Cassini-Huygens Mission Status Report
Artist concept of Cassini at Saturn. Image credit: NASA/JPL PASADENA, Calif. – The Cassini spacecraft will swap to a backup set of propulsion thrusters in mid-March due to degradation in the performance of the current set of thrusters.
The thrusters are used for making small corrections to the spacecraft’s course, for some attitude control functions, and for making angular momentum adjustments in the reaction wheels, which also are used for attitude control.
The current set of eight thrusters, referred to as branch A, has been in use since Cassini’s launch more than 11 years ago. The redundant set, branch B, is an identical set of eight thrusters.
Propulsion engineers began to see a lower performance from one of the thrusters on branch A in October. A second branch A thruster is also now showing some degraded performance.
An extensive review with the propulsion system contractor, Lockheed Martin Space Systems, Denver, Colo., the thruster manufacturer, Aerojet, Sacramento, Calif., and propulsion experts at NASA’s Jet Propulsion Laboratory, Pasadena, Calif., was completed last week. The recommendation was made to swap to side B as soon as is practical.
Mid-March is the earliest practical opportunity to make the swap. This allows time for the team to properly test and prepare the sequence of commands that will be sent to the spacecraft. Science planners have identified a period where no high-priority science will be lost during the switch, which will be done over a seven-day window. It also is a time when no navigation maneuvers are required to maintain the spacecraft’s trajectory.
The swap involves commanding a latch valve to open hydrazine flow to the B side, and powering on some thruster control electronics. No pyrotechnic devices are involved in the swap, and the action is fully reversible if necessary.
Almost all Cassini engineering subsystems have redundant backup capability. This is only the second time in Cassini’s 11 years of flight that the engineering teams have gone to a backup system. The backup reaction wheel was brought online a few years ago and is currently functioning as one of the three prime wheels.
Cassini successfully completed its four-year planned tour and is now in extended mission operations.
More information on the mission is available at: http://saturn.jpl.nasa.gov and http://www.nasa.gov/cassini . The Cassini-Huygens mission is a cooperative project of NASA, the European Space Agency and the Italian Space Agency. JPL, a division of the California Institute of Technology in Pasadena, manages the Cassini mission for NASA’s Science Mission Directorate, Washington, D.C. The Cassini orbiter and its two onboard cameras were designed, developed and assembled at JPL.
Mars Rover Team Diagnosing Unexpected BehaviorMars Exploration Rover Mission Status Report
Artist concept showing one of two Mars Exploration Rovers. Image credit: NASA/JPL-Caltech/Cornell University UPDATED on Jan. 29: Spirit Working Well While Diagnostics Continue
Diagnostic activities performed by Spirit on Thursday, Jan. 29 narrowed the range of factors that may have contributed to its unexpected behavior earlier in the week. No clear explanation has been established yet. Spirit is healthy and responding to commands. It recorded and returned images of nearby scientific targets. The rover team plans further diagnostics on Friday of Spirit’s inertial measurement unit — a combined gyroscope-and-accelerometer device that measures rover movements and attitude. Spirit may resume driving over the weekend.
CORRECTION on Jan. 28: In paragraph 3–Early Tuesday, Spirit reported that it had followed the commands, and in fact had located the sun, but not in its expected location.
PASADENA, Calif. – The team operating NASA’s Mars Exploration Rover Spirit plans diagnostic tests this week after Spirit did not report some of its weekend activities, including a request to determine its orientation after an incomplete drive.
On Sunday, during the 1,800th Martian day, or sol, of what was initially planned as a 90-sol mission on Mars, information radioed from Spirit indicated the rover had received its driving commands for the day but had not moved. That can happen for many reasons, including the rover properly sensing that it is not ready to drive. However, other behavior on Sol 1800 was even more unusual: Spirit apparently did not record the day’s main activities into the non-volatile memory, the part of its memory that persists even when power is off.
On Monday, Spirit’s controllers at NASA’s Jet Propulsion Laboratory in Pasadena, Calif., chose to command the rover on Tuesday, Sol 1802, to find the sun with its camera in order to precisely determine its orientation. Not knowing its orientation could have been one possible explanation for Spirit not doing its weekend drive. Early Tuesday, Spirit reported that it had followed the commands, and in fact had located the sun, but not in its expected location.
“We don’t have a good explanation yet for the way Spirit has been acting for the past few days,” said JPL’s Sharon Laubach, chief of the team that writes and checks commands for the rovers. “Our next steps will be diagnostic activities.”
Among other possible causes, the team is considering a hypothesis of transitory effects from cosmic rays hitting electronics. On Tuesday, Spirit apparently used its non-volatile memory properly.
