M.  Bekhti, A. Oussedik
Centre National des Techniques Spatiales,
BP 13, Arzew 31200, Algeria.

Professor M.N. Sweeting,
Centre for Satellite Engineering Research,University of Surrey,
Guildford, Surrey GU2 7XH, UK

Abstract

The Centre National des Techniques Spatiales (CNTS) in Arzew-Algeria and Surrey Satellite TechnologyLimited (SSTL) at the University of Surrey-U.K. signed in August 2000 a long-term collaborative programme in microsatellite technology transfer and training.

The short term main objective of this programme is the know how transfer which was designed to give full hands on training for 11 engineers, during 15 months, in satellite engineering techniques at Surrey. The programme includes the design, realization and tests of the Algerian microsatellite (AlSAT-1) and the launch into low Earth orbit in 2002. AlSAT-1 will carry as a main payload a multi-spectral earth observation imager. Digital store and forward communications can be experienced between two points and autonomous GPS positioning techniques also accomplished.

The longer-term objective of the programme is to generate a cadre of trained personnel in Algeria who will establish the future national capability for small micro and minisatellites for a variety of commercial and scientific research applications.

AlSAT-1 will be part of an international (BNSC-UK, China, Nigeria and Thailand) disaster-monitoring constellation (DMC) of 5 microsatellites dedicated for monitoring disasters throughout the earth such as floods, fires, earthquakes, volcanoes, large-scale industrial accidents and civil strife. When there are no disasters, AlSAT-1 will be used for Algerian purposes such as monitoring desertification, industrial and marine pollution, agricultural monitoring, geophysics mapping and fire detection. The nature of the mission is that the 5 microsatellites, when coordinated together, can produce a daily revisit with a 32 m resolution multispectral imaging and 600 km ground track. AlSAT-1 will use the flight proven modular SSTL bus from previous missions but will carry a push broom imager for the first time on SSTL microsatellites. As a part of the constellation and to maintain a daily coverage, AlSAT-1 will be equipped with a propulsion system for orbit corrections.

This paper outlines the Algerian microsatellite programme as part of a Technology transfer between CNTS (Algeria) and SSTL (U.K.).

 Introduction

Every year natural and manmade disasters cause devastating problems worldwide in terms of loss of life, widespread human suffering and huge economic losses. Remote sensing satellites can contribute to mitigating such devastations through early warning, event monitoring and later analysis.

Existing earth observation satellites provide useful information to disaster management organizations but their limited swath coverage and lengthy revisit times, added to cloud cover, mean that data is very often unavailable in the timescales needed for effective use. Networks of earth observation satellites have been proposed in order to improve the swath and revisit time. However, the high cost of conventional remote sensing satellites has previously led to business failures.

The last decade has witnessed a fantastic step forward in space with the advent of highly capable and yet low cost microsatellites and minisatellites able to provide high quality imagery from space but with an order of magnitude reduction in both cost and timescale.

In 1996, at the IAF congress in Beijing, Surrey Satellite Technology Limited proposed a disaster-monitoring constellation of 7 microsatellites to meet this urgent need. During 1999, Surrey Satellite Technology Limited (SSTL) developed the disaster-monitoring constellation (DMC) design to the interested organizations. To be operational, the disaster-monitoring constellation (DMC) needs a minimum of 5 microsatellites to provide an image anywhere on the earth in 24 hours. In comparison, other systems such as Landsat-7, give the same image anywhere in the entire world in 17 days.

The rule for the DMC is that each satellite participating in the constellation must be partially or fully funded by a different nation. In the case of AlSAT-1, the satellite is funded by the Ministry of Higher Education and Research and is now being built at SSTL as part of a know how and transfer programme. AlSAT-1 is the new generation of SSTL enhanced micro satellite weighing 100-130 kg. The innovative idea behind this approach is that every member pays for its satellite but the overall contribution of the five countries has a better synergy and therefore overall better costs, timescales and results. When the satellites are not being used for DMC purposes, each satellite is therefore monitored and controlled in orbit by its owner. Algeria is a huge country and the second largest on the African continent with an area greater than 2.5 million square kilometers. It is a very demanding country of this type of technology for various fields of applications. This is why Algeria is planning for the next decade a space programme to cover: telecommunication, particularly in remote regions and the south of the country, remote sensing for agriculture, water resources, mining, oil fields, fishing, desertification, marine and atmosphere pollutions and positioning for seismology on the Mediterranean basin.

Technology transfer and training programme

1.      Know how transfer course:

1.1     Short course: at the beginning of the programme and during 4 weeks, a spacecraft-engineering course was given to the Algerian team. This is an intensive postgraduate level course consisting of an introduction to satellite engineering techniques, launch vehicles, the space environment, the ground station and quality assurance.

1.2     Technical lectures: this is a series of lectures by senior SSTL engineers describing each of the subsystems and payloads of the current generation of SSTL microsatellites with an overview of AlSAT-1 subsystems and the payload.

1.3     Technology training: this programme provides the TT team with the technological information. Assisted by SSTL engineers, the Algerian team participates in the design phases of AlSAT-1. The main tasks in which the TT team will be involved are as follows:

·          Mission analysis,

·          Subsystem and payload design,

·          Assembly integration and tests,

·          Environment test,

·          Launch campaign and launch,

·          In orbit commissioning and operations.

