JET PROPULSION LABORATORY
CALIFORNIA INSTITUTE OF TECHNOLOGY
NATIONAL AERONAUTICS AND SPACE ADMINISTRATION
September 1, 1999
NEW CASSINI MOON IMAGES SHOW SPACECRAFT CAMERA IS IN TOP FORM
New images and brief movies of the Moon, taken by the camera
system on NASA's Saturn-bound Cassini spacecraft when it flew
through the Earth-Moon system two weeks ago, are available at
http://photojournal.jpl.nasa.gov/
and at
http://ciclops.lpl.arizona.edu/
The black-and-white lunar images were among a sequence taken of the Moon by Cassini's sophisticated camera during the August 17 flyby of Earth. Cassini, launched in October 1997, flew past Earth to gain enough energy to reach distant Saturn in 2004, where the spacecraft will make detailed studies for four years.
"These are the first images taken by Cassini for both photogenic and scientific purposes, and they illustrate that the cameras are functioning beautifully," said Dr. Carolyn C. Porco, team leader of the 14-member Cassini imaging team and an associate professor of planetary sciences at the University of Arizona in Tucson.
The images released today are a wide-angle movie, a narrow- angle video clip, the Moon in ultraviolet and a "triptych" (a three-paneled composite image) of the Moon. The face of the Moon seen in these images is nearly identical to that seen from Earth.
They were taken from a distance of about 234,000 miles (377,000 kilometers) about 80 minutes prior to Cassini's closest approach to Earth. The lunar images were taken to calibrate the camera system using a familiar and well-studied target. (No images of Earth were planned or taken during Cassini's flyby.)
At Saturn, Cassini's imaging system will search for lightning, investigate the cloud structure and meteorology of Saturn's and Titan's atmospheres, image the surfaces of Saturn's many icy satellites, study the ring system, and peer through the hazy atmosphere of Titan to view that moon's intriguing surface. The camera system is one of a dozen scientific instruments on the spacecraft.
Cassini is a joint mission of NASA, the European Space Agency and Italian Space Agency, and is managed by NASA's Jet Propulsion Laboratory, Pasadena, CA, for NASA's Office of Space Science, Washington DC. JPL is a division of the California Institute of Technology, Pasadena, CA.
University of Arizona News Services
Sept. 1, 1999
Cassini images and brief video clips are being released today on the Internet at http://ciclops.lpl.arizona.edu, the official web site of the Cassini Imaging Science Team, and at http://photojournal.jpl.nasa.gov.
CICLOPS, the Cassini Imaging Central Laboratory for Operations, is the hub of imaging team operations and is located in the Lunar and Planetary Laboratory at the University of Arizona in Tucson. CICLOPS houses the Cassini Imaging Diary, the collection of released images that will document Cassini's travels over the next decade as it makes its way by Jupiter and into Saturn orbit for its four-year tour of the Saturn system.
"These are the first images taken by Cassini for both photogenic and scientific purposes, and they illustrate that the cameras are functioning beautifully" said Carolyn C. Porco, leader of the 14-member Cassini Imaging Science Team (ISS). "The cameras promise a bonanza of imaging delights at Jupiter in late 2000 and at Saturn beginning in the year 2004," she added. Porco is associate professor of planetary sciences at the University of Arizona in Tucson.
The images released today are a wide-angle movie, a narrow-angle video clip, the moon in ultraviolet and "triptych" of the moon. They were taken from a distance of about 234,000 miles about 80 minutes prior to Cassini¹s closest approach to Earth.
The wide-angle movie is a brief movie taken with the ISS wide-angle camera as the Cassini spacecraft glided by the moon. The narrow-angle video is a 3-frame clip made from the highest resolution images taken as the moon passed through the narrow-angle field of view. The moon in ultraviolet is one of the best, highest resolution frames taken at ultraviolet wavelengths during Cassini¹s closest approach to the moon. The "triptych" of the moon is a composite image made from the three narrow-angle Cassini images included in the video clip.
The Cassini Imaging Science System was specifically designed for exploring the Saturn system, and includes spectral filters and imaging capabilities for a multitude of scientific objectives. At Saturn, Cassini¹s imaging system will search for lightning, investigate the cloud structure and meteorology of Saturn¹s and Titan¹s atmospheres, photograph the surfaces of Saturn¹s many icy satellites, study the ring system and peer through Titan¹s hazy atmosphere to view that moon¹s mysterious surface. The imaging system will be further tested and used in studying Jupiter and its satellites and rings during the Cassini Jupiter flyby in late 2000, Porco said.
The ISS consists of two framing cameras. The narrow-angle camera is a reflecting telescope with a focal length of 2000 mm and a field of view of 0.35 degrees. The wide-angle camera is a refractor with a focal length of 200 mm and a field of view of 3.5 degrees. (The full moon as seen from Earth would cover a half degree of the sky. The narrow-angle camera view of the moon seen from Cassini at moon closest approach is about 70 percent of that.)
Each camera is outfitted with a large number of spectral filters which, taken together, span the electromagnetic spectrum from the ultraviolet (2000 Angstroms) to the infrared (1.1 microns). The Cassini cameras cover a wavelength region four times greater than did Voyager cameras that visited the outer solar system planets in the 1980s.
At the heart of each camera is a charged coupled device (CCD) detector consisting of a 1024 square array of pixels. The data system allows many options for data collection, including choices for a data-compression technique called "on-chip summing."
