Mission Description and Operations
The New Gravitational wave Observatory (NGO) mission will employ three spacecraft deployed in a 'V' configuration with an arm length of 106 kilometres, positioned in heliocentric, Earth trailing orbits (HETOs). 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 three spacecraft will be launched using two Soyuz vehicles. One will carry the two 'Daughter' spacecraft and their propulsion modules to an orbit with an apogee of
The Daughter spacecraft will be launched first; the optimum launch window lasts for six continuous months per year, with year-round launches possible by incurring a ΔV penalty of 100 ms-1. Optimal launch timing for the Mother spacecraft is six months after the daughters, but it could be launched up to 12 months after the daughters with extra propellant supplies in its propulsion module allowing it to 'catch up' with a
The selection of the operational orbits for NGO is influenced by a number of drivers:
Selecting HETOs represents the best compromise between the various drivers. Slow-drift, Earth-trailing orbits have been selected, with the plane of the constellation inclined at 60° with respect to the ecliptic and the three spacecraft 'cartwheeling' annually around the centre of the constellation - a configuration that has been shown to be stable for at least six years. At the end of the transfer phase, the orbits will be 10° behind Earth, giving a nominal ground-to-constellation distance of 2 × 107 kilometres. After four years, the planned drift will have increased the ground-to-constellation distance to 5 × 107 kilometres; this distance further increases to 6.5 × 107 kilometres after six years. This distance poses a limit to the full bandwidth telemetry download to ground. If the mission were to be extended beyond this time, a reduction in the amount of data downloaded would become necessary.
The operational phase of the NGO mission will be divided into the following phases:
The NGO ground segment will comprise the Mission Operations Centre (MOC), based at ESA's European Spacecraft Operations Centre (ESOC), and the Science Ground Segment (SGS). The latter is composed of the Science Operations Centre (SOC, operating from ESA's European Space Astronomy Centre (ESAC)) – responsible for coordinating the development of the science operations ground segment and its operations to optimise the scientific return of the NGO mission; the Science Data Processing Centre – responsible for generating and providing main science products to the SOC; and the Instrument Operations Teams – responsible for the payload-related activities to be performed during the operations.
Communication between the spacecraft and the ground station during the operational phase will use the ESA 35-metre antenna at Cebreros, Spain.
During the science operations phase, nominal communication is scheduled every second day to one of the three spacecraft. The nominal communication schedule will be superseded by an extended communication schedule in the case of, for example, an upcoming black hole merger event – which can be predicted with sufficient notice.
(For more detailed information about NGO mission operations please consult the NGO assessment study report (Yellow Book) - see link in right-hand menu.)