Monthly Newsletter

June 2003

Mission Update –
Heading towards six months since launch, SORCE continues to make excellent daily solar observations, with nightly stellar observations for calibration. Scientists and engineers continue to verify the instrument calibrations and data processing software. As of the end of May, measurements are being validated, and some preliminary data are being distributed to the science community through the Goddard Space Flight Center DAAC.

Spacecraft and Instrument Status –
All spacecraft systems continue to perform exceptionally well. The spacecraft is in its nominal Sun pointing mode, and is making two scheduled contacts each day. There are no plans to change spacecraft operations in the near future.
The calibration process continues on all of the SORCE instruments, which are currently operating in normal mode. The preliminary data products generated are meticulously reviewed, and compared to earlier instrument expectations. The data are also compared with observations of similar instruments on other spacecrafts currently operating. After investigating the similarities and anomalies, scientists work towards data validation by improving data processing code.
The weekly SORCE Status Report is available on the SORCE website at It summarizes the spacecraft activity, ground contacts, the instrument measurements, spacecraft and instrument planning, and data processing.

A Closer Look at the SOLSTICE
Instrument –

This newsletter explores the preliminary data results from the SOLSTICE (Solar Stellar Irradiance Comparison Experiment) instruments. There are two identical SOLSTICE instruments onboard SORCE. They each measure ultraviolet solar and stellar radiation from 115 to 320 nm. SOLSTICE A and B are unique in that they also measure the irradiances from a group of 18 bright blue stars for calibration purposes. The intrinsic variability of these stars is insignificant making this precise calibration possible.

The SOLSTICE instruments are performing very well, collecting precise radiation measurements. Scientists are comparing the SOLSTICE measurements from SORCE to the measurements collected from the SOLSTICE instrument on board the UARS experiment, launched in 1991. The results are very similar, but the SORCE SOLSTICE has a better spectral resolution at all the wavelengths. Following are two plots comparing SORCE and UARS SOLSTICE measurements.

Click on image for larger view
This plot shows that the wavelength measurements from the SORCE SOLSTICE (black line) extend to the left much further than the UARS SOLSTICE (red line). SORCE SOLSTICE wavelength range in FUV extends down to 115 nm.

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