Comet Rendezvous Asteroid Flyby
Encyclopedia
The Comet Rendezvous Asteroid Flyby (CRAF) was a cancelled plan for a NASA
led exploratory mission designed by the Jet Propulsion Laboratory
during the mid-to-late 1980s and early 1990s, that planned to send a spacecraft to encounter an asteroid, and then to rendezvous with a comet and fly alongside it for nearly three years. The project was eventually canceled when it went over budget; most of the money still left was redirected to its twin spacecraft, Cassini-Huygens
, destined for Saturn
, so it could survive Congressional
budget
cutbacks. Most of CRAF's scientific objectives were later accomplished by the smaller NASA spacecraft Stardust
and Deep Impact, and the rest will be accomplished by ESA's flagship Rosetta mission.
series of spacecraft, CRAF was to closely examine a comet
during a part of its orbit
around the Sun
. It was to launch a heavily instrumented penetrator/lander into the comet's nucleus
to measure temperatures and chemical composition. CRAF's other instruments would collect data on the comet's nucleus, its coma
, and its
dust
and ion
cloud and tail. CRAF was also to provide the first close-up look at how a comet's coma and its tail of dust and ions form. CRAF and Cassini missions were a collaborative project of NASA, the European Space Agency and the federal space agencies of Germany
and Italy
, as well as the United States Air Force
and the United States Department of Energy
.
CRAF was to be launched aboard a Titan IV
-Centaur
rocket in August 1995, but as of February 1991 the launch date was swapped with Cassini and CRAF's launch was moved back to February 1996. The new launch profile included a Venus
gravity assist, that added eight months to the planned flight time but offered an increase in payload and better alternatives if the February 1996 launch window
was missed. The trajectory
would carry CRAF out to the asteroid belt, where a propulsion maneuver would send the spacecraft back toward Earth for a gravity assist boost. CRAF would fly past Earth
in July 1997 to take up its final flight path. By using gravity assist, NASA can launch spacecraft aboard rockets that have less thrust than would be needed for a direct flight.
The spacecraft was to encounter an asteroid
named 449 Hamburga
in January 1998 en route to the comet. CRAF would take photograph
s and deploy other scientific measurements during the encounter period. Asteroid 449 Hamburga is about 88 kilometres (54.7 mi) in diameter and is a carbonaceous type asteroid.
CRAF's planned cometary target was Comet Kopff. It is named for August Kopff
, who discovered it on August 22, 1906, during an observing session at Koenigstuhl Observatory near Heidelberg
, Germany
.
Ninety-four years after Kopff's discovery, CRAF would arrive at the rendezvous point with Comet Kopff — in August 2000. Comet and spacecraft would be at the distance of Jupiter
's orbit, and 850 days before closest approach to the Sun, or perihelion. CRAF would fire its penetrator/lander at the comet in August 2001, then would continue to fly beside Kopff. The spacecraft would take data for a total of two and two-thirds years, until about 109 days after they pass closest to the Sun and are outward bound again. It was to be the first time a spacecraft would have flown in formation with a comet, though a U.S. spacecraft, International Cometary Explorer
(ICE), flew by Comet Giacobini-Zinner in 1985, spacecraft from several countries encountered Comet Halley
in 1986, and the Giotto spacecraft flew past Comet Grigg-Skjellerup in 1992.
The comet rendezvous would allow study of matter that scientists think is the original, relatively unchanged material left behind when a cloud of dust and gas collapsed to form the solar system
4.6 billion years ago. Scientists believe comets now reside in a distant region of the solar system called the Oort cloud
. Current theory holds that gravitational nudges from stars in the Sun's neighborhood send some comets from the Oort cloud falling toward the Sun.
The CRAF spacecraft would fly extremely close to the comet's nucleus, within 10 kilometres (6.2 mi). The close-up exploration would take place before the coma and tail begin to build, it would observe the nucleus as it becomes active in the growing sunlight and begins to have its lighter elements boil off and form a coma and tails. Later the spacecraft would move in and out through the coma and down the tail to study their properties and the complex processes occurring in them, and to collect samples of dust for detailed analysis on board the spacecraft.
