Two areas of interest are elaborated: Saturn mission design history, and Saturn's place in NASA's program plans. The first area provides a view of how changing concepts and techniques can affect mission design and science return. The second puts Saturn in perspective with regard to its role in NASA's overall planetary program

Wallace, R. A.

English

NASA Technical Reports Server

BACKGROUND OF THE S W *  
MISSION 
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SATURN MISSION DESIGN HISTORY 
Sab~rn mission design can be broken into two pieces. The first piece relates to 
how you reach Saturn from Earth, the second with what you do when you arrive there. 
The first Table shows a development history for Saturn missions covering the period 
from 1964 to the present. Throughout this time period, technology and the timely dwel- 
opment of interplanetary trajectory techniques have made missions to Saturn more science 
effective by allowing delivery of larger and larger payloads. The first  item in Table 1 
shows the requirements of sending a package to Saturn if we do it the same way we did 
for the Ranger lunar, Mariner 1962 Venus, and Mariner 1964 Mars missions. These 
were first attempts to scope the outer planet exploration problem. Mission analysts 
found that direct ballistic trajectories to Saturn were very expensive, quite a bit more 
so than trajectories to Jupiter. 
*SOP is nn abbreviuion for Saturn Orbim Dud Pro- h u m  bound sprcccnft combining thm major systems: M orbiter, r 
Saturn probe, and a Titan probe. 
https://ntrs.nasa.gov/search.jsp?R=19790008588 2020-03-22T01:38:37+00:00Z
Table 1. Saturn Missions - Development History 
Study 
Specificauon of ballistic 
trajectory requirements 
Jupiter gravity-assist 
trajectory discovered 
Pioneer/lroyager mission 
designs 
Jupiter Orbiter studies 
VEGA and AVEGA techniques 
discovered 
Saturn Orbiter/Satellite Tour 
Study 
Titan mission studies 
Ion Drive techniques applied to 
Saturn mission 
Dates Conclusion 
Energy requirements very high 
Energy requirements comparable to 
Jupiter mission requirements 
Excellent reconnaissance missions to 
Jupiter and Saturn fea sible 
Jupiter Orbiter missions very 
attractive and feasible; satellite tour 
techniques defined; outer planet probes 
studied in detail 
Energy requirements reduced; flight 
times increased 
JOP techniques applied to Saturn; 
considered VEGA/AVE GA 
Titan lander/probe missions 
conceptualized; scientifically reward- 
ing missions described 
Energy requirements and flight times 
reduced 
2 SOP mission feasible in variety of 
ways; science priorities required for 
further mission design 
In 1966 Gary Flandro discovered a family of Jupiter gravity-assist trajectories 
which now brought Saturn into the same hunch vehicle range a s  Jupiter missions. The 
Pioneer and Voyager missions were designed on the basis of thest. earlier trajectory 
analyses, and our first outer planet reconnaissance missions were born. The Voyager 
mission design aided the solution to the problem of satellite encounter design, develop- 
ing techniques in timing the launch and providing maneuvers which would maximize 
satellite science return consistent with planetary science desires. 
With the Pioneer and Voyager mission designs underway, interest developed in 
an exploratory mission to Jupiter which would allow longer times to investigate the 
extensive Jupiter system. The Jupiter Orbiter Probe (now Galileo) mission design 
developed satellite gravity-assist techniques which allowed satellite tours while in orbit 
around the parent body. 
While the Jupiter orbiter design was being developed, a new interplanetary 
trajectory technique was found which allowed delivery of greater payloads to the outer 
planets. The technique calls for  a trajectory which i s  first directed in towards the Sun 
odth a pobsible Venus close flyby and/or deep space propulsion manuever, and then 
return to Earth for an Earth gravity-assist a s  the trajectory carr ies  the spacecraft out 
to the outer planets (VEGA and A VEGA trajectories). Not only a r e  the payloads larger, 
but the opportunities for such missions a r e  available over a greater period of years 
than the direct Jupiter gravity-assist missions t~ Saturn. The drawback, and it is a 
major one, is that la- to arrival times a r e  increased over the already long flight times 
