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After downloading scientific data and bypassing a chaotic thruster, NASA's Kepler mission resumed its search for planets around other stars after a two-month break, but engineers expect the ship to run out of fuel .
NASA said in a statement on Wednesday that the Kepler telescope had started collecting new scientific data on Aug. 29 for its 19th observation campaign after the controllers assessed a problem with one of the eight spacecraft propellers used for pointing.
Engineers suspended Kepler's scientific observations in early July after on-board sensors detected a drop in fuel pressure, a sign that the spacecraft's fuel is low. Engineers are unsure of the exact amount of hydrazine fuel in Kepler's tank. They rely on pressure data, calculation of utilization rates, and other means to estimate the fuel supply to the spacecraft.
The managers decided to put Kepler in a fuel-efficient hibernation state until early August, when the satellite had to emit Earth and start downloading stored scientific data. in his onboard memory.
Officials did not want to risk the spaceship running out of fuel and losing the last set of data captured by Kepler's telescope and 95-megapixel camera, designed to search for dimples in the light from distant stars .
Last month, Kepler woke up from hibernation and relayed observations to scientists via NASA's Deep Space Network, but officials did not immediately proceed to the next mission observation cycle – known as the name of Campaign 19 – as planned. A Kepler update published by NASA on August 24 indicated that engineers were reviewing the spacecraft's health status and determining a "full range of options and next steps".
It turned out that officials were studying the behavior of one of Kepler's thrusters.
"After being woken from sleep mode, the spacecraft configuration was changed due to the unusual behavior of one of the thrusters," NASA said Wednesday. According to preliminary indications, the pointing performance of the telescope can be somewhat degraded. We still do not know how much fuel remains; NASA continues to monitor the health and performance of the spacecraft.
Alison Hawkes, a spokesman for NASA's Ames Research Center, said the engineers had decided to eliminate the awkward thruster when the spacecraft was accurately pointed, according to a report by Space News. She added that the unusual behavior of the thruster could be a symptom of Kepler's low fuel level, in which case the other thrusters could present problems.
"By eliminating the use of the thruster for precision pointing, we are protecting ourselves against the fact that this problem is not related to fuel," Hawkes told Space News.
Launched in March 2009, Kepler now relies on its propellers to keep its telescope constantly focused on starfields after two of the four reaction wheels of the spacecraft failed earlier in the mission. Kepler needed at least three reaction wheels to maintain his gaze towards a preselected field of more than 150,000 stars in the Cygnus and Lyra constellations and with the loss of the second gear wheel in 2013.
The engineers devised a new way for Kepler to search for exoplanets using a combination of propellant fire, the remaining two reaction wheels, and solar pressure to accurately maintain the spacecraft. Rather than focusing on a single star field, Kepler's extended mission – known as K2 – examines part of the sky for about 80 days, then moves to another part of the sky for the next campaign.
The observatory needs stable pointing to detect weak planetary transits, and the use of solar pressure for pointing stability depends on the position of the sun relative to Kepler when the spacecraft flies around the solar system in an orbit earthly.
Since Kepler's launch, observations during the main and extended missions have allowed astronomers to confirm the discovery of 2,652 worlds surrounding other stars, as well as more than 2,700 exoplanet candidates requiring follow-up. According to NASA, scientists who have analyzed Kepler's data have so far verified the existence of more than 30 Earth-sized planets in so-called habitable areas of their stars – at the proper distance to harbor the liquid water.
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Follow Stephen Clark on Twitter: @ StephenClark1.
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