Scenario 7 - Moving Target
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, front office) Constellation Ops Contact: Anneke Visser, MERIDIAN Constellation Operations (Rotterdam)
Anneke rang at 05:40, which tells you how her night went. Space Surveillance has a conjunction on SAR-2 with a spent upper stage. Rotterdam decides at 14:00; if it is go, the burn is at 14:11, which is between your passes. Small burn. New orbit, slightly.
Here is the problem with slightly: every prediction this station makes, and every place program-track will send the dish, comes from an element set that will describe an orbit the bird is not in. Work SAR-1 first. It did not burn, and I want you to know what right looks like before you meet wrong.
- Charlie (text, 1344)
Conjunction Notice
Section titled “Conjunction Notice”Ref: MER-OPS-CAM-2027-014 From: A. Visser, MERIDIAN Constellation Operations To: All MERIDIAN ground sites Subject: MERIDIAN-SAR-2 collision-avoidance manoeuvre, go / no-go 14:00Z
Space Surveillance has flagged a conjunction between MERIDIAN-SAR-2 and a spent upper stage. Go / no-go is at 14:00Z; if go, the burn executes at 14:11:00Z. It is a small along-track adjustment; the spacecraft is healthy and the payload schedule is unaffected.
If we burn, treat your SAR-2 element set as stale from that moment and load the post-burn elements before your 14:18 window. The pass shift is under ten seconds. The pointing error at a 4 m Ku beamwidth is not.
- Anneke
| Item | Value |
|---|---|
| Spacecraft | MERIDIAN-SAR-2 (NORAD 61702) |
| Manoeuvre | Along-track avoidance burn, 14:11:00Z if go |
| Element change | Mean anomaly +0.03°, about 3.5 km along track |
| Effect on the 14:18 Galway pass | Timing shifts by under a second; pointing solution on the old set is half a degree off at culmination |
| Distribution | Post-burn set (epoch 14:11:30Z) reaches the console within two minutes of the burn; the Pass Schedule ephemeris panel flags it STALE |
SAR-1 is not involved. Its elements are current and stay current.
Pass Plan (epoch 13:45:00 UTC, 5° mask)
Section titled “Pass Plan (epoch 13:45:00 UTC, 5° mask)”| Contact | AOS | Rise az | Max Elevation | LOS | Elements |
|---|---|---|---|---|---|
| MERIDIAN-SAR-1 | 14:03:10 | 000° | 28° at 14:06:45, 761 km | 14:10:18 | Current. The baseline. |
| MERIDIAN-SAR-2 | 14:18:42 | 130° | 25° at 14:22:10, 828 km | 14:25:40 | Stale after 14:11 if the burn is go |
Decode windows (C/N ≥ 8 dB): SAR-1 about 14:05 to 14:08:30, peak ~11 dB at culmination; SAR-2 on current elements about 14:20:45 to 14:23:40, peak ~10 dB.
What stale looks like
Section titled “What stale looks like”| Elements | Pedestal | Carrier on RX analysis |
|---|---|---|
| Current | LOCKED | Rises with elevation: about 4 dB at 10°, 7 dB at 14°, 10 dB at the top |
| Stale (post-burn, old set) | LOCKED | Present but weak, peaks around 3 dB on the rising leg and then falls as the bird climbs, to about -5 dB at culmination |
A fixed along-track error is a bigger angle at shorter range: 3.5 km is 0.1° at 2,000 km and 0.25° at 828 km. The closer the bird, the worse the miss. Program-track lock means the pedestal is where it was told to go; it does not mean it was told right.
Element Sets
Section titled “Element Sets”| Set | Epoch | Describes |
|---|---|---|
| SAR-2, on file at turnover | 2027-03-15 14:00Z | The orbit before the burn |
| SAR-2, post-burn distribution | 2027-03-15 14:11:30Z | The orbit after it |
An element set is a snapshot of the orbit at its epoch. Anything the spacecraft does after that instant is invisible to it. Two clocks run on every set: the calendar, which erodes it slowly (drag and model error grow the along-track error by hundreds of metres a day at 360 km), and the thruster, which breaks it at once. Rotterdam distributes fresh elements every few days for the first reason and within minutes for the second.
