Changes between Version 17 and Version 18 of TBR/UserApp/Space/Proba_2

Nov 29, 2011, 9:52:28 PM (8 years ago)


  • TBR/UserApp/Space/Proba_2

    v17 v18  
    172172Furthermore, to increase the pointing accuracy of the SWAP instrument, the AOCS SW also provides inflight
    173173compensation of thermo-elastic misalignments of the star tracker relative to the instrument.
    174 = ESA Proba-2 =
    176 '''Proba-2''', Proba stands for PRoject for OnBoard Autonomy. The Proba satellites are among the smallest spacecraft
    177 ever to be flown by ESA, but they are making a big impact in the field of space technology. Proba-2 is the
    178 second of the series, building on nearly eight years of successful Proba-1 experience.
    182 Following on from the success of PROBA-1, which successfully completed its technological goals in its first
    183 year of flight and continues to provide valuable scientific data now into its fifth operational year,
    184 PROBA-2, now in phase C/D and due for launch in September 2007, will once again fly a suite of new
    185 technology demonstrators with an ‘added value’ science package of four experiments. Altogether there are
    186 seventeen new developments being flown on Proba-2, divided into two groups: platform technologies which
    187 are part of the infrastructure and are mission critical and passenger technologies to gain flight heritage and
    188 experience before committing them to the infrastructure of other missions. Of the four Science experiments, two
    189 are dedicated to solar physics. The two other will study the space weather (plasma physics)
    190 The paper will provide an overview of the PROBA-2 mission and spacecraft along with a description of the
    191 scientific payload and technology experiments
    193 = 1.1. Mission objectives =
    195 The PROBA 2 mission objectives, as deduced from the ESA requirements, can be summarized as follows:
    196  *   PROBA 2 will be a platform to demonstrate and validate new, advanced technologies in order to promote their usage in future missions,
    197  *   As such, PROBA 2 shall accommodate a number of selected technology experiments,
    198  *   PROBA 2 shall furthermore accommodate a series of scientific payloads, in the fields of space environment (plasma) and solar observations;
    199  *   The PROBA 2 system shall be designed to support an in-orbit operational lifetime of 2 years;
    200  *   The PROBA 2 orbit shall be preferably a LEO Sun-synchronous orbit with minimized eclipse time;
    201  *   PROBA 2 shall have a high degree of spacecraft autonomy and ground support automation.
    202 = 1.2. Launch and orbit =
    204 PROBA 2 is planned to be launched from Plesetsk, Russia, in September 2007, on a Rockot launcher.
    205 PROBA 2 will be a secondary-passenger of the launch of the SMOS (ESA) spacecraft. It will be directly
    206 injected in a Sun-synchronous LEO orbit, with an altitude between 700-800 km (baseline 728km) and
    207 with the LTAN at 6:00 AM +/- 15 minutes. The orbit injection accuracy provided by the launcher is sufficient
    208 to guarantee that the LTAN will remain within 6:00 AM +/- 45 minutes without the use of onboard propulsion.
    209 The orbital period is approximately 100 minutes. The targeted orbit is eclipse-free for 9 months per year,
    210 thus making the orbit well suited for the solar observing instruments. Maximum eclipse duration during the
    211 eclipse season is less than 20 minutes. Since the orbit remains acceptable for the solar
    212 observations during the complete mission lifetime, propulsion is not needed to support the mission.
    213 However, as is documented below, a propulsion system is accommodated onboard PROBA 2 as a technology
    214 demonstration.
