Advanced Question TransX "Orbits to Icept" Setting

[Shadow Addict]

With the help of flytandem's amazing tutorials (as well as all the posts he's made on O-F), I am overcoming my prejudice against TransX and learning how to use it for slingshots. I haven't actually tried any slings yet, but I've set up a few improvised ones that I THINK would work if I tried to fly them. I have a question that I haven't found any conclusive answer to, though. What is the Orbits to Icept setting for? I'm assuming that it means Orbits to Intercept, which makes sense, but I can't exactly visualize what it does. All I know about it right now is that it makes the Cl. App on my planned Venus to Venus slings stop flying around everywhere, and I'm sure it has a more concise purpose than that.

 

[agentgonzo]

What is the Orbits to Icept setting for? I'm assuming that it means Orbits to Intercept

Yes, that's correct. It is used when you will not be intercepting the planet at the next pass.

So, for example, if you were to launch from Earth on a transfer to Venus that would have you perform your TVI, but then complete 3 entire orbits of the sun before you actually encounter Venus, you would set the Orbits to Icept to be 3.0.

It can be useful for multiple slings on the same object. For example, when Cassini-Huygens went to Saturn, it did a VVEJ-GA (Venus twice, then earth, then Jupiter). In that case, your TransX stage for the second Venus encounter should be set to 1.0 as it will be exactly one orbit after you depart Venus. It's also useful when you are planning resonant transfer trajectories.

Hope that explains it.

 

[Shadow Addict]

That helps a lot, thanks. I'm am still a bit confused about one thing, and that's setting it to .5. I guess it means you intercept after half an orbit? Isn't that how a normal Hohmann transfer works anyway?

 

[agentgonzo]

That helps a lot, thanks. I'm am still a bit confused about one thing, and that's setting it to .5. I guess it means you intercept after half an orbit? Isn't that how a normal Hohmann transfer works anyway?

I think so, and yes, that's how a Hohmann transfer works. It seems to be fine leaving it at 0.0 for the initial orbit (whether you are intersecting after perihelion (if transferring to a planet in a higher orbit) or before it), but if you are intercepting on subsequent orbits I've found that it sometimes works to set it to (eg 2.5) if intercepting after perihelion. YYMV

 

[Shadow Addict]

Okay, I'm pretty sure I understand it now. Thanks so much, I'm really starting to love TransX.

 

[flytandem]

Yes the value of Orbits to Icept is how many orbits are omitted before it starts looking for closest approach. So the cl app is always AFTER that number of orbits has gone by.

I usually will toggle the value up and down and often there are a couple of values that are the same. Example it may say that orbits value is 2.5 or 3 and it has the same value and date of cl app for each. This gives me a better idea of how many times I go around the central body before arriving at that cl app location.

It also counts down as you go. For example, you may have set the orbits to icept to be 3.5 for the cl app you want. As you are warping ahead and going around you will notice that it automatically drops to 3, then 2.5, then 2 etc. This way you don't have to count it yourself and will know when you are one that last half orbit heading in for the arrival at the target planet or ship.

 

[Shadow Addict]

I have another TransX question and I'll just ask it here instead of making a new topic: what exactly does Inherit Velocity do? I guessed that if you want to do a regular slingshot, Inherit Velocity should be left on, but if you want to do a powered slingshot, it should be turned off and the velocity should be adjusted manually. Is this close to right or am I way off?

 

[agentgonzo]

I have another TransX question and I'll just ask it here instead of making a new topic: what exactly does Inherit Velocity do? I guessed that if you want to do a regular slingshot, Inherit Velocity should be left on, but if you want to do a powered slingshot, it should be turned off and the velocity should be adjusted manually. Is this close to right or am I way off?

Correct. If you turn the inherit velocity off, your burn will be at periapsis and (I think), you get a burn screen like in the normal manvoeuvre screen. It's been ages since I did it.

 

[Shadow Addict]

Thanks a lot! I'm starting to understand TransX a lot better. Now, off to attempt an Earth launch to a Venus sling that will take me back to Earth DD