Engineering topics

Sackett, L. L.

Publications and source records attributed to Sackett, L. L..

13 records

NASA NTRS1983

Stability of the Shuttle on-orbit flight control system for a class of flexible payloads

The stability of the Space Shuttle on-orbit flight control system is determined for a class of payloads for which the payload is tilted out of the orbiter bay and the bending can be modeled as localized at a pivot. Examples are the Inertial Upper Stage or the Centaur with attached spacecraft during deployment. The many inertial, geometric, and jet option parameters are reduced to a smaller set which allows the determination of stability or instability as a function of bending frequency and the other elements of the set. The resulting stability charts, which are presented, can be used by payload designers and misssion planners to predict possible instability without elaborate analysis or simulation.

Kirchwey, C. B.↗

NASA NTRS1979

Comet rendezvous mission design using Solar Electric Propulsion

A dual comet (Halley Flyby/Tempel 2 Rendezvous) mission, which is planned to be the first to use the Solar Electric Propulsion System (SEPS), is to be launched in 1985. The purpose of this paper is to describe how the mission design attempts to maximize science return while working within spacecraft and other constraints. Science requirements and desires are outlined and specific instruments are considered. Emphasis is on the strategy for operations in the vicinity of Tempel 2, for which a representative profile is described. The mission is planned to extend about one year past initial rendezvous. Because of the large uncertainty in the comet environment the Tempel 2 operations strategy must be highly adaptive.

Sackett, L. L.↗

NASA NTRS1979

Optimization of multiple flyby trajectories

A procedure has been developed which minimizes total delta-V (instantaneous velocity change) for a multiple flyby trajectory with constraints on flyby altitude and orientation. The solution is found by varying the locations of maneuver points between each flyby to minimize the delta-Vs at the maneuver points. Each trajectory segment connecting consecutive maneuver points is found by solving an N-body analog to Lambert's problem. Multiconic techniques are used for trajectory propagation and for computation of the state transition matrix. The constrained parameter optimization problem is converted to an unconstrained problem by means of penalty functions and then solved with a quasi-Newton algorithm utilizing analytic first derivatives. This procedure has been successfully applied to Galileo satellite tour trajectories.

Damario, L. A.↗

NASA NTRS1979

Solar-electric geocentric transfer

Time-optimal or nearly-time-optimal trajectory computer program developed for solar-electric geocentric transfer considers yaw motion only, yaw and roll only, and unconstrained motion configurations.

Malchow, H. L.↗

NASA NTRS1977

SUNSPOT: A computer program for producing optimal solar sail planetocentric trajectories

The input, output and subroutines, including listings, for the SUNSPOT code are described. SUNSPOT can calculate time optimal planetocentric trajectories including orbit-to-orbit transfer and orbit to a subescape point. Trajectories about the the four inner planets can be calculated, and shadowing, oblateness, and solar motion may be included. A penalty function may be included to prevent trajectories which intersect the planet's surface.

Sackett, L. L.↗

NASA NTRS1977

Optimal solar sail planetocentric trajectories

The analysis of solar sail planetocentric optimal trajectory problem is described. A computer program was produced to calculate optimal trajectories for a limited performance analysis. A square sail model is included and some consideration is given to a heliogyro sail model. Orbit to a subescape point and orbit to orbit transfer are considered. Trajectories about the four inner planets can be calculated and shadowing, oblateness, and solar motion may be included. Equinoctial orbital elements are used to avoid the classical singularities, and the method of averaging is applied to increase computational speed. Solution of the two-point boundary value problem which arises from the application of optimization theory is accomplished with a Newton procedure. Time optimal trajectories are emphasized, but a penalty function has been considered to prevent trajectories which intersect a planet's surface.

Sackett, L. L.↗

NASA NTRS1977

Optimal solar sail spiral to escape

A solar sail is being considered for various solar system missions, such as a comet rendezvous and a planetary sample return. Such missions might include a planetocentric escape or capture trajectory segment. This paper considers a method for calculating time optimal planetocentric solar sail spiral trajectories to near escape and orbit to orbit transfers. A number of examples illustrate trajectories generated with a computer program, SUNSPOT, based on this analysis.

