Changes between Version 3 and Version 4 of TBR/UserApp/Space/ProbaV


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Timestamp:
Dec 4, 2011, 1:34:45 PM (8 years ago)
Author:
Iliyankatsarski
Comment:

/* ProbaV */ new section

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  • TBR/UserApp/Space/ProbaV

    v3 v4  
    390390|+'''Figure 4: Overview of the transmitter architecture (CNES, TES)'''
    391391|-
     392|[wiki:File:ProbaV_AutoF.jpeg? File:ProbaV AutoF.jpeg?]|}
     393|}
     394
     395{| align="center"
     396|+'''Figure 5: Photo of the X-band transmitter (image credit: CNES, ESA)'''
     397|-
     398|[wiki:File:ProbaV_AutoE.jpeg File:ProbaV AutoE.jpeg]
     399|}
     400=  ProbaV  =
     401
     402
     403#REDIRECT [wiki:ESA_Proba-V ESA Proba-V]
     404=  ProbaV  =
     405
     406
     407
     408[[TOC(TBR/UserApp/Space/ProbaV, depth=2)]]
     409
     410The ‘V’ in its name stands for Vegetation: Proba-V will fly a reduced-mass version of the Vegetation instrument currently on board the Spot satellites to provide a daily overview of global vegetation growth.
     411
     412{| align="center"
     413|+'''PROBA V'''
     414|-
     415|[wiki:File:Probav-shiny_large0.jpg 450px]
     416|}
     417
     418 
     419Bearing a different designation from its predecessors, Proba-V is an operational as well as experimental mission, designed to serve an existing user community.
     420
     421The aim is to guarantee data continuity for the Vegetation dataset once the current Spot missions end.
     422
     423{| border="1"
     424|+ '''Proba-V facts and figures'''
     425|-
     426|Launch date:
     427|mid-2012
     428|-
     429|Mass:
     430|160 kg
     431|-
     432|Orbit:
     433|Sun-synchronised polar orbit, 820 km, with a 10:30 AM local time at the descending node
     434|-
     435|Instrument:
     436|Newly designed version of the Vegetation instrument flown on the Spot series
     437|-
     438|Guest technology payloads:
     439|Gallium Nitride amplifier incorporated in communication subsystem; Energetic Particle Telescope and one other payload to be decided at a later stage
     440|-
     441|Prime contractor:
     442|Qinetiq Space Belgium
     443|-
     444|Payload developer:
     445|OIP Space Systems
     446|-
     447|Ground Station:
     448|Satellite’s mission control centre in Redu, Belgium complemented by a data reception station to be located in the north of Europe.
     449|-
     450|Launcher:
     451|To be decided – designed to be compatible with Vega, Soyuz or Falcon 1E launchers.
     452|}
     453
     454=  PROBA-V (Project for On-Board Autonomy - Vegetation) =
     455
     456
     457The PROBA-V (Vegetation) mission definition is an attempt, spearheaded by ESA and CNES, to accommodate an improved smaller version of the large VGT (Vegetation) optical instrument of SPOT-4 and SPOT-5 mission heritage on a small satellite bus, such as the one of PROBA-2.
     458
     459As of 2008, small satellite technologies have reached a level of maturity and reliability to be used as a platform for an operational Earth observation mission. Furthermore, advancements in the techniques of detectors, optics fabrication and metrology are considered sufficiently mature to permit the design of a compact multispectral optical instrument. 1) 2) 3) 4) 5) 6) 7) 8) 9) 10)
     460
     461The C/D Phase started in July 2010. The system CDR (Critical Design Review) took place in the spring of 2011. The acceptance review is planned for Dec. 2011 and the flight acceptance review is planned for the spring of 2012.. ESA is responsible for the overall mission, the technological payloads and for the launcher selection.
     462
     463Background: The VGT instruments (VGT1 & VGT2), each with a mass of ~160 kg and fairly large size, have provided the user community with almost daily global observations of continental surfaces at a resolution of 1.15 km on a swath of ~2200 km. The instruments VGT1 on SPOT-4 (launch March 24, 1998) and VGT2 on SPOT-5 (launch May 4, 2002) are quasi similar optical instruments operating in the VNIR (3 bands) and SWIR (1 band) range.
