ESA’s Philae lander battled against the odds on Friday, transmitting key scientific data before its batteries were depleted. Due to the unplanned location – following a couple of bounces on Comet 67P/Churyumov-Gerasimenko earlier this week – Philae was unable to draw the required power from its solar arrays, resulting in a battle against time to conduct its mission objectives.
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Even if Philae never awakens from what could now be a permanent slumber, the mission has been a huge, historical success.
The ambitious mission involved ten years of transit since the Rosetta/Philae launch in 2004, culminating in the first ever soft landing on a comet.
There were a number of technical issues, which did not come as a major surprise, given the complex nature of the mission. However, none proved to be insurmountable per the mission goals.
Philae’s stunning departure from Rosetta did go to plan. However, problems involving the cold gas thruster system that was to aid the lander’s touchdown, along with the issue of the harpoons failing to fire to hold Philae in place, the spacecraft was unable to remain in the designated landing area.
Notably, Philae’s initial touchdown was bang on target, touching down in the pre-selected landing site named Agilkia.
However, the lander bounced back up as far as a kilometer, before returning to a new location on the comet, bouncing one more time, prior to then coming to rest on the surface.
Philae’s eventual resting point saw it in a rather precarious position, with one leg in the air.
This raised concerns the lander would not be able to properly deploy its drill – a key element of the mission, with the goal of gathering samples from the comet, in turn potentially providing answers to questions as important as the origin of life on Earth.
It was then revealed that Philae’s location was not ideal for its solar arrays, required to gain power from the Sun. The lander was shadowed by a cliff, a major issue – not helped by the fact the lander was not in its correct orientation, hindering the power collection of the arrays that are located around its body.
Despite the challenges, the little spacecraft and its team battled on via the creation of a plan to push through as many scientific goals as possible before Philae’s battery power ran out.
That plan called for an incredibly busy Friday, first calling for Philae to drill into the surface of the comet, in order to gather samples, before sending the results as part of a data package during a short window of opportunity later in the day.
There was a risk that, due to Philae’s position, the drilling could have failed or pushed the lander into an even worse position. The drilling was classed as successful.
However, Philae was running out of time, with battery power starting to diminish, and a key communication pass with Rosetta still to be conducted. There was a risk Philae’s work would never have been received back on Earth if the communications between the two spacecraft did not return.
Thankfully, the Rosetta team were one step ahead of the situation, putting into place a plan for Philae to muster the strength to raise itself by just four centimeters, while rotating its body by 35 percent.
The goal was to provide just enough additional exposure of the solar arrays to sunlight, in order to give Philae a fighting chance of having enough power complete its tasks and be able to gain a communications link with Rosetta at the end of Friday.
“The rotation of the lander’s body could result in more power if one of the larger solar panels can catch the illumination that is falling on the smaller,” noted ESA’s Mark McCaughrean, senior science advisor.
“All things being equal, the same amount of sunlight falling on a larger panel should result in more power being generated.”
The plan worked.
Following a tense wait, communication was regained for the key transmission of data from Philae’s work on the comet.
The results showed all of the science instruments were deployed, including the instruments that required mechanical movement, such as APXS, MUPUS, and the drill, SD2, that delivered samples to the PTOLEMY and COSAC instruments inside the lander.
“We’ve got data – all the house-keeping data and data from COSAC (The COmetary SAmpling and Composition experiment – used for detecting and identifying complex organic molecules),” flashed a report from Stephan Ulamec, Lander manager at Germany’s DLR. “The drill (SD2) moved up and down, but we don’t yet know what we have.”
Soon it was shown Philae was fighting against fading battery power, as expected. However, the intrepid lander showed true spirit and kept firing data at Rosetta, ahead of it being transmitted back to Earth.
Eventually, Philae’s batteries were depleted, with not enough sunlight available to recharge. Philae fell into ‘idle mode’ – with all of its instruments and most systems on board shut down.
However, the lander’s team were overjoyed with the data Philae managed to send before entering its slumber.
“Prior to falling silent, the lander was able to transmit all science data gathered during the First Science Sequence,” added Mr. Ulamec. “This machine performed magnificently under tough conditions, and we can be fully proud of the incredible scientific success Philae has delivered.”
Contact was confirmed as lost at 00:36 UTC, not long before the scheduled end of communications that would have happened when Rosetta orbited below the horizon.
Philae’s future is now uncertain. The lander could get lucky if sufficient sunlight falls on the solar panels to generate enough power to wake it up.
The next possible communication slot to know if Philae had come back to life started at 10:00 UTC on Saturday when Rosetta passed overhead and listened for a signal. However, there was no communication received.
Future opportunities may arise as the comet closes in on its pass by the Sun. However, it is unknown how long Philae can survive in its current state.
Regardless of the eventual outcome, the Rosetta mission has already been a huge success, as scientists begin to pour over the large amounts of data that is now in their possession, all thanks to a brave little lander called Philae.
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(Images via ESA and DLR)