The Cassini-Huygens Mission to SaturnANS Nuclear CafeFebruary 20, 2013, 2:57PM|Stan TackettCassini-Huygens is a Flagship-class NASA-ESA-ASI robotic spacecraft sent to the Saturn system. It has studied the planet and its many natural satellites since its arrival there in 2004, as well as observing Jupiter and the Heliosphere, and testing the theory of relativity. Launched in 1997 after nearly two decades of gestation, it includes a Saturn orbiter Cassini and an atmospheric probe/lander Huygens that landed in 2005 on the moon Titan. Cassini is the fourth space probe to visit Saturn and the first to enter orbit, and its mission is ongoing as of 2013. It is powered by a plutonium power source, and has facilitated many landmark scientific discoveries in its mission to the stars. A Cassini RTG before installationBecause of Saturn's distance from the Sun, solar arrays were not feasible as power sources for this space probe. To generate enough power, such arrays would have been too large and too heavy. Instead, the Cassini orbiter is powered by three radioisotope thermoelectric generators (RTGs), which use heat from the natural decay of about 33 kg (73 lb) of plutonium-238 (in the form of plutonium dioxide) to generate direct current electricity via thermoelectrics. The RTGs on the Cassini mission have the same design as those used on the New Horizons, Galileo, and Ulysses space probes, and they were designed to have a very long operational lifetime. At the end of the nominal 11-year Cassini mission, they will still be able to produce 600 to 700 watts of electrical power. One of the spare RTGs for the Cassini mission was used to power the New Horizons mission to Pluto and the Kuiper belt. A glowing-hot plutonium pellet that will become the power source for the probe's RTGTo gain interplanetary momentum while in flight, the trajectory of the Cassini mission included several gravitational slingshot maneuvers: two fly-by passes of Venus, one more of the Earth, and then one of the planet Jupiter. The terrestrial fly-by maneuver was successful, with Cassini passing by 500 km (310 mi) above the Earth on August 18, 1999. Had there been a malfunction causing the Cassini space probe to collide with the Earth, NASA's complete environmental impact study estimated that, in the worst case (with an acute angle of entry in which Cassini would gradually burn up), a significant fraction of the 33 kg of plutonium-238 inside the RTGs could have been dispersed into the Earth's atmosphere. NASA estimated the odds against that happening at more than 1 million to one.Selected events and discoveries for CassiniCassini made its closest approach to Jupiter on December 30, 2000, and made many scientific measurements. About 26,000 images of Jupiter were taken during the months-long flyby. Cassini produced the most detailed global color portrait of Jupiter yet (see image at right), in which the smallest visible features are approximately 60 km (37 mi) across. The New Horizons mission to Pluto captured more recent images of Jupiter, with a closest approach on February 28, 2007.A major finding of the flyby, announced on March 6, 2003, was of Jupiter's atmospheric circulation. Dark "belts" alternate with light "zones" in the atmosphere, and scientists had long considered the zones, with their pale clouds, to be areas of upwelling air, partly because many clouds on Earth form where air is rising. But analysis of Cassini imagery showed that individual storm cells of upwelling bright-white clouds, too small to see from Earth, pop up almost without exception in the dark belts.Other atmospheric observations included a swirling dark oval of high atmospheric-haze, about the size of the Great Red Spot, near Jupiter's north pole. Infrared imagery revealed aspects of circulation near the poles, with bands of globe-encircling winds, with adjacent bands moving in opposite directions. The same announcement also discussed the nature of Jupiter's rings. Light scattering by particles in the rings showed the particles were irregularly shaped (rather than spherical) and likely originate as ejecta from micrometeorite impacts on Jupiter's moons, probably Metis and Adrastea.Tests of General RelativityOn October 10, 2003, the Cassini science team announced the results of tests of Einstein's Theory of General Relativity, which were done by using radio waves that were transmitted from the Cassini space probe. This remains the best measurement of post-Newtonian parameter γ; the result γ = 1 + (2.1 ± 2.3) - 10-5 agrees with the predictions of standard General Relativity.The radio scientists measured a frequency shift in the radio waves to and from the spacecraft, while those signals traveled close to the Sun. According to the Theory of General Relativity, a massive object like the Sun causes space-time to curve, and a beam of radio waves (or light, or any form of electromagnetic radiation) that passes by the Sun has to travel farther because of this curvature.The extra distance that the radio waves traveled from the Cassini craft, past the Sun, to the Earth delayed their arrival. The amount of this time delay provided a sensitive test of the calculated predictions of Einstein's Relativity Theory.Although some measurable deviations from the values that