Cassini ISS scientists are:
The Cassini mission, which is a joint mission of NASA, the European Space Agency (ESA) and the Italian Space Agency (ASI) is scheduled to reach Saturn in mid-2004. The Cassini orbiter will then begin its 4-year study of Saturn, its rings, moons and magnetic environment. The spacecraft carries ESA's Huygens probe. The probe will detach from the orbiter a few months after arrival at Saturn and parachute six science instruments to the surface of Titan.
The Cassini mission is managed by NASA's Jet Propulsion Laboratory in Pasadena, Calif., for NASA¹s Office of Space Science, Washington, D.C. JPL is a division of the California Institute of Technology.
August 18, 1999
The spacecraft, which carries 72 pounds of radioactive plutonium fuel to make electricity, reached its closest point to Earth around 11:30 p.m. before heading for the outer solar system.
When it reaches Saturn in 2004, Cassini is to spend four years studying the planet, its rings and some of its 18 moons. The spacecraft was launched from Cape Canaveral in late 1997.
It will be a few days before NASA can say exactly how close Cassini came to Earth, but they expected it to reach about 725 miles above the southeastern Pacific Ocean.
Everything went flawlessly, according to Cassini's controllers at the agency's Jet Propulsion Laboratory in Pasadena, Calif.
"On time, on target, as usual," said NASA spokeswoman Mary Beth Murrill.
NASA's critics had feared the probe could stray off course, crash to Earth, burn up and release some of its cancer-causing plutonium. NASA put the odds of that happening at less than 1 in 1 million.
Despite the successful flyby, the nuclear foes say they will continue protesting NASA's use of the radioactive fuel that has been used to power 27 missions to date.
"It's a game of cosmic Russian roulette, and it appears that this time the gun has fired with a blank in it," said Michio Kaku, a physics professor at the City University of New York and an opponent of nuclear power in space.
"But NASA hasn't learned its lesson yet. There are eight more plutonium (missions) being planned. There are eight more bullets in the chamber."
NASA officials say they use the fuel only on flights when solar power isn't viable because the probes travel too far from the sun.
Through its natural decay, the plutonium releases heat that is converted into electricity to power a spacecraft's instruments.
The other plutonium flights possible include missions to the Jupiter moon Europa, where an ocean may be entombed beneath an icy crust. Pluto, which has yet to be studied by NASA probes, also is a target.
"It appears likely that we'll use it again," NASA spokesman Doug Isbell said from agency headquarters in Washington, D.C. "We've got a proven record, and we are quite confident that it can be done safely."
NASA Space Science News for August 18, 1999
Just Passing By Earth: Earthlings bid farewell to the Cassini spacecraft last night as the Saturn-bound mission successfully completed a highly accurate pass of Earth. The flyby gave Cassini a boost in speed, sending the spacecraft on toward the ringed planet. This story includes a tutorial on gravity assist maneuvers.
JET PROPULSION LABORATORY
CALIFORNIA INSTITUTE OF TECHNOLOGY
NATIONAL AERONAUTICS AND SPACE ADMINISTRATION
August 17, 1999
Earthlings bid farewell to the Cassini spacecraft tonight as the Saturn-bound mission successfully completed a highly accurate pass of Earth at 8:28 p.m. Pacific Daylight Time (03:28 Universal Time August 18). The flyby gave Cassini a 5.5-kilometer-per- second (about 12,000-mile-per-hour) boost in speed, sending the spacecraft on toward the ringed planet more than 1 billion kilometers (almost one billion miles) away.
Engineers at NASA's Jet Propulsion Laboratory confirmed that the spacecraft flew past Earth at an altitude of about 1,171 kilometers (727 miles), passing most closely above the eastern South Pacific at -23.5 degrees latitude and 231.5 degrees longitude. Cassini may have been visible from small islands in that area, such as Pitcairn Island or Easter Island.
The spacecraft remains in excellent health as it continues along its seven-year-long journey to Saturn. Having completed its cruise among the inner planets, Cassini's future now resides in the cold, dark realm of the outer planets. The spacecraft will pass by Jupiter on December 30, 2000; the giant planet's gravity will bend Cassini's flight path to put it on course for arrival into orbit around Saturn on July 1, 2004.
Cassini's mission is to study Saturn, its moons, elaborate rings, and its magnetic and radiation environment for four years. Cassini will also deliver the European Space Agency's Huygens probe to parachute to the surface of Saturn's moon Titan. Titan is of special interest partly because of its many Earthlike characteristics, including a mostly nitrogen atmosphere and the presence of organic molecules in the atmosphere and on its surface. Lakes or seas of ethane and methane may exist on its surface.
The Cassini/Huygens program is a joint endeavor of NASA, the European Space Agency and the Italian Space Agency. The Cassini orbiter, built by NASA, and the Huygens probe, provided by the European Space Agency (ESA), were mated together and launched as a single package from Cape Canaveral, Florida, on October 15, 1997. Cassini's dish-shaped high-gain antenna was provided for the mission by the Italian Space Agency. At Saturn, the Huygens probe will detach from Cassini to parachute to the surface of Titan on November 30, 2004.
Nine of Cassini's 12 science instruments were turned on to make observations of the Earth/Moon system. Scientific and engineering data from the Earth flyby will be transmitted by Cassini to receiving stations of NASA's Deep Space Network over coming days.