In December 2002 the spacecraft and the comet would make their closest approach to the Sun. They would then head outward again toward aphelion near Jupiter's orbit. On March 31, 2003, the Comet Rendezvous Asteroid Flyby, first primary mission of Mariner Mark II, would end. At that time the Cassini mission, with the second Mariner Mark II spacecraft, would be in its Saturnian-tour phase.
class spacecraft developed for NASA by JPL were a new design approach advocated by NASA's Solar System Exploration Committee and were intended for flights in the 1990s to the outer planets and primitive bodies, such as comets and asteroids.
CRAF was to be the first Mariner Mark II mission. The second mission, called Saturn Orbiter Titan Probe or SOTP (later Cassini-Huygens
), was a Saturn
orbiter with a probe designed to plunge into the atmosphere of the ringed planet's largest satellite, Titan
. CRAF and SOTP were to use identical Mariner Mark II spacecraft, but each was to carry unique science instruments
.
The mission's scientific payload was selected in October 1986. It was to include:
NASA
The National Aeronautics and Space Administration is the agency of the United States government that is responsible for the nation's civilian space program and for aeronautics and aerospace research...
led exploratory mission designed by the Jet Propulsion Laboratory
Jet Propulsion Laboratory
Jet Propulsion Laboratory is a federally funded research and development center and NASA field center located in the San Gabriel Valley area of Los Angeles County, California, United States. The facility is headquartered in the city of Pasadena on the border of La Cañada Flintridge and Pasadena...
during the mid-to-late 1980s and early 1990s, that planned to send a spacecraft to encounter an asteroid, and then to rendezvous with a comet and fly alongside it for nearly three years. The project was eventually canceled when it went over budget; most of the money still left was redirected to its twin spacecraft, Cassini-Huygens
Cassini-Huygens
Cassini–Huygens is a joint NASA/ESA/ASI spacecraft mission studying the planet Saturn and its many natural satellites since 2004. Launched in 1997 after nearly two decades of gestation, it includes a Saturn orbiter and an atmospheric probe/lander for the moon Titan, although it has also returned...
, destined for Saturn
Saturn
Saturn is the sixth planet from the Sun and the second largest planet in the Solar System, after Jupiter. Saturn is named after the Roman god Saturn, equated to the Greek Cronus , the Babylonian Ninurta and the Hindu Shani. Saturn's astronomical symbol represents the Roman god's sickle.Saturn,...
, so it could survive Congressional
United States Congress
The United States Congress is the bicameral legislature of the federal government of the United States, consisting of the Senate and the House of Representatives. The Congress meets in the United States Capitol in Washington, D.C....
budget
Budget
A budget is a financial plan and a list of all planned expenses and revenues. It is a plan for saving, borrowing and spending. A budget is an important concept in microeconomics, which uses a budget line to illustrate the trade-offs between two or more goods...
cutbacks. Most of CRAF's scientific objectives were later accomplished by the smaller NASA spacecraft Stardust
Stardust (spacecraft)
Stardust is a 300-kilogram robotic space probe launched by NASA on February 7, 1999 to study the asteroid 5535 Annefrank and collect samples from the coma of comet Wild 2. The primary mission was completed January 15, 2006, when the sample return capsule returned to Earth...
and Deep Impact, and the rest will be accomplished by ESA's flagship Rosetta mission.
