Using a Surrogate Ship for a TransX Plan

There are ways to reduce the guesswork and more specifically plan the type of trips that TransX isn't really set up for. For example if you are sitting on the moon and want to plan a trip to Mars, you don't really have the same tools available as if you were sitting on the Earth to plan it. Moreover if you want to utilize the efficiency of dropping through the Earth's gravity well to do the eject burn at the Pe when going from moon to mars then the phase of the moons orbit when doing the TEI is critical to having your Pe at the Earth properly oriented. But how to know when the correct moon's phase (launch date) is? Just eyeball it?

Using a surrogate ship that is just sitting anywhere on the Earth or orbiting it is a convenient way to do it. Create it with the scenario editor if you like. Then make a plan for this ship to leave Earth and have a low Pe for the ejection burn. Either edit the ship's orbit with the editor or fly it into the correct orbit. Then target the surrogate to find the best trajectory to depart the moon to arrive at Earth on the correct alignment.

The image at right allows you to mouse over it and back out again to switch between the two ships plans. Mouse OUT of the image and it shows the Stage 1, Escape Plan, for the ship sitting on Earth. The Pe is oriented to the lower right. Then mouse OVER for the Stage 2, Eject Plan, of the ship coming to Earth from the moon which is the ship that will actually go to Mars. Compare the orientations of each ship's orbit around the Earth. Carefully use a straight edge like a sheet of paper against your computer screen. If you want to make one yourself, have a scenario like the stock Delta-glider/Brighton Beach scenario and edit the date to 55117.7 MJD and for the deltaglider on the Earth (GL-01) have an eject to Mars set up with pro=3.188k, date=55121.9322, outward=398.8, pl.change.=0. For the ship on the moon set up an eject with prograde of about -880 m/s. You can't save the scenario plans for both ships, any save will only save the plan of the ship in focus at time of the save. But it does remember the plans of both ships while orbiter is running.

There is a bit of an art to it but it is very workable. You advance the time which brings the moon toward the correct phase, approximate the launch date and be sure that the surrogate ship plan uses this date. Actually you make it about 3.5 days later to account for the time to drop from moon to low earth Pe. But when you change the date of the TMI for the surrogate, it will require changing the transfer velocities a bit. And this will slightly affect the orientation of the Pe. Then advance the date putting the moon exactly into phase and set up a TEI plan for the ship on the moon.

If there is a large plane change in the surrogate's plan then it becomes less reliable. And the moon doesn't orbit Earth exactly on the ecliptic so you may be rounding the Earth at not an ideal inclination. You could toggle the various views if you like. But better is to make your surrogate ship an active helper. The following is a description if you decide to fly the ship into place. (The other option is using the scenario editor.)

Place it into orbit just a few hours before time to launch your ship from the moon. Have its orbit with a lunar node exactly at the moon's current location,....

Then when arriving at a node swing the plan eject orientation over the ship and burn Normal+ or Normal- as necessary to align it with the plan. If there is a large plane change you may affect your orbit being over the moon's location. If so advance time about 20 minutes till you are mid way between the lunar nodes and plane change to swing the orbit back over the lunar node. Then next time you are over a lunar node again swing the eject orientation over your position and do the plane change to reduce the relative inclination. Repeat a 3rd time if necessary. Your surrogate orbit is now aligned both with the eject plan (left image below) and to intersect the moons orbit exactly at the current moon location (right image below).

Now, your ship on the moon simply creates an eject plan to the Earth to arrive there in plane with the slave ship's orbit. This is easy to approximate by making the Scales to view as "Target" and graph projection as "Plan". Play with plane change eject variable to make the view the most normal to the slave ship orbit. You will notice that when you are getting close to normal, the white axis of intersection line will swing crossways (90 degrees) to the imaginary line connecting earth and moon.

No need to actually make a rendezvous obviously, just being within a degree or two of its alignment when arriving at Earth allows an efficient completion of your main plan. Now all that's left is to do the flight from the moon to Earth and there you simply set up a manoevre with prograde burn near the Earth Pe and adjust all the variables as needed including adjusting date a tiny bit before or after earth Pe to make your Interplanetary injection burn.

This surrogate system can also be used when doing the TMI from low lunar orbit too. Meaning going directly moon to Mars with no gravity well burn at the earth. The problem had always been to know what direction to launch from lunar surface for this to be a prograde burn (no plane change) to head to Mars. Use the surrogate and raise the Pe up to the distance of the moon to get the orientation and approximate velocity values of the TMI. Moon being in proper phase is very helpful. Then roughly set up this as an eject orientation for the moon with roughly ths same plane change in the plan and launch onto a heading to follows this eject orbit. Then once in orbit cancel the plan and replace it with a specific manoevre. It's amazing how well this can provide a nice "prograde from orbit" manoevre burn with not very much plane change.