Scenario 10 - Priority Tasking
Shift Turnover Notes
Section titled “Shift Turnover Notes”Date: Thursday 18 March, 1518 Local (Galway runs UTC in March) Station: GW-01 Galway, Ireland - NATS Europe Operator on Duty: You, solo Constellation Ops: Anneke Visser, MERIDIAN Constellation Operations (Rotterdam; on the line for the pass) Customer: Erik Halvorsen, Nordic Maritime Watch (urgent tasking, waiting on an answer)
Routine afternoon until 15:15, when Nordic Maritime Watch rang with a vessel that stopped reporting off the Faroes. Erik has a box and he has one pass that covers it, and that pass is a low one. Tasking request is below; Rotterdam has released the bird.
The morning maintenance run left its fingerprints on the chain: BUC gain wound down to 18 dB for the sweep, and TX modem 1 still on SAR-2’s 1,435 command IF from Tuesday’s rotation. Nothing is faulted. Nothing is set for this pass either.
Everything on this shift is arithmetic done in advance. Sweep the station, do the worksheet, build the EIRP one step at a time and park the dish before the horizon, because there is no time to do any of it after.
- Turnover note, 1516
Urgent Tasking Request NMW-URG-2027-0318
Section titled “Urgent Tasking Request NMW-URG-2027-0318”| Item | Value |
|---|---|
| Requester | Erik Halvorsen, Nordic Maritime Watch |
| Target box | 62.5° N, 7.5° W, 40 km square (Faroes) |
| Requirement | SAR imagery of the box today, before the vessel moves |
| Only window covering the box | MERIDIAN-SAR-1, Galway horizon, 15:35 to 15:44 UTC |
| Method | Collect tasked by command early in the pass; imagery downlinked on the same pass |
Constellation Ops release (A. Visser, 15:17):
“MER-OPS-2027-0421. SAR-1 released to GW-01 for the 15:35 pass: imaging block free, command link keyed, key Valid on your console. Be aware of the geometry. At 18 degrees the range at closest approach is 1,040 km and the uplink needs more EIRP than any pass you have flown from Galway. The amplifier stays linear. A splattered band costs me more than a missed collect.”
Pass Plan and Command Window (epoch 15:18:00 UTC)
Section titled “Pass Plan and Command Window (epoch 15:18:00 UTC)”| Item | Time |
|---|---|
| MERIDIAN-SAR-1 AOS | 15:34:59 (az 027°, north-northeast) |
| Command window opens | 15:35:19 |
| Max elevation 17.8°, slant range 1,040 km | 15:39:31 |
| Command window closes | 15:43:43 |
| MERIDIAN-SAR-1 LOS | 15:44:03 (az 159°) |
Southbound, 9.1 minutes horizon to horizon. MERIDIAN-SAR-2 rises at 16:24:59 (25.0° at 16:29:43, LOS 16:34:26) and is not tasked; it does not cover the box.
Command Request MER-OPS-2027-0421
Section titled “Command Request MER-OPS-2027-0421”| Item | Value |
|---|---|
| Target | MERIDIAN-SAR-1 (NORAD 61701) |
| Command | SAR-TASK-URGENT |
| Timing | Early in the window; the imaging block arms before closest approach and needs the lead time |
| Requirements | Uplink Doppler compensation engaged; key Valid; ACK inside the window |
| Command | Mnemonic | Tasked This Pass |
|---|---|---|
| Task urgent SAR collect | SAR-TASK-URGENT | Yes |
| Start recorder playback | REC-PLAYBACK | No |
| Payload to safe mode | PLD-SAFE | No |
Low-Pass Link Budget (worksheet inputs)
Section titled “Low-Pass Link Budget (worksheet inputs)”| Parameter | Value | Note |
|---|---|---|
| Satellite EIRP | 31.3 dBm | Unchanged |
| Slant range at max elevation | 1,040 km | Acceptance was 761 km |
| Free-space path loss at 11,686 MHz | 174.1 dB | Acceptance was 171.4 dB |
| GW-01 receive antenna gain | 50.4 dBi | |
| System noise temperature | 131 K | |
| Occupied bandwidth | 36 MHz | QPSK 3/4 imagery carrier |
| Miscellaneous losses | 1.2 dB | Acceptance used 1.0. The atmospheric path at 18° is about three times longer than at the zenith; gaseous absorption at Ku adds a couple of tenths |
| Design figure, predicted C/N | ~8.3 dB | Worksheet must agree within 1.0 dB |
| Demodulator threshold | 4.2 dB C/N | QPSK 3/4: Es/N0 5.0 dB in the 30 Msps carrier |
| Required margin at Commit Link | 3.0 dB (C/N 7.2 dB), measured live |
Reference: C/N = EIRP + Grx − FSPL − Limpl − 10 log10(k · Tsys · B), k = −228.6 dBW/K/Hz. EIRP is quoted in dBm.
| Segment | Approximate time |
|---|---|
| C/N at or above 7 dB | 15:38:15 to 15:40:45 |
| C/N at or above 8 dB | About 40 s either side of 15:39:31 |
Uplink EIRP Plan
Section titled “Uplink EIRP Plan”Build it from the modem outward. GW-01’s HPA is a 2.5 W Ku solid-state amplifier run at fixed gain, ALC off: its output is its input plus its gain, and the back-off sets that gain from the rated 16 dBm drive (an attenuator in front of the output stage). A weak drive comes out weak, decibel for decibel, so the number at the end of the chain is only right if every stage before it is.