     464
     465The Vegetation instruments were jointly developed and funded by France, Belgium, Italy, Sweden, and the EC (European Commission). The consortium of CNES, BelSPO (Federal Public Planning Service Science Policy), SNSB (Swedish National Space Board) and VITO (Flemish Institute for Technological Research) is providing the user segment services (data processing, archiving, distribution). Vegetation principally addresses key observations in the following application domains:
     466
     467 *  General land use in relation to vegetation cover and its changes
     468
     469 *  Vegetation behavior to strong meteorological events (severe droughts) and climate changes (long-term behavior of the vegetation cover)
     470
     471 *  Disaster management (detection of fires and surface water bodies)
     472
     473 *  Biophysical parameters for model input devoted to water budgets and primary productivity (agriculture, ecosystem vulnerability, etc.).
     474
     475As of 2008, a Vegetation archive of 10 years of consistent global data sets has been established permitting researchers access on a long-term basis. The SPOT-5 operational lifetime is estimated to expire in 2012. Pleiades, the next French satellite for Earth Observation, is solely dedicated to high-resolution imaging (on a fairly narrow swath) and will not embark any instrument providing vegetation data.
     476
     477Since the SPOT series spacecraft will not be continued and the SPOT-5 spacecraft will eventually fail — there is of course a great interest in the EO user community to the Vegetation observation in the context of a smaller mission, affordable to all concerned. 11)
     478
     479PROBA-V will continue the production of Vegetation products exploiting advanced small satellite technology. However, this implies in particular a redesign of the Vegetation payload into a much smaller unit to be able to accommodate it onto the PROBA bus.
     480
     481Overview of key requirements of the PROBA-V mission - and some improvements compared to SPOT/Vegetation:
     482
     483 *  Data and service continuity: filling the gap between SPOT-VGT and the Sentinel-3 mission
     484
     485 *  Spectral and radiometric performance identical to VGT
     486
     487 *  GSD: 1 km mandatory, improved GSD is highly disirable: 300 m (VNIR bands), 600 m (SWIR band). Image quality and geometric accuracy, equal to or better than SPOT-VGT
     488
     489 *  Provision of daily global coverage of the land masses in the latitudes 35º and 75º North and in the latitudes between 35° and 56° South, with a 90% daily coverage of equatorial zones - and 100% two-daily imaging, during day time, of the land masses in the latitudes between 35º North and 35º South..
     490
     491
     492{| align="center"|[wiki:File:ProbaV_Auto12.jpeg File:ProbaV Auto12.jpeg]|}
     493
     494Figure 1: Artist's view of the PROBA-V spacecraft (image credit: ESA) 12) 13)
     495
     496An extensive feasibility study and trade-off work was undertaken to identify a solution that could meet not only the technical challenges, but that could also be developed and tested within a tight budget of a small satellite mission.
     497
     498The PROBA-V project of ESA includes the Space Segment (platform contract award to QinetiQ Space NV of Kruibeke, Belgium - formerly Verhaert), the Mission Control Center (Redu, Belgium) and the User Segment (data processing facility) at VITO NV. VITO (Vlaamse instelling voor technologisch onderzoek - Flemish Institute for Technological Research) is located in northern Belgium. VITO’s processing center of VGT1 and 2 data (SPOT-4 and SPOT-5) is operational since 1999. VITO is also the prime investigator and data service provider of PROBA-V for the user community including product quality control. 14)
     499
     500Implementation schedule:
     501
     502 *  The Phase B of the project started in January 2009
     503
     504 *  SRR (System Requirements Review) is in Q4 of 2009
     505
     506 *  PDR (Preliminary Design Review) in Q2 of 2010
     507
     508 *  HMA (Heterogeneous Mission Access) and QA4EO (Quality Assurance for Earth Observation) implementation for user data. Planned interoperability with GSCDA V2 (GMES Space Component Data Access Version 2).
     509
     510[wiki:File:ProbaV_Auto11.jpeg File:ProbaV Auto11.jpeg]
     511Figure 2: PROBA-V project organization (image credit: ESA, Ref. 9)
     512= Spacecraft: =
     513
     514
     515An industrial team, led by QinetiQ Space NV (Belgium), is supported by several European subcontractors and suppliers, and is responsible for the development of the flight satellite platform, the vegetation payload and the Ground Segment.
