ISO Background articles

The ISO Programme

J. Steinz & A. Linssen

ISO Project, ESA Directorate of the Scientific Programme, ESTEC, Noordwijk, The Netherlands

ISO, the Infrared Space Observatory, will provide astronomer's with an unprecedented opportunity - and the only one for the next 10 years - to make scientific observations of weak infrared radiation sources. The development of the Observatory proved to be a challenging task: there was little available experience with the advanced technologies required for such a new infrared-astronomy mission. The scientific instruments were developed by groups of scientific institutes and industry under national funding. The satellite was developed, manufactured, integrated and tested by an industrial consortium made up of 32 companies, mostly from Europe. ESA is performing the flight operations. The USA and Japan are also contributing to the mission in return for observation time.


ISO, the Infrared Space Observatory, is a general purpose telescope facility to be used by the scientific community. It will provide infrared astronomers with an unprecedented opportunity - the only one in the world for at least the next decade - to make scientific observations of a wide variety of weak infrared radiation sources. The first major opportunity for European scientists was using IRAS, the Dutch-British-American Infrared Astronomical Satellite, which flew in 1983. The next possibility using a European satellite after ISO (in 1995) will be with ESA's FIRST (Far Infrared and submillimetre Space Telescope), which is proposed for launch in 2006.

ISO was conceived in the early 1970s. The Phase A study was completed in 1982 and in March 1983, ESA's Science Programme Committee (SPC) approved ISO as a project of ESA's Science Programme. The design and development phase of the project started in late 1986. The satellite has now been successfully tested and is waiting in Kourou, French Guyana, to be launched in early November of this year. The satellite will be operated from ESA's Villafranca ground station near Madrid, Spain. A second ground station, at Goldstone, California, will be used to relay telecommands and to receive telemetry from the satellite for several hours each day.

An overview of the organisation of the pro-ject, the satellite procurement approach and development programme follow.

International cooperation

Both the USA and Japan had expressed great interest in using ISO. As a result, ESA made a special agreement with NASA, and Japan's Institute of Space and Astronautical Sciences (ISAS): NASA is providing the second ground station and ISAS is supporting the flight operations; in return, NASA and ISAS will each be allotted a half hour per day of ISO's time for use by their scientists.

Project organisation

The overall project organisation is shown in Figure 1. Central to this organisation is the ESA Project Team which is located at ESA's European Research and Technology Centre, ESTEC, in Noordwijk, The Netherlands. This project team, part of the ESA Directorate of the Scientific Programme, is responsible for the management of the development, launch and in-orbit commissioning of the satellite. The ESA Space Science Department assumes responsibility during the subsequent routine operations phase of the mission, with the spacecraft operations being delegated to ESOC.

The main groups involved in the development of the project are described below.

ISO Project Organisation
Figure 1. ISO project organisation

Principal Investigator groups

ISO has four Principal Investigators (PIs), one for each of the scientific instruments. The scientific instruments were developed under national funding, with each Principal Investigator being responsible for his or her own scientific instrument. Each instrument was developed by a group involving many institutes and industries. Over 45 organisations in total were involved. Figure 2 lists these organisations by country and instrument name.

PI Organisations
Figure 2. Principal Investigator (PI) organisations by country and instrument

The PIs are responsible to the ESA Project for the delivery of their scientific instruments for integration and testing with the satellite. In return for the effort of developing the instrument, the PIs are guaranteed the use of ISO for about one-third of its total operations time in orbit. The PIs plan this guaranteed time in great detail and share it with their many Co-Investigators and Scientific Associates, about 100 astronomers in total. The remaining two-thirds of ISO's operations time is open to the scientific community, i.e. any scientist in Europe, the USA or Japan, through the submission of observing proposals (see the following article, 'Using ISO').

Science Team

The ISO Science Team (IST) is an advisory group appointed by ESA's Director of the Scientific Programme to advise ESA on all scientific aspects of the mission. The IST consists of the ESA Project Scientist, the four PIs, five Mission Scientists providing independent advice, and a representative from the ESA Project Team and both ISAS and NASA. The IST has followed the development of the project and has met quarterly to address the important scientific issues that have arisen during the development phase.

Satellite Prime Contractor

The Satellite Prime Contractor, Aerospatiale (F), was responsible for the design and development of the satellite and for the integration and testing of the scientific instruments with the satellite. The industrial organisation required to design and develop the hardware required to build and test the satellite consisted of 32 companies. The structure and each participant's contribution are shown in Figures 3 and 4.

Industrial Consortium
Figure 3. Structure of the industrial consortium that developed, manufactured, integrated and tested the ISO satellite

Industrial Contractors
Figure 4. Industrial contractors by country contribution

Launcher authority

Arianespace is providing the launch vehicle and all associated launch services. The interfaces and operations with ISO, however, are unusually complex because of ISO's need for frequent liquid helium cryogenic servicing until shortly before launch. Arianespace has had to make special provisions to cope with the more complicated and longer duration launch campaign and combined operations with the launch vehicle.

