HEO - Daylight Tracking

Some things to consider...

What makes daylight so special?

Day: Background noise level is higher

Night: Rangegate, FOV... who cares?

What makes HEOs so special?

The array measures 239 millimeters in length, 194 millimeters in width, and 37 millimeters in height and weighs 1.27 kilograms. At normal light incident angle, the aperature of an individual cube corner is a rectilinear hexagon equivalent in area to a circle 28.6 millimeters in diameter.

1. Degnan, J.J., Pavlis, E.C., "Laser Ranging to GPS Satellites with Centimeter Accuracy", GPS World, 9, 1994

... they are not known as HEOsfor nothing!

... they are far away!

HEO - Tracking: Link Budget

npe = q ET

hc

t G t 14R2

2A r r T a

2 T c2

Range Dependence

System Divergence ≈ 1

2

http://www.wettzell.ifag.de/publ-cgi-bin/linkbudget.py

good collimation required!

HEO - Tracking: Pointing

• Collimation reduces the spatial Coverage

• The further the Target is away, the more it hurts

• Because of a worse SNR, scanning also takes a lot longer

• All this adds to Observer Frustration - Result: NO PASSES

Daylight - Tracking: “The 3 Buddies”

Laserbeam Pointing

Telescope Pointing

(Mount Model)

Receiver Field of View

• The Receiver FOV is limited: Background Light!

• The Pointing defines the Tracking Offsets

• If the Cross Section between FOV and Laser reduces to 0 --> no Returns

• The further the Satellite is away, the more the 3 Buddies separate --> the worse it gets.

Daylight - Tracking: “Secondaries”

• The Receiver FOV wants to be small - reduces Amount of Background Light

• Narrow Spectral Filtering is less important than common Lore tells us...

• The Rangegate wants to be short - NO Problem for current Predictions

• Observer Motivation (Big Issue)! - Noone loves frustrating Jobs

CONT05 CAMPAIGN PASS SEGMENTS CUMULATIVE DATA YIELD SINCE 01-SEP-2005

Station PAD WAVE GPS35 GPS36 GLONASS87 GLONASS89 GLONASS95 TOTAL--------------- ----- ----- ----- ----- --------- --------- --------- -----Maidanak 1864 5320 5 5 3 13Simeiz 1873 5320 1 4 5Riga 1884 5320 1 1Mcdonald Observ 7080 5320 8 8 11 3 4 34Yarragadee 7090 5320 39 2 53 35 51 180Greenbelt 7105 5320 1 1 10 5 17Monument Peak 7110 5320 14 11 14 14 18 71Changchun 7237 5320 2 1 3Tanegashima 7358 5320 2 2Hartebeesthoek 7501 5320 17 36 53Zimmerwald 7810 4230 9 16 16 19 16 76Zimmerwald 7810 8460 7 13 15 20 15 70Mt Stromlo 7825 5320 2 7 11 6 26Riyadh 7832 5320 19 17 9 11 56Graz 7839 5320 6 7 13 10 7 43Herstmonceux 7840 5320 6 8 8 8 30Wettzell 8834 5320 4 3 15 11 17 50 ----- ----- --------- --------- --------- ----- 109 84 187 199 151 730