# Presentation: 445864

## GLAS Overview

- Dr. Eleanor Ketchum
- GLAS Systems Engineer

## AGENDA

- Nominal Science Ops Scenario
- GLAS Commands
- Description of Autonomous Functions
- Rountine Checks
- Safing
- Troubleshooting Features
- Checkout/Turn-on
- Anticipated Calibration Activities (General)
- Summary

## Nominal Science Operations

- GLAS always on

## Commandable Things (1 of 3)

- Switch/Select lasers - approximately every 1.5 years
- Other Switches/Selects - maybe never, but perhaps once
- altimetery detectors
- oscillator
- altimeter digitizer
- Get diagnostics

## Manual power off (lasers, heaters, etc)
Command parameter change (see list below)
Command patch s/w and static memory (see below)
Steer Lidar Beam Steering Mechanism
on the backscatter (pointing/steering) - autonomous holding, commanded steering
test, i.e. off the green LED - commanded test steer
Temperature sweep the etalon (at laser change)

- Command parameter change (see list below)
- Command patch s/w and static memory (see below)
- Steer Lidar Beam Steering Mechanism
- on the backscatter (pointing/steering) - autonomous holding, commanded steering
- test, i.e. off the green LED - commanded test steer
- Temperature sweep the etalon (at laser change)

- Commandable Things (2 of 3)

## Manual adjustment of the amplifier gain 
Power off (any of) the lidar detectors (HVPS)
Self test mode(s)
(TBD) slow start –up/diagnostic mode for trouble shooting and ground testing

- Power off (any of) the lidar detectors (HVPS)
- Self test mode(s)
- (TBD) slow start –up/diagnostic mode for trouble shooting and ground testing

- Commandable Things (3 of 3)

## Commandable Software/ Parameters (1 of 4)

- All Flight Software
- Ground finding, including filtering
- Etalon temperature tuning
- All Memory/Data Bases
- DEM - Approximate size without header/overhead - 128 Kbytes

## Current Parameter List - once calibrated, rarely change (not more than daily)
Set Transmit threshold
Set Return threshold coefficients 
Set Sample offset tables 
Set Number of ocean samples 
Set Number of land samples 
Set echo threshold to a constant, give value 
Set Gain parameters (both transmit and receive) 
Set Gain to constant, give value 

- Set Transmit threshold
- Set Return threshold coefficients
- Set Sample offset tables
- Set Number of ocean samples
- Set Number of land samples
- Set echo threshold to a constant, give value
- Set Gain parameters (both transmit and receive)
- Set Gain to constant, give value

- Commandable Software/ Parameters (2 of 4)

## Current Parameter List, con’t
Set weighting factor coefficients 
Select one of following for orbital information: GPS / Spacecraft / Orbital Uplink table.
Mask off use of one or more filters, give filter numbers in mask
Force range window location, give location
Force range window size, give size
Uplink Orbital Table -- table gives DEM grid #’s and range vs time.

- Set weighting factor coefficients
- Select one of following for orbital information: GPS / Spacecraft / Orbital Uplink table.
- Mask off use of one or more filters, give filter numbers in mask
- Force range window location, give location
- Force range window size, give size
- Uplink Orbital Table -- table gives DEM grid #’s and range vs time.

- Commandable Software/ Parameters (3 of 4)

## Current parameter list, con’t
Range bias uplink table -- table gives range bias versus time (may only be one entry).
Turn ON/OFF use of range biases.
Request that entire digitized waveform be sent to ground (4Mbytes downlinked).

- Range bias uplink table -- table gives range bias versus time (may only be one entry).
- Turn ON/OFF use of range biases.
- Request that entire digitized waveform be sent to ground (4Mbytes downlinked).

- Commandable Software/ Parameters (4 of 4)

## Command  Management

- 1553 commands received by remote terminal and sent to appropriate processor
- If command gets to GLAS and is properly processed: command process counter increments
- If command gets to GLAS and is rejected: command rejected counter increments
- Command counters in telemetry all the time

## Autonomous  Functions (1 of 2)

- 532 Beam Steering
- 532 beam steering mechanism is steered/fine tuned by ground command at TBD frequency (maybe one a day, and only over dark earth), then mechanism constantly controls itself to stay in position
- At first turn on, or when no return is sensed, full field of view is scanned.
- Manual override available to perform full field of view scan, as well as ability to override autonomous scan.