Science and spacecraft operations

The ESA Space Science Department is responsible for the science operations, i.e. the in-flight operations of the scientific instruments. It developed the necessary software at ESTEC. This software development was a difficult and challenging undertaking, mainly because of the high degree of automation required to perform scientific observations. It is further complicated by the many constraints to be respected to ensure the safety of the satellite even if control from the ground is lost.

ESA's space operations centre, ESOC in Darmstadt, Germany, is responsible for the ground segment and for operating the spacecraft. ESOC will control the satellite from its operations control centre at Darmstadt during the Launch and Early Orbit Phase, i.e. the first four days after launch. After this critical phase of the flight, the satellite and its scientific instruments will be controlled from the ISO Control Centre at Villafranca, Spain, where both the science operations and spacecraft operations teams are co-located.

ESOC is also coordinating its operations with NASA-JPL, which is providing the second ground station for ISO at Goldstone, and with ISAS in Japan, which is providing support for ISO's flight operations.

Satellite development


A number of specific features of ISO had to be taken into account to establish the industrial policy regarding the satellite development. In particular, there was little experience available anywhere in the world with respect to infrared astronomy. Only one major mission, IRAS, had been flown. The expertise available in the field of space cryogenics and the assembly, integration and verification of large super-fluid- helium cryostats, was also very limited. Only two companies in Europe had relevant experience: Aerospatiale (formerly SNIAS) which had developed a laboratory model liquid-helium cryogenic facility, and Daimler-Benz Aerospace (formerly MBB) which had manufactured a development model of a German infrared laboratory (GIRL).

It was decided that the Phase B design should be carried out by one prime contractor who would lead several subcontractors. (Competitive parallel studies was not considered a realistic option because of various constraints, such as the need for confidentiality, that impede progress and creativity.) ESA's Industrial Policy Committee (IPC) approved, in April 1984, the proposal to enter into direct negotiation with Aerospatiale which would lead a consortium of companies that would include Daimler-Benz (formerly MBB) and Linde AG (D). It was also decided that critical technology items such as cryostat components and telescope mirrors would be developed in parallel to the Phase B design activities.

In November 1986, the IPC approved the placing of the Phase B contract and work started in industry in early December 1986. By the end of Phase B, 15 companies were involved in the work. Following the successful completion of Phase B, the Phase C/D contract was placed with Aerospatiale and work started at the end of March 1988. The industrial consortium was extended to include a number of companies that had been selected through competitions that Aerospatiale as Prime Contractor conducted in an effort to meet the overall geographical distribution and cost targets for Phase B and C/D. Competitions were conducted for the following items:

At a later stage during Phase C/D, more competitions were held for the cryo-electronics unit and the data handling decoder. As a result, the final industrial consortium for ISO comprised 32 companies, with one prime contract and 44 sub-contracts. The final structure of the industrial consortium that developed, manufactured, integrated and tested the ISO satellite is depicted in Figures 3 and 4.

The total price for the Phase C/D is made up of cost-reimbursement prices associated with a cost-incentive scheme, and firm-fixed or fixed prices with variation. The percentage of the price consigned to a cost reimbursement is higher than in a typical scientific spacecraft mission, i.e. about 70%. This is due to the very advanced technology of the payload module and the greater-than-usual development risk. Also, the demanding mission requirements, such as those of the attitude and orbit control subsystem, imply a high technical risk and therefore also dictate a cost-reimbursement arrangement.

Development plan

The ISO satellite (in particular the cryogenic cooling system) and its scientific instruments (e.g. the detectors) employ very advanced technologies and therefore demand an extensive development plan. The plan, however, must be sufficiently flexible to cope with unexpected problems. (The development plan is described in another article, The ISO Spacecraft , in this issue.) The main technical challenges encountered were with the scientific instruments, the telescope, the cryogenic subsystem and cryostat, the attitude control subsystem and the star tracker. The difficulties have all been successfully overcome.

The project schedule is shown in Figure 5. The overall development at system level was ultimately accomplished using two models:

- A Development Model (DM):
The Service Module was essentially a structural/thermal model with dummy mass units. The Payload Module (cryostat) was built in full flight configuration. Nearly all development problems were resolved using this model.

- A Protoflight Model (PFM):
All of the DM's shortcomings were corrected on the PFM and the PFM was then subjected to qualification tests. This approach was extremely successful: the final PFM test sequence did not reveal any new major problems. Clearly, all the major problems had been identified and resolved on the DM.

All units were required to be delivered in two models, a flight model and a flight spare (which is generally a refurbished qualification model). The availability of flight spare units contributed greatly to the success of the programme: small problems could be easily resolved by simply exchanging units and thus avoiding any major delays. The scientific instruments also benefitted because the flight model and flight spare could be alternately improved in parallel to the satellite development.

ISO Project Schedule
Figure 5. ISO project schedule

Projected costs

The total project costs, based on the expected lifetime of 18 months, are predicted to be 713 MAU based on 1994 economic conditions.


The satellite qualification and acceptance test programme and all tests with the ground segment have been successfully completed. The satellite and all its associated support equipment were transported by ship to the launch range in Kourou, French Guiana, in June 1995. The satellite was fully tested again in Kourou and is now waiting to be installed on the Ariane launch vehicle to be launched in early November 1995.