Downlink Trades

1. Downlink Trades P. Roger Williamson Hansen Experimental Physics Laboratory Stanford University GLAST Collaboration Meeting GSFC February 10, 1999

2. Raw generated data rate Average L1T Trigger Rate ~ 1700 Hz Assuming bits per event ~ 10000 Average generated bit rate ~ 17 Mbps Downlink dumps Nominal X-band link selected to be 150 Mbps Contact delta cost estimated to be $40 - $250 per 10 minute contact for ground base station use in 2005 One 10 minute contact per day = 1 Mbps average Sixteen 10 minute contacts per day = 16 Mbps average Cost range for full usage ~ $230 k/yr to $1.5 M/yr Ancillary instruments ? 300 kbps has no room for GRB or other monitor GRB monitor may need high data rate Does SC need access to the X-band link? Downlink Trade --- Data Rates prw 2/10/99

3. Integration and Test Full rate data output tests reduce test time Checkout on orbit Dump full rate data for TBD weeks Data used for algorithm checkout Data used for calibration Mission operations Management options for dump increased Permits trade off in onboard power consumption vs dumps per day Provides margin for onboard processing requirement Provides method for management of acceptable data loss (could be reduced to 0.0% caused by downlink) Science operations Increased knowledge of onboard processing algorithms and calibration Increased gamma efficiency (managed) Increased margin for onboard processing triggers Decreased time to complete checkout and begin science operations Downlink Trade --- Operations prw 2/10/99

4. IDB single link data rate ~ 100 Mbps (150 Mbps?) X-band formatter input rate = 150 Mbps If SSR, then output rate = 150 Mbps into formatter SSR input rate = 150 Mbps from SI then have option to omit SSR or bypass or use Implement formatter and input link from SI with single VME card in SC computer (copy of NEMO 200 Mbps board with reduced data rate) Board supplied by SI and integrated and tested by SC Downlink Trade --- Onboard Systems prw 2/10/99

5. Downlink Dumps Contact delta cost estimated to be $40 - $250 per 10 minute contact for ground base station use in 2005 ( 1 Mbps average ) Sixteen 10 minute contacts per day = 16 Mbps average Cost range for full usage ~ $230 k/yr to $1.5 M/yr Integration and Test GSE costs increase 300 kbps vs 150 Mbps rates to dump data from SI (unless use ground umbilical) reduces test time Mission Operations Software development time to reduce errors decreased Personal time to handle errors decreased Time to checkout decreased Diagnostic time, problem solving time reduced Downlink Trade --- Costs prw 2/10/99

6. Cost SSR SI to X-band link Downlink contacts per day Processing onboard Power Software complexity Fault recovery and diagnostic capability Integration and test time Data loss Ground data handling and processing Science return Downlink Trade --- Trade Space prw 2/10/99