Computer program incorporates new isolation procedure to determine interplanetary trajectories which utilize a maximum of three flybys. Program also computes singe planet flybys and direct transfer trajectories. The three principle systems employed in MIST-1 use as their fundamental plane the mean plane of the earth's orbit around the sun

Davis, D. A.

Roberts, G. R.

English

NASA Technical Reports Server

December 1970	 Brief 70-10603 
NASA TECH BRIEF 
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, 
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nology Utilization Division, NASA, Code UT, Washington, D.C. 20546. 
Multibody Interplanetary Swingby Trajectories( MIST-I) 
The problem: 
To provide a computer operated procedure for 
determining interplanetary trajectories which use 
the gravitational perturbation of an intermediate 
planet to shape the trajectory. 
The solution: 
MIST-1 is designed to allow a mission analyst to 
investigate the advantages and disadvantages associ-
ated with two mission types and to determine the char-
acteristics of multiplanet swingbys. 
. How it's done: 
When a vehicle approaches a planet on a free fall 
trajectory, the gravitational influence of that body 
can radically alter the vehicle's trajectory about the 
sun. Advantage may be taken of this perturbation to 
plac the probe on a trajectory which will intercept 
another planet. Some planetary configurations when 
allied with certain trajectories will even yield multi-
planet flybys. The new isolation procedure incorpor-
ated in this program will rapidly determine those 
trajectories which utilize a maximum of three flybys. 
The program will also compute single planet flybys 
and direct transfer trajectories. 
Most isolation techniques proceed sequentially 
along the trajectory path; i.e., a trajectory is run from 
planet A to planet B. With that portion of the total 
trajectory fixed, an attempt is made to find a tra-
jectory which will link planet B to planet C and allow 
a zero V linkage with the A to B leg. This is very 
time consuming and also leads to variable total trip 
time. The procedure described in this program is very 
rapid since it requires a minimum of trial trajectories 
to be generated and also allows the total trip time to 
be input as a fixed quantity. 
The three principle systems employed in MIST-1 
use as their fundamental plane the mean ecliptic, the
mean plane of the earth's orbit around the sun. Their 
principle axis is established by the ascending node of 
the mean ecliptic on the mean celestial equator, a 
plane coplanar with the earth's mean equator. This 
ascending node is usually referred to as the vernal 
equinox for it marks the point at which the mean sun 
appears to cross the mean equator from south to 
north. 
In all modes of operation, the program first deter-
mines the heliocentric conic which connects the centers 
of two planets and which requires a given trip time. 
With a known planetary ephemerides, this calcu-
lation is completely equivalent to the classical orbit 
determination problem in which a time and two posi-
tion vectors are given. From the several techniques 
available, an extension of Lambert's theorem was 
chosen for use in MIST-I. The theorem expresses the 
trip time as a function of the magnitudes of the posi-
tion vectors, the magnitude of the chord separating 
the end points of those vectors, and the semimajor 
axis of the transfer conic. 
Notes: 
1. This program is written in FORTRAN H for use 
on the IBM 360 computer. 
2. Inquiries should be made to: 
COSMIC 
Barrow Hall 
University of Georgia 
Athens, Georgia 30601 
Reference: B70-10603 
Source: D. A. Davis and G. R. Roberts of

The Boeing Company

under contract to

Marshall Space Flight Center

(MFS-15081)
Category 09 
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Multibody Interplanetary Swingby Trajectories /MIST-1/

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