PROBA-1 rolls in its orbit to take images: the satellite’s platform and payload work as one: spinning reaction wheels guided by a star tracker roll it up to 25º side to side and ±55º/±36º along its path. This helps PROBA-1 to compensate for its 7.5 km/s speed, like a photographer panning to snap a moving target. So each target can be seen on up to 5 different angles (-55º, -36º, nadir view, +36º and +55º)
User's of the PROBA-1 satellite to date include:
- more than 60 Earth Observation Principal Investigators from scientific institutes within Europe
- space weather and space debris scientific communities
- EduProba (Belgian schools and universities)
PROBA-1 is a technology demonstration mission funded within the frame of ESA’s General Support Technology Programme. It is managed by ESA’s Control and Data Systems Division within the Department of Electrical Engineering, part of the Directorate for Technical and Operational Support at ESA/ESTEC.
It was the first ESA spacecraft with fully autonomous capabilities, meaning it was designed to perform virtually unaided, performing everyday tasks like navigation, payload and resource management with little involvement by staff at ESA's ground station in Redu, Belgium.
The innovative design and operating systems were the result of ESA's collaboration with prime contractor Verhaert Design and Development of Belgium, working alongside other European companies and universities. PROBA-1 has given engineers the opportunity to evaluate the advantages of autonomous spacecraft operation.
PROBA-1's payload was designed to be controlled by a computer system 50 times more powerful than its counterpart onboard ESA's full-size solar observing satellite, SOHO, allowing the micro-satellite to combine in-orbit technology demonstration, such as an onboard mission planning and onboard navigation and failure detection, with some useful monitoring of Earth's environment.
The instruments on board were CHRIS (Compact High Resolution Imaging Spectrometer, from SIRA/UK), DEBIE (Debris In-Orbit Evaluator, from Patria Finnanvitec, Finland) and SREM (Standard Radiation Environment Monitor, from Contraves, Switzerland). PROBA-1 also carries two imagers, a Wide Angle Camera (WAC) and a High Resolution Camera (HRC) with a 10 metre resolution, both built by OIP of Belgium.
Cameras are used by students from selected Belgian schools whose experiment proposals have been accepted under the EDUPROBA project.
Images of Earth and other data gathered by PROBA-1 are sent to a webserver located at the ESA ground station in Redu, Belgium, where scientists are able to access the information over the Internet as soon as it is delivered from the satellite.
In the first three months after launch, the satellite was tested by Verhaert from the ground station in Redu. The satellite was then handed over to ESA and the scientific user community. PROBA-1 was originally expected to operate for at least two years.
A high degree of spacecraft on-board autonomy, together with ground-station automation, considerably reduces the need for ground operations. Proba-1 aims to use and demonstrate automatic functions, both onboard and in the mission ground segment.
PROBA-1 onboard automatic functions include:
- nominal operation and resource management
- computation and control of camera pointing and scanning from raw inputs from users (target latitude, longitude and altitude)
- payload operations scheduling and execution
- data communications management
The spacecraft mass is 94 kg, with 25 kg dedicated to scientific and Earth observation instruments, in addition to the technology demonstration payloads. The principal objective is the in-orbit evaluation of new spacecraft technologies. PROBA-1, however, has also been intended as a flight opportunity for Earth observation instruments that can benefit from the agile pointing capabilities and the autonomy features of the satellite.
PROBA-1 onboard automatic functions include all payload operations scheduling and execution, target fly-by prediction and control of camera pointing and scanning from raw user inputs (target latitude, longitude and altitude). The point and stare requirements of the High Resolution Camera (HRC), as well as the multiple image scan requirement to support Bi-directional Reflectance Distribution Function (BRDF) measurements with the Compact High Resolution Imaging Spectrometer (CHRIS) are satisfied with the specified accuracy, by this small and agile gyro-less platform, whose attitude determination is based on autonomous star tracker only.
The main Earth imaging payload, CHRIS, weighing only 14 kg, is used to measure directional spectral reflectance. The instrument is capable of imaging up to 200 spectral bands simultaneously at full resolution with a spatial resolution of 20m at nadir and swath width of 15 km. The HRC is a black and white camera with a miniaturised Cassegrain telescope providing 5m geometrical resolution images. Each image covers a ground area of approximately 4 km by 4 km. The pointing agility of the spacecraft allows both cameras to take multiple images of the same target area at different viewing angles on the same orbital pass.
PROBA-1 is compatible with Ariane ASAP5 and PSLV launcher requirements. Its structure is built using aluminium honeycomb panels. Body-mounted solar panels provide power to the spacecraft and a Li-Ion battery is used for energy storage. A centrally switched regulated bus distributes the power to the units and instruments.
An ERC32 (SPARC) based computer provides the computing power for all the platform functions and a TSC21020 (DSP) provides the processing power to the imaging payload. All software components, either in the central computer or embedded in the spacecraft units can be reprogrammed in flight. The S-band telecommunications subsystem is omnidirectional and CCSDS-compatible. The set of ACNS units support Earth and inertial 3-axis attitude pointing as well as on-board navigation and manoeuvring computations. The thermal control of the spacecraft is completely passive. The table below summarizes the characteristics of the spacecraft.
The main elements of the ground segment are: a fully steerable S-band antenna of 2.4m, a baseband equipment, a control system based on the ESA SCOS II system (used also during the ground test and integration phase), a planning system and a data server. A unique script language allows an interface with the telemetry and the telecommand server of the control system and to control all the pass activities from the preparation to the post-processing phase and most of the ground segment units.
A key element of the automation of the ground segment tasks, progressively put in place along the mission, is that they allow automatic email generation in case of any warning messages. It is completed by the automated pass template tool which schedules the pass activities and provides a graphical interface of the activities statuses.
The PROBA-1 development approach includes several innovative aspects. A design-to-cost approach was adopted according to European Cooperation for Space Standardisation category 3 project classification. This involved using COTS (commercial off-the-shelf) equipment and units; simulation-based development, verification and testing; automated software generation; extensive use of test and operations infrastructure commonalities; and a highly integrated ESA-industry design and development team. The NORAD Two Lines Elements (TLEs), automatically retrieved from the internet, are used to predict with the COTS software, the ground station visibilities. The antenna pointing angles are also derived from the TLEs.
PROBA-1 ground-segment automatic functions include:
- spacecraft pass operations
- spacecraft performance evaluation
- high-level user requests to spacecraft via Internet