The mission is managed by NASA's Jet Propulsion Laboratory, Pasadena, CA. JPL is a division of the California Institute of Technology.
ESA
Paris, 18 August 1999
Engineers at ESA’s control centre ESOC in Darmstadt, Germany, and NASA's Jet Propulsion Laboratory, in Pasadena, California, confirmed that the spacecraft came within about 1171 kilometres of Earth, as planned, passing over the eastern South Pacific. Cassini-Huygens may have been visible from small islands in that area, such as Pitcairn or Easter Island. The closest approach point is located at 23.5° South and 128.5° West.
"Everything worked just perfectly and we’re very happy," said Jean-Pierre Lebreton, ESA project scientist for Huygens. "Now we’re looking forward to an exciting mission of discovery inside the atmosphere and on the surface of Titan, the largest moon of Saturn."
The spacecraft remains in excellent condition as it continues its seven-year flight to Saturn. Having completed its cruise among the inner planets, Cassini-Huygens’ future now lies in the cold, dark realm of the outer planets. It will pass by Jupiter on 30 December 2000; the giant planet's gravity will bend the spacecraft's trajectory, which will put it on course for arrival in orbit around Saturn on 1 July 2004.
During the Earth flyby, nine of the twelve scientific instruments on Cassini were turned on to gather data on the Earth/Moon system. The Huygens Probe and its six scientific instruments remained dormant during the Earth flyby. The next bi-annual in-flight Probe checkout activities will take place in mid-September.
The Cassini-Huygens mission is to study Saturn, its magnetic and radiation environment, moons and rings for four years. The European Space Agency's Huygens probe will separate from Cassini and parachute to the surface of Titan. Titan is especially interesting, not least because of its many Earth-like characteristics, including an atmosphere made up mostly of nitrogen and the presence of organic molecules in its atmosphere and surface. Lakes or seas of ethane and methane may be found on its surface.
Notes:
Cassini-Huygens is a joint programme of NASA, ESA and the Italian Space Agency (ASI). The Cassini orbiter, built by NASA, and the Huygens probe, provided by ESA, were mated together and launched as a single package from Cape Canaveral, Florida, on 15 October 1997, by a Titan 4-B rocket. ASI provided Cassini’s high-gain antenna.
Cassini-Huygens will enter orbit around Saturn on 1 July 2004. The Huygens probe will separate from Cassini to parachute through the atmosphere to the surface of Saturn’s largest moon, Titan, in November that year.
More information about the Huygens mission can be found at:
http://sci.esa.int/huygens/
More information about the Cassini mission is available at:
http://www.jpl.nasa.gov/cassini
More information on ESA is available at:
http://www.esa.int
NASA Space Science News for August 17, 1999
Cassini & Polar Join Forces: A bit of interplanetary luck will let two separate space missions take advantage of each other's instruments Tuesday evening. Cassini spacecraft, making a turn at Earth on its way to Saturn, and Polar, exploring the Earth-space environment above the North Pole, will make coordinated measurements in the magnetosphere.
August 16, 1999
The probe is to fly within 725 miles of its home, using the force of Earth's gravity to gain speed for its long journey into the outer solar system.
NASA engineers have been directing these planetary "flybys" of deep space probes since the 1960s, tallying more than 100 successes. But that fact doesn't comfort those who worry Cassini's plutonium-fueled mission could be trouble.
Their concern: Cassini could stray off course, plummet through Earth's atmosphere and release some of its radioactive plutonium.
NASA scientists say the chance of such a mishap is remote and put the odds at less than 1 in 1 million.
Independent experts agree the risks are extremely small, but even those who support NASA's mission say bringing a plutonium-laden spacecraft back toward Earth is not free of danger.
"The risk may not be as low a probability as NASA says, though it's still quite low," said Frank Von Hippel, a nuclear physicist and professor of science, technology and public policy at Princeton University in New Jersey. "But this is still not something we want to repeat many times."
Launched in October 1997 from Cape Canaveral Air Station, Cassini is on a $3.3-billion mission to explore Saturn, its intricate rings and a handful of the planet's 18 moons.
The spacecraft is to arrive at Saturn in July 2004, drop a probe onto the surface of the moon Titan - which might contain the basic building blocks for life - and spend four years exploring the Saturn.
To do its work, Cassini carries a dozen science instruments and 72 pounds of radioactive plutonium to generate power. The plutonium releases heat as it decays, producing energy that is converted into electricity.
Such plutonium systems have been used on 27 NASA missions to date, including the Voyager flights to explore the outer solar system and the Galileo probe's ongoing expedition at Jupiter.
Those forays are considered landmark missions that have given scientists unprecedented information about the birth and evolution of Earth's neighborhood.
NASA officials say the radioactive fuel is a last resort used only when a spacecraft can't rely on solar power to make electricity.
In Cassini's case, the 6-ton probe would need solar panels the size of a tennis court to cull enough energy from the sun while working at Saturn. Officials say such panels would have made Cassini too heavy to launch.
As it is, there was not a rocket powerful enough to send Cassini on a direct path toward Saturn. That's why the spacecraft must make four planetary flybys to reach its target.
The spacecraft gains speed with each maneuver, having completed two flybys already of Venus. A final flyby of Jupiter is planned in December 2000.
