1. Horizon Algorithm Descriptions John Abbott Derek Willis August 14 th, 2007

2. Model Data Buffer Model Variables W = max data recorder capacity X = current data recorder capacity Y = max number of files Z = current number of files Input Image ID (int) [inImageID] Image Filesize (double) [inFileSize] Output Pass/fail (bool) Buffer State Does inFilesize + X exceed W? Set pass/fail to pass Set state variables (Add file to buffer, increase X by inFileSize, increase Z by 1) End No Yes Set pass/fail to fail Start Assumptions FIFO Buffer Seakr model P9 SSDR Power used = 105W continuous W = 1.4Tbits Y = 256 (educated guess) State Variables Current data recorder capacity Current number of files Current buffer file order (map of type int as key(ID) and type double as value(filesize) Does Z +1 exceed Y? No Yes * May want to include the time a file is written to the data buffer in order to calculate the time from collect to exploitation (end to end)

3. Ground Comm Model Assumptions Terminals are located at: (deg:min) Hawaii Tracking Station (HTS), Kaena Point Satellite Tracking Station, Hawaii; callsign HULA.Kaena Point Satellite Tracking StationHawaii (21:34N, 158:15W) Vandenberg Tracking Station (VTS), California; callsign COOK.California (34.50N, 120:30W) Diego Garcia Station (DGS), Diego Garcia, BIOT; callsign REEF.Diego GarciaBIOT (7:27N, 72:37E) Thule Tracking Station (TTS), Thule Air Base, Greenland; callsign POGO.Thule Air BaseGreenland (76:31N, 68:36W) Guam Tracking Station (GTS), Guam; callsign GUAM.Guam (13:37N, 144:52E) Colorado Tracking Station (CTS), Schriever AFB, Colorado; callsign PIKE.Schriever AFBColorado (38:8N, 104:5W) Telemetry & Command Station (TCS), RAF Oakhangar, in England, ostensibly operated by the United Kingdom; callsign LION.RAF OakhangarEnglandUnited Kingdom (51:07N, 00:54W) New Hampshire Station (NHS), New Boston AFS, New Hampshire; callsign BOSS.New Boston AFSNew Hampshire (42:57N, 71:38W) All from SMAD Elevation angle constraints = x deg (Assume 10 deg for now) Processing time = (pixels * flops/pixel * sec/flop * efficiency factor) – Assume: pixels from Geoff Veit model, flops/pixel = ?, sec/flop = ?, efficiency factor = 40% Processed filesize = inFileSize * processing factor – Assume: Processing factor = ? Exploitation time = processed filesize / daterate to end user – Assume: T1 datarate (1.5Mbps) – This would likely change based on how large we anticipate the EO files being (Need Geoff Veit model to determine) General Inputs Geographic coordinates of ground stations Look angle constraints for the ground stations (build into access model) Processing time (function of filesize & ground architecture) Exploitation time (function of filesize & ground architecture) Process fileExploit file Input Image ID (int) [inImageID] Image Filesize (double) [inFileSize] Output Image ID Processing time Exploitation time Processed image filesize (double) General purpose PC = 3.6GHz = flop/sec flops/pixel = 1500 (Dependent on image processing algorithm) Efficiency factor = 40% (engineering estimate) Processing factor = 0.5 (assume good quality jpeg compression) The ground station network for EO -1 consists of: EDC Sioux Falls, SD (LGX), 43.536, -96.731 (Decimal) Hobart, Australia (HGS) 42deg 54 min South, 147 deg 18min East Svalbard, Norway (SGS) 78.13N, 15.33E (DMS) Poker Flat, Alaska (PF1) 65.12, -147.47 (decimal)

4. Spacecraft Comm Model 2 Payloads Comm Assumptions The comm system is a fixed dish for simplicity (could be gimbaled in the future if required or a phased array) Since we are unaware of the location or operation of the payloads, the dish would be mounted on an arm as to not interfere with payload operation. A phased array could also be installed provided the bus could provide enough power (unknown right now) Use the phased array All EO filesizes are the same (circular sun-synch orbits as discussed in the meeting should not alter the geometry of collections) Reasoning: To minimize the amount of bus movement the payloads and the dish are all pointed at the earth at all times. This should provide more opportunities to image and downlink without having to wait for the bus to move into the proper orientation. General Inputs Location of antenna in body coordinates (add to the access model) Antenna half angle cone (add to the access model) = 60 deg Average downlink datarate = X-band at 105 Mb/sec (USGS EO-1) – This would entirely depend on the filesizes being collected by the imager(s). Larger files may require a different frequency band which supports a larger datarate Power used by the antenna in on/off modes = 45W engineering estimate of 15W off Data taken from: http://ldcm.nasa.gov/tech_transfer/Wideband_Downlink/12_Code567Tech_Edwards.ppt http://eo1.gsfc.nasa.gov/Spacecraft/eo1Spacecraft.html Assume the fixed dish has the same properties as the phased array until we know more about the system architecture

5. Spacecraft Comm Model Input Ground station access time Current buffer state Variables W = downlink trigger (percentage of recorder capacity, will be driven by Geoff Veit EO model data size) X = current data recorder capacity Y = Downlink datarate Z = Time to downlink Is X > W? End No Yes Take top file In data buffer [tempFile] Set Z = tempFile(size)/Y Is time into access + Z > access time end? Set time into access = 0 Remove file from buffer Set time into access = Time into access + Z No Yes Is X > 0? No Start Yes Output Current buffer state