    215 = 1.3. Ground segment =
    217 As for PROBA1, the PROBA2 spacecraft will be operated from the Redu Ground station (Belgium).
    220 PROBA 2 has a weight of less than 130 kg and belongs to the class of the mini-satellites (Figure 1). Its
    221 structure is built using aluminum and CFRP honeycomb panels. Triple junction Gallium Arsenide solar cells,
    222 body mounted on 1 panel and mounted on 2 deployable panels, provide the power to the spacecraft and a Li-Ion
    223 battery is used for energy storage. A battery-regulated, centrally switched 28V bus distributes the power to the
    224 units and the instruments. A high performance computer, based on the LEON processor provides the
    225 computing power to the platform and for instrument data processing. It accommodates the memory for
    226 house-keeping data storage as well as a mass memory for the payload image data. The telecommunications
    227 subsystem is designed to establish and maintain spaceground communications link with the ground segment
    228 while the spacecraft remains sun-pointing. It is CCSDS compatible for up- and downlink in the S-band. The set
    229 of ACNS units support Sun-pointing, inertial 3-axis attitude pointing as well as Earth pointing and a series
    230 of attitude maneuvers. Furthermore, it performs all required navigation and maneuvering computations
    231 onboard. The spacecraft platform provides full redundancy
    233 [wiki:File:PROBA2_Auto11.jpeg File:PROBA2 Auto11.jpeg]
    234 PROBA 2 block diagram
    236 = 2.1. PROBA 2 platform =
    237 = 2.1.1. Mechanical and thermal =
    239 The PROBA 2 structure is derived from the PROBA 1 structure and is compatible with launchers such as
    240 ROCKOT, PSLV and DNEPR. The carrying part of the structure is composed of 3 aluminum honeycomb panels
    241 mounted in an H-structure and a bottom board. Almost all units are mounted on these inner panels. The bottom
    242 board acts as the interface with the launcher. All outer panels without solar cells mounted on them consist of
    243 aluminum honeycomb panels as well. They are painted black/white according to the needs of the thermal
    244 subsystem. The 2 deployable solar panels, as well as one outer panel with solar cells consist of honeycomb
    245 panels with aluminum core and CFRP sheets. The sheets supporting the solar cells are covered with kapton
    246 for electrical insulation. The deployable panels are permanently connected to the spacecraft body by hinges
    247 based on Carpentier joints. The Carpentier joints  provide the opening torque at the moment of panel
    248 release as well as the self-locking in the deployed position. During launch, the stowed panels are kept in
    249 the stowed condition by the hold-down and release mechanism. This mechanism utilizes thermal knives to
    250 release each panel by software command in orbit.
    252 The thermal control of the spacecraft is intended to be passive as far as possible. The sun-pointing attitude
    253 results however in a considerable thermal gradient through the spacecraft, making as such a completely
    254 passive thermal control difficult to achieve and heaters are foreseen to control the battery temperature. Heaters
    255 are also required to de-contaminate specific parts of the solar observation instruments. The SWAP instrument
    256 (see below) has a radiator mounted on the side of the spacecraft in order to keep the detector as cold as
    257 possible.
    259 [wiki:File:PROBA2_Auto14.jpeg File:PROBA2 Auto14.jpeg]
    260 Figure 3 PROBA 2 internal structure and accommodation
    262 2.1.2. Attitude control and Navigation system
    263 The PROBA 2 ACNS is strongly based on the PROBA 1 ACNS. The latter was a complex system providing (i)
    264 3-axis attitude control including high accuracy pointing and maneuvering capabilities in different pointing
    265 modes, (ii) full spacecraft attitude control based only on target oriented commands and (iii) the demonstration of
    266 new technologies. Furthermore, it was developed relying heavily on the use of Computer-Aided Software
    267 Engineering tools. The PROBA 2 ACNS includes the full PROBA 1 ACNS, with the additional functionality
    268 to support the solar observation mission. This includes an improved Sun-model and the possible inclusion of a
    269 sun-sensor in the control loop. Furthermore, the ACNS incorporates a technology demonstration of a series of
    270 new algorithms:
    271  *  low-cost determination of the attitude and orbit using temperature, light and/or magnetic-field
    272 sensors;
    273  * the use of a Square-Root Unscented Kalman Filter (SR-UKF) for attitude and orbit
    274 determination;
    275  *  autonomous, high-precision, recurrent largeangle manoeuvre capability during the Sun-
    276 Observation Mode to avoid star-sensor blinding by the Earth
    278  Finally, the ACNS functions support automatic “image paving” for the Sun-Imaging instrument (SWAP)
    279  in order to increase its actual field of view. PROBA 2, as PROBA 1, has been fitted with a highaccuracy
    280  double head star tracker, with GPS receiversand with a set of reaction wheels for the nominal ACNS
    281 operation. This set of sensors and actuators is complemented with the magnetotorquers and 3-axis
    282 magnetometers. As explained above, PROBA 2 carries as well an additional star tracker, an additional GPS, an
    283 additional magnetometer and a Sun Sensor as technology demonstrations.