are calculated using the General Theory of Relativity are predicted by some unusual cosmological models, no deviations were found by this experiment. Previous tests using radio waves that were transmitted by the Viking and Voyager space probes were in agreement with the calculated values from General Relativity to within an accuracy of one part in one thousand. The more refined measurements from the Cassini space probe experiment improved this accuracy to about one part in 51,000, with the measured data firmly supporting Einstein's General Theory of Relativity.New moons of SaturnUsing images taken by Cassini, three new moons of Saturn were discovered in 2004. They are very small and were given the provisional names S/2004 S 1, S/2004 S 2, and S/2004 S 5, before being named Methone, Pallene, and Polydeuces at the beginning of 2005.On May 1, 2005, a new moon was discovered by Cassini in the Keeler gap. It was given the designation S/2005 S 1, before being named Daphnis. The only other known moon inside Saturn's ring system is the moon Pan.A fifth new moon was discovered by Cassini on May 30, 2007, now known as Anthe.A press release on February 3, 2009, showed a sixth new moon found by Cassini. The moon is approximately 1/3 of a mile in diameter within the G-ring of the ring system of Saturn, and is now named Aegaeon.A press release on November 2, 2009, mentions the seventh new moon found by Cassini on July 26, 2009. It is presently labeled S/2009 S 1, and is approximately 300 m (984 ft.) in diameter in the B-ring system.Phoebe flybyOn June 11, 2004, Cassini flew by the moon Phoebe. This was the first opportunity for closeup studies of this moon since the Voyager 2 flyby. It also was Cassini's only possible flyby for Phoebe due to the mechanics of the available orbits around Saturn.The first closeup images were received on June 12, 2004, and mission scientists immediately realized that the surface of Phoebe looks different from asteroids visited by spacecraft. Parts of the heavily cratered surfaces look very bright in those pictures, and it is currently believed that a large amount of water ice exists under its immediate surface.Saturn rotationIn an announcement on June 28, 2004, Cassini program scientists described the measurement of the rotational period of Saturn. Since there are no fixed features on the surface that can be used to obtain this period, the repetition of radio emissions was used. These new data agree with the latest values measured from Earth, and constitute a puzzle to the scientists. It turns out that the radio rotational period has changed since it was first measured in 1980 by Voyager, and that it is now six minutes longer. This does not indicate a change in the overall spin of the planet, but is thought to be due to movement of the source of the radio emissions to a different latitude, at which the rotation rate is different.Orbiting SaturnOn July 1, 2004, the Cassini spacecraft flew through the gap between Saturn's F and G rings and achieved orbit, after a seven-year voyage. Cassini is the first spacecraft to ever orbit Saturn.The Saturn Orbital Insertion maneuver performed by Cassini was complex, requiring the craft to orient its high-gain antenna away from Earth and along its flight path, to shield its instruments from particles in Saturn's rings. Once the craft crossed the ring plane, it had to rotate again to point its engine along its flight path, and then the engine fired to decelerate the craft by 622 m/s (1391 mph) to allow Saturn to capture it. Cassini was captured by Saturn's gravity at around 8:54 p.m. Pacific Daylight Time on June 30, 2004. During the maneuver, Cassini passed within 20,000 km (12,000 mi) of Saturn's cloud tops.Titan flybysCassini had its first distant flyby of Saturn's largest moon, Titan, on July 2, 2004, only a day after orbit insertion, when it approached to within 339,000 km (211,000 mi) of Titan and provided the best look at Titan's surface to date. Images taken through special filters (able to see through the moon's global haze) showed south polar clouds thought to be composed of methane, and surface features with widely differing brightness. On October 27, 2004, the spacecraft executed the first of 45 planned close flybys of Titan, when it flew a mere 1,200 kilometers above the moon. Almost four gigabits of data were collected and transmitted to Earth, including the first radar images of the moon's haze-enshrouded surface. It revealed the surface of Titan (at least the area covered by radar) to be relatively level, with topography reaching no more than about 50 meters in altitude. The flyby provided a remarkable increase in imaging resolution over previous coverage. Images with up to 100 times better resolution were taken and are typical of resolutions planned for future Titan flybys.Huygens lands on TitanCassini released the Huygens probe on December 25, 2004, by means of a spring and spiral rails intended to rotate the probe for greater stability. Huygens entered the atmosphere of Titan on January 14, 2005, and after a two-and-a-half-hour descent landed on solid ground. Although Cassini successfully relayed 350 of the pictures that it received from Huygens of its descent and landing site, a software error failed to turn on one