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Farquhar, R. W.

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

At least 37 records · Page 2
All sourcesNASA NTRSDOE OSTI
NASA NTRS1976

Mission design for a halo orbiter of the earth

The International Sun-Earth Explorer (ISEE) scientific satellite to be stationed in 1978 in the vicinity of the sun-earth interior libration point to continuously monitor the space between the sun and the earth, including the distant geomagnetic tail is described. Orbit selection considerations for the ISEE-C are discussed along with stationkeeping requirements and fuel-optimal trajectories. Due to the alignment of the interior libration point with the sun as viewed from the earth, it will be necessary to place the satellite into a 'halo orbit' around the libration point, in order to eliminate solar interference with down-link telemetry. Parametric data for transfer trajectories between an earth parking orbit (altitude about 185 km) and a libration-point orbit are presented. It is shown that the insertion magnitude required for placing a satellite into an acceptable halo orbit is rather modest.

Farquhar, R. W.↗
NASA NTRS1976

Mission strategy for cometary exploration in the 1980's

A specific plan for a sequence of cometary intercept missions in the 1980's is reported. Each mission is described in detail and the supporting role of ground based cometary observations is included. Only three launches are required in the proposed mission sequence for six cometary encounters with comets Encke, Giacobini-Zinner, Borrelly and Halley. Cometary ephemerics errors are reduced to very small values because of a favorable earth-comet orbital geometry for Encke 1980, and excellent earth based sighting conditions exist for the entire 1985 mission set.

Farquhar, R. W.↗
NASA NTRS1975

Shuttle-launched multi-comet mission 1985

A low-cost multi-comet intercept mission with a launch in March 1985 is proposed. Two cometary spacecraft of identical design will be placed into a low earth parking orbit using a single Shuttle launch vehicle. Solid kick stages will then be used to boost each spacecraft into its required interplanetary trajectory. It is planned to have one spacecraft intercept comet Giacobini-Zinner in September 1985 and then go on to comet Borrelly with an encounter in December 1987. Earth swingby maneuvers will be used to achieve the double cometary intercept. The other spacecraft will be targeted for a pre-perihelion encounter with Halley's comet in December 1985.

Farquhar, R. W.↗
NASA NTRS1974

Mission design for a ballistic slow flyby Comet Encke 1980

Preliminary mission analyses for a proposed 1980 slow flyby (7-9 km/s) of comet Encke are presented. Among the topics covered are science objectives, Encke's physical activity and ephemeris accuracy, trajectory and launch-window analysis, terminal guidance, and spacecraft concepts. The nominal mission plan calls for a near-perihelion intercept with two spacecraft launched on a single launch vehicle. Both spacecraft will arrive at the same time, one passing within 500 km from Encke's nucleus on its sunward side, the other cutting through the tail region. By applying a small propulsive correction about three weeks after the encounter, it is possible to retarget both spacecraft for a second Encke intercept in 1984. The potential science return from the ballistic slow flyby is compared with other proposed mission modes for the 1980 Encke flyby mission, including the widely advocated slow flyby using solar-electric propulsion. It is shown that the ballistic slow flyby is superior in every respect.

Farquhar, R. W.↗
NASA NTRS1974

Mission strategy for cometary exploration in the 1980's

A sequence of ballistic intercept missions to comets is proposed. The mission set is composed of a well-known group of periodic comets whose physical properties are dissimilar. In addition to full descriptions of the nominal mission profiles, earth-based sighting conditions and estimates of cometary ephemeris errors are presented for each target comet. The first mission of the sequence is a slow flyby (approximately 8 km/sec) of Encke's comet near its perihelion in 1980. Because of a near resonance in the orbital periods of Encke and the spacecraft, it is possible to retarget the spacecraft for a second Encke encounter in 1984. The second mission of the sequence also consists of two cometary encounters but in this case different comets are involved; Giacobini-Zinner in 1985 and Borrelly in 1987. The final mission of the sequence calls for a simultaneous launch of two spacecraft towards Halley's comet in 1985. One spacecraft is targeted fo a pre-perihelion intercept at a heliocentric distance of 1.37 AU.

Farquhar, R. W.↗
NASA NTRS1974

Mission design for a ballistic slow-flyby of comet Encke 1980

Preliminary mission analyses for a proposed 1980 slow flyby (7 to 9 km/sec) of comet Encke are presented. Among the topics covered are: science objectives, Encke's physical activity and ephemeris accuracy, trajectory and launch-window analysis, terminal guidance, and spacecraft concepts. The nominal mission plan calls for a near-perihelion intercept with two spacecraft using a single launch vehicle. Both spacecraft arrive at the same time, one passing within 500 km from Encke's nucleus on its sunward side, the other cutting through the tail region. By applying a small propulsive correction about three weeks after the encounter, it is possible to retarget both spacecraft for a second Encke intercept in 1984. The potential science return from the ballistic slow flyby is compared with other proposed mission modes for the 1980 Encke flyby mission including the widely advocated slow flyby using solar-electric propulsion. It is shown that the ballistic slow flyby is superior in every respect.

