Criticality: Use caution under advisement of EOF personnel

Frequency: In the event of instrument power off; after eclipse season

Duration (Approx.): 7-8 passes

Constraints: Yes - see below

This procedure describes a normal instrument power up sequence that should be followed assuming that the reason the instrument was powered off was not due to an instrument failure or safing action, but instead for a reason such as safehold in which the instrument was not at fault. The case described below allows for the instrument to be powered up in a minimum time. Cases in which the instrument was powered off due to a safing action will require re-planning and possible trouble shooting while bringing the instrument on-line which may alter the power up procedure.

Instrument recovery should always be done under the advisement of EOF personnel and S/C OE.

1. TI_DPU_on - makes sure instrument safing action points are disabled (the CC spits out ‘funny’ telemetry until it the boot is complete which trip safing action points), turns on NEB, DPU, instrument safing action points, loads control computer patches, performs a reset to the Data Handling Computer (DHC), and sends a command to make sure power is off to all mechanisms.

Verification: See ‘inst_ov’ and ‘dpu_sequence’ pages

3. TI_me_on - turns on instrument mechanisms (filter wheels, quadrant selector, shutter, wedge motors, focus mechanism). The proc first sends resets to all of the mechanisms. This is to initialize software parameters to know values before applying power. Mechanism power is then applied and all are reset again - this reset actually moves the all mechanisms to reset positions. Commands are then sent to put all mechanisms to home positions.

4. Centering the Focus Mechanism

This activity depends on where the focus mechanism was left at when power was removed from the DPU. The EOF will direct this activity when the time arises. The procedures below give some idea as to the type of centering that will be needed, particularly TI_focus_101299.

5. TI_lt_on - turns on the guide telescope. The GT/ISS parameters will change after on-orbit calibrations are performed at which time the gains and offsets will be changed in this proc - look to the proc for verification.

* The loop may be closed later after the S/C is in Fine Sunpoint Mode

6. TI_dh_setup - sets up the Data Handling Computer for operation. This proc will reset the high speed serial line to the SCS (it was seen that during DHC powerup, garbage data gets sent to the HSS fifo), reset the APU, load firmware from the CC to the DHC (the DHC does not contain EEPROM), sets the computer to run, loads the ‘instruction queue’ (this is a program that processes all image data before sending it to the SCS), initializes several parameters and returns firmware and queue version numbers for verification.

Similar to control computer patches, TI_dhc_patches, will load any necessary patches to the queue program.

7. DHC Table Loads

Since the DHC contains no EEPROM, a number of tables must be loaded for the DHC to use that the queue program will use in its processing. These tables are contained in TI_dhc_ldtabs1and TI_dhc_ldtabs2 which each take ~5 minutes for each proc to complete. TI_dhc_ldtabs2 was modified in May, '98 to include new bad pixel table loads, T99106bp1.01 and T99106bp2.01.

8. TI_cm_on - turns on the CCD camera. This proc will turn on the power relay, reset the electronics, initialize the summing mode to 1x1 (full CCD readout; partial reads are possible), initialize parameters and clear any flags that may have been previously set. The camera has two amplifiers with different gains (A will be used for flight, while B has seen extensive use during I&T). Both gains are set for each amp and a picture is taken using each amp to make the settings ‘effective’ in the camera electronics memory.

The DHC must be setup prior to turning the camera on. When the camera turns on, it sends some 'funny' data to the DHC, usually causing a DHC error. However if the DHC is not there to respond, it can get into a strange state itself. In addition, the power surge from the camera can hang the transceiver on the DHC side when not powered. See MxL for more info in this area.

TI_cm_on includes the taking of two pictures to setup the amplifiers. The wavelength table should first be loaded so that the mechanisms will go to the proper positions.

9. Enabling the DHC CCD Safety Routine

The DHC Safety Check Routine creates a histogram of a full CCD image frame binned to 8x8. Tests a specific bin and if the counts in that bin exceed a threshold increments the danger frame counter and clears the safe frame counter. If the danger frame counter exceeds the danger counter threshold, set the danger flag in the return block. If the histogram bin does not exceed the threshold, increment the safe frame count. If the safe frame count exceeds the safe frame threshold, clear danger frame counter

Two procedures exist to enable this feature, TI_ccd_protdis and TI_ccd_protenb. They are essentially the same procedure except for the failure threshold levels they set. TI_ccd_protdis sets the levels so that failures are impossible while TI_ccd_protenb sets accurate thresholds.

10. Loading Observing Sequences

Since the instrument observing sequences change frequently, the EOF will supply the most recent sequence and reference table loads used by the Control Computer. The FOT will uplink these with their nominal table load procedure, TI_DPU_load. The first four tables usually take 2-3 minutes to load while the larger frame and sequence load files take about 5 minutes. The most recent tables are listed below:

• Wavelength Table - T99285wld.02

• Target Table - T99285tld.01

• AEC Table - T99285ald.01

• PZT Offset Table - T99285pld.01

• It is expected that frame and sequence loads will change in the future so they will not be documented here

11. Running Test Sequences to Verify Performance

Four "engineering sequences" have been identified to run after the instrument is fully operational. The spacecraft must be in Fine Sunpoint Mode before execution (the proc checks this as well). The EOF should select an appropriate sequence.

Focus_wluv: STD.focus_wluv 0xED1 - Takes a series of images through a large focus range in a couple

UV wavelengths. This sequence takes about 3 minutes to complete.

Cammera Modes: DPM.ift.cmmodes 0x2F0 - Sequence of images in all camera summing and extraction

modes

Wavelength Scan: CPM.ift.wlscan 0x350 - Scan the entire wavelength table. Take full frame images at

each wavelength and extract 64x64 pixel area from the center.

Mosaic: DPM.ift.mosaic 0x310 - Do Full Disk Mosaic with no delays. Take full frame images at each

wavelength and extract 64x64 pixel area from the center.

Anomalous DPU Current

The expected value for DPU current will be 0.6 to 0.8 depending on essential bus current (as bus voltage drops, current drawn will rise). Expect a slight current rise while loading EEPROM from the CC. The EEPROM is left unpowered until needed for loading. Expect a slight rise in DPU current while resetting and initializing the mechanisms. These current spikes are most noticeable with the quadrant selector (~0.3 A), the focus mechanism (~0.4 A), and the shutter (~0.5 A).

If the telescope was powered off via NEB, the camera and mechanism relays will still be latched. The current will run high (~0.88 on 10/12/99) until the "power off all mechanisms" command, ICPWALOF, is sent in the proc TI_DPU_on.

Throughout I&T the following characteristics have been observed:

1. QS fails to reach home position at cold temps; this was corrected by supplying a power for a slightly longer time; additionally a software bug, now corrected, caused the encoders to be misread

2. After vibration tests, the wedge motors occasionally became stuck; this occurred because the encoders had shifted and were no longer adjusted such that the timing was proper for all 180 steps
3. On 10/12/99 after a safehold event, the QS was commanded to 20/UV after reset but instead went to 10/195. There have been a number of QS miscommutations which seem to be increasing as the mission continues. It is thought that this is a similar miscommutation. Issue the reset and QS to 20/UV commands as found in the proc TI_me_on to remedy the situation.

Control Computer Crashes

Anomaly report #95 details an instance where the CC crashed while loading EEPROM to DHC. Although the resolution detail problems with GSE setup in the lab and is the likely culprit, this anomaly should be kept in mind if a similar problem is encountered on orbit. In any event, power off the DPU and try again.