Subject: [NEXTEL-1] Communication blackouts expected soon for SOHO

From: [email-masked]
Date: Thu, 03 Jul 2003 18:20:37 -0400

Communication blackouts expected soon for SOHO

The Solar and Heliospheric Observatory (SOHO) project launched on 2 December, 1995
by the European Space Agency (ESA) and NASA is experiencing technical difficulties
with its main antenna. As a result, the team involved with SOHO expects 18-day
communication blackouts every three months for the foreseeable future.

The malfunctioning high-gain antenna is used for high-data-rate communication with
the earth. SOHO is said to be an essential element in the array of satellites and
ground-based observatories designed to monitor activity on the surface of the sun
and its effect on the earth’s atmosphere. Its location at First Lagrangian
point—where, about 1.6 million km from Earth, the gravitational forces of the
planet and the sun are in balance and keep spacecraft in position—help it detect
magnetic storms headed towards the planet. Storms of this nature can disrupt
satellite and radio communications.

On 4 May, engineers discovered a discrepancy between the commanded versus measured
antenna positions. The antenna usually moves on two axes, vertical and horizontal.
"The horizontal movement is no longer taking place," a NASA spokesman said.
Normally, as the satellite and the earth orbit the sun, the antenna is constantly
repositioned so its 14-degree-wide beam stays centered on the earth.  The
restriction of the antenna movement will mean that some data will be lost until
the problem can be fixed.

Project scientist Bernhard Fleck said he thinks that a motor or gear assembly may
be causing the observatory’s high-gain antenna to malfunction.

NASA said that despite the malfunction, the spacecraft is operating safely. ESA
and NASA engineers are currently assessing options to resolve the situation, or to
minimize the scientific data loss.

The satellite does have a low-gain antenna. It will be used to maintain SOHO’s
position and perform spacecraft and instrument diagnostics since it can transfer
data whether or not a receiver is in its line of sight.

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