Asteroid Flyby Research Articles

Trajectory options for low-cost missions to asteroids

We consider a wide variety of gravity-assist trajectories using Venus, Earth and Mars to obtain low launch energy trajectories to four large asteroids in the main belt. These trajectories are constructed by analytic and numeric search techniques. We optimize promising trajectories for minimum total Δ V and search for additional (nontargeted) asteroid flybys. Several optimized opportunities with multiple asteroid flybys are reported, followed by a discussion of general characteristics of the various trajectory types.

Rosetta: The ESA comet rendezvous mission

Rosetta was selected in November 1993 for the ESA Cornerstone 3 mission, to be launched in 2003, dedicated to the exploration of the small bodies of the solar system (asteroids and comets). Following this selection, the Rosetta mission and its spacecraft have been completely reviewed: this paper presents the studies performed the proposed mission and the resulting spacecraft design. Three mission opportunities have been identified in 2003–2004, allowing rendezvous with a comet. From a single Ariane 5 launch, the transfer to the comet orbit will be supported by planetary gravity assists (two from Earth, one from Venus or Mars); during the transfer sequence, two asteroid fly-bys will occur, allowing first mission science phases. The comet rendezvous will occur 8–9 years after launch; Rosetta will orbit around the comet and the main science mission phase will take place up to the comet perihelion (1–2 years duration). The spacecraft design is driven (i) by the communication scenario with the Earth and its equipment, (ii) by the autonomy requirements for the long cruise phases which are not supported by the ground stations, (iii) by the solar cells solar array for the electrical power supply and (iv) by the navigation scenario and sensors for cruise, target approach and rendezvous phases. These requirements will be developed and the satellite design will be presented.

Near Earth Asteroid Rendezvous: Mission Overview

The Near Earth Asteroid Rendezvous (NEAR) mission launched successfully on February 17, 1996 aboard a Delta II-7925. NEAR will be the first mission to orbit an asteroid and will make the first comprehensive scientific measurements of an asteroid's surface composition, geology, physical properties, and internal structure. It will orbit the unusually large near-Earth asteroid 433 Eros for about one year, at a minimum altitude of about 15 km from the surface. NEAR will also make the first reconnaissance of a C-type asteroid during its flyby of the unusual main belt asteroid 253 Mathilde. The NEAR instrument payload is: a multispectral imager (MSI), a near infrared spectrometer (NIS), an X-ray/gamma ray spectrometer (XRS/GRS), a magnetometer (MAG), and a laser rangefinder (NLR), while a radio science investigation (RS) uses the coherent X-band transponder. NEAR will improve our understanding of planetary formation processes in the early solar system and clarify the relationships between asteroids and meteorites. The Mathilde flyby will occur on June 27, 1997, and the Eros rendezvous will take place during February 1999 through February 2000.

Trajectory design for the mission ‘Hannes’

Trajectory design for the multiple asteroid flyby mission ‘Hannes’, which is to be launched in 2002 and to last six years, is considered. Different mission options form a tree of ‘opportunities’ which is presented. Nodes of the tree are the Earth and Mars swingbys, each branch contains several sets of asteroids which can be flown by. However some branches of the tree require rather powerful launch vehicle like Molniya. Other branches are analysed in details; they include VEGA maneuver, and smaller launch vehicle (such as Kosmos or Rockot) can be used for them. Several possible spacecraft trajectories are given. Some of them include up to seven or eight asteroid flybys with total delta-V for the deep space maneuvers within 1200 m/s. Among the asteroids are such as Ceres, Pallas, Vesta etc. Tables containing main mission characteristics and figures presenting the spacecraft trajectories are given.