1.4     Training model: this programme is designed to give the Algerian team full practical experience and skills through working on one of recent SSTL satellites. The training model consists of the manufacture and laboratory testing of all subsystems.

2.      Academic training:

Surrey Space Centre provides formal academic training and qualifications through postgraduate M.Sc taught and research courses and PhD in satellite engineering. For the long-term national space programme, Algeria started this training in space techniques in 2001 with 4 M.Scs and 4 PhDs covering several aspects of satellite engineering.

AlSAT-1 payload

The Algerian satellite is one of SSTL’s new generation microsatellites in a sense that it carries a new type of push broom sensors. These types of sensors can previously only be found in larger commercial satellites. Because of the advance in electronics and semiconductor integration on a single chip, nowadays these sensors are being implemented by SSTL on microsatellites.

AlSAT-1 is designed to view the earth surface with a 32 m resolution in three spectral bands (R, G, NIR) and a ground track of 600 km. The spectral bands were chosen to correspond to those used by commercial satellites in the following wavelengths (in _micrometer) 0.5-0.6 _micrometer, 0.6-0.7 , 0.7-0.8 ). The imaging system comprises two cameras for each spectral band and two sensors with 10 000 pixels each. This represents a huge quantity of data for the electronics on board (processors, SSDR, fast clocks) to deal with.

The cameras provide 32 m ground resolution in 3 spectral bands capable of giving detailed information on earth resources, land use and effects of pollution and natural disasters using 2x10 000 pixels linear array detectors digitized to 8 bits radiometric resolution (256 levels). The image swath width is 600 km and the imager can collect images continuously along the flight track. The images are stored on board the microsatellite via the On Board Computer (OBC) and Controller Area Network (CAN) in the 2x512 Mbytes Solid State Data Recorder (SSDR) for later transmission to ground via digital packet error controlled links at 8 Mbit/s in S-band.

However, on the satellite there will be an option to do “windowing”. By using this technique, we can take images of 100x100 km and thus extend the track range.

             Figure 1: AlSAT-1 imager

AlSAT-1 platform

AlSAT-1 structure design is based on standard SSTL Aluminum machined module trays which house the electronics. Once different modules are stacked together, this will give maximum stiffness for the structure, particularly during launch. This modular structure has been used successfully by SSTL on 20 missions with different payload requirements.

Four body mounted gallium Arsenide (GaAs) solar array panels generate the on board electrical power. The panels will generate each 60-Watts and the energy is stored in a 4 Ah nickel cadmium (NiCd) rechargeable battery.

D= Delta (USA); A= Ariane; T=Tsyklon (CIS); Z= Zenit (CIS); R= Rokot (CIS) ; At=Athena ; S=SS18

# = Technology transfer & training mission * Built in Korea using SSTL platform and KAIST payload

Table 1: SSTL Micro/Minisatellite Missions.

Mission ground station

In order to promote space activities in Algeria prior to the launch of the AlSAT-1 micro satellite, the Centre National des Techniques Spatiales (CNTS) has requested a VHF/UHF ground station to be provided by Surrey Satellite Technology Limited (SSTL) within the know how transfer programme and installed during September 2001 in the CNTS premises in Arzew-Algeria. This ground station will serve to train the TT engineer on operations on SSTL microsatellites where permitted by their owners prior to the launch of AlSAT-1.

The satellite mission operations and control ground station, operating in S-band, will be installed at the CNTS premises in January 2002 to be ready for the TT responsible engineer to operate AlSAT-1 after launch into Low Earth Orbit (LEO).

Post-launch commissioning of the microsatellite will be done from this ground station by a joint SSTL/national team in collaboration with the SSTL ground station in the UK acting as backup.

Figure 2: S-band antenna for AlSAT-1 ground station.

Launch

In general, in order to keep the overall mission cost low, SSTL’s satellites have generally been launched as secondary payloads into low earth orbit.

For DMC, it is intended to have a meeting here in Guildford of the five participating countries late this year to decide about the launch agency and options.

SSTL, because of their experience over the last missions, have already been approached by space agencies such as Russia and China to launch DMC satellites.

Conclusions

SSTL has developed an effective satellite technology transfer and training programme, built around its unique combination of academic and commercial environment enabling in-depth, rigorous academic training to be enhanced with detailed 'hands-on' practical experience with advanced micro satellites and mini satellites for communications, space science, remote sensing and in-orbit technology demonstration missions.

This will enable Algeria to develop an evolutionary, low-risk and affordable space programme in collaboration with Surrey starting with an enhanced 100 kg microsatellite, and developing progressively through increasingly capable 300-400kg mini satellites in a long-term programme.

References

1.        Space engineering and technology transfer training at surrey, Sweeting M.N., IAF conference, 1996.

2.        The role of small, cost effective spacecraft in developing countries, Ward J.W., Sweeting M.N., proc. Space commercialization: role of developing countries, university of Tennessee, Nashville, Tennessee, USA, march 5-10, 1989.

3.        UoSAT microsatellites missions, Sweeting M.N., IEE electronics and communication engineering journal, vol. 4, No. 3, June, 1992, pp. 141-150.

4.       Micro satellite and Mini satellite Programmes at the University of Surrey for Effective Technology Transfer & Training in Satellite Engineering; Sweeting M N., Proc. of Int. Symp. on Satellite Communications and Remote Sensing, 20-22 Sept 1995, Xi'an China.