Electronic Data System

J. J. Wortman, Electrical and Computer Engineering Department, North Carolina State University, Raleigh, NC 27695

P. C. Kassel, Langley Research Center, National Aeronautics and Space Administration, Hampton, VA 23665

John P. Oliver Institute for Space Science and Technology, 1810 NW 6th Street, Gainesville, FL 32601

I. Introduction

The electronic data system served five basic purposes (1) it provided electrical power to the MOS sensors (2) it monitored and recorded the impacts on the MOS sensors (3) it monitored and recorded data from sun sensors located on each panel (tray) that contained MOS sensors (4) it monitored and recorded selected data on the MOS sensors' status (i.e. whether the detector was shorted or open) as well as housekeeping data such as temperature and battery voltage (5) it provided the clock for determining the relationship between impacts and LDEF position. The philosophy of the experiment utilized the standard LDEF Experiment Power and Data System (EPDS) and supplemented it with the necessary electronics to monitor and record the desired data. The EPDS will not be discussed in detail in this report since it was common to many experiments.

II. System Description

The basic design of the system is shown in Figure 1 and consists of a 6 panel electronics package located in each tray to support the MOS detector and sun sensors in that tray, a master control package, batteries, and an EPDS. A diagram of the master control package is shown in Figure 2 and the panel electronics package is shown in Figure 3. The panel electronics package contained the signal conditioning circuits, the counters including time and sensor counters, the memory elements, and the memory control circuits. Figures 4A and 4B are schematics of the signal conditioning circuits. Figure 5 shows the sun sensor diagram. Figure 6 shows the battery backup arrangment. A Lockheed tape recorder (referred to as MTM in the drawings) was used to record the data. The experiment was designed to acquire and store data for 9 monthes. The original intent was to retrieve the LDEF after 9 months which was not done until after approximately 5 1/2 years. The IDE tape recorder recorded data for 346 days before it ran out of tape. Listed below in Table 1 are the engineering drawings for the electronic system described above. These drawings are part of the LDEF archives. Table 1 - IDE Drawings

Drawing Title			Drawing Number
Time and impact counter 	LD-103
Master control			LD-201
Memory and control		LD-102
Sensor inport			LD-101
Data format			LD-IDE/DF
IDE detector simulator		LD-

Figure 7 is a block diagram of the EPDS.

III. Batteries

Two 7.5 volt lithium batteries were connected in parallel to power the EPDS and the 7.5 volt part of the sensor voltage.

The 0.4 micrometer detectors were powered by a 28 volt battery (nominal voltage of 32 V) plus the 7.5 volt batteries mentioned above. The nominal voltage was 39-40 volts.

The 1.0 micrometer detectors were powered by 28 volt batteries in series plus the 7.5 battery to give a nominal voltage of 71-72 volts. A 12 volt battery powered the recorder.

Figures 8, 9, 10, 11 and 12 are plots of the bias voltages recorded during the time data was stored on the recorder. Upon return, the battery voltages were measured and it was found that the 7.5 volt supply was discharged as well as the 28 volt supplies that powered the 0.4 micrometer detectors. However the two 28 volt supplies that powered the 1.0 micrometer detectors were found to be good. This was very fortunate because they provided continuous power for the full 5 1/2 year mission. Consequently the 1.0 micrometer detectors discharged and recharged for the full mission. By counting the discharge craters before the mission and after the mission one can compare the data with other witness plate experiments that were exposed for the entire mission. This was done and reported (see also) in this database.

IV. System Operation and Status

V. Post Flight Power up

The IDE post flight test was intended to determine the operating condition of the IDE electronics and the condition of the 1.0 micron sensors on the (D-6) south panel. The IDE Electronics, Power and Data System (EPDS) with fresh batteries was connected to the D-6 panel and allowed to collect data on the tape recorder as had been done in space. The results of this test are summarized in the tables below.

Clock Calibration:    Seconds = Count * M  +  B					

     M    =	1.6377				
     B     =	-0.1837				

+------------+-------------+-------+-----------+----------+--------------+
| Record     |   Record	   |       |           |          |              |
| Number     | Clock Count | Days  | Date      | Time     | Comments     |
+------------+-------------+-------+-----------+----------+--------------+
| Start Test |       0     |       | 22-Mar-91 | 11:20 AM |              |
|   1        |    5328     |  0.10 | 22-Mar-91 |  1:45 PM | First Record |
|   2        |   10672     |  0.20 | 22-Mar-91 |  4:11 PM |              |
|  69        |  368720     |  6.99 | 29-Mar-91 | 11:04 AM |              |
| 144        |  769520     | 14.59 |  6-Apr-91 |  1:24 AM |              |
| 263        | 1405456     | 26.64 | 18-Apr-91 |  2:41 AM |              |
| 275        | 1469584     | 27.86 | 19-Apr-91 |  7:52 AM | Last Record  |
+------------+-------------+-------+-----------+----------+--------------+
|                       Stop test before next record                     |
+------------+-------------+-------+-----------+----------+--------------+
| 276        | 1474928     | 27.96 | 19-Apr-91 | 10:18 AM |              |
+------------+-------------+-------+-----------+----------+--------------+