of the Cassini receivers and resulted in the loss of the other 350 pictures.Enceladus flybys Enceladus backdropped by Saturn's ring shadows in 2007During the first two close flybys of the moon Enceladus in 2005, Cassini discovered a "deflection" in its local magnetic field that is characteristic for the existence of a thin but significant atmosphere. Other measurements obtained at that time point to ionized water vapor as being the atmosphere's main constituent. Cassini also observed water ice geysers erupting from the south pole of Enceladus, which gives more credibility to the idea that Enceladus is supplying the particles of Saturn's E ring. Mission scientists hypothesize that there may be pockets of liquid water near the surface of the moon that fuel the eruptions, making Enceladus one of the few bodies in the Solar System known to contain liquid water.On March 12, 2008, Cassini made a close flyby of Enceladus, getting within 50 km of the moon's surface. The spacecraft passed through the plumes extending from its southern geysers, detecting water, carbon dioxide, and various hydrocarbons with its mass spectrometer, while also mapping surface features with its infrared spectrometer that were measured to be at much higher temperature than their surroundings. Cassini was unable to collect data with its cosmic dust analyzer due to an unknown software malfunction.Radio occultations of Saturn's ringsIn May 2005, Cassini began a series of occultation experiments to measure the size-distribution of particles in Saturn's rings, and measure the atmosphere of Saturn itself. For more than four months, Cassini completed orbits designed for this purpose. During these experiments, Cassini flew behind the ring plane of Saturn, as seen from Earth, and transmitted radio waves through the particles. The radio signals were received on Earth, where the frequency, phase, and power of the signal were analyzed to help determine the structure of the rings.Spoke phenomenon verifiedIn images captured September 5, 2005, Cassini detected spokes in Saturn's rings, previously seen only by the visual observer Stephen James O'Meara in 1977 and then confirmed by the Voyager space probes in the early 1980s.Lakes of TitanRadar images obtained on July 21, 2006, appear to show lakes of liquid hydrocarbon (such as methane and ethane) in Titan's northern latitudes. This is the first discovery of currently-existing lakes anywhere besides Earth. The lakes range in size from one to 100 kilometers across. Titan "sea" (left) compared at scale to Lake Superior (right)On March 13, 2007, the Jet Propulsion Laboratory announced that it had found strong evidence of seas of methane and ethane in the northern hemisphere of Titan. At least one of these is larger than any of the Great Lakes in North America. A Saturnine hurricaneIn November 2006, scientists discovered a storm at the south pole of Saturn with a distinct eyewall. This is characteristic of Earth's hurricanes and had never before been seen on another planet. Unlike a Terran hurricane, the storm appears to be stationary at the pole. The storm is 8,000 kilometers (5,000 mi) across, and 70 kilometres (43 mi) high, with winds blowing at 560 km/hr (350 mph).Great Storm of 2010 and its aftermath Storm in the North 2011On October 25, 2012, Cassini witnessed the aftermath of the massive Great White Spot storm that recurs roughly every 30 years on Saturn. Data from Cassini's composite infrared spectrometer instrument indicated a powerful discharge from the storm that caused a temperature spike in the stratosphere of Saturn 150 °F (83 kelvins) above normal. Simultaneously, a huge increase in ethylene gas was detected by NASA researchers at Goddard Research Center in Greenbelt, Maryland. Ethylene is a colorless and odorless gas that is highly uncommon on Saturn and is produced both naturally and through man-made sources on Earth. The storm that produced this discharge was first observed by Cassini on December 5, 2010, in Saturn's northern hemisphere. The storm is the first of its kind to be observed by a spacecraft in orbit around Saturn as well as the first to be observed at thermal infrared wavelengths, allowing scientists to observe the temperature of Saturn's atmosphere and track phenomena that are invisible to the naked eye. The spike of ethylene gas that was produced by the storm reached levels that were 100 times more than those thought possible for Saturn. Scientists have also determined that the storm witnessed was the largest, hottest stratospheric vortex ever detected in our solar system, initially being larger than Jupiter's Great Red Spot.Mission extensionOn April 15, 2008, Cassini received funding for a two-year extended mission. This consisted of 60 more orbits of Saturn, with 21 more close Titan flybys, seven of Enceladus, six of Mimas, eight of Tethys, and one targeted flyby each of Dione, Rhea, and Helene. The extended mission began on July 1, 2008, and was renamed the Cassini Equinox Mission as it coincided with Saturn's equinox.A proposal was submitted to NASA for a second mission extension, provisionally named the extended-extended mission or XXM. This was subsequently approved and renamed the Cassini Solstice Mission. It will see Cassini orbiting Saturn 155 more