Link loss recovery strategy using sun sensor and beacon signal in Mars orbiter Mission

Paper number

IAC-15,C1,6,11,x29727

Author

Ms. Ritu Karidhal, ISRO Satellite Centre (ISAC), India

Coauthor

Dr. Kesavaraju V, ISRO Satellite Centre (ISAC), India

Year

2015

Abstract

Mars Orbiter Mission is India's first Interplanetary Mission launched in November ,2013 and aimed
to reach MARS in September ,2014. Mars Orbiter Mission carries two antennas Medium Gain An-
tenna(MGA) with field of View of 40o and one High Gain Antenna(HGA) with field of view of 2o . The
nominal attitude of spacecraft ensures Earth Pointing and continuous link with the ground station. Dur-
ing any anomaly with respect to Link-loss , spacecraft enters SAFE mode and the recovery is executed
by onboard computer in an autonomous way . There are two paths of recovery . The first path uses Star
sensors , gyros and onboard loaded reference attitude(Earth pointing attitude) to re-establish the link
with HGA. But in case of unavailability of Star Trackers updates , the alternative path uses Sun Sensor
and the Beacon Signal from Ground to re-establish the attitude pointing and henceforth the communica-
tion with larger FOV antenna i.e. MGA. This paper discusses about the methodology involved in Using
Sun Sensor and limited FOV antenna to re-establish the communication link.
Sun and Earth Geometry During Cruise Phase During the Cruise Phase i.e. heliocentric orbit phase
of Mars Orbiter Mission , Sun and Earth Angle at spacecraft varies with the minimum of 14 0 to the
maximum of 110 degrees.
Methodology to Re-establish Communication Link Once the spacecraft enters SAFE Mode , the ac-
quisition process starts with Sun-Acquisition Using Sun-Sensors , wherein the Sun is aligned along a
selected axis-direction depending upon the relative separation of Earth and Sun at that instant . The
direction about which Sun should be aligned is stored in EEPROM memory area. After the completion
of Sun-Acquisition , the spacecraft is made to rotate about the Sun-Line ( Earth Search Mode) in order
to bring Earth Pointing Vector within the FOV of MGA). MGA is mounted in positive roll and positive
yaw quadrant at an angle of 35 degrees from roll towards yaw. During the link-loss , ground station doesn't
receive any telemetry and it starts sending the Beacon Signal towards the spacecraft direction. Once the
onboard receives the signal from ground , the search rate is brought to zero and the attitude is held at
the current orientation which enables continuous communication with the spacecraft and hence acquires
the spacecraft to its nominal attitude

Abstract document

IAC-15,C1,6,11,x29727.brief.pdf

Manuscript document

IAC-15,C1,6,11,x29727.pdf (🔒 authorized access only).

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