Mission Operations

Lunar approach and landing scenario

Arecibo Observatory/Cornell Univ. (courtesy D. Campebell)

The planned EuroMoon 2000 mission sequence in lunar orbit consists of:

• Injection of the Orbiter + Lander composite spacecraft into polar Low Lunar Orbit (LLO) at an altitude of 200 km (possibly 500 km).

• Separation of the Orbiter from the Lander. Spacecraft commissioning (three weeks) and Sun-pointing attitude acquisition.

• Preliminary gravity-field determination in the 200 km orbit by tracking the orbit from Earth (for deciding at what altitude to operate the gravity experiment), and preliminary low-resolution mapping (one month).

• Lowering of the Orbiter's altitude to 100 km, with nadir- pointing attitude, whilst the Lander remains parked at the original 200 km altitude, in a Sun-pointing attitude.

• Release of a subsatellite into a 'frozen' orbit at about 100 km altitude.

• Gravity experiment lasting two to three months, depending on the subsatellite's lifetime. The Orbiter should not be manoeuvred during this experiment (thrusters used as little as possible), which implies that the operation of other experiments needing precise pointing is temporarily impaired. The microwave instrument, for example, may be operated during this phase, but not the high-resolution camera.

• High-resolution imaging from the Orbiter for about one month, during which the necessary sophisticated image processing would be conducted back on Earth. In principle, landing may be attempted during any orbit, but communications constraints will determine the duration of this period in terms of phasing requirements.

• Descent and touchdown of the Lander. This may occur as soon as processed gravity-field and high-resolution imaging data are available and the communications constraints are satisfied.

The duration of the Lander's surface operations is, in principle, not limited (permanent sunlight). The primary mission, however, may last in the order of four months, whilst the Orbiter's global mapping and other science operations will continue for a further 8 9 months.

An alternative mission concept would use the Lander and the Orbiter as satellite and subsatellite, respectively, for the gravity experiment (although this has not yet been analysed in detail).