2. System Description

2.3 Electronics

2.3.1 Low-Voltage Power Supplies
2.3.2 High-Voltage Power Supplies
2.3.3 DEP
2.3.4 Sensors

The WUPPE flight electronics is illustrated in Figure 2.3-1a. The electronics is physically located on the radiators (Figure 2.3-1b).

Figure 2.3-1a : Block diagram of the WUPPE flight electronics.

Figure 2.3-1b : The WUPPE electronics placement on the -Y and -Z radiators.


Figure 2.3-2 depicts the electrical interfaces between the Spacelab and the experiment.

Figure 2.3-2 : Electrical interfaces.

All electronics are powered from a Low-Voltage Power-Supply (LVPS) system which uses the regulated 28 V Spacelab power (see Figure 2.3-3). This powers the DEP-card cage, the detector-card cage and the I/F electronics box.

Figure 2.3-3 : Spacelab power is transformed by a Low-Voltage Power Supply.

The DEP controls the filter- and aperture-wheel motors, secondary articulation motors, detectors, TEC and IMC. High-Voltage power-supplies include the ZOD and SPD image-tube supplies (6 kV), the pitch and yaw IMC-actuator supplies (1 kV), and the test-lamp supply (0.6 kV). All high-voltage power-supplies are powered by conditioned power from the LVPS, switched by Discrete Output (DO) from the WCO display (section 3.2). Sensors include voltage/current monitors, thermistors, and bright-object sensor, all available to the Experiment Computer (EC) through Analog Input (AI) lines, and additional thermal sensors and telescope tube-strain monitors, read by the DEP and available through telemetry.


TABLE 2.3-1

Power Consumption

Heater Power

Heater Island    Resistance    Current*    Power*
                  [Ohms]        [Amps]     [Watts]
Telescope           3.53         6.49       148.7
DEP Radiator        6.86         3.34        76.5
I/F Radiator       12.82         1.79        40.9
TEC Radiator        6.86         3.34        76.6
                                14.96       342.5

 * At 22.9 Volts, Minimum Voltage with 15 Amps current.

Electronics Power

System           Peak Power*    Mean Power    Comment

DEP                 113.6          113.6      Turned on by LVPS relay
Dtr HVPS              7.6            7.6      Turned on by a DO
TEC                  30.0           26.0      Controlled by DEP
IMC HVPS              4.0            4.0      Turned on by a DO
Filter Mtr           19              5.0      Typical 1 sec duration
Aper Mtr             19              5.0      Typical 1 sec duration
Sec Mtr              39              2.0      Typical 10 sec duration
Door Mtr             20              -.-      Typical 45 sec duration
Test Lamp            20              -.-      Checkout only

                                   163.2      Assume typical duty cycle

 * Assume constant 28.0 V at input to LVPS.



2.3.1 Low-Voltage Power Supplies

The power drawn by the various electronic subsystems is shown in Table 2.3-1. Input voltage to the LVPS is assumed to remain at 28 V. The three units which comprise the LVPS are physically located at the rear of the instrument between the DEP and I/F electronics (the temperature of this unit is monitored on the WAC display), and forward on the drive ring.

2.3.2 High-Voltage Power Supplies

The ZOD and SPD proximity-focus microchannelplate (MCP) image tubes are powered by two identical programmable High-Voltage Power-Supply systems. They are placed on the -Z Radiator beside the TEC heat pipe for temperature stability, and are sealed in dry nitrogen. They are turned on by a DO from the WCO display, but are controlled by the DEP. Each power supply has three voltage outputs:

1) Cathode to MCP: 180V (gate on), -30V (off)

2) MCP: 200 - 850 V(programmable)

3) MCP to Phosphor : 4800 V

Phosphor is ground, so the Cathode is at approximately -6 kV. The tubes may be "gated" off by reverse-biasing the first stage; the tubes are then as insensitive as if the HVPS were off. The gates on both tubes are left off except during actual observing, and in the ZOD the gate is also used to control exposure time. The gain of the tubes are controlled through the MCP voltage: in the SPD there are two settings and in the ZOD 4 settings, each separated by 10x in sensitivity. An MCP voltage monitor is read by the DEP and reported on the WCO display. A schematic of the SPD is shown in Figure 2.3-4.