times, conducting 54 additional flybys of Titan, and 11 more of Enceladus. The chosen mission ending is a series of very close Saturn passes, passing inside the rings, then a plunge into the Saturn atmosphere around the 2017 northern summer solstice, to destroy the spacecraft._______________________ TackettStan Tackett holds undergraduate degrees in mathematics and computer science, and is currently pursuing a Master's degree in computer science with specializations in uses of artificial intelligence in the nuclear industry. His interests in nuclear engineering include nuclear propulsion for space travel, fusion, computational fluid dynamics and reactor physics. In his spare time he reads Piers Anthony as much as possible, and enjoys writing and editing crossover science fiction stories.Tags:cassininasaplutoniumrtgspace applicationsstan tackettShare:LinkedInTwitterFacebook
DOE steps up plutonium production for future space explorationThis high-resolution still image is from a video taken by several cameras as NASA’s Perseverance rover touched down on Mars on February 18. Credits: NASA/JPL-CaltechNASA’s Perseverance rover, which successfully landed on Mars on February 18, is powered in part by the first plutonium produced at Department of Energy laboratories in more than 30 years. The radioactive decay of Pu-238 provides heat to radioisotope thermoelectric generators (RTGs) like the one onboard Perseverance and would also be used by the Dynamic Radioisotope Power System, currently under development, which is expected to provide three times the power of RTGs.Idaho National Laboratory is scaling up the production of Pu-238 to help meet NASA’s production goal of 1.5 kg per year by 2026, the DOE announced on February 17.Go to Article
NASA’s radioisotope-powered science will persevere on MarsMembers of the Perseverance rover team in Mission Control at NASA’s Jet Propulsion Laboratory react after receiving confirmation of a successful landing. Photo: NASA/Bill IngallsNASA mission control and space science fans around the world celebrated the safe landing of the Mars 2020 Perseverance rover on February 18 after a journey of 203 days and 293 million miles. Landing on Mars is difficult—only about 50 percent of all previous Mars landing attempts have succeeded—and a successful landing for Perseverance, the fifth rover that NASA has sent to Mars, was not assured. Confirmation of the successful touchdown was announced at NASA’s Jet Propulsion Laboratory in Pasadena, Calif., at 3:55 p.m. EST.“This landing is one of those pivotal moments for NASA, the United States, and space exploration globally—when we know we are on the cusp of discovery and sharpening our pencils, so to speak, to rewrite the textbooks,” said acting NASA administrator Steve Jurczyk. “The Mars 2020 Perseverance mission embodies our nation’s spirit of persevering even in the most challenging of situations, inspiring, and advancing science and exploration. The mission itself personifies the human ideal of persevering toward the future and will help us prepare for human exploration of the Red Planet.”Only radioisotope thermoelectric generators (RTG) can provide the long-lasting, compact power source that Perseverance needs to carry out its long-term exploratory mission. Perseverance carries an RTG powered by the radioactive decay of plutonium-238 that was supplied by the Department of Energy. ANS president Mary Lou Dunzik-Gougar and CEO and executive director Craig Piercy congratulated NASA after the successful landing, acknowledging the critical contributions of the DOE’s Idaho National Laboratory, Oak Ridge National Laboratory, and Los Alamos National Laboratory.Go to Article
Statement on the successful landing of NASA's Perseverance rover on MarsANS congratulates NASA for the successful landing of Perseverance on Mars. We look forward to watching from afar its exploration of the Red Planet and search for past microbial life. This is a proud moment as well for nuclear science and technology as a multi-mission radioisotope thermoelectric generator will be powering the rover to mission success.Go to Article
INL seeks efficiency boost for radioisotope-powered spacecraftThe RTG used to power the Mars Perseverance rover is shown here being placed in a thermal vacuum chamber for testing in a simulated near-space environment. Source: INLThe Department of Energy’s Idaho National Laboratory is celebrating the scheduled landing of the Perseverance rover on the surface of Mars in just two days’ time with a live Q&A today, February 16, from 3 p.m. to 4:30 p.m. EST).INL and Battelle Energy Alliance, its management and operating contractor, are already looking ahead to the next generation of plutonium-powered spacecraft: the Dynamic Radioisotope Power System (Dynamic RPS). INL announced on February 15 that it is partnering with NASA and the DOE to seek industry engagement to further the design of this new power system.Go to Article
