A Power-Efficient BPSK Communications System for Small Satellites

Many of the small satellites which have been launched or designed to date have used Frequency Shift Keyed (FSK) modulation for the communications link. FSK necessarily suffers a best-case signal to-noise ratio (SNR) loss of 3 dB for coherent demodulation. Many, if not most, of the FSK systems in use today employ non coherent demodulation which suffers additional SNR loss. This means that small satellites using FSK must use two or more times the minimum power required for the communications link. A small satellite using two watts for an FSK communications link could save at least 1 watt by using Bi-Phase Shift Keying (BPSK) or one of the other power-optimal modulations. This saved power would then be available for payloads or for increased data communications. Alternately, a satellite with one-half the solar-cell surface area could be used Cynetics Corporation has tested a commercially available 9.6 Kb/sec communications system which uses asynchronously detected, non-coherent FSK. This system has a measured implementation loss of 23.6 dB, which is roughly 20 dB worse than the 3 dB implementation loss one might expect. When the additional 3 dB FSK loss is considered, this system was 23 dB worse than a simple BPSK system with a 3 dB implementation loss. This means that this FSK system would require two hundred times (23 dB) as much satellite transmitter power as a reasonable BPSK system. Cynetics is completing the development of a 9.6 Kb/sec (BPSK) satellite communications link using synchronous matched-filter data detection. BPSK is one of the optimal pulse modulation methods (in an SNR and power-efficiency sense) which can save substantial power in a satellite transmitter. Cynetics\u27 BPSK system modulates and demodulates at the standard satellite communications IF frequency of 70 MHz. The expressed performance 1S a 10 b1t error rate for -116 dBm (2.5 x 10 watts) received signal power at the input to a 0.5 dB noise figure low-noise amplifier

The BREMSAT Phase-Modulated Communications Link

BREMSAT is a small scientific satellite being constructed by the west German Zentrum fur angewandte Raumfahrttechnologie und Mikrogravitation (ZARM), at Bremen University. BREMSAT\u27s payload consists of five scientific experiment packages. The satellite is scheduled for Get-Away-Special (GAS) Canister launch during the German D-2 shuttle mission in March 1992. Cynetics Corporation is constructing the TT&C link for the satellite, using its standard CMX9600 modem. This modem is the result of Cynetics\u27 development program for phase-modulated (PM) communications systems for small satellites. The CMX9600 is a 9.6 KC/s, Bi-Phase Shift Keyed (BPSK) modem using a 70-MHz IF and synchronous matched-filter detection. As we reported at the 1989 Small Satellite Conference, many small satellite systems use Frequency-Shift Keying (FSK) for communications. FSK is a sub-optimal modulation which suffers a best-case 3 dB degradation in signal-to-noise ratio when coherently demodulated. When non-coherent demodulation is used, as it often is, additional degradation in signal-to-noise ratio occurs. Antipodal phase modulations, such as Bi-Phase Shift Keying (BPSK) and Quadra-Phase Shift Keying (QPSK) are optimal modulations which do not suffer the signal-to-noise ratio degradations of FSK. Thus, when phase-modulation is used for downlinking, the satellite\u27s transmitter power can be decreased. This saved power is available for payload and bus operations. Or, a smaller satellite with less solar cell area may be used. FSK has been utilized in the past due to the perception that implementing an FSK system is simpler that implementing a phasemodulation system. However, with the advent of off-the-shelf phase-modulation TT&C links, such as the CMX9600, satellite system designers can easily incorporate the more power efficient phase modulation techniques into their satellites

Tracking Small Satellites using Translated GPS

This paper discusses using translated GPS for tracking small satellites, the technical trade-offs involved, and the position and timing accuracies which are achievable using translated GPS. The Global Positioning System (GPS) uses the relative times-of-arrival of multiple spread-spectrum signals at an antenna to determine the position of the antenna. The system can also determine the time the antenna was at that position. The direct sequence spread spectrum signals are transmitted from GPS satellites whose orbital position and timing (the ephemeris data) are accurately known. Once the GPS signals are received at the antenna, their relative timings are fixed, and are not changed in subsequent amplifications and signal processing. This fact can be used to track small satellites to a high degree of accuracy without placing a GPS receiver on the satellite. A GPS antenna is placed on the satellite, and the received signals are amplified, converted to a new frequency, and retransmitted to a ground-based GPS receiver. In the most cost-effective arrangement, the ground GPS receiver consists of a low-noise amplifier, a frequency converter to the original GPS frequencies, and an off-the shelf GPS receiver. The off-the-shelf receiver may be coupled to a computer for extensive post-processing. Such post-processing is currently available for IBM PC\u27s. The advantages of this translated-GPS tracking are that high order GPS receivers with large amounts of post-processing can be used for tracking spacecraft, while leaving the spacecraft electronics very simple. This allows highly precise, inexpensive, and power-efficient GPS systems to be used on small satellites without: the risk of non space-qualified GPS receivers: the expense of space-qualified receivers: or the power-consumption of high-order receivers

