Ultra-Stable Oscillator / Atomic Clock
Ovenized Quartz USO + Rubidium Atomic Clock (Redundant)
Dual-tier timing source comprising an ultra-stable quartz oscillator (USO) for short-term stability and a rubidium (or mercury-ion DSAC-class) atomic clock for long-term stability, providing the Ark's master frequency and time reference.
Purpose
Generate a precise, stable frequency and time reference that supports coherent two-way Doppler measurement with DSN, autonomous navigation, mesh TDMA timing, and 100-year mission timekeeping with bounded drift.
Context
Heart of the Ark's timing system; outputs feed L3-COM-TIME-DIST (distribution) and directly to L3-COM-EARTH-XBAND (transponder reference) and L3-COM-EARTH-MOD (symbol clock). Calibrated periodically against L3-COM-TIME-SYNC (external references). Drift drift is critical for self-localisation when DSN/LunaNet unavailable.
Principles
- ▸Quartz USOs use thermally-stabilized (ovenized) high-Q crystal resonators to achieve Allan deviation ~10⁻¹³ at 1–1000 s integration
- ▸Rubidium atomic clocks lock a quartz oscillator to the 6.835 GHz hyperfine transition of ⁸⁷Rb — Allan deviation ~10⁻¹² at 1 s, ~10⁻¹⁴ at 10⁴ s, lifetime ~15 years
- ▸Mercury-ion clocks (Deep Space Atomic Clock, DSAC) achieve Allan deviation 2×10⁻¹⁵ at 1 day, enabling one-way radiometric navigation
- ▸Oscillator phase noise and aging set the long-term drift; periodic calibration against external reference resets the drift accumulation
- ▸Allan deviation σy(τ) is the standard short/medium-term stability measure (deviation of fractional frequency over integration time τ)
- ▸Hadamard deviation and Modified Allan deviation distinguish white-noise versus flicker-noise contributions
Typical implementations
- ▸AccuBeat USO — Allan deviation 5× better than 5×10⁻¹³ at 1–1000 s; selected by ESA JUICE mission
- ▸JPL Deep Space Atomic Clock (DSAC) — flown June 2019; ground demo Allan deviation 2×10⁻¹⁵ at 1 day
- ▸Microsemi 5071A cesium beam — laboratory standard, Allan ~5×10⁻¹³ at 1 day
- ▸LKD Aerospace USO — radiation-tolerant quartz, used on commsats
- ▸ESA Compact ultra-high stability atomic clock for space (Nebula PL)
Lunar considerations
- ▸Temperature stability is critical — USO oven must hold temperature to ~100 µK; lunar thermal cycling poses challenge
- ▸Radiation hardening: GCR and SEPs can perturb atomic clock electronics and shift quartz frequency via ionization-induced trapped charge
- ▸Magnetic field stability matters for Rb clocks — lunar weak magnetic environment is favorable
- ▸Vibration sensitivity: USO acceleration sensitivity ~10⁻⁹/g — Ark mounted USO is benign (no rocket vibration), but seismic events from moonquakes need consideration
- ▸Long-term aging: quartz aging ~5×10⁻¹⁰/year, Rb ~5×10⁻¹¹/year — over 100 years this compounds and requires periodic calibration from L3-COM-TIME-SYNC
Specifications
Functional
| primary function | Generate stable 10 MHz reference and master time count |
| inputs | 28 V DC power from L1-PDM (always-on rail), Calibration corrections from L3-COM-TIME-SYNC (periodic), Thermal control from L1-TCS (sub-K oven stability) |
| outputs | 10 MHz sinusoidal reference (≤5×10⁻¹³ Allan at 1 s), 1 PPS (one-pulse-per-second) time reference, Time-of-day register (UTC seconds + sub-second), Health telemetry (oven temperature, lock status, aging trend) |
| primary source | Rubidium atomic clock |
| secondary source | Ovenized quartz USO |
| allan deviation 1s | 5e-13 |
| allan deviation 1000s | 1e-13 |
| allan deviation 1day | 5e-14 |
| aging per year | 5e-11 |
| frequency output mhz | 10.0 |
| redundancy | primary + cold spare, both monitored |
Physical
| mass kg | 6.0 |
| dimensions | 200 × 200 × 150 mm |
| materials | Quartz crystal (SC-cut or AT-cut, 5 MHz fundamental), Rb cell (glass with ⁸⁷Rb vapor + buffer gas), Permalloy magnetic shield, Aluminum oven block with multi-layer insulation, Rad-hard low-noise oscillator chip |
| operating temperature c | -20, 50 |
| oven internal temperature stability uk | 100 |
| radiation tid krad | 30 |
Operational
| power consumption w warmup | 20 |
| power consumption w steady | 8 |
| thermal range c | -20, 50 |
| lifetime years | 15 |
| mtbf hours | 200000 |
| warm up time min | 30 |
Interfaces
Provides
- 10 MHz reference and 1 PPS time tick for distribution
- Coherent reference for two-way Doppler
- Symbol clock reference
- Master time tag for telemetry and logging
Requires
- Always-on 28 V supply for continuous operation
- Stable thermal interface (<0.1°C variation) at clock baseplate
- External calibration corrections (GNSS, DSN)
Cite this entry
Lunar Ark Codex. "Ultra-Stable Oscillator / Atomic Clock" (L3-COM-TIME-USOC). Retrieved 10 September 2026, from https://lunarark.com/entry/L3-COM-TIME-USOC
Licensed CC-BY-SA 4.0. You may reuse and adapt this entry with attribution, under the same licence.