摘要:

TheUoSAT-2spacecraft was designed and built at the University of Surrey and launched into a low Earth orbit within the remarkably short timescale of 6 months and on a budget of £450000. It has demonstrated clearly both the feasibility and potential of inexpensive yet sophisticated spacecraft, and has also shown that such projects can be undertaken successfully by a compact university team. Launched by NASA as a secondary payload in March 1984,UoSAT-2has mission objectives that support cost-effective spacecraft design and operation, evaluation of new technologies in the space environment, provision of flight opportunities for modest space science payloads, evaluation of novel communications services, and the promotion of space education.UoSAT-2is fully commissioned and operational in orbit, supporting daily experiments on a weekly schedule under the automatic control of an on-board computer. Investigations of digital store-and-forward communications, the effect of the space radiation environment on VLSl devices, CCD Earth imaging, auroral particle-wave studies, spacecraft engineering and space education experiments are being pursued.

DOI:10.1049/jiere.1987.0077

出版商:IERE    

年代:1987

数据来源: IET

摘要:

Four panels of Si solar cells provide power to charge packs of NiCd battery cells via a battery charge regulator. Regulated + 10 V, − 10 V and + 5 V supplies from a centralized power regulating system, as well as + 14 V unregulated battery voltage, are supplied to a power distribution module which uses bipolar transistors to switch power as required to different loads. AsUoSATis in eclipse for over one-third of its orbit, batteries with good cyclic performance must be provided.UoSAT-2operates on a negative power budget where the power required to keep all systems fully operational is greater than the solar power available. Consequently, significant groundstation effort is required to monitor and manage the power system. Future satellites may incorporate a microprocessor-driven control element in a further step towards system autonomy.

DOI:10.1049/jiere.1987.0089

出版商:IERE    

年代:1987

数据来源: IET

摘要:

Telemetry and telecommand functions on board a spacecraft are key subsystems that must exhibit exemplary performance, reliability and integrity. This paper reviews the operational experience gained in low Earth orbit with the telemetry and telecommand subsystems on board theUoSAT-1spacecraft. The impact of that experience on the subsequent design and implementation of these subsystems for theUoSAT-2spacecraft are discussed and the orbital performance described.

DOI:10.1049/jiere.1987.0088

出版商:IERE    

年代:1987

数据来源: IET

摘要:

TheUoSAT-2spacecraft incorporates two ground-programmable computers. The primary computer is based around an RCA 1802 microprocessor and is intended for general-purpose management and data collection purposes within the spacecraft, whilst the secondary computer, based on the National Semiconductor NSC-800 microprocessor, controls the Digital Communications Experiment and has a more limited interface to the rest of the spacecraft. This paper describes how the experience gained from operating theUoSAT-1spacecraft led to an enhanced primary computer design onUoSAT-2.

DOI:10.1049/jiere.1987.0087

出版商:IERE    

年代:1987

数据来源: IET

摘要:

Following the launch and successful operation of the twoUoSATspacecraft, a mini operating system has been implemented on the primary on-board computers of each satellite. Known as the ‘Diary’, it enables a range of spacecraft activities to be performed in a regular sequence, or at times defined by a real-time clock/calendar facility.This paper provides an insight into the philosophy of the system structure, and gives details pertaining to the design constraints imposed by the nature of the target processor. An outline description of the Main Tasks is given, together with examples of the various data formats utilized. The problems associated with sending and receiving data from spacecraft in low, polar Earth orbits are discussed, and methods used in overcoming these difficulties are detailed.Following on the development of the Diary system, originally forUoSAT-2, it was modified for use onUoSAT-1thereby greatly enhancing the operational capability of that satellite in orbit. The paper identifies the modifications necessary for the Diary to run on theUoSAT-1primary spacecraft computer.

DOI:10.1049/jiere.1987.0086

出版商:IERE    

年代:1987

数据来源: IET

摘要:

Gravity-gradient torques are very weak and are, alone, unable to provide a satisfactory degree of pointing precision and, if undamped, exhibit considerable libration. Thus, passive gravity-gradient torques are augmented onUoSAT-2by the use of magnetic torques generated through the use of ‘magnetorquer’ coils, which are commutated with the local geomagnetic field vector according to control algorithms implemented by an onboard computer.The attitude dynamics, stabilization procedures, attitude determination procedures and orbital results ofUoSAT-2are described, indicating the expected limits of performance and plans for future work.

DOI:10.1049/jiere.1987.0085

出版商:IERE    

年代:1987

数据来源: IET

摘要:

The Digital Communications Experiment (DCE) in orbit on theUoSAT-2satellite was designed to gain flight experience with the hardware and software necessary to operate a store-and-forward communications service from a satellite in low-Earth orbit. Since its commissioning in early 1986, the DCE has been used to relay up to 30 pages of information per day among groundstations in the USA and the UK; the Amateur Radio Service uses the DCE to relay messages among Local Area Packet-radio Networks. The DCE is also running an electronic mail system designed to interact with one user at a time.

DOI:10.1049/jiere.1987.0084

出版商:IERE    

年代:1987

数据来源: IET

摘要:

Models of mechanisms which explain the electron and ion distributions in the aurora and magnetosphere need refining; recent models are based on various wave-particle interactions. The nature of the Earth's radiation environment is first described before outlining the sensors and experiments onUoSATwhich, it is hoped, will aid in resolving the dynamics of space plasma under a variety of conditions. By correlating the measurements fromUoSAT-2and from the SwedishVIKINGspacecraft, it is possible to distinguish between the spatial and temporal distribution of particles.

DOI:10.1049/jiere.1987.0083

出版商:IERE    

年代:1987

数据来源: IET

摘要:

The Earth imaging experiment onUoSAT-2is a further development of the study, started withUoSAT-1, into the feasibility of providing low cost spacecraft imaging facilities to meet the requirements of scientists and meteorologists. It is also intended to demonstrate an alternative, inexpensive space imaging capability to agencies not wishing to rely solely on the satellite imaging programmes sponsored by the USA, USSR and ESA.Based on solid state charge coupled device (CCD) technology, a small low cost camera was designed and built for incorporation intoUoSAT-2. This camera is designed to satisfy the medium resolution requirement (approx 2–3 km) which is sufficient for many meteorology and climatology applications.The image data generated by the CCD camera is digitized and stored in the Digital Store and Readout (DSR) memory experiment also on-boardUoSAT-2. The DSR is a general purpose 192 kbyte CMOS storage facility which supports error-protected downlink transmission using CRC and Fire block coding.This paper describes the design and operation of both the imaging and DSR experiments on the spacecraft.

DOI:10.1049/jiere.1987.0082

出版商:IERE    

年代:1987

数据来源: IET

摘要:

UoSAT-1was launched in 1981 into a low Earth polar orbit, controlled by the groundstation at the University of Surrey and supporting a worldwide community of experimenters. Still operational after six years in orbit,UoSAT-1has experienced operational problems which have been overcome through imaginative use of the extremely flexible spacecraft system architecture. These problems and their solution, as well as the successes—since more of value is often learned from adversity than immediate success—are described.

DOI:10.1049/jiere.1987.0081

出版商:IERE    

年代:1987

数据来源: IET