RHU Webinar: Surviving the Lunar Night
25 May 2026
Webinar Series – Episode 4 | Presented by Scott Edwards
This fourth instalment in our entX webinar series builds on the previous session on GenX and deep dives into our Radioisotope Heating Unit (RHU). In this second Space and Defense episode, Scott Edwards explores one of the most persistent challenges in lunar exploration: surviving the lunar night.
A single lunar day-night cycle spans approximately 28 Earth days, with around 14 days of continuous darkness. During that period, surface temperatures plummet to approximately −190°C. At those extremes, batteries fail, electronics shut down, and most payloads are effectively lost. The result is a hard ceiling on mission duration: 10 to 14 days, then termination.
The entX Radioisotope Heating Unit (RHU) is engineered specifically to break through that ceiling.
Continuous Heat, Not Stored Energy
Unlike battery-based thermal systems, the RHU generates heat continuously through radioisotope decay. This heat maintains critical systems within their operational temperature range throughout the lunar night. The goal isn't to power the system, it's to keep it alive.
A Commercially Deployable Approach
What sets the entX RHU apart is our approach to isotope selection and system architecture. We avoid plutonium-based systems, which are scarce, heavily regulated, and commercially inaccessible. Instead, we leverage isotopes from established nuclear medicine supply chains, significantly reducing regulatory friction and enabling genuine scalability.
This isn't just about technical feasibility. It's about making RHUs commercially deployable.
From Days to Months
The mission impact is substantial. With RHU integration, we move from single lunar day missions to potential durations of months or even beyond a year. That shift fundamentally transforms mission economics and architecture.
You're no longer designing for survival. You're designing for persistence.
Validation and Flight Path
The entX team has developed a 3U lunar payload demonstrator incorporating the RHU, thermal switch, and thermal management system. The radioisotope fuel was created at ANSTO's OPAL nuclear reactor in Sydney, confirming our simulations and thermal studies. The system has undergone extensive testing; ballistics, thermal vacuum, vibration, and durability assessments.
Thermal modelling demonstrates survivability through up to six lunar nights. That's a significant step-change from the current 10–14 day limitation.
Working With Industry
We're collaborating with lunar lander companies and payload developers including ispace (Japan) and Australia's Fleetspace. Alongside the Australian Space Agency and the South Australian Government, we've completed detailed engineering feasibility studies confirming RHU viability for lunar night survival.
Beyond technical validation, these studies demonstrate direct commercial value: incorporating our RHU reduces launch mass and saves on the order of US$1–2 million compared to battery-based heating solutions.
Path to Flight Heritage
entX is progressing toward flight heritage through a US-based suborbital launch with payload recovery. Critically, we're undertaking the Nuclear Flight Safety process through a US national laboratory, the same facility that has assessed NASA's plutonium-based RTGs.
No private company has successfully completed this process to date. We intend to be the first.
Scalable Architecture
The RHU scales across mission requirements. We've assessed configurations from sub-watt through to 10-watt systems, supporting everything from small payloads to lander subsystems. At higher power levels, we're seeing mass reductions of 2–5× compared to battery heating solutions.
The takeaway is simple: the RHU doesn't just extend missions, it enables entirely new mission architectures.
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