[meteorite-list] ESA Says Rosetta in Good Shape After 31-Month Snooze

[Ron Baalke]

http://www.spaceflightnow.com/rosetta/140129update/

ESA says Rosetta in good shape after 31-month snooze
BY STEPHEN CLARK
SPACEFLIGHT NOW
January 29, 2014

A first look at the European Space Agency's Rosetta spacecraft after its 
reactivation last week shows the probe endured an unprecedented power-saving 
hibernation with few problems, giving engineers confidence the mission 
can continue the final leg of its decade-long pursuit of a little-known 
comet thought to harbor the building blocks of life.

Since Rosetta was roused from sleep Jan. 20, European engineers have established 
full control over the spacecraft and begun evaluating the probe's power, 
command and control, propulsion and attitude control systems.

The verdict: Rosetta is healthy and ready for its high-stakes approach 
to comet Churyumov-Gerasimenko. In August, the $1.7 billion mission will 
arrive in the icy world's neighborhood, becoming the first spacecraft 
to enter orbit around a comet.

In November, Rosetta will eject a small German-built lander to latch on 
to the comet to collect panoramic imagery and drill into its mysterious 
surface -- another first in space exploration.

Rosetta's only blemish while asleep was found in the spacecraft's software. 
The glitch caused the probe's on-board computer to reboot at the start 
of the activation sequence Jan. 20, giving tense ground controllers at 
the Rosetta operations center in Germany a few extra minutes to wait before 
receiving the first signal from the spacecraft.

"We indeed had some issues in the software during the hibernation mode," 
said Andrea Accomazzo, Rosetta's spacecraft operations manager. "We are 
analyzing them, [but] they do not affect at all the current and future 
spacecraft activities. We had never seen them before."

Accomazzo said engineers switched on Rosetta's X-band transmitter to hasten 
the probe's download of telemetry to the ground, giving the control team 
a more detailed look at the spacecraft's condition.

Rosetta's solar panels appeared healthy, generating plenty of electricity 
for the spacecraft's busy year ahead. Temperatures inside Rosetta's propellant 
tank were running a bit cooler than expected, but well within specifications, 
according to a post on ESA's Rosetta mission blog.

Engineers continued their methodical checkout of Rosetta over the weekend, 
spinning up three of the craft's four reaction wheels and transitioning 
responsibility for pointing and attitude control to the  wheels from the 
probe's rocket thrusters, Accomazzo told Spaceflight Now.

Accomazzo said one of the three wheels now controlling Rosetta's orientation 
continued to show "non-nominal behavior" first observed before Rosetta 
entered hibernation in June 2011.

The other problematic reaction wheel will be held in reserve. Rosetta 
was designed to operate on three reaction wheels, but engineers devised 
new software to employ two wheels to keep the spacecraft pointed properly, 
ensuring its solar panels remain aimed at the sun, the antenna turned 
toward Earth and its science instruments trained on the comet once the 
probe arrives.

Paolo Ferri, ESA's head of mission operations, told reporters in December 
that two of Rosetta's reaction wheels showed "noise" before the craft 
went to sleep in 2011.

Ferri said engineers also found a way around a leak in Rosetta's helium 
pressurization system. The controllers will operate Rosetta's propulsion 
system at lower pressures than planned, sacrificing fuel efficiency to 
ensure the spacecraft does not run out of helium gas required to push 
propellant into Rosetta's engines.

Ground teams adjusted Rosetta's trajectory and tested the probe's thrusters 
at low pressure before it went into hibernation, and Ferri said the results 
were positive.

"We do not expect a problem," Ferri said. "We have enough fuel."

Over the next few weeks, engineers will configure Rosetta's on-board solid-state 
mass memory for the storage of science and operations data before downloading 
the telemetry to Earth, according to  ESA.

Accomazzo said controllers will not know the status of Rosetta's 11 science 
instruments, which include a suite of cameras, spectrometers and dust 
monitors, until they are scheduled to be powered up in late March.

Rosetta's Philae lander, riding piggyback on the orbiter mothership, will 
also be switched on in late March to verify its condition after Rosetta's 
multi-year cruise.

Engineers expect Rosetta to be fully checked out in time for a critical 
engine burn in May to bend the probe's path toward Churyumov-Gerasimenko 
and set up for the craft's arrival in the comet's vicinity this summer.

When Rosetta enters orbit around the comet in August, it will begin more 
than a year of up-close observation as Churyumov-Gerasimenko speeds closer 
to the sun, activating plumes of icy vapors as solar heating builds up 
in 2015.

The primordial world was locked into the inner solar system by the immense 
gravity of Jupiter during a close encounter with the gas giant a half-century 
ago. With a nucleus measuring about two-and-a-half miles across, it originated 
in the farthest reaches of the solar system and, like all comets, was 
knocked toward the sun after billions of years in the frozen distant Oort 
cloud.

"[Comets] are time capsules," said Mark McCaughrean, senior scientific 
advisor in ESA's science and robotic exploration directorate. "They are 
remnants of the birth of the solar system. They go back to the beginning 
of the solar system more than 4.6 billion years ago."

Rosetta's mission follows a series of European and NASA robotic probes 
dispatched for fleeting flybys of comets. ESA's Giotto spacecraft flew 
past Halley's comet in 1986, and the U.S. space agency sent several missions 
to visit comets in the 2000s.