NEAR Voyage 6: Earth Flyby

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Earth Swingby, A Dry Run For Eros:
January 23-26, 1998

By January 1998, NEAR had completed two-thirds of its journey to Eros. The mission engineers, programmers, planners, and scientists had characterized the instruments' and the spacecraft's performance during cruise and the Mathilde flyby. Now it was time for a dry run of operations at Eros, with all instruments on and taking measurements, and the spacecraft pointing them at their targets. Earth and the moon are perfect targets: because they are well understood, we had a "cheat sheet" for how the instruments' measurements should look.

To get its gravitational "kick" from Earth, NEAR swooped over Eurasia, following a track that took it low over Saudi Arabia. As NEAR headed out into the southern sky it looked back at Earth, imaging the South African coast, Antarctica and the Southern Ocean. Telescopic observers photographed and tracked the spacecraft as it sped though the sky.

Image of the region southwest of the Saudi Arabian capital of Riyadh,
taken from a range of 685 kilometers (430 miles) on January 23, 1998.

Image of coast of South Africa acquired by NEAR on January 23, 1998.

Image of Antarctica and the Southern Ocean, taken from a range
of 260,000 kilometers (160,000 miles) on January 23, 1998.

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Video of NEAR speeding though Earth's sky,
captured by a telescope on January 23, 1998.

Coordinated observations by the MSI imager and the NIS spectrometer provided a dress rehearsal for observations of Eros. In its first full-up in flight test, NIS returned accurate infrared spectra of Antarctic ice, as measured through Earth's murky atmosphere.

Location of measurements of Antarctica by NEAR's near-infrared
spectrometer (NIS) taken on January 23, 1998.

The spectrum of Antarctic snow taken by NEAR's near-infrared spectrometer (NIS) on
January 23, 1998. This NIS spectrum agrees closely with laboratory measurements
of ice particles, when adjusted for the murkiness of Earth's atmosphere at
infrared wavelengths. "A" denotes atmospheric features in the spectrum

These five images of Antarctica, beginning clockwise from upper left, were among several hundred acquired over one and a half days as NEAR sped away after the January 1998 swingby. These images and others were projected onto a map to show the whole continent illuminated at once. The difference in resolution of different parts of Antarctica reflects the difference in the distances at which the images were acquired.

As NEAR receded from Earth, it took a "movie" of the spinning Earth from high above Antarctica. Similar "movies" will be taken at Eros. The only brief interruption was to turn to view the moon, from a unique point: from the same distance as Earth (400,000 kilometers or 250,000 miles), but over the lunar south pole -- an impossible vantage point from Earth!

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Video showing Earth receding from NEAR after the January
1998 swingby, based on hundreds of image acquired over
one and a half days as NEAR sped away.

Montage of images of Earth and the moon acquired by NEAR on January 23, 1998.

Both bodies were viewed from a range of 250,000 miles (400,000 kilometers), approximately the same as the distance between them. In this perspective, never seen before, both our planet and its moon are at the relative size that each appears when viewed from the other. But they are viewed from above their south poles, a perspective not attainable from either body because the moon orbits high above Earth's equator. For viewing purposes, the moon is shown five times brighter, and ten times closer to Earth, than in reality.

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