The merits of Small Satellite missions have been assessed by the Agency's Scientific Projects Department looking, specifically from the science viewpoint, at means for implementing such missions in the complex environment within which multi-national agencies such as ESA must operate.
During the early phases of the space age, satellites tended to be small, being limited by both the available technology and launch capability. As the technology improved and as launchers became more powerful, the size of the payloads naturally grew apace. In the expanding economies of the time, there was a public desire to explore the new environ-ment, and a feeling that space activities were at the cutting edge of engineering and scientific development. Funds were therefore made available to support the growth. The much-changed environment of today - an austere funding climate - is now encouraging a strong user interest in cheaper and more frequent missions, an interest that is forcing the established space agencies to rethink their approach to spacecraft procurement and mission design.
The ESA Science Programme has a strong interaction with the scientific community and is well aware of the latter's wishes. Consequently, the Agency has expended considerable effort in recent years on exploring several options for small scientific satellite missions, but so far without reaching any definite conclusions as to how to implement such missions in the context of the ESA scientific programme.
The first relevant mention of small missions was associated with the approval of the Space Science:Horizon 2000 strategic plan for European space science, in 1985. Within this plan, a small-mission programme was foreseen in addition to the use of the Space Station and the European Retrievable Carrier 'Eureca'. As a consequence, consideration was given to the possible procurement of ESA's Cluster-mission spacecraft using similar procurement rules to those employed for the AMPTE mission. It was concluded at that time, however, that the changes needed to apply a similar 'small satellite'approach to Cluster were too wide-ranging and so different from current practice that they were unlikely to be approved by the ESA funding authorities in time for that mission. The Cluster project has therefore proceeded along more classical lines.
Nevertheless the Agency, ever mindful of the need to increase the frequency of mission opportunities, continued to seek, in accord-ance with the planned objectives of the Horizon 2000 plan, means of introducing smaller, cheaper missions into its programme. A special users group was set up within the Science Directorate to identify means of increasing the number of flight opportunities and to foster interest in and develop an approach by which small missions and individual payloads could be flown at low cost. At that time, flight opportunities on Space Station/Columbus and Eureca were being given high priority, as well as potential small 'self-contained' missions.
In 1990, the Pinkau Committee, which had been conducting a policy review of the ESA Science Directorate, confirmed that small missions should be included in the ESA programme with the promise that 10 MAU of savings would be freed for that purpose. One idea was that Member States could procure missions under the overall management of the Agency, but without the normal constraints such as an equitable geographical return on an individual-mission basis.
Later that year, therefore, the Agency issued a 'Call for Ideas'for small missions in an attempt to assess the potential interest. Some 52 proposals were received and evaluated by the ESA advisory groups. From this menu, two missions were selected for further study by way of being good typical examples of small missions in two different areas of science:
The aim of the study was to explore technical feasibility, to verify the scientific return, and to assess the potential cost.
The response to the Call for Ideas and the resulting study of the SOLID and CUBE examples showed that there were some genuine, scientifically justifiable, small-mission ideas seeking a launch opportunity (Table 1), and so in March 1992 a Workshop was organised to explore the possibilities further.
From the study, and also from the conclusions of the Workshop, however, it emerged that there were a number of fundamental technical, managerial and policy subjects that had to be addressed before such a programme of missions could be considered for practical implementation.
Theey included the need for a Europeansmall launcher, the constrained industrial procurement policy applied by the ESA Member States (the 'geographical return'), and the need for a more flexible personnel policy within the Member States, ESA, and Industry.
All of this led ESA to the conclusion that the setting up of a small-mission programme would be a lengthy process, precluding any short-term start to such a programme. Nevertheless, in recognition of the community interest, it was proposed that ESA would continue to consider small-satellite programmes within the Member States and would pursue small-mission opportunities with the Member States on a case-by-case basis. In addition, the Agency included a specific request for small-mission proposals in its November 1992 'Call for Mission Proposals'.
Although some 13 small-mission proposals had been received for consideration by April 1993, and were carefully evaluated by both the ESA Science Working Groups and the ESA Space Science Advisory Committee, none were recommended for further study.
Today, the term 'small satellite' means different things to different people and, depending on whom you ask, can range from the extremely simple to the relatively complex. If the individual scientist is asked to propose a small mission, many replies will be received. If, however, a group of scientists is asked, a discussion is started on the relative merits of small satellites, but without having a proper definition of what truly constitutes a small-satellite mission.
Having asked the individual (via a Call for Proposals) and having asked the group (via the ESA Advisory Bodies), the Agency now finds itself in the middle of such a discussion and faced with the questions:
In order to answer them, the ESA Science Directorate is presently making a wide-ranging study of the issues involved - both scientific and organisational (see panels on following pages) - with a view to developing a Directorate policy towards the procurement of small satellites for, or by, the European scientific community. This study, which will eventually embrace a wide cross-section of the European scientific community, is being carried out in three distinct phases, as shown in Figure 1.