+-----------+-------------+-------+-----------+----------+--------+
| Discharge |    Event    |       |           |          | Record |
| Events    | Clock Count | Days  | Date      | Time     | Number |
+-----------+-------------+-------+-----------+----------+--------+
| 1         |      72     |  0.00 | 22-Mar-91 | 11:21 AM |   1    |
| 2         |    1872     |  0.04 | 22-Mar-91 | 12:11 PM |   1    |
| 3         |    2456     |  0.05 | 22-Mar-91 | 12:27 PM |   1    |
| 4         |    2648     |  0.05 | 22-Mar-91 | 12:32 PM |   1    |
| 5         |    3976     |  0.08 | 22-Mar-91 |  1:08 PM |   1    |
| 6         |    8704     |  0.16 | 22-Mar-91 |  3:17 PM |   2    |
| 7         |  365536     |  6.93 | 29-Mar-91 |  9:37 AM |  69    |
| 8         |  765232     | 14.50 |  5-Apr-91 | 11:27 PM | 144    |
| 9         | 1400664     | 26.55 | 18-Apr-91 | 12:31 AM | 263    |
+-----------+-------------+-------+-----------+----------+--------+

Sensor status did not change during this test.          

HEX:  FE  CD  4D  BF  
Bits:  "1111  1110"  "1100  1101"  "0100  1101"  "1011  1111"

IDE Post Flight Test Results
1.0 micron Sensors on South (D-6) Panel

Two aditional pieces of data are included with the sensor status data. The "In Flight % Inactivity" is just the % of records that showed a status of "0" during the IDE active life (first 11 months in space). The sensor status was determined by monitering the sensor leakage current. For these sensors leakage current greater than 8.5 micro Amps. would reduce the voltage on the sensor to less than 28 volts and the status would be "0"; leakage current less than 7.5 micro Amps. would indicate sensor voltage greater than 32 volts and the status would be "1". The status data was sampled and recorded once every 2.4 hours.

The "Post Test Capacitance" was measured as the sensors were removed from the panel.

+--------+----------+-----------+------------+------------+-------------+
|        |          |           |            |            |  Post Test  |
| EPES   |          | Post Test | In Flight  | Post Test  | Capacitance |
| Data # | Sensor # |   Status  | % Inactive | % Inactive |      nF     |
+--------+----------+-----------+------------+------------+-------------+
| 49     | 1380     | 1         |  6.23      |   0.00     | 65.60       |
| 50     | 1339     | 1         |  6.96      |   0.00     | 65.20       |
| 51     | 1301     | 1         |  5.20      |   0.00     | 64.80       |
| 52     | 1251     | 1         |  5.70      |   0.00     | 64.20       |
| 53     | 1188     | 1         |  4.32      |   0.00     | 65.10       |
| 54     | 1398     | 1         |  6.90      |   0.00     | 65.70       |
| 55     | 1367     | 1         |  5.32      |   0.00     | 65.60       |
| 56     | 1187     | 0         | 45.55      | 100.00     | Short       |
| 57     | 1211     | 1         |  5.90      |   0.00     | Open        |
| 58     | 1246     | 1         |  3.70      |   0.00     | 64.40       |
| 59     | 1206     | 0         |  3.76      | 100.00     | 65.50       |
| 60     | 1394     | 0         |  5.73      | 100.00     | Short       |
| 61     | 1362     | 1         |  4.08      |   0.00     | 65.40       |
| 62     | 1311     | 1         |  3.11      |   0.00     | 64.60       |
| 63     | 1253     | 0         |  2.85      | 100.00     | 68.20       |
| 64     | 1212     | 1         |  2.67      |   0.00     | 65.40       |
| 65     | 1366     | 0         |  5.17      | 100.00     | 65.80       |
| 66     | 1314     | 1         |  3.76      |   0.00     | 64.80       |
| 67     | 1263     | 0         |  3.29      | 100.00     | 69.50       |
| 68     | 1225     | 0         |  2.44      | 100.00     | 66.20       |
| 69     | 1160     | 1         |  2.29      |   0.00     | 65.30       |
| 70     | 1369     | 1         |  7.25      |   0.00     | 65.60       |
| 71     | 1337     | 0         |  9.19      | 100.00     | 65.20       |
| 72     | 1295     | 1         |  4.41      |   0.00     | 64.50       |
| 73     | 1269     | 1         |  4.26      |   0.00     | 64.60       |
| 74     | 1209     | 0         |  4.52      | 100.00     | 65.40       |
| 75     | 1186     | 1         |  2.23      |   0.00     | 65.00       |
| 76     | 1252     | 1         | 38.00      |   0.00     | 64.20       |
| 77     | 1325     | 1         |  6.96      |   0.00     | 64.90       |
| 78     | 1264     | 1         |  5.70      |   0.00     | 64.50       |
| 79     | 1243     | 1         |  4.05      |   0.00     | 64.20       |
| 80     | 1196     | 1         |  6.20      |   0.00     | 65.20       |
+--------+----------+-----------+------------+------------+-------------+

IDE Post Flight Test Results
1.0 micron Sensors on South (D-6) Panel ( Sensor Status )

VI. System Status

Klaus G. Paul, 7-9-1994