Figure 2.3-4 : Schematic of the Spectrometer Detector.

The IMC High-Voltage Power Supplies are two identical high-speed programmable supplies which supply 0 - 1000 V at high frequency to the pitch and yaw PZT actuators. They are located on the drive ring and are also sealed in dry nitrogen. They are turned on by a DO from the WCO display, but are controlled by hardwired electronics using the IMC-input signal and the mirror-position feedback-sensors.

The Test-Lamp Power Supply is a self-contained supply which directly feeds 600 V to the ultraviolet Test Lamp in the aperture door (see section 2.1.9). It is located on the drive ring. It is turned on by a DO from the WCO page and is not controlled by the DEP. A hardware switch located on the aperture-door jamb prevents the lamp from being turned on if the two door position indicators do not agree that the door is closed.


2.3.3 DEP

The electronics section of the experiment is under the control of the DEP. Most of the DEP digital logic is modularized on plug-in cards located in a card "cage" based on a modified version of the commercial-industry standard-bus, STD, concept. The heart of the DEP cage is a Motorola 6809 microprocessor. The address space of the DEP is shown in Table 2.4-1. Three 16 k byte Electrically-Eraseable Read-Only Memory (EEROM) modules contain the DEP program and object-parameter list, and a 16 k byte dynamic Random-Access Memory (RAM) module is used for data buffering. CCTV modules contain 6 k byte of memory which may be accessed by the DEP and by a Cathode-Ray Tube-Controller (CRTC) video generator. The processor interacts with the EC via the Remote-Acquisition Unit (RAU) interface modules, and outputs telemetry via the High-Rate Multiplexer (HRM) module. An IMC Module allows control and monitoring of the IMC input signal. A monitor module allows for direct communication on the ground - for testing and integration - by RS-232 communication link with the DEP and for address break-point monitoring, a debugging tool. The module will be powered down during nominal flight operations. The entire DEP cage is copied as a redundant unit, located on the same radiator.

The DEP controls a second card cage, the "detector" cage, through a buffered communication line. The detector cage performs the detector control, stepper motor control, and sensor monitor functions.

2.3.4 Sensors

Table 2.3-2 summarizes all WUPPE sensors.Their locations are shown in Figure 2.3-5. All hardwired inputs available to the EC are also available to the DEP through an A/D convertor (listed as "analog" in the table). All engineering data available to the DEP are sampled once per second and embedded in the HRM telemetry stream, and the EC displays are reconstructed by the EGSE on the ground. Certain data available only to the DEP are forwarded to the EC via a serial message, which is included in the General Measurement Loop (GML) and sent once per second.

Sensors not described elsewhere in this document are described below.