Despite the rover’s unexplained behavior, Mars Exploration Rovers’ Project Manager John Callas of JPL said Wednesday, “Right now, Spirit is under normal sequence control, reporting good health and responsive to commands from the ground.”
JPL, a division of the California Institute of Technology, Pasadena, manages the Mars Exploration Rover project for the NASA Science Mission Directorate, Washington. Spirit and its twin, Opportunity, landed on Mars in January 2004 and have operated 20 times longer than their original prime missions.
The Human Factor: Understanding the Sources of Rising Carbon Dioxide
The Human Factor: Understanding the Sources of Rising Carbon Dioxide
Artist concept of the Orbiting Carbon Observatory. Image credit: NASA/JPL
Full image and caption Every time we get into our car, turn the key and drive somewhere, we burn gasoline, a fossil fuel derived from crude oil. The burning of the organic materials in fossil fuels produces energy and releases carbon dioxide and other compounds into Earth’s atmosphere. Greenhouse gases such as carbon dioxide trap heat in our atmosphere, warming it and disturbing Earth’s climate.
Scientists agree that human activities have been the primary source for the observed rise in atmospheric carbon dioxide since the beginning of the fossil fuel era in the 1860s. Eighty-five percent of all human-produced carbon dioxide emissions come from the burning of fossil fuels like coal, natural gas and oil, including gasoline. The remainder results from the clearing of forests and other land use, as well as some industrial processes such as cement manufacturing. The use of fossil fuels has grown rapidly, especially since the end of World War II and continues to increase exponentially. In fact, more than half of all fossil fuels ever used by humans have been consumed in just the last 20 years.
Human activities add a worldwide average of almost 1.4 metric tons of carbon per person per year to the atmosphere. Before industrialization, the concentration of carbon dioxide in the atmosphere was about 280 parts per million. By 1958, the concentration of carbon dioxide had increased to around 315 parts per million, and by 2007, it had risen to about 383 parts per million. These increases were due almost entirely to human activity.
While we are able to accurately measure the amount of carbon dioxide in the atmosphere, much about the processes that govern its atmospheric concentration remains a mystery. Scientists still do not know precisely where all the carbon dioxide in our atmosphere comes from and where it goes. They want to learn more about the magnitudes and distributions of carbon dioxide’s sources and the places it is absorbed (sinks). This knowledge will help improve critical forecasts of atmospheric carbon dioxide increases as fossil fuel use and other human activities continue. Such information is crucial to understanding the impact of human activities on climate and for evaluating options for mitigating or adapting to climate change.
Scientists soon expect to get some answers to these and other compelling carbon questions, thanks to the Orbiting Carbon Observatory, a new Earth-orbiting NASA satellite set to launch in early 2009. The new mission will allow scientists to record, for the first time, detailed daily measurements of carbon dioxide, making more than 100,000 measurements around the world each day. The new data will provide valuable new insights into where this important greenhouse gas is coming from and where it is being stored.
Before humans began emitting significant amounts of carbon dioxide into the atmosphere, the atmospheric uptake and loss of carbon dioxide was approximately in balance. “Carbon dioxide in the atmosphere remained pretty stable during the pre-industrial period,” said Gregg Marland of Oak Ridge National Laboratory in Oak Ridge, Tenn. “Carbon dioxide generated by human activity amounts to only about four percent of yearly atmospheric uptake or loss of carbon dioxide, but the result is that the concentration of carbon dioxide in the atmosphere has been growing, on average, by four-tenths of one percent each year for the last 40 years. Though this may not seem like much of an influence, humans have essentially tipped the balance of the global cycling of carbon. Our emissions add significant weight to one side of the balance between carbon being added to the atmosphere and carbon being removed from the atmosphere.
“Plant life and geochemical processes on land and in the ocean ‘inhale’ large amounts of carbon dioxide through photosynthesis and then ‘exhale’ most of it back into the atmosphere,” Marland continued. “Humans, however, have altered the carbon cycle over the last couple of centuries, through the burning of fossil fuels that enable us to live more productively. Now that humans are acknowledging the environmental effects of our dependence on fossil fuels and other carbon dioxide-emitting activities, our goal is to analyze the sources and sinks of this carbon dioxide and to find better ways to manage it.”
Current estimates of human-produced carbon dioxide emissions into the atmosphere are based on inventories and estimates of where fossil fuels are burned and where other carbon dioxide-producing human activities are occurring. However, the availability and precision of this information is not uniform around the world, not even from within developed countries like the United States.