A Comparison of Digital Modulation Methods for Small Satellite Data Links

The selection of a good modulation scheme for a satellite data link should involve careful consideration of several factors. Bit-error-rate (BER), initial cost, power consumption, circuit complexity, channel linearity, reliability, and bandwidth must be considered and weighed in the selection process. This paper examines and compares various modulation methods applicable to small satellite data links. The performance of frequency-shift keying (FSK), bi-phase-shift keying (BPSK), quadrature-phase-shift keying (QPSK), offset QPSK (OQPSK), minimum-shift keying (MSK), and on-off keying (OOK) are compared. The use of a non-linear transmitter amplifier is normally desirable because of its power efficiency. Because of this, a near constant envelope modulation scheme is desired. Power efficiency and bandwidth efficiency may also be important. In regards to these and other criteria, OQPSK has good characteristics and is recommended

Using Digital Signal Processors on Small Satellites

Digital Signal Processing integrated circuits (DSPs) have improved terrestrial communications systems by allowing the implementation of greatly improved transmitters and receivers. In applications from dial-up modems, to echo-free conference phones, to customer-specific hearing aids, DSPs have allowed the implementation of functions that would be impractical without them. However, DSPs have had limited use in small satellites due to lower available data rates and relatively high power consumption. Also, most of the existing DSPs have not been space qualified. Improvements in semiconductor processes are allowing the construction of integrated circuits (ICs) with much smaller features. In fact, 0.6 micron processes are becoming generally available. Newer DSP ICs based on these processes have greater speeds and greatly reduced power consumption compared to their predecessors. This paper covers the general use of DSP ICs in small satellites, where the power consumption of on-board circuitry must be minimized. It then discusses DSP power consumption, the achievable DSP data rates, general radiation hardness for the existing DSPs, and the advantages and disadvantages of using DSP- based communication 1 systems in small satellites. The paper shows that the power consumption of presently available DSPs is now sufficiently low, and their processor speeds are now sufficiently high for application to some small satellite systems

Results from the Advance Power Technology Experiment on the Starshine 3 Satellite

The Starshine 3 satellite was put into orbit on September 30, 2001 as part of the Kodiak Star mission. Starshine 3’s primary mission is to measure the atmospheric density of the thermosphere and serve as a learning outreach tool for primary and secondary school age children. Starshine 3 also carries a power technology experiment. Starshine 3 has a small, 1 Watt power system using state-of-the-art components. Eight small clusters of solar cells are distributed across the surface. Each cluster consists of a 6-cell string of 2 cm x 2 cm, GaInP/GaAs/Ge, triple-junction solar cells. These cells have twice the power-to-area ratio as traditional silicon solar cells and 25% more power than GaAs cells. Starshine 3 also carries novel integrated microelectronic power supplies (IMPS). The idea behind an IMPS unit is to allow greater flexibility in circuit design with a power source not tied to a central bus. Each IPS is used to provide 50 microwatts of continuous power throughout the mission. Early results show that this design can be used to provide continuous power under very adverse operating conditions

Campus Vol VIII N 1

Howard Studio. Chris Doner . Picture. 0. Hawk, Pete and Don Shackelford. Prose. 2. Lefevre, Ioe. A Matter Of Propriety. Prose. 3. Porter, Bob. And, In Just 7 Days-You Too Can Be a Freshman! . Picture. 4. Martin, Lyn. And, In Just 7 Days-You Too Can Be a Freshman! . Prose. 4. Clapp, joy. Resignation . Prose. 6. Hawk, Pete. Mile Faces Life: A Case History . Prose. 8. Cook, Mike. A Definition of modernity . Poem. 9.; Miller, Ted. Untitled. Poem.9. Moore, Jules. On Picnics . Poem. 9. Emmet, June. Untitled. Poem. 9. Jacobs, Edward R. Orson Got Angry Again . Prose. 10. Ski-U-Mah. Contemporary Humor . Prose. 13. Pine Needle. Untitled. Prose. 13.; Anonymous. Untitled. Prose. 13

Effective Rheology of Bubbles Moving in a Capillary Tube

We calculate the average volumetric flux versus pressure drop of bubbles moving in a single capillary tube with varying diameter, finding a square-root relation from mapping the flow equations onto that of a driven overdamped pendulum. The calculation is based on a derivation of the equation of motion of a bubble train from considering the capillary forces and the entropy production associated with the viscous flow. We also calculate the configurational probability of the positions of the bubbles.Comment: 4 pages, 1 figur

Alignment of the ALICE Inner Tracking System with cosmic-ray tracks

37 pages, 15 figures, revised version, accepted by JINSTALICE (A Large Ion Collider Experiment) is the LHC (Large Hadron Collider) experiment devoted to investigating the strongly interacting matter created in nucleus-nucleus collisions at the LHC energies. The ALICE ITS, Inner Tracking System, consists of six cylindrical layers of silicon detectors with three different technologies; in the outward direction: two layers of pixel detectors, two layers each of drift, and strip detectors. The number of parameters to be determined in the spatial alignment of the 2198 sensor modules of the ITS is about 13,000. The target alignment precision is well below 10 micron in some cases (pixels). The sources of alignment information include survey measurements, and the reconstructed tracks from cosmic rays and from proton-proton collisions. The main track-based alignment method uses the Millepede global approach. An iterative local method was developed and used as well. We present the results obtained for the ITS alignment using about 10^5 charged tracks from cosmic rays that have been collected during summer 2008, with the ALICE solenoidal magnet switched off.Peer reviewe