     516
     517The spacecraft bus (fully redundant) is of heritage from the PROBA-1 and PROBA-2 missions (structure, avionics, AOCS, OBS with minor modifications). The PROBA-V spacecraft has a total mass of ~160 kg, and a volume of 80 cm x 80 cm x 100 cm. The three-axis stabilized platform is designed for a mission lifetime of 2.5 years (Ref. 7). 15)
     518
     519The spacecraft resources management is built around ADPMS (Advanced Data and Power Management System), which is currently flying on PROBA-2. The data handling part of ADPMS is partitioned using compact PCI modules. A cold redundant mass memory module of 16 Gbit is foreseen for PROBA-V. The newly developed mass memory will use NAND flash technology.
     520
     521The power distribution and conditioning part of ADPMS supplies an unregulated bus, with each equipment having its internal DC/DC converter. The power conditioning system is designed around a Li-ion battery.
     522
     523[wiki:File:ProbaV_Auto10.jpeg File:ProbaV Auto10.jpeg]
     524Figure 3: PROBA-V spacecraft accommodation (image credit: QinetiQ Space)
     525
     526AOCS (Attitude and Orbit Control Subsystem) provides three-axis attitude control including high accuracy pointing and maneuvering in different spacecraft attitude modes. The AOCS SW is an extension of the one of PROBA-2, including the following algorithms required by the on-board autonomous mission and payload management: 16)
     527
     528- Prediction of land/sea transitions using a land sea mask to reduce the amount of data generated
     529
     530- Optimization of attitude in Sun Bathing mode to enhance incoming power while avoiding star tracker blinding
     531
     532- Momentum dumping without zero wheel speed crossings during imaging
     533
     534- Estimations of remaining spacecraft magnetic dipole to reduce pointing error
     535
     536- Autonomous avoidance of star tracker Earth/Sun blinding
     537
     538- Inertial mode with fixed scanning rate for moon calibration.
     539
     540The AOCS hardware selection for PROBA-V consists of a high accuracy double star tracker head, a set of reaction wheels, magnetotorquers, magnetometers and a GPS receiver.
     541
     542The main AOCS modes are: Safe, Geodetic, Sun Bathing and Inertial mode.
     543
     544- The satellite Safe mode is used to detumble the spacecraft after separation from the launcher and it will be used to recover from spacecraft anomalies.
     545
     546- The Geodetic mode is used during nominal observation of the Earth’s vegetation. In this mode the payload is pointed towards the geodetic normal to the Earth’s surface. An extra steering compensation, yaw-steering, is added in this mode, to minimize the image distortion caused by the rotation of the Earth. This yaw-steering maneuver ensures that the spectral imagers are oriented such that the lines of pixels are perpendicular to the ground-trace at each moment. In this mode the star trackers and the GPS receiver are used as sensors and the reaction wheels as actuators.
     547
     548- On each orbit, the spacecraft enters the Sun Bathing mode from -56º latitude until entry of eclipse. This is to enhance the incoming power.
     549
     550- The Inertial mode coupled with an inertial scanning of the Moon at a fixed rate is used for monthly radiometric full moon instrument calibration purposes. The pointing towards the moon takes 2.5 min, 9 min for scanning the moon and 2.5 min to return to nominal observation mode. It is sufficient to have the moon in the FOV of the SI (Spectral Imager) for a number of pixels.
     551
     552Beyond the technology demonstration through the PROBA program, it is also noted that the AOCS software technology developed in the course of this program is now the baseline of the AOCS of a major operational mission of the GMES (Global Monitoring for Environment and Security) program: Sentinel-3. NGC Aerospace Ltd (NGC) of Sherbrooke, (Québec), Canada was responsible for the design, implementation and validation of the autonomous GNC (Guidance, Navigation and Control) algorithms implemented as part of the AOCS software of PROBA-1 and PROBA-2. NGC has the same responsibilities for the PROBA-V mission (Ref. 16).
