, Md. — With a fully assembled spacecraft ready to enter environmental testing by spring, engineers at NASA’s Goddard Space Flight Center here are feeling confident that the $700 million Solar Dynamics Observatory (SDO) they have been building for the past three-and-a-half years will be ready to launch by December.

The team’s confidence is a welcome change from last summer, when Goddard officials went to NASA headquarters to request more time to get the spacecraft to the launch pad. The SDO’s launch was delayed three months, to Dec. 1, adding about 2 percent to a price tag that otherwise has not changed much since development began.

Liz Citrin, the NASA SDO project manager, said it became apparent last summer that making the originally scheduled Aug. 30 launch readiness date would be difficult given the number of issues the team still had left to address.

“Across the board we experienced challenges implementing the new technologies, from the instrument detectors all the way down to the ground receivers,” she said.

Although the SDO is regarded by scientists as the successor to the

12-year-old Solar and Heliospheric Observatory (SOHO) – which is perhaps best known for its stunning, false-color, full-view images of the sun –


is no mere replacement.

While fewer in number than those aboard SOHO, the SDO’s instruments are more advanced and designed to operate 24 hours a day, seven days a week, sending down a steady stream of significantly higher-resolution images. Brent Robertson, the SDO observatory manager at Goddard, said the satellite will be sending down about 1.5 terabytes of data per day.

“It’s equivalent to sending down a [Hollywood] movie every six minutes,” Robertson said.

To catch all that data, NASA will rely on a pair of Ka-band antennas located at White Sands Missile Range in New Mexico. Citrin said the antennas are spaced about 5 kilometers apart, reducing the odds of the occasional fast-moving thunderstorm interfering with the SDO’s weather-sensitive transmission frequency.

The last of the SDO’s three main instruments, a suite of four telescopes known as the Atmospheric Imaging Assembly, arrived at Goddard in December. Built by the Lockheed Martin Advanced Technology Center in Palo Alto, Calif., the Atmospheric Imaging Assembly was a late substitution for another instrument NASA decided was not going to be ready in time. Despite starting development a year late, the Lockheed-led team caught up to the rest of the program, Citrin said, delivering a finished instrument within three months of the arrival of the first SDO instrument to come through the door – the Extreme Ultraviolet Variability Experiment built by the University of Colorado at Boulder.

With all three instruments in hand by mid December, the Goddard team was able to integrate the SDO’s instrument module with the spacecraft bus and celebrate the new year with a spacecraft that awaits only the installation of its newly arrived solar arrays. Robertson said Jan. 9 that the arrays were undergoing testing and would be installed in February. From there, the observatory will be thoroughly checked out before leaving its clean room for several months of environmental tests slated to begin in March with electromagnetic interference testing.

Dean Pesnell, the NASA

SDO project scientist, said he was looking for a fairly boring year of testing, with the spacecraft performing as expected every step of the way.

said the team has five weeks of slack built into the schedule to deal with any problems that could crop up between now and Dec. 1, when the SDO is supposed to be ready to lift off from Cape Canaveral Air Station in Florida. Whether the spacecraft will actually launch when ready, however, is another matter.

“We have a launch readiness date, not a reserved launch date,” said Rob Lilly, SDO deputy project manager. “The manifest is a little crowded, but fluid.”

The SDO, which has multiple launch opportunities per month, is vying for end-of-the-year range time against NASA’s Lunar Reconnaissance Orbiter, which is starting to come together in a neighboring section of Goddard’s Building 7, and a U.S. Air Force mission, Lilly said.

A United Launch Alliance Atlas 5 rocket is slated to launch the 3,200 kilogram SDO into a geosynchronous transfer orbit. From there, the spacecraft will use its onboard propulsion system – the first bi-propellant propulsion system built by Goddard – to circularize its orbit at 36,000 kilometers.

To the team’s evident pleasure, the integration work has gone smoothly, and many of the engineers that had been assigned to the propulsion system have moved over to help out with the Lunar Reconnaissance Orbiter. “The propulsion system was mated to the spacecraft bus one Saturday in October and it went just flawlessly,” Robertson recalled. “So we are really happy with that.”