On-Board Data Handling

On-Board Data Handling

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 (TTC) subsystem.

In the earlier decades of the space industry, the OBDH function was usually considered a part of the TTC, 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 TTC, which is these days concerned solely with the RF link between the ground and the spacecraft.

Functions commonly performed by the OBDH are:

  • Reception, error correction and decoding of telecommands (TCs) from the TTC
  • 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 TTC.
  • Management and distribution of time signals

Contents

Telecommand reception

The OBDH receives the TCs as a synchronous PCM data stream from the TTC

Telecommand execution

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 telecommands

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 telecommands

Similar to time tagged commands are commands which are stored for execution until the spacecraft is at a specified position. These are most useful for earth observation satellites, which need 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

The modern OBDH always uses an on-board computer (OBC) which 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 etc. 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.


Wikimedia Foundation. 2010.

Игры ⚽ Нужен реферат?

Look at other dictionaries:

  • Data logger — Cube storing technical and sensor data A data logger (also datalogger or data recorder) is an electronic device that records data over time or in relation to location either with a built in instrument or sensor or via external instruments and… …   Wikipedia

  • On-board — may refer to: On Board Diagnostics On Board Data Handling In computing, the term on board often refers to controllers or other devices that are integrated onto a motherboard, used in the metaphoric sense, as well as referring to them being… …   Wikipedia

  • Board portal — A board portal is collaborative software that allows board of directors to securely access board documents and collaborate with other board members electronically. History The passing of the Sarbanes Oxley Act has placed significant legal and… …   Wikipedia

  • Board of directors — For other uses of trustee , trusty , and related terms, see Trustee (disambiguation). Board Room redirects here. For the Board Room member lounge, see Alaska Airlines. trustee in trust redirects here. A board of directors is a body of elected or… …   Wikipedia

  • BusinessObjects Data Integrator — Business Objects s Data Integrator is a data integration and ETL tool that was previously known as ActaWorks. The Data Integrator product consists primarily of a Data Integrator Job Server and the Data Integrator Designer. It is commonly used for …   Wikipedia

  • Printed circuit board — Part of a 1983 Sinclair ZX Spectrum computer board; a populated PCB, showing the conductive traces, vias (the through hole paths to the other surface), and some mounted electrical components A printed circuit board, or PCB, is used to… …   Wikipedia

  • Electronic Data Interchange — (EDI) refers to the structured transmission of data between organizations by electronic means. It is more than mere E mail; for instance, organizations might replace bills of lading and even checks with appropriate EDI messages. It also refers… …   Wikipedia

  • Flight data recorder — An example of a flight data recorder; the underwater locator beacon is the small cylinder on the far right. (English translation of warning message: FLIGHT RECORDER DO NOT OPEN) …   Wikipedia

  • Customs Handling of Import & Export Freight — (CHIEF) is the computer system of the United Kingdom s revenue and customs services, HMRC. CHIEF manages both the declaration and movement of goods into and out of the United Kingdom and is a means by which UK traders communicate with counterpart …   Wikipedia

  • Control Data Corporation — (CDC) was a supercomputer firm. For most of the 1960s, it built the fastest computers in the world by far, only losing that crown in the 1970s after Seymour Cray left the company to found Cray Research, Inc. (CRI). CDC was one of the nine major… …   Wikipedia

Share the article and excerpts

Direct link
Do a right-click on the link above
and select “Copy Link”