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

[Ron Baalke]

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.