Mission Characteristics

Mission Operations

Mission Characteristics

EQUATOR-S has been launched into a 200 x 35800 km Geostationary Transfer Orbit (GTO) as an Auxiliary Payload on an Ariane-4 from Kourou on 2 December 1997. After separation from the launch vehicle (23 minutes after lift-off) and spin-up to 50 rpm, EQUATOR-S fired its own solid-propellant kick-motor (a Thiokol Star 13A) on 11 December 1997 and propelled itself into a 500 x 67300 km, 22.3 hours near-equatorial orbit. Apogee is initially located near local noon, and will then precess by almost 2 hours local time every month. Magnetorquing will slowly (within 150 days) erect the spin-axis and bring the spinrate to 40 rpm. The anticipated mission duration is two years.

Displays of the EQUATOR-S orbit and those of the other IASTP spacecraft can be obtained from NASA's SSCWeb.

Table 3 lists some of the key mission characteristics.

Mission Operations

EQUATOR-S is operated by the German Space Operations Center (GSOC) of the DLR in Oberpfaffenhofen near Munich that is also responsible for Mission Analysis. To reduce cost, the mission is supported at a level of 3 hours a day.

Command uplink is via a 15-m antenna dish. Telemetry downlink is either via the 15-m dish or via a 30-m dish that allows 262 kbps telemetry dumps at high altitudes. The antennas are all located at Weilheim, Germany. GSOC performs health and safety checks of spacecraft and science instruments, command uploads, mass-memory dumps, attitude checks, orbit determination, and generates Master Data Records on CD-ROMs for distribution to the Data Center at MPE in Garching.

The spacecraft can hold up to 1024 time-tagged commands that control execution of spacecraft and payload operations. A new set of time-tagged commands is uploaded every third or fourth day during a regular real-time contact.

As the capacity (192 MByte) of the mass memory limits on-board data storage to 13.5 hours in LR telemetry and 3.4 hours in HR telemetry, only a portion of each 22-hour orbit can be covered. A Master Science Plan (MSP), generated by the Science Team, specifies in advance where along each orbit (and at what TM-rate) science data are to be collected, and in which modes the instruments are to be operated.

(Example of routine operation)