The interplanetary trajectory characteristics for missions to Uranus, which employ an intermediate swingby of Saturn to reduce the total trip time are summarized. Opportunities for such swingby missions will occur from 1979 through 1987 and not again until 2025. The general trajectory characteristics (C sub 3; departure, swingby, and arrival dates; swingby radius; and arrival speed) are evaluated, and payload and launch window information for a Titan 3E/Centaur/TE-364-4 class launch vehicle is provided

Manning, L. A.

English

NASA Technical Reports Server

N A S A TECHNICAL
M E M O R A N D U M
ON
CNIi
X
m NASA TM X-2914
IS*
F I L
" • ••"
SUMMARY OF SATURN SWINGBY
MISSIONS TO URANUS
by Larry A. Manning
Ames Research Center
Moffett Field, Calif. 94035
NATIONAL AERONAUTICS AND SPACE ADMINISTRATION • WASHINGTON, D. C. • SEPTEMBER 1973
https://ntrs.nasa.gov/search.jsp?R=19730022995 2020-03-23T01:48:11+00:00Z
1. Report No.
KASA TM
2. Government Accession No. 3. Recipient's Catalog No.
4. Title and Subtitle
SUMMARY OF SATURN SWINGBY MISSIONS TO URANUS
5. Report Date
September 1973
6. Performing Organization Code
7. Author(s)
Larry A. Manning
8. Performing Organization Report No.
"A-5001
9. Performing Organization Name and Address
NASA Ames Research Center
Moffett Field, Calif. 94035
10. Work Unit No.
790-91-41-02-15
11. Contract or Grant No.
12. Sponsoring Agency Name and Address
National Aeronautics and Space Administration
Washington, D. C., 20546
13. Type of Report and Period Covered
Technical Memorandum
14. Sponsoring Agency Code
15. Supplementary Notes
16. Abstract
The report summarizes the interplanetary trajectory characteristics for missions to Uranus, which employ an inter-
mediate swingby of Saturn to reduce the total trip time. Opportunities for such swingby missions will occur from 1979
through 1987 and not again until 2025. The general trajectory characteristics (C3 ; departure, swingby, and arrival dates;
swingby radius; and arrival speed) are evaluated, and payload and launch window information for a Titan IIIE/Centaur/
TE-364-4 class launch vehicle is provided.
17. Key Words (Suggested by Author(s))
Trajectories
Saturn swingby
Uranus missions
Payload size
18. Distribution Statement
Unclassified - Unlimited
19. Security Qassif. (of this report)
Unclassified
20. Security Classif. (of this page)
Unclassified
21. No. of Pages
22
22. Price*
Domestic, $2.75
Foreign, $5.25
' For sale by the National Technical Information Service, Springfield, Virginia 22151
page
SUMMARY OF SATURN SWINGBY MISSIONS TO URANUS
Larry A. Manning
Ames Research Center
SUMMARY
The report summarizes the interplanetary trajectory characteristics for missions to Uranus,
which employ an intermediate swingby of Saturn to reduce the total trip time. Opportunities for
such swingby missions will occur from 1979 through 1987 and not again until about 2025. The
general trajectory characteristics (C3; departure, swingby, and arrival dates; swingby radius; and
arrival speed) are evaluated, and payload and launch window information for a Titan IIIE/Centaur/
TE-364-4 class launch vehicle is provided.
INTRODUCTION
The trip time for missions to the outer planets increases with the radius of the planetary orbit.
Beyond Saturn, calculated trip times exceed the capabilities of currently available launch vehicles
and spacecraft, for which 5 to 7 years' reliable performance is considered maximum. Swingbys of
Jupiter or Saturn provide one means of achieving a reduction in trip time. Launch opportunities
for such missions to Uranus with Jupiter swingbys occur from 1978 to 1983, with trip times in the
later years of that period approaching those of direct trips due to the distant (120-200 rj) passages
at Jupiter (ref. 1); swingbys of Saturn to Uranus are possible between 1979 and 1987, with the early
opportunities in that period constrained by the requirement to clear Saturn's rings.
In effect a handbook of Saturn swingbys to Uranus, this report provides the data necessary to
select launch opportunities of interest for a particular mission and to determine the principal mis-
sion constraints. The data also are interpreted in terms of present launch vehicle payload capability
in the last two sections.
GENERAL TRAJECTORY CONTOURS
Heliocentric trajectories between Earth and Saturn and subsequent trajectories between Saturn
and Uranus were calculated by a patched conic digital computer program similar to the program
described in reference 1. Ephemeris data for Earth, Saturn, and Uranus were also taken from that
report.
Trajectory data are shown in contour diagrams of Uranus arrival date vs. Earth departure date for
each of the eight launch opportunities from 1979 through 1987 (figs. 1-8). All dates are measured in
the Julian calendar. The data consist of the following contours: (1) the Earth departure hyperbolic
excess speed V^, in emos; (2) the Saturn swingby date, SD; (3) the Saturn swingby radius rp, in
Saturn radii; and (4) the Uranus arrival hyperbolic excess speed, Va, in emos. The entire region is not
available for use, however, because of the rings of Saturn, which extend in the equatorial plane
2.26 /"£; and perhaps even further (* 5 r$) if some recent observations are verified (ref. 2).
The launch energy C3 is computed by multiplying V^ by the Earth's mean orbital speed
