In-orbit demonstration
Testing new technology in Earth orbit
The demonstration in orbit is the last step in the technology development ladder. It is necessary to demonstrate new technology products, in particular when the users require evidence of flight heritage or when there is high risk associated to their utilization. It serves to demonstrate incipient techniques for research, for monitoring, for satellite operations. It provides valuable data to characterize the space and spacecraft environment and is a test bench for new development and operation practices.
It is achieved through experiments in carriers of opportunity, e.g. the International Space Station, or through dedicated small satellites such as the Proba series of small spacecraft.
These Proba satellites are among the smallest spacecraft ever to be flown by ESA, but they are making a large impact in the field of space technology. These are missions dedicated to the demonstration of innovative technologies, supported through ESA's General Support Technology Programme (GSTP) which has the purpose of preparing and proving new components and hardware for space.
While a standard operational satellite can be as large as a truck, a Proba spacecraft is only the size of a small domestic washing machine. These small dimensions help cut mission complexity and cost, and also make it simpler to find cheap piggyback launch opportunities. Lower costs make it possible to take more risks than a standard mission can.
The motive is to increase the availability of flight-testing opportunities: the individual characteristics of the space environment can be simulated on the ground at ESTEC and other facilities, but it is only by being in space that performance gets tested for real. The resulting status of 'flight proven' is highly desirable for components and systems – up at the very top of ESA's Technology Readiness Level (TRL) scale.
Proba-1
Proba is short for 'Project for Onboard-Autonomy': the purpose of Proba-1, launched in 2001, was to demonstrate a spacecraft could operate itself with minimal ground control. Equipped with a hyperspectral imaging instrument, the satellite was designed with a sufficiently high level of autonomy that it requires only the terrestrial coordinates of an imaging target – which users can deliver via the internet - and Proba-1 lines itself up automatically using only an advanced star tracker and GPS receiver to acquire the image, shoot and deliver it.
Its other technological innovations include multiple uses of commercial off the shelf (COTS) components, ESA's first flight of high-efficiency and radiation-resistant triple-junction gallium-arsenide solar cells, the first employment of lithion-ion batteries in low Earth orbit and a high performance computer system including 'autocoding' facilities to automatically generate onboard navigation software as required.
Having long since fulfilled its two-year technology demonstration assignment, Proba-1 remains fully operational. Redesignated as an ESA Earth Observation mission it has returned thousands of images in support of environmental research and applications.
Proba-2
The Proba - 2 mission is due to launch during 2009 together with ESA's Soil Moisture and Salinity Satellite (SMOS). Equipped with a quartet of science instruments focused on solar and space weather observations, Proba-2 also incorporates a suite of new technologies for demonstration both within its spacecraft platform and as additional payload 'passengers'.
Mission-critical infrastructure technologies include a new type of lithion-ion battery; an advanced data and power management system; combined carbon-fibre and aluminium structural panels; new models of reaction wheels, star trackers and GPS receivers plus an upgraded telecommand system.
Proba-2's passenger technologies include a digital Sun sensor; dual-frequency GPS receiver; an innovative fibre sensor system for monitoring temperatures and pressures around the spacecraft; a new star tracker development being flight-tested in advance of its planned use aboard the Bepi-Colombo mission to Mercury; a very high-precision flux-gate magnetometer, used to measure magnetic fields, potentially for use in terms of navigation and attitude control as well as science; an experimental solar panel equipped with a concentrator, to study the temperature and performance consequences of focusing solar flux on photo-voltaic cells; a resistojet xenon gas propulsion system and a solid state nitrogen gas generator to pressurise propellant tanks, and a powerful miniaturised exploration micro-camera (X-CAM) with panoramic optics.
Altogether 17 new technological developments are being flown on Proba-2. During its planned two year lifespan, the mission will autonomously obtain images of the solar disk in the same manner that Proba-1 obtains images of the Earth's surface.
Proba-3
This mission is currently in the planing stages, with a mission set for a 2012 timeframe. Proba-3 is conceived as a project for the development of formation flying technologies, aiming at providing sufficient confidence to future operational missions on these techniques and technologies.
The mission will comprise two closely-flying small platforms with the ability to closely control their attitude and separation down to a millimetre range, and equipped with a solar corona-observing instrument for added scientific value.
Formation flying has multiple applications as it allows to overcome the performance limitations imposed by practical physical size. Apertures, focal lengths, baselines will not be limited by what can be accommodated in a single big satellite. For instance the two small platforms of the Proba-3 mission will build a giant sun coronograph providing orders of magnitude increase in performance with respect to previous instruments. Formation flying is at the heart of some of ESA's most ambitious missions such as the planet-hunting Darwin mission.
Proba - V
The advanced platforms developed for the Proba-1 and 2 missions refined with the demonstrated technologies, will be used to carry a multispectral Earth observing instrument to provide enhanced data continuity to the Vegetation sensor carried by France's SPOT-4 and SPOT-5 missions. The sensor itself will deploy new technology such as the very compact wide field of view telescope and new detectors.
Proba – V will show how new technologies allow small satellites to support operational systems.
The future
Responding to feedback from the European space sector, the current GSTP cycle includes a dedicated In-Orbit Demonstration (IOD) element, making it likely that more technology demonstrators will be designed and flown besides the mission already launched and the others in preparation. To maximise their utility beyond technology demonstration alone, the IOD satellites will also incorporate ”guest”payloads whenever possible.
