Viking1 and Viking2 flight notes.

Used IMFD exclusively for navigating to Mars, MOI and EDL setup.
IMFD configured for "Apollo P30" style burns (burn vector fixed).

TRANS MARS INSERTION (TMI)
Used IMFD Course/Target Intercept + IMFD Orbit Eject.
Its a long burn (>60s) so you MUST start the burn at least 1/2 burn-duration BEFORE nominal IMFD Orbit Eject burn start time. Otherwise efficiency is not good, there will be dV shortfall.

In retrospect, I'm not sure this was the easiest way of doing the TMI!


MID COURSE CORRECTION (MCC)
Used IMFD Course/Target Intercept(with offset) + IMFD Map(Plan view)
I find it more intuitive to tweak the IMFD Target Intercept "offset" parameters and watch the result on IMFD Map(Plan view). Targeting the MOI at 1500km alt, Periapsis 8deg down-range of landing site, as follows:
Viking1 Periapsis Lat. 28N Long. 40W
Viking2 Periapsis Lat. 50N Long. 142E (WRONG! Should have been 146E)

MCC1 performed when dV at minimum on IMFD Course Intercept.
MCC2 at about 1/2 remaining distance.

MCC3 performed 2-3 days before MOI, using IMFD Base Approach, parameters:
Target: viking(1/2)_landing_site
Alt.   1500000
ReA. 0
Ant.  -8


MARS ORBIT INSERTION (MOI)
Used IMFD Course/Delta Velocity + IMFD Map
Burn time and dV tweaked to keep periapsis at same point on IMFD Delta Velocity display, and at correct lat/long for the next one or two periapses on IMFD Map(Plan View).


MARS ORBIT CORRECTIONS (OC)
NOTE: Using high time acceleration >1000 around periapsis caused my orbit to change significantly (maybe I should check my Orbiter2016 propagation settings?)

OC1 to OC3 used IMFD Course/Delta Velocity + IMFD Map.
Small burns prograde or retrograde to keep periapsis at correct location on IMFD Map.

OC4 used IMFD Base Approach to trim the orbit ready for Aeroshell jettison and EI burn.
Same parameters for IMFD Base Approach as MCC3.


AEROSHELL EI BURN
Used IMFD Base Approach, parameters:
Target: viking(1/2)_landing_site
Alt.   243000
ReA. 16.8
Ant.   17.3
(Set the burn up in the Viking orbiter, pre-Aeroshell jettison, to find burn time for min.dV - jettison before that!)

Made a small trajectory-trim burn 1hr before EDL using same IMFD Base Approach parameters.

ENTRY DESCENT LANDING (EDL)
Orient Aeroshell heads-up, AoA ~ -20deg, by 300km alt.
Enjoy the ride down!

BrianJ
Aug.2025
 
