BAE Systems will invest in UK technology firm Prismatic's development of a solar-powered high-altitude, long-endurance (HALE) unmanned air vehicle.

Prismatic has been working since 2016 on the 35m (115ft)-wingspan UAV – dubbed PHASA-35, which stands for persistent high-altitude solar aircraft – and last year flight tested a quarter-scale model of the design.

BAE Systems says it will invest in the aircraft's development and flight testing, which is scheduled to begin in 2019.

"We were keen to invest in the programme as part of our long-term strategy to explore new technologies and solutions in air and space," says Michael Christie, the manufacturer's strategy director for air systems.

Financial details for the partnership have not been disclosed.

Prismatic founder and managing director Paul Brooks says it is "great to have the support of a world-leading technology company like BAE Systems". He describes the aircraft as a "proven, cost-effective and reliable system".

Engineers predict that the UAV will be able to continuously operate at altitude as a pseudo-satellite for up to a year before requiring maintenance. It is designed to provide surveillance and communications functions.

The aircraft will weigh 150kg (330lb) and have two electrically driven propellers that will be powered by solar panels during the day and by batteries at night.

Prismatic says such UAVs represent a "significantly cheaper alternative to conventional satellite technology". Airbus and Facebook are pursuing similar HALE projects with their respective Zephyr and Aquila programmes.