Trouble with complex TransX plan

[YL3GDY]

Hi All.

The ideas of using Moon as a launch pad for interplanetar trips are well-known. Recently I have decided to fly from Moon orbit to Mars using TransX MFD. Transfer from LEO to Moon orbit was OK: I reached 2000 km high circular intermediate orbit.

But troubles started when I was planning flight to Mars. I tried to make such plan: 1st stage - Escape(MAJ:Moon), 2nd stage - Escape(MAJ: Earth, MIN: Moon), 3rd stage - Eject(MAJ:Sun, MIN: Mars). But 2nd stage became in TransX to an Eject stage, but on 3rd I couldn't see closeist approach distance.

So how to plan such trip correctly?

P.S. I was flying on DGIV, if it affects.

 

[flytandem]

I haven't been able to play with Orbiter for a couple months now. Busy with other projects. But it doesn't really surprise me that this post sat for a couple of days without a response, it's a tough problem. The following tutorial might help.

http://www.flytandem.com/orbiter/tutorials/Surrogate/index.htm

It could be called cheating to create another ship to assist in the planning of the first. But perhaps it's can be justified by pretending that the ship at or on the moon is the real ship and it has the ability to run a sim of an imaginary ship at the earth to then use it to set up some dates and orbital planes to be used by the "real" ship on the moon.

When leaving the moon for an interplanetary trip, I like to drop to a close pass at the Earth. Doing a burn at the Pe, just above th Earth's atmosphere, is a very fuel efficient way to depart to the other planets. The trick is to set up a plan from the Earth such that it's eject burn is at a location that is opposite where the moon is. This way a ship dropping from the moon will have a chance to simulate an intercept with the ship orbiting the Earth, but when it's getting close to the Earth, just a few hours from the planned intercept with the ship that has the plan to eject interplanetarily, it can simply set up a maneuver that takes it to the same planet that the surrogate ship had a plan set up to do. After all it's the same date, in the same orbital plane and has the Pe in the right place.

This whole concept of using a surrogate and dropping into the gravity well take using transx up to a much higher difficulty that just setting up plans and maneuvers. But that's what makes it fun.

 

[TSPenguin]

I actualy sat here and hoped you would answer this one.
Unfortunately, your answer is much more complex than I had hoped for

 

[YL3GDY]

Thank you for the link, flyandem! I've read it, quite interesting method.

These days I was thinking about any way to get to Mars from Moon, and I have only imagined such plan(but it's far less precise and based on intuition):

1. Plan an eject to Mars, as sitting on Earth. This gives an approximate date of starting from Moon.
2. Find a closeist full Moon to this date (I've been using Cartes du Ciel calender).
3. Then wait for ship to get at point of orbit opposite to Earth this date(or close to it).
4. Perform an eyeball burn to get out of Earth & Moon SOI.
5. Make an on-route course correction via maneuvre mode.

But this plan requires a lot of fuel and a lot of luck I've tried it, but efficiency was very bad. I've ran out of fuel in DGIV with fuel reserve "trip to mars" during a maneuvre.

 

[flytandem]

Let me try a different explanation.

Let's pretend the Earth is viewed from above meaning we are looking down on the north pole.

Let's say the Earth is at the 6 o'clock position for its orbit around the sun. And Mars is in good position for leaving Earth to head to Mars. This would mean Mars may be something like the 5 o'clock position or so.

Now a ship leaving earth for Mars is perhaps first going counterclockwise around the Earth in a parking orbit and it has a month long window in which it can leave Earth to head to Mars. Let's say it starts on the 1st of the month and ends on the 30th.

The burn to leave Earth is at about the 9 o'clock position for this eject burn but might actually change a bit during this month long window. It might be more like 8 o'clock position at the start and become more like the 10 o'clock position near the end of the month. We'll just say 9 o'clock for simplicity.

So there is a ship on the moon that wants to go to the moon. A smart option would be for it to wait till the moon is at about the 3 o'clock position in its orbit around the Earth, then the ship eject from the moon and falls toward Earth. It would be rounding the Earth at about the 9 o'clock position at its closest point and going a fast speed because it has all that speed from falling from the moon. It only then needs a fairly small kick perhaps 700 or 800 m/s to create the eject burn to head to Mars.

Everything above is just a rough outline of what's happening.


Now some considerations.

We know the month-long window has the eject happening at a different time. Perhaps the moon it as 3 o'clock position on the 21st of the month. This would mean the ship leaving the moon would fall for 4 days and arrive on the 25th. This means the eject position is closer to the 10 o'clock position at the Earth. So we need to leave the moon when its more like at the 4 o'clock position. That happens on the 19th. So that would mean the ship arrives at Earth on about the 23rd. It changes the eject a bit again but perhaps from this we can just approximate it and decide to go with the ship leaving the moon on the 19th plus a few hours.

And we have to round the Earth in a way that allows an eject burn. If we aren't careful maybe we arrive at Earth going over the poles and have no way to turn this into an eject going the correct direction.

So the answer could be to first set up a ship to depart Earth on about the 23rd plus a few hours to match when the moon ship is arriving. And we can be in many orientations in our orbit around the Earth. All these work for our eject to Mars but the only way for a ship falling from the moon to be going in the same plane as that ship in low Earth orbit planning the Mars eject is if the moon is in the same plane as well.

So we first start at the time when we are a few hours perhaps from when the ship is to leave the moon. The date is the 19th. We place a ship in orbit around the Earth. Have the Earth orbit ship go around the Earth until it is crossing the orbit of the moon, at a node with the moon. At that point we swing the transx eject plan orientation around so it too is at the ship's location. It will tell us we are not in plane in all likelihood. That's ok, burn normal or antinormal to bring it into the correct plane. Yes it burns fuel, but this is an imaginary ship. Think of it as the orbinauts in the lunar ship having a copy of Orbiter to simulate a ship at the Earth. You can use the scenario editor if you like to change its orbit. So we haven't changed our location just what direction we are going as we are still at the node with the moon plus we are in plane with a good eject plan to head to Mars in 4 days from this time.

Now we set up a transx plan for the ship leaving the moon. It's goal is to rendezvous with the ship at the Earth. Remember to get the rendezvous date fairly close to when the Earth ship has planned to go to Mars.

As you are getting closed to Earth just ignore the rendezvous you had with the Earth ship. Just start looking at a maneuver somewhere near the closest approach at Earth to head to Mars.