(29.8 km/sec) and squaring the result. One parameter of concern, but not shown, is the Earth
departure declination, which determines the launch vehicle azimuth and departure plane change
penalties. Values between ±28.5° incur no penalty. Declinations greater than this occur for combina-
tions of early launch date and long trip times during the 1979 and 1980 launch opportunities. The
effect of this parameter is further discussed in the payload analysis section.
The use of swingby radius of greater than 2.26 r§ reveals some interesting features of the
early opportunities. Figures 1 and 2 indicate that for V^ = 0.4 emos, the arrival date at Uranus is
about the same for launches in both 1979 and 1980. In addition, launch windows of about 16
days are the maximum that can be achieved. Launch windows maximize in 1982-1989 and then
reduce again for trip times of less than those for direct Uranus missions (i.e., about 3000 days).
Swingby parameters at Saturn are seen to be effectively constant for a fixed arrival date at Uranus.
LAUNCH VEHICLE PAYLOAD
The utility of the preceding results in mission planning was enhanced through their application
to the payload capability of the Titan IIIE/Centaur/TE-364-4 launch vehicle as shown in figure 9.
A spinning class of interplanetary spacecraft (e.g., Pioneer 10 and 11) with a Viking type shroud
was assumed. The TE-364-4 is spun up prior to ignition; therefore, a spin table is required on top
of the Centaur stage. Spacecraft heavier than 545 kg (1200 Ib) require additional interstage structure,
and curve therefore is not continuous for larger payloads. Figure 9 also shows the relationship
between V^ and C3 for the payload range of interest.
PAYLOAD CONTOURS
Data from the preceding sections were combined to obtain the launch capability and windows
for the Titan IIIE/Centaur/TE-364-4 vehicle (figs. 10 through 17). A payload range of 420 to 500
kg was selected as representative of a variety of outer planet missions (e.g., flyby or probe), and trip
times were constrained to be less than those for direct Uranus missions of similar payload (3000
days).
Each figure has two parts, designated (a) launch window, and (b) passage conditions. Contours
of Uranus arrival date are shown in part (a) as a function of Earth departure date for constant pay-
load with lines of constant trip times superimposed. The curves in part (b) indicate the variations in
Saturn swingby date and the associated swingby radii. The swingby date and radius are shown for
roughly the middle of the launch window. Small variations exist across the window so that the lines
shown are actually narrow bands; additional data for the appropriate opportunity are provided in
the opening section.
The curves of figures 10 through 17 are used as follows. Starting with a given payload require-
ment and a desired launch window length, part (a) provides the departure date range and the Uranus
arrival date. The possibility of conjunction at either Uranus or Saturn can be checked, as well as the
departure declination and its implications for launch. From the selected Uranus arrival date part (b)
can be entered and the Saturn swingby date determined from the abscissa. The Saturn swingby
radius for each swingby date is given on the scale to the right.
Figures 10 through 17 indicate several constraints. A swingby radius constraint of 2.26 rg is
imposed to avoid the outer limit of the ring system. Any resulting limit on the available Uranus
arrival date region is shown on the swingby date line. The possibility of passage through gaps in the
ring or inside the inner edge of the accepted ring system was not considered. Shaded bands denote
arrival times corresponding to periods of Earth-Uranus conjunction or swingby times at Earth-
Saturn conjunction; these regions are to be avoided for reasons of degraded communications and
Earth-based observations.
The line where the Earth departure declination equals 28.5° (i.e., the latitude of the launch
site) is shown for the 1979 and 1980 launch opportunities. For later arrival dates at Uranus, this
declination is exceeded and a small payload penalty (5 kg or less) for azimuths other than 90° must
be considered. For declinations greater than 33°, an additional penalty must be considered to
account for the necessary "dogleg" (i.e., plane change) Earth orbit departure maneuvers. A 5° change
typically reduces the payload by less than 15 kg for the class of spacecraft considered. The payload
contours shown account for these penalties. For all other launch opportunities, the departure
declination is less than 28.5° for the arrival-departure region shown.
Ames Research Center
National Aeronautics and Space Administration
Moffett Field, Calif. 94035, June 22, 1973
REFERENCES
1. Anon.: Jupiter Swingby Missions to Saturn, Uranus, Neptune, and Pluto. NASA SP—35, vol. 3, pt. 8,1969.
2. Feibelman, W. A.: Concerning the "D" Ring of Saturn. Nature, vol. 214, 1967, p. 793.

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Figure 6.- Uranus missions using Saturn swingby (1985). V^: Departure hyperbolic excess speed,
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Summary of Saturn swingby missions to Uranus

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