Computer program has been designed to handle computations for low thrust missions rapidly and with acceptable accuracy. Program defines performance and system requirements of electrically-propelled unmanned planet-orbiter and flyby missions. The program is written in FORTRAN 4 for use on an IBM 360 or CDC 6600 computer

Mascy, A. C.

English

NASA Technical Reports Server

September 1972	 B72-10299 
NASA TECH BRIEF 
Ames Research Center 
NASA Tech Briefs announce new technology derived from the U.S. space program. They are issued to encourage 
commercial application. Tech Briefs are available on a subscription basis from the National Technical Information 
Service, Springfield, Virginia 22151. Requests for individual copies or questions relating to the Tech Brief program may 
be directed to the Technology Utilization Office, NASA, Code KT, Washington, D.C. 20546. 
Rapid Analysis of Electric Propulsion Missions 
Analysis of rocket-engine performance for advanced 
propulsion systems usually involves detailed studies 
of trajectories. For missions with electric propulsion 
devices which provide low thrusts, computations of 
optimized trajectories are complex because they in-
volve integration of the equations of motion and solu-
tion of the many boundary-value problems needed to 
optimize system parameters. Existing computer pro-
grams are quite inflexible and do not allow study of 
various options; moreover, the slow execution speeds 
of most programs have excluded their use in investi- 
gating the wide range of variables necessary to identi-
fy commonality in mission and system characteristics. 
A computer program has been specially designed 
to handle computations for low-thrust missions ra-
pidly and with acceptable accuracy. The program 
defines the performance and system requirements of 
electrically-propelled unmanned planet-orbiter and 
flyby missions; it is based on the use of existing launch 
vehicles for the earth launch-phase and the use of 
high-thrust upper stages (or low-thrust spiral maneu-
vers) for earth departure- and planet arrival-phases. 
The characteristics of the launch vehicles and high-
thrust stages may be specified in lieu of built-in 
programmed values. The electric propulsion system 
may be completely optimized, or may be constrained 
in power level, thrusting time, propulsion system spe-
cific mass, or departure and arrival velocities. Rather 
than integrate the low-thrust trajectory, functional 
relationships for the energy requirements of precom-
puted optimum trajectories (obtained from accurate 
computer programs) are stored within the code. 
Curve-fitting procedures are used in defining the
energy parameters as a function of time and hyper-
bolic excess velocity at earth departure and planet 
arrival. A method of system optimization based on 
the near invariance of certain parameters with system 
variables was found to be quite accurate. Low-thrust 
and high-thrust planetocentric operations are ex-
pressed analytically, and their velocity is matched 
with the heliocentric phase. Correlation with exact 
trajectory data is excellent, and the compute times 
are less than a second per fully optimized case. 
Most important are the fail-safe and user-conveni-
ence features of the code. Convergence is assured for 
any case which has a solution. In all other instances, 
the code repairs any damage to its logic and proceeds 
to the next input case. This facilitates the running of 
numerous cases with large ranges in parameters. The 
input has been simplified through the use of collo-
quial variables such as the proper names of launch 
vehicles and planets, and the straightforward spell-
ing of parameters to indicate their functions. The 
coding has been kept relatively simple so that the 
logic flow may be followed easily and changed to suit 
particular needs. 
Notes: 
1. This program is written in FORTRAN IV for use 
on an IBM-360 or CDC 6600 computer. 
2. Inquiries concerning this program should be ad-
dressed to: 
COSMIC 
Barrow Hall 
University of Georgia 
Athens, Georgia 30601 
Reference: B7240299
(continued overleaf) 
This document was prepared under the sponsorship of the National
	 Government assumes any liability resulting from the use of the 
Aeronautics and Space Administration. Neither the United States
	 information contained in this document, or warrants that such use 
Government nor any person acting on behalf of the United States
	 will be free from privately owned rights.
https://ntrs.nasa.gov/search.jsp?R=19720000298 2020-03-17T03:28:21+00:00Z
Patent status: 
No patent action is contemplated by NASA. 
Source: Alfred C. Mascy
Ames Research Center
(ARC-10430) 
B72-10299	 Category 09


Rapid analysis of electric propulsion missions

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