Engineering topics

Johnson, T. S.

Publications and source records attributed to Johnson, T. S..

17 records

NASA NTRS1989

Performance and modeling of the GSFC pointing acquisition and tracking system for laser communications

In this paper the NASA Goddard Space Flight Center (GSFC) laser communication pointing, acquisition, and tracking laboratory demonstration program is discussed. This program entails the construction of a flexible brass-board simulation tool, and a supporting computer simulation effort. The result of this program will be a viable test bed to support the design and specification of space-based laser communication terminals and, additionally, to address critical performance issues such as tracking robustness in the presence of background (e.g., stellar or earth) noise and/or internally generated thermal noise.

Fox, N. D.↗

NASA NTRS1982

Studies of atmospheric refraction effects on laser data

The refraction effect from three perspectives was considered. An analysis of the axioms on which the accepted correction algorithms were based was the first priority. The integrity of the meteorological measurements on which the correction model is based was also considered and a large quantity of laser observations was processed in an effort to detect any serious anomalies in them. The effect of refraction errors on geodetic parameters estimated from laser data using the most recent analysis procedures was the focus of the third element of study. The results concentrate on refraction errors which were found to be critical in the eventual use of the data for measurements of crustal dynamics.

Dunn, P. J.↗

NASA NTRS1977

NASA Goddard Space Flight Center

The contribution of the Goddard Space Flight Center to the National Geodetic Satellite Program is reported. All of the major types of tracking systems, including those employing optical, electronic, range-and-range-rate, and laser technologies, which were developed and operated by Goddard, are described. The MINITRACK data were used to derive geodetic results. The methods used for the analysis of these data are presented.

Berbert, J. H.↗

NASA NTRS1975

Satellite laser ranging work at the Goddard Space Flight Center

Laser ranging systems, their range and accuracy capabilities, and planned improvements for future systems are discussed, the systems include one fixed and two mobile lasers ranging systems. They have demonstrated better than 10 cm accuracy both on a carefully surveyed ground range and in regular satellite ranging operations. They are capable of ranging to all currently launched retroreflector equipped satellites with the exception of Timation III. A third mobile system is discussed which will be accurate to better than 5 cm and will be capable of ranging to distant satellites such as Timation III and LAGEOS.

Mcgunigal, T. E.↗

NASA NTRS1975

Satellite laser ranging work at the Goddard Space Flight Center

The pulsed-laser satellite ranging systems presently being operated by the Goddard Space Flight Center are described along with their range and accuracy capabilities. The major subsystems are outlined, operation of the fixed system and the two mobile systems is discussed, and the performance of all three systems is evaluated. It is noted that these systems have an accuracy of better than 10 cm on a carefully surveyed range as well as in regular satellite ranging operations and are capable of ranging to all currently launched retroreflector-equipped satellites with the exception of Timation III. Future improvements discussed include a third mobile system which will be able to range distant satellites, such as Timation III, with an accuracy of better than 5 cm and the use of a frequency-doubled Nd:YAG laser in place of the ruby lasers now being employed.

Mcgunigal, T. E.↗

NASA NTRS1975

Satellite laser ranging work at the Goddard Space Flight Center

The paper describes the satellite laser ranging system at the Goddard Space Flight Center, its range and accuracy capabilities, and planned improvements for future systems. Major subsystems are described, including the laser, optical/mechanical, receiver, computer/software, timing, and laser data preprocessing subsystems. Operational considerations are examined, with attention given the mobile station layout, manpower requirements, and transportability. System performance is considered, with emphasis on system accuracy (calibration, stability, clock synchronization, atmospheric propagation correction) and range capability.

Mcgunigal, T. E.↗

NASA NTRS1974

Progress in laser ranging to satellites - Achievements and plans

Theoretical and mathematical considerations involved in the design of retroreflectors for the GEOS-C and Timation III laser ranging satellites are described, laser ranging systems used by the Goddard Space Flight Center are reviewed, and planned systems changes are outlined. Equations are derived for the design of a cube corner array on a gravity gradient stabilized satellite in a circular orbit, and the required cube corner for GEOS-C is computed. Use of fixed threshold triggers and electronic and analytic pulse height compensation in present laser ranging systems is discussed. Proposed changes are outlined, including the incorporation of split gate triggers and trackers into the ranging systems and the use of analog and digital centroid measurement techniques. A theoretical consideration of the effects of velocity aberration on the reflected light beam is appended.

Plotkin, H. H.↗

NASA NTRS1972

Polar motion from laser tracking of artificial satellites.

Measurements of the range to the Beacon Explorer C spacecraft from a single laser tracking system at Goddard Space Flight Center have been used to determine the change in latitude of the station arising from polar motion. A precision of 0.03 arc second was obtained for the latitude during a 5-month period in 1970.

Smith, D. E.↗

NASA NTRS1972

Polar motion from laser tracking of artificial satellites

Laser ranges to the Beacon Explorer C spacecraft from a single Goddard Space Flight Center tracking system were used to determine the change in latitude of the station arising from polar motion. A precision of 0.03 arcsecs rms was obtained for the latitude during a five-month period in 1970.

Smith, D. E.↗

NASA NTRS1972

Improved laser ranging accuracy through dynamic threshold compensation

During a polar motion experiment (in which two laser ranging systems on a north-south line simultaneously tracked a satellite to determine motion of the pole), techniques for improving both the range noise and range bias were demonstrated. The corrections to the measured ranges (based on received signal levels relative to a fixed correction that would have been applied if pulse height information was not available) are given. It was shown that even existing long pulse systems (20 to 40 nsec duration) can be improved to the 20 to 30 cm level of precision without major or expensive changes to the system.

Johnson, T. S.↗

NASA NTRS1971