The first phase of activity has now been completed. During this phase, several meetings have taken place within ESA, each concentrating on a particular topic:
The initial findings can be summarised as follows:
Definition of 'small satellites'
This topic has proved to be the most elusive in that, despite all the studies made in the Executive and elsewhere, and the plethora of opinions expressed, there is still no universally accepted definition of what constitutes a 'small satellite'. Some authors use mass, others cost and short development times, while still others use relative complexity. The conclusion of the group is that the best criterion for defining a small mission is cost, from which all other parameters may be inferred.
As a reference for discussion, a total mission cost of about half a medium-mission budget, i.e. less than 160 MAU, has been assumed as the small-satellite threshold. Other, lower, financial thresholds could also be considered. One such set of parameters derived using this approach is shown in Table 2. It is consistent with the current definition of a small science mission.
The sounding-rocket experience
The sounding-rocket model is a good starting point for any discussion of small satellites in the context of the ESA Scientific Programme as, over the period 1968- 1972, some 183 launches were conducted with a 75% success rate. The procurement approach taken is summarised in Table 3.
Many of these early concepts could be applied today to a small-satellite programme, given the will to take the risks and to accept this level of success rate. It is worth noting that, although it was accepted initially that the sounding-rocket programme was a 'high-risk'venture, failure was treated sufficiently seriously that additional costs were eventually incurred in an attempt to preclude future failures!
Experiment selection
The selection of the PIs would be simplified. It could be the case, for example, that proposals that did not meet the technical constraints would not be accepted for scientific evaluation. The project team would be responsible for the initial screening (the sounding-rocket approach). Another constraint could be that only instruments that used established payload technology would be considered, to avoid development risks and consequent programme delays.
Review of procurement approach
The current approach to procurement will certainly need to be modified if small satellites are to be procured by ESA. To this end, some suggestions are to:
The practicality of these suggestions needs careful assessment by all interested parties.
Launcher options
This aspect is the most uncertain as the only assured source of suitable small launchers so far is the United States, although there have been discussions on the possible use of Russian vehicles launched from European launch sites. In addition, a possible European small launcher is under study, but it is in a very early stage of definition. Ariane is not really a suitable vehicle in this context, as launch opportunities would be dictated by the availability of space with the 'big users'(shared launches); it could, however, be considered for 'one-off'types of small mission, using the triple-launch configuration.
For the moment, therefore, the conclusion is that launchers such as LLV, Taurus and Pegasus would be the most viable.
The legal framework
Successful implementation of a technically- and cost-effective small scientific satellite programme would require, a priori, a critical examination of the procedures under which the hardware and services, including launches and ground services, are procured. Above all, a rapid decision-making process must be ensured so the development work is not hindered or complicated. Other elements that need to be considered are: the access to small launchers; ESA's role vis-a-vis that of the Member States and Industry; and the timing and conditions of approvals.
A detailed examination of the various applicable texts - in particular the ESA Convention, the terms of reference of the Agency's Science programme Committee (SPC) and Industrial Policy Committee (IPC), and the General Clauses and Conditions of Contract - will have to be made. If necessary, changes or waivers will have to be agreed.
Small-satellite operations
The operations process from inception to execution needs to be kept simple. Options range from full, but simplified, involvement of ESA's European Space Operations Centre (ESOC), to complete delegation of the task to the PIs. The decision as to where the boundary point lies will be determined by the level of responsibility that ESA has for a particular mission.
While the ESA Science Programme Directorate has, as yet, no fixed policy on the practicality and potential for the introduction of a small-satellite programme, there is a recognised need to reduce the overall costs of missions, which would allow more flight opportunities and a small-spacecraft programme. Studies are therefore continuing, together with an exhaustive dialogue in the coming months with all potential participants - in the agencies, industry and institutes - to arrive at a definitive conclusion. If a small-satellite programme does emerge, all well and good, but even if it does not the European scientific community and ESA's delegate bodies will at least have a better idea of what can and what cannot be done within the boundaries of the ESA Science Programme. Any necessary changes will have been quantified and the basic data will be available for continued reference.
Related questions are:
In the latter case, can the diversion of the funds be justified as, due to the fixed level of funding available, the main programme of activity would be delayed to accommodate the small-mission funding?
The answers to these questions need careful assessment by the community, so that there is a full understanding of what small missions mean and so that the benefits and the drawbacks are understood and accepted by all interested parties.
While this is a rather specific example, and recognising that a small-satellite programme could be structured to give coordinated science results, it nevertheless serves to high-light the need to ensure that the limited funds that may be available for small missions are used effectively. The chosen missions must enhance the overall science return and provide opportunities at the individual level that are at least as good as those presently provided by the larger missions.
An alternative approach could be to fix the spacecraft design at the start and to offer PIs fixed accommodation and resources. Then, some flexibility may be possible in that the experiments could be selected during the programme and not all at the start. An advantage of this approach would be that all spacecraft hardware would be identical
To implement a small-satellite programme, many changes to current practice would be needed to approach the sounding-rocket philosophy. These changes would require the attention and approval of the ESA Council to ensure compliance with European policy. Careful preparation is needed to ensure that the proposed changes are indeed appropriate. The present study will specifically challenge established practice to prepare for eventual discussion at Council level.
Having answered that, the next question is:
Finally, a commonly heard remark is that:
ESA Bulletin Nr. 80.