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Pernicka, Henry J.

Publications and source records attributed to Pernicka, Henry J..

5 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS2007

Low-Thrust Control of a Lunar Mapping Orbit

A method is presented for generating and maintaining a lunar mapping orbit using continuous low-thrust hardware. Optimal control theory is used to maintain a lunar orbit that is low-altitude, near-polar, and Sun-synchronous; three typical requirements for a successful lunar mapping mission. The analysis of the optimal control problem leads to the commonly seen two-point boundary value problem, which is solved using a simple indirect shooting algorithm. Simulations are presented for a 50-day mapping duration, in which it is shown that a very tight control is achieved with thrust levels below 1 N for a 1000 kg spacecraft. A straightforward approach for using the method presented to compute missions of any duration is also discussed.

Harl, Nathan↗
NASA NTRS2003

Design and Test of a Tethered Pair of Satellites: Equipment Requirements

A recent development in spacecraft mission design involves the increasing use of Distributed Spacecraft Systems (DSS). Several key technologies must mature sufficiently to facilitate these missions, including the use of spacecraft flying in tightly controlled formations. Such formations may be controlled using "free flying" navigation schemes, or alternatively may use tethers to constrain the formation geometry. An investigation has been initiated here to further develop this technology using two small spacecraft connected by a short tether. After insertion into orbit, the tether will be extended and various data collected on the performance of the dual-spacecraft "formation." At some later time, the tether will be cut, and the spacecraft pair will be navigated in a manner to maintain a geometry as closely as possible to that of the tethered configuration. Comparisons and evaluations of the two modes of operation can then be made so that the merits of both approaches are available to mission designers.

Pernicka, Henry J.↗
NASA NTRS1993

A strategy to rotate the Mars Observer orbit node line to advance the mapping schedule

The Mars Observer (MO) spacecraft was successfully launched on September 25, 1992 and will arrive at Mars on August 24, 1993. At Mars, the spacecraft will study the planet's surface, atmosphere, and gravitational and magnetic fields. In order to achieve these scientific objectives, MO will be placed in a 2 PM (descending node) sun-synchronous orbit. Upon arrival at Mars, however, the longitude of the descending node will be approximately 15 deg greater than the desired value. The baseline plan requires a 59 day `waiting' period for the correct solar orientation to occur. During this period, 28 days are required for scientific experimentation but the remaining 30.6 days potentially could be eliminated. The strategy developed in this study examined the possibility of using any `excess' Delta-V available at Mars arrival to rotate the node line to the desired value and thus allow mapping to begin earlier. A preliminary analysis completed prior to launch is described that examined the entire launch period including the required Delta-V to perform the needed nodal rotation. A more detailed study performed after launch is also summarized.

Pernicka, Henry J.↗