On
Sept. 21, 2014, the Mars Atmosphere and Volatile Evolution spacecraft
will complete roughly 10 months
of travel and enter orbit around the Red
Planet.
The orbit-insertion maneuver will be carried out as the spacecraft
approaches Mars, wrapping up an interplanetary journey of 442 million
miles (711 million kilometers). Six thruster engines will fire briefly
for a “settling” burn that damps out deviations in pointing. Then the
six main engines will ignite two by two in quick succession and will
burn for 33 minutes to slow the craft, allowing it to be captured in an
elliptical orbit.
This milestone will mark the culmination of 11 years of concept and
development for MAVEN, setting the stage for the mission’s science
phase, which will investigate Mars as no other mission has.
“We’re the first mission devoted to observing the upper atmosphere of
Mars and how it interacts with the sun and the solar wind,” said Bruce
Jakosky, principal investigator for MAVEN at the University of Colorado
in Boulder.
These observations will help scientists determine how much gas from
Mars’ atmosphere has been lost to space throughout the planet’s history
and which processes have driven that loss.
En route
Procedures to line up MAVEN for proper orbit insertion began shortly
after MAVEN launched in November 2013. These included two
trajectory-correction maneuvers, performed in December 2013 and February
2014.
Calibration of the mission’s three suites of science instruments –
the Particles and Fields Package, the Remote Sensing Package and the
Neutral Gas and Ion Mass Spectrometer – was completed during the cruise
phase to Mars.
“Every day at Mars is gold,” said David Mitchell, MAVEN’s project
manager at NASA’s Goddard Space Flight Center in Greenbelt, Maryland.
“The early checks of instrument and spacecraft systems during cruise
phase enable us to move into the science collection phase shortly after
MAVEN arrives at Mars.”
The voyage also gave the team an opportunity to take data on the
interplanetary solar wind using the Fields and Particles Package.
Meanwhile, teams in California, Colorado and Maryland carried out
rehearsals of the entire orbit insertion twice. The science team also
performed a weeklong simulation of the planning and implementation
required to obtain science data. Two months prior to arrival at Mars,
all instruments were turned off, in preparation for orbit insertion.
Into orbit
During orbit insertion, MAVEN will be controlled by its on-board
computers. By that time, the team will have uploaded the most up-to-date
information about the spacecraft’s location, velocity and orientation.
The insertion instructions will have been updated, and the fuel valves
will be open, to warm the fuel to an operating temperature of about 77
to 79 degrees Fahrenheit (25 to 26 degrees Celsius).
If all goes well, the spacecraft will need no further commands from
the ground. The important exception is that final trajectory corrections
could be made, if needed, 24 hours or 6 hours prior to insertion. That
would only happen, however, if the navigation team concluded that the
spacecraft was coming in at too low of an altitude.
Otherwise, during the last 24 hours, the spacecraft will carry out
preprogrammed procedures to make all systems as “quiet” as possible,
which is the safest condition for orbit insertion. These steps include
automatically executing a new version of the fault protection, which
will tell the craft how to react to an on-board component anomaly
leading up to or during orbit insertion.
In addition, the spacecraft will have to reorient itself so that the
thrusters are pointed in the correct direction for the burn. In this
final orientation, MAVEN’s high-gain antenna, which is used for most
communication with the spacecraft, will point away from Earth. During
that period, MAVEN’s low-gain antenna will be used for limited
communication capacity at a reduced data rate.
At last, the insertion will begin. For the next 33 minutes, the craft
will burn more than half the fuel onboard as it enters an orbit 236
miles (380 kilometers) above the northern pole.
Three minutes after the engines turn off, the MAVEN computers will
reinstate the normal safeguards, reorient the spacecraft to point the
high-gain antenna toward Earth, and reestablish normal communications.
At that point, MAVEN will transmit the data obtained during the
insertion back to Earth, along with information on the state of the
spacecraft, and the MAVEN team will learn if everything worked properly.
“Then, there will be a sigh of relief,” said Carlos Gomez-Rosa, MAVEN mission and science operations manager at Goddard.
Later, the team will upload new instructions for the science portion
of the mission, as well as turn on and check out the science
instruments.
New view of Mars
The team will perform six maneuvers to move the spacecraft from its
insertion orbit into the four-and-a-half-hour orbit that will be used to
gather science data.
This science orbit will be elliptical, with the spacecraft flying
about 90 miles (approximately 150 kilometers) above the surface at
periapsis, or closest point, in the orbit to “sniff” the upper
atmosphere. At apoapsis, the farthest point from the surface, MAVEN will
pull back 3,900 miles (roughly 6,300 kilometers) to observe the entire
atmosphere.
With each pass, MAVEN will make measurements of the composition, structure and escape of atmospheric gases.
“MAVEN’s orbit through the tenuous top of the atmosphere will be
unique among Mars missions,” said Jakosky. “We’ll get a new perspective
on the planet and the history of the Martian climate, liquid water and
planetary habitability by microbes.”
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