Posat 1 [SSTL]
PoSAT-1 (Portugese Satellite) is a collaborative research mission, combining
tailor-made technology transfer, training, and a sophisticated ground and space segment
The PoSAT-1 microsatellite has been built at the University of Surrey within a
collaborative programme in satellite technology between a consortium of Portuguese
academia and Industry (LNETI, EFACEC, OGMA, MARCONI, ALCATEL, IST, UBI & CEDINTEC) and
the Univerity of Surrey, managed through Surrey Satellite Technology Ltd.
The PoSAT collaboration is similar in scope to SSTL's highly successful programme with
South Korea, which led to the launch of KITSAT-1 in 1992. It has encompassed the
installation by SSTL of a satellite groundstation near Lisbon, and the construction of an
engineering model satellite by a national team in Portugal. Meanwhile, on-the-Job training
and technology transfer to Portugal has been achieved by a team of seven Portuguese
engineers working alongside SSTL engineers at Surrey on the design, construction and test
of the first Portuguese satellite, PoSAT-1, for launch by Ariane in September 1993.
PoSAT-1 uses the SSTL modular microsatellite platform, previously proven on three
research (UoSAT-3,4 and 5) and two commercial missions (S80/T and KITSAT-1). It carries a
wide range of payloads:
- Earth Imaging System (EIS)
The PoSAT-1 EIS consists of two Charge-Coupled Device (CCD) imagers, two lenses and a
Transputer Data Processing Experiment to provide on-board image processing and data
compression. One imager has a wide field of view with 2 km ground resolution, the second
narrow field imager provides 200m ground resolution.
- Star Sensor
The star sensor is based on the same technology as the EIS, but is optimised for imaging
the faint light from stars for use as part of the spacecraft's attitude determination
system. The star-field image is analysed by the Transputer Data Processing Experiment and
the resulting measurement data returned on the On-Board-Computer.
- GPS Navigation
PoSAT-1 carries a Global Positioning System (GPS) receiver based on the Trimble TANS-II
receiver. The received data is decoded and filtered by the Transputer Data Processing
Experiment to provide the satellite position and velocity as well as an accurate on-board
time reference. This enables the satellite to generate its own orbital element set,
provide scheduling and synchronisation to other on-board computers, and allow
groundstations equipped with a GPS
receiver to experiment with applications for real-time
differential GPS data.
- Cosmic Ray Experiment (CRE)
The CRE monitors the space radiation environment experienced in orbit by the satellite and
enables analysis of its effect on spacecraft semiconductor electronics. The CRE contains a
large area PIN diode and multi-channel analyser capable of detecting energetic particles
with a wide range of Linear Energy Transfer to build up a spectrum of observed energies of
particles within the spacecraft. Special RADFET's are also incorporated to monitor the
accumulated ionising dose. The larger memory devices in the on-board computers are
regularly 'washed' to detect and log Single Event Upset (SEU) information.
- Digital Signal Processing Experiment (DSPE)
The DSPE consists of two Texas Instruments processors from the TMS320 series, the C25 and
C30. The DSPE can be used as a programmable communications modem to modulate the downlink
data from, or demodulate uplink data for the OBC, thus enabling experiments with new
modulation techniques optimised for Low Earth Orbit satellite mobile communications.
- Store and Forward communications
The main On-Board Computer (OBC), based on an 80C186 8 MHz processor with 16MByte of Static
RAM, also supports digital Store and Forward communications using AX25 packet protocols
and communications links optimised for communications using very low cost, simple and
portable groundstations. The Store and Forward system employs a 9.6 kbps uplink and 9.6 and
38.4 kbps downlink data rates.