Currently on its way toward Earth, Cassini should reach its closest point 725 miles away around 11:28 p.m. EDT Tuesday.
At that time, the spacecraft will be soaring over the southeastern Pacific Ocean with Easter Island the nearest land mass.
Gravity will work like a slingshot and hurl the spacecraft away from Earth with a little more speed. NASA officials say the maneuver should unfold perfectly.
The spacecraft already has traveled more than 1.6 billion miles since launch, performing well and giving no cause for worry.
"At this point in the mission with the spacecraft performing so well, it's just not credible that it could hit Earth," said Bob Mitchell, Cassini's program manager at NASA's Jet Propulsion Laboratory in Pasadena, Calif.
But while critics concede it isn't likely, they still worry a major failure could cripple the spacecraft and send it hurtling through Earth's atmosphere where the fiery descent could tear it apart and release plutonium.
"It looks as if the flyby could be flawless. However, that's partly due to the skill of NASA and partly due to luck," said Michio Kaku, a professor of theoretical physics at the City University of New York. "There's always a wild card" that could cause a failure.
His concerns center on Cassini's plutonium, which is the largest amount ever carried on a spacecraft.
Condensed into the form of golf ball-sized pellets, the plutonium is packaged evenly among three canisters. It is not the highly explosive material used in nuclear weapons.
As long as the plutonium remains intact, it is not dangerous to humans, said Bernard Cohen, a health physicist and expert on plutonium hazards at the University of Pittsburgh in Pittsburgh, Pa.
"It would have to get into the air as very, very fine particles that could be inhaled to be a problem," Cohen said.
If inhaled, plutonium particles could travel to the lungs, radiate tissues and eventually lead to lung cancer. Or they could move into the bloodstream and be carried to the liver or bones.
Doctors don't agree on how much plutonium could be deadly. Some think a single particle could lead to cancer. Others, including Cohen, dismiss that notion as "plain screwy."
In any case, NASA officials say little of Cassini's plutonium would be reduced to breathable powder even if an accident sent the spacecraft crashing to Earth.
A maximum 370 grams of the material would be released in breathable form, leading to contamination of about 6 square miles of land and 120 cancer deaths during a 50-year period, according to NASA and U.S. Department of Energy documents.
Critics think NASA's assessment is grossly optimistic. Besides, they maintain any amount of plutonium is too dangerous.
"I'm very much in favor of the space program, but I think the use of plutonium in space is a manifestation of organized insanity," said John Gofman, a physicist on the team that developed the atomic bomb for the United States during World War II. "All I can say is that I'll be praying for the success of the flyby."
NASA officials say there is little danger because the plutonium is packaged inside super-hard, multi-layered canisters designed to tumble as they fall.
The tumbling is designed to keep any one side of the canister from getting heated enough to crack open and vaporize the plutonium inside.
Even so, officials acknowledge some plutonium could be leaked high in the atmosphere. The plutonium particles would then get caught up in atmospheric winds and spread out around the world.
In such a case, the amount of radiation to any one person would be miniscule, said Otto Raabe, a professor of radiation health biophysics at the University of California at Davis.
Even in a worst case where all 72 pounds of Cassini's plutonium were vaporized, Raabe said the resulting radiation would be less than the amount people already get on a daily basis from natural sources.
"It would be a very small fraction of the normal background radiation we receive every day from normal sources" such as cosmic rays, Raabe said.
Kaku is more concerned about what could happen if intact canisters reached Earth and struck an urban area.
"If you hit a hard surface like rock or concrete, there is a potential for the release of some plutonium," said Rich Furlong, a program manager at the DOE, which oversees the manufacture of NASA's plutonium canisters. "But there would not be a release if they landed in water. It just depends on the surface at impact."
If the canisters fell apart on impact, Kaku worries individual pellets inside could break open, allowing bits of plutonium dust to float in the air.
The dust could be carried for many miles, potentially exposing thousands of people to radioactive particles.
In the ensuing cleanup, DOE documents say people would be forced to move, buildings would have to be destroyed and vegetation torn up.
"Once it hits the ground and pulverizes into respiratory particles, I think all of us can agree we're talking about a national or international catastrophe," Kaku said.
NASA officials maintain the risk of such a calamity is very low. However, the agency is thinking about forgoing any bypasses of Earth on future missions carrying plutonium.
On the drawing boards now are flights to Pluto and another to the Jupiter moon, Europa. Each would require some plutonium power. As a result, NASA is considering what paths their craft could take without coming near Earth.
"We're still confident that we can do these things with incredible safety, but obviously, it's something we'd like to avoid if we can," said Doug Isbell, a NASA spokesman at agency headquarters in Washington, D.C.
In the end, NASA's supporters say there is no way to search the outer solar system without plutonium fuel. They say Cassini's potential discoveries at Saturn justify the use of the radioactive material.
"There is no way to do space exploration without some risk," said Jim Longuski, a professor of aeronautics and astronautics at Purdue University in Indiana. "The question is what is the balance between the risk and the potential payoff? In this case, I think the benefit far outweighs the miniscule risk involved."
NASA Space Science News for June 24, 1999
Venus Lends a Helping Hand: En route to Saturn, the Cassini spacecraft flew less than 400 miles above Venus today gaining a boost in speed from that planet's gravity. This story includes a tutorial on "gravity assist" maneuvers and how they are used to propel spacecraft to the outer planets.
