SpaceUM-Polar
3U SpaceVPX System Utility Module
SpaceVPX VITA 78 Dual-String Switching LCL per Slot <1 ms Switchover
DESCRIPTION
The SpaceUM-Polar is a 3U SpaceVPX (VITA 78) System Utility Module that provides dual-string redundancy management, per-slot power switching via latching current limiters (LCLs), 100 MHz reference clock distribution, and hardware reset control for the SpaceVPX-BP-DS dual-string backplane. It monitors both OBC-A and OBC-B strings continuously and executes autonomous string switchover in under one millisecond in response to a detected OBC fault — without requiring ground-station intervention or any action from the failed OBC. Housekeeping telemetry (per-slot current, voltage, and temperature) is reported over I2C and SpaceWire management bus.
KEY FEATURES
- Dual-String Switching: Monitors OBC-A and OBC-B independently; autonomous switchover in <1 ms
- <1 ms Switchover: Sub-millisecond active / standby string transition — no ground intervention required
- 100 MHz Clock: Dual reference clock sources; SpaceUM selects and distributes active clock to all slots
- HK Telemetry: Per-slot current and voltage telemetry via I2C — <1% accuracy
- >30 krad TID: Radiation-tolerant switching components; latch-up immune
- Autonomous FDIR: String switchover logic implemented in radiation-hard state machine — not software-dependent
- LCL per Payload Slot: 6 latching current limiters with adjustable 1 A – 5 A trip threshold per slot
- Hardware Watchdog: Independent hardware watchdog per string; triggers switchover on OBC timeout
- Per-Slot Reset: Individual power-on-reset and watchdog-triggered reset per SLT3-PAY slot
- SpaceWire Management: SpaceWire command and telemetry interface to both OBC strings
- 3 W Nominal: Low self-power consumption — 5 V from backplane utility plane
- ∼140 g: Minimal mass contribution to dual-string system configuration
SWITCHING & REDUNDANCY
- Strings supported: 2 — String A (OBC-A) and String B (OBC-B)
- Switchover trigger: OBC watchdog timeout, OBC power fault, or ground command via SpaceWire
- Switchover time: <1 ms (from fault detection to active string established on payload slots)
- Switchover logic: Radiation-hard state machine — independent of OBC software on either string
- Return-to-prime: Configurable: manual command only, or automatic on OBC-A recovery
- LCL channels: 6 — one per SLT3-PAY slot (independent enable, fault detection, telemetry)
- LCL trip threshold: 1 A to 5 A adjustable per channel via I2C command register
- LCL response time: <10 µs from overcurrent detection to channel isolation
- LCL state after trip: Latched off — requires explicit SpaceWire or I2C reset command to re-enable
LCL PARAMETERS
- LCL type: Electronic circuit breaker with fold-back current limiting
- Channel count: 6 (one per SLT3-PAY slot)
- Operating voltage: 5 V (main) and 12 V (optional) — configurable per channel
- Current range: 1 A to 5 A in 0.25 A steps (I2C-programmable)
- On-state resistance: <50 mΩ per channel
- Current telemetry: 12-bit ADC per channel; ±1% accuracy; reported over I2C at up to 1 kHz
- Voltage telemetry: 12-bit ADC per rail; ±0.5% accuracy
- Thermal telemetry: PCB temperature sensor; ±1°C accuracy
CLOCK & RESET DISTRIBUTION
- Reference clock: 100 MHz LVDS — dual sources (one from each string oscillator input)
- Clock selection: Automatic — switches to alternate source within 1 clock cycle on primary failure
- Clock distribution: Buffered LVDS to all backplane slots — <100 ps jitter
- Reset outputs: Per-slot power-on-reset (POR) and watchdog reset — LVTTL open-drain
- POR delay: Configurable 10 ms – 500 ms per slot (I2C-programmable)
- SpaceWire mgmt.: One SpaceWire link to OBC-A and one to OBC-B — ECSS-E-ST-50-12C; up to 200 Mbps
- I2C bus: I2C-compliant management bus; address-configurable; 400 kHz fast mode
- Firmware: Embedded radiation-hard state machine; no field-programmable logic
MECHANICAL
- Form factor: 3U SpaceVPX (VITA 78) Utility Module
- Slot profile: SLT3-SWI (Switch / Utility)
- Dimensions: 100 × 160 mm (220 mm depth option)
- Connector: VITA-46 MULTIGIG RT2
- Cooling: Conduction-cooled, VITA 48.2 wedge-lock
- Power: 3 W nominal (5 V rail)
- Operating temp.: −40°C to +85°C
- Mass: ∼140 g
- TID: >30 krad (Si); latch-up immune
COMPATIBLE SYSTEMS
- SpaceVPX-BP-DS: Required for dual-string operation
- OBC-Polar VPX: OBC-A and OBC-B under SpaceUM supervision
- OBC-64 VPX: OBC-A and OBC-B under SpaceUM supervision
- PolarStore-2S / 4S: LCL-protected SATA payload slots
- PolarStore-2N / 4N: LCL-protected NVMe payload slots
- PSU-Polar-3U: Power input monitored by SpaceUM telemetry
