Apollo Fusion Electric-Propulsion Test Chamber
A space-simulation vacuum chamber for firing and qualifying Hall-effect satellite thrusters
Apollo Fusion was a California electric-propulsion company — based in Mountain View and founded in 2016 by Mike Cassidy and Ben Longmier — that developed the Apollo Constellation Engine (ACE), a compact Hall-effect thruster for satellites. Instead of burning chemical propellant, ACE ionizes an inert gas such as krypton or xenon and accelerates it electromagnetically, producing a small but extraordinarily efficient thrust that satellites use for orbit raising, station-keeping, and end-of-life deorbit. Building on magnetically-shielded Hall-thruster technology licensed from NASA's Jet Propulsion Laboratory, ACE became a leading commercial in-space propulsion system, selected by satellite builders including York Space Systems. In 2021 the launch company Astra Space acquired Apollo Fusion — a deal worth roughly $50 million plus performance earn-outs — and rebranded the product as the Astra Spacecraft Engine, making electric propulsion a cornerstone of its integrated space platform.
Developing and qualifying an electric thruster means firing it in the vacuum of space — and that is where Red Line Chambers of Salt Lake City, Utah, comes in. Red Line built the vacuum test chamber Apollo Fusion uses to operate its Hall thrusters under space-simulating conditions.
Because a firing thruster continuously releases a plume of ionized propellant, the chamber must pull and hold a hard vacuum even while gas is being injected, which demands a large, robust vessel with generous port access for vacuum pumps, electrical and propellant feedthroughs, diagnostics, and the thruster itself. The system Red Line delivered pairs a tall vertical chamber with a horizontal test chamber and domed access door, studded with precision flanged ports and viewports — giving Apollo Fusion's engineers a versatile, high-integrity environment for thruster operation and instrumentation. Building a vacuum system of this scale that seals reliably, holds accurate port geometry, and withstands repeated test cycles is exacting, one-off work of exactly the kind Red Line Chambers specializes in.
The test chamber is foundational to the ACE program: an electric thruster can only be characterized, tuned, and life-tested inside a chamber that faithfully reproduces the vacuum of space. By delivering this hardware, Red Line Chambers supported one of the most successful commercial electric-propulsion programs in the new space economy — technology that, now under Astra, helps satellites maneuver and extend their missions in orbit. The project stands alongside Red Line Chambers' work on frontier astronomical instruments as a demonstration of the company's range: from cryogenic astronomy cameras to space-simulation chambers for propulsion, translating demanding engineering requirements into reliable, deployable vacuum hardware.
Program & Chamber Specifications
Customer | Apollo Fusion (Mountain View, CA) |
Acquired by | Astra Space, 2021 |
Application | Electric-propulsion / space simulation |
Article under test | Apollo Constellation Engine (ACE) |
Thruster type | Hall-effect electric propulsion |
Propellant | Krypton / Xenon |
Thruster power | ~400 W (class) |
Thruster dry mass | 7.6 kg |
Chamber configuration | Vertical vessel + horizontal test chamber |
Access | Domed door + multi-port flanges |
Environment | High-vacuum thruster operation |
Fabricator | Red Line Chambers, Inc. |
Apollo Fusion Electric-Propulsion Test Chamber Project Gallery
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