Zeno Power Radioisotope Heating Unit

History

The Zeno Power Radioisotope Heating Unit is a compact radioisotope heat source intended to provide passive thermal energy for spacecraft operating in extremely cold environments. A unit using americium-241 is planned to fly as part of Zeno Power's Survive-the-Night package on a Firefly Aerospace Blue Ghost lunar lander mission scheduled for 2028.

The planned demonstration is intended to show that radioisotope heating can keep spacecraft systems warm during the lunar night, when solar energy is unavailable and temperatures can fall to extreme levels. The package is designed to remain functional long enough to transmit a signal after several days of lunar-night operation.

The mission will be Zeno Power's first space mission and is intended as both a technology demonstration and a pathfinder for regulatory processes associated with launching commercial radioisotope systems.

Development and lunar demonstration

Firefly Aerospace and Zeno Power announced their agreement on August 19, 2026. According to SpaceNews, the Zeno Power payload is planned for a Blue Ghost mission scheduled to launch in 2028. The payload forms a self-contained Survive-the-Night package intended to operate during the lunar night.

The demonstration responds to an incentive included by NASA in a Commercial Lunar Payload Services task order for technologies capable of surviving the lunar night. Firefly Aerospace was one of three companies selected for that task order in June 2026.

Firefly Aerospace is preparing processes for safely integrating the nuclear payload with the Blue Ghost lander and conducting the associated testing and launch preparations. SatNews also reported that Firefly and Zeno Power were beginning structural and thermal interface work ahead of payload integration.

Zeno Power is also working to increase production capacity for radioisotope heating units in anticipation of possible future lunar missions. Firefly has stated that it will use results from the initial demonstration to assess how the technology could be incorporated into later missions, including applications for individual payloads or larger portions of a lander.

Design

The Zeno Power Radioisotope Heating Unit is a passive heat source fueled by americium-241. Radioactive decay produces thermal energy without requiring sunlight or electrical power from the spacecraft. The unit planned for the Blue Ghost demonstration is designed to provide 5 watts of thermal energy.

The RHU itself is described as approximately the size of a silver dollar. The companies have not disclosed its mass, volume, detailed internal construction, or complete containment arrangement.

Survive-the-Night package

The RHU is incorporated into a self-contained demonstration package that also includes communications, electrical power, and related subsystems. Its heat is intended to keep these components warm while the package remains exposed to lunar-night conditions. SpaceNews reported temperatures for the planned test environment falling to approximately -170 degrees Celsius.

The demonstration objective is deliberately simple: after operating into the lunar night, the package is expected to transmit a signal confirming that it remains functional. Zeno Power stated that a successful transmission five days into the lunar night would meet the intended demonstration requirement.

Radioisotope fuel

The unit uses americium-241 rather than plutonium-238 as its radioisotope heat source. Zeno Power has stated that it is building a supply chain for americium-241 to support future demand for radioisotope heating and power systems.

The RHU produces heat directly from radioactive decay. It is distinct from Zeno Power's separate work on radioisotope power systems using Stirling generators to produce electrical power.

Program status

The Zeno Power Radioisotope Heating Unit remains scheduled for its first space demonstration on a Firefly Aerospace Blue Ghost mission planned to launch in 2028. The mission has not yet occurred.

Firefly Aerospace is working on payload integration, safety processes, testing, and launch preparations. Zeno Power is simultaneously preparing for possible larger-scale production of RHUs for future lunar missions.

The demonstration is also intended to exercise regulatory approval processes for a commercial radioisotope payload. Zeno Power has described regulatory approval as an important part of proving that the technology can not only be built but also flown.

Specifications (Blue Ghost demonstration RHU)

General characteristics

• Type: Radioisotope heating unit
• Heat source: Americium-241
• Approximate size: About the size of a silver dollar
• Planned carrier: Firefly Aerospace Blue Ghost lunar lander
• Planned launch: 2028

Performance

• Thermal output: 5 W
• Function: Passive heating of the Survive-the-Night package during the lunar night