[meteorite-list] Traffic Around Mars Gets Busy

[Ron Baalke]

http://www.jpl.nasa.gov/news/news.php?feature=4572

Traffic Around Mars Gets Busy
Jet Propulsion Laboratory 
May 4, 2015

[Graphic]
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: 
NASA/JPL-Caltech 

* Five active spacecraft are orbiting Mars, an increase of two since last 
summer

* An enhanced system warns if two orbiters may approach each other too 
closely

NASA has beefed up a process of traffic monitoring, communication and 
maneuver planning to ensure that Mars orbiters do not approach each other 
too closely.

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 
working.

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 
the orbiters.

"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 
complementary instruments.

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:

http://mars.jpl.nasa.gov

http://www.nasa.gov/mars


Media Contact

Guy Webster
Jet Propulsion Laboratory, Pasadena, Calif.
818-354-6278
guy.webster at jpl.nasa.gov 

2015-150