Engineering topics

Lundy, S. A.

Publications and source records attributed to Lundy, S. A..

5 records

NASA NTRS1984

Comet rendezvous

A Mariner Mark II spacecraft rendezvous mission with comet Kopff has been recommended by NASA's Solar System Exploration Committee, and is scheduled for a Shuttle launch in 1990. The spacecraft, which is scheduled to encounter the comet in 1994, will conduct a series of experiments including the study of the cometary nucleus, coma, and tail during perihelion passage; the determination of the nucleus and coma chemical/isotropic composition; the description of the nucleus's size, mass, rotation period, and pole occultation; distinctions of gas and dust hydrodynamics; and distinctions of solar wind interactions with the coma. The three-axis-stabilized spacecraft will be modular in design, and will incorporate a 490-Newton Insat engine, Viking Orbiter propulsion tanks, an Integrated Platform Pointing and Attitude Control Subsystem, and several scientific instruments. The spacecraft's Radio Frequency Subsystem will only use X-band telemetry with a downlink frequency of 8415 MHz, and an uplink frequency of 7161 MHz. The power sources in the present design include one radioisotope thermoelectric generator, three 3 Ah batteries, and a solar panel of approximately 7 sq m.

Draper, R. F.↗

NASA NTRS1984

The Mariner Mark II Comet Rendezvous/Asteroid Flyby Mission

The Comet Rendezvous/Asteroid Flyby will be the first mission in the Mariner Mark II program. The July 1990 launch will result in a fast flyby of the asteroid Tanete in May 1991 and a rendezvous with comet Kopff in February 1994, 879 days before comet perihelion. The spacecraft will return detailed data on the comet nucleus and its environment for nearly 1000 days. Several important comet characteristics will not be precisely known until the spacecraft performs its first measurements, which means that operations strategies must be adaptable to a range of conditions. In addition, the operation of a spacecraft in a dusty environment near a low-mass body imposes unique constraints on trajectory and orbit design.

Stetson, D. S.↗

NASA NTRS1984

Strategy for the IRAS all-sky survey

IRAS (the Infrared Astronomical Satellite) was launched on January 25, 1983 (January 26 GMT) with the primary purpose of performing an infrared survey of the entire celestial sphere. To ensure completeness and reliability, every point of sky was to be covered by a minimum of four separate scans of the telescope field-of-view, and as much as possible with six, with certain added timing constraints on the elapsed interval between scans. These strong requirements for sky coverage, combined with a restricted, rotating viewing-window, made extensive planning for the survey strategy, both pre-launch and during operations, a necessity. The result was that on November 21 (November 22 GMT), when the liquid helium required for cooling was depleted, 96 percent of the sky was covered to the minimum depth of four and 71 percent was coverd to depth six or more.

Lundy, S. A.↗

NASA NTRS1980

Use of the transect method in satellite survey missions with application to the infrared astronomical satellite /IRAS/

The coverage of the celestial sphere or the surface of the earth with a narrow-field instrument onboard a satellite can be described by a set of swaths on the sphere. A transect is a curve on this sphere constructed to sample the coverage. At each point on the transect the number of times that the field-of-view of the instrument has passed over the point is recorded. This information is conveniently displayed as an integer-valued histogram over the length of the transect. The effectiveness of the transect method for a particular observing plan and the best placement of the transects depends upon the structure of the set of observations. Survey missions are usually characterized by a somewhat parallel alignment of the instrument swaths. Using autocorrelation and cross-correlation functions among the histograms the structure of a survey has been analyzed into two components, and each is illustrated by a simple mathematical model. The complex, all-sky survey to be performed by the Infrared Astronomical Satellite (IRAS) is synthesized in some detail utilizing the objectives and constraints of that mission. It is seen that this survey possesses the components predicted by the simple models and this information is useful in characterizing the properties of the IRAS survey and the placement of the transects as a function of celestial latitude and certain structural properties of the coverage.

Mclaughlin, W. I.↗

NASA NTRS1979

Mission design for the infrared astronomical satellite /IRAS/

IRAS, a joint United States, Netherlands, United Kingdom astronomical satellite, is scheduled to be launched early in 1981 with the purpose of completing an all-sky survey in the infrared wavelengths from 8 to 120 microns and to observe objects of special interest. The mission design is driven by thermal constraints primarily determined by the Sun and Earth; the orbit and survey strategy must be chosen so as to satisfy the mission requirements before the cryogenic system is depleted of its liquid helium. Computer graphics help the designer choose valid survey strategies and evaluate resulting sky coverage.

Lundy, S. A.↗