Figure 1. The release of the European Retrievable Carrier (Eureca) from the Space Shuttle on 2 August 1992
In the world-wide search for the lowest cost (and hopefully most cost effective) approach for undertaking space missions, several strategies have recently been recommended by various parties. This article addresses these approaches in addition to the so-called 'use what you have' alternative which suggests flying science- and technology-oriented space missions using readily available facilities, i.e. the 'Eureca system'. Its technical and cost advantages in comparison to, for example, the 'small satellite' approach are discussed, concentrating on the optimal usage of currently restricted funds for the generation of new in-orbit mission products rather than building further space and ground segment elements.
Currently, most governments involved in space exploration have significantly reduced funding for unmanned space missions. In order to be able to conduct meaningful space activities despite this shortage of funds, many new 'low-cost' approaches have evolved, including:
In the overall competition for retaining or obtaining work, low-cost missions are often offered without addressing the overall cost-efficiency. This means that funds are used for new in-orbit or ground facilities or, as is the case of some small satellites, for generating data which has already been measured during earlier missions, rather than developing novel and, as yet unavailable, mission products. Such mission products include:
The success of a mission can be measured by the quantity, quality and timely delivery of its products. Such measurements, if honestly applied, are also suitable for determining the overall cost efficiency of a mission. This would require:
Seen from this perspective it is obvious that the greatest cost efficiency for any mission is achieved when we maximise the overall return of useful products and the mission success probability while minimising appropriate life cycle cost. Cost efficiency is thus not dependent on the size of a mission (e.g. small or large satellites). The size of a satellite or mission is mainly a function of the required mission product characteristics and of the associated production capacity as well as a function of available funds to satisfy either the full demand or only a part of it.
Nearly all of the previous traditional European missions were in this sense very cost-efficient since full mission success (98.5% or higher) was achieved even in cases where severe satellite in-orbit anomalies occurred.
Nevertheless, triggered mainly by reduced financial resources and by the higher demands of an increasingly broader product user community, there is a strong requirement for more frequent flight opportunities with shorter lead times to launch, at significantly lower cost than traditional projects. Obviously, cost reduction must be achieved in all areas, such as the satellite procurement process (e.g. implement simplest design, use available elements), the launch cost (e.g. minimise mass) and the ground segment and mission operation costs (e.g. use of available infrastructure, off-line versus on-line control).
Potential solutions for more frequent, short-notice and low-cost missions are:
With reference to the latter 'use what you have approach', Europe possesses a powerful, high-tech and flight-proven retrievable carrier, Eureca, which was designed for at least five flights, and an existing ground segment infrastructure for its in-orbit operation. So far, the system has been used for one 11-month mission (from 31 July 1992 - 1 July 1993) which was a big success from a mission-product and technology-return point of view. The reuse of the Eureca system for future missions offers significant advantages in terms of technical capabilities, reliability, fast turn-around, low-cost and overall cost-efficiency compared to most of the other low-cost approaches.
Eureca background
Eureca (European Retrievable Carrier) was developed by Deutsche Aerospace (DASA) under ESA contract as a re-usable, multi-disciplinary platform for microgravity, science and technology missions. Its design life was based on at least five flights, each lasting from several months to nearly one year, and an on-ground turn-around time of maximum two years. Eureca is launched and retrieved by the US Space Shuttle. Bringing Eureca back to Earth following its first mission proved to be an invaluable contribution not only to payload and mission product owners, but also to technical areas dealing with in-orbit performance validation and, in particular, with the identification of the causes of in-orbit anomalies. The results of spacecraft in-flight anomaly investigations often point to several potential failure sources which can be sufficient for workaround mission continuation, but only post flight on-ground investigations can unambiguously identify the real causes. Results of this nature from the first Eureca flight have provided important contributions for the improvement of other satellites prior to their launches!
Figure 1. The release of the European Retrievable Carrier (Eureca) from the Space Shuttle on 2 August 1992
Eureca's flight was controlled from the ESA/ESOC Mission Control Centre in Darmstadt, Germany throughout all phases (i.e. launch and early orbit phase (LEOP), commissioning, payload utilisation, rendezvous and retrieval) using its multi-project ground segment infrastructure. The Eureca-1 payload included sixteen active instruments (six for microgravity research, two for space radiation research, five for space science research, three for technology demonstrations) and a number of entirely passive payloads. Overall, a degree of mission exploitation close to 100% was achieved throughout the experimental phase.
