Government: Space Science Astronomy: Solar Observatory
Inclined Geostationary orbit on Mar 12.28:
Perigee / Apogee
35362 x 35616 km
NASA Goddard Space Flight Center
NASA Goddard Space Flight Center
Mass at launch
box + 2 panels
4.5 long, 2.22 side
HMI, AIA, EVE
2 panels, span 6.25
A technician puts the finishing touches on NASA's Solar Dynamics Observatory. Credit: NASA
SDO is the lead mission in NASA's Living With a Star (LWS) program. It
will study the Sun at optical, ultraviolet and soft X-ray wavelengths from an inclined geosynchronous Earth orbit. The spacecraft was built in-house
at NASA-Goddard; the mission is managed by GSFC and its control center is located there. What's new about SDO is that it will image the whole sun at
very high cadence - typically returning new high resolution solar images every ten seconds, allowing the rapid evolution of solar activity to be
studied. SDO will replace many of the capabilities of the elderly SOHO spacecraft which has been monitoring the Sun for 15 years.
SDO consists of a box-shaped service module with a GSFC-developed bipropellant propulsion system and a high gain antenna, topped by two tapered
solar array wings and a science instrument module. The spacecraft has a dry mass of 1650 kg; at launch it also carries a propellant load of 1450 kg
for its main bipropellant Aerojet/Redmond R4D apogee thruster, which has a thrust of 445 Newtons. The propulsion system also contains 8 smaller 22N
thrusters for attitude control.
SDO will be launched from Space Launch Complex 41 at Cape Canaveral by a Lockheed-Martin Atlas V 401 model space launch vehicle, serial
number AV-021, with a CCB first stage powered by one RD-180 engine, a single-engine RL-10A-powered Centaur second stage, and a 4-m Large Payload
Fairing. The first stage will separate 4 minutes 9s after launch and the first Centaur burn will last from T+4:19 to T+15:17. SDO and Centaur AV-021
will then be in an elliptical parking orbit. At T+1 hour 42 min 43s the Centaur will reignite for 3 min 15 s to reach a 2500 x
35355 km x 28.5 deg transfer orbit. SDO and AV-021 will separate at T+1h
48 min 46s, and over a period of several days the observatory will raise its orbit to geosynchronicity.
After a total of 4 main engine firings, the spacecraft will be on station in view of the TDRS main ground station complex at White Sands.
SDO carries three main instruments - AIA, EVI and HMI, comprising a total of six imaging telescopes, three spectrographs and a photometer.
AIA, the Atmospheric Imaging Assembly (Lockheed/Palo Alto, A. Title, with telescopes built at the Smithsonian Astrophysical
Observatory) will make temperature maps of the solar corona with 10
second cadence. The four 0.20m aperture normal-incidence EUV telescopes each have their 4096x4096 pixel CCD focal planes divided in two, with different narrow band filters on each half. The filters are centered on spectral lines which provide temperature diagnostics.
- AIA Telescope 1 sees 335A and 131A; (1 Angstrom = 0.1 nanometres).
- AIA Telescope 2 sees 211A and 193A;
- AIA Telescope 3 sees 171A and a half-aperture measuring the UV and optical at 1600A (Carbon IV), 1700A (UV continuum) and a broad filter centered on 4500A (optical continuum).
- AIA Telescope 4 sees 304A and 94A.
AIA sees the whole solar photosphere in its 41 arcmin field of view and has a spatial resolution of 0.6 arcseconds. It's this instrument that will provide the mission's most photogenic data.
EVE, the EUV Variability Experiment (Colorado/LASP, Woods) measures the EUV irradiance using its ESP, MEGS-A and MEGS-B spectrographs and the MEGS-SAM and MEGS-P instruments. EVE doesn't have spatial resolution, it just sums all the light from the Sun to make spectra.
- ESP (EUV Spectro-Photometer) is a non-focussing
transmission grating spectrograph with 4 bands
covering the 170-380A EUV range plus a zero order flux measurement in
the 1-70A (0.2-12 keV) soft X-ray band, with 0.25 second cadence.
- MEGS-A, the first part of the Multiple EUV Grating Spectrograph, covers
the 50-370A EUV range with 1A resolution and 10s cadence on a 2048 x
1024 pixel CCD. It is a grazing incidence spectrograph.
- MEGS-B is a normal incidence grating spectrograph for
the 350-1050A FUV range; it also includes a photodiode, MEGS-P,
for a measurement of the 1215A Lyman alpha line UV flux
- MEGS-SAM is a pinhole camera for 1-70A X-ray event data. It shares the MEGS-A
detector but has a separate aperture.
A version of EVE was test-flown on rocket NASA 36.233US on 2006 Oct 28, and further rockets will be flown during SDO's operation to help calibrate the instrument's accurate measurement of total solar output.
HMI, the Helioseismic and Vector Magnetic Imager (Stanford, Scherrer) is a single 0.14m-aperture telescope with a tunable filter and two 4096 x 4096 CCDs.
It observes a 50A bandpass around 6768A in the optical, which contains a Ni I absorption line. Measurements of the Doppler shift and Zeeman splitting of this line generate maps of solar surface oscillations and the solar magnetic field.
The field of view covers the whole solar disk with 1 arcsecond resolution.
Other solar space observatories currently in operation include Hinode, TRACE, RHESSI, SORCE, STEREO A/B and the SXI imager on GOES 14.
SDO was launched on Feb 11, 2010 aboard Atlas mission AV-021. AV-021 entered a 175 x 3706 km x 28.7 deg parking orbit and then a 2480 x 35369 km x 28.6 deg
transfer orbit. SDO separated from the Centaur and will now use its onboard R4D thruster to raise the orbital period from 11 hours to 24 hours.
AV-021 vented its remaining propellant, leaving it in a slightly lower 2397 x 33517 km x 28.4 deg orbit.
SDO reached geosynchronous orbit at 102.9W on Mar 18, 2010. Orbit is now 35781 x 35790 km x 28.1 deg, and SDO's telescope doors are open to the
Sun with all instruments undergoing checkout and so far looking healthy.