Double Star Equatorial and Polar
21 Sep 2009



Double Star, a mission made of two satellites, one in a polar orbit and one in an equatorial orbit, studies the effects of the Sun on Earth.

Two satellites in the Earth's orbit.

​​​​​Artist's impression of Double Star orbiting the Earth

Credit: ESA
RAL Space Involvement

EPOS (European Payload Operation Service)

Solar Terrestrial Physics

Main Objectives
To study the effects of the Sun on the Earth's environment

Launch Date
Equatorial: 29 Dec 2003​
Polar: 26 Jul 2004


Further project information 

​Double Star European Payload Operations Service  

The European Payload Operations Service (EPOS) was set up within RAL Space to support the ESA Project Science Team, the European instrument teams, and the Chinese Mission Operations Centre. EPOS designed, developed, implemented, tested, and now operates the system and tools required to support DSP science operations under contract to ESA. Double Star celebrated its first year of combined operations on 17 August 2005.

TC-1 orbits the Earth about six times in one week and TC-2 orbits the Earth about fifteen times in one week. The week is the basic unit for EPOS's operational role, the so-called Planning Period. The first part of EPOS's operational role is to accept, validate and ingest weekly segments of the overall science plan, called the Master Science Plan (MSP), produced by the Chinese Center for Space Science and Applied Research (CSSAR) in Beijing.

The second part of EPOS's operational role is the generation of a consolidated payload command schedule from the MSP segment, a process which has several steps. This is a complex event scheduling task, requiring the application of complex instrument-specific rules and constraints to the framework provided by the MSP. RAL Space has developed EVHA (EVent Handler and Associator) a programming language which allows the easy implementation, update and execution of complex conditional statements. EVHA allows EPOS to efficiently and robustly, produce instrument-specific command schedules which are then iterated with the instrument scientist teams. EPOS actually works eight or more weeks ahead of command execution, which means it is dealing with several Planning Periods at any one time. RAL Space has developed a GUI to support and control this complex set of operational activities. The process culminates in the production of a consolidated payload command schedule covering one week, which is then delivered to CSSAR.

The third part of EPOS's operational role is the provision of an operational website which supports the European instrument science teams and ESA in their planning.

For more information please contact: RAL Space Enquiries