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# Slackwater — SLS-101 (Program HERON)

**Public name:** Slackwater  **Tracking #:** SLS-101  **Codename:** HERON
**Category:** Surface Vessels (USV)  **Fiscal Year:** FY2023
**Contract award:** 14 March 2023

## Summary

Slackwater is Salish Littoral Systems' long-endurance ISR surface drone — the
company's first production platform and the anchor of the surface line. HERON is
built for persistent, low-signature presence in contested littorals: weeks on
station, multi-INT collection, and a hull-form tuned for fuel economy over speed.
It is the reference airframe-equivalent against which later USVs (ORCA) are
benchmarked.

## Notional Capabilities

- Hybrid solar-assisted diesel-electric drivetrain; 60+ day nominal endurance
- Retractable multi-INT ISR mast (EO/IR, radar, SIGINT-ready payload bays)
- "Level 4" mission autonomy with collision avoidance and re-planning in
  GNSS-denied conditions (HERON ships the CEDAR / SLS-301 stack)
- Sea-state 5 transit, sea-state 4 sustained collection
- Low-probability-of-intercept SATCOM + line-of-sight mesh backhaul

## Program References

- Niu, H., Ji, Z., Savvaris, A., Tsourdos, A., & Carrasco, J., "Model Checking
  for Decision Making System of Long Endurance Unmanned Surface Vehicle," 2021.
  [arXiv:2102.10604](https://arxiv.org/abs/2102.10604)
- Salish Littoral Systems, *Decision-Making Architecture for Long-Endurance
  Unmanned Surface Vehicles*, SLS Technical Memorandum TM-101-A, 2023.
- "Synergistic Hierarchical AI Framework for USV Navigation: Swin-Transformer
  Perception, T-ASTAR Planning, and Energy-Aware TD3 Control," *Sensors*, 2025.
  [PMC12349642](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC12349642/)
- SLS Maritime Autonomy Group, *Multi-Source Energy Budgeting for Persistent
  Surface ISR*, SLS White Paper WP-HERON-02, 2023.

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