Problem Trans Lunar Injection Burn Problems

[Royalkin]

I have used several MFDs (TransX, IMFD, Transfer MFD) in attempts to induce a trans lunar injection burn, however due mostly to my lack of capabilities with burns, and also these MFDs, I cannot achieve an orbit around the Moon. I suspect since I seem to undershoot (the spacecraft arrives at the proposed intersection early) the Moon, I am not achieving a precise ejection vector from Earth orbit.

What frustrates me is that it seems as though I must maintain a precise ejection vector "manually", and for all my attempts I simply cannot achieve this. It seems to me that with the sophisticated software that would be on board these spacecrafts, there would be a guidance program that would at least maintain a proper ejection vector while I manually burn?

I really enjoy Orbiter, but this aspect of it has me almost pulling my hair out, and I want to learn how to do this. I have followed several tutorials, and while I believe I am doing the same things they are, I am not able to achieve a stable lunar orbit.

I do admit, while I have some understanding of orbital mechanics, I don't know it all, and yes I have tried to read the manuals. If I have something wrong in my analysis, please correct me.

 

[agentgonzo]

You will generally need to perform one or more Mid Course Correction burns to keep you on the correct trajectory. Very few people do a single burn to get to lunar orbit (Apollo did these too).

Imfd and ltmfd have autopilots to keep you pointed in the correct direction during the burn. Transx and transfer mfd do not

 

[Royalkin]

Thanks Gonzo, can you or someone else point in the direction of a good IMFD tutorial?

 

[jarmonik]

You can't get into a lunar orbit with one burn. You will need a lunar orbit insertion burn (LOI). The TLI burn can only get you into a lunar fly-by. The LTMFD is probably to most accurate in TLI and has a mathematical accuracy of roughly 100 meters if measured in a lunar fly-by altitude. However, the accuracy of the burn is roughly 5km to 15km and will depend about frame-rate, thrust and luck. Every attempt to make it more accurate has failed.

 

[orbekler]

You can't get into a lunar orbit with one burn. You will need a lunar orbit insertion burn (LOI)....However, the accuracy of the burn is roughly 5km to 15km...

Yes, but your Lunar Transfer is so accurate, that I completed free returns even without MCC.

 

[Tommy]

IMFD Full Manual/Playbacks includes a section on lunar transfers. If I can ever find the time to finish my part of it, the second version will include a a lesson on setting up a free return trajectory, and a lesson on performing a highly off-plane (ISS to Brighton Beach) lunar transfer with Delta Velocity program.

[ame="http://www.orbithangar.com/searchid.php?ID=4142"]IMFD Full Manual/Playbacks[/ame]

 

[orbekler]

...the second version will include ...a lesson on performing a highly off-plane (ISS to Brighton Beach) lunar transfer with Delta Velocity program.

IMFD Full Manual/Playbacks

I cant' wait fot the Delta Velocity Program tutorial!:thumbup:

 

[Tommy]

I cant' wait fot the Delta Velocity Program tutorial!

Hopefully I'll find some time to finish soon - I need to finish the manual entry for the "Advanced Concepts" section (covers using Target Offsetting and/or Delta Velocity to MCC's earlier and more accurately, and targeting a planet's moon directly when coming from another planet - the flight is KSC to landed on Titan without refueling (stock DG) and having a bit over 1/3 main fuel remaining. Unfortunately, IMFD doesn't work well with recordings that far from the Sun - Map's predictions jump around too much (works fine when flying - it's a recorder issue) so the manual portion is critical.

The main part of the Delta -V tutorial is finding the right time to go (must arrive near a node) and how to use Map to ensure your groundtrack passes over a target base. Delta Velocity program is quite simple to use - if you know the mechanics of the transfer you are trying to accomplish!

 

[Cras]

IMFD Full Manual/Playbacks

This is an absolutely must have if you use IMFD. It is just awesome.

 

[asbjos]

TLCC?

Hey

While you are talking about the excelent Lunar Transfer MFD, I have a question. When you are on the program TLI, it stands one place: "FSt: TLI". You can change it to "FSt: TLCC or Launch".
What does TLCC stand for, and what is the difference between a TLCC-burn and a TLI-burn?

Thanks anyway!

 

[orbekler]

I'm a bit rusty with LTMFD, but if I'm not wrong first you start with TLI (Trans-Lunar-Injection) program to escape from LEO and then you apply a TLCC (Course Correction), when you're pretty far away from Earth.

 

[agentgonzo]

I'm a bit rusty with LTMFD, but if I'm not wrong first you start with TLI (Trans-Lunar-Injection) program to escape from LEO and then you apply a TLCC (Course Correction), when you're pretty far away from Earth.

Correct. The Injection burn (TLI) takes you from LEO into a lunar transfer orbit (going to the moon) and is one big burn with the Main engines. The Course Correction in a small 'trim' burn done en-route to correct your trajectory a small amount. It's normally done with the RCS thrusters.