Overview
Designed to be the first of the planned Mariner Mark IIMariner Mark II
Mariner Mark II was NASA's planned family of unmanned spacecraft for the exploration of the outer solar system that were to be developed and operated by JPL between 1990 through the year 2010....
series of spacecraft, CRAF was to closely examine a comet
Comet
A comet is an icy small Solar System body that, when close enough to the Sun, displays a visible coma and sometimes also a tail. These phenomena are both due to the effects of solar radiation and the solar wind upon the nucleus of the comet...
during a part of its orbit
Orbit
In physics, an orbit is the gravitationally curved path of an object around a point in space, for example the orbit of a planet around the center of a star system, such as the Solar System...
around the Sun
Sun
The Sun is the star at the center of the Solar System. It is almost perfectly spherical and consists of hot plasma interwoven with magnetic fields...
. It was to launch a heavily instrumented penetrator/lander into the comet's nucleus
Comet nucleus
The nucleus is the solid, central part of a comet, popularly termed a dirty snowball. A cometary nucleus is composed of rock, dust, and frozen gases. When heated by the Sun, the gases sublimate and produce an atmosphere surrounding the nucleus known as the coma...
to measure temperatures and chemical composition. CRAF's other instruments would collect data on the comet's nucleus, its coma
Coma (cometary)
frame|right|The [[153P/Ikeya-Zhang|comet Ikeya-Zhang]] exhibiting a bright, condensed coma In astronomy, a coma is the nebulous envelope around the nucleus of a comet. It is formed when the comet passes close to the Sun on its highly elliptical orbit; as the comet warms, parts of it sublimate...
, and its
dust
Cosmic dust
Cosmic dust is a type of dust composed of particles in space which are a few molecules to 0.1 µm in size. Cosmic dust can be further distinguished by its astronomical location; for example: intergalactic dust, interstellar dust, interplanetary dust and circumplanetary dust .In our own Solar...
and ion
Ion
An ion is an atom or molecule in which the total number of electrons is not equal to the total number of protons, giving it a net positive or negative electrical charge. The name was given by physicist Michael Faraday for the substances that allow a current to pass between electrodes in a...
cloud and tail. CRAF was also to provide the first close-up look at how a comet's coma and its tail of dust and ions form. CRAF and Cassini missions were a collaborative project of NASA, the European Space Agency and the federal space agencies of Germany
Germany
Germany , officially the Federal Republic of Germany , is a federal parliamentary republic in Europe. The country consists of 16 states while the capital and largest city is Berlin. Germany covers an area of 357,021 km2 and has a largely temperate seasonal climate...
and Italy
Italy
Italy , officially the Italian Republic languages]] under the European Charter for Regional or Minority Languages. In each of these, Italy's official name is as follows:;;;;;;;;), is a unitary parliamentary republic in South-Central Europe. To the north it borders France, Switzerland, Austria and...
, as well as the United States Air Force
United States Air Force
The United States Air Force is the aerial warfare service branch of the United States Armed Forces and one of the American uniformed services. Initially part of the United States Army, the USAF was formed as a separate branch of the military on September 18, 1947 under the National Security Act of...
and the United States Department of Energy
United States Department of Energy
The United States Department of Energy is a Cabinet-level department of the United States government concerned with the United States' policies regarding energy and safety in handling nuclear material...
.
CRAF was to be launched aboard a Titan IV
Titan IV
The Titan IV family of space boosters were used by the U.S. Air Force. They were launched from Cape Canaveral Air Force Station, Florida, and Vandenberg Air Force Base, California. At the time of its introduction, the Titan IV was the "largest unmanned space booster used by the Air Force."The...
-Centaur
Centaur (rocket stage)
Centaur is a rocket stage designed for use as the upper stage of space launch vehicles. Centaur boosts its satellite payload to geosynchronous orbit or, in the case of an interplanetary space probe, to or near to escape velocity...
rocket in August 1995, but as of February 1991 the launch date was swapped with Cassini and CRAF's launch was moved back to February 1996. The new launch profile included a Venus
Venus
Venus is the second planet from the Sun, orbiting it every 224.7 Earth days. The planet is named after Venus, the Roman goddess of love and beauty. After the Moon, it is the brightest natural object in the night sky, reaching an apparent magnitude of −4.6, bright enough to cast shadows...
