New jet engine enables efficiency at every speed for cheaper orbital launches
A startup is touting a hybrid jet engine that uses an electrically driven compressor to remain efficient from takeoff to high supersonic speeds, with the goal of serving as a reusable first stage for cheaper orbital launches. Commenters probe whether air‑breathing stages can meaningfully reduce launch costs compared to today’s reusable rockets, raising concerns about thrust‑to‑weight, power supply mass, hypersonic airflow, and structural penalties for air‑launched vehicles. Some see the concept as an incremental extension of geared turbofan and air‑turboramjet ideas that may be better suited to missiles or hypersonic aircraft than to mainstream orbital launch.
Engine concept and claimed innovation
- Engine uses a turbine-driven generator powering electric motors on the compressor/fan; likened to a “diesel-electric locomotive” for jets.
- Goal: vary compressor speed independently of turbine to stay efficient from takeoff through ~Mach 2.7, then hand off to a ramjet on a second stage and eventually a rocket.
- Some see this as an extension of geared turbofans or air turborockets; others think the continuously variable, electric-driven compressor is genuinely novel.
Power source, weight, and efficiency questions
- Major skepticism about using batteries due to mass; several infer the turbine mostly powers the generator, with perhaps short-duration storage (supercaps or jettisonable batteries).
- Concerns about transmission losses in the turbine→generator→motor chain; supporters argue short burn times and cryogenic cooling could keep total efficiency high (claims of >95% in the thread, though not detailed).
- Doubts that electric motors light enough to spin large compressors at >20,000 rpm are practical with current tech.
Air‑breathing first stages vs rockets
- Many note first stages are more constrained by thrust-to-weight and cost per unit thrust than by Isp; air-breathers are far worse on T/W than rockets.
- Several argue reusable rockets (e.g., Falcon 9–class) have largely undercut the case for winged/air-breathing first stages.
Altitude vs velocity and air-launch value
- Repeated reminder: orbit is mostly about horizontal speed (~8 km/s), not altitude; altitude saves only a small fraction of required energy.
- Starting from a fast aircraft (even SR‑71 speeds) gives only a small fraction of orbital energy.
- Air-launch and balloon-launch concepts are critiqued as marginal gains for substantial structural and operational complexity.
Comparisons to SABRE, Skylon, and other concepts
- SABRE/Skylon cited as more capable but vastly more complex precooled air-breathing rocket systems; skepticism after decades without deployment.
- New engine seen as simpler but also lower performance; may not beat current rockets economically.
- Rotating detonation engines and scramjets mentioned but clarified as different technologies from this design.
Applications and strategy
- Some think this engine is better suited to drones, missiles, or hypersonic cruise rather than orbital launch.
- Others note “space” is a powerful marketing hook; speculation that military or missile customers might be the real near-term market.
Unclear aspects
- Actual achievable flight regime (max Mach, altitude) and detailed thermal management remain unclear from available information.
- Whether it can genuinely “act as a first stage” (vertical launch) versus powering a carrier aircraft is also not definitively established.