1. GLAST LAT Project18 July 2005 1 GLAST Large Area Telescope: NCR 529 Systems Engineering R. Bright Gamma-ray Large Area Space Telescope

2. GLAST LAT Project18 July 2005 2 Outline Problem Statement & Current Results History/Background Future Options Potential Testing

3. GLAST LAT Project18 July 2005 3 Problem Statement & Current Results TKR FM3 errors started after connection to TEM GLAT1835. –Revised integration sequence pairs TKR to Flight TEM for first time in Grid. Errors are frequency but intermittent. Errors appear to be sensitive to clock frequency. Unlikely that MCM has degraded. Most likely that TEM to MCM interaction induces problem. Other 5 towers were tested over frequency and do not exhibit the failure.

4. GLAST LAT Project18 July 2005 4 History & Background Tracker Module FM3 testing did not exhibit MCM errors. –Trackers are tested at lower voltage than Flight TEMs provide. Lower voltage was stress case for other failures. –MCM 11377 tests were error free. TEM GLAT1835 test results were nominal. –Review of TEM EICIT data for CCA board indicates in family performance. –TEM Clock signal quality is not measured.

5. GLAST LAT Project18 July 2005 5 History & Background (continued) Error signature is identical to Tracker MCM level error, NCR 104 which was for failures on other MCMs. Exact cause of error at MCM level was not determined. Higher voltage increases occurrence of error. MCM GCRC resistor value changed from 75 ohms to 100 ohms to mitigate error. Paper work from Teledyne for MCM rework cannot be trusted. Random inspection revealed multiple cases of reworked MCMs with no documentation. No MCMs were found that had not been reworked to new resistor value. Most likely that MCM has 100 ohm resistor. No other known failure modes could induce this error signature.

6. GLAST LAT Project18 July 2005 6 Future Options Repair Tracker FM3 MCM –Risk to hardware perceived to be high. –Risk to schedule perceived to be high. R&R TEM GLAT1835 –Risk to hardware perceived to be medium. –Risk to schedule perceived to be medium. –May not be successful in removing failure. Use-As-Is (UAI) –1 of 6 towers installed in Grid exhibit this error. –Other towers yet to be integrated may exhibit this error. –Environmental testing may provoke error. –Flight S/W impact is expected to be none based on discussions with M. DeKlotz. –ISOC impact is unknown. –SAS impact is unknown. –User community impact is unknown. –NASA opinion has not been solicited.

7. GLAST LAT Project18 July 2005 7 Potential Testing Possible that power off resistance measurements at GLAT1835 GT-6 connector will be nominal. –Repair of Tracker FM3 MCM is unlikely. Future errors in Integrated Flight Towers may be mitigated by return to single flight tower integration before installing in Grid.