gravity assist, that added eight months to the planned flight time but offered an increase in payload and better alternatives if the February 1996 launch window
Launch window
Launch window is a term used in spaceflight to describe a time period in which a particular launch vehicle must be launched. If the rocket does not launch within the "window", it has to wait for the next window....
was missed. The trajectory
Trajectory
A trajectory is the path that a moving object follows through space as a function of time. The object might be a projectile or a satellite, for example. It thus includes the meaning of orbit—the path of a planet, an asteroid or a comet as it travels around a central mass...
would carry CRAF out to the asteroid belt, where a propulsion maneuver would send the spacecraft back toward Earth for a gravity assist boost. CRAF would fly past Earth
Earth
Earth is the third planet from the Sun, and the densest and fifth-largest of the eight planets in the Solar System. It is also the largest of the Solar System's four terrestrial planets...
in July 1997 to take up its final flight path. By using gravity assist, NASA can launch spacecraft aboard rockets that have less thrust than would be needed for a direct flight.
The spacecraft was to encounter an asteroid
Asteroid
Asteroids are a class of small Solar System bodies in orbit around the Sun. They have also been called planetoids, especially the larger ones...
named 449 Hamburga
449 Hamburga
449 Hamburga is a large Main belt asteroid. It is classified as a C-type asteroid and is probably composed of carbonaceous material.It was discovered by Max Wolf and A. Schwassmann on October 31, 1899 in Heidelberg....
in January 1998 en route to the comet. CRAF would take photograph
Photograph
A photograph is an image created by light falling on a light-sensitive surface, usually photographic film or an electronic imager such as a CCD or a CMOS chip. Most photographs are created using a camera, which uses a lens to focus the scene's visible wavelengths of light into a reproduction of...
s and deploy other scientific measurements during the encounter period. Asteroid 449 Hamburga is about 88 kilometres (54.7 mi) in diameter and is a carbonaceous type asteroid.
CRAF's planned cometary target was Comet Kopff. It is named for August Kopff
August Kopff
August Kopff was a German astronomer who discovered several comets and asteroids. He worked in Heidelberg, then joined the Humboldt University of Berlin where he became the Director of the Institute for Astronomical Calculation.He discovered some comets, including periodic comet 22P/Kopff and the...
, who discovered it on August 22, 1906, during an observing session at Koenigstuhl Observatory near Heidelberg
Heidelberg
-Early history:Between 600,000 and 200,000 years ago, "Heidelberg Man" died at nearby Mauer. His jaw bone was discovered in 1907; with scientific dating, his remains were determined to be the earliest evidence of human life in Europe. In the 5th century BC, a Celtic fortress of refuge and place of...
, Germany
Germany
Germany , officially the Federal Republic of Germany , is a federal parliamentary republic in Europe. The country consists of 16 states while the capital and largest city is Berlin. Germany covers an area of 357,021 km2 and has a largely temperate seasonal climate...
.
Ninety-four years after Kopff's discovery, CRAF would arrive at the rendezvous point with Comet Kopff — in August 2000. Comet and spacecraft would be at the distance of Jupiter
Jupiter
Jupiter is the fifth planet from the Sun and the largest planet within the Solar System. It is a gas giant with mass one-thousandth that of the Sun but is two and a half times the mass of all the other planets in our Solar System combined. Jupiter is classified as a gas giant along with Saturn,...
's orbit, and 850 days before closest approach to the Sun, or perihelion. CRAF would fire its penetrator/lander at the comet in August 2001, then would continue to fly beside Kopff. The spacecraft would take data for a total of two and two-thirds years, until about 109 days after they pass closest to the Sun and are outward bound again. It was to be the first time a spacecraft would have flown in formation with a comet, though a U.S. spacecraft, International Cometary Explorer
International Cometary Explorer
The International Cometary Explorer spacecraft was originally known as International Sun/Earth Explorer 3 satellite, launched August 12, 1978. It was part of the ISEE international cooperative program between NASA and ESRO/ESA to study the interaction between the Earth's magnetic field and the...
