Could it be possible that a lander the size of a washing machine, thought to be lost nearly four months ago following its passing into shadow, might still be generating signals? Beginning today, the European Space Agency’s (ESA) Rosetta spacecraft, orbiting Comet 67P/Churyumov-Gerasimenko, began its search for signs of life from its lander, Philae, which “fell asleep” due to depleted battery power within days of its November 2014 touchdown.
The German Aerospace Center, DLR, reported that if certain conditions are met, it may be possible for Rosetta to communicate with the lander—in fact, it’s possible that the lander might already be “awake” to some degree, under reduced power conditions. The comet is currently making a closer approach to the Sun, which increases the probability of the “return of Philae.” As the comet, orbiter, and lander receive more solar energy, there are more opportunities for Philae to stop “napping,” and start analyzing.
DLR stated that in order for Philae to get back to work, several conditions must first be met. The interior of the lander must be “warmed up” to a temperature of -45 degrees Celsius. In addition, Philae must be able to generate at least 5.5 watts from its solar panels. According to DLR, “As soon as Philae ‘realises’ that it is receiving more than 5.5 watts of power and its internal temperature is above –45ºC, it will turn on, heat up further and attempt to charge its battery.” A common household lightbulb, by comparison, is rated at 60 watts. Philae was designed in part to withstand low-power operations.
Since November, when the lander began its hibernation, it has been storing up all solar energy received. However, the landing site (called “Abydos”) receives very little sun; according to camera views, Philae seems to be surrounded by rocky, cliff-like formations. Philae infamously made three touchdowns in November, as its landing harpoons did not deploy as expected; as a result, it did not come to rest at its planned landing site, which would have resulted in more solar exposure.
At present time, Comet 67P/Churyumov-Gerasimenko is 230 million kilometers from the Sun, and continues to travel closer. Conditions may be too cold at this time for Philae to awaken, but according to DLR’s Stephan Ulamec, Philae’s project manager, “ … [I]t it is worth trying. The prospects will improve with each passing day.” He also added, “Philae currently receives about twice as much solar energy as it did in November last year,” which was the time frame when Philae stopped transmitting data. DLR stated that its engineers have engaged in “blind commanding” with the lander to maximize internal heating and conserve energy; while the lander may not be able to respond to these commands, it is still possible for them to be executed.
While it is possible that Philae may already be “awake,” the lander must generate 19 watts of power to begin science operations and two-way communication with the Rosetta orbiter, which would then relay its signals back to Earth.
DLR added the reason why these next few days are critical in possible re-establishment of signal: “Between 12 and 20 March, the Rosetta orbiter is transmitting to the lander and listening for a response. The most likely time for contact is during the 11 flybys where the orbiter’s path puts it in a particularly favourable position with respect to the lander during comet ‘daytime’ – when Philae is in sunlight and being supplied with power by its solar panels. Communication will be attempted continuously because Philae’s environment could have changed since landing in November 2014.”
If DLR’s engineers receive a signal back from Philae, they will begin to assess the lander’s health and that of its 10 science instruments on-board. Depending on the amount of power available, the engineers will begin to assess which experiments and scientific work can take place.
DLR stated optimistically, “If the battery can be charged as planned, measurements can be carried out during the comet night, enabling, for example, long-term measurements.” Ulamec also added: “If we cannot establish contact with Philae before 20 March, we will make another attempt at the next opportunity. Once we can communicate with Philae again, the scientific work can begin.”
The landing of Philae upon Comet 67P/Churyumov-Gerasimenko—the first ever of its kind in spaceflight history—was one of 2014’s greatest scientific achievements. Despite its landing(s) in a less-than-optimal area and its early hibernation, the plucky little lander fulfilled all of its science goals. A previous AmericaSpace article detailed the stunning achievement; Dr. Ken Kremer wrote in November, “[Philae] lasted nearly 57 hours and also successfully accomplished the first-ever research investigations from the surface of a comet, and transmitted a full science data package before entering hibernation for an unknown period of time, after the on-board battery power was exhausted.”
Perhaps the “hibernation for an unknown period of time” is at its end, as DLR’s engineers and space buffs all over the world hold their breaths for renewed contact.
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