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Appendix D. AACS Position and Rate Data

Source: Document 625-610, 8/27/84

The AACS Position and Rate Data record is designed to a RIM cycle containing 91 minor frames. Each minor frame corresponds to a MOD91 count. The AACS record shall be placed onto each Science EDR as well as the Engineering EDR in time order. The logical record structure is diagrammed in Figure 1.

Figure 1. AACS Record

Standard Header
(17 - 32 bit words
AACS Position and Rate Data
(546 - 32 bit words

Processing Start/Stop. Refer to Subsection 5.2.

Record Buildup. AACS record buildup shall proceed with the extraction from the appropriate bit locations from minor frames 1 through 91 of each RIM cycle. Subsection 5.2 defines the basic data extraction procedure.

Record Header. The AACS record shall receive a standard record header; refer to Section 4. (Ed. note: Section 4 is incorporated into this handbook as Appendix B, SEDR Files.)

Record Subheader. The AACS record shall not receive a subheader.

Data Block. The AACS data block contains data extracted from bits 3200 through bits 3391 of each of the 91 minor frames of a RIM cycle from the golay compressed LRS data block of the input SDR record. Specified word locations shall be maintained within the data block. Refer to Figure 2 for data block format and GLL-3-280 Appendix A (below) for detailed definitions.

Figure 2. AACS Data Block Format.


Source: GLL-3-280, Rev. A, Appendix A

Figure 3. Variable Packet Replacement Memory Readout

Description. The CDS shall collect the memory readout data from the desired subsystem and create a memory readout structure identical to paragraph A2.3.1. This structure will replace the first 7 variable packets in the engineering frame.

AACS Position and Rate Data. The AACS shall provide pointing vector and rate data. The pointing vector information shall be provided in the Earth Mean Equator (EME) 1950.0 coordinate system, the Ecliptic (ECL) 1950.0 coordinate system, and spacecraft relative coordinate system. The LRS data schematic is shown in Figure 4 and described further in Table 1.

Figure 4. AACS Position and Rate Data

EME - 50 Coordinates Platform Rate Rotor
Spin
Motion
Delta
16
ECL - 50
Coordinates
S/C Relative
Coordinates
Rotor Attitude Platform Attitude Rotor
Spin
Position
Angle
16
Cone
Position
16
Clock
Position
16
RA
16
DEC
16
TWIST
16
RA
16
DEC
16
TWIST
16
CONE
16
CROSS
CONE
16

Table 1. AACS Position and Rate Data

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Updated 10/1/04, T. Hunt-Ward
tizby@ftecs.com