The on-board data handling (OBDH) subsystem of a spacecraft is the subsystem which carries and stores data between the various electronics units and the ground segment, via the telemetry, tracking and command (TT&C) subsystem.[1]
In the earlier decades of the space industry, the OBDH function was usually considered a part of the TT&C, particularly before computers became common on board. In recent years, the OBDH function has expanded, so much that it is generally considered a separate subsystem to the TT&C, which is these days concerned solely with the RF link between the ground and the spacecraft.[2]
Functions commonly performed by the OBDH are:
Reception, error correction and decoding of telecommands (TCs) from the TT&C
Forwarding of telecommands for execution by the target Avionics
Storage of telecommands until a defined time ('time tagged' TCs)
Storage of telecommands until a defined position ('position tagged' TCs)
Measurement of discrete values such as voltages, temperatures, binary statuses etc.
Collection of measurements made by other units and subsystems via one or more data busses, such as MIL-STD-1553
Real-time buffering of the measurements in a data pool
Provision of a processing capability to achieve the aims of the mission, often using the data collected
Collation and encoding of pre-defined telemetry frames
Storage of telemetry frames in a mass memory
Downlinking of telemetry to the ground, via the TT&C
The OBDH receives the TCs as a synchronous PCM data stream from the TT&C
Telecommand executionedit
The desired effect of the telecommand may be just to change a value in the on-board software, or to open/close a latching relay to reconfigure or power a unit, or maybe to fire a thruster or main engine. Whichever effect is desired, the OBDH subsystem will facilitate this either by sending an electric pulse from the OBC, or by passing the command through a data bus to the unit which will eventually execute the TC. Some TCs are part of a large block of commands, used to upload updated software or data tables to fine tune the operation of the spacecraft, or to deal with anomalies.
Time-tagged telecommandsedit
It is often required to delay a command's execution until a certain time. This is often because the spacecraft is not in view of the ground station, but may also be for reasons of precision. The OBC will store the TC until the required time in a queue, and then execute it.
Position-tagged telecommandsedit
Similar to time-tagged commands are commands that are stored for execution until the spacecraft is at a specified position. These are most useful for Earth observation satellites, which need to start an observation over a specified point of the Earth's surface. The spacecraft, often in Sun-synchronous orbits, take a precisely repeating track over the Earth. Observations which are taken from the same position may be compared using interferometry, if they are in close enough register.
The precise position required is sensed using GPS.
Once a position tagged command has been executed, it may be flagged for deletion or left to execute again when the spacecraft is once again over the same point.
Processing functionedit
The modern OBDH always uses an on-board computer (OBC) that is reliable, usually with redundant processors. The processing power is made available to other applications which support the spacecraft bus, such as attitude control algorithms, thermal control, failure detection isolation and recovery. If the mission itself requires only a small amount of computing power (such as a small scientific satellite) then the payload may also be controlled by the software running on the OBC, to save launch mass and the considerable expense of a dedicated payload computer.
^Cutler, James W.; Beningo, Jacob (2021-01-01), Cappelletti, Chantal; Battistini, Simone; Malphrus, Benjamin K. (eds.), "10 - On-board data handling systems", Cubesat Handbook, Academic Press, pp. 199–219, ISBN978-0-12-817884-3, retrieved 2022-02-09
^"Onboard Computers and Data Handling". www.esa.int. Retrieved 2022-02-09.
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This article needs additional citations for verification Please help improve this article by adding citations to reliable sources Unsourced material may be challenged and removed Find sources On board data handling news newspapers books scholar JSTOR February 2022 template removal help The on board data handling OBDH subsystem of a spacecraft is the subsystem which carries and stores data between the various electronics units and the ground segment via the telemetry tracking and command TT amp C subsystem 1 In the earlier decades of the space industry the OBDH function was usually considered a part of the TT amp C particularly before computers became common on board In recent years the OBDH function has expanded so much that it is generally considered a separate subsystem to the TT amp C which is these days concerned solely with the RF link between the ground and the spacecraft 2 Functions commonly performed by the OBDH are Reception error correction and decoding of telecommands TCs from the TT amp C Forwarding of telecommands for execution by the target Avionics Storage of telecommands until a defined time time tagged TCs Storage of telecommands until a defined position position tagged TCs Measurement of discrete values such as voltages temperatures binary statuses etc Collection of measurements made by other units and subsystems via one or more data busses such as MIL STD 1553 Real time buffering of the measurements in a data pool Provision of a processing capability to achieve the aims of the mission often using the data collected Collation and encoding of pre defined telemetry frames Storage of telemetry frames in a mass memory Downlinking of telemetry to the ground via the TT amp C Management and distribution of time signalsContents 1 Telecommand reception 2 Telecommand execution 3 Time tagged telecommands 4 Position tagged telecommands 5 Processing function 6 See also 7 References 8 External linksTelecommand reception editThe OBDH receives the TCs as a synchronous PCM data stream from the TT amp CTelecommand execution editThe desired effect of the telecommand may be just to change a value in the on board software or to open close a latching relay to reconfigure or power a unit or maybe to fire a thruster or main engine Whichever effect is desired the OBDH subsystem will facilitate this either by sending an electric pulse from the OBC or by passing the command through a data bus to the unit which will eventually execute the TC Some TCs are part of a large block of commands used to upload updated software or data tables to fine tune the operation of the spacecraft or to deal with anomalies Time tagged telecommands editIt is often required to delay a command s execution until a certain time This is often because the spacecraft is not in view of the ground station but may also be for reasons of precision The OBC will store the TC until the required time in a queue and then execute it Position tagged telecommands editSimilar to time tagged commands are commands that are stored for execution until the spacecraft is at a specified position These are most useful for Earth observation satellites which need to start an observation over a specified point of the Earth s surface The spacecraft often in Sun synchronous orbits take a precisely repeating track over the Earth Observations which are taken from the same position may be compared using interferometry if they are in close enough register The precise position required is sensed using GPS Once a position tagged command has been executed it may be flagged for deletion or left to execute again when the spacecraft is once again over the same point Processing function editThe modern OBDH always uses an on board computer OBC that is reliable usually with redundant processors The processing power is made available to other applications which support the spacecraft bus such as attitude control algorithms thermal control failure detection isolation and recovery If the mission itself requires only a small amount of computing power such as a small scientific satellite then the payload may also be controlled by the software running on the OBC to save launch mass and the considerable expense of a dedicated payload computer See also editSpacecraft busReferences edit Cutler James W Beningo Jacob 2021 01 01 Cappelletti Chantal Battistini Simone Malphrus Benjamin K eds 10 On board data handling systems Cubesat Handbook Academic Press pp 199 219 ISBN 978 0 12 817884 3 retrieved 2022 02 09 Onboard Computers and Data Handling www esa int Retrieved 2022 02 09 External links edithttps ecss nl standard ecss e st 50 04c space data links telecommand protocols synchronization and channel coding Retrieved from https en wikipedia org w index php title On board data handling amp oldid 1185401827, wikipedia, wiki, book, books, library,
