September 25, 2018

NASA’s Kepler telescope nears end of mission


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Artist’s concept of the Kepler observatory. Credit: NASA

Nearly a decade after launching from Cape Canaveral on a planet-hunting quest that has netted 2,650 new confirmed worlds beyond our solar system, NASA’s Kepler telescope has paused its observations after on-board sensors detected it is running low on fuel.

Kepler’s dwindling fuel supply was not a surprise to mission managers, and engineers previously projected the spacecraft would run out of propellant this year. The observatory uses the fuel to point toward new star fields in search of planets, and to orient its radio transmitter toward Earth.

Ground controllers interrupted Kepler’s current observing campaign July 2 after sensors inside the spacecraft’s propulsion system detected “an anomalous drop in fuel pressure,” according to a status update posted on the mission’s website.

Such a telemetry signature is one sign of low fuel, and officials decided to pause its current science observations, known as Campaign 18, until all of the telescope’s recorded scene data can be downlinked to Earth during a four-day pre-arranged period booked with the Deep Space Network starting Aug. 2.

Until then, Kepler will remain in a fuel-conserving hibernation-like mode with no science observations planned. NASA officials said they decided to put Kepler into safe mode to preserve 51 days of “high-quality” science data stored on the spacecraft’s solid state recorder, guarding against the risk of running out of fuel before the information can be transmitted to Earth.

Once Kepler empties its fuel tank, the spacecraft will no longer be able to point its antenna toward Earth, cutting off communications with the observatory. Kepler orbits the sun, and is currently located around 100 million miles from Earth.

Assuming the data downlink in early August is successful, Kepler will resume its science mission Aug. 6 by aiming its 37-inch (95-centimeter) telescope toward a new field of stars to begin a new observing period known as Campaign 19. Kepler’s 95-megapixel camera is designed to sense the telltale dips in starlight caused by a passing planet.

Kepler launched March 6, 2009, from Cape Canaveral aboard a Delta 2 rocket. The mission’s primary science phase ended in 2013 after the failure of two of the spacecraft’s four reaction wheels, which kept the telescope steadily pointed at its stellar targets.

Managers devised a new way of using Kepler with only two operating reaction wheels, and the mission is currently in an extended phase known as K2. Scientists have confirmed the discovery of 2,650 planets around other stars using Kepler data, and there are more than 2,700 planet candidates detected by Kepler that require follow-up observations.

NASA officials cautioned that Kepler’s next planet-hunting season starting in August may not be completed if the spacecraft is running on its final bits of fuel.

Kepler launched with 12 kilograms, or a little over 3 gallons, of hydrazine fuel, but it does not carry a fuel gauge. Instead, engineers must monitor data on fuel pressure and catalog fuel consumption to estimate how much propellant remains for the spacecraft’s thrusters.

When the spacecraft runs out of fuel, controllers hope to send commands to turn off Kepler’s radio transmitters and disable on-board software that would automatically turn them back on, a measure to ensure the telescope does not interfere with radio traffic on future space missions.

NASA’s newest mission dedicated to the search for planets, the Transiting Exoplanet Survey Satellite, launched in April. It is designed to look for planets around bright, nearby stars, while Kepler sought more distant exoplanets.

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Follow Stephen Clark on Twitter: @StephenClark1.


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