Remote sensing of comets and asteroids

In the past Quadrennium, we have observed a fragmented comet collide with Jupiter, and discovered a population of objects of the order of hundreds of kilometers in diameter beyond the orbit of Neptune, a probable source region of short period comets. We are still in the age of discovery as studies of the solar system continue. The discovery of many small asteroids with the same surface composition as the second largest main belt asteroid, 4 Vesta, has opened our eyes to a pathway by which certain meteorites reach earth and by which asteroids collide and their orbits evolve. This evidence for delivery of meteorites was found by pushing existing observing techniques to their limits. An expanded capability for detecting returned radar echoes from asteroids permits the extraction of basic information about their position, shape, spin state, size and surface texture which is equivalent to that acquired from a flyby of a robotic spacecraft. We will never send spacecraft to as many asteroids as can be studied from the ground, so the contributions of ground‐based astronomy at all wavelengths provides insights into the chemical and physical diversity of the asteroids and comets. Remote sensing is carried out by ground‐based and Earth‐orbiting telescopic studies, and robotic spacecraft traveling through the solar system. In the past Quadrennium, we have viewed data returned from two main belt asteroid flybys missions which represent the transition of asteroids as targets of astronomical study t o subjects of geological study. Scientists using the Galileo spacecraft additionally made the serendipitous discovery of Dactyl, a satellite of 243 Ida, the first direct proof that satellites orbit asteroids. The significant advances discussed below have occurred because of 1) chance discovery (the discovery of Comet Shoemaker‐Levy 9 and Dactyl), 2) the interaction between theoretical predictions and observational programs (discovery of trans‐ Neptunian objects, 3) the use of available technology pushed to its limits of sensitivity (discovery of small asteroids with the same surface composition as 4 Vesta,) and 4) the consequence of technical upgrading of facilities. The latter provides fundamental facts about the diverse physical characteristics of small solar system bodies. A prime example is advancing knowledge derived from radar astronomy. Our new knowledge has generated a modified view of the number and nature of the small bodies in the solar system and how they formed and evolved through time.

Solar wind interaction with small bodies: 1. Whistler wing signatures near Galileo's closest approach to Gaspra and Ida

Abstract Data from Galileo's two asteroid flybys reveal magnetic fluctuations that we interpret as perturbations of the solar wind magnetic field caused by an interaction with the nearby asteroid. The scale sizes of the bodies (∼14 km for Gaspra and ∼30 km for Ida) are intermediate between the ion and electron gyroradii, which implies that the asteroid-imposed perturbations propagate in the whistler mode. Special properties of the whistler mode include phase velocities that can exceed the solar wind speed and confinement of the disturbance to directions nearly aligned with the magnetic field. These features of the interaction impose a structure on the solar wind disturbance that differs greatly from the forms familiar for either magnetized or unmagnetized bodies of magnetohydrodynamic spatial scales. We examine both data and computer simulations of the interaction with special attention to what can be inferred about the interaction itself from analysis of the data.

NASA team sought for Moon, asteroid mission

The NASA Solar System Exploration Division will soon be soliciting members for the Clementine Science Team through a research announcement. The Clementine mission is being sponsored by the Space Defense Initiative and will be launched in January 1994 to fly lightweight sensors and other components in a long‐exposure space mission and to collect significant science data on the Moon while in polar orbit for several months, and then while flying at close range past the near‐Earth asteroid Geographos in August 1994.The science team will assist with scientific calibration and documentation of the instruments, assist in planning the science observations, and validate and archive the science data in the NASA Planetary Data System. The team will be composed of experts in various aspects of data collection, reduction, and archiving to ensure that the data collected is of the highest quality possible. Science team members will have proprietary data rights for several months after the asteroid flyby date, which is the nominal end‐ofmission date.

Galileo trajectory design

The Galileo spacecraft was launched by the Space Shuttle Atlantis on October 18, 1989. A two-stage Inertial Upper Stage propelled Galileo out of Earth parking orbit to begin its 6-year interplanetary transfer to Jupiter. Galileo has already received two gravity assists: from Venus on February 10, 1990 and from Earth on December 8, 1990. After a second gravity-assist flyby of Earth on December 8, 1992, Galileo will have achieved the energy necessary to reach Jupiter. Galileo's interplanetary trajectory includes a close flyby of asteroid 951-Gaspra on October 29, 1991, and, depending on propellant availability and other factors, there may be a second asteroid flyby of 243-Ida on August 28, 1993. Upon arrival at Jupiter on December 7, 1995, the Galileo Orbiter will relay data back to Earth from an atmospheric Probe which is released five months earlier. For about 75 min, data is transmitted to the Orbiter from the Probe as it descends on a parachute to a pressure depth of 20–30 bars in the Jovian atmosphere. Shortly after the end of Probe relay, the Orbiter ignites its rocket motor to insert into orbit about Jupiter. The orbital phase of the mission, referred to as the satellite tour, lasts nearly two years, during which time Galileo will complete 10 orbits about Jupiter. On each of these orbits, there will be a close encounter with one of the three outermost Galilean satellites (Europa, Ganymede, and Callisto). The gravity assist from each satellite is designed to target the spacecraft to the next encounter with minimal expenditure of propellant. The nominal mission is scheduled to end in October 1997 when the Orbiter enters Jupiter's magnetotail.

