached surface in a controllable manner.

3:00 p.m. Calibration Techniques for Low‐Cost Star Trackers

Tom Dzamba, John Enright – Ryerson University

ABSTRACT: This study presents a series of cost‐effective strategies for calibrating star trackers for microsatellite missions. We examine three such strategies that focus on the calibration of the imaging detector, geometric lab calibration, and optical calibration due to lens aberrations. Procedures are developed that emphasize speed of implementation, and accuracy, while trying to minimize manual setup procedures. Preliminary results show that employing existing camera calibration techniques reduces the variation in pixel sensitivity by approximately 10%, averaged across each pixel color given the use of a color imager. Although not substantial, this reduction in pixel variation helps preserve the Gaussian illumination pattern of imaged stars, aiding in correct centroid location. Results pertaining to the lab calibration show accurate star placement, in angular terms, to 4.3x10^‐3 rads across most of the field of view. This provides an accurate, low‐cost, variable solution for characterizing sensor performance; specifically pattern matching techniques. Finally, we present some initial results from lens aberration characterization. Using a Gaussian model of the star image shape gives trends consistent with astigmatism and field curvature aberrations. Together, these calibrations represent tools that aim to improve both development and manufacture of modern microsatellite star trackers.

3:15 p.m. The ADPMS Ready for Flight: An Advanced Data & Power Management System for Small Satellites and Missions

Koen Puimège, Jo Bermyn‐ Verhaert Space

ABSTRACT: In a contract for ESA, Verhaert Space developed a state‐off‐the‐art control unit for small satellites. Built on the experience gained with the PROBA‐I satellite that has been in daily use since its launch in 2001. This next generation avionics has been developed and will have its first in‐orbit demonstration in 2009 as the satellite control unit for PROBA‐II. The objective of this paper is to explain the benefit of this avionics and its architecture towards small satellite integrators.

The ADPMS presented in this paper is designed for rapid adaptation to a diversity of next generation satellites. It provides the fundamental bus‐elements and allows the addition of third‐party cards thanks to its open ‘plug and play’ architecture, resulting in a more optimal spacecraft design and a reduced software effort with a consequent reduction in recurrent development costs and a much shorter production cycle.

3:30 p.m. Rapid Assembly of Spacecraft Structures for Responsive Space

Shazad Sadick, Roopnarine, Irene Yachbes – Honeybee Robotics Spacecraft Mechanisms Corporation

ABSTRACT: In order to achieve a six‐day spacecraft architecture, the assembly, integration & testing (AI&T) of the Satellite Bus could be drastically reduced by stocking component‐ready modular panels for assembly. The assembly of the structure itself, however, needs to be accelerated from the typical process of securing panels with dozens of mixedsize fasteners and the associated verification, tooling, and documentation that must also take into consideration the need to pass electrical and thermal connections across panels of the bus. A method for rapidly providing a stiff mechanical attachment across panels of a spacecraft bus, while simultaneously providing electrical and thermal continuity, helps to further realize the goals of Responsive Space (RS). A fastening strategy has been developed for enabling rapid assembly of a spacecraft bus structure using Honeybee’s patented Quick Insertion Nut (QIN) technology. The QINs are embedded in manifolds which reside at each edge inside the spacecraft bus (the manifold includes panel‐to‐panel electrical interconnects) and together form a skeletal structure for the spacecraft panels. Initial FEA analyses show that a bus construction based on this concept is capable of meeting the natural frequency requirements for a wide array of launch vehicles and that the QINs themselves are capable of withstanding very high tensile loads with positive margins of safety.

3:30 p.m. Follow that Ground Station! And Double the Data Throughput Using Polarization Diversity

Peter Garner, Nigel Phillips, Andrew Cawthorne, Alex da Silva Curiel, Phil Davies, Lee Boland – Surrey Satellite Technology Ltd./Surrey Space Centre

ABSTRACT: This paper describes the X‐Band Antenna Pointing Mechanism to be used for the first time as part of the Payload Downlink Chain on‐board the SSTL‐300 platform for the upcoming NigeriaSAT‐2 mission, due for launch late in 2009. NigeriaSAT‐2 is a high performance Earth Observation mission designed for a 7.5 year lifetime to achieve 2.5m imagery in a panchromatic waveband along with 5m and 32m imagery in four mutli‐spectral channels. The spacecraft will deliver high data throughput on an agile platform, whilst still maintaining high levels of pointing accuracy during downlink opportunities. All of this will be included in a 300Kg satellite. The innovative Antenna Pointing Mechanism developed by Surrey Satellite Technology Limited incorporates a compact circularly polarized antenna with a narrow 3dB beam‐width of 25degrees and bore‐sight gain of 15dBiC. It also houses the necessary drive electronics and structural elements to provide a nimble, 2‐axis antenna solution. The pointing accuracy of the unit is better than 1 degree and the maximum slew rate is better than 20deg/s, at acceleration rates up to 4deg/s/s. Such low‐cost and compact yet agile antenna systems have not been used previously on small satellite missions and as such, the Antenna Pointing Mechanism is an enabling technology in the commercialization of small Earth Observation spacecraft missions. Numerous design trades were made along the development path of the Antenna Pointing Mechanism and these are covered in this paper. Additionally a treatment of the use of polarization diversity on the NigeriaSAT‐2 mission as a way of doubling the data throughput capability is reported.