Sackett, L. L.↗

NASA NTRS1975

Solar electric geocentric transfer with attitude constraints: Analysis

A time optimal or nearly time optimal trajectory program was developed for solar electric geocentric transfer with or without attitude constraints and with an optional initial high thrust stage. The method of averaging reduces computation time. A nonsingular set of orbital elements is used. The constraints, which are those of one of the SERT-C designs, introduce complexities into the analysis and the solution yields possible discontinuous changes in thrust direction. The power degradation due to VanAllen radiation is modeled analytically. A wide range of solar cell characteristics is assumed. Effects such as oblateness and shadowing are included. The analysis and the results of many example runs are included.

Sackett, L. L.↗

NASA NTRS1975

Effect of attitude constraints on solar-electric geocentric transfers

The present work assesses the increase in flight time and fuel consumption due to introducing attitude constraints on both the thrust vector and the plane of the solar cell arrays on geocentrically orbiting spacecraft. A modified version of the SECKSPOT computer program calculates nearly time-optimal trajectories for the constrained case of zero pitch and roll. Unconstrained cases are generated with the SECKSPOT code. It is concluded that with a pitch constraint but without a roll constraint, power would not be a function of thrust direction, and so the time-optimal thruster direction would be along the projection of the primer vector in the plane normal to the radius vector. The roll constraint would cause power to become a function of thrust angle and sun angle. For certain sun angles the locus of the ratio of power to maximum power is concave and thus there may be jumps in the control angle. Comparisons are made for a SERT-C type mission between constrained and unconstrained cases in an inverse square gravity field.

Sackett, L. L.↗

NASA NTRS1974

Optimal high- and low-thrust geocentric transfer

A computer code which rapidly calculates time optimal combined high- and low-thrust transfers between two geocentric orbits in the presence of a strong gravitational field has been developed as a mission analysis tool. The low-thrust portion of the transfer can be between any two arbitrary ellipses. There is an option for including the effect of two initial high-thrust impulses which would raise the spacecraft from a low, initially circular orbit to the initial orbit for the low-thrust portion of the transfer. In addition, the effect of a single final impulse after the low-thrust portion of the transfer may be included. The total Delta V for the initial two impulses must be specified as well as the Delta V for the final impulse. Either solar electric or nuclear electric propulsion can be assumed for the low-thrust phase of the transfer.

Sackett, L. L.↗

NASA NTRS1974

A users manual for a computer program which calculates time optical geocentric transfers using solar or nuclear electric and high thrust propulsion

This manual is a guide for using a computer program which calculates time optimal trajectories for high-and low-thrust geocentric transfers. Either SEP or NEP may be assumed and a one or two impulse, fixed total delta V, initial high thrust phase may be included. Also a single impulse of specified delta V may be included after the low thrust state. The low thrust phase utilizes equinoctial orbital elements to avoid the classical singularities and Kryloff-Boguliuboff averaging to help insure more rapid computation time. The program is written in FORTRAN 4 in double precision for use on an IBM 360 computer. The manual includes a description of the problem treated, input/output information, examples of runs, and source code listings.

Sackett, L. L.↗

NASA NTRS1973

Optimal low thrust geocentric transfer

A computer code which will rapidly calculate time-optimal low thrust transfers is being developed as a mission analysis tool. The final program will apply to NEP or SEP missions and will include a variety of environmental effects. The current program assumes constant acceleration. The oblateness effect and shadowing may be included. Detailed state and costate equations are given for the thrust effect, oblateness effect, and shadowing. A simple but adequate model yields analytical formulas for power degradation due to the Van Allen radiation belts for SEP missions. The program avoids the classical singularities by the use of equinoctial orbital elements. Kryloff-Bogoliuboff averaging is used to facilitate rapid calculation. Results for selected cases using the current program are given.

Edelbaum, T. N.↗

NASA NTRS1972

Comparison of two sensors for outer planet mission onboard navigation.

Onboard instruments have been shown to be an effective aid to navigation on missions to the outer planets. The relationship of two possible candidate navigation instruments, an image tube (television) and a scanning photometer, with other systems such as data processing and attitude control is discussed. Certain key problem areas relating to the design of each sensor are considered, and the scientific uses of each sensor are examined. The navigational efficacy of both instruments is illustrated by some selected results from a navigation and guidance simulation of outer planet missions. It is concluded that both devices are viable alternatives for onboard outer planet navigation.

Malchow, H. L.↗