CoMA ? An advanced space experiment forin situ analysis of cometary matter

Exploring one of the most pristine bodies in our solar system — a comet — with a spacecraft will be a great step towards a deeper understanding of our solar system's beginnings. We here present the advanced space experiment CoMA (cometarymatteranalyzer), which will be flown on NASA's cometary rendezvous and asteroid flyby mission CRAF. CoMA is a high resolution time-of-flight secondary ion mass spectrometer. It will analyze μm-sized cometary dust grains and cometary gases with an unprecedented mass resolution and will yield data about the elemental, isotopic, and molecular composition.

Candidates for Office, 1992–1994: Union Candidates: President‐elect

AGU member since 1960. Senior Research Scientist at the Jet Propulsion Laboratory, California Institute of Technology. Principal scientific interest is space plasma physics. B.A. 1954, Cornell Univ.; M.S. 1956, Univ. of Illinois. Employed at Jet Propulsion Laboratory since 1956. Visiting appointments at Cambridge Univ. 1975, Caltech 1986–1987, and Univ. of California, Los Angeles 1990–1991. Investigator on nine space experiments to study the solar wind or comets. Project Scientist for the Comet Rendezvous Asteroid Flyby mission. Past member of numerous NASA committees. Currently member of the National Research Council's Space Studies Board and Chair of its Committee on Solar and Space Physics. Over 100 refereed publications, most in AGU journals. One patent. Honors include NASA Exceptional Scientific Achievement Award 1970 and Fellow of AGU 1989. AGU service as Secretary and President of Solar‐Planetary Relationships Section, Associate Editor of J. Geophys. Res. (Space) and Editor‐in‐Chief of Rev. Geophys. 1989–1992.

Visible and infrared mapping spectrometer for exploration of comets, asteroids, and the saturnian system of rings and moons

AbstractThe science objectives and system design for a Visible and Infrared Mapping Spectrometer (VIMS), an imaging spectrometer for planetary exploration, are described. The instrument development is the result of a collaboration between scientists and engineers from the United States, Italy, and France. NASA has selected VIMS as a facility instrument for the Comet Rendezvous Asteroid Flyby (CRAF) Mission, and as a candidate facility instrument for the Cassini Mission to explore Saturn and its rings and moons. (A facility instrument is provided by the project for the use of a science team which was selected on the basis of individual competitive science proposals.) VIMS covers the spectral range from 0.35 to 5.2 μm with a nominal spatial resolution of 0.5 milliradians (pixel size) and spectral resolutions (spectral width) of 7 nm at 0.35–1.0‐ μm wavelength and 16nm at 1.0–5.2‐μm wavelength. The nominal pixel size is 0.5 × 0.5 mrad2. The two separate missions are scheduled to be launched by NASA from the Eastern Test Range at Cape Canaveral, Florida, using the Titan IV Launch Vehicle. The planned launch date for the Cassini Mission is November 1995. The planned launch date for the CRAF Mission is February 1996.

CRAF science cut; Cassini teams selected

In mid‐November the National Aeronautics and Space Administration selected the principal investigators and science teams for the Cassini mission to Saturn and “de‐selected” two instruments on the Comet Rendezvous'Asteroid Flyby (CRAF) mission. The cancellation of the instruments—the penetrator and the scanning electron microscope and particle analyzer—was made to keep the costs of the joint CRAF/Cassini project within the $1.6 billion limit mandated by Congress. CRAF's costs had become a concern earlier this year due in part to increased cost estimates for the penetrator and the spacecraft's radioisotope thermoelectric generators and a decrease in funding for the spacecraft propulsion module, which is being provided by Germany. After a cost review of the program by NASA's Qffice of Space Science and Applications and recommendations by the National Research Council's Space Science Board, NASA decided that both the penetrator and the scanning electron microscope would have to be cut to keep CRAF within its budget.