     553
     554EPS (Electric Power Subsystem): The PVA (Photo-Voltaic Array) uses GaAs triple junction cells with an of efficiency of 28%. To obtain the operating voltage of 31.5 V, 18 cells are included in each string in series with a blocking diode. The PVA consists of a total of 25 solar strings taken into account the loss of one string on the most contributing PVA panel. The average solar string power under EOL conditions (summer solstice and T = 40°C) yields 12.8 W. The maximal incoming power at EOL during an orbit is 144 W. The energy budget for PROBA-V is derived for a bus power consumption of 140 W assuming a worst case day in the summer and while not taken into account the effect of albedo. A worst case power budget analysis indicated a maximum capacity discharge of 1.66 Ah. Use of a Li-ion battery. The battery cells provide a capacity of 1.5 Ah per string. The PROBA-V battery is sized to 12 Ah taking into account capacity fading and loss of a string.
     555
     556Launch: A launch of the PROBA-V spacecraft as a secondary payload is planned for Q4 2012. The primary launcher is currently assumed to be Vega with the VESTA adapter.
     557
     558Orbit: Sun-synchronous orbit, altitude = 820 km, inclination = 98.8º, LTDN (Local Time on Descending Node) = 10:30 hours (with a drift limited between 10:30 and 11:30 AM during the mission lifetime).
     559
     560RF communications: S-band for TT&C transmissions and low-gain antennas with omni-directional up- and downlink capability. The uplink symbol rate will be fixed at 64 ks/s, while the downlink can be set to a high rate (< 2 Ms/s) for nominal imaging or to a low rate at 329 ks/s for off-nominal conditions. The CCSDS protocol is used for the TT&C transmissions.
     561
     562X-band downlink of payload data is in X-band at a data rate of 35 Mbit/s. The onboard mass memory is 88 Gbit. The Redu station (Belgium) is being used for TT&C communication services. The X-band uses two cold redundant high-rate X-band transmitters and two nadir pointing isoflux antennas, both RHCP.
     563
     564The S-band transceivers will be connected to RS422 outputs (cross strapped) of ADPMS while the X-band transmitters (8090 MHz) will be connected to the LVDS outputs not cross-strapped. The X-band link budget results in a link margin of 6 dB which will allow a reduction of the RF output power. Therefore the X-band transmitter will be designed (customer furnished item) to support various output power settings such that after commissioning, a lower output power might be selected.
     565
     566Data compression: The massive amount of data produced by the instrument is beyond the capabilities of the bandwidth available on board of a small satellite. Data are reduced by using a lossless data compression algorithm implemented in a specific electronics. The data compression ratio obtained using standard CCSDS compression algorithms (CCSDS 133.0 B-1) is shown in Table 2.
     567
     568Spectral band
     569       
     570
     571Compression ratio
     572
     573Blue 10.8
     574
     575Red 7.2
     576
     577NIR 5.4
     578
     579SWIR 2
     580
     581Table 2: Overview of compression rates
     582
     583The selection of an S-band transceiver and the development of an innovative and generic X-band transmitter for small satellites has been initiated in a collaborative program between CNES and ESA and is funded under GSTP-5 (General Support Technology Program-5). The X-band transmitter is a high-performance device optimized for the needs and constraints of small platforms for which small volume, low mass, low power consumption, and low cost cost are important parameters. Moreover, some key features such as modulation (filtered Offset-QSK), coding scheme (convolutional 7 ½), data and clock interfaces (LVDS packet wire serial interface) have been selected in compliance with CCSDS recommendations, but also to ease the interoperability with most of the existing on-board computers and ground station demodulators. 17)
     584
     585The development of the new X-band transmitter is based almost exclusively on COTS components to achieve at the same time high performances and low recurrent cost. The transmitter also features an innovative functionality with an on-board programmable RF output power from 1-10 W which allows to match finely with the chosen bit rate, and to reduce as much as possible the margins of the link budget and therefore the consumption power. PROBA-V is the first mission to use this newly developed transmitter. The transmitter has a mass of 1 kg, a size of 160 mm x 115 mm x 46 mm, an in-orbit life time of 5 years, and a radiation hardness of 10 krad. Data rates from 10-100 Mbit/s are available. The X-band transmitter was manufactured by TES Electonic Solutions of Bruz, France. 18)
     586
     587[wiki:File:ProbaV_AutoF.jpeg? File:ProbaV AutoF.jpeg?]