24 June 1999
At 21.30 BST on June 24, Cassini and its European-built Huygens probe flew about 620 kilometers (388 miles) above the cloud tops of Venus in order to obtain a boost in speed from the planet's gravity. A number of science instruments in which UK scientists are involved were switched on during this brief encounter. However, they will have to wait for a while to study the new information. Data obtained during the flyby will trickle back to Earth at a fairly slow rate via the low gain antenna since Cassini's more powerful high gain antenna is acting as a sunshield and pointing away from the Earth.
The Cassini Plasma Spectrometer (CAPS) instrument, with its Ion Beam Spectrometer and Electron Spectrometer, was turned on about 7 hours before closest approach to Venus. Dr. Andrew Coates of Mullard Space Science Laboratory is the team leader for the Electron Spectrometer part of this instrument, while Rutherford Appleton Laboratory is also involved. CAPS is investigating how the electrically charged particles of the solar wind interact with the non-magnetic planet. "This will be a useful practice for the Cassini investigation of Saturn's giant moon Titan, which we think also has no magnetic field," said Dr. Coates.
At the same time, the Radio and Plasma Wave Science (RPWS) instrument was used to study radio emissions from the planet and waves in the sea of charged particles surrounding Venus. RPWS was activated just over eleven hours before Venus closest approach. Although a search for radio 'whistlers' caused by lightning proved fruitless during Cassini's first flyby of Venus in 1998, many scientists are convinced that such storms are common on the cloud-shrouded planet. Dr Hugo Alleyne and the late Dr. Les Woolliscroft of the University of Sheffield provided data compression software for the RPWS experiment.
Although Venus has no internal dynamo to generate a magnetic field, it does act as a barrier, slowing the incoming solar wind to subsonic speeds on its sunward side. This sudden deceleration causes a shock wave as the solar particles approach and flow around the planet. Cassini's Dual Technique Magnetometer (MAG) should have observed this Venusian bowshock as the spacecraft ploughed through the boundary into a region known as the ionosheath. Principal scientific investigator for MAG is Professor David Southwood of Imperial College, London.
Although Cassini's Imaging Science Subsystem (ISS) was activated to obtain about 10 images of the cloud tops during the flyby, the pictures themselves will be of little scientific value. The main purpose of the images was to calibrate the wide and narrow angle cameras in preparation for more intensive use on arrival at Saturn. Imaging opportunities were limited during the flyby since the spacecraft and its cameras were not to be manoeuvred and remained pointing in one fixed direction. Professor Carl Murray of Queen Mary and Westfield College, London is a member of the ISS team.
While most of the spacecraft's instruments have been switched off since launch in October 1997, the Cosmic Dust Analyser (CDA) instrument has been operating continuously since March 25. It is expected to continue sending back data for nearly another decade. During its first 41 days of measurements, the instrument detected at least 7 dust impacts, but the source of these particles is not yet determined. However, it seems likely that CDA's chemical analyser, which has been provided by the University of Kent, has returned the first data ever obtained on the composition of an interplanetary dust particle. Professor Tony McDonnell from Kent is one of the CDA investigators. Rutherford Appleton Laboratory also contributed to the design and manufacture of this instrument.
In order to benefit from this technique and reach the ringed planet, the 5650 kilogram Cassini had to be launched inward towards Venus. Only after completing two Venus flybys, a flyby of Earth and one of Jupiter, will the bus-sized spacecraft have accelerated sufficiently to reach Saturn.
On August 18, Cassini will fly past Earth at an altitude of 1,166 kilometers (725 miles), about five times higher than the Space Shuttle's orbit. This Earth swingby will bend Cassini's flight path so that it heads towards Jupiter. Passing about 9.7 million kilometers (6 million miles) from the gas giant on 30 December 2000, it will use Jupiter's gravity to change course and speed for its final destination of Saturn.
Saturn is ten times further from the Sun than the Earth - about 1,430 million kilometers (900 million miles). Cassini's arrival is scheduled for 1 July 2004. Over the following four years, it will conduct 27 different scientific investigations of the giant planet's atmosphere and magnetosphere, its magnificent rings, and sixteen of the known moons. The largest of these, Titan, is particularly fascinating since it has a thick, cloudy atmosphere which is mostly made of nitrogen but also contains hydrocarbons such as methane - similar to the atmosphere of the early Earth but much colder.
Cassini will complete more than 60 orbits of Saturn, including about 45 close flybys of Titan and about 20 flybys of some of the smaller, icy moons. This tour is made possible by using planet-sized Titan's gravity to alter Cassini's orbit each time the craft swoops to within a few thousand kilometres of the moon's orange cloud tops.
The mission is an international venture involving the National Aeronautics and Space Administration (NASA), the European Space Agency (ESA), and the Italian Space Agency (ASI), as well as several European academic and industrial partners. The United States is responsible for the main Cassini spacecraft which will be inserted into orbit around Saturn in July 2004. Attached to the mother craft will be the European Space Agency's Huygens probe, whose task is to parachute onto the unexplored surface of Titan, the largest of Saturn's moons.
More than 616,400 signatures sent to NASA from citizens in 81 countries have been recorded on a high-tech data disk installed on the Cassini spacecraft.
