NOZOMI, Sun, Earth and Moon in a Straight Line

Status Report From: Institute of Space and Astronautical Science (ISAS)
Posted: Tuesday, April 10, 2001

The spacecraft NOZOMI, scheduled to enter Mars orbit early in the year 2004, is cruising smoothly along its heliocentric orbit. The distance from earth is 360 million km, and it takes at least 20 minutes for radio waves to reach the spacecraft. Thus, it takes 40 minutes for answers to return after commands have been sent.

On the morning of January 10, 2001, a total lunar eclipse occurred, and exactly at that time, NOZOMI moved behind the sun as viewed from the earth. Four celestial bodies (one man-made spacecraft) arranged in a straight line is a very rare event. Of course, the event has no special meaning for researchers other than Nostradamus.

However, since NOZOMI was located on the opposite side of the sun, solar noise prevents contact for about three weeks. From December 28, 2000, until January 20, 2001, NOZOMI was incommunicado. Because of this, which is known by the astronomical term "conjunction," which of course had been predicted during the orbit design, the NOZOMI project team proceeded with various preparations for the safe completion of the voyage.

The NOZOMI's high-gain antenna has an extremely powerful 1.4 deg. beam, and during "conjunction" this is automatically raised to 30 deg., but the beam must face the earth directly. If an error creeps into this equation, then contact becomes very difficult and communication with the NOZOMI may be abandoned.

Though no-one doubted the abilities of the attitude control group, the moment scheduled for January 20 was a nerve-wracking time as many worried that contact with the probe could successfully be re-established after three weeks. Thus, on the morning of January 20, the entire project team heaved a sigh of relief when the 64m antenna of the Usuda Deep Space Center successfully received a signal from the NOZOMI spacecraft on schedule.

We managed to confirm the accuracy of attitude control, and also that, after three weeks out of contact, all the probe's sections were in the same good condition as at departure. While not exactly the same as "sending a small child on a trip," the results deepened the team's confidence in NOZOMI.

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