(ICE), flew by Comet Giacobini-Zinner in 1985, spacecraft from several countries encountered Comet Halley
Comet Halley
Halley's Comet or Comet Halley is the best-known of the short-period comets, and is visible from Earth every 75 to 76 years. Halley is the only short-period comet that is clearly visible to the naked eye from Earth, and thus the only naked-eye comet that might appear twice in a human lifetime...
in 1986, and the Giotto spacecraft flew past Comet Grigg-Skjellerup in 1992.
The comet rendezvous would allow study of matter that scientists think is the original, relatively unchanged material left behind when a cloud of dust and gas collapsed to form the solar system
Solar System
The Solar System consists of the Sun and the astronomical objects gravitationally bound in orbit around it, all of which formed from the collapse of a giant molecular cloud approximately 4.6 billion years ago. The vast majority of the system's mass is in the Sun...
4.6 billion years ago. Scientists believe comets now reside in a distant region of the solar system called the Oort cloud
Oort cloud
The Oort cloud , or the Öpik–Oort cloud , is a hypothesized spherical cloud of comets which may lie roughly 50,000 AU, or nearly a light-year, from the Sun. This places the cloud at nearly a quarter of the distance to Proxima Centauri, the nearest star to the Sun...
. Current theory holds that gravitational nudges from stars in the Sun's neighborhood send some comets from the Oort cloud falling toward the Sun.
The CRAF spacecraft would fly extremely close to the comet's nucleus, within 10 kilometres (6.2 mi). The close-up exploration would take place before the coma and tail begin to build, it would observe the nucleus as it becomes active in the growing sunlight and begins to have its lighter elements boil off and form a coma and tails. Later the spacecraft would move in and out through the coma and down the tail to study their properties and the complex processes occurring in them, and to collect samples of dust for detailed analysis on board the spacecraft.
In December 2002 the spacecraft and the comet would make their closest approach to the Sun. They would then head outward again toward aphelion near Jupiter's orbit. On March 31, 2003, the Comet Rendezvous Asteroid Flyby, first primary mission of Mariner Mark II, would end. At that time the Cassini mission, with the second Mariner Mark II spacecraft, would be in its Saturnian-tour phase.
Spacecraft design
Mariner Mark IIMariner Mark II
Mariner Mark II was NASA's planned family of unmanned spacecraft for the exploration of the outer solar system that were to be developed and operated by JPL between 1990 through the year 2010....
class spacecraft developed for NASA by JPL were a new design approach advocated by NASA's Solar System Exploration Committee and were intended for flights in the 1990s to the outer planets and primitive bodies, such as comets and asteroids.
CRAF was to be the first Mariner Mark II mission. The second mission, called Saturn Orbiter Titan Probe or SOTP (later Cassini-Huygens
Cassini-Huygens
Cassini–Huygens is a joint NASA/ESA/ASI spacecraft mission studying the planet Saturn and its many natural satellites since 2004. Launched in 1997 after nearly two decades of gestation, it includes a Saturn orbiter and an atmospheric probe/lander for the moon Titan, although it has also returned...
), was a Saturn
Saturn
Saturn is the sixth planet from the Sun and the second largest planet in the Solar System, after Jupiter. Saturn is named after the Roman god Saturn, equated to the Greek Cronus , the Babylonian Ninurta and the Hindu Shani. Saturn's astronomical symbol represents the Roman god's sickle.Saturn,...
orbiter with a probe designed to plunge into the atmosphere of the ringed planet's largest satellite, Titan
Titan (moon)
Titan , or Saturn VI, is the largest moon of Saturn, the only natural satellite known to have a dense atmosphere, and the only object other than Earth for which clear evidence of stable bodies of surface liquid has been found....
