# Presentation: 691848

## Section 10

_***Section 10***_
***Advanced Land Imager (ALI)***

*** ******. . . Constantine J. Digenis***
*MIT/LL ALI Program Manager *

## Advanced Land Imager (ALI)

***Advanced Land Imager (ALI)***

***ALI is an instrument incorporating several new technologies that promise better performance, at a lower cost, of future Landsat missions.***
***The relatively warm operating temperature of the HgCdTe detectors makes possible passive cooling of the focal plane which greatly simplifies instrument operation.***
***ALI was designed, assembled, environmentally tested and calibrated by the MIT Lincoln Laboratory***
***The Focal Plane System was supplied by Raytheon/ SBRS***
***The telescope was supplied by SSG Inc.***

## Advanced Land Imager (ALI)

## ALI Block Diagram

## ALI Instrument Requirements

***ALI Instrument Requirements***

## ALI Verification Matrix

## ALI Calibration Matrix

## Internal Reference Lamps

***Internal Reference Lamps***

***Three lamps in an integrating sphere, fed from a constant current source at reduced voltage, turned on sequentially.***
***Lamp: Custom version of Welch Allyn 997418-6, Krypton gas, color temperature 3085******°******K, life 300 hrs (700 hrs as used).***
***Life testing: 8 lamps, 12,000 cycles (30 sec on, 30 sec off) followed by continuous on time until lamp burn-out.***
***Minimum life: 390 hrs (total on time),***
***Average life: 613 hrs,***
***Maximum life: 795 hrs. ***
***Total flight lamp on time to-date: ~32 hrs.***
***Measured focal plane response change from Dec. 98 (ALI T/V) to Jul. 00 (S/C T/VII), all 3 lamps on, focal plane at 220******°K.***
***± ******2 %, all bands,***
***Repeatability of lamp readings: ******±****** 1 %.***

## Telescope Cover Cycles

***Telescope Cover Cycles***

***	******	******	******	******	******	***_***ALI***_***	***_***FPE***_
***From ALI Assembly to S/C Integration (17 Mar 99)******	******1,697******	******585***
***From S/C Integration to 28 Mar 00******	****** (Red Team Rev)   519******	******  38***
***From 28 Mar 00 through 31 Jul 00 (Launch Sim)******	******   270******	******  10***
***Total******	******	******	****** ******	******	******	******2,486******	****** 633***

***Total Operating Hours******Excluding Subsystem Testing***

***Mechanism Life Test (STM)******	******3,900***
***Ground Tests (Flight ALI)******	******   282***
***350-day Mission (4 DCE’s/day)******	******1,400******	***

## Problem Reports

***Problem Reports***

**Condensable material deposited on the focal plane filters when the focal plane was at 220°K in vacuum.**
**ALICE did not respond to restart command.**

**Focal plane was baked out at 273°K. Condensable material effects were reduced by an order of magnitude.  Plan in place to conduct additional bake-outs on orbit, as needed.**
**Procedure error. Restart command was issued before execution of previous command was completed.**
** **

_**PR**_**	****	**_**Problem**_**	****	****      **_**Resolution**_
**12**

**Note: All issues resolved except source of contamination (PR 12).**
**The subject will be discussed further by Mike Woronowicz.**

## Summary of Open Items fromMarch Red Team Review

***Summary of Open Items from******March Red Team Review***

***Verification matrix (p. 10-18).  No update necessary.***
***Operating hours (p. 10-35).  See p. 10-9 for current number.***
***Technology effort to improve mirror stray light performance (p. 10-45).  Work still in progress at SSG under direct NASA supervision (Dr. Ritva Keski-Kuha).***
***Focal plane contamination (pp. 10-59 to 10-67).  See following Special Topic.***

## Statement of Readiness

***Statement of Readiness***

***ALI demonstrates breakthrough technologies***
***Large MS-PAN array operating warm,***
***Wide-angle telescope,***
***Silicon carbide mirrors,***
***In-flight calibration scheme.***
***Calibration tests have thoroughly characterized ALI.***
***ALI operated nominally during T/V II.***
***Flight test will validate Landsat data continuity.***
***At least 200 scenes for comparison with Landsat 7.***
***ALI is ready for flight.***
***No residual issues or Red Book candidates.***

