Engineering topics

Farquhar, Robert W.

Publications and source records attributed to Farquhar, Robert W..

10 records

NASA NTRS1993

Trajectory design for a lunar mapping and near-Earth-asteroid flyby mission

In August, 1994, the unusual asteroid (1620) Geographos will pass very close to the Earth. This provides one of the best opportunities for a low-cost asteroid flyby mission that can be achieved with the help of a gravity assist from the Moon during the years 1994 and 1995. A Geographos flyby mission, including a lunar orbiting phase, was recommended to the Startegic Defense Initiative (SDI) Office when they were searching for ideas for a deep-space mission to test small imaging systems and other lightweight technologies. The goals for this mission, called Clementine, were defined to consist of a comprehensive lunar mapping phase before leaving the Earth-Moon system to encounter Geographos. This paper describes how the authors calculated a trajectory that met the mission goals within a reasonable total Delta-V budget. The paper also describes some refinements of the initially computed trajectory and alternative trajectories were investigated. The paper concludes with a list of trajectories to fly by other near-Earth asteroids during the two years following the Geographos opportunity. Some of these could be used if the Geographos schedule can not be met. If the 140 deg phase angle of the Geographos encounter turns out to be too risky, a flyby of (2120) Tantalus in January, 1995, has a much more favorable approach illumination. Tantalus apparently can be reached from the same lunar orbit needed to get to Geographos. However, both the flyby speed and distance from the Earth are much larger for Tantalus than for Geographos.

Dunham, David W.↗

NASA NTRS1991

Mercury Orbiter: Report of the Science Working Team

The results are presented of the Mercury Orbiter Science Working Team which held three workshops in 1988 to 1989 under the auspices of the Space Physics and Planetary Exploration Divisions of NASA Headquarters. Spacecraft engineering and mission design studies at the Jet Propulsion Lab were conducted in parallel with this effort and are detailed elsewhere. The findings of the engineering study, summarized herein, indicate that spin stabilized spacecraft carrying comprehensive particles and fields experiments and key planetology instruments in high elliptical orbits can survive and function in Mercury orbit without costly sun shields and active cooling systems.

Belcher, John W.↗

NASA NTRS1990

Halo-orbit and lunar-swingby missions of the 1990's

A significant number of spacecraft are planning to use halo orbits and lunar-swingby trajectories in the next decade. Four spacecraft will be placed into halo orbits around the earth's sunward libration point, while two others will be stationed near the sun-earth L2 libration point in the distant geomagnetic tail. Six spacecraft, including two of the aforementioned halo orbiters, will make use of lunar-swingby maneuvers to fulfill their mission objectives. Thus, a total of ten spacecraft, five from the Soviet Union, two from Japan, two from the United States, and one from the European Space Agency, will employ halo orbits and/or lunar-swingby trajectories in the 1990's. Pertinent facts are presented for each of these missions.

Farquhar, Robert W.↗

NASA NTRS1990

A launch window study for GEOTAIL's double lunar swingby trajectory

The GEOTAIL spacecraft of the International Solar-Terrestrial Physics Program will use a series of paired lunar swingbys to explore distant parts of the earth's magnetic tail. A 21-day launch window has been calculated for GEOTAIL, in July and August 1992, to start its distant-tail phase with a first lunar swingby (S1) on September 8, 1992. The main launch window in July utilizes 4.5 revolutions in a transfer orbit to S1, with a mid-August contingency window that uses 2.5 transfer-orbit revolutions before S1. Designing a good distant-tail trajectory, and then accurately matching it at S1 for every day in the launch window, seems to be the easiest and most reliable strategy. However, the total delta-V costs of the current designs can probably be reduced, possibly with the help of new interactive software that can be run on personal computers.

Dunham, David W.↗

NASA NTRS1990

Use of libration-point orbits for space observatories

The sun-earth libration points, L1 and L2, are located 1.5 million kilometers from the earth toward and away from the sun. Halo orbits about these points have significant advantages for space observatories in terms of viewing geometry, thermal and radiation environment, and delta-V expediture.

