1. GLAST Large Area Telescope:
Gamma-ray Large Area Space Telescope
GLAST Large Area Telescope:
Integration and Test Planning
Steve Ritz
Goddard
LAT Instrument Scientist

2. Integration and Test Outline
Context: status at February review, actions, and I&T committee
Work of the committee, highlights of issues
Next steps

3. February Review Comments and Recommendations (excerpts)
There was considerable discussion of the plan for a final beam test of a few towers, rather than the whole device. The project personnel discussed the trade-offs involved, and demonstrated it to be adequate to the needs of the project. Such a review of each major system test across the project should be completed, focusing on the technical need and expectations, and allowing a reasonable time for the analysis of results.
At the current staffing levels, the workload over the next six months will be heavy and if problems arise, personnel will be stretched thin. The Committee supports the hiring of additional personnel to join the capable staff already on hand.
Recommendations
1. Hire an integration and test expert, now scheduled for late FY 2001, as soon as possible.
2. Complete the performance specifications, at least to Rev 0, by the time of the
Preliminary Design Baseline Review.
3. Complete the Interface Control Documents, at least to Rev 0, by the time of the Preliminary Design Baseline Review.
4. Create the verification and test plan, working with the other subprojects, to confirm the requirements, timing, and resources required to implement this plan.
5. Include testing of the LAT by independent personnel in the verification and test plan.

4. I&T Committee (started work March 01)
Martin Nordby – SLAC (LAT I&T manager, ENV test subcommittee chair)
Eduardo do Couto e Silva – SLAC (Beam test subcommittee chair)
Hartmut Sadrozinski – UCSC (TKR)
Niccola Mazziotta – Bari/ITALY (TKR)
Bernard Phlips – NRL (CAL)
Bertrand Cordier – CEA/FRANCE (CAL)
Bob Hartman – GSFC (ACD, EGRET experience)
Scott Williams – Stanford (IOC)
Tony Waite – SLAC (Elex/Flight SW)
Michael Lovellette – NRL (Functional testing, DAQ, …)
Ed Shippey – GSFC (GLAST Mission I&T lead)
Steve Ritz – GSFC (Chair)
Tune Kamae – SLAC (ex-officio, ITM)
Tim Thurston – SLAC (ex-officio, ISE)
Committee meets via VRVS. See minutes and documents at

5. Highlights of Issues: Enviromental Testing
Full-LAT vibe testing
Options under discussion
At issue are the many mechanical and electrical connections (bolts and connectors) in the LAT that will not be verified by subsystem testing.  Thus, the question of the full-LAT vibe test is really a question of  how best to do the workmanship testing on these connections.  For example, would acoustic testing alone accomplish this task?
Issues being worked by Nordby and Shippey with Scott Gordon and Sharon Seipel.

6. Highlights of Issues: Functional Testing
Two main aspects:
Functional testing, at defined levels, of the full LAT at successive stages of environmental and performance testing First draft document exists. Needs review.
Verification testing during LAT integration. In particular
interfaces and operability of newly-integrated parts must be verified at each stage of the integration in a schedule-conscious manner. At the stage of turning discussions into a document.

7. Highlights of Issues: On-orbit Calibration
Main reason is to integrate the ground-based and on-orbit calibration activities so that the completeness of the testing and verification of the proposed techniques can be assessed.
Table completed, reviewed within the committee and by other experts within the collaboration
Task/Purpose
When/Frequency/Duration
Test to Verify Technique
Establish the internal alignment of the LAT using galactic cosmic rays.  Requirement: <7(TBR) arcsec.
First done at turn-on, after initial functional check-out, with dedicated runs: estimate we need ~106 events [see note here].  If done on the ground (30 Hz accumulation), this corresponds to 10 hours of data taking.  It may be possible to do this on-orbit at higher rate using flight software, but that adds complexity.  The above estimate assumes internal tray alignment
Done continuously at a low level during normal operations with pass-throughs.
It may be useful to do dedicated half-day runs quarterly to verify the internal alignment.
Can be done at any time during LAT I&T when DAQ is operational using sea-level cosmic-ray induced muons.  We estimate that the full LAT can be aligned this way in less than one day.
Calibrate alignment between LAT and Observatory GN&C system.  Requirement: <7(TBR) arcsec.
First done after turn-on, functional checkout, and internal alignment.  The current plan is to do a pointed observation near the galactic anticenter, where several bright, well-known, separated point sources will be in the FOV simultaneously.  As with EGRET, it may be helpful to use timing on pulsars to select photons during known peak phases to reduce background contamination.  Current estimate is that this alignment can be done in ~one week of observation (TBR).
The observation will be repeated at intervals ranging from quarterly to annually, depending on the expected and observed stability and reliability of the alignment.  First-year plan will be defined after S/C contractor is selected.
Done piecewise during beam test PSF studies.  Also possible to use mock data challenge to validate the software tools.  The error budget for both this calibration and the internal alignment must be established

