IIRVs serve the same purpose as Two-Line Elements, to provide information about the orbit of a spacecraft in order to allow a prediction of its position at some time in the near future.
The Improved Inter-Range Vector (IIRV) message is a standard message from Goddard Space Flight Center (GSFC). The message contains six (6) lines. This document contains the format and description of the Improved Inter-Range Vector message.
Each of the six lines in the message is terminated by two (2) carriage returns followed by two (2) line feeds. There are no spaces between fields on a line.
If there are multiple vectors being sent in the same message, the following will be repeated for each subsequent vector:
03uuuuuuu010GIIRV MANY 1111736801nnndddhhmmsssssccc sxxxxxxxxxxxxsyyyyyyyyyyyyszzzzzzzzzzzzccc sxxxxxxxxxxxxsyyyyyyyyyyyyszzzzzzzzzzzzccc mmmmmmmmaaaaakkkksrrrrrrrccc ITERM GAQD
| Line No. | No. of Bytes | Format | DESCRIPTION |
|---|---|---|---|
| 1 | 2 | 03 | Message Type (Operations Data Message) |
| 7 | uuuuuuu | Message ID, 0000000 to 9999999 | |
| 1 | 0 | Message source (Flight Dynamics Facility) | |
| 2 | 10 | Message class (nominal) | |
| 5 | "GIIRV" | Message start | |
| 1 | ASCII space | Originator of message (GSFC) | |
| 4 | "MANY" | Routing indicator (multiple destinations) | |
| 2 | 1 | 1 | Vector type (free flight, routine on-orbit) |
| 1 | 1 | Data source (nominal/ planning) | |
| 1 | 1 | Transfer type (Interrange) | |
| 1 | 1 | Coordinate system (Geocentric true-of-date rotation) | |
| 4 | 7368 | Support Identification Code | |
| 2 | 01 | Vehicle Identification Code | |
| 3 | nnn | Sequence number incremented for each vector in a set of vector data, 000 to 999 | |
| 3 | ddd | Day of year, 001 to 366 | |
| 9 | hhmmsssss | Vector epoch in UTC, hh = 00 to 23, mm = 00 to 59, sssss = 00000 to 59999 (milliseconds, implied decimal point three places from right) | |
| 3 | ccc | Checksum for line 2; calculated by summing the decimal equivalent of the preceding characters in the line, counting spaces as 0 and negative signs as 1 | |
| 3 | 13 | sxxxxxxxxxxxx | X component of the position vector in meters. s = "-" for negative sign or ASCII space for positive sign |
| 13 | syyyyyyyyyyyy | Y component of the position vector in meters | |
| 13 | szzzzzzzzzzzz | Z component of the position vector in meters | |
| 3 | ccc | Checksum for line 3 | |
| 4 | 13 | sxxxxxxxxxxxx | X component of the velocity vector in meters per second, with a resolution to the nearest millimeter per second; assumed decimal point is three places from the right. |
| 13 | syyyyyyyyyyyy | Y component of the velocity vector in meters per second, with a resolution to the nearest millimeter per second; assumed decimal point is three places from the right. | |
| 13 | szzzzzzzzzzzz | Z component of the velocity vector in meters per second, with a resolution to the nearest millimeter per second; assumed decimal point is three places from the right. | |
| 3 | ccc | Checksum for line 4 | |
| 5 | 8 | mmmmmmmm | Mass of the satellite in kilograms with a resolution to the nearest tenth of a kilogram; assumed decimal point is one place from the right. Must contain all zeros if not used. |
| 5 | aaaaa | Average satellite cross-sectional area in square meters with a resolution to the nearest hundredth of a square meter; assumed decimal point is two places from the right. Must contain all zeros if not used. | |
| 4 | kkkk | Dimensionless drag coefficient; assumed decimal point is two places from the right. Must contain all zeros if not used. | |
| 8 | srrrrrrr | Dimensionless solar reflectivity coefficient; s = "-" for negative sign or blank for positive sign, assumed decimal point is six places from the right. May contain all zeros if not used. | |
| 3 | ccc | Checksum for line 5 | |
| 6 | 5 | "ITERM" | Indicates end of message |
| 1 | ASCII blank | ||
| 4 | "GAQD" | Originator routing | |
| 7 | 10 | "GIIRV MANY" | Identifies message start, originator and routing indicator for second vector set |
| 8-12 | same as lines 2-6 for a second vector set | Second vector set | |
| 13- | repeat lines 7-12 for each subsequent vector set | Additional vector sets |
References: igs_icd.pdf, "Landsat 7 to International Ground Station (IGS) Interface Control Document", 30 September 1997 Revision A, GSFC. Document number 430-11-06-009-A.
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