The New Gravitational wave Observatory (NGO) mission will employ three spacecraft deployed in a V configuration with an arm length of 109 metres, positioned in heliocentric, Earth trailing orbits (HETOs) with the plane of the constellation inclined at 60° to the ecliptic. Gravitational waves will be detected by measuring changes in path length between free falling test masses housed in each of the spacecraft to picometre accuracy.
The selection of the operational orbits for NGO is influenced by a number of drivers:
- the requirement for a benign environment for the payload; minimisation of non-gravitational perturbations to allow accurate micro-propulsion control;
- the thermal character of the orbit has to be stable, to avoid a widely varying thermal environment or thermal shocks;
- the orbit must allow the quasi-static equilateral triangular constellation to be maintained without active control;
- distance from the Earth must be accounted for by the communications subsystem design and the requirement is to not exceed absolute distances between any spacecraft and Earth of 7.5 × 107 kilometres.
Selecting HETOs represents a good compromise between the various drivers.
The spacecraft at the apex of the 'V' is referred to as the 'Mother' spacecraft; those at the ends of the arms are 'Daughter' spacecraft. The mission will be launched by two Soyuz vehicles, one carrying the Mother spacecraft, the other the two Daughter spacecraft. Each spacecraft will be equipped with a propulsion module that will manoeuvre it during a 14-month transfer to its operational orbit. Once on orbit, the propulsion modules will be separated to ensure that they do not disturb the payload.
Following commissioning of the spacecraft systems and payloads, science observations will begin. After transfer and commissioning the operational phase of the mission will last for two years, with the consumables and orbit design allowing the possibility of an additional four years of operations.