[meteorite-list] Traffic Around Mars Gets Busy
From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Mon, 4 May 2015 15:51:58 -0700 (PDT)
Traffic Around Mars Gets Busy
Jet Propulsion Laboratory
May 4, 2015
This graphic depicts the relative shapes and distances from Mars for five
active orbiter missions plus the planet's two natural satellites. It illustrates
the potential for intersections of the spacecraft orbits. Image Credit:
* Five active spacecraft are orbiting Mars, an increase of two since last
* An enhanced system warns if two orbiters may approach each other too
NASA has beefed up a process of traffic monitoring, communication and
maneuver planning to ensure that Mars orbiters do not approach each other
Last year's addition of two new spacecraft orbiting Mars brought the census
of active Mars orbiters to five, the most ever. NASA's Mars Atmosphere
and Volatile Evolution (MAVEN) and India's Mars Orbiter Mission joined
the 2003 Mars Express from ESA (the European Space Agency) and two from
NASA: the 2001 Mars Odyssey and the 2006 Mars Reconnaissance Orbiter (MRO).
The newly enhanced collision-avoidance process also tracks the approximate
location of NASA's Mars Global Surveyor, a 1997 orbiter that is no longer
It's not just the total number that matters, but also the types of orbits
missions use for achieving their science goals. MAVEN, which reached Mars
on Sept. 21, 2014, studies the upper atmosphere. It flies an elongated
orbit, sometimes farther from Mars than NASA's other orbiters and sometimes
closer to Mars, so it crosses altitudes occupied by those orbiters. For
safety, NASA also monitors positions of ESA's and India's orbiters, which
both fly elongated orbits.
"Previously, collision avoidance was coordinated between the Odyssey and
MRO navigation teams," said Robert Shotwell, Mars Program chief engineer
at NASA's Jet Propulsion Laboratory, Pasadena, California. "There was
less of a possibility of an issue. MAVEN's highly elliptical orbit, crossing
the altitudes of other orbits, changes the probability that someone will
need to do a collision-avoidance maneuver. We track all the orbiters much
more closely now. There's still a low probability of needing a maneuver,
but it's something we need to manage."
Traffic management at Mars is much less complex than in Earth orbit, where
more than 1,000 active orbiters plus additional pieces of inactive hardware
add to hazards. As Mars exploration intensifies, though, and will continue
to do so with future missions, precautions are increasing. The new process
was established to manage this growth as new members are added to the
Mars orbital community in years to come.
All five active Mars orbiters use the communication and tracking services
of NASA's Deep Space Network, which is managed at JPL. This brings trajectory
information together, and engineers can run computer projections of future
trajectories out to a few weeks ahead for comparisons.
"It's a monitoring function to anticipate when traffic will get heavy,"
said Joseph Guinn, manager of JPL's Mission Design and Navigation Section.
"When two spacecraft are predicted to come too close to one another, we
give people a heads-up in advance so the project teams can start coordinating
about whether any maneuvers are needed."
The amount of uncertainty in the predicted location of a Mars orbiter
a few days ahead is more than a mile (more than two kilometers). Calculating
projections for weeks ahead multiplies the uncertainty to dozens of miles,
or kilometers. In most cases when a collision cannot be ruled out from
projections two weeks ahead, improved precision in the forecasting as
the date gets closer will rule out a collision with no need for avoidance
action. Mission teams for the relevant orbiters are notified in advance
when projections indicate a collision is possible, even if the possibility
will likely disappear in subsequent projections. This situation occurred
on New Year's weekend, 2015.
On Jan. 3, automated monitoring determined that two weeks later, MAVEN
and MRO could come within about two miles (three kilometers) of each other,
with large uncertainties remaining in the exact passing distance. Although
that was a Saturday, automatic messages went out to the teams operating
"In this case, before the timeline got short enough to need to plan an
avoidance maneuver, the uncertainties shrank, and that ruled out the chance
of the two spacecraft coming too near each other," Guinn said. This is
expected to be the usual pattern, with the advance warning kicking off
higher-level monitoring and initial discussions about options.
If preparations for an avoidance maneuver were called for, spacecraft
commands would be written, tested and approved for readiness, but such
commands would not be sent to a spacecraft unless projections a day or
two ahead showed probability of a hazardous conjunction. The amount of
uncertainty about each spacecraft's exact location varies, so the proximity
considered unsafe also varies. For some situations, a day-ahead projection
of two craft coming within about 100 yards (100 meters) of each other
could trigger a maneuver.
The new formal collision-avoidance process for Mars is part of NASA's
Multi-Mission Automated Deep-Space Conjunction Assessment Process. A side
benefit of it is that information about when two orbiters will be near
each other -- though safely apart -- could be used for planning coordinated
science observations. The pair could look at some part of Mars or its
atmosphere from essentially the same point of view simultaneously with
Odyssey, MRO and MAVEN -- together with NASA's two active Mars rovers,
Opportunity and Spirit -- are part of NASA's robotic exploration of Mars
that is preparing the way for human-crewed missions there in the 2030s
and later, in NASA's Journey to Mars strategy.
NASA's Goddard Space Flight Center manages the MAVEN project for the NASA
Science Mission Directorate, Washington. MAVEN's principal investigator
is based at the University of Colorado's Laboratory for Atmospheric and
Space Physics. JPL, a division of the California Institute of Technology
in Pasadena, manages NASA's Mars Exploration Program and the Odyssey and
MRO projects for the Science Mission Directorate. Lockheed Martin Space
Systems, Denver, built all three NASA Mars orbiters.
For more about NASA's Mars Exploration Program, visit:
Jet Propulsion Laboratory, Pasadena, Calif.
guy.webster at jpl.nasa.gov
Received on Mon 04 May 2015 06:51:58 PM PDT