Procedure to offset Apollo TLI burn





Screen Shot


Load Apollo 11 - TLI scenario where you will have atleast 600 seconds to the burn. Open Target Intercept program and Map program as shown in a screen shot above.

Setup default offset values and Make sure the offset reference is set to "Vel. Frame"

Lon = 4.0
Lat = 4.0
Rad = 8.0M

GET = 75:54:28 Required time of arrival to the moon. That's almost equal to the time of LOI burn

After seting the default values. Find an optimal time of ejection (TEj) in realtime mode. Then switch into the Off-Axis mode and fine tune the TEj as required. If you change the TEj afterwards the offset settings will be obsolete. When looking at the Map program we are interested only about 3 values

GET - Time Of true arrival to the Moon.
PeA - Perilune Altitude.
EqI - Inclination to the Lunar equator.

We need to adjust offset settings (Lon, Lat and Rad) so that the real flight data displayed in a Map program will match the mission requirements. In this procedure Apollo-11 flight is used. Required settings will depend about the initial earth orbit. So, don't expect to see exactly the same values.

Procedure

Step 1
We want a perilune altitude of 110km in a Map-program. Now Adjust the "Rad" - offset value to match this requirement. Increasing the Rad will increase the perilune altitude.

If the inclination is allready correct you can skip steps 2 and 3

Step 2
The inclination (EqI) must be as close to 180 as possible. For Apollo 11 it won't go much above 176. Best way to effect this value is adjusting "Lat"-offset value. If the "Lat"-value is too low or too high then the EqI will be lower. At first, adjust "Lat" setting few steps and see how it is effecting into the EqI.

Step 3
Step 2 will effect into the perilune altitude so redo step 1

Step 4
Then, Inspect the GET values from the Offset-screen and the Map program. Required time of arrival is displayed in Offset-screen and your actual time of arrival is displayed in a Map program. Now, do you arrive to the moon too EARLY ? Or too LATE ?

If your arrival is too LATE, then increase Lon-setting by 1.0 degrees.
If your arrival is too EARLY, then decrease Lon-setting by 1.0 degrees.

If your date of arrival to the Moon is correct you have done it. Otherwice go back to step 1




This method can be used to offset a midcourse-corrections in that case realtime burn guidance mode should be used (not Off-Axis). However, a midcourse-correction may only require a small burn in a pro or retrograde direction so dV-program might do that. If using this method to setup MC2 burn here are initial start values.

Lon = -15.0
Lat = 2.0
Rad = 10.2M