We went through a full rehearsal of the spacecraft and instrument activities leading up to the orbit insertion maneuver, which is the rocket engine firing that will finally put NEAR into orbit around Eros.

All of these activities have to be scripted and loaded on the spacecraft in advance, and last week, we tested the command script on the spacecraft - happily, all went well.

What makes the encounter day all the more 'interesting', however, is that critical science observations are scheduled just before the orbit insertion maneuver.

NEAR has been targeted to pass directly between the Sun and Eros about 11 hours before the maneuver, so that a spectral map of Eros can be taken at "zero phase angle". We call this operation the "Low Phase Flyby".

The phase angle is the angle made by the sun, Eros (at the vertex), and NEAR - when this angle is zero, NEAR is exactly between the Sun and Eros. In this geometry, there are no shadows on the surface as seen by NEAR.

This geometry yields the best infrared spectrometer measurements of the brightness of Eros in various infrared "colors", or wavelengths of light - more on spectrometry in two weeks. The infrared spectrometer can't detect areas of Eros that are in shadow, so we want to minimize the shadow area.

Currently, it's summer time at the north pole of Eros, and the sun never sets there (just as in the land of the midnight sun on Earth above the Arctic Circle).

When NEAR flies through zero phase angle on Valentine's Day, it will obtain spectral maps of the northern hemisphere of Eros. This is the only time during the entire Eros rendezvous that NEAR will be able to obtain zero phase observations over the northern hemisphere.

Once NEAR is in orbit around Eros, after the orbit insertion, the phase angle will remain near 90 degrees (because that is better for imaging science - more on that next week).

Of course, since it's summer in the northern hemisphere of Eros, it's winter in the south, and the sun never rises there.

That means NEAR can't take images or obtain infrared spectra of the southern regions, where the sun does not shine, until the seasons change later in the year.

Of course, we do intend to map all of Eros, so NEAR is scheduled to make another zero phase observation of the southern hemisphere of Eros next October.

So, the only times that we will obtain observations at small phase angles will be during the encounter day itself, looking at the northern portion of Eros, and on one other day in October looking at the southern part of Eros.

For science reasons alone, these are critical observations - they are expected to yield the highest quality infrared spectra that will distinguish the mineral composition of Eros. But we must also get into orbit successfully only a matter of hours later.

Since the entire sequence, low phase flyby plus orbit insertion maneuver, must be loaded in advance and executed autonomously by the spacecraft, last week's test included both sets of activitites. Here's hoping that encounter day goes just as smoothly.

Upcoming Spacecraft Activities:

In addition to regular DSN tracking and taking of OpNav images, the following are operationally significant activities planned through Eros orbit insertion. Please consult the NEAR Flight Timeline for more details regarding upcoming science activities.

Jan 28  Eros Satellite Search B
Feb 2   Rendezvous Maneuver
Feb 4   Eros Satellite Search C
Feb 8   Rendezvous Maneuver and Momentum Bias
Feb 9   Eros Satellite Search D
Feb 14  Eros Orbit Insertion

NEAR NEWS
NEAR Snaps Eros
Laurel - January 18, 2000 - The photo album of "NEAR's trip to Eros" has a new page: the first image from the spacecraft's approach to the asteroid. Taken January 12, with NEAR's Multispectral Imager, the picture was posted today on the NEAR Web site. More photos will follow in the weeks leading up to NEAR's Feb. 14 rendezvous with Eros.

NEAR Reports At SpaceDaily NEAR Begins To Return Eros Science First Asteroid Rendezvous Days Away Engine Burn Puts NEAR On Target For Eros Hero NEAR But Far Away NEAR Returns Basic Eros Data Cutting It Fine In Deep Space Fast Hack Saves NEAR Burn Puts NEAR Back On Track Better NEAR Than Never NEAR Crisis In Deep Space Is Eros A Dusty World NEAR Mission Excitment Growing Eros Orbital Countdown Begins Eros 433 A Speck In The Void NEAR Closing in on Eros 433 Mathailde 253 A Battered Shell

NEAR Links NEAR Mission Status Cornell Astronomy NEAR Mission Control Discovery Program NOE's At Planetary Society Related Baskets TECH SPACE DEEP SPACE ONE STARDUST NEWS

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