Australia’s Eris Rocket: Hybrid Engines and Future Challenges

Introduction

On July 30, 2025, Gilmour Space’s 25-meter Eris vehicle—Australia’s first privately developed orbital-class launch rocket—ignited at the newly operational Bowen Orbital Spaceport in Queensland. The long-anticipated mission ended after just 14 seconds when two of its four hybrid Sirius engines failed in quick succession, causing the booster to stall above the pad and tumble into a nearby field. Though the inaugural flight fell short of orbit, the test provided invaluable data on hybrid propulsion, regulatory hurdles, and the roadmap for future Australian launches.

Launch Attempt and Immediate Anomalies

Flight Sequence and Failure Timeline

1. Engine Ignition and Liftoff (T+0 s): All four Sirius hybrid motors reached full throttle, delivering roughly 360 kN total thrust.
2. First Engine Out (T+5 s): Telemetry and high-speed imagery indicate one Sirius unit lost chamber pressure, dropping thrust to zero.
3. Second Engine Failure (T+12 s): The control system compensated by gimbaling remaining engines, but a second propulsion loss led to insufficient lift-to-weight ratio.
4. Stall and Impact (T+14 s): Without corrective thrust, Eris pitched over and impacted a cleared zone ~250 m from the pad, generating a plume of smoke and debris.

“I thought best case was maybe 40 seconds of flight time, but I’ll take 14 as a win,” said cofounder and CEO Adam Gilmour in a post-launch debrief. “Getting off the pad and clearing the tower under real conditions is a huge step forward.”

Safety and Environmental Assessment

• No injuries or significant environmental damage reported.
• Civil Aviation Safety Authority (CASA) confirmed no damage to the pad structure.
• Minor hydrogen peroxide residue cleaned under Australian Space Agency guidelines.

Technical Deep Dive: Hybrid Propulsion Systems

Hybrid rockets combine a solid fuel grain with a liquid or gaseous oxidizer. Gilmour’s Sirius engines use hydroxyl-terminated polybutadiene (HTPB) and high-concentration hydrogen peroxide (H₂O₂), offering:

• Throttle Control: Unlike solid motors, hybrids can be throttled and shut down.
• Simplified Plumbing: Only oxidizer lines require valves and pumps; no cryogenic tanks for the first stage.
• Cost Advantages: Lower fabrication complexity compared to full liquid systems.

Key specifications:

• Thrust per Sirius engine at sea level: ~90 kN
• Sea-level specific impulse (I_sp): ~260 s
• Operational pressure: ~7 bar
• Single-use design: each motor is fired only once, limiting ground testing.

By contrast, the third-stage Phoenix engine uses RP-1 kerosene and liquid oxygen, generating ~30 kN vacuum thrust and I_sp ~320 s for precise orbital insertion.

Industry Perspectives

“Hybrid propulsion occupies a niche between solids and liquids. Gilmour’s approach reduces complexity but compound age and sealing present unique reliability challenges,” said Dr. Alice Brown, propulsion expert at the Australian National University.

Regulatory, Environmental, and Operational Factors

Gilmour Space endured an 18-month approval process under CASA’s Part 101 regulations and environmental clearances from the Queensland government. Extended storage of the assembled Eris vehicle in a coastal hangar exposed sensitive components to salt air, likely contributing to seal degradation in the hybrid motors.

• Approval Timeline: Rocket completed April 2024; launch license granted July 2025.
• Corrosion Mitigation: Future vehicles will undergo accelerated drying cycles and rust-inhibitor treatments.
• Environmental Safeguards: Spill containment berms and peroxide neutralization protocols now standard at Bowen Spaceport.

Market Position, Competitive Landscape, and Future Roadmap

The Eris launcher targets the growing small-sat (<500 kg) market, competing with vehicles such as Rocket Lab’s Electron and Virgin Orbit’s LauncherOne. Eris is designed to carry up to 305 kg to LEO at an advertised price point of ~$6 million per launch. Australia’s newly expanded Space Infrastructure Fund just increased public support by AUD 10 million to shore up domestic launch capabilities.

Second Vehicle and Engine Upgrades

• Second Eris structure complete; engine builds resume after detailed post-flight tests.
• New hybrid grain formulation and updated peroxide plumbing scheduled for bench testing Q4 2025.
• Projected second launch window: early 2026, pending full-engine validation.

Broader Strategic Implications

• National Sovereignty: Reduces reliance on overseas launch infrastructure.
• Supply Chain Development: Stimulates local composites, avionics, and propellant industries.
• Export Potential: Opens markets in Southeast Asia and the Pacific for responsive small-sat access.

Conclusions and Lessons Learned

Though the Eris maiden flight ended abruptly, the test achieved:

1. Validation of pad systems, telemetry links, and flight software under live conditions.
2. Insight into hybrid engine aging after prolonged storage.
3. Refinement of regulatory and environmental processes for future campaigns.

As Enrico Palermo, head of the Australian Space Agency, stated: “Innovation requires testing—and sometimes failure. Gilmour’s milestone brings Australia one step closer to routine domestic launches.” With enhanced propulsion designs and an accelerating regulatory framework, Gilmour Space aims to transform the Bowen coast into a global small-sat launch hub by 2027.