Q:
- Are we supposed to give it a single initial velocity and let it go or do we constantly need to provide it with acceleration/course readjustment?
- We have been told to give a range of suitable initial velocities. Do we have to manually experiment with values and determine this range?
- What direction are we supposed to launch the satellite in? Is it simply towards the direction of mars, or are we to launch it where mars would be after some time has passed?
A:
This is an open-ended experiment so you can make your own decisions about the satellite mass and initial position / velocity, what search strategy to use etc. Then, in your report, you should explain what you did and why. Having said that, you are not expected to incorporate a booster for mid-course adjustments - setting the initial velocity is sufficient.
Q:
Hi, is it okay to assume that all planets start along the x axis at the beginning of the simulation?
So, saying their initial y coordinate is 0 and their initial x coordinate is what their radius from the sun is?
A:
Yes, you can assume that the planets start at y=0 in the initial timestep. In this case they x-coordinate will be the radius from the sun.
A number of you have asked me where you can find the input parameters for the sun and planets for the project.
You'll need to look up the orbital radii and masses. One place to try is:
https://nssdc.gsfc.nasa.gov/planetary/factsheet/
You can then use the same approach as for CP5 to set the initial positions and velocities of the planets, using the mass of the sun to calculate the velocities. This is the central potential approximation, which it's reasonable to use because the mass of the sun is much larger than that of any of the planets.
An alternative approach is to use the ephemerides (computed positions of the celestial bodies), which you can generate at the JPL Horizons System app at:
https://ssd.jpl.nasa.gov/horizons/app.html
To use this, you should change the settings to:
• Ephemeris Type - Change to Vector Table
• Target Body - Change to Mercury/Venus/Earth etc
• Coordinate Centre - Type @sun to set everything relative to the sun
• Time Specification - Change values as required
Leave the other settings as default.
The output includes (among other things) the x and y components of position (in AU) and of velocity (in AU/day) at the specified time.
Either of these approaches is fine; you can make your own decision about which to use.