strategic: InterSatelliteLink CRD — SDA OCT v3.1.0 conformant Xn-NTN abstraction (unblocks #69)

[thc1006]

Summary

Introduce InterSatelliteLink CRD: declarative Xn-NTN inter-gNB link establishment over optical inter-satellite links (OISL), conformant to SDA Optical Communications Terminal Standard v3.1.0. Unblocks the data-plane portion of #69 (SessionContinuity) by giving the controller a first-class abstraction for cross-satellite Xn traffic.

Why file now

• SDA OCT Standard v3.1.0 (June 2023) is the open interoperability spec — fixed wavelengths 1553.33 nm / 1536.61 nm, OOK-NRZ modulation, defined PAT (Pointing-Acquisition-Tracking).
• Commercial OISL terminals shipping in 2025/2026:
  • Mynaric Condor Mk3
  • Honeywell / Ball OISL
  • Tesat ConDoR
  • BAE Systems compact lasercom
• Rapidtek roadmap: two more 8U CubeSats by EOY 2026 with inter-satellite communication capability — direct target hardware.
• 3GPP Rel-19 Xn over OISL is a marquee feature for regenerative payload constellations (AccelerComm consortium reference architecture uses Option-2 split gNB with DU on payload, requiring Xn over ISL).
• feat: enforce SessionContinuity during failover #69 SessionContinuity was paused on data-plane work because the cross-satellite Xn primitive was missing; this CRD provides exactly that.

Proposed scope (no code)

1. ADR docs/adr/inter-satellite-link-design.md:
   • CRD shape: endpoints (2 satellite refs), physicalLayer (standard, wavelengthNm, modulation), purpose (Xn-NTN / user-plane / control), pointing schedule, BER / RX-power telemetry.
   • Field-by-field conformance to SDA OCT v3.1.0 §3 (physical layer) and §4 (PAT).
   • Visibility-window computation: reuse SatelliteEphemeris SGP4 stack to determine when two satellites can mutually point.
2. First reference provider: provider-mock (simulator for CI deterministic testing).
3. Roadmap providers: vendor SDKs as they become available — Mynaric SDK, Honeywell SDK, Tesat ConDoR.
4. Integration with feat: enforce SessionContinuity during failover #69: InterSatelliteLink becomes the data-plane primitive that SessionContinuity reconciles against.

Open questions

• Cross-vendor interoperability is the SDA OCT spec promise but unproven in field; how do we structure conformance testing?
• Multi-link load balancing across multiple OISL terminals on the same satellite — controller responsibility or provider?
• Pointing schedule under conjunction-avoidance maneuvers — must read ConjunctionAlert state to suspend pointing windows.

Why this matters — impact: Strategic, medium-high; unblocker for #69

• Work effort: Medium.
• Priority: Medium-high — required for Rel-19 regenerative payload demos; unblocker for paused feat: enforce SessionContinuity during failover #69 work.

References

Standards

• SDA OCT Standard v3.1.0: https://www.sda.mil/wp-content/uploads/2023/06/SDA_OCT_Standard-3.1.0_Signed_Web_Version.pdf
• SDA OISL Standard v2.1.2: https://www.sda.mil/wp-content/uploads/2023/12/SDA-OISL-Standard-v2.1.2.pdf
• CCSDS Optical Communications WG (NASA NTRS): https://ntrs.nasa.gov/api/citations/20190032532/downloads/20190032532.pdf
• ESA ESTOL air-interface for terabit/s optical links

Commercial terminals

• May 2025 satsearch survey of 15 commercial OISL systems: https://blog.satsearch.co/2025-05-01-15-laser-communications-systems-for-inter-satellite-links-isls-in-leo-that-you-can-buy-in-may-2025

3GPP

• Rel-19 NTN payload architecture (Ericsson): https://www.ericsson.com/en/blog/2024/10/ntn-payload-architecture
• AccelerComm AX-RG regenerative NTN PHY: https://www.accelercomm.com/solutions/accelercomm-ax-rg

Cross-link: #69 (SessionContinuity — direct unblocker), #65 (provider pattern), #72, parent epic.