The Orbiting Carbon Observatory’s highly sensitive instrument will measure the distribution of carbon dioxide, sampling information around the globe from its space-based orbit. Though the instrument will not directly measure the carbon dioxide emissions from every individual smokestack, tailpipe or forest fire, scientists will incorporate the observatory’s global measurements of varying carbon dioxide concentrations into computer-based models. The models will infer where and when the sources are emitting carbon dioxide into the atmosphere.
“The Orbiting Carbon Observatory data differ from that of other missions like the Atmospheric Infrared Sounder instrument on NASA’s Aqua satellite by having a relatively small measurement ‘footprint,’” said Kevin Gurney, associate director of the Climate Change Research Center at Purdue University in West Lafayette, Ind. “Rather than getting an average amount of carbon dioxide over a large physical area like a state or country, the mission will capture measurements over scales as small as a medium-sized city. This allows it to more accurately distinguish movements of carbon dioxide from natural sources versus from fossil fuel-based activities.”
“Essentially, if you visualize a column of air that stretches from Earth’s surface to the top of the atmosphere, the Orbiting Carbon Observatory will identify how much of that vertical column is carbon dioxide, with an understanding that most is emitted at the surface,” said Marland. “Simply, it will act like a plane observing the smoke from forest fires down below, with the task of assessing where the fires are and how big they are. Compare that aerial capability with sending a lot of people into the forest looking for fires. In this vein, the observatory will use its vantage point from space to peer down and capture a picture of where the sources and sinks of carbon dioxide are, rather than our cobbling data together from multiple sources with less frequency, reliability and detail.”
Gurney believes the Orbiting Carbon Observatory will also complement a NASA/U.S. Department of Energy jointly-funded project he is currently leading called Vulcan.
“Vulcan estimates the movement of carbon dioxide through the combustion of fossil fuels at very small scales. Vulcan and the Orbiting Carbon Observatory together will act like partners in closing the carbon budget, with Vulcan estimating movements in the atmosphere from the bottom-up and the Orbiting Carbon Observatory estimating sources from the top-down,” he said. “By tackling the problem from both perspectives, we’ll stand to achieve an independent, mutually-compatible view of the carbon cycle. And the insight gained by combining these top-down and bottom-up approaches might take on special significance in the near future as our policymakers consider options for regulating carbon dioxide across the entire globe.”
For more information on this topic, see: http://www.nasa.gov/oco and http://oco.jpl.nasa.gov .
Artist concept of Stardust-Next. Image credit: NASA/JPL
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Saturday, Feb. 7, marks the 10th anniversary of the launch of NASA’s well-traveled Stardust spacecraft.
Launched on Feb. 7, 1999, Stardust , covered 3-billion-miles during its first seven years in space before returning the world’s first samples from a known comet. Stardust’s tennis racket-like, aerogel-lined collector was extended to capture particles hurtling at it at about six times the speed of a rifle bullet, as the spacecraft flew within 240 kilometers (149 miles) of comet Wild 2 in January 2004. The return capsule landed Jan. 15, 2006, in Utah, carrying both interstellar and comet particles, completing the first U.S. space mission to return extraterrestrial material from beyond the orbit of Mars. Two days later the capsule was transported to a curatorial facility at NASA’s Johnson Space Center in Houston.
With its prime mission complete, NASA re-designated the Stardust mission as Stardust-NExT. Short for Stardust-New Exploration of Tempel, Stardust-NExT is a low-cost, Discovery Program mission of opportunity that will expand the investigation of comet Tempel 1 initiated by NASA’s Deep Impact spacecraft. The extended mission tasks the Stardust spacecraft to fly by the comet Tempel 1 on Feb. 14, 2011. During the flyby, it will obtain high-resolution images of the comet?s coma and nucleus, as well as measurements of the composition, size distribution, and flux of dust emitted into the coma. Mission planners hope Stardust-NExT will provide important new information on how Jupiter-family comets evolve and how they formed 4.6 billion years ago.
The Jet Propulsion Laboratory, a division of the California Institute of Technology, Pasadena, manages Stardust-NExT for the NASA Science Mission Directorate, Washington, D.C. Joseph Veverka of Cornell University, Ithaca, N.Y., is the mission’s principal investigator. Lockheed Martin Space Systems, Denver, manages day-to-day mission operations.
While the Stardust spacecraft is unavailable for public viewing at present (it is more than 13.5 million kilometers, or 8.4 million miles, from Earth), the public can view its sample return capsule. In Jan. 2006, the capsule became the fastest manmade object ever to enter Earth’s atmosphere at over 46,400 kilometers per hour (28,800 mph). The capsule is on display at the National Air and Space Museum’s Milestones of Flight Gallery in Washington.
To learn more about the mission, visit http://stardustnext.jpl.nasa.gov/ .
February 7, 2009 at 2:30 am
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