Siân Cleaver

Siân Cleaver is an engineer at Airbus Defence & Space, the prime contractor for the European Service Module (ESM) that provides propulsion, power, and life support for the Orion spacecraft. On Day 8 of Artemis II, Cleaver gave the first public quotes from an ESM contractor engineer during the active flight, telling Nature that the translunar injection burn performed "perfectly to plan" and that the precision had eliminated several of the planned trajectory correction manoeuvres.

The European Service Module is a European contribution to Artemis built under an ESA contract awarded to Airbus in 2014. It is derived from the Automated Transfer Vehicle (ATV) that supplied the International Space Station between 2008 and 2015. Each ESM costs approximately €200 million and contains four main engines, 33 thrusters, solar arrays generating 11 kilowatts of power, and life support consumables. Airbus is contracted to build a total of six ESMs for the Artemis programme. The ESM-2, used on Artemis II, was delivered to Kennedy Space Center in late 2023.

Cleaver's confirmation that ESM performance exceeded conservative pre-flight predictions strengthens ESA's negotiating position ahead of the June 2026 Council meeting, where Director General Josef Aschbacher must present a Gateway recovery plan following the programme's cancellation. ESA faces the question of what Artemis contributions it can offer without a destination beyond lunar orbit, and demonstrated hardware reliability is among the few unambiguous assets it brings to that renegotiation.