[meteorite-list] Indian Mars Mission Hit By Snag (MOM)

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Mon, 11 Nov 2013 15:17:16 -0800 (PST)
Message-ID: <201311112317.rABNHGHX004239_at_zagami.jpl.nasa.gov>

http://www.bbc.co.uk/news/science-environment-24900271

Indian Mars mission hit by snag
By Paul Rincon
BBC News
November 11, 2013
 
India's mission to Mars has hit a snag, after a planned engine burn failed
to raise the spacecraft's orbit around Earth by the intended amount.

The problem occurred during a manoeuvre designed to boost the craft's
maximum distance from 71,623km to 100,000km.

A problem with the liquid fuel thruster caused the 1,350kg vehicle to
fall short of the mark.

But the head of the Indian Space Research Organisation (Isro) said the
spacecraft remained "healthy".

As a solution, the Mars Orbiter Mission (MOM) - known informally as Mangalyaan,
or Mars-craft - will be commanded to execute an additional thruster firing
at 05:00 IST on Tuesday (23:30 GMT on Monday) to make up for the shortfall.

However, independent experts contacted by the BBC said they were puzzled
by the stated circumstances surrounding the glitch.

Instead of flying directly to Mars, the $72m (?45m) probe is scheduled
to orbit Earth until the end of the month, building up the necessary velocity
to break free from our planet's gravitational pull.

This was the fourth in a series of five engine burns known as "midnight
manoeuvres" because several constraints require that they are carried
out in the early hours of the morning.

Speaking to Pallava Bagla, science editor at Indian broadcasting network
NDTV, Isro's chairman K Radhakrishnan said: "The spacecraft is healthy
and it encountered a problem when a specific redundancy test was being
conducted and it failed to reach the desired velocity it was to achieve."

In that redundancy test, two coils in the liquid engine were supposed
to be energised simultaneously.

Isro chief K Radhakrishnan said the spacecraft was healthy despite the
glitch.
"When you are going so far away, if one thing fails, you want to have
a standby option. Everything is almost doubled up on the satellite, which
is why they were not able to carry so much scientific equipment," Mr Bagla
explained.

The failure of the test and the spacecraft's consequently reduced velocity
raised the spacecraft's apogee (the point in its orbit farthest away from
Earth) from 71,623km to just 78,276km - about 25% of the way to the target
of 100,000km.

Mr Bagla told BBC News that the attempt on Monday morning used up about
2kg of the craft's 852kg fuel load.

But he added that the spacecraft's insertion into Earth orbit after launch
on 5 November had been so precise, 6kg of liquid fuel had been saved.
Even with Monday's glitch, the mission still had a fuel surplus of 4kg.

Nevertheless, Mr Radhakrishnan said that a failure analysis committee
would examine why the problem occurred.

Cause for concern?

But independent experts approached by the BBC said they were baffled by
how the coil test could have contributed to a loss of thrust.

"Using the primary and redundant coils of the [engine's] solenoid valve
of itself should not necessarily lead to a lack of thrust," a source told
me on condition of anonymity.

"It should be a configuration they will have tested on the ground, which
may mean this lack of thrust is nothing to do with the coils and that
it's another issue."

The source explained: "It's very strange," adding: "The redundant coil
should not act against the primary one in any way."

Alternative causes could include one or both propellant valves failing
to open within the engine, or a lack of propellant in the first case.
The latter scenario could indicate a catastrophic fuel leak that would
almost certainly spell the end for the mission. But there are reasons
to doubt this failure mode because less powerful liquid fuel thrusters
on the spacecraft continued to work during the burn, the expert said.

Another possible reason for the loss of thrust could have been melting
in the combustion chamber during a previous firing that broke the fuel
nozzle.

However, all eyes will now be on the next engine burn, which should clarify
whether or not there are bigger concerns over the health of the spacecraft.

If the additional firing on Tuesday can successfully bridge the gap, a
final midnight manoeuvre on 16 November will boost the apogee to 192,000km.

On 1 December, the engine will be fired again for its "trans-Martian injection",
despatching the craft on a 300-day journey to Mars.

On 24 September next year, the engine will be fired again to slow down
the spacecraft, enabling it to be captured by Mars' gravity and placed
into orbit.

India's PSLV rocket - the second choice for the mission after a beefier
launcher failed - was not powerful enough to send the MOM on a direct
flight to Mars.

So engineers opted for a method of travel called a Hohmann Transfer Orbit
to propel the spacecraft from Earth to Mars with the least amount of fuel
possible.
Received on Mon 11 Nov 2013 06:17:16 PM PST


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