     588Figure 4: Overview of the transmitter architecture (CNES, TES)
     589
     590[wiki:File:ProbaV_AutoE.jpeg File:ProbaV AutoE.jpeg]
     591Figure 5: Photo of the X-band transmitter (image credit: CNES, ESA)
     592=  ProbaV  =
     593
     594
     595
     596[[TOC(TBR/UserApp/Space/ProbaV, depth=2)]]
     597
     598The ‘V’ in its name stands for Vegetation: Proba-V will fly a reduced-mass version of the Vegetation instrument currently on board the Spot satellites to provide a daily overview of global vegetation growth.
     599
     600{| align="center"
     601|+'''PROBA V'''
     602|-
     603|[wiki:File:Probav-shiny_large0.jpg 450px]
     604|}
     605
     606 
     607Bearing a different designation from its predecessors, Proba-V is an operational as well as experimental mission, designed to serve an existing user community.
     608
     609The aim is to guarantee data continuity for the Vegetation dataset once the current Spot missions end.
     610
     611{| border="1"
     612|+ '''Proba-V facts and figures'''
     613|-
     614|Launch date:
     615|mid-2012
     616|-
     617|Mass:
     618|160 kg
     619|-
     620|Orbit:
     621|Sun-synchronised polar orbit, 820 km, with a 10:30 AM local time at the descending node
     622|-
     623|Instrument:
     624|Newly designed version of the Vegetation instrument flown on the Spot series
     625|-
     626|Guest technology payloads:
     627|Gallium Nitride amplifier incorporated in communication subsystem; Energetic Particle Telescope and one other payload to be decided at a later stage
     628|-
     629|Prime contractor:
     630|Qinetiq Space Belgium
     631|-
     632|Payload developer:
     633|OIP Space Systems
     634|-
     635|Ground Station:
     636|Satellite’s mission control centre in Redu, Belgium complemented by a data reception station to be located in the north of Europe.
     637|-
     638|Launcher:
     639|To be decided – designed to be compatible with Vega, Soyuz or Falcon 1E launchers.
     640|}
     641
     642=  PROBA-V (Project for On-Board Autonomy - Vegetation) =
     643
     644
     645The PROBA-V (Vegetation) mission definition is an attempt, spearheaded by ESA and CNES, to accommodate an improved smaller version of the large VGT (Vegetation) optical instrument of SPOT-4 and SPOT-5 mission heritage on a small satellite bus, such as the one of PROBA-2.
     646
     647As of 2008, small satellite technologies have reached a level of maturity and reliability to be used as a platform for an operational Earth observation mission. Furthermore, advancements in the techniques of detectors, optics fabrication and metrology are considered sufficiently mature to permit the design of a compact multispectral optical instrument. 1) 2) 3) 4) 5) 6) 7) 8) 9) 10)
     648
     649The C/D Phase started in July 2010. The system CDR (Critical Design Review) took place in the spring of 2011. The acceptance review is planned for Dec. 2011 and the flight acceptance review is planned for the spring of 2012.. ESA is responsible for the overall mission, the technological payloads and for the launcher selection.
     650
     651Background: The VGT instruments (VGT1 & VGT2), each with a mass of ~160 kg and fairly large size, have provided the user community with almost daily global observations of continental surfaces at a resolution of 1.15 km on a swath of ~2200 km. The instruments VGT1 on SPOT-4 (launch March 24, 1998) and VGT2 on SPOT-5 (launch May 4, 2002) are quasi similar optical instruments operating in the VNIR (3 bands) and SWIR (1 band) range.
     652
     653The Vegetation instruments were jointly developed and funded by France, Belgium, Italy, Sweden, and the EC (European Commission). The consortium of CNES, BelSPO (Federal Public Planning Service Science Policy), SNSB (Swedish National Space Board) and VITO (Flemish Institute for Technological Research) is providing the user segment services (data processing, archiving, distribution). Vegetation principally addresses key observations in the following application domains:
     654
     655 *  General land use in relation to vegetation cover and its changes
     656
     657 *  Vegetation behavior to strong meteorological events (severe droughts) and climate changes (long-term behavior of the vegetation cover)
     658
     659 *  Disaster management (detection of fires and surface water bodies)
     660
     661 *  Biophysical parameters for model input devoted to water budgets and primary productivity (agriculture, ecosystem vulnerability, etc.).
