Engineering topics

Mcdonald, Frank B.

Publications and source records attributed to Mcdonald, Frank B..

4 records

NASA NTRS1993

Role of drifts and global merged interaction regions in the long-term modulation of cosmic rays

The paper shows that the long-term modulation of 0.2- to 3-GV galactic and anomalous cosmic rays over the 22-year heliomagnetic cycle is basically a combination of two solar related processes, the cumulative effect of long-lived global merged interaction regions (GMIRs) and large-scale particle gradient and curvature drifts in the interplanetary magnetic field. This paradigm for cosmic ray modulation is based on the observed changes in cosmic ray intensity from solar minimum to solar maximum over successive solar cycles (21 and 22) using data from 1 AU and from the outer heliosphere. For cycle 21, the 1977-1980 modulation is dominated by GMIRs. In cycle 22, it is shown that drifts are an important but not dominant factor for galactic cosmic ray modulation with the current sheet related drift effects decreasing with increasing rigidity and heliocentric distance.

Mcdonald, Frank B.↗

NASA NTRS1992

The cosmic radiation in the heliosphere at successive solar minima

Cosmic ray observations at 1 AU are compared for the last three solar minimum periods along with the 1977/1989 and 1987 Pioneer 10 and Voyager 1 and 2 data from the outer heliosphere. There is good agreement between the 1965 and 1987 Galactic cosmic ray H and He spectra at 1 AU. Significant and complex differences are found between the 1977/1978 and 1987 measurements of the Galactic and anomalous cosmic ray components at 1 and 15 AU. In the outer heliosphere there are negative latitudinal gradients that reach their maximum magnitude when the inclination of the outer heliosphere current sheet is at a minimum. The radial gradients decrease with heliocentric distance as about 1/r exp 0.7 and do not differ significantly at the successive solar minima. The measured radial and latitudinal gradients are used to estimate the particle transport parameters in the outer heliosphere. Using the local interstellar He spectrum of Webber et al. (1987), it is estimated that the modulation boundary is of the order of 160 AU.

Mcdonald, Frank B.↗

NASA NTRS1988

Space science in the United States

Despite the hiatus in spacecraft launches after the Space Shuttle Challenger accident in 1986, the U.S. space program continues to generate research data on the basis of the productive operation of 18 scientific spacecraft. Attention is presently given to NASA's planned missions for the 1990s in such fields as astronomy and astrophysics (the Hubble Space Telescope, the Extreme UV Explorer), solar system exploration (the Magellan Venus orbiter, the Galileo Jupiter orbiter), space physics (the Tethered Satellite System, the Combined Release and Radiation Effects Satellite), earth science (the Upper Atmospheric Research Satellite), and microgravity sciences (the International Microgravity Observatory).

Alexander, Joseph K.↗

NASA NTRS1987

Space research - At a crossroads

Efforts which must be expended if U.S. space research is to regain vitality in the next few years are discussed. Small-scale programs are the cornerstone for big science projects, giving both researchers and students a chance to practice the development of space missions and hardware and identify promising goals for larger projects. Small projects can be carried aloft by balloons, sounding rockets, the Shuttle and ELVs. It is recommended that NASA continue the development of remote sensing systems, and join with other government agencies to fund space-based materials science, space biology and medical research. Increased international cooperation in space projects is necessary for affording moderate to large scale missions, for political reasons, and to maximize available space resources. Finally, the establishment and funding of long-range goals in space, particularly the development of the infrastructure and technologies for the exploration and colonization of the planets, must be viewed as the normal outgrowth of the capabilities being developed for LEO operations.

Mcdonald, Frank B.↗