    285 As on PROBA 1, the star tracker is the main attitude determination sensor. It provides full-sky coverage and
    286 achieves the high accuracy required for Sun pointing. The sensor can autonomously reconstruct the
    287 spacecraft’s inertial attitude starting from a “lost in space” attitude with a performance of a few arc-seconds
    288 up to an arc-minute. The attitude can be reconstructed at relatively high inertial rates, which allows the ACNS
    289 software to perform gyro-less rate measurements sufficiently accurately to control large-angle precise and
    290 stable manoeuvres. The model selected to fly on PROBA 2 is the micro-autonomous stellar compass (m-
    291 ASC), a next generation of the star tracker to that flown onboard PROBA 1. It requires less electrical power,
    292 has a lower mass and smaller volume, can connect to 4 camera heads instead of to 2 (although only 2 are used
    293 in PROBA 2) and provides attitude output at 4 Hz instead of 2 Hz. The star tracker is provided by the
    294 Technical University of Denmark. Orbit and time knowledge is acquired autonomously
    295 from measurements performed by a GPS receiver. As a technology demonstration, PROBA 2 flies a redundant
    296 set of Phoenix GPS receivers provided by DLR.
    298176[wiki:File:PROBA2_Auto2.jpeg File:PROBA2 Auto2.jpeg]
    321199The orbital information allows pointing of the  spacecraft towards any point on Earth (by using as well
    322 an onboard Earth-rotation ephemeris calculator), to autonomously determine the optimal moments for a
    323 high-angle maneuver to avoid sensor blinding by the Earth and to perform accurate Sun-pointing.
    324 The generation of control torques is by means of four reaction wheels (Dynacon, Canada) mounted in a
    325 tetrahedron configuration. Their inertia capacity is 0.65 Nms and their maximum torque capacity is 30 mNm.
    326 The reaction wheels are an evolution of those used on the Canadian MOST mission.
    328 All ACNS sensors and actuators are controlled by the ACNS software running on the central LEON based
    329 computer and provides functions including:
    330  *  Navigation (NAV) which consists in the onboard Kalman filter based autonomous
    331 estimation of the orbit using GPS measurements and the on-board autonomous
    332 determination of the attitude using data from the star tracker, digital Sun sensor and
    333 magnetometers. The navigation function also includes the prediction for all the mission
    334 related orbital events (eclipses, next Earth target passages, next ground station flybys, Earth exclusion angle etc…).
    335  *   Guidance (GDC) which consists in the onboard autonomous generation of the commanded reference attitude profiles and
    336 manoeuvres, depending on the spacecraft operational mode. The guidance function also includes the computation of the control error,
    337 the difference between the desired and the current, estimated, dynamical state.
    338  *   Control (CTL) which consists in the determination and execution of the necessary control commands that will bring the current
    339 dynamical state of the spacecraft coincident with the desired state. The control function also includes the maintenance of internal
    340 dynamic variables within specified boundaries (e.g. reaction wheel speed).
    341  *   Failure Detection & Identification (FDI) which consists in monitoring the inputs, the internal
    342 and output variables and parameters of the AOCS software to test them for numerical and/or physical validity.
    343 Furthermore, to increase the pointing accuracy of the SWAP instrument, the AOCS SW also provides inflight
    344 compensation of thermo-elastic misalignments of the star tracker relative to the instrument.
    346202The PROBA 2 operational modes for the ACNS are as follows:
    506362The Thermal Plasma Measurement Unit comprises a Sensor Block, which consist of probes and preamplifiers, and a Processing Block. TPMU contains 3 experiments which measure the total ion density and electron temperature, the ion composition and ion temperature, and the floating potential of the satellite body.
    531365= Providing flight opportunities =
    585419To ensure on board autonomy, mission control system development is an integral part of the overall mission programme, along with the associated operations. Development occurs incrementally, with progressive validation taking place throughout activities ranging from software development, spacecraft integration and system testing to in-orbit operations.