8. TASK FREQUENCY/DURATION TEST TO VERIFY TECHNIQUE
Calibrate CAL energy scales
Done continuously using galactic CNO flux.  See estimates by Grove(slides 19-26) for precision.
Planned CAL tests at GSI heavy ion beams.
Calibrate ACD scales to precision specified in the ACD level III specification.
Done continuously using galactic cosmic ray flux and PHA readout.
Done during beam test electron/hadron tests and sea-level cosmic ray muon tests.
Verify L1T efficiencies.
Done continuously using redundant triggers, specifically the CAL-LO trigger as a check on the TKR trigger.
Done during beam test electron/hadron tests and sea-level cosmic ray muon tests.  Must establish the precision requirement, based on the effective area knowledge error budget.
Calibrate systematic offsets with viewing angle ("fish-eye" effect, etc.)
Done after LAT-Observatory alignment after turn-on.  Observe bright, known point source (e.g., Vela) at 4 (TBR) viewing angles (q, f).  Total time: ~1 week.
More detailed understanding of any subtle effects will be obtained during the first year all-sky survey, binned by viewing angle on known sources.
Monitored over mission life using known sources.
Done during photon beam test PSF studies, but does this drive requirements unnecessarily on fixture and beam position knowledge?
Verify PSF over FOV
Done after LAT-Observatory alignment after turn-on.  The same observations used to calibrate the systematic offsets will be used for this analysis.
Done during beam test PSF studies.
Verify background rejection using first-year data, analyzing the extra-galactic diffuse measurement in bins of varying background rates.
Done during first-year all-sky survey.
N/A, but software tools can be validated during mock data challenge.
Effective area uniformity map of instrument (e.g., Willis analysis of EGRET data).
N/A
Verify effective area over energy range (e.g., check for "Kniffen factors")
Done during first-year all-sky survey.  Measure known source flux (e.g., Crab) to lowest LAT energies.
Low energy gamma beam tests.

9. Highlights of Issues: Ground Calibration
Every performance requirement has a defined test.
The LAT energy range and field of view are vast – testing will consist of a combination of simulations, beam tests, cosmic-ray induced ground-level muon tests, and other direct tests.
Draft matrix exists, under review.
Test matrix being matched to (and iterated with) available beams and facilities. Test time requirements with these facilities being evaluated.
Obvious need for complete simulations and analyses well in advance of the tests.
Strong diversity of opinion within the collaboration on several issues, taking time to come to agreement. These include
layout of the calibration towers for the tests, use of engineering models in earlier testing
photon beam choice, diagnostics requirements
extent and strategy for hadron beam testing
any justification for full-LAT beam testing? (mainly a functional test issue, not needed for calibration)

10. Example: Beam Test Tower Layout
55° 1 GeV gamma
View from front
Region around 55°is important, since the effective area is falling rapidly here.
For off-axis, cross-tower studies, a 1x4 arrangement is much more useful than 2x2. Also better for CAL studies, since wider range of r.l. accessible. Also better for backsplash studies, since wider range of tile distances available.
Note, however, 1x4 allows only limited phi studies.
Likely solution is to have separate 2x1 tower mounts and run in 2 configurations.

11. Status, Next Steps
Very productive discussions within the committee, but work on documents did not progress as planned during 2nd half of June and July, due mainly to personnel over-commitment. I&T Manager (E. Bloom) and I&T Engineer (B. Grist) now on board.
Committee will finish synthesizing the discussion results for use by I&T personnel, who will develop the full I&T plan.