| Step | Item | Now | For this pass |
|---|---|---|---|
| 1 | BUC gain | 18 dB (maintenance run) | 23 dB, the station standard. With 18 dB, a 4 dB back-off delivers the EIRP of a 9 dB one (0.3 W instead of 1 W), with every indicator green |
| 1 | BUC compression | 11 dBm out, far under the 28 dBm P1dB | 16 dBm at 23 dB, still 12 dB under P1dB: out of compression |
| 2 | HPA back-off | 10 dB | 4 dB (6 dB more EIRP: 24 dBm becomes 30 dBm). Below 3 dB the amplifier is overdriven and the IMD alarm trips; the IM3 (2-tone) readout worsens about 2 dB per dB of back-off given up (about −46 dBc at 10 dB, −35 dBc at 4) |
| 3 | HPA output, amplifier up | Disabled | At least 0.5 W into the feed (about 1 W expected at 4 dB on this chain); read on the TX chain power meter once the modem is on air and the HPA is enabled |
| After LOS | HPA back-off | 4 dB | Back to 10 dB. 4 dB was the exception for one geometry; on a normal pass it is 6 dB over the coordinated level and an interference risk |
An amplifier driven past its linear region makes new frequencies out of the ones it was given; they go up the same dish at the same EIRP into channels that belong to somebody else.
Link Parameters
Section titled “Link Parameters”LNB high-side: IF = LO − RF (13,100 MHz). BUC low-side: RF = IF + LO (12,600 MHz).
| Signal | IF (MHz) | RF (MHz) | Format |
|---|---|---|---|
| SAR-1 telecommand uplink | 1,405 | 14,005 | QPSK 3/4, 36 MHz, −7 dBm modem. TX modem 1 is on 1,435 (SAR-2) and must be retuned |
| SAR-1 telemetry beacon | 1,389 | 11,711 | CW; visible from the horizon |
| SAR-1 imagery downlink | 1,414 | 11,686 | QPSK 3/4, 36 MHz |
Doppler: up to ±270 kHz on the downlink (receiver follows), up to ±325 kHz on the uplink (compensated at the TT&C console, required for an ACK; engage it before AOS, not at it).
GW-01 Equipment Status
Section titled “GW-01 Equipment Status”| Equipment | Status | Notes |
|---|---|---|
| 4 m Ku tracker | Powered, manual, parked az 5° / el 3° | Park on the rise azimuth, 027° / el 5°, before AOS |
| LNB | 13,100 MHz LO, reference locked | Stable |
| GPSDO | Locked, 9 satellites | Disciplined |
| RX modem 1 | 1,414 MHz / 36 MHz / QPSK 3/4 | Pre-tuned for SAR-1 imagery |
| TX modem 1 | 1,435 MHz / 36 MHz / QPSK 3/4 / −7 dBm | SAR-2’s command IF from Tuesday. Retune to 1,405. Not transmitting |
| BUC | 12,600 MHz LO, reference locked, 18 dB gain | Restore 23 dB. No drive present |
| HPA | Powered, output disabled, 10 dB back-off | Modem on air before this goes live; off before the carrier stops |
| COMSEC key | Valid | No rotation scheduled |
| Link Analysis console | Low-pass card loaded, worksheet blank | Predicted panel reads NO SOLUTION until computed |
| Tasking log | Blank | One entry: command, EIRP exception, result |
Tasking Checklist
Section titled “Tasking Checklist”Before AOS (15:34:59)
Section titled “Before AOS (15:34:59)”- Dashboard: only the RX AGC no-carrier warning (noise only, empty sky), no faults; GPS Timing: GPSDO locked, no holdover; TX Chain: BUC on reference
- Link Analysis: worksheet computed, prediction agrees with the card
- BUC gain 23 dB, out of compression
- HPA back-off 4 dB; no overdrive alarm
- TX modem 1 on 1,405 MHz; TT&C: uplink Doppler compensation engaged
- Tracker parked az 027° / el 5°
In the Window
Section titled “In the Window”- Program-track MERIDIAN-SAR-1; beacon on RX analysis as she clears the horizon
- TX modem on air, then HPA enabled; at least 0.5 W on the power meter
- SAR-TASK-URGENT sent early; ACK in Command History
- RX modem locked on 1,414 MHz; C/N above 6 dB held for 30 s
- Commit Link pressed at max elevation with live margin at or above 3 dB
After LOS (15:44:03)
Section titled “After LOS (15:44:03)”- Chain down: HPA off, BUC muted, carrier off
- HPA back-off restored to 10 dB
- Tasking log: command and ACK, the EIRP exception and its restoration, measured C/N against 8.3 predicted at 18°
- Report to Erik: what he got, and what this geometry means for the next box
End of Briefing
Section titled “End of Briefing”Every pass this station has flown so far had margin to waste. This one has under four decibels over threshold, the commit needs three of them, and a customer is waiting on the frames.
The numbers say it closes. Read the chain before you set it, set the amplifier, do the worksheet, and be pointed at the horizon when she comes over it. Anneke is listening, Erik is waiting, and there is no second window.
Good luck.