fuel, the nitrous oxide oxidiser is handled as a bulk commodity and pumped into the spacecraft's oxidiser tank in the field. Tier One therefore has a mobile delivery system for nitrous oxide, which they call MONODS (mobile nitrous oxide delivery system). The MONODS is built on an open trailer, which can be carried by road in conventional manner. It consists principally of a tank, a temperature control unit, and a generator to power the temperature control unit. The nitrous oxide is stored at room temperature, at a pressure of . The MONODS is refilled from a commercial supplier, which uses tankers and delivers the nitrous oxide at about and . The MONODS heats the nitrous oxide to room temperature, increasing its pressure. Propulsion testing Tier One has a mobile thrust test stand, known as the test stand trailer (TST). The advantage of making it mobile is that all the mounting and instrumentation work can be done in the hangar, so that at the test site all that needs to be done is to fill the oxidiser tank (from the MONODS) and conduct the firing. The test stand replicates the essential structural components of the spacecraft. It has an oxidiser tank and associated fittings identical to the one used in flight. This means that the motor test also automatically performs appropriate vibration, stress, and heat tests of the spacecraft structure. The crew cabin, however, is not replicated. For ground-based thrust tests, a rocket nozzle with an expansion ratio of 10:1 is used, differing from the 25:1 nozzle used at altitude during actual flight. The test stand is instrumented to record not only thrust but also side force and temperature and strain experienced by components. Data is recorded on a computer in a bunker at the test site. The data acquisition computer is remotely controlled from mission control. Flight simulator The SpaceShipOne flight simulator consists of a simulator program and a cockpit. The flight simulator program aims to accurately simulate SpaceShipOne's behaviour under any circumstances and in all phases of flight. Rather than having a model of SpaceShipOne's overall flight behaviour, it uses computational fluid dynamics to model the air around the craft. It calculates the aerodynamic and other forces operating on the craft, taking into account the positions of its control surfaces. This simulation is based on the computer modelling that was used during the design process and refined using data