The UK’s Largest Nitrous Oxide Hybrid

Pulsar’s Origin

Pulsar is CUSF’s biggest engine yet. Conducted by a team of 30 undergraduates as a reaction to the failure of the off-the-shelf motor on Martlet III, the 18-month project to build a hybrid engine culminated in a successful hot fire test of Pulsar at Airborne Engineering Ltd in January 2019. The engine runs on a combination of Nitrous Oxide and High Density Polyethylene and during testing, delivered over 50,000 Ns of total impulse – proving it as the biggest Nitrous Oxide hybrid ever fired in the UK. Instead of continuing with integration onto Martlet IV for a launch to 20km, the team has decided to use the expertise gained and pursue more complex bipropellant engines as part of the space-shot Griffin Program.



Total Impulse


Firing Duration


The Oxidiser Tank

A 53 litre Nitrous Oxide tank designed for flight pressures of 45 bar, with pressure relief valves, burst discs and vent holes to eliminate BLEVE risk.

The Nozzle

An 80% bell nozzle machined from Y459 fine-grained Graphite fixed into position with a ceramic retainer ring.

The Injector

An impinging-jet injector to provide excellent Nitrous Oxide mixing when introduced into the chamber.

The Chamber

An aluminium casing lined with Tufnol for ablative cooling and protection from hot combustion gases.

The Fuel

Four sections of High-Density Polyethylene fuel grain act as the solid propellant for the hybrid mix.


The 2019 test of Pulsar at Airborne Engineering Ltd.

Behind the Scenes

Thorough analysis of the regression rates of HDPE allowed modelling of the motor burn in Python in preliminary design, while trajectory analysis using RASAero and CUSF’s CamPyRos was used for motor sizing.

Injector pressure drops were maintained above a threshold and an diffuser was included to eliminate flow reversal through the injector during chamber pressure oscillations.

Safety of our team while testing and firing Pulsar are of utmost concern and every precaution has been taken to ensure this. Appropriate recommendations following Nitrous Oxide handling were followed, as well as pressure vessel design to prevent BLEVE.

Instrumentation to monitor operation was used for engine shut-down outside nominal behaviour. Power failure, and chamber burn-through were also considered.

We would like to thank Airborne Engineering Ltd. for the gracious help in test firing Pulsar in 2019 – our Pulsar test campaign would not have been possible without them. We are incredibly proud to maintain a strong working relationship, with several of our alumni proceeding to Airborne after graduation.


All in One Engine Modelling

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Get in touch! Reach out to contact[at]cusf.co.uk to find out more.