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/SNIAS (F) which had developed a laboratory model liquid-helium cryogenic facility, and DASA (D) which had manufactured a development model of a German infrared laboratory (GIRL).

**Figure 2.2:** *Structure of the industrial consortium that developed, manufactured, integrated and tested the ISO satellite.*
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ESA's Industrial Policy Committee (IPC) decided, in April 1984, that the Phase B should be carried out by one prime contractor, who would be responsible for the design and development of the satellite and for the integration and testing of the scientific instruments. The prime contractor would lead a consortium of companies formed by several subcontractors. 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 with Aerospatiale as the satellite prime contractor 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 again 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 the prime contractor conducted in an effort to meet the overall geographical distribution and cost targets for Phase B and C/D.

**Figure 2.3:** *Industrial contractors by country contribution.*
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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 2.2 and 2.3.

The total price for the Phase C/D was 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 was higher than in a typical scientific spacecraft mission, i.e. about 70%. This was 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, implied a high technical risk and therefore also dictated a cost-reimbursement arrangement.

2.2.2 Model development and costs

The ISO satellite (in particular the cryogenic cooling system) and its scientific instruments employed very advanced technologies and therefore demanded an extensive development plan. The main technical challenges encountered were with the scientific instruments, the telescope, the cryogenic subsystem and cryostat, the Attitude and Orbit Control Subsystem and the Star-Tracker. The difficulties were all successfully overcome.

**Figure 2.4:** *The pre-launch ISO project schedule.*
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The project schedule is shown in Figure 2.4. The overall development at system level was ultimately accomplished using two models:

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 benefited because the flight model and flight spare could be alternately improved in parallel to the satellite development.

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

ISO was approved in 1983 at a cost of 258MAU, assuming 1982 economic conditions and 1983 exchange rates. During the Development Phase, there were a number of technical problems including the liquid helium valves, the telescope, the liquid helium tank, the attitude and orbit sub-system and science operations. These problems and the launch slip from May 1993 to November 1995 led to a number of cost increases. Additionally, the scope of the programme was extended by the extension of orbital operations by 1year and the approval of Post-Operations and Active Archive Phases. The final cost of ISO was 615 Meuros at mixed economic conditions. This corresponds to 480.1 Meuros when backdated to the same economic conditions as the approval level of 258 Meuros in 1983. The final cost includes not only the effect of problems and delays in the development but also various enhancements to the mission such as a 1-year extension of operations and the addition of the Post-Operational (3.5 years) and Active Archive (5 years) phases.

2.2 Satellite Development

2.2.1 Industrial consortium

2.2.2 Model development and costs