required by the previortsly defined techniques. 
In i975, with interest increasing in the Jupiter orbiter mission, analysis of a 
Saturn orbiter applied the techniques of the Jupiter orbiter mission a s  well a s  the new 
VEGA and AVEGA techniques, and found such a mission concept to be feasible enough 
to warrant further study. 
In the last few years technology has been advancing to the point where a new low 
thrust propulsive technique will be available to NASA which will allow realization of 
difficult, but scientifically exciting missions. The major problem with Saturn mission 
designs up through the 1970's was the restriction to relatively low payloads associated 
with long flight times. Ion drive techniques use a low thrust, continltously operating 
device acting over a period of years. Combining the ion drive techniques with the Earth 
gravity-assist techniques discovered earlier provides the possibility of delivering a 
highly interesting science package to the Saturn system. 
Studies conducted last year at JPL and scheduled studies this year a r e  focused 
on a Saturn Orbiter Dual Probe (SOP') mission design. One of the major reasons for 
holding the Saturn Workshop is to provide science reconimendations for an intelligent 
design of such a mission. What kind of science retura should the mission designers 
focus their study on? 
S G P ~  AND NASA's PLANETARY PROGRAM 
The timing for this workshop is appropriate. The Pioneer and Voyager 
missions will be returning important data between 1979 and 1981, in time to focus the 
 SO^ design for a launch after 1985. Ion drive and trajectory software development 
will be available for launches i n  the mid-1980's and beyond. Mission concept and 
feasibility design is now required so that later systems definition and design can take 
place and dovetail with the technology development and science base. Science recom- 
mendations a r e  key to this continuing design process. 
Table 2 shows the current 1979-83 planetary exploration five-year plan. TNs 
plan is the end result of consultations with the scientific community, mission planners 
in NASA, Congress, aad the Office of Management and Budget. 
2 Several plans were considered. It should be noted that SOP was part of all  of 
2 them. The SOP mission is considered a high priority mission by NASA. 
Table 2. Planetary New Starts - FY 1979- 53 
hIission New Start/'Launch A1 ission Type 
Venus Orbital laaging Radar (VOIR) 1980/1984 Exploratory 
~alley/Tempel-2 Rendezvous 1981/1985 Reconnaissance 
Saturn Orbiter Dual Probe (Sop2) 1983/1987 Exploratory 
Mars Program Technology Development 1982!- Intensive Science 
- 
DISCUSSION 
D. HERMAN: Let me comment on the degree of commitment by NASA to an 
2 SOP ;\Iission. F i r s t  of all, in the Fiscal 1979 Budget, recently submitted to the 
Congress, there is a separate five millicn dollar line item f o ~  the development of ion 
drive. The first  intended use of that sjestem i s  to effect a comet rendezvous, probably 
with comet Tempe1 2. The second intended use of that system would be for  SO^. 
At the FY 1979 Budget P r e s s  Conference, Dr. Frosch stated that i t 's  time to 
take ion drive out of b a n g  a laboratory curiosity and to develop i t  towards a flight 
propulsion syste,n; that's SXSA's intent. 
With respect to the five-gear plan, we were given budget guidelines by the 
Office of Slanagement and Budget to plan the missions that we want to  do in the next 
five years.  We a r e  ~ b l i g e d  every fiscal year  to submit a revised five-year plan that i s  
consistent with the budget. Our own input to ;hat five-year plan was to show the SOP 2 
mission a s  a Fiscal  1982 new s ta r t  with a 1986 launch. The Administrator, in review- 
ing the five-year plan, adjusted the timetable to shift the sop2 new s ta r t  to FY 1983, 
ar~d that is where i t  now stands. But we must s t i l l  plan a s  if  the SO$ Mission could 
indeed be a Fiscal 1982 New Start and a 1936 launch because something could happen 
to the Mars program to cause us  to rever t  to the original timetable. Our assessment 
is that the  SOP^ :vlisaion will go either a s  Fiscal 1982 o r  a Fiscal 1983 New Start with 
a launch either in 1986 o r  1987. 


Background of the SOP sup 2

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