MISSIONS.DAT
contains counters and race info on the ongoing acts. At the start of the game (beginner level) research in your home zone and terror in a random zone is initiated. After that each new month you will get two new missions, one of which is a terror mission (beginner level).
Structure of a mission entry
Each mission has 4 words. With 7 acts on 12 zones these are 672 bytes. E.g. infiltration(3) in Europe(4) would have the offset 3*8+4*(7*8)=0xF8.
offset meaning 0 ufo-counter on the ufos within the mission (FFFF, the mission is not active) 2 sub-ufo-counter used for some missions 4 time-counter, 30 minutes to next ufo 6 alien race of mission
The races are:
0 Sectoid 1 Snakeman 2 Ethereal (need to check) 3 Muton (need to check) 4 Floater
Timetable of a mission
When a mission starts, the ufo-counter is set to 0 and the time-counter to some act-depending time. The time-count is reduced every 30 minutes. When 0, an ufo will appear, the ufo-counter (or the sub-counter on some mission) will be increased and a new random time-counter for the new ufo will be set.
Note on the timing
The randomization makes it difficult to generalize ufo appearances, but there seem to be some categories:
immediate 1h 0.5-2.5h hard 2.5h 2.5h 2.5h a day 1d 20h-30h some days 3d 2d-5d a week 1w 5.5d-8.5d two weeks 2w 10d-18d longer 1m e.g.46 days
A time followed by * denotes an exact non-randomized time of arrival.
Also, shooting down a UFO will immediately increase the time before the next UFO scheduled in the same act/zone. The duration types of these delays have not been properly verified. A casual overview suggests that when a retaliation act is not scheduled in response to the shootdown, the additional delay is of the same order as the original scheduling delay.
If a retaliation act is scheduled in response to the shootdown, the additional delay can be of a higher order than the original scheduling delay.
Battlescape missions do not affect the scheduling of future UFOs.
[Zaimoni: need to revise the following to work on ufo-c/sub-ufo-c pairs where relevant. Remove this comment when completely revised]
Research
A undisturbed research mission on beginner level would look like this:
ufo-c time-c ufo-type 0/0 1d s.Scout (start of game Research mission is 2.5h fixed time. This is for later ones) 1/0 1w m.Scout 2/0 1w l.Scout 2/1 3d l.Scout
Harvest
ufo-c time-c ufo-type 0/0 3d s.Scout 0/1 3d s.Scout 0/2 1w s.Scout 1/0 3d l.Scout 1/1 3d l.Scout 2/0 1w Harvester 2/1 3d Harvester 3/0 1d Battleship
Abduction
ufo