UK seeks low-cost engines for aerial effectors

The UK is seeking low-cost, single-use engines that can be used for current and future air systems, munitions, and one-way capabilities.  

According to an announcement by the UK Ministry of Defence (MoD) on 1 June, the country requires platforms that “bridge the performance gap” between hobbyist, model engines and more exquisite systems.  

The announcement says that an invitation to tender (ITT) was due for release the week commencing 15 June, however this has not yet been made publicly available. Evaluations from the ITT are expected to consider the design, development, and ground testing of prototype engines.  

The requirement is part of the second version of Project ‘Callisto’, the original version of which was launched in June 2025. The initial project set out to identify a low-cost propulsion system for a long-range one-way effector to be developed under 2024’s Project ‘Brakestop’. However, the MoD emphasises that this new Project Callisto is now separate from Brakestop.  

What capabilities are required?  

According to the MoD, the ITT will run as two separate lots, named Callisto Light and Callisto Heavy.  

Callisto Light requires engines with a thrust class of 750N, while Callisto Heavy requires a class of 1.75-2kN. These measurements will be considered as the maximum continuous thrust output under static, sea-level atmospheric conditions.   

Capable of operating on either aviation turbine fuel or diesel, both types of engines must have a minimum life of 10 hours. Additionally, from stationary positions, Callisto Light engines should be able to accelerate to over 95% maximum thrust in under three seconds, while Callisto Heavy engines must do so in under five.  

The MoD stipulates that the engines must be suitable for rapid design iteration, allowing any issues to be addressed during testing and should be adaptable to the requirements of future platforms.  

Additionally, the engines must be optimised for scaled production using common manufacturing methods and facilities in the UK. 

Entering the competition  

Companies will be able to apply for one or both lots, with each treated as separate submissions.   

The cost per unit for Callisto Light engines will be GBP20,000 or under, while Callisto Heavy engines will be GBP50,000 or under.  

As part of the ITT evaluation, paper-based down selection is projected for the week of 13 July, with face-to-face pitches anticipated for the week of 27 July. Validation and verification visits to industry partner facilities are expected in August.

Independent testing is estimated to take place from March 2027.