## Special Topic:

***Decontamination of the ALI Focal Plane***

***. . . Jeff Mendenhall***
*MIT/LL ALI Systems Engineer*

## History of ALI Contamination

***History of ALI Contamination***

***First detected during thermal cycling of ALI at Lincoln Laboratory - October 1998***
***Focal plane contamination eliminated after FPA warmed to >-5oC (268K)***
***ALI baked out under vacuum***
***1 week at 303******°******K - early January 1999***
***2 days at 303******°****** K - late January 1999***
***3 hours at 273******°****** K - October 1999 (T/V1)***
***1 day at 273******°****** K - July 2000 (T/VII)***
***Virtual elimination of contamination effects observed after each bakeout***
***Focal plane radiator heaters added to instrument to provide on orbit decontamination if needed - February 1999***
***Contamination observed during thermal vacuum testing of spacecraft at GSFC - October 1999 and July 2000***
***Visual inspection of focal plane after boil-off at the end of thermal vacuum testing indicated no contamination present on focal plane - November 1999***

## Detection of Contamination 

***Detection of Contamination ***

**F1, Fold**
**Mirror**

**Telescope**
**Axis**

**Main Focal**
**Plane Array**

**Cal Lamp**
**Assembly**

**Illuminated by Internal Source**

**Illuminated by External Source**

***Comparison of internal reference lamp data with external source simulating a ground scene shows a reduction in the pixel to pixel variability in the latter case by a factor of ~4.******  ***
***The difference is due to the different f-number of the telescope (7.5) from the internal reference lamp system (40).***

## Summary of T/V II Contamination Monitoring

***Summary of T/V II Contamination Monitoring***

***±5% Pixel to Pixel (P2P) variations observed within 1 day of cooldown for all bands (corresponding to ±1% for ground scene)***
***No additional growth of P2P variations after first day***
***No mean level changes observed***
***Decontamination of FPA successful***
***P2P variation again observed after second cool down***

## History of Band 3 During 1st Half of T/V II 

- S/C from 293 K to 303 K, FPA at 255K for 12 hours

- S/C at 303 K, FPA at 220 K for additional 9 hours,

- S/C at 273 K, FPA at 220 K for additional 29 hours

- S/C at 273 K, FPA at 220 K for additional 30 hours

- S/C at 273 K, FPA at 220 K for additional 19 hours

- S/C at 273 K, FPA at 220 K for additional 72 hours

- S/C at 303 K, Following FPA transition to 273 K and 220 K (20 hours)

- Baseline data = Start of T/VII at ambient temperature and pressure

## Band 3 Decontamination During T/V II 

- Baseline data = Start of T/VII at ambient temperature and pressure
- S/C at 303 K

- FPA at 230 K

- FPA at 250 K

- FPA at 255 K

- FPA at 240 K

- FPA at 260 K

- FPA at 265 K

- FPA at 270 K

## Comparison of T/V I & II Contamination Monitoring

***Comparison of T/V I & II Contamination Monitoring***

***Pixel to Pixel Variations***
***±10% Pixel to Pixel variations observed during T/V1***
*corresponding to ±2.5% for a ground scene*
*** ******±5% Pixel to Pixel variations observed during T/VII***
*corresponding to ±1% for a ground scene*
***Mean level variations***
***No mean level variations observed during T/V1 at 220******°****** K***
***No mean level variations observed during T/VII at 220******°****** K***
***Lamp and focal plane stability***
***±1% change in FPA response to reference lamp stimulus between T/V1 and T/VII (290******°****** K and 220******°****** K)***

## Decontamination Plan

***Decontamination Plan***

***Continuous purging of the telescope cavity with Nitrogen removes any outgassing products from the telescope cavity during I&T.***
***Outgas ALI focal plane for ~5 days following Day 5 data acquisition.***
***Monitor focal plane contamination using on-board reference lamp source.***
***Conduct on orbit bake-out as needed to remove contaminants.***
***Turn on bake-out heater on FPA radiator and all telescope heaters.***
***Telescope door partially open.***
***Duration: warm-up, from 220******°****** K to 275******°****** K, ~11 hrs;  cool down ~6 hrs;  dwell at warm plateau ~7hrs.***
***Initial bake-out frequency is projected to be every 2 weeks.***
***Preserves goal of 5% radiometric accuracy.***

## Summary

***Summary***

***Contamination of ALI focal plane identified at Lincoln Laboratory, cleared through boil-off, and later observed at GSFC at reduced level***
***On-board reference lamp sensitive and effective tracker of contamination***
***Heating of focal plane to >265******°******K will drive off contaminant***
***Focal plane radiator heater ability to outgas focal plane demonstrated during thermal vacuum testing at GSFC***
***On-orbit decontamination will require 1 day ***
***Acquisition of VNIR data still possible during this period***