Techniques for Capture of Low Velocity (<200 m/s) Particles

Collection of low velocity, micron-size, dust particles (~50 - 200 m/s) is an upcoming challenge for dust instruments aboard NASA’s Comet Rendezvous and Asteroid Flyby (CRAF) mission, scheduled for launch in 1995. There will be three dust analysis instruments on board, each of which will capture cometary dust intact for analysis by different techniques. Each instrument has its own restrictions on dust collection processes because of differing techniques and science goals. SEMPA, the Scanning Electron Microscope and Particle Analyzer, is one of the CRAF dust analysis instruments. The work reported here examines particle capture in light of SEMPA’s particular functional requirements. These include particle visibility for imaging and x-ray analysis, high contrast, no interfering x-ray lines, and collection without size discrimination. A number of collection techniques have been tested in our laboratory with dust from a free-expansion, gas-drag dust gun that accelerates micron-size dust to ~50 - 200 m/s, the expected relative velocity of the spacecraft and the dust at the comet.

Plan-IT-2: The next generation planning and scheduling tool

Plan Integrated Timelines (Plan-IT) is a scheduling program which has been demonstrated and evaluted in a variety of scheduling domains (Spacelab, Deep Space Network, Comet Rendezvous and Asteroid Flyby, Telescience, and Space Station Power). This paper discusses the capability enhancements being made for the next generation of Plan-IT, called Plan-IT-2. Plan-IT-2 represents a complete rewrite of the original Plan-IT, incorporating major changes as suggested by our application experiences with the original Plan-IT. A few of the enhancements described in the paper are additional types of constraints, such as states and resettable-depletables (batteries), dependencies between constraints, multiple levels of activity planning during the scheduling process, pattern constraing searching for opportunities as opposed to just minimizing the amount of conflicts, additional user-definable features for display and handling of diverse multiple time systems, and reduction in both the size and the complexity for adapting Plan-It-2 to address different problem domains. As the complexity of software on future spacecraft increases, so will planning and scheduling activities for the spacecraft. For a ground support tool to handle the scheduling/planning for spacecraft, from manual to automatic operation, the tool must: 1) contain multiple levels of planning, from goal planning down to the detailed command level; 2) be adaptable to changes in the structure of the activities; 3) consider the resource constraints at multiple planning levels; 4) be adaptable to changing rules and strategies as mission goals and requirements change; and 5) be user-natural (program operation is both user-friendly and intuitive to the user). Plan-IT-2 is the second step in bringing this capability to the sequencing domain. Plan-It-2's robust representation of the elements involved in the spacecraft sequencing process should serve as good preparation for coping with future spacecraft systems that may have various levels of autonomous behavior.

Future Solar System Missions

After a decade long hiatus in launches beyond Earth orbit, NASA’s planetary exploration program is again moving forward, beginning with the Magellan launch to Venus in May 1989 and the Galileo launch to Jupiter in October 1989. These spacecraft will reach their targets in August 1990 and December 1995, respectively. Both are missions of longstanding priority, Magellan to provide the first global high resolution mapping of the cloud-shrouded Venus surface, Galileo to make comprehensive measurements of the Jovian system in follow-up to the 1979/1980 Voyager flybys.Beyond these two missions there are other already approved missions: the Mars Observer for launch in 1992, the Comet Rendezvous and Asteroid Flyby CRAF mission (Fig. 1) for launch in 1995, and the Cassini mission (Figs. 2 and 3) to Saturn and its moon Titan for launch in 1996. The very diversity of these five missions and their targets (Venus, the Jovian system, Mars, comet Kopff, asteroids Gaspra and Ida by Galileo, Hamburga by CRAF, and Maja by Cassini, and the Saturnian system, is indicative of the strategy being pursued in the program: one of deliberate breadth that seeks to explore all three main classes of solar system bodies (the terrestrial planets, the outer giants and their moons, and the primitive small bodies).

