A close call between two Mars-orbiting satellites in January this year has prompted US' National Aeronautical & Space Administration (NASA) to issue advisories/warnings as and when required to all satellite controlling agencies, including Indian Space Research Organisation (ISRO) to engage in a concerted effort to avoid collision between satellites around the Red Planet.

ISRO scientists have not yet received one but are expecting it to be issued to them whenever ISRO's Mars Orbiter Mission (MOM), also called Mangalyaan, comes close to the other satellites. The new formal collision-avoidance process for Mars is part of NASA's multi-mission automated deep-space conjunction assessment process. But the advantage of this is that prior information about two orbiters being at a safe distance but near each other could make way for coordinated science observations. Two or more satellites in such a position could look at parts of Mars or its atmosphere from essentially the same point of view simultaneously with complementary instruments to gather more data in a shorter time.

This is part of NASA beefing up the process of traffic monitoring, communication and manoeuvre planning to ensure that Mars-orbiting satellite, in their varying orbits, do not collide with each other.

The urgency of satellite traffic management is because there were never so many active satellites around the Red Planet. There are presently five active satellites including India's MOM and NASA's Mars Atmosphere and Volatile Evolution (MAVEN) that joined the 2003 Mars Express from ESA (the European Space Agency), the 2001 Mars Odyssey and the 2006 Mars Reconnaissance Orbiter (MRO) (both by NASA), in September 2014 in orbits around Mars.

Moreover, the number of Mars-bound satellites are sure to grow in the years to come with a human mission to Red Planet being planned around 2030. ISRO spokesperson DP Karnik told Bangalore Mirror that ISRO headquarters in Bengaluru was aware of such a plan but no advisory/warning has yet been received by ISRO headquarters. 

NASA's plan involves alerting the respective mission teams only when they foresee two or more satellites coming close to each other, raising the threat of collision.

All five active Mars orbiters - including India's MOM - use the communication and tracking services of NASA's Deep Space Network, which is managed at NASA's Jet Propulsion Laboratory. This brings trajectory information together, and engineers can run computer projections of future trajectories out to a few weeks in advance to assess collision risks.

"It's a monitoring function to anticipate when traffic will get heavy," NASA website www.nasa.gov quotes 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 manoeuvres are needed."

Scientists say whenever such a situation arises, the satellites can be slowed down or their orbits raised or lowered by using on-board thrusters to avoid getting too close to other satellites. In some situations, a day-ahead projection of two satellites coming within about 100 metres of each other could trigger a manoeuvre.

On January 3 this year, automated monitoring had determined that two weeks later, MAVEN and MRO would could come within about two miles (three kilometres) of each other. 

There was much uncertainty over what would happen, but the satellites passed each other at safer distances. Scientists also say this is expected to be a usual pattern now, which is why an advance warning system should be in place. 

Quelle: Bangalore Mirror