TLI checklist (Standard)

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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 real Apollo this burn was calculated by mission control. The burn data were uploaded to the Saturn Instrument Unit (IU) and the Apollo Guidance Computer (AGC). In Project Apollo there is no mission control simulation yet, so we have to do that a different way, by using the Orbiter MFDs.

TLI burn calculation

At first the burn data have to be calculated. "Burn data" mean the time when the burn will happen and the velocity difference the burn will cause. The exact values you need is the time to ejection in seconds and the delta velocity in m/s. After that the burn data will be entered in the DSKY and then the AGC will do the burn automatically. There are three Orbiter MFDs capable to do the burn data calculation:

  • The build-in Transfer MFD
    Use it as explained in the Orbiter user's manual. It's probably the easiest way to do it, but it's also not very accurate.
  • The build-in TransX MFD
    One of the best tutorials explaining how to use the TransX MFD for the TLI burn is still the NASSP 5.2 tutorial made by SaturnV, there the "2. Translunar injection" section.
  • Jarmo Nikkanen's Interplanetary MFD (IMFD) 4.2.1
    It's available at Jarmo's site. This is probably the most accurate and pursuable way to calculate the burn, because it has a very precise trajectory prediction. Thanks to Jarmo there's a very good tutorial how to setup an Apollo TLI burn and we suggest to use it.

The TLI burn was done in the 2nd orbit after earth orbit insertation, please keep that in mind when setting up the burn. So the time to ejection normally should be roughly about 2h 30min or 9000s, if you do the calculation directly after earth orbit insertation.

TLI preparation

After you managed to see the (decreasing) time to ejection (not the time to burn, the AGC does that by itself) and the delta velocity in on of these MFDs, wait until the time to burn is about 30min or 1800s, then you can continue a little bit more historically correct:

Time Procedure
TLI preparation
cb SECS ARM (2) - close
SECS LOGIC (both) - on (up)
SECS PYRO ARM (2) - on (up)
Set Digital Event Timer (DET) to 51:00, stopped
Start program P15
Key V37 N15E
  F 06 33
(Wait until time to burn is
exactly 20min or 1200s)
  F 06 14
Enter delta velocity
in the format +XXXXX
  F 06 95
  16 95
  R1: Time to burn
  R2: Delta velocity
  R3: Velocity at engine cutoff

Start P15 "TLI initiate/cutoff ".

Set time to burn to 20min

For example +03150 for 3150 m/s

Monitor burn data

TLI burn sequence

The AGC does the TLI burn fully automatically. You can inhibit the TLI burn sequence by switching the XLUNAR INJECT switch to SAFE until 18s before SIVB ignition, after that you can do this by using the S-II/S-IVB LV STAGE switch (permanent inhibit when used 12s after SIVB ignition or later).

Time Procedure
  Automatic TLI burn sequence [1]

Checklist TLI (Standard).gif

ca. 5 min
DSKY blanks (Ave G on)
SII SEP lt - on
SII SEP lt - out
LV ENG 1 lt - on
SIVB ignition
LV ENG 1 lt - out
LV ENG 1 lt - on
SIVB cutoff
LV ENG 1 lt - out
  F 37 00

Run program 0,
the AGC idling program.
  1. Apollo 15 CSM Launch Checklist. July 9, 1971. NASA Manned Spacecraft Center. Houston, Texas. PDF [A15_LAUNCH_CHECK]