Cassini II Interplanetary Mission Design

1
Cassini II Interplanetary Mission Design

• Final Project
• ASEN 5519
• Spring, 2004

2
Overview

• Brainstorm potential trajectories
• VVEJGA, VEEGA, EVEEGA, VEEJGA, etc.
• Generate pork chop plots for each segment of the
  mission
• Check plots for dates with equal V8s at each
  swingby
• Use this to find potential launch / swingby /
  arrival windows
• Check each swingby to make sure that the radius
  of closest approach is above the planets surface
  (and atmosphere?)
• Minimize Launch C3 and Arrival V8

3
Potential Routes

• VVEJGA
• Cassini did it
• Only one Earth flyby
• Constrained by Jupiter-Saturn synodic period
• VEEGA
• Only three flybys
• Many opportunities
• Several options for EE leg
• EVEEGA
• May reduce cost compared with VEEGA
• Three Earth flybys
• VEEJGA
• Additional Jupiter flyby may reduce cost compared
  with VEEGA
• Constrained by Jupiter-Saturn synodic period

4
Assume VEEGA

• Porkchop plots for
• Earth Venus (launch)
• Venus Earth1
• Earth2 Saturn (arrival)
• Earth1 Earth2 segment
• Lambert doesnt work well here (360 transfer)
• Resonant orbit (21, 31, 32, 52, etc)
• Well talk about this in a minute

5
Flyby Constraints

• Venus, Earth1, and Earth2 flybys
• Datein Dateout
• Seems obvious, but dont forget it!
• V8,in V8,out
• Rp gt Rsurface

6
Earth Venus, 1989 Opportunity
JDVGA 2447932.5 V8 6.25 km/s
JDLaunch 2447807.5 C3 15.5 km2/s2
7
Venus EGA1, 1989 Opportunity
JDEGA1 2448235.5 V8 8.9 km/s
JDVGA 2447932.5 V8 6.25 km/s
8
EGA2 Jupiter, 1992 Opportunity
JDJupiter 2450164 V8 5.8 km/s
JDEGA2 JDEGA1 2365.25 2448966 V8 8.9 km/s
9
Venus Flyby
V8,VGA,in is a bit more than 6 km/s
V8,VGA,out is a bit more than 6 km/s
10
Venus Flyby

• Use Lamberts problem software to numerically
  verify that the V8s match
• Search the state space to find best matches
• Use B-Plane software to verify that the flyby
  does not hit Venus
• Rp,VGA gt RVenus

11
Earth Flyby
V8,EGA,in is about 9 km/s
V8,EGA,out is about 9 km/s
12
EGA1 EGA2

• Resonant orbit
• See handout for constructing resonant orbits

13
Grand Tour

• Two tried and true methods for choosing launch,
  flyby, and arrival dates
• Brute Force Method
• Use method above to find best windows
• Loop over nearby dates
• Make sure V8s match up
• Make sure you dont hit the surface
• Choose best combination of dates
• 4 Nested Loops, long run-time
• Hill-Climbing Technique
• Use method above to find best approximate dates
• Calculate a metric for the tour
• Perturb the tour and calculate the new metric
• Work to minimize the metric

14
Hints

• Ive found VEEGA trajectories that do work!
• VEEGA 1
• Launch from Earth in the latter half of 2010
• Arrive at Saturn in 2021
• EE 2-year resonant orbit
• VEEGA 2
• Launch from Earth in the latter half of 2010
• Arrive at Saturn in 2022
• EE 3-year resonant orbit