TransX Sling Earth or direct escape from the Moon

rpiolends

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Using transx, IMFD, or both how can I determine if I should sling earth to get to jupiter, or direct fly from low moon orbit.

Once determined, how do I setup that transfer?
 

dgatsoulis

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If your starting point is the Moon (Luna), it is always better to drop to LEO altitude and perform a second burn there to get to your destination. The more the transfer Delta-V (Total DV in TransX or oV in IMFD), the more the savings compared to leaving directly from the Moon.

For a direct flight, the best tool to use is IMFD.

www.youtube.com/watch?v=i2iB3CXirVk

The two burns method can be setup only with TransX. There are a couple of ways to do it, (surrogate ship or 2 instances of TransX). For more accuracy, you can handle the burns themselves using IMFD's Delta Velocity and Map programs.

This link from flytandem is very useful for making a plan with a surrogate ship in TransX.

This post from BrianJ is for making a Moon to Mars TransX plan without the help of a surrogate ship. The starting point is from lunar orbit.

These excellent videos from David Courtney, walk you through the process of setting up the flight with TransX from the lunar surface. Very highly recommended.

www.youtube.com/watch?v=Zk8-nPBtYeY

www.youtube.com/watch?v=p0KubAYmD_Q

(more examples to be uploaded soon).

One small technical detail. It is not a sling, not even a powered slingshot. For a trajectory to be considered a slingshot, you need to enter the system with a hyperbolic trajectory. In this case you -standing on the Moon- are already in an elliptical orbit around the Earth. It is just a 2 burns method to leave the Earth-Moon system. One burn to leave the Moon and drop to a low altitude over Earth and a second burn there to escape the Earth.

There is also a third way to make these flights (moon→other planet), which is a 3 burns method.
1.You leave the moon and go to a high apoapsis relative to the parent planet.
2.At apoapsis you lower your periapsis as close to the planet as you can. (And take care of any plane change needed)
3. At periapsis you perform the ejection burn.

Not really applicable in the Earth-Moon system, but it's a really useful method if you are landed on a moon of the outer planets. (IIRC, it even works for Deimos-Mars). The down-side is the additional flight-time.

Welcome to the forums
:cheers:
 

blixel

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These excellent videos from David Courtney, walk you through the process of setting up the flight with TransX from the lunar surface. Very highly recommended.

Thanks dgats. If you hadn't spent so much time chatting with me via Skype, I never would have figured it out. Once I understood it, I really wanted to record the process so I wouldn't forget it myself.

I would also like to point to this document I've been working on which outlines the process Dimitris taught me. It's not done, but I've got a large portion of completed. So between the video and this document, you should be able to figure it out (eventually).

http://goo.gl/T1CqzL

Once again, a big thanks to dgats for showing me all of this.


One small technical detail. It is not a sling...

Good to know. I'll refer to it as dropping to Earth rather than "slinging" Earth, from now on.
 

Shifty

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The two burns method can be setup only with TransX. There are a couple of ways to do it, (surrogate ship or 2 instances of TransX). For more accuracy, you can handle the burns themselves using IMFD's Delta Velocity and Map programs.

I'm pretty sure you can set up the second burn in IMFD. Tutorial 6 (page 100) in Mark Lieberbaum's [ame="http://www.orbithangar.com/searchid.php?ID=4142"]IMFD manual[/ame] explains how to set it up for a Luna-to-Mars transfer.
 

dgatsoulis

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I'm pretty sure you can set up the second burn in IMFD. Tutorial 6 (page 100) in Mark Lieberbaum's IMFD manual explains how to set it up for a Luna-to-Mars transfer.

That is incorrect.
Yes, there are two burns in that playback, but all the energy to leave the Earth-Moon system comes from the first burn, when the spacecraft is in low lunar orbit. The second burn is a correction. The flight is still considered a single burn to Mars.

If you had watched the first video of the post you quoted, you'd have seen the correct way to set it up.
I am using the same Earth-Mars window as Playback #6, using a single burn from low lunar orbit, to get to Mars using only 58% of the dV for the initial burn compared to Mark&Tommy's playback and a mere 7 m/s for corrections.

DV expenditure and flight-time are the best indicators.

IMFD's Full manual playback #6:

1st burn from LLO: 2579 m/s
1st MCC at perigee: 202 m/s
2nd MCC: 144 m/s
3rd MCC: 141 m/s
4th MCC: 37 m/s
Total: 3103 m/s

--There are additional MCCs after the 4th one, but they have to do with base alignment/periapsis at arrival.

1st burn mjd: 52019.68 - arrival at periareion mjd: 52303.94 - Time Of Flight: 284.26 days

The flight in my video:

1st burn from LLO: 1504 m/s
1st MCC: 5 m/s
2nd MCC 2 m/s
Total: 1511 m/s

1st burn mjd: 52007.47 - arrival at periareion mjd: 52295.28 - Time Of Flight: 287.81 days

As you can see, you can make the same flight with ~ half the dV compared to the playback. Both flights are single burn solutions for a Moon to Mars journey.

To get the dV expenditure even lower, you need a 2 burns solution. The first burn escapes the Moon but NOT the Earth-Moon system. The second burn -made at Earth periapsis- is the one that escapes the Earth-Moon system and gets you to Mars. You save ~ 300 m/s compared to the single burn solution, for approximately the same Time Of Flight.

This kind of flight cannot be setup with IMFD. You need TransX for the initial setup and then you can perform the burns with IMFD.
 

Shifty

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This kind of flight cannot be setup with IMFD. You need TransX for the initial setup and then you can perform the burns with IMFD.

Thanks much for the clarification. I've been wondering for awhile if and why TransX was actually necessary for interplanetary mission planning. Time to pull up some tutorials.:)
 
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