     662
     663As of 2008, a Vegetation archive of 10 years of consistent global data sets has been established permitting researchers access on a long-term basis. The SPOT-5 operational lifetime is estimated to expire in 2012. Pleiades, the next French satellite for Earth Observation, is solely dedicated to high-resolution imaging (on a fairly narrow swath) and will not embark any instrument providing vegetation data.
     664
     665Since the SPOT series spacecraft will not be continued and the SPOT-5 spacecraft will eventually fail — there is of course a great interest in the EO user community to the Vegetation observation in the context of a smaller mission, affordable to all concerned. 11)
     666
     667PROBA-V will continue the production of Vegetation products exploiting advanced small satellite technology. However, this implies in particular a redesign of the Vegetation payload into a much smaller unit to be able to accommodate it onto the PROBA bus.
     668
     669Overview of key requirements of the PROBA-V mission - and some improvements compared to SPOT/Vegetation:
     670
     671 *  Data and service continuity: filling the gap between SPOT-VGT and the Sentinel-3 mission
     672
     673 *  Spectral and radiometric performance identical to VGT
     674
     675 *  GSD: 1 km mandatory, improved GSD is highly disirable: 300 m (VNIR bands), 600 m (SWIR band). Image quality and geometric accuracy, equal to or better than SPOT-VGT
     676
     677 *  Provision of daily global coverage of the land masses in the latitudes 35º and 75º North and in the latitudes between 35° and 56° South, with a 90% daily coverage of equatorial zones - and 100% two-daily imaging, during day time, of the land masses in the latitudes between 35º North and 35º South..
     678
     679
     680{| align="center"
     681|-
     682|[wiki:File:ProbaV_Auto12.jpeg File:ProbaV Auto12.jpeg]
     683|}
     684
     685Figure 1: Artist's view of the PROBA-V spacecraft (image credit: ESA) 12) 13)
     686
     687An extensive feasibility study and trade-off work was undertaken to identify a solution that could meet not only the technical challenges, but that could also be developed and tested within a tight budget of a small satellite mission.
     688
     689The PROBA-V project of ESA includes the Space Segment (platform contract award to QinetiQ Space NV of Kruibeke, Belgium - formerly Verhaert), the Mission Control Center (Redu, Belgium) and the User Segment (data processing facility) at VITO NV. VITO (Vlaamse instelling voor technologisch onderzoek - Flemish Institute for Technological Research) is located in northern Belgium. VITO’s processing center of VGT1 and 2 data (SPOT-4 and SPOT-5) is operational since 1999. VITO is also the prime investigator and data service provider of PROBA-V for the user community including product quality control. 14)
     690
     691Implementation schedule:
     692
     693 *  The Phase B of the project started in January 2009
     694
     695 *  SRR (System Requirements Review) is in Q4 of 2009
     696
     697 *  PDR (Preliminary Design Review) in Q2 of 2010
     698
     699 *  HMA (Heterogeneous Mission Access) and QA4EO (Quality Assurance for Earth Observation) implementation for user data. Planned interoperability with GSCDA V2 (GMES Space Component Data Access Version 2).
     700
     701{| align="center"
     702|-
     703|[wiki:File:ProbaV_Auto11.jpeg File:ProbaV Auto11.jpeg]
     704|}
     705
     706Figure 2: PROBA-V project organization (image credit: ESA, Ref. 9)
     707= Spacecraft: =
     708
     709
     710An industrial team, led by QinetiQ Space NV (Belgium), is supported by several European subcontractors and suppliers, and is responsible for the development of the flight satellite platform, the vegetation payload and the Ground Segment.