Farquhar, Robert W.↗

NASA NTRS1989

Trajectories for spacecraft encounters with Comet Honda-Mrkos-Pajdusakova in 1996

Early in 1996, the relatively bright short-period Comet Honda-Mrkos-Pajdusakova (HMP) will pass only 0.17 astronomical unit from the earth, providing both an unusually favorable apparition for ground-based observers and an opportunity for a spacecraft to reach Comet HMP on relatively low-energy trajectories. The Japanense Institute of Space and Astronautical Sciences Sakigake spacecraft is expected to fly by Comet HMP on February 3, 1996, after utilizing four earth swingbys to modify its orbit. If the camera on the ESA Giotto spacecraft is inoperable, Giotto may also be sent to Comet HMP. In addition, 1-year earth-return trajectories to Comet HMP are described, along with some that can be extended to encounter Comet Giacobini-Zinner in 1998.

Dunham, David W.↗

NASA NTRS1989

Double-lunar swingby trajectories for the spacecraft of the International Solar Terrestrial Physics program

The ISEE-3 satellite carried out the first extensive exploration of the distant geomagnetic tail during 1983. ISEE-3's orbit was altered with four lunar gravity assists that alternately decreased and increased its orbital energy while keeping the apogees aligned in the antisolar direction. Two spacecraft of the International Solar Terrestrial Physics program will use similar double-lunar swingby orbits to study the solar wind and the geomagnetic environment. Geotail will be built in Japan for the Institute of Space and Astronautical Sciences; its main purpose will be to explore the earth's geomagnetic tail. Wind is a NASA spacecraft that will monitor the solar wind upstream from the earth and will also study the bowshock region of the magnetosphere. Current plans call for launches of both by NASA with expendable launch vehicles during the second half of 1992.

Dunham, David W.↗

NASA NTRS1989

The International Cometary Explorer comet encounter and earth-return trajectory

ICE experienced a successful encounter with Comet Giacobini-Zinner on September 11, 1985. The comet-intercept trajectory, earth-return trajectory, and two cases of a possible 2014 capture trajectory are presented. Also, the essential propulsive trajectory correction maneuvers and the projected August 10, 2014 lunar swingby maneuver are discussed. The targeting methodology used for designing the trajectories is also discussed.

Roberts, Craig E.↗

NASA NTRS1987

A Voyager-style tour of comets and asteroids 1994-2005

A low cost program that links a dual-comet flyby sample-return mission with a multicomet/asteroid tour is proposed. Two spacecraft are used to carry out this program: a three-axis stabilized Observer-class spacecraft and a smaller spin-stabilized sample-return probe. The Observer spacecraft uses earth-swingby and propulsive maneuvers to accomplish the small-body tour, which includes flybys of three comets (Tempel-1, Tempel-2, and Encke) and two asteroids (46-Hestia and 433-Eros) over a 12-year period. Two of these comets (Tempel-1 and Tempel-2) are also the shared targets, the Observer serves as a navigational aid for the probe, which scoops up dust particles as it flies through the cometary atmosphere. After collecting the cometary dust samples, the probe returns to a low earth orbit where it is recovered by the Space Shuttle.

Farquhar, Robert W.↗

NASA NTRS1986

Orbital acrobatics in the Sun-Earth-Moon system

Unconventional trajectory techniques for space missions in the Sun-Earth-Moon system, including libration-point orbits, gravity-assist maneuvers, and Earth-return trajectories are reviewed. The ISEE-3/ICE flight experience is used to illustrate the utility of libration-point orbits called halo-orbits. Five lunar gravity-assist maneuvers used by the ISEE-3/ICE spacecraft are discussed. The final lunar swingby sent the spacecraft into a heliocentric trajectory that will eventually intercept Comet Giacobini-Zinner. As an example of the Earth-return trajectory concept, a proposed mission that includes flybys of three comets and two asteroids is described.

Farquhar, Robert W.↗