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[[File:LLST_Ground_Stations.jpg|frame|right]]

=Lunar Lasercom Ground Terminal=

=Lunar Lasercom Ground Terminal=

==Link Acquisition Process==

==Link Acquisition Process==

A 1558 nm laser beacon is projected at the expected location of the LLST. To have a sufficient power density while still scanning through the uncertainty ellipse of the satellite location (a computed 191 μrad angular uncertainty), a ‘step-stare’ system is used. The beacon points at a given point in the uncertainty ellipse for 5 seconds, enough time that a link would be detected, and cycles to the next point if nothing is received, using a wide 110 μrad angular diameter beam. This method scans for roughly 100 seconds, cycling through the 19 steps. With an acquisition and tracking detector, the beacon is received and the 1550 nm downlink laser is returned. Since there is no uplink data transmission, a free-running LLST clock is used without locking. Once the downlink laser is received, at roughly 3.6 nW/m2, the beacon beam is narrowed to 40 μrad and the LLST control loop is adjusted to receive the beacon with higher precision, now boosted to 36 nW/m2. This concludes the link acquisition process, with roughly 90% of downlink signal power being directed at the receiver.

A 1558 nm laser beacon is projected at the expected location of the LLST. To have a sufficient power density while still scanning through the uncertainty ellipse of the satellite location (a computed 191 μrad angular uncertainty), a ‘step-stare’ system is used. The beacon points at a given point in the uncertainty ellipse for 5 seconds, enough time that a link would be detected, and cycles to the next point if nothing is received, using a wide 110 μrad angular diameter beam. This method scans for roughly 100 seconds, cycling through the 19 steps. With an acquisition and tracking detector, the beacon is received and the 1550 nm downlink laser is returned. Since there is no uplink data transmission, a free-running LLST clock is used without locking. Once the downlink laser is received, at roughly 3.6 nW/m², the beacon beam is narrowed to 40 μrad and the LLST control loop is adjusted to receive the beacon with higher precision, now boosted to 36 nW/m². This concludes the link acquisition process, with roughly 90% of downlink signal power being directed at the receiver.

==LLST Downlink Margins==

==LLST Downlink Margins==

Minimum irradiation above atmosphere: 1.66 nW/m2

Minimum signal power: -215 dB-W

|Minimum irradiation above atmosphere:

Signal power on detector: -98.2 dB-W

|1.66

Mean background photon flux: 5.18 Mph/s

|nW/m2

Mean photon flux: 140 Mph/s

Link margin: -3 dB

|Minimum signal power:

| -215

|dB-W

|Signal power on detector:

| -98.2

|dB-W

|Mean background photon flux:

|5.18

|Mph/s

|Mean photon flux:

|140

|Mph/s

|Link margin:

| -3

|dB

==Use for OPALS==

==Use for OPALS==

=Lunar Lasercom Optical Ground System=

=Lunar Lasercom Optical Ground System=

The Lunar Lasercom Optical Ground System (OGS) is another auxiliary ground station for the LLST, located on Tenerife and operated by ESA. The minimum downlink irradiance at the border of the atmosphere is specified at 0.17 nW/m^2

The Lunar Lasercom Optical Ground System (OGS) is another auxiliary ground station for the LLST, located on Tenerife and operated by ESA. The minimum downlink irradiance at the border of the atmosphere is specified at 0.17 nW/m². It does things.

[[Category:Optical Communications]]

[[Category:Satellites]] [[Category:Optical Communications]]