     711
     712The spacecraft bus (fully redundant) is of heritage from the PROBA-1 and PROBA-2 missions (structure, avionics, AOCS, OBS with minor modifications). The PROBA-V spacecraft has a total mass of ~160 kg, and a volume of 80 cm x 80 cm x 100 cm. The three-axis stabilized platform is designed for a mission lifetime of 2.5 years (Ref. 7). 15)
     713
     714The spacecraft resources management is built around ADPMS (Advanced Data and Power Management System), which is currently flying on PROBA-2. The data handling part of ADPMS is partitioned using compact PCI modules. A cold redundant mass memory module of 16 Gbit is foreseen for PROBA-V. The newly developed mass memory will use NAND flash technology.
     715
     716The power distribution and conditioning part of ADPMS supplies an unregulated bus, with each equipment having its internal DC/DC converter. The power conditioning system is designed around a Li-ion battery.
     717
     718
     719{| align="center"
     720|-
     721|[wiki:File:ProbaV_Auto10.jpeg File:ProbaV Auto10.jpeg]
     722|}
     723
     724Figure 3: PROBA-V spacecraft accommodation (image credit: QinetiQ Space)
     725
     726AOCS (Attitude and Orbit Control Subsystem) provides three-axis attitude control including high accuracy pointing and maneuvering in different spacecraft attitude modes. The AOCS SW is an extension of the one of PROBA-2, including the following algorithms required by the on-board autonomous mission and payload management: 16)
     727
     728- Prediction of land/sea transitions using a land sea mask to reduce the amount of data generated
     729
     730- Optimization of attitude in Sun Bathing mode to enhance incoming power while avoiding star tracker blinding
     731
     732- Momentum dumping without zero wheel speed crossings during imaging
     733
     734- Estimations of remaining spacecraft magnetic dipole to reduce pointing error
     735
     736- Autonomous avoidance of star tracker Earth/Sun blinding
     737
     738- Inertial mode with fixed scanning rate for moon calibration.
     739
     740The AOCS hardware selection for PROBA-V consists of a high accuracy double star tracker head, a set of reaction wheels, magnetotorquers, magnetometers and a GPS receiver.
     741
     742The main AOCS modes are: Safe, Geodetic, Sun Bathing and Inertial mode.
     743
     744- The satellite Safe mode is used to detumble the spacecraft after separation from the launcher and it will be used to recover from spacecraft anomalies.
     745
     746- The Geodetic mode is used during nominal observation of the Earth’s vegetation. In this mode the payload is pointed towards the geodetic normal to the Earth’s surface. An extra steering compensation, yaw-steering, is added in this mode, to minimize the image distortion caused by the rotation of the Earth. This yaw-steering maneuver ensures that the spectral imagers are oriented such that the lines of pixels are perpendicular to the ground-trace at each moment. In this mode the star trackers and the GPS receiver are used as sensors and the reaction wheels as actuators.
     747
     748- On each orbit, the spacecraft enters the Sun Bathing mode from -56º latitude until entry of eclipse. This is to enhance the incoming power.
     749
     750- The Inertial mode coupled with an inertial scanning of the Moon at a fixed rate is used for monthly radiometric full moon instrument calibration purposes. The pointing towards the moon takes 2.5 min, 9 min for scanning the moon and 2.5 min to return to nominal observation mode. It is sufficient to have the moon in the FOV of the SI (Spectral Imager) for a number of pixels.
     751
     752Beyond the technology demonstration through the PROBA program, it is also noted that the AOCS software technology developed in the course of this program is now the baseline of the AOCS of a major operational mission of the GMES (Global Monitoring for Environment and Security) program: Sentinel-3. NGC Aerospace Ltd (NGC) of Sherbrooke, (Québec), Canada was responsible for the design, implementation and validation of the autonomous GNC (Guidance, Navigation and Control) algorithms implemented as part of the AOCS software of PROBA-1 and PROBA-2. NGC has the same responsibilities for the PROBA-V mission (Ref. 16).
