The US Air Force will consider a supersonic engine among three propulsion options now under review for the long range standoff (LRSO) missile, according to an acquisition notice released on 26 February.

The LRSO is expected to replace the Boeing AGM-86 air launched cruise missile, a subsonic weapon powered by a Williams F107 turbofan engine.

The USAF is considering two subsonic engine options – a derivative of an existing engine with 5% greater fuel efficiency and an advanced engine offering up to 20% better fuel efficiency, according to the request for information released by the LRSO branch of the Air Force Life Cycle Management Center.

A third option under review is a supersonic engine that would be sized comparably to “existing small core expendable engines”, the acquisition document says.

In the past, the USAF has said the LRSO would be a stealthy cruise missile, but never specified whether the weapon would fly at speeds below Mach 1.0, between M1.0 and 5.0 (supersonic) or even faster (hypersonic).

The same document lays out the USAF’s plans for developing and producing the LRSO. At least five engines will be delivered to support a technology maturation and risk reduction phase. Another 89 engines will support an engineering and manufacturing development phase of the programme. Up to 1,000 engines will ultimately be needed for a five-year production run, the request for information says.

The USAF has proposed to accelerate the LRSO acquisition programme by two years in the fiscal year 2016 budget request submitted to Congress last month.