Question AMSO TLI Burn

[Shifty]

At long last, I've decided to work my way through at least one of the Apollo missions using AMSO. Started with the Apollo 11 lift-off scenario. Launch autopilot worked great and I've enjoyed listening to the mission audio. I followed the instructions carefully to set up IMFD for the TLI burn (Offset/Off-Axis/Vel. Frame/Adjust Lat/Long/Rad for a proper PeA, EQI, and PeT.) I perform the burn using IMFD's autoburn, but after it's complete, the PeA and PeT are off by a significant amount. I figured maybe I missed a setting somewhere, so I tried loading the "Apollo 11 Step 5" scenario included with AMSO, which is supposed to be all set up with IMFD. Just hit autoburn and watch. But, when the scenario loads, PeA is negative and PeT is off by a couple minutes. So, I tweak those back into place, but the burn still ends up off (typically with a PeA of 300km instead of 112km.) OK, maybe I can correct this with the MCC burn, but over the 10 minutes after the burn is complete (I verified engines are off), the PeA rises to over 1000km and keeps rising. There's probably something simple I'm missing, but I can't figure out what's going on.

 

[Shifty]

After a week, I finally completed the Apollo 11 mission, start to finish, including the mildly silly, but pretty cool, helicopter recovery at the end. Turns out LTMFD is way more accurate and useful (though less flexible) than IMFD for lunar missions. (IMFD is still nice for its map mode, which lets you see the whole free-return trajectory.) I'm considering writing an AMSO For Dummies document, similar in purpose and scope to the pilot's reference cards that are available in French on ACSoft's website. AMSO is actually pretty accessible and easy to run; it's just hard to flip through all the detailed documentation to figure out exactly what to do when.

 

[PhantomCruiser]

"AMSO For Dummies document" that would be pretty handy. I enjoy the AMSO missions, but have not been able to do one from end-to-end (work, real life, wife, etc).

A quick reference guide was something I thought would help out a lot. I hope you do it!

 

[Shifty]

"AMSO For Dummies document" that would be pretty handy. I enjoy the AMSO missions, but have not been able to do one from end-to-end (work, real life, wife, etc).

A quick reference guide was something I thought would help out a lot. I hope you do it!

I posted a rough draft here.

 

[RonDVouz]

I had a pretty long weekend off so I decided on doing Apollo 16 in full for John Young's birthday last week, by the end of the weekend I had completed all the J type missions. I'm still pretty amazed at the surface textures for Hadley and Taurus Littrow (OMG ORANGE SOIL!). Glad to see they included House Rock in the Descartes site. I found that using the actual mission times gave me reasonably accurate results, you just have to scan through all the other mission tasks (like the S-IVb venting procedures) to get to the TIg for TLI, TLCC and TECC. Punch in the number and go.

http://history.nasa.gov/SP-4029/Apollo_08i_Timeline.htm

You can change the mission number in the URL to get the mission timeline for that specific flight. (i.e. /Apollo_09i_; /Apollo_10i_ so on)

Skipping the time ahead at 1000x during the cruise phases cut the time down to about 3 to 4 hours to complete a mission, depending on who gets fatigued during the EVAs (I found the mission commander doesn't get winded from hopping for a few minutes).

Had a LOT of time on my hands. :lol:

Oh, and I prefer Lunar Transfer MFD. Simpler than Interplanetary, I was having issued with the off plane settings too. LTMFD does it for you.

 

[Tommy]

There are two probable reasons for the inaccuracy you experienced with IMFD. One possible reason is if you do not have "Non-spherical Gravity Sources" enabled in the Orbiter launchpad. IMFD assumes non-spheriical is enabled.

The second reason is that Target Intercept calculates the burn as a point event - instant. It assumes the entire delta V is applied instantaneously - and the data it gives to Map is based on that point burn. It's the Autoburn Program that applies the burn integration math to help account for the non-instant burn time. Autoburn doesn't re-calculate the burn as it goes along - it only re-calculates the integration. It tries to leave you on a vector as close to the course vector determined by Target Intercept, but the longer a burn takes, the less accurate it is.

LTMFD handles this a bit differently, and is more accurate than IMFD's Target Intercept program.

Although I still use IMFD for lunar transfers, I do them with the Delta-V program rather that Target Intercept.

 

[boogabooga]

There are two probable reasons for the inaccuracy you experienced with IMFD. One possible reason is if you do not have "Non-spherical Gravity Sources" enabled in the Orbiter launchpad. IMFD assumes non-spheriical is enabled.

The second reason is that Target Intercept calculates the burn as a point event - instant. It assumes the entire delta V is applied instantaneously - and the data it gives to Map is based on that point burn. It's the Autoburn Program that applies the burn integration math to help account for the non-instant burn time. Autoburn doesn't re-calculate the burn as it goes along - it only re-calculates the integration. It tries to leave you on a vector as close to the course vector determined by Target Intercept, but the longer a burn takes, the less accurate it is.

LTMFD handles this a bit differently, and is more accurate than IMFD's Target Intercept program.

Although I still use IMFD for lunar transfers, I do them with the Delta-V program rather that Target Intercept.

You need to switch from "realtime" to "off-axis" in IMFD's Target Intercept mode for lunar transfers, or in IMFD's Orbit Eject mode for interplanetary transfers. Most people don't think this matters too-much, but this will give the Map an accurate prediction of your trajectory.

I assure you that the Target Intercept + Map can give extremely accurate results.