     753
     754EPS (Electric Power Subsystem): The PVA (Photo-Voltaic Array) uses GaAs triple junction cells with an of efficiency of 28%. To obtain the operating voltage of 31.5 V, 18 cells are included in each string in series with a blocking diode. The PVA consists of a total of 25 solar strings taken into account the loss of one string on the most contributing PVA panel. The average solar string power under EOL conditions (summer solstice and T = 40°C) yields 12.8 W. The maximal incoming power at EOL during an orbit is 144 W. The energy budget for PROBA-V is derived for a bus power consumption of 140 W assuming a worst case day in the summer and while not taken into account the effect of albedo. A worst case power budget analysis indicated a maximum capacity discharge of 1.66 Ah. Use of a Li-ion battery. The battery cells provide a capacity of 1.5 Ah per string. The PROBA-V battery is sized to 12 Ah taking into account capacity fading and loss of a string.
     755
     756Launch: A launch of the PROBA-V spacecraft as a secondary payload is planned for Q4 2012. The primary launcher is currently assumed to be Vega with the VESTA adapter.
     757
     758Orbit: Sun-synchronous orbit, altitude = 820 km, inclination = 98.8º, LTDN (Local Time on Descending Node) = 10:30 hours (with a drift limited between 10:30 and 11:30 AM during the mission lifetime).
     759
     760RF communications: S-band for TT&C transmissions and low-gain antennas with omni-directional up- and downlink capability. The uplink symbol rate will be fixed at 64 ks/s, while the downlink can be set to a high rate (< 2 Ms/s) for nominal imaging or to a low rate at 329 ks/s for off-nominal conditions. The CCSDS protocol is used for the TT&C transmissions.
     761
     762X-band downlink of payload data is in X-band at a data rate of 35 Mbit/s. The onboard mass memory is 88 Gbit. The Redu station (Belgium) is being used for TT&C communication services. The X-band uses two cold redundant high-rate X-band transmitters and two nadir pointing isoflux antennas, both RHCP.
     763
     764The S-band transceivers will be connected to RS422 outputs (cross strapped) of ADPMS while the X-band transmitters (8090 MHz) will be connected to the LVDS outputs not cross-strapped. The X-band link budget results in a link margin of 6 dB which will allow a reduction of the RF output power. Therefore the X-band transmitter will be designed (customer furnished item) to support various output power settings such that after commissioning, a lower output power might be selected.
     765
     766Data compression: The massive amount of data produced by the instrument is beyond the capabilities of the bandwidth available on board of a small satellite. Data are reduced by using a lossless data compression algorithm implemented in a specific electronics. The data compression ratio obtained using standard CCSDS compression algorithms (CCSDS 133.0 B-1) is shown in Table 2.
     767
     768Spectral band
     769       
     770
     771Compression ratio
     772
     773Blue 10.8
     774
     775Red 7.2
     776
     777NIR 5.4
     778
     779SWIR 2
     780
     781Table 2: Overview of compression rates
     782
     783The selection of an S-band transceiver and the development of an innovative and generic X-band transmitter for small satellites has been initiated in a collaborative program between CNES and ESA and is funded under GSTP-5 (General Support Technology Program-5). The X-band transmitter is a high-performance device optimized for the needs and constraints of small platforms for which small volume, low mass, low power consumption, and low cost cost are important parameters. Moreover, some key features such as modulation (filtered Offset-QSK), coding scheme (convolutional 7 ½), data and clock interfaces (LVDS packet wire serial interface) have been selected in compliance with CCSDS recommendations, but also to ease the interoperability with most of the existing on-board computers and ground station demodulators. 17)
     784
     785The development of the new X-band transmitter is based almost exclusively on COTS components to achieve at the same time high performances and low recurrent cost. The transmitter also features an innovative functionality with an on-board programmable RF output power from 1-10 W which allows to match finely with the chosen bit rate, and to reduce as much as possible the margins of the link budget and therefore the consumption power. PROBA-V is the first mission to use this newly developed transmitter. The transmitter has a mass of 1 kg, a size of 160 mm x 115 mm x 46 mm, an in-orbit life time of 5 years, and a radiation hardness of 10 krad. Data rates from 10-100 Mbit/s are available. The X-band transmitter was manufactured by TES Electonic Solutions of Bruz, France. 18)
     786
     787
     788{| align="center"
     789|+'''Figure 4: Overview of the transmitter architecture (CNES, TES)'''
     790|-
    392791|[[File:ProbaV_AutoF.jpeg? ]]|}
    393792|}