. CRAF and SOTP were to use identical Mariner Mark II spacecraft, but each was to carry unique science instruments
Measuring instrument
In the physical sciences, quality assurance, and engineering, measurement is the activity of obtaining and comparing physical quantities of real-world objects and events. Established standard objects and events are used as units, and the process of measurement gives a number relating the item...
.
Instrumentation
All of the phenomena associated with comets were to be examined by CRAF's instruments. And because of the long duration of the planned rendezvous — almost three years — it was expected to fill in many of the major gaps in scientific understanding of the strange objects.The mission's scientific payload was selected in October 1986. It was to include:
- Cameras to photograph the nucleus, coma and tail, and changes that occur as Kopff orbits the Sun. Photos also would help scientists determine the comet's size and structure, the location of its poles, its rotation rate and geological structure.
- A surface penetrator-lander to be fired into Kopff's nucleus. The instruments aboard the penetrator-lander would collect a sample of cometary ices, study how they change when heated, and perform a chemical analysis of the gases released from the ice. The penetrator would bury its tip, which will contain a gamma-ray spectrometer measuring abundances of as many as 20 chemical elements, up to one meter (three feet) below the comet's surface. The penetrator was to carry accelerometers to determine Kopff's surface strength and its resistance to puncture, and thermometers to measure temperatures beneath the surface. The penetrator/lander would radio its findings to the spacecraft, which will then relay them to Earth.
- Mass spectrometerSpectrometerA spectrometer is an instrument used to measure properties of light over a specific portion of the electromagnetic spectrum, typically used in spectroscopic analysis to identify materials. The variable measured is most often the light's intensity but could also, for instance, be the polarization...
s to study composition of gases released by the nucleus and the cloud of plasmaPlasma (physics)In physics and chemistry, plasma is a state of matter similar to gas in which a certain portion of the particles are ionized. Heating a gas may ionize its molecules or atoms , thus turning it into a plasma, which contains charged particles: positive ions and negative electrons or ions...
(ionized gas) surrounding the nucleus.
- Dust counters, collectors and analyzers to capture samples of the comet's dust and study them on board. The information would help scientists determine the chemical elements that make up the dust and ice. In addition, the mass, size, shape and composition of individual dust grains will be measured.
- A visual and infraredInfraredInfrared light is electromagnetic radiation with a wavelength longer than that of visible light, measured from the nominal edge of visible red light at 0.74 micrometres , and extending conventionally to 300 µm...
mapping spectrometer to study chemical composition of the coma and the surface of the nucleus as they change with time.
- A magnetometerMagnetometerA magnetometer is a measuring instrument used to measure the strength or direction of a magnetic field either produced in the laboratory or existing in nature...
and a plasma-wave analyzer to measure interactions between the coma and electrically charged particles streaming from the Sun. The magnetometer was also to measure the comet's intrinsic magnetic field, if it has one.
External links
- CRAF info from NSSDC
- "Assessment of Planned Scientific Content of the CRAF Mission" by Drs. Robert O. Pepin and D.M. Hunten, chair and past chair, respectively, the Committee on Planetary and Lunar Exploration, of the National Academy of SciencesUnited States National Academy of SciencesThe National Academy of Sciences is a corporation in the United States whose members serve pro bono as "advisers to the nation on science, engineering, and medicine." As a national academy, new members of the organization are elected annually by current members, based on their distinguished and...
, 1985 - "Assessment of Planned Scientific Content of the CRAF Mission" by the National Academy of SciencesUnited States National Academy of SciencesThe National Academy of Sciences is a corporation in the United States whose members serve pro bono as "advisers to the nation on science, engineering, and medicine." As a national academy, new members of the organization are elected annually by current members, based on their distinguished and...
, 1987 - "On the Scientific Viability of a Restructured CRAF Science Payload" by the National Academy of SciencesUnited States National Academy of SciencesThe National Academy of Sciences is a corporation in the United States whose members serve pro bono as "advisers to the nation on science, engineering, and medicine." As a national academy, new members of the organization are elected annually by current members, based on their distinguished and...
, 1990