TABLE 2.3-2

Sensor Summary

Function                  Location         EC I/F         DEP I/F

LVPS Voltage               I/F Box          AI 17          Analog
LVPS Current                --"-            AI 19            -"-
Heater Voltage              --"-            AI 21            -"-
Heater Current              --"-            AI 22            -"-
+5V, +-12V DEP              --"-            AI 4,5           -"-
+5V, +-15V Dtr              --"-            AI 2,6           -"-
+28V Motor                  --"-            AI 1             -"-
+28V HVPS                   --"-            AI 7             -"-
TEC Volts                   --"-            AI 3             -"-
Primary Mirror Temp.       Pri. Mir.        AI 9             -"-
Second. Mir. Temp.         Sec. Mir.        AI 12            -"-
Spectrometr. Temp.        Spectrometer      AI 10            -"-
DEP Radiator Temp.        DEP Radiator      AI 8             -"-
I/F Box Radiatr. Temp.    I/F Radiator      AI 15            -"-
TEC Radiator Temp.        TEC Radiator      AI 14            -"-
LVPS Temp.                  LVPS #1         AI 11            -"-
Drive Ring Temp.           Drive Ring       AI 16            -"-
Sec. Mtr. #1 Position       Mtr. #1         (ser) *          -"-
Sec. Mtr. #2 Position       Mtr. #2         -"-              -"-
Sec. Mtr. #3 Position       Mtr. #3         -"-              -"-
SPD Gain                   SPD HVPS         (ser)            -"-
ZOD Gain                   ZOD HVPS         -"-              -"-
Audio Amplitude           Drive Ring        ...              -"-
Motor LVPS Current          I/F Box         ...              -"-
BOS                        Sunshade         AI 13            -"-
Tube Strain #1           Near Mtr. #1       (ser)            -"-
Tube Strain #2           Near Mtr. #2       -"-              -"-
Tube Strain #3           Near Mtr. #3       -"-              -"-
Reticon Temp. (broad)      Reticon          (ser)            -"-
Reticon Temp. (fine)        --"-            -"-              -"-
Filter Sensor            FW Encoder         (ser)         4 bits + 1
Aperture Sensor          AW Encoder         -"-              -"-
Door, Sec., FW Mtr.Cur    Motor ctls.       ...           1 bit x 7
Door Latch Unlocked       Door Jamb         DI 18          1 bit
Prim. Door Open           Door Mech.        DI 2           1 bit
Bkup Door Open              --"-            (ser)          1 bit
Prim. Door Closed         Door Jamb         DI 3           1 bit
Bkup Door Closed            --"-            (ser)          1 bit
DEP Timeout             Detector cage       DI 1           1 bit
F/A Motor Overtemp.       F/A Mtrs.         ...           1 bit x 2
IMC Position Sensors      Sec. Mir.         ...            Analog

* (ser) indicates that this information is contained in the DEP serial message; 
see section 3.

Figure 2.3-6 : Heater (shaded areas) and sensor locations.


The audio-amplitude monitor is a contact microphone, actually an accelerometer, mounted to the drive ring which senses mechanism vibrations for debugging purposes. On the ground, it runs directly to a speaker at the EGSE; in flight, the peak audio amplitude is encoded once per second and put into the telemetry stream. Since the characteristic amplitude of each operation is known, it will be used to debug mechanism-related problems in flight. The LVPS current drawn by the motors is similarly monitored and is used for mechanism-fault debugging.

The Bright-Object Sensor (BOS) consists of three photodiodes located on the sunshade-arm supports at 120 degree intervals around the door aperture. Each is sensitive to the stray visible light passing through the forward sunstop on the sunshade, and an object within approximately 23 degrees of the line of sight will fall directly on one of the sensors. The current from the photodiodes is summed and sensed with a logarithmic amplifier. The display is in astronomical magnitudes referenced to the full moon; see Table 2.3-3. Any reading brighter than full moon within 23 degrees is considered to be a risk to an ungated detector. During flight, if the DEP is in status "Standby" (slew configuration), it will enter a submode "BOP" which continues the activities of Standby but inhibits the Setup command. During observations, the EC monitor for this reading will be activated with the same threshhold. The threshhold reading may be modified by special procedure (section 3.2.7). On the ground the threshhold will be disabled, since the door will remain closed.


Table 2.3-3

Bright Object Sensor Sensitivity

                               Source        BOS Delta Mag

                            Dark Current         4.4
                            Moon (Phase 60°)     3.7
                            Moon (Full)          0.0
                            Room Lights         -4.5 
                            Bright Earth       -10.9  
                            Sun                -12.4  

The telescope-tube-strain sensors consist of three Invar struts spaced 120 degrees (near the secondary drive motors) around the outside of the tube; they are fixed at the front of the tube and attached to Linear-Voltage Displacement-Transducers (LVDT's) which sense the thermally induced difference in length between the Invar struts and the aluminum of the tubes. These values are included in the focus position displayed on the WOB display to aid in focus adjustment. They will also detect unanticipated asymmetric distortions which would lead to pointing drifts.

A more detailed block diagram of the WUPPE electronics can be found in the Payload Flight Data File (PFDF). A block diagram concerning internal interfaces with the Spacelab electronics and heater power is given there as well; for electrical interfaces refer also to the Instrument Interface Agreement (IIA). Specifications and descriptions of individual electronics modules are available at SAL upon request.