Pass Schedule Ephemeris Panel Reference
Section titled “Pass Schedule Ephemeris Panel Reference”| Display | Meaning |
|---|---|
| NOMINAL | No manoeuvre notice; the loaded set is the current distribution |
| EPHEMERIS STALE | A manoeuvre notice has been received for this spacecraft and the loaded elements pre-date it |
| Load Updated Ephemeris | Replaces the element set with the post-manoeuvre distribution; predictions and program-track update immediately |
| UPDATED | Current elements loaded; pass predictions and pointing are trustworthy again |
Link Parameters
Section titled “Link Parameters”LNB is high-side injection: IF = LO − RF (13,100 MHz LO).
| Signal | RF (MHz) | IF (MHz) | Format |
|---|---|---|---|
| SAR-1 imagery downlink | 11,686 | 1,414 | QPSK 3/4, 36 MHz |
| SAR-1 telemetry beacon | 11,711 | 1,389 | CW |
| SAR-2 imagery downlink | 11,730 | 1,370 | QPSK 3/4, 36 MHz |
| SAR-2 telemetry beacon | 11,703 | 1,397 | CW |
The Doppler profile changes by a negligible amount for a burn this size; the receiver frequency plan is unchanged. A clean reacquisition is the 1,397 MHz beacon on RX analysis, the modem locked on 1,370 MHz, and C/N at or above 8 dB through what is left of the high-elevation segment.
GW-01 Equipment Status (as yesterday’s shift left it)
Section titled “GW-01 Equipment Status (as yesterday’s shift left it)”| Equipment | Status | Notes |
|---|---|---|
| 4 m Ku tracker | Powered, manual, stowed az 180° / el 3° | Program-track available; park on az 000° / el 5° for SAR-1, az 130° / el 5° for SAR-2 |
| LNB | 13,100 MHz LO, reference locked | Stable |
| GPSDO | Locked, 9 satellites | Disciplined. Timing is half of an element set. |
| RX modem 1 | 1,370 MHz / 36 MHz / QPSK 3/4 | Yesterday’s SAR-2 carrier. Retune to 1,414 MHz for SAR-1, back to 1,370 MHz for SAR-2. |
| Spectrum analyzer | 1,414 MHz centre, 60 MHz span | 1,389 MHz / 2 MHz for SAR-1; 1,397 MHz / 2 MHz (beacon) for SAR-2 |
| BUC / HPA | No drive / output disabled | No uplink tasking this shift |
Shift Checklist
Section titled “Shift Checklist”Before the baseline (13:45 – 14:03)
Section titled “Before the baseline (13:45 – 14:03)”- Dashboard: only the RX AGC no-carrier warning (noise only, empty sky); no faults
- GPS Timing: GPSDO locked, not in holdover
- Pass Schedule: both element sets current, epoch 14:00
- RX modem 1: 1,414 MHz; analyzer centre 1,389 MHz, span 2 MHz
- ACU: tracker parked az 000° / el 5°, then program-track, target MERIDIAN-SAR-1
The baseline (14:03 – 14:10)
Section titled “The baseline (14:03 – 14:10)”- Beacon on RX analysis; modem locked; C/N ≥ 8 dB through the high segment, ≥ 9 dB at culmination
- The curve remembered: up with elevation, peak at the top, down the other side
Between passes (14:10 – 14:18)
Section titled “Between passes (14:10 – 14:18)”- Ephemeris log: SAR-1 result with the set and epoch it was flown on
- Burn executed 14:11 (Anneke’s text); RX modem 1 to 1,370 MHz; analyzer centre 1,397 MHz
- ACU: manual, tracker parked az 130° / el 5° on the old prediction
The stale attempt (14:18 – 14:20)
Section titled “The stale attempt (14:18 – 14:20)”- Program-track on MERIDIAN-SAR-2 on the old set; pedestal reads LOCKED
- RX analysis: carrier weak, C/N under 5 dB and falling as elevation rises
Reacquisition (14:20 – 14:25)
Section titled “Reacquisition (14:20 – 14:25)”- Pass Schedule: SAR-2 reads EPHEMERIS STALE; Load Updated Ephemeris; reads UPDATED
- 1,397 MHz beacon comes up on RX analysis; modem locked; C/N ≥ 8 dB
After LOS
Section titled “After LOS”- Ephemeris log: the stale attempt, the load, the reacquisition; reported to Rotterdam
End of Briefing
Section titled “End of Briefing”The element set is this station’s entire model of where the satellite is. A stale set is not a degraded antenna; it is a precise antenna pointed at the wrong place, and the closer the bird gets, the more wrong it is.
Anneke has been up since before five and has done her part. Fly the baseline, watch the miss, load the elements, take the pass, and tell Rotterdam the bird came up where it should.
Good luck.