UK investment in the Cassini-Huygens mission amounts to 7.4 million pounds, of which 4.48 million pounds is being spent on the orbiter experiments and 2.92 million pounds on the probe investigations. Most of this is provided by the Particle Physics and Astronomy Research Council (PPARC).
PPARC is the UK Government-funded body providing support for basic research in elementary particles and the forces of Nature; planetary and solar research, including space physics; astronomy, astrophysics and cosmology.
Further information on the Cassini-Venus and Earth flybys can be found at:
http://www.jpl.nasa.gov/cassini/msnstatus/cassguide.html
Further information on the Cassini mission can be found on these Web pages:
Artist's impressions of the mission are available from:
http://www.maths.qmw.ac.uk/Astronomy/Cassini/art_cass/
The Cassini spacecraft is presently traveling at a speed of approximately 143,000 kilometers/hour (~89,000 mph) relative to the sun and has traveled approximately 464 million kilometers (~288 million miles) since launch on October 15, 1997.
The most recent Spacecraft status is from the DSN tracking pass on Thursday, 04/02, over Canberra. The Cassini spacecraft is in an excellent state of health and is executing the C7 sequence nominally.
Inertial attitude control is being maintained using the spacecraft's hydrazine thrusters (RCS system). The spacecraft continues to fly in a High Gain Antenna-to-Sun attitude. It will maintain the HGA-to-Sun attitude, except for planned trajectory correction maneuvers, for the first 14 months of flight.
Communication with Earth during early cruise is via one of the spacecraft's two low-gain antennas; the antenna selected depends on the relative geometry of the Sun, Earth and the spacecraft. The downlink telemetry rate is presently 40 bps except for the probe checkout playbacks at 948 bps which are done over specially-requested 70m DSN passes.
From Friday, 03/27, through Monday, 03/30, there were no changes in spacecraft configuration.
On Tuesday, 03/31, the first of seven data playbacks occurred for Huygens Probe Checkout #2. The Probe checkout activity occurs approximately every 6 months. The series of data playbacks from the SSR will provide detailed information on the results of the checkout.
On Wednesday, 04/02, the Solid State Recorder (SSR) record and playback pointers were reset, according to plan. This housekeeping activity, done approximately weekly, maximizes the amount of time that recorded engineering data is available for playback to the ground should an anomaly occur on the spacecraft.
Also on Wednesday, the now standard SSR Flight Software Partition maintenance activity was performed. This activity repairs any SSR double bit errors (DBEs) which have occurred in the code-containing portions of the Flight Software partitions during the preceding period.
Finally, on Wednesday, the second data playback occurred for Probe Checkout #2.
On Thursday, 04/02, the spacecraft was commanded back to the state in which the A unit of the Probe Support Avionics (PSA) is identified as prime. At the termination of each Probe checkout activity, the spacecraft switches to the B unit of the PSA. The commanding to reset the PSA to the A unit is a standard post-checkout housekeeping activity which establishes the desired hardware state for the next Probe checkout.
Upcoming events:
Activities scheduled for the week of 4/03 - 4/09 include: the remaining 5 (of 7) Probe Checkout data playbacks (4/03 through 4/07), and an SSR pointer reset (4/06).
Probe: Huygens: Second In-Flight Checkout
ESA reports that a first look at the (Probe Checkout #2) data indicates that their overall quality is good and that in most respects the Probe behaved as expected. However, the AGC (Automatic Gain Control) telemetry measurements on both chains seems to have dropped further (by 3 to 4 dB), with respect to the values of the first in-flight checkout. The AGC level is a measurement in the umbilical (mated) configuration. ESA has formed an investigation team to understand these telemetry measurements.
DSN Coverage:
Over the past week Cassini had 10 scheduled DSN tracks occurring from 03/27 through 4/02. In the coming week there will be 9 DSN passes.
Other Program Activities
On Friday, 3/27, the Program determined that because of navigation accuracy, that no trim maneuver is required for the final leg of the mission's first Venus gravity assist swingby, planned for April 26, 1998.
ESA
Paris, 24 October 1997
"It all went very smoothly, " said Jonh Dodsworth, ESOC's flight operations Director, "We had the option to continue checks on 26 October in case of difficulty, but we don't need to. That's good news".
ESOC established connection with the Huygens probe at 10:09 hrs, Central European Time on 23 October, using NASA's link to Cassini. Thanks to ESOC's new flight operations system, engineers and scientists responsible for the mission could check quite quickly that Huygens is alive and well in all respects.
ESA's project management team, and representatives of the contractors who built Huygens, were able to report that the engineering system and subsystems are all performing nominally.
The principal investigators from Europe and the USA, in charge of the six instruments on Huygens, were also present for the tests. Each experiment was checked for functionality :
- HASI to analyse Titan's atmosphere and weather
- DWE to measure wind speeds during the descent
- GCMS to analyse chemical compounds on Titan
- ACP to break down aerosols for chemical analysis
- DISR to produce images and spectra of Titan
- SSP to determine the nature of Titan's surface.
"Six experiments, six green lights", said Jean-Pierre Lebreton, ESA's project scientist.
The project manager for Huygens is Hamid Hassan. In Darmstadt he too declared himself pleased with the check-out of the Huygens systems, subsystems and instruments.
"We will now let Huygens go back to sleep, except for the planned six monthly checkouts" Hassan said. The probe will remain in that condition for the seven-year journey to Saturn. But we now have every reason to expect a successful outcome to this unprecedented mission".