The control methodology used encompassed mission planning, pre-programming of on-board activities for up to 60 hours ahead in the on-board master schedule, on-board autonomous execution of all activities listed in the master schedule, storage of data products and appropriate housekeeping telemetry in the on-board mass memory, on-board autonomous fault management, dumping of mass memory data content during ground station passes, transmission of dumped data to the OCC and, finally, provision of science data to investigators via a dedicated Data Distribution System (DDS). Eureca and its payload were kept continuously productive although the Mission Control Centre was on-line with the spacecraft for less than 6% of the total in-orbit time. This first mission also provided significant experience in collaborating with NASA's Shuttle Control Center in Houston (JSC) during Eureca's deployment and retrieval.
Eureca system capabilities
The baseline Eureca-2 mission is a 6 to 9 month stay in a 51.6 degree inclination orbit at an altitude of around 500 km. Such a mission provides opportunities for multi-disciplinary science, for in-orbit technology investigations and flight-qualification activities. A first Eureca re-flight could be arranged for as early as the second half of 1999.
The science possibilities encompass microgravity research with a number of facilities (e.g. AMF, MFA, PCF, ERA) used during the first Eureca flight, or other science payloads (e.g. for Sun or Earth observation, astronomy, particle impact research, space physics, etc.) compatible with the Eureca infrastructure and its orbital environment.
Essential characteristics of the Eureca space and ground segment available for payload support during future missions are listed in Tables 1 and 2. In many respects, this existing infrastructure offers significantly more powerful support functions than can reasonably be expected with a small-satellite approach. Currently, no other approach could facilitate such a powerful support infrastructure with such a short turn-around for flying a multitude of complex payloads over an extended period. There is also the important advantage with Eureca that all payloads are returned at the end of the mission to their owners for post-flight assessment and/or reuse on later flights. This is a particular advantage for technology validation/demonstration payloads.
Table 1. Eureca on-board characteristics
Table 2. Eureca payload operations support characteristics
Cost aspects
Since the Eureca infrastructure has already been paid for by Member States, the costs for a re-flight would be limited to satellite refurbishment and payload integration activities, the launch and retrieval flight services, the ground segment activation, the operations preparations for new payloads, and mission operation services. The turn-around time between project approval and launch would be approximately 2 years, the anticipated degree of mission exploitation could be as high as 98% and data products could be available to payload owners within less than 24 hours if so required.
The Eureca re-flight approach allows a reduction in the cost of flying complex, ambitious and demanding payloads to around 100 KECU per kg of payload. In other words, financing authorities would be able to provide payload owners with a flight opportunity for e.g. 100 kg of payload for only 10 MECU. This is approximately 20 times cheaper than the traditional approach. This price could be further reduced for subsequent flights, depending on the degree of repair required between flights.
The life-cycle costs for a number of small satellites (launch masses between 200 and 400 kg) currently being pursued in Europe are between 200 and 325 KECU per kg of payload, i.e. more than twice the projected Eureca cost.
However, there remains the fact that one Eureca flight costs approximately 3 times as much as one of the above-mentioned small satellites. Nonetheless, approximately 10 or more such small satellites would have to be flown to achieve the mission-product return of a single Eureca flight. Eureca's significantly superior payload support infrastructure, overall high mission success probability and the value of the post-mission payload return must also be factored in. Clearly, building even a small simple satellite around each payload is not necessarily the most cost-efficient approach. It does, however, ease the task of funding authorities and creates a new industrial marketing field, whereas the 'use what you have' approach concentrates the spending on providing mission products, which is perhaps the primary objective of space undertakings.
This commercial approach foresees recovering mission costs mainly by payload flight ticket sales or equivalent arrangements. The flight ticket price is based on a pro-rata sharing of on-board resources - e.g. mass, telemetry, command/control operations, power, orbit/ attitude control - between payloads.
Further information about the possibilities offered and projected costs associated with this proposed commercial Eureca re-flight opportunity can be obtained from:
Daimler-Benz Aerospace AG
Space Infrastructure
Attention : Mr Wolfram LORK
P.O. Box 28 61 56
D-28361 Bremen
GERMANY
Tel. (49) 421 539 5870
Fax (49) 421 539 5074
E-mail Eureca@ERNO.DE
ESA Bulletin Nr. 91