Farquhar, R. W.↗
NASA NTRS1973

Quasi-periodic orbits about the translunar libration point.

Analytical solutions for quasi-periodic orbits about the translunar libration point are obtained by using the method of Lindstedt-Poincare and computerized algebraic manipulations. The solutions include the effects of nonlinearities, lunar orbital eccentricity, and the sun's gravitational field. For a small-amplitude orbit, the orbital path as viewed from the earth traces out a Lissajous figure. This is due to a small difference in the fundamental frequencies of the in-plane and out-of-plane oscillations. However, when the amplitude of the in-plane oscillation is greater than 32,379 km, there is a corresponding value of the out-of-plane amplitude that will produce a path where the fundamental frequencies are equal. This synchronized trajectory describes a 'halo orbit' of the moon.

Farquhar, R. W.↗
NASA NTRS1973

Missions to comets

Missions to comets are outlined that form the basis for a new program to send a space probe to a comet. Simple flythroughs of the comet head will provide information about the composition of the ionized and neutral particles that make up the cometary atmosphere and on effects of solar-wind interaction with the comet. Projected are missions to the comets Grigg-Skjellerup, Encke, and Halley.

Farquhar, R. W.↗
NASA NTRS1972

Two early missions to the comets.

Early missions to the comets Grigg-Skjellerup in 1977 and Encke in 1980 are suggested as precursors to more ambitious missions to Encke rendezvous in 1984 and Halley intercept in 1986. The spacecraft structures, power systems, telemetry, configurations, and launch vehicles considered appropriate for these two missions are actual equipments ready for applications. The mission objectives would be exploration of the nature of the solar wind interaction with comets, the composition of the gaseous cometary atmosphere, and possibly the details of the trailing portion of a comet (ion and dust tails).

Farquhar, R. W.↗
NASA NTRS1972

Cometary Explorer to Grigg-Skjellerup 1977

The mission analysis and technical summary of the spacecraft and its subsystems are presented for an Explorer flight to investigate the solar wind interaction with the Grigg-Skjellerup coma. The basic spacecraft system is the same as Explorer 43 and 47, and the mission characteristics which distinguish this mission from previous IMP missions are discussed. The physical and chemical characteristics of the comet's nucleus and coma are described, and the spacecraft trajectory and scientific payloads required to study the solar wind-cometary atmospheric interaction are considered.

Ness, N. F.↗
NASA NTRS1972

Quasi-periodic orbits about the translunar libration point.

Analytical solutions for quasi-periodic orbits about the translunar libration point are obtained by using the method of Lindstedt-Poincare and computerized algebraic manipulations. The solutions include the effects of nonlinearities, lunar orbital eccentricity, and the sun's gravitational field. For a small-amplitude orbit, the orbital path as viewed from the earth traces out a Lissajous figure. This is due to a small difference in the fundamental frequencies of the in-plane and out-of-plane oscillations. However, when the amplitude of the in-plane oscillation is greater than 32,379 km, there is a corresponding value of the out-of-plane amplitude that will produce a path where the fundamental frequencies are equal. This synchronized trajectory describes a 'halo orbit' of the moon.

Farquhar, R. W.↗
NASA NTRS1972

Early missions to comets

Two specific early missions to the comets Grigg-Skjellerup in 1977 and Encke in 1980 are proposed as precusor missions to Encke rendezvous and Halley intercept in 1986. The mission guidelines and principal objectives are presented. The spacecraft IMP was chosen for the flythrough mission for Grigg-Skjellerup in 1977, and the Helios spacecraft for the Encke mission in 1980. The mission trajectories are summarized in graphs.

Farquhar, R. W.↗
NASA NTRS1972

A halo-orbit lunar station.

A relay satellite following a halo trajectory will always maintain line-of-sight contact with the earth and the moon's far side. The Integrated Program Plan for lunar exploration in the 1980s and beyond calls for a fully reusable earth-moon transportation system. The principal elements of the system are a Translunar Shuttle, a Lunar-Orbit Space Station or Halo-Orbit Space Station, and a Lunar Space Tug. It is shown that a halo-orbit space station could offer important operational and performance advantages compared to a lunar-orbit station in a second-generation lunar program.

Farquhar, R. W.↗