NASA names ANS member Bhavya Lal as acting chief of staffLalNASA has appointed ANS member Bhavya Lal as the space agency's acting chief of staff. She served as a member of the Biden Presidential Transition Agency Review Team for the agency, NASA said.ANS contribution: Lal cofounded and is cochair of the policy track of the ANS annual conference on Nuclear and Emerging Technologies in Space (NETS). She has contributed as an author and guest editor for the upcoming NETS 2020 special issue of ANS technical journal Nuclear Technology.In addition, she helps organize a seminar series on space history and policy with the Smithsonian National Air and Space Museum.Go to Article
American Nuclear Society recommends NNSA use surplus plutonium for clean energyLa Grange Park, IL – The American Nuclear Society (ANS) is recommending that the National Nuclear Security Administration (NNSA) consider using surplus plutonium from nuclear weapons as fuel for advanced reactors to generate carbon-free energy, rather than diluting and disposing 34 metric tons of weapons-grade plutonium at the Waste Isolation Pilot Plant (WIPP) in New Mexico as proposed by the NNSA.Go to Article
Trump leaves space nuclear policy executive order for Biden teamA hot fire test of the core stage for NASA’s Space Launch System rocket at Stennis Space Center in Mississippi was not completed as planned. The SLS is the vehicle meant to propel a crewed mission to the moon in 2024. Source: NASA TelevisionAmong the executive orders President Trump issued during his last weeks in office was “Promoting Small Modular Reactors for National Defense and Space Exploration,” which builds on the Space Policy Directives published during his term. The order, issued on January 12, calls for actions within the next six months by NASA and the Department of Defense (DOD), together with the Department of Energy and other federal entities. Whether the Biden administration will retain some, all, or none of the specific goals of the Trump administration’s space nuclear policy remains to be seen, but one thing is very clear: If deep space exploration remains a priority, nuclear-powered and -propelled spacecraft will be needed.The prospects for near-term deployment of nuclear propulsion and power systems in space improved during Trump’s presidency. However, Trump left office days after a hot fire test of NASA’s Space Launch System (SLS) rocket did not go as planned. The SLS rocket is meant to propel crewed missions to the moon in 2024 and to enable a series of long-duration lunar missions that could be powered by small lunar reactor installations. The test on January 16 of four engines that were supposed to fire for over eight minutes was automatically aborted after one minute, casting some doubt that a planned November 2021 Artemis I mission can go ahead on schedule.Go to Article
NNSA to hold virtual public meetings regarding Surplus Plutonium Disposition ProgramThe Department of Energy’s National Nuclear Security Administration will hold two virtual public meetings on a new environmental impact statement for its Surplus Plutonium Disposition Program (SPDP). The meetings will be held on Monday, January 25, from 5 p.m. to 9 p.m. (ET) and Tuesday, January 26, from 7 p.m. to 11 p.m. (ET). Participants can join by computer, telephone, or other device. A Notice of Intent contains a full description of the proposal and other options for providing public comment until February 1.The program: The SPDP EIS will analyze alternatives for the disposition of 34 metric tons of surplus plutonium using the capabilities at multiple sites across the United States. The NNSA’s preferred alternative, the dilute and dispose approach (also known as plutonium downblending), includes converting pit and non-pit plutonium to oxide, blending the oxidized plutonium with an adulterant, and emplacing the resulting transuranic waste underground in the Waste Isolation Pilot Plant (WIPP), in New Mexico. The approach would require new, modified, or existing capabilities at the Savannah River Site in South Carolina, Los Alamos National Laboratory in New Mexico, the Pantex Plant in Texas, and WIPP.Go to Article
U.K. launches study into nuclear-powered space explorationA new research contract between the U.K. Space Agency and Rolls-Royce will see planetary scientists working together to explore nuclear power as an energy source for deep space missions in the decades to come. The effort is similar to one that the United States is undertaking through NASA."Space nuclear power and propulsion is a game-changing concept that could unlock future deep-space missions that take us to Mars and beyond," said Graham Turnock, chief executive of the U.K Space Agency, on January 12. "This study will help us understand the exciting potential of atomic-powered spacecraft, and whether this nascent technology could help us travel further and faster through space than ever before."Go to Article
The year in review 2020: Research and ApplicationsHere is a look back at the top stories of 2020 from our Research and Applications section in Newswire and Nuclear News magazine. Remember to check back to Newswire soon for more top stories from 2020.Research and Applications sectionARDP picks divergent technologies in Natrium, Xe-100: Is nuclear’s future taking shape? The Department of Energy has put two reactor designs—TerraPower’s Natrium and X-energy’s Xe-100—on a fast track to commercialization, each with an initial $80 million in 50-50 cost-shared funds awarded through the Advanced Reactor Demonstration Program. Read more.Go to Article