SDO | Solar Dynamics Observatory - Specifications
SDO SPECIFICATIONS
This section provides details about the SDO spacecraft, when it will be launched, and SDO's planned orbit. Please note that details in the design will change as the mission matures.
The science of the Solar Dynamics Observatory will be performed on a spacecraft that allows both nearly continuous observations of the Sun and a science data downlink rate over of 100 Megabits per second (Mbps). These two requirements determined the orbit and spacecraft design as well as the definition of the SDO Mission. SDO Mission FactSheet
Satellite
- 3-Axis stabilized & robust spacecraft.
- Launch mass of 3100 kg (weight of 6800 lbs); 270 kg payload, 1400 kg fuel.
- Spacecraft is 2.2 x 2.2 x 4.5 m, solar panels are 6.5 m across when extended.
- Solar panels cover an area of 6.6 m², producing 1450 W of power. The homeplate shape prevents the solar panel from blocking the high-gain antennas.
- Science data is sent to the ground at a rate of ~130 Mbps on a continuous, high rate data stream at a Ka-Band frequency of ~26 GHz.
Launch
- SDO will be ready in December of 2008 for a launch on an Atlas V from SLC 41 at Cape Canaveral.
- The observatory will be delivered into a geosynchronous transfer orbit (GTO) by the Atlas V. SDO's propulsion system will then perform a circularization maneuver to boost the spacecraft into geosynchronous orbit (GEO).
- SDO's main engine is a bi-propellant system using monomethyl hydrazine (MMH) fuel and nitrogen tetroxide (NTO) oxidizer. Thrusters using the same fuel and oxidizer mix will keep SDO in the correct orbit during the mission.
Orbit
- The rapid cadence and continuous coverage required for SDO observations led to placing the satellite into an inclined geosynchronous orbit. This allows for a nearly-continuous, high-data-rate, contact with a single, dedicated, ground station.
- Nearly continuous observations of the Sun can be obtained from other orbits, such as low Earth orbit (LEO). If SDO were placed into an LEO it would be necessary to store large volumes of scientific data onboard until a downlink opportunity. The large data rate of SDO, along with the difficulties in managing a large on-board storage system, resulted in a requirement of continuous contact.
- The disadvantges of this orbit include higher launch and orbit acquisition costs (relative to LEO) and eclipse (Earth shadow) seasons twice annually, During these 2-3 week eclipse periods, SDO will experience a daily interruption of solar observations. There will also be three lunar shadow events each year from this orbit.
- This orbit is located on the outer reaches of the Earth's radiation belt where the radiation dose can be quite high. Additional shielding was added to the instruments and electronics to reduce the problems caused by exposure to radiation. Because this a a Space Weather effect, SDO is affected by the very processes it is designed to study!
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