A8.1 General Description

A8.1.1 Overview

This Software Interface Specification (SIS) describes the contents and format of the Supplementary Experiment Data Record (SEDR) and the formats of the tapes for transferring SEDR data to the ULS Principal Investigators (PIs).

A8.1.2 Scope

Record and tape formats and data types will be covered in this document. There is only one SEDR format for the entire ULS mission. A separate tape format is created for each PI host computer

A8.1.3 Applicable Documents

A8.1.4 System Site

Subsystem Medium and Location. SEDR and SEDR tapes are generated on the UNISYS computer at the Information Processing Center (IPC) of the Jet Propulsion Laboratory (JPL).

Data Sources, Destinations, and Transfer Method. Data for the SEDR are derived from two sources: navigational parameters from the Navigational System DPTRAJ program and spacecraft spin axis orientation information from the ESOC Attitude History file. SEDR will be provided to PIs with an ongoing experiment aboard the ULS spacecraft. The transfer method for the SEDR will be by magnetic tapes.

ULS PIs may request a printout of all SEDR parameters for their own use at JPL during critical mission periods.

General Method and Frequency. The ULS Data Management Team (DMT) is responsible for the generation of SEDR. DMT will generate an SEDR file once a month containing data for the previous one-month period.

DMT will generate a set of Predict SEDR (PSEDR) that covers the entire ULS mission from launch to end-of-mission. DMT may generate additional predict SEDR on request from PIs. These may cover shorter periods than the nominal PSEDR, or may be generated using a more accurate trajectory, or both.

Labeling and Identification (Internal/External). No internal magnetic tape labels exist on SEDR tapes. The SEDR records will have three SFDU headers which contain such information as project identifier, file identifier, and date and time of file generation.

An external tape number will be placed on the SEDR tape reel and strap. This tape number is comprised of the three letter designation of the experiment and the six digit SEDR identification code. The following coding scheme will be used:

The following tables provide a detailed description of the breakdown of the SEDR tape number.

Table A8-1 Experiment designator versus number

Table A8-2 Mission phase code

Table A8-3 SEDR type code

The following is an example of a SEDR tape number:

Example: SIM 072103

Breakdown of the tape number “SIM 072103” is given as follows: This SEDR tape is designated for the Simpson experimenters (SIM) in Chicago (07). The SEDR data on the tape covers a portion of the cruise period between the second and third trajectory correction maneuvers or TCMs (2). The SEDR is the original “final,” not a remake (1). Finally, this is the third in the series of SEDR tapes for the indicated mission phase (03).

A8.1.5 Assumptions and Constraints

Usage Constraints. The SEDR will be distributed in accordance with SIS 2tg on the generation and delivery of SEDR tapes.

Data Accuracy and Conventions. Data accuracy is defined in the ULS Mission Operations System Functional Requirements Document, Data Records System Functional Requirements (ULS-MOS-3-700).

Double precision (72 bits on the UNISYS) computation is used, but output to the SEDR is single precision (32 bits).

Fill data will be indicated by the value “1000.” Note that the only possible fill data are the spin axis orientation data and the sun aspect angle during periods when the spacecraft is performing a maneuver.

DMT will inform PIs of any changes to the astronomical constants or conventions used on the SEDR. Viz., this SIS will continue to be maintained.

Time Tags. Each SEDR record is tagged with the time of the epoch for which the SEDR data are in effect. Both UTC and spacecraft clock count will be used in the time tagging. Time in UTC is equivalent to the spacecraft event time of the EDR. Spacecraft clock count will be computed from the spacecraft event time and will be consistent with the EDR.

The accuracy of the computed spacecraft clock count will be kept within ± 100 milliseconds of actual correlated relationships between spacecraft clock count and spacecraft event time. The smallest unit of computed spacecraft clock count is one one-thousandth of a count (2 milliseconds).

This requirement to maintain the required accuracy of the computed relationship between spacecraft event time and spacecraft clock count will account for the drift in spacecraft clock rate and any resets or rollovers of the spacecraft clock counter.

The SEDR does not provide any indication of spacecraft clock resets or rollovers. Such events will be noted in the logs and summaries which will accompany each shipment of SEDR.

Next: A8.2 Interface Characteristics

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