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The description on its file description page there is shown below.
This image upscaled image with terrible compression artifacts. If a higher-quality image is available, please consider replacing this one; otherwise, a replacement under a free license should be found or provided.
The factual accuracy of this illustration is disputed. The grid representing the gravitational field/potential or space-time curvature is obviously qualitatively wrong (looks like a Gaussian instead of power-law).
Summary
DescriptionGPB circling earth.jpg
Artist concept of Gravity Probe B orbiting the Earth to measure space-time, a four-dimensional description of the universe including height, width, length, and time.
The NASA website hosts a large number of images from the Soviet/Russian space agency, and other non-American space agencies. These are not necessarily in the public domain.
The SOHO (ESA & NASA) joint project implies that all materials created by its probe are copyrighted and require permission for commercial non-educational use. [2]