Using the STK Astrogator Targeter to get to Mars

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					                 ASEN 5519: Interplanetary Mission Design Lab
                                Spring, 2005

                          Project 1: Galileo’s Mission to Jupiter
                                    Assigned: Mar. 10
                                      Due: Mar. 31


             Name:_____________________________________________



Introduction

Project 1 will be the full reconstruction of Galileo’s interplanetary cruise to Jupiter. This
includes both the theoretical work done in Matlab (i.e., pork chop plots) and the
visualization constructed in STK. You will need to turn in several things, but don’t
worry about writing a professional report (that will your final project!).

Galileo’s Critical Events

The following events occurred during the baseline Galileo mission:

                    Table 1. Critical Events in Galileo’s VEEGA trajectory

                Event                   Calendar Date                Julian Date

                        Launch           October 8, 1989 00:00:00     2447807.5

                Venus Flyby (VGA)       February 10, 1990 00:00:00    2447932.5

                Earth Flyby (EGA1)      December 10, 1990 00:00:00    2448235.5

                Earth Flyby (EGA2)      December 9, 1992 12:00:00     2448966.0

                Jupiter Arrival (JOI)    March 21, 1996 12:00:00      2450164.0



You already know how to build a trajectory from one planetary flyby to the next using
JPL’s planetary ephemeredes, your Lambert solver software, and your B-Plane targeting
software. You’re familiar with constructing resonant orbits. Plus, you already know a
thing or two about constructing TCM’s and obeying Planetary Quarantine Requirements.
The only thing that you don’t know in this mission is how to construct the launch and the
Jupiter Orbit Insertion (JOI) maneuver.




                                                                                           1
Launch

Quite a few factors go into constructing a launch, including the latitude of the launch site,
the azimuth constraints on that launch site (launches in the U.S. can’t go over land, or
even fishing vessels!), whether or not the launch will include a parking orbit, etc. We
may do a special topics lab on launches; for now, we will keep it simple.

Once the dates of the mission have been chosen, then Lambert’s solution will provide the
V∞ vector required to depart from the Earth onto the interplanetary trajectory. It is fairly
simple to use STK to target the Right Ascension and Declination of the Launch
Asymptote with respect to the ecliptic. Thus, the easiest way to model the launch is to
convert the V∞ vector into its spherical components: RLA (Right Ascension of the
Launch Asymptote), DLA (Declination of the Launch Asymptote) and C3 (corresponding
to the magnitude of the vector). Then you can set up STK to target the launch conditions
as best as it can. We will do this with respect to the ecliptic. Here are the steps again:

    • Step 1: Use Lambert on the chosen dates to construct                     in Cartesian
      coordinates.
    • Step 2: Convert to C3, DLA, RLA with respect to the ecliptic:
           o


           o


           o

    • Step 3: Set up the launch in STK:
         o Follow the procedures we followed in Lab 5, except to target the VGA.




                                                                                           2
Jupiter Orbit Insertion

Use the library or the links on the class website to find information about Galileo’s first
orbit about Jupiter (Jup 1). If you can’t find any information, then use your own
knowledge about orbits and orbit insertion maneuvers (or perform trade studies) to fill in
the appropriate information. In your report, please let us know how you arrived at your
information about Jup 1. At a minimum, you need to have numbers for Galileo’s radius
of closest approach at the Jupiter Orbit Insertion (rpJOI) and Jup 1’s orbital period. It
would also be helpful to have the inclination of the orbit. If you have any more
information, please include it in your write-up.

Use this information to construct the JOI maneuver. In STK, construct your final TCM
en-route to Jupiter to target a radius of closest approach to Jupiter equal to rpJOI. Then at
that point, use STK’s targeter to target an impulsive maneuver that will put Galileo into
an orbit with the correct orbital period. If you can, target an appropriate inclination as
well (this may require better targeting at the TCM in order to hit the B-Plane at a more
appropriate location).


The Project

1. Construct Pork Chop Plots for each segment of the mission: Launch-VGA, VGA-
   EGA1, EGA2-JOI. Be sure to make the windows large enough to see the overall
   structure of the plots. Turn these in with your write-up and be sure to identify the
   point in each pork chop plot that corresponds to Galileo’s trajectory.

2. Use Lab 7 to construct the Earth-Earth resonant orbit. Use the V∞ vectors constructed
   in that lab to target the gravity assists for Step 3.

3. Use your B-Plane code to provide the following information about each gravity assist:
          rp, the radius of closest approach
          B-dot-R
          B-dot-T

                     Also: given the dates in this trajectory, how close are the V∞
                     magnitudes before and after each gravity assist? i.e., what is
                                 for each gravity assist? How can we improve this
                     quantity?

4. Compute the launch parameters: C3, RLA, DLA with respect to the ecliptic.

5. Determine the JOI parameters: rpJOI, PJOI, etc.

6. Construct the trajectory in STK. Use the following guidelines for your trajectory:
           After launch and each gravity swingby, insert at least one TCM to target the
            next critical event. In reality there would be many TCM’s and many of


                                                                                           3
         them would be used to obey Planetary Quarantine Requirements and
         whatnot, but we’ll keep it simple and use only one (or more if needed).
        Use your best judgment when locating each TCM. Include the dates and
         magnitudes in your write-up; mention your motivations for where you
         located each TCM (early in the segment, late in the segment, etc). The
         magnitudes will not be zero, so don’t worry if they get to be 10’s or 100’s
         of m/s. If they’re larger than 1 km/s, let us know – there might be a
         problem!

7. Include screen shots of the inner trajectory and the outer trajectory in your write-
   up. Include a screen shot of the first Jupiter orbit.

8. Include any references that you have regarding information you obtained about
   the JOI maneuver or anything else in the project.




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