JET PROPULSION LABORATORY
The Cassini spacecraft is operating as planned while it cruises through space on its way to the planet Saturn and the scientific wonders that await Earth-bound scientists there. According to Cassini Spacecraft Development Manager Chris Jones, the spacecraft continues its mission in "just right" condition. "Spacecraft and mission operations have been exceptional," said Cassini Deputy Program Manager Ronald Draper.
A major milestone was met today with the first checkout of the European Space Agency's Huygens probe. While results are still being evaluated, initial reports from the Huygens Probe Operations Centre in Darmstadt, Germany, are that the test data looks very good. The Huygens probe will perform investigations of Saturn's moon Titan. Launch latches were successfully released on several instruments this week: the Cassini Plasma Spectrometer, the Composite Infrared Spectrometer, and the Magnetosphere Imaging Instrument. Deploy of the three plasma wave antennas is planned for later this week. These antennas are 10 meters (about 33 feet) in length and are used as an electric field sensor, which is part of the Radio and Plasma Wave Science instrument that measures electrical and magnetic fields in the plasma of interplanetary space and Saturn's magnetosphere.
The spacecraft's velocity relative to Earth is at about 4.1 kilometers per second (about9,170 miles per hour). Velocity is expected to decrease slowly over the next two to three months. Cassini is now over 3,000,000 kilometers (over 1,800,000 miles) from Earth. NASA's Deep Space Network is providing continuous communications with Cassini through its 34-meter dish antennas located in California, Spain, and Australia.
The Cassini spacecraft was launched from Cape Canaveral, FL, at 4:43 a.m. EDT on October 15.
JET PROPULSION LABORATORY
October 20, 1997 12:30 p.m. PDT
Cassini's different systems and subsystems are being checked out by engineers during the launch and early cruise sequence. The Ultra-Stable Oscillator, which provides a very stable downlink frequency source for the radio science investigation, has been activated and is operating properly. The Deep Space Transponder, the radio receiver on Cassini, is receiving commands from ground controllers and is working correctly. Launch data from the solid state recorder continues to be played back and analyzed. Launch latches will be released on several instruments this week: the Cassini Plasma Spectrometer, the Composite Infrared Spectrometer, and the Magnetosphere Imaging Instrument. Current plans call for checkout of the Huygens probe later this week.
The spacecraft's velocity relative to Earth is at about 4.1 kilometers per second (about 9,170 miles per hour). Velocity is expected to decrease slowly over the next two to three months. NASA's Deep Space Network is providing communications with Cassini through its 34-meter dish antennas located in California, Spain, and Australia.
The Cassini spacecraft was launched from Cape Canaveral, FL, at 4:43 a.m. EDT on October 15.
European Space Agency
Paris, 15 October 1997
About 500 representatives of the scientific, engineering and industrial teams in Europe, which created the Huygens Probe, were present at Cape Canaveral for the Cassini Huygens launch. They saw the powerful boosters of the Titan launcher light up the pre-dawn sky.
The launch sequence concluded with the completion of the second firing and separation of the Centaur upper stage rocket. NASA's ground station at Canberra, Australia, obtained good signals from Cassini an hour after launch.
The European Space Operations Centre (ESOC) at Darmstadt will monitor the condition of the Huygens spacecraft. Their report is expected in 8-10 days' time.
The next major event will be the swingby of Cassini Huygens at Venus on 21 April 1998. This is the first of a sequence of "gravity-assist" operations at Venus, the Earth and Jupiter, to accelerate the spacecraft.
JET PROPULSION LABORATORY October 16, 1997 11:30 a.m. PDT
At one day and nine hours following launch, Cassini is traveling at a velocity of about 4.2 kilometers per second (about 9,223 miles per hour) relative to Earth. Engineers are beginning to look at data from when the Centaur separated from Cassini to correlate after-the-fact information on spacecraft systems with predicted performance. Telemetry recorded on Cassini's solid state recorder will be played back later this week. Extra commands to shut off two commandable heaters (out of 50) for the star camera were added. Radio plasma wave antennas will be deployed in ten days. Updates for engineering software are scheduled for today and tomorrow.
There are no anomalies with the spacecraft, according to Cassini mission director Chris Jones. "I can't recall a launch as perfect as this one," he said, adding that "everything we see is within predictions, with no failures."
From the "JPL Universe"
October 3, 1997
Launch is scheduled for Monday, Oct. 13 at 1:55 a.m. Pacific Daylight Time. The launch window runs for 140 minutes each day and moves earlier by about six minutes each day in the primary launch period, which runs through Nov. 15.
The Cassini orbiter, with the Huygens Titan probe back onboard, was successfully mated with the launch vehicle in mid- September following the quick completion of clean-up and repair work on the Huygens Probe after a small area of the probe's thermal protection blanketing and insulating foam was damaged by overly forceful air from a launch pad cooling system.
The probe and orbiter were given a clean bill of health, joined together once again, and rolled out to the launch pad on Sept. 14. Mating with the launch vehicle was completed the following day.
"We're back on track and have high confidence we will launch within the optimum launch period," said Deputy Program Manager Ronald Draper at JPL.
"As the launch of Cassini and Huygens approaches, all those involved in preparation for this historic event seem to find themselves in a state of controlled frenzy," said Program Manager Dick Spehalski. "It is difficult to convey the heightened sense of anticipation, alertness and, yes, anxiety, which permeates all our last-minute work."