Design and numerical simulation of a 3-D electron plasma analyzer that resolves both energy and elevation angle

The Comet Rendezvous and Asteroid Flyby Mission (CRAF) will include, as one of its complement of thirteen scientific instruments, a plasma electron analyzer capable of providing 3-dimensional measurements of the energy and angular distribution of electrons in the solar wind, asteroidal and cometary environments. After initial instrument selection, mission planners at JPL suggested that an instrument capable of performing angular scanning electronically rather than mechanically be investigated. This paper describes the computer design of the new CRAF plasma electron detector, consisting of an electronic scanning component, called the “elevation analyzer”, and an energy analyzing component based on the Soft Particle Spectrometer (SPS) and its successor, the Spectrographic Particle Imager (SPI). Numerical simulation of each component's operation — consisting of ray-tracing particles through the electrostatic field of each analyzer and collecting statistics on those particles successfully transmitted — is used to determine the energy and angular response functions of each component and the design dimensions that optimize these responses.

Thermal evolution of Comet P/Tempel 1—Representing the group of targets for the CRAF and CNSR missions

The properties of the outer layers of comets considered for the future Comet Rendezvous and Asteroid Flyby and Comet Nucleus Sample Return missions are studied, by following numerically the thermal evolution of spherically symmetric models of the nucleus, in the orbit of Comet P/Tempel-1. The evolution starts from isothermal (10°K) and homogeneous nuclei, composed of amorphous ice and dust. The crystallization of amorphous ice at 137°K is taken into account. As the ice sublimates, a permanent dust mantle is allowed to accumulate, at a rate which is proportional to the sublimation rate. Evolutionary sequences are computed for different values of the density, the dust/ice mass ratio, and the (constant) fraction of the dust which is not carried away with the sublimating ice. The main conclusions are (a) the temperatures at the outer and inner surfaces of the dust mantle are not very sensitive to changes in the parameters; (b) although the dust is assumed permeable to water vapor, the rate of erosion of the nucleus slows down as the dust mantle grows and its insulating effect increases; (c) the temperature at a depth of 10 m is ∼160°K for all models considered and hence, the ice at this depth is crystalline; (d) the total thickness of the crystalline ice layer, between the dust mantle and the amorphous ice core, varies from 40 to 240 m, depending on the parameters assumed. Consequently, it should be difficult for the probes of the two comet missions to sample pristine amorphous ice, unless they are aimed at the bottom of an active crater.

Comets and Their Composition

Recent theoretical and observational studies of comets are reviewed, with an emphasis on in situ data from spacecraft encounters with P/Giacobini-Zinner (September 1985) and P/Halley (March 1986). Topics addressed include clues on the origin and permanence of the Oort cometary cloud, observations of cometary nuclei far from the sun, the Halley nucleus, compositional and physical data from comae studies, and the parent molecules in comet ices. Also discussed are quantitative analyses of coma production; special features in the tail of P/Giacobini-Zinner; and proposals for (1) observations to detect distant giant comets, (2) high-resolution spectroscopic studies of comae, and (3) additional spacecraft missions such as the NASA Comet Rendezvous and Asteroid Flyby.

A proposed comet nucleus penetrator for the comet rendezvous asteroid flyby mission

Among the major objectives of NASA's program of space exploration is a better understanding of the origin and evolution of the solar system. Crucial to this objective is the study of comets, which are thought to be the most primitive, pristine bodies remaining in the solar system. The importance of the study of comets has led NASA to plan a mission to rendezvous with comet Tempel 2 in 1997. Critical to the understanding of comets will be measurements of the nucleus material to determine its elemental and isotopic composition, its mechanical properties, and its thermal state and properties. This paper describes a proposal for a Comet Nucleus Penetrator to accomplish these measurement goals. The Comet Nucleus Penetrator will implant instruments into the comet's nucleus beneath a probable volatile-depleted surface mantle into material more representative of the bulk composition of the nucleus.

PLAN-IT: Scheduling assistant for solar system exploration

At the Jet Propulsion Laboratory (JPL), the scheduling of spacecraft activities is a complex endeavor for which streamlining is always being sought. Using the Comet Rendezvous Asteroid Flyby mission (CRAF—proposed for 1993 launch) as a development base, PLAN-IT (a frame-based expert scheduling system shell) has been adapted to assist in one phase of schedule generation. PLAN-IT CRAF automatic scheduling routines attempt to return a “good-cut” schedule which can be adjusted by an expert with time-saving graphic manipulation tools. Work to date has led to a “GO” decision on technical factors for online capability development.