Keep the shuttle flying: Fwd: Kepler space telescope in emergency mode

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From: "Gary Johnson" <gjohnson144@comcast.net>
Date: April 9, 2016 at 9:42:31 PM CDT
To: "Gary Johnson" <gjohnson144@comcast.net>
Subject: FW: Kepler space telescope in emergency mode

Kepler space telescope in emergency mode
April 9, 2016 Stephen Clark
Artist's concept of the Kepler observatory. Credit: NASA
Mission controllers are trying to diagnose a problem that put NASA's Kepler planet-hunting observatory in emergency mode nearly 75 million miles from Earth this week.
Circling the sun in an orbit just outside Earth's, Kepler is in an extended mission searching for worlds around other stars.
Engineers discovered the spacecraft was in emergency during a regularly-scheduled communications session Thursday, NASA said in a statement.
The agency said emergency mode is the observatory's lowest operational mode and is fuel-intensive, meaning the spacecraft is burning its finite supply of hydrazine fuel at a faster rate than usual.
Managers declared a spacecraft emergency, giving the Kepler team priority access to NASA's Deep Space Network, a global array of communications antennas used to contact faraway space probes, officials said in a statement.
"Recovering from EM (emergency mode) is the team's priority at this time," the statement said.
At Kepler's distance from Earth, it takes 13 minutes for a communications signal to travel to the spacecraft and back, according to NASA.
The problem that led to Kepler's default into emergency mode occurred some time between April 4 — the craft's last normal communications session — and the contact April 7.
Kepler was about to conduct a flip maneuver to aim its 3.1-foot (95-centimeter) telescope in the direction the spacecraft is traveling in its orbit. The observatory has been pointing in the opposite direction.
The change in orientation was supposed to allow Kepler to point toward the center of the Milky Way galaxy to take part in a search for rogue planets, bodies that are careening through the galaxy without orbiting a star. Ground-based observatories also planned to participate in the project.
Officials said Friday that the anomaly aboard Kepler apparently occurred before the flip maneuver.
Kepler is in an extended science campaign dubbed K2 that began in 2014 after two of the four reaction wheels aboard the observatory failed, rendering the spacecraft unable to maintain the ultra-stable pointing required for its original mission.
The wheels spin between 1,000 and 4,000 rpm, generating momentum for precise pointing of the telescope. Two wheels are not enough to keep the telescope staring at the same region of the sky for long durations, and Kepler's chemical rocket thrusters do not have fine pointing capability.
During Kepler's four-year primary mission — from the observatory's launch in March 2009 until early 2013 — the craft aimed its telescope at the same field of more than 150,000 stars in the constellations Cygnus and Lyra. Astronomers sought an Earth-sized planet at just the right distance from a sun-like star in hopes of discovering something like an "Earth analog" where life could exist.
Kepler's 95-megapixel camera watches for the slight dimming of starlight caused when an object passes between the star and the telescope.
Scientists adjusted the observation plan for the K2 mission with the loss of two reaction wheels, programming Kepler to shift its gaze to different parts of the sky every few months.
Astronomers analyzing data acquired by Kepler discovered more than 1,000 confirmed exoplanets, making the mission the most prolific planet-hunter in history. About 4,000 other exoplanet candidates have been detected by Kepler, but those discoveries are provisional and require follow-up observations to confirm they are not false positives.
Officials previously said the failure of another reaction wheel would further degrade its pointing precision, likely spelling the end of Kepler's science mission.

© 2016 Spaceflight Now Inc.

Kepler mission declares spacecraft emergency
by Jeff Foust — April 9, 2016

NASA's Kepler spacecraft has been on an extended mission called K2 after two of its four reaction wheels failed in 2013. Credit: NASA
PHOENIX — Spacecraft controllers are working to restore control of NASA's Kepler astronomy spacecraft after it entered an "emergency mode," disrupting science observations, the mission's manager said April 8.
In a statement, Charlie Sobeck, Kepler mission manager, said that spacecraft operators found the spacecraft was in emergency mode during a scheduled communications session with the spacecraft April 7. Sobeck described that emergency mode as the spacecraft's lowest operational mode and is "fuel intensive."
Kepler appeared to enter emergency mode about 36 hours before the communications session, but Sobeck didn't state what might have caused the incident. The spacecraft was operating normally during its prior communications session April 4.
Work to recover the spacecraft is hindered by its distance from the Earth of nearly 120 million kilometers. Sobeck said the mission has declared a spacecraft emergency to get priority access to NASA's Deep Space Network to aid in efforts to recover the spacecraft.
Controllers found the spacecraft was in emergency mode during a communications session originally intended to reorient the spacecraft for its next observational campaign. Kepler is currently in an extended mission known as K2 where it observes regions of the sky for about three months at a time to search for extrasolar planets and study other astronomical phenomena.
The K2 mission emerged from an earlier problem with the spacecraft. The failure of two of the four reaction wheels on Kepler, used to provide stable pointing, forced NASA to end Kepler's primary mission of observing the same region of the sky in 2013, four years after launch. Engineers developed an alternative pointing mode using the spacecraft's remaining reaction wheels and solar pressure to allow it to observe regions of the sky for months at a time while minimizing the use of propellant.
Until the recent emergency mode, Kepler had experienced few problems during its extended mission. "The spacecraft has operated beautifully, with scarcely a whiff of trouble," Sobeck wrote in a March 11 mission update. Spacecraft engineers, he said then, had adjusted spacecraft parameters to take "a bit more risk" to improve the efficiency of science observations. "In response, the spacecraft appears to have rewarded our trust by operating more smoothly than it has at any other time in its history."
That good performance had been a boon for scientists, who have been using Kepler for studies ranging from continued searches for exoplanets to studies of supernova explosions. At the time Kepler went into emergency mode, controllers were preparing to begin its ninth observing campaign of the K2 mission.
Even if spacecraft controllers recover Kepler, the fuel used during emergency mode could shorten the mission's lifetime. Fuel is one of the key limiting factors in the life of the spacecraft, along with communications as the spacecraft drifts away from the Earth in its orbit around the sun. Kepler had been using less fuel than originally projected, making further extensions of its mission feasible.
Prior to the current anomaly, project officials were optimistic Kepler could operate well into 2018. "The spacecraft health is very good," said John Troeltzsch, Kepler program manager at Ball Aerospace, the mission's prime contractor, at an American Astronomical Society meeting in Florida in January. "We're in good shape to get out to Campaign 17," an observing run planned for mid-2018.

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