Scenario 3 - Two-Way Street
Shift Turnover Notes
Section titled “Shift Turnover Notes”Date: Wednesday, 1345 Local (Galway runs UTC in March) Station: GW-01 Galway, Ireland - NATS Europe Operator on Duty: You Site Lead: Charlie Brooks (on-site, RF room) Constellation Ops Contact: Anneke Visser, MERIDIAN Constellation Operations (Rotterdam)
Accepted for receive as of yesterday’s card. Today the station earns the other half of its licence.
Rotterdam has a command for SAR-1 on the 14:03 pass and their flight rules say it comes from a station with a demonstrated clean uplink. That is us, or it is nobody until the next window. One thing: the HPA never goes live without drive behind it. I have watched a site cook an amplifier that way and I would rather not watch it twice.
- Charlie (text, 1344)
Command Request
Section titled “Command Request”Ref: MER-OPS-2027-0311 From: A. Visser, MERIDIAN Constellation Operations To: GW-01 Galway Priority: Routine, window-bound
GW-01: please uplink REC-PLAYBACK to MERIDIAN-SAR-1 on your 14:03 UTC pass. Onboard recorder is at 71% and the next Nordic tasking block starts before your following window. Acknowledgement is required in the pass; the spacecraft rejects anything received outside its command window.
Your carrier must be Doppler-compensated. Our receiver has a narrow acquisition band and the bird cannot tell you it is off frequency - it simply does not answer.
Thank you, and welcome to the network.
- Anneke
| Command | Mnemonic | Tasked This Pass |
|---|---|---|
| Start recorder playback | REC-PLAYBACK | Yes |
| Payload to safe mode | PLD-SAFE | No |
| Reset OBC watchdog | OBC-WDT-RESET | No |
Pass Plan and Command Window (5° mask, epoch 13:45:00 UTC)
Section titled “Pass Plan and Command Window (5° mask, epoch 13:45:00 UTC)”| Item | Time |
|---|---|
| MERIDIAN-SAR-1 AOS | 14:03:10 |
| Command window opens | 14:03:40 |
| Max elevation (28°) | 14:06:45 |
| Command window closes | 14:10:00 |
| MERIDIAN-SAR-1 LOS | 14:10:18 |
MERIDIAN-SAR-2 rises at 14:18:42 and is not tasked. The TT&C console shows window status live; a command sent while it reads closed comes back NAK regardless of everything else being right. A NAK is information: the Detail column says why.
Uplink Plan
Section titled “Uplink Plan”BUC is low-side injection: RF = IF + LO (12,600 MHz LO). No spectrum inversion on the transmit side. The receive LNB is high-side and unchanged from acceptance.
| Path | IF (MHz) | LO (MHz) | RF (MHz) | Format |
|---|---|---|---|---|
| SAR-1 telecommand uplink | 1,405 | 12,600 (BUC) | 14,005 | QPSK 3/4, 36 MHz, −7 dBm modem |
| SAR-1 telemetry beacon (down) | 1,389 | 13,100 (LNB) | 11,711 | CW |
| SAR-1 imagery downlink | 1,414 | 13,100 (LNB) | 11,686 | QPSK 3/4, 36 MHz |
The acceptance crew left transmit modem 1 on their 1,400 MHz test carrier. Five megahertz off, and the spacecraft receiver never hears you.
Doppler Across the Pass
Section titled “Doppler Across the Pass”| Link | Frequency | Peak Doppler | Handling |
|---|---|---|---|
| Downlink | 11.7 GHz | ±270 kHz | Receiver AFC follows it |
| Uplink | 14.0 GHz | ±325 kHz | Pre-compensated at the console; the spacecraft cannot chase it |
The range rate at AOS is closing at roughly 7 km/s, passes through zero at culmination, and opens at the same rate on the way out. Uplink compensation is a switch on the TT&C tab; it slews the command carrier against the predicted rate so the spacecraft sees 14,005 MHz throughout. Engage it before the pass.
Transmit Chain Status (as left)
Section titled “Transmit Chain Status (as left)”| Equipment | Status | Notes |
|---|---|---|
| TX modem 1 | 1,400 MHz / 36 MHz / QPSK 3/4 / −7 dBm | Powered, not transmitting. Retune to 1,405. |
| BUC | 12,600 MHz LO, reference locked, gain 23 dB, muted | Stays muted until the carrier is up |
| HPA | Powered, output disabled | 2.5 W Ku SSPA (34 dBm P1dB), fixed gain, 10 dB back-off: about 24 dBm (0.25 W) from the BUC’s 16 dBm |
| OMT | TX pol H / RX pol V | 28.5 dB cross-pol isolation |
| 4 m Ku tracker | Manual, parked az 5° / el 3° | Program-track available |
| GPSDO | Locked, 9 satellites | Disciplined; the BUC LO is locked to it |
TT&C Console Reference
Section titled “TT&C Console Reference”| Display | Meaning |
|---|---|
| Window status | Open or closed against the pass window above |
| Uplink Doppler Compensation | Must be engaged before any send |
| Command Stack: XMIT | Queues the mnemonic; result posts to Command History |
| ACK | Spacecraft verified and executed the command; it answered on the next telemetry frame |
| NAK | Rejected; the Detail column states why (no compensation, key, or out of window) |
Key status starts Valid and no rotation is scheduled this shift.
Uplink Checklist
Section titled “Uplink Checklist”Before the Pass (13:45 – 14:03)
Section titled “Before the Pass (13:45 – 14:03)”- GPS Timing: GPSDO locked; TX Chain: BUC on external reference
- TX modem 1 retuned to 1,405 MHz (IF = 14,005 − 12,600)
- Pass Schedule: window 14:03:40 – 14:10:00 confirmed
- TT&C: uplink Doppler compensation engaged
- Step 1: TX modem 1 on air, BUC still muted
- Step 2: BUC unmuted, HPA still disabled
- Step 3: HPA output enabled, not overdriven (10 dB back-off)
- Antenna: program-track on MERIDIAN-SAR-1; beacon on RX analysis
In the Window (14:03:40 – 14:10:00)
Section titled “In the Window (14:03:40 – 14:10:00)”- TT&C window reads OPEN
- REC-PLAYBACK sent from the Command Stack
- ACK in Command History; read what it proves
After LOS
Section titled “After LOS”- HPA output disabled
- BUC muted
- TX modem 1 off air
- Command log: what went up, what came back, chain cold
End of Briefing
Section titled “End of Briefing”Until today, GW-01 has only ever listened. The first time a station radiates at a spacecraft is the first time it can do harm to one, which is why Rotterdam’s flight rules exist and why Anneke’s note is polite but not optional.
Get the ACK. Bring the amplifier down properly. Charlie is in the RF room, and he will hear it if you don’t.
Good luck.