TLI checklist (Quickstart)

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The next step on our journey to the moon is the Trans Lunar Injection, also called TLI. With a single burn of the SIVB engine we'll escape the EPO and extend our orbit so that we reach the moon. In future versions hopefully there will be a TLI "autopilot", at the moment you have to do it by your own. Of course you can do the TLI burn as you like, but we suggest to use the IMFD off-plane intercept program together with the auto burn feature.

Interplanetary MFD (IMFD)

Attention
You have to install and activate Jarmo Nikkanen's Interplanetary MFD (IMFD) 4.2.1 to do the TLI burn as explained below.

You can use the generic cockpit to control IMFD by using it's key codes, but we suggest to use the MFDs on the main panel or the G&N lower equipment bay panel just because there are easier to use. The following is no IMFD manual or tutorial, but just a short "checklist" to configure IMFD, use the IMFD manual for more informations on how to use it.

  • Open IMFD
  • Choose "Course" and then the "Off-Plane Intercept" program.
  • Press TGT, enter "Moon"


  • Press PG
  • Press Z+ until you see the earth on the MFD.
  • Press PG


  • Press NXT until TIn (time to intercept) is highlighted.
  • Press SET, enter "280k", this is a good default value we can start with.


  • Press ADJ until 10x is displayed.
  • Press NXT until TEj (time to ejection) is highlighted.
  • IMFD chooses a default TEj automatically, but the real TLI burn was done during the 2nd orbit, so we have to move the ejection point one orbit later. Press +, the solid blue "earth radius line" begins to move counterclockwise around the earth, continue until the line is one orbit further, TEj should be now about 8000k to 9000k.
  • Press ADJ until 1x is displayed.
  • Press + or - , watch if the burn time (BT) decreases and play with different settings to find the point where the time (BT) is minimal.


  • Now we've calculated a burn (or IMFD did that for us), but since the SIVB is quite low on fuel we should do some more burn time optimization: Press NXT until TIn (time to intercept) is highlighted.
  • Press ADJ until 10x is displayed.
  • Press + to increase the time to interception and look if the burn time (BT) decreases. If it does, increase TIn further to minimize BT, but make TIn not greater than 320k, otherwise you'll arrive at the moon a little bit late.
  • Now you can again optimize TEj a little bit as explained above, again to minimize your burn time (BT).


  • Burn calculation is done, now we let IMFD do the burn. Press PG.
  • Press AB (autoburn).
  • If you like use time acceleration until time to burn (TtB) is about 200s.
  • Wait until autoburn is complete.

Transfer MFD

Another option for calculating TLI parameters involves use of the Transfer MFD (included in the base Orbiter installation). This method involves calculating the burn parameters (delta velocity and time until burn) within the MFD, then inputting the values into the AGC or the Project Apollo MFD TLI burn program. It is simpler to use than the IMFD method, albeit less precise.


  • Open Transfer MFD (Shift + X)
  • Select MOON as the target (Shift + T)
  • Switch to HTO Mode (Shift + X)


Notice in the current configuration, the display reads NO INTERSECT. Enough DeltaV must be added in order for our orbit to intersect with the Moon.


  • Add DeltaV (Shift + = to increase, Shift + - to decrease)


You should add enough DeltaV for the NO INTERSECT message to disappear, and an elliptical orbit to appear. One end of the orbit should be at the center of the Moon, the other should protrude slightly from the surface. Continue adding or decreasing DeltaV until you are happy with the displayed orbit.


  • Note the value in the Dv field: this is your Delta Velocity.
  • Align the white Intersect line with the dotted orange line (Shift + < and Shift + >)


Set your intersect line slightly ahead of the dotted line, in order for the two to be perfectly lined up by the time the TLI burn actually takes place. Once you are happy with the displayed parameters, you should input them into either the AGC (the CSM AGC controls the burn) or the Project Apollo MFD (the S-IVB IU controls the burn).

AGC P15 burn

  • Press VERB 37 NOUN 15 ENTER on the DSKY. This starts the TLI program.
  • Press VERB 22 ENTER to edit the Time Until Burn field (Row Two).
  • Check the DTe field in Transfer MFD. This displays seconds until burn. Decide on a point at which to run the program (ex. when DTe=1.200k) then divide by 60 to calculate time in minutes.
  • Enter the time until burn which you decided upon in minutes (ex. +00020) but do NOT press ENTER yet!
  • Wait until the DTe field reads the same as the value you inputted into the DSKY.
  • Press PROG.
  • Press VERB 21 ENTER, then input the calculated Dv value (ex. +03150) (Row Three).
  • Press PROG to complete the pre-start procedure.
  • For a countdown, press VERB 16 ENTER. The top row displays time to burn in minutes and seconds, the second displays delta velocity, and the third displays the predicted cutoff velocity.
  • Ensure all RCS and engine gimbal systems are activated before T-1:30.

At T-1:30, the AGC will orient the spacecraft prograde, and at T-0:00 the main engine will ignite.

Project Apollo MFD burn

  • Open Project Apollo MFD
  • Press TLI from the main menu.
  • Press V and enter the Dv value in meters/second.
  • Press T and enter time until burn in seconds (ex. 1200)
  • Check the DTe field in Transfer MFD, until it reaches your inputted time.
  • Press RUN to run the TLI program.
  • Ensure all RCS and engine gimbal systems are activated before T-1:30.

At T-1:30, the AGC will orient the spacecraft prograde, and at T-0:00 the main engine will ignite.

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