## Etalon Temperature Tuning
 Nominally at TBD frequency (maximum every 5 -10 minutes), laser fire picked off to a pin diode, wavelength checked, set temperature computed, and etalon temperature controlled.
A full temperature sweep is available (manually only) at initialization/laser switch. 
Altimeter Ground Finding Software
Ground found autonomously and appropriate waveform sent to  ground per shot.  Some parameters, for instance digital elevation model element used, are updated on a one second (frame) boundary.  

-  Nominally at TBD frequency (maximum every 5 -10 minutes), laser fire picked off to a pin diode, wavelength checked, set temperature computed, and etalon temperature controlled.
- A full temperature sweep is available (manually only) at initialization/laser switch.
- Altimeter Ground Finding Software
- Ground found autonomously and appropriate waveform sent to  ground per shot.  Some parameters, for instance digital elevation model element used, are updated on a one second (frame) boundary.

- Autonomous  Functions (2 of 2)

## Routine Checks

- Power management
- GLAS internally distributes and manages power for MEU
- Spacecraft UV conditions cause power shut off
- FOT to check for yellow and red limits
- Thermal management
- Instrument thermally isolated from spacecraft and internally controlled
- Spacecraft providing 16 (TBR) temperature monitors which come down in telemetry
- Spacecraft to cut power to lasers and MEU  if temperature range on spacecraft temperature monitors exceeded (TBR).
- FOT to check for yellow and red limits
- Science data management
- Routine checks of science data for health and safety

## Safing

- During various levels of observatory trouble, GLAS autonomously shut down for power saving, no “safing” necessary :
- At first level: MEU off (detectors off)
- At second level: laser, LRS, gyro heaters off (gyro tracker on)
- At third level: only GLAS emergency heaters on
- In emergency mode:
- monitor GLAS temps
- monitor sun vector in body coordinates
- Return to science operation via modified start up, includes careful laser turn-on procedure and steering beam, adjusting gains, sweeping the etalon (detailed procedures by MOR).

## Troubleshooting Features

- All software, commandable parameters, other parameters can be sent to ground
- All boards have idle, science, and engineering modes
- Ability to command beam steering, etalon tuning, manual gain settings, OTS, delay line, etc.

## GLAS Checkout

- Launch

- GLAS gyro
- on

- Spacecraft Checkout,
- Monitor GLAS temps

- GLAS tracker
- on

- MEU powered
- on

- Monitor H/K data

- Enable detectors, etc,
- one at a time.

- Bake out/vent time passed,
- Turn on laser 1 per
- procedure

- Enable laser 1,
- command to fire

- Steer beam
- sweep etalon

- Set gains, parameters
- Calibrate system

- Aliveness check
- with OTS,
- steer beam

- Data every orbit
- during some periods

## GLAS Turn-On Sequence

- TBD

## Beam steering - initial full scan (may have been done already)
Temperature tune the etalon from cold - full wavelength sweep (may have been done)
Calibration maneuvers/scenarios
Continued software parameter/coefficient updating and commanding (fine tuning)
Gyro misalignment determination using spacecraft roll maneuvers and combining start tracker and gyro data in post processing.
Characterization of motion between the spacecraft provided star tracker and the GLAS star tracker 
Other?

- Temperature tune the etalon from cold - full wavelength sweep (may have been done)
- Calibration maneuvers/scenarios
- Continued software parameter/coefficient updating and commanding (fine tuning)
- Gyro misalignment determination using spacecraft roll maneuvers and combining start tracker and gyro data in post processing.
- Characterization of motion between the spacecraft provided star tracker and the GLAS star tracker
- Other?

- Anticipated GLAS Calibration Activities at Checkout

## GLAS Operations Summary

- In science mode: GLAS operating - hands off
- Some commanding - no more often then daily, if that
- A few autonomous functions
- A few things to watch per pass
- Diagnostics, engineering modes to aid in troubleshooting, along with ability to patch in s/w