[meteorite-list] Europe Monitors Venus Express Probe's Fading 'Ghost'

[Ron Baalke]

http://news.discovery.com/space/europe-monitors-venus-express-orbiters-fading-ghost-150112.htm

Europe Monitors Venus Express Probe's Fading 'Ghost'
by Ian O'Neill
Discovery News
January 12, 2015

On Nov. 28, the European Space Agency (ESA) lost contact with its veteran 
Venus Express orbiter as it ran out of fuel.

Lacking the juice to maintain the satellite's altitude and pointing, the 
mission's high gain antennae drifted away from Earth and communication 
was lost. However, mission control has been able to track Venus Express' 
X-band "ghost" from 150 million miles away.

Although telemetry cannot be received from and commands cannot be sent 
to Venus Express, the probe's high gain antennae emits an X-band carrier 
signal that mission controllers have been able to lock onto. The signal 
has been acting as a beacon of sorts, allowing ESA to watch the satellite's 
orbit decay. But soon, as the probe drops uncontrollably closer to the 
planet's atmosphere, even a lock on this carrier signal will be lost and 
Venus Express will suffer a fiery end.

"On New Year's day, we saw a weak but detectable signal level and could 
lock onto it for most of the almost-5-hour tracking pass using the Cebreros 
deep-space tracking station," said Rick Blake, Venus Express spacecraft 
operations engineer at the European Space Operations Center in Darmstadt, 
Germany, in an ESA blog update.

"But on 7 January, we only got carrier lock on a more weakened signal 
for just five percent of the pass; on 8 January, we were back to a good 
lock for most of the pass, so it's definitely an unpredictable situation. 
We plan to continue monitoring the signal level in January until we 
see it has disappeared for good," he added.

Last year, as the mission was approaching its end, ESA decided to carry 
out a series of daring orbital maneuvers that would see the spacecraft 
"surf" on the outermost layers of Venus. Those aerobraking maneuvers allowed 
unprecedented measurements of the planet's outermost atmospheric gases 
and a series of re-boosts pushed its lowest orbital approach back up to 
285 miles in altitude in July.

Under the assumption there would be enough propellant for another orbital 
correction in late November, mission managers decided to try to counter 
the natural drag caused by the Venusian atmosphere with another series 
of boosts. Alas, it seems the fuel ran out half-way through, sealing Venus 
Express' fate.

With no fuel left to adjust where the spacecraft was pointing, communications 
were lost a few days later.

And now, as mission control watches the X-band carrier signal slowly dwindle, 
the only way is down for a mission that has been exploring Venus since 
2006.

It is currently thought to come within 80 miles of the planet's surface 
during its closest passes and, by Jan. 20, the spacecraft is predicted 
to drop to 75 miles. "My personal guess is that the spacecraft will start 
breaking up soon after that," said Blake.

After 8 years of exploring Earth's hellish "twin" world, the Venus Express 
mission will come to an end, shooting through Venus’ atmosphere as a man-made 
meteor. But until then, we'll keep trying to lock onto the weakening carrier 
signal, our last ghostly point of contact with an unprecedented planetary 
mission.