    587420= External links =
    589  *  [ Official Page]
    591  *  [ Factsheet]
    624 = Providing flight opportunities =
    626 The Proba satellites are part of ESA’s In orbit Technology Demonstration Programme: missions dedicated
    627 to the demonstration of innovative technologies. In orbit demonstration is the last step on the technology
    628 development ladder. New technology products need to be demonstrated in orbit, particularly when users
    629 require evidence of flight heritage or when there is a high risk associated with use of the new technology.
    630 In orbit demonstration is achieved through experiments on carriers of opportunity, e.g. the International
    631 Space Station, or through dedicated small satellites such as the Proba series, which were created to increase
    632 the availability of flight-testing opportunities.
    633 = Ensuring a competitive European industry =
    636 Small, low-cost missions allow small companies access to space and provide them with the experience that is essential for European industries to be competitive and innovative.
    637 = Commitment to technological innovation =
    640 Proba-2 is the result of ESA’s commitment to technological innovation. Altogether, 17 new technological developments and four scientific experiments are being flown on Proba-2.
    641 = Technology demonstrations =
    643  = '''The technology demonstrations are:''' =
    646  *  a new type of lithium-ion battery, developed by SAFT (FR)
    647  *  an advanced data and power management system, containing many new component technologies including the LEON processor developed by Verhaert Space (BE)
    648  *  combined carbon-fibre and aluminium structural panels, developed by Apco Technologies SA (CH)
    649  *  new models of reaction wheels from Dynacon (CA), startrackers from DTU (DK) and GPS receivers from DLR (DE)
    650  *  an upgraded telecommand system with a decoder largely implemented in software by STT- SystemTechnik GmbH (DE)
    651  *  a digital Sun-sensor, developed by TNO (NL)
    652  *  a dual-frequency GPS receiver, developed by Alcatel Espace (FR)
    653  *  a fibre-sensor system for monitoring temperatures and pressures around the satellite, developed by MPB Communications Inc. (CA)
    654  *  a new startracker development being test-flown before use on the BepiColombo mission, developed by Galileo Avionica (IT)
    655  *  a very high-precision flux-gate magnetometer, developed by DTU (DK)
    656  *  an experimental solar panel with a solar flux concentrator, developed by CSL (BE)
    657  *  a xenon gas propulsion system using resistojet thrusters and a solid-state nitrogen gas generator to pressurise the propellant tanks, developed by SSTL (GB) and Bradford (NL)
    658  *  an exploration micro-camera (X-CAM), developed by Micro-cameras & Space Exploration (CH)
    659  *  new GNC algorithms developed by NGC (CA)
    660 = '''The two solar observation experiments are:''' =
    663  *  a Large Yield Radiometer (LYRA) that will monitor four bands in a very wide ultraviolet spectrum, with Centre Spatial de Liège as lead institute supported by the Royal Observatory of Belgium as scientific leader and with an international team comprising PMOD (CH), IMOMEC (BE) and BISA (BE)
    664  *  an extreme-ultraviolet telescope (SWAP) using new pixel sensor technology (APS), that will make measurements of the solar corona in a very narrow band, with Centre Spatial de Liège as lead institute supported by the Royal Observatory of Belgium and with an industrial team comprising Alcatel-Lucent (BE), AMOS SA (BE), DELTATEC (BE), Fill
    665 Factory NV (BE) and OIP NV (BE)
    666 = '''The two space weather experiments are:''' =
    669  *  Dual Segmented Langmuir Probes (DSLP), which will measure electron density and temperature in the background plasma of the Earth’s magnetosphere
    670  *  a thermal plasma measurement unit (TPMU), that will measure ion densities and composition
    672 Both were developed by a Czech consortium, led by the Institute of Atmospheric Physics, Academy of Sciences of the Czech Republic (CZ).
    674 In total, ten European countries and Canada were involved in the construction of the Proba-2 satellite.
    675 = Effective Engineering =
    678 To ensure on board autonomy, mission control system development is an integral part of the overall mission programme, along with the associated operations. Development occurs incrementally, with progressive validation taking place throughout activities ranging from software development, spacecraft integration and system testing to in-orbit operations.
    680 =  =External links==
    682422 *  [ Official Page]