Cassini, in development since 1989, is a cooperative endeavor of NASA, the European Space Agency (ESA) and the Italian Space Agency, or Agenzia Spaziale Italiana (ASI). The spacecraft, which contains 12 scientific experiments, will orbit Saturn for four years following its arrival on July 1, 2004. The ESA-built Huygens probe -- representing the first descent of a probe to a moon of another planet and by far the most distant landing ever attempted on another object in the solar system -- will parachute into Titan's thick atmosphere carrying another six scientific instrument packages.
During the course of Cassini's mission, it will execute more than 40 targeted close flybys of Titan, many as close as 950 kilometers (about 590 miles) above the surface.
The most complex interplanetary spacecraft ever built, Cassini is a follow-on to the brief reconnaissance of Saturn performed by the Pioneer 11 spacecraft in 1979 and the Voyager 1 and 2 encounters of 1980 and 1981.
"We have built the Cassini spacecraft and Huygens probe to be as strong and capable as possible," Spehalski said. "They have passed all their reviews and rigorous testing. We have made the launch as safe as possible.
"In the final moment, we must step back and become observers as the awesome rocket lifts skyward. We will set aside our labors at that final moment and watch the spacecraft soar away from Earth and leave us behind. We will wish our robots a safe journey. This will be an exhilarating, exciting and proud moment."
NASA Headquarters, Washington, DC
Department of Energy, Washington, DC
October 3, 1997
"NASA and its interagency partners have done an extremely thorough job of evaluating and documenting the safety of the Cassini mission. I have carefully reviewed these assessments and have concluded that the important benefits of this scientific mission outweigh the potential risks," said OSTP Director Dr. John H. Gibbons, who signed the launch approval.
NASA Administrator Daniel S. Goldin said, "I am confident in the safety of the Cassini mission, and I fully expect that it will return spectacular images and scientific data about Saturn, in the same safe and successful manner as the Voyager, Galileo and Ulysses missions."
White House launch approval is required by presidential directive due to the type of power source used to provide electrical power for the Cassini spacecraft and its scientific instruments, and the heater units that it carries to keep the spacecraft's instruments and electronics warm in deep space.
The Radioisotope Thermoelectric Generators (RTGs) and Radioisotope Heater Units used to power Cassini and keep its internal systems warm have been used in previous NASA missions ranging from Apollo to Galileo, and have been approved by five previous administrations ranging from Nixon to Bush. RTGs produce power by the heat generated through the natural radioactive decay of non-weapons grade plutonium dioxide, which is transformed into electricity by solid-state thermoelectric converters.
Before Administrator Goldin sent the request for launch approval to OSTP, two separate processes were completed to address the environmental and safety aspects of the mission. NASA completed an Environmental Impact Statement in June 1995 and a supplement in June 1997, as required by the National Environmental Policy Act and NASA policy.
Consistent with long-standing Presidential policy, the Department of Energy (DOE) prepared over the past seven years a comprehensive Safety Analysis Report. In addition, an Interagency Nuclear Safety Review Panel, including safety experts from DOE, NASA, the Department of Defense (DOD), the Environmental Protection Agency (EPA), and a technical advisor from the Nuclear Regulatory Commission conducted a comprehensive evaluation of the safety analysis. This panel was supported by over 50 scientific experts from academia and industry.
DOD, EPA and DOE have written to the NASA Administrator confirming that, in their view, the safety analysis conducted for the mission is comprehensive and thorough.
Cassini is a cooperative endeavor of NASA, the European Space Agency (ESA) and the Italian Space Agency, or Agenzia Spaziale Italiana. The mission will send a sophisticated robotic spacecraft, equipped with 12 scientific experiments, to orbit Saturn for a four-year period and study the Saturnian system in detail. The ESA- built Huygens probe that will parachute into Titan's thick atmosphere carries another six scientific instrument packages.
Saturn is the second-largest planet in the solar system and is made up mostly of hydrogen and helium. Its placid-looking, butterscotch-colored face masks a windswept atmosphere where jet streams blow at 1,100 miles per hour and swirling storms roil just beneath the cloud tops. Previous spacecraft passing by Saturn found a huge and complex magnetic environment, called a magnetosphere, where trapped protons and electrons interact with each other, the planet, rings and surfaces of many of the moons.
Although it is believed to be too cold to support life, haze- covered Titan is thought to hold clues to how a primitive Earth evolved into a life-bearing planet. It has an Earth-like, nitrogen- based atmosphere and a surface that many scientists believe probably features chilled lakes of ethane and methane. Scientists believe that Titan's surface is probably coated with the residue of a sticky brown organic rain.
The launch of Cassini aboard a Titan IV-B/Centaur launch vehicle is scheduled for 4:55 a.m. EDT on October 13 from Cape Canaveral Air Station, FL. An on-time launch will deliver the Cassini mission to Saturn almost seven years later on July 1, 2004. Cassini's primary mission concludes in July 2008.
Opposition against the Cassini/Huygens mission arose because of the plutonium the spacecraft is carrying in its RTGs and heating units. If the Titan launcher would explode during launch, the plutonium could be released in our atmosphere. ASTRONET does not take sides in this matter of pro's and con's, but simply links to web sites discussing this matter.
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