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About the SDO Mission


(Click on each instrument to view details)

Spacecraft mass at launch (total) : 3200 kg (payload 270 kg; fuel 1400 kg).
Length overall (along the Sun-pointing axis): 4.5 m; each side is 2.22 m.
Overall span (solar panels extended): 6.25 m.

SDO: The Solar Dynamics Observatory is the first mission to be launched for NASA's Living With a Star (LWS) Program, a program designed to understand the causes of solar variability and its impacts on Earth. SDO is designed to help us understand the Sun's influence on Earth and Near-Earth space by studying the solar atmosphere on small scales of space and time and in many wavelengths simultaneously.

SDO's goal is to understand, driving towards a predictive capability, the solar variations that influence life on Earth and humanity's technological systems by determining

How the Sun's magnetic field is generated and structured
How this stored magnetic energy is converted and released into the heliosphere and geospace in the form of solar wind, energetic particles, and variations in the solar irradiance.

Launch

SDO was launched 10:23am EST on February 11, 2010 on an Atlas V from SLC 41 at Cape Canaveral.


Science

SDO will study how solar activity is created and how Space Weather comes from that activity. Measurements will be made of the interior of the Sun, the Sun's magnetic field, the hot plasma of the solar corona (the outermost layer of the solar atmosphere), and the irradiance that creates the ionospheres of the planets.

SDO will help us to understand the how and why of the Sun's magnetic changes. It will determine how the magnetic field is generated and structured, and how the stored magnetic energy is released into the heliosphere and geospace. SDO data and analysis will also help us develop the ability to predict the solar variations that influence life on Earth and humanity's technological systems.

SDO will measure the properties of the Sun and solar activity. There are few types of measurements but many of them will be taken. For example, the surface velocity is measured by HMI. This data can be used for many different studies. One is the surface rotation rate, which must be removed to study the others. After subtracting the rotation, you have the oscillation and convective velocities. The latter look like billows of storm clouds covering the Sun. Hot gas moves outward at the center of the billows and downward at the edges, just like boiling water. By looking at these velocities you can see how sunspots affect the convection zone. By looking at a long sequence of data (more than 30 days), you see the oscillations of the Sun. These patterns can be used to look into and through the Sun.

Mission Science Objectives:

The scientific goals of the SDO Project are to improve our understanding of seven science questions:
  1. What mechanisms drive the quasi-periodic 11-year cycle of solar activity?
  2. How is active region magnetic flux synthesized, concentrated, and dispersed across the solar surface?
  3. How does magnetic reconnection on small scales reorganize the large-scale field topology and current systems and how significant is it in heating the corona and accelerating the solar wind?
  4. Where do the observed variations in the Sun's EUV spectral irradiance arise, and how do they relate to the magnetic activity cycles?
  5. What magnetic field configurations lead to the Coronal Mass Ejections, filament eruptions, and flares that produce energetic particles and radiation?
  6. Can the structure and dynamics of the solar wind near Earth be determined from the magnetic field configuration and atmospheric structure near the solar surface?
  7. When will activity occur, and is it possible to make accurate and reliable forecasts of space weather and climate?

Instruments

SDO will fly three scientific experiments:

  • Atmospheric Imaging Assembly (AIA)
  • EUV Variability Experiment (EVE)
  • Helioseismic and Magnetic Imager (HMI)

Each of these experiments perform several measurements that characterize how and why the Sun varies. These three instruments will observe the Sun simultaneously, performing the entire range of measurements necessary to understand the variations on the Sun.

This set of instruments will:

  1. Measure the extreme ultraviolet spectral irradiance of the Sun at a rapid cadence
  2. Measure the Doppler shifts due to oscillation velocities over the entire visible disk
  3. Make high-resolution measurements of the longitudinal and vector magnetic field over the entire visible disk
  4. Make images of the chromosphere and inner corona at several temperatures at a rapid cadence
  5. Make those measurements over a significant portion of a solar cycle to capture the solar variations that may exist in different time periods of a solar cycle

Specs

SDO is a Sun-pointing semi-autonomous spacecraft that will allow nearly continuous observations of the Sun with a continuous science data downlink rate of 130 Megabits per second (Mbps). The spacecraft is 4.5 meters high and over 2 meters on each side, weighing a total of 3100 kg (fuel included). SDO's inclined geosynchronous orbit was chosen to allow continuous observations of the Sun and enable its exceptionally high data rate through the use of a single dedicated ground station.

I. 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.

II. Launch

  • SDO was launched 10:23am EST on February 11, 2010 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.

III. 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 Space Weather effect, SDO is affected by the very processes it is designed to study!

Additional Reading

      SDO Mission FactSheet (pdf)

      SDO Mission & Launch Overview (pdf)

      SDO Guide (pdf)




  Information Source: sdo.gsfc.nasa.gov   

  Image Credits: NASA/Goddard

2010 Stanford SOLAR Center