This tutorial is designed to take you from a surface position on Mars and create a next stage with an eject plan to Venus. It is to be used in conjunction with a scenario called "Mars surface to Venus" which is available here. Extract it into your Orbiter folder and run it in "Window" mode.|
Bring up Transx in both MFD's.
In the right MFD...
click "VW" if needed to make be in the "Setup".
click "++" to make the target as "Escape"
click "FWD" to create a next stage.
click "++" as need to get a target as "Venus".
click "VW" as needed to get "View:Eject Plan".
SET VARIABLES to HIT the TARGET:
click "VAR" and you'll see that you can scroll through 3 directions for a velocity change and a date much like you get with the Manoeuvre mode. Think of what you would have to do to Mars if you wanted it to fall toward the orbit of Venus. It would have to be slowed down, or thrusted retrograde with respect to it's orbit around the sun.
click "VAR" to get "Prograde"
click "--" several times to get the yellow ellipse being created to drop its Pe to touch the orbit of Venus. Remember your "ADJ" increment changes.
|Switch the "VAR" to "Eject Date" and click the "++" as needed to bring the two yellow radius lines close together. These represent the positions of the closest point of the planned trajectory to Venus. Your right MFD should be able to look something like the following image at this point.|
Notice that the white line crossing the orbit of Venus is fairly vertical. This line is the intersection of the orbital planes of the planned trajectory and Venus. We need to swing it around to be closer to the yellow dashed radius lines. In the right MFD...|
click "VAR" as needed to get "Ch. plane Vel"
click "++" and "--" adjusting the increment "ADJ"as needed
Go back and adjust all 4 variables repeatedly now to minimize the "Cl. App." (closest approach). The following image is what you might be close to.
LAUNCHING: (THE ESCAPE PLAN) |
There is no autopilot that launches you onto course. Instead you will be shown an ejection trajectory that you must manually launch into. You will create a circular orbit of height matching the Pe of the ejection hyperbola and also get the orbit into the correct alignment. You get to specify the height of the orbit and then choose a launch time and heading. The combination of launch time and heading helps with the alignment. Here are some specific steps....
SET Pe Distance
This sets the circular orbit height you will manoeuvre into before the eject burn.
In the left MFD in Stage 1
click "VW" if needed to get "Escape Plan"
click "VAR" until you see "Pe Distance"
click "++" and "--" to adjust (remember "ADJ" for increments")
Note: The higher the value the more fuel to get into your your parking orbit. The lower the more rapidly you'll be passing the eject point and the more precise your burn timing needs to be. I suggest for Mars try 250 Km above the surface= 3.640 M.
Launch TIME and HEADING
There are a couple of methods for choosing a launch time and heading depending on your particular situation. In both cases here is some important info on the graphics you see in Stage 1 with View:Escape Plan. The white line that bisects the circle is the axis of the alignment nodes of the eject orientation and your hypothetical orbit that you will launch into. You will want to swing this white line using the adjustment of the Ej Orientation variable. Make it cross the center of the green ellipse. There are both ends of the white line you can swing around to check for launch heading. Practice while several days ahead just to get a feel for ho it works.
To make the graphics easier to understand set the projection to "Focus" as follows
click "VW" for "Setup"
click "VAR" for "Graph projection"
click "++" for "Plan"
Method 1: Earth or Mars (like in this scenario)
In the case of a planet where it's rotating fairly quickly but is moving fairly slowly around it's orbit then use the planet rotation to help save fuel by specifying a heading (outlined below) that's the same direction the planet's rotating using the initial motion of the rotation to reduce the speed you'll need to burn to. Earth and Mars are 90 degrees heading and Venus is 270 degrees. If you are parked near the poles of the planet then launching with the rotation doesn't help much. The actual eject date value will not be exact but errors are small in the case of planets like Earth of Mars if we're talking about a few hours difference. So warp ahead and slow to real time about 0.5 MJD ahead of the planned launch date. Then as you warp slowly forward (try warp=100 or 1000) keep swinging the white line over the ellipse and watch the launch heading value in the lower left. When it is close to 90 degrees you are at a good time to launch and do so with a heading into orbit as stated in the launch heading.
Method 2: Moons of Jupiter (another example) If you are on a planet or moon that's not rotating very fast but is moving quickly around it's orbit then eject time is critical and not heading since there is little help from the rotation but moon positions change a lot in just a couple of hours. You would in this case warp ahead to stop before the planned eject date an amount of time based on the time it will take in orbit to reach the eject periapsis. Then find the launch heading by swinging the white line to center over the green ellipse. For example: An approximate low orbital period is 0.1 MJD for moons like Callisto. If you are finding you are 1.2 orbits from current location to the eject periapsis then start the launch 1.2 * 0.1=.12 MJD before the planned eject date.
The following image is our Mars scenario during the adjustment with a specified launch heading of 82.05 degrees.
At that point you should change heading. By trial and error you could bank your wings to a left 45 degree bank angle and allow a turn of 1 or 2 degrees heading change and level the wings again. If the Rel. Inc. value is climbing then quickly bank the other way and change heading to 1 or 2 degrees right of the original launch heading. A later version of TransX has small white circles on the white line just outboard of the planet surface. A filled in circle means a right turn is needed and an empty circle means a left turn is needed. Maintain this new heading while the alignment drops.
Soon the white line will start to swing a full 180. The trick is to return your heading back toward the original and bank only as needed to try to get the white line to be 90 degrees relative to your position. Yes 90 degrees CROSS to your growing green ellipse.
You may also readjust the Eject Orientation while climbing out. What you should try is to adjust it to bring the white line closer to your position but ahead of you (counterclockwise from the end of the green ellipse). And repeart changing heading to swing the line again 90 to the green ellipse. At this point you will see that even slight changes in your heading will cause the white line to easily swing. You might find "R. Inc." during your burn into orbit is consistently under 1 degree.
Look at the suggested ejection DV shown in stage 1 and create a maneuver with that much prograde. You'll notice you now have two separate yellow dashed hyperbolas. Then swing the date of the maneuver (using hyper increment) to rotate the dashed trajectory around and place it exactly on top of that for the plan. Then go to stage 2 and make all the plan variables zero, this will remove the plan in stage 1 so that the data will be for that of the maneuver. In Stage 1, readjust the prograde value and date value a tiny bit and include values in plane change if needed to make your final destination (in this case Venus) a direct hit just like you would with any "maneuver". Now it's just a matter of doing a maneover using the target to orient your direction.
MID COURSE CORRECTION:
You are now on your way to Venus. You will probably want to do a mid course correction at some point usually 1/2 to 3/4 the way around the planned trajectory to the target.
In the right MFD...
click "FWD" if needed to get to the stage where the Maj: is Venus. click "VW" to get "Encounter"
In the left MFD set up the "Manoeuvre" as you have already learned how to do in previous exercises. Here's an image of the Encounter with Venus after the midcourse correction.