Engineering topics

Troy, B. E., Jr.

Publications and source records attributed to Troy, B. E., Jr..

14 records

NASA NTRS1975

Effect of grid transparency and finite collector size on determining ion temperature and density by the retarding potential analyzer

The effects of the grid transparency and finite collector size on the values of thermal ion density and temperature determined by the standard RPA (retarding potential analyzer) analysis method are investigated. The current-voltage curves calculated for varying RPA parameters and a given ion mass, temperature, and density are analyzed by the standard RPA method. It is found that only small errors in temperature and density are introduced for an RPA with typical dimensions, and that even when the density error is substantial for nontypical dimensions, the temperature error remains minimum.

Troy, B. E., Jr.↗

NASA NTRS1975

Electron temperatures in the wake of an ionospheric satellite

We present measurements of electron temperature (Te) made by a retarding potential analyzer and a Langmuir probe (both flush-mounted on the spin-stabilized satellite Explorer 31) to investigate the variation of Te around the satellite. Most of the time there is a Te variation, which repeats for given ionospheric conditions. The variation is strongly controlled by the angle between the velocity vector and the probe normal, Te usually being enhanced in the near wake of the satellite. Magnetic field control of Te, if it is present, is hidden by the stronger velocity vector control. Our results indicate that the magnitude of the Te enhancement in the wake does not depend on the average ion mass (M), although the electron density depletion in the wake is strongly correlated with M.

Troy, B. E., Jr.↗

NASA NTRS1973

Equatorial airglow and the ionospheric geomagnetic anomaly.

Ogo 4 observations of the O I (6300-A) emissions have revealed a global pattern hitherto undetected from the ground-based observations. It is seen that the postsunset emission of O I (6300 A) in October 1967 is very asymmetrical with respect to the geomagnetic equator in certain longitude regions and shows poor correlation with the electron density measured simultaneously from the same spacecraft. This asymmetry is less marked in the UV airglow, O I (1356 A), which appears to vary as the square of the maximum electron density in the F region. The horizon scan data of the 6300-A airglow reveal that the latitudinal asymmetry is associated with asymmetry in the height of the O I (6300-A) emission and hence with the altitude of the F2 peak. From the correlative studies of the airglow and the ionospheric measurements the mechanisms of the UV and the 6300 A emissions are discussed in terms of the processes involving radiative and dissociative recombination. Theoretical expressions are developed which relate the airglow data to the ionospheric parameters.

Chandra, S.↗

NASA NTRS1973

The angular distribution of ion flux around an ionospheric satellite.

Ion measurements from the Explorer 31 satellite were used to determine the angular distribution of ions around the satellite. The ion distributions were compared with the electron distributions measured on the same satellite. It is shown that the electron currents (fluxes) in the wake are always larger than the ion currents for a wide domain of plasma parameters. A quantitative comparison of the ion fluxes with a neutral approximation model for the angular distribution is considered. It is found that the ion fluxes become progressively larger than the corresponding computed neutral fluxes as the angle of attack increases from 0 to 180 deg.

Samir, U.↗

NASA NTRS1973

The effect of grid transparency and finite collector size on determining ion temperature and density by the retarding potential analyzer

The analysis of ion data from retarding potential analyzers (RPA's) is generally done under the planar approximation, which assumes that the grid transparency is constant with angle of incidence and that all ions reaching the plane of the collectors are collected. These approximations are not valid for situations in which the ion thermal velocity is comparable to the vehicle velocity, causing ions to enter the RPA with high average transverse velocity. To investigate these effects, the current-voltage curves for H+ at 4000 K were calculated, taking into account the finite collector size and the variation of grid transparency with angle. These curves are then analyzed under the planar approximation. The results show that only small errors in temperature and density are introduced for an RPA with typical dimensions; and that even when the density error is substantial for non-typical dimensions, the temperature error remains minimal.

Troy, B. E., Jr.↗

NASA NTRS1972

The equatorial airglow and the ionospheric geomagnetic anomaly

OGO D observations of OI (6300A) emissions reveal a global pattern in the equatorial airglow undetected from the ground-based observations. The post sunset emission rate of OI is generally asymmetrical with respect to the geomagnetic equator and shows no apparent correlation with the ultraviolet airglow (OI 1304 and 1356A) and F region electron density measured simultaneously from the same spacecraft. Both the ultraviolet airglow and the ion density measured in the altitude region of 450 km follow similar latitudinal variations and exhibit properties of the equatorial ionospheric anomaly. The asymmetry in OI emission can be attributed to the asymmetry in the height of the F 2 maximum inferred from the height of the maximum emission. From correlative studies of the airglow and the ionospheric measurements, the mechanisms for the ultraviolet and the 6300A emission are discussed in terms of the processes involving radiative and dissociative recombinations. A relationship between molecular oxygen density and the integrated OI emission rate is derived and the feasibility of using this relationship for estimating O2 density is discussed.

Chandra, S.↗

NASA NTRS1971

Experiment S026: Ion wake measurement

Measurements of the ion-wake and electron-wake structure and other perturbations of the ambient medium produced by the Gemini spacecraft in orbit are reported. Thruster firings in the TDA-south configuration produced a decrease in the observed ion flux to the outboard ion sensor, an apparent increase in the ion flux to the inboard ion sensor, and an enhanced electron concentration to the outboard electron sensor. Visual inspection of strip-chart data was indicative that definitive wake-cone angles could be determined. It also was apparent for many cases that the electron distribution followed the ion depletion effects; this was indicative that the wake was a plasma, not an ion wake. Analysis of the data from the GATV orbits was indicative that electron and ion temperatures were higher than was estimated. The high electron temperature accounted for the sensor saturation observed during the mission. This temperature measurement was 0.3 electron volt at a 200-n. mi. altitude during daytime conditions. Spacecraft wake structure has been observed as far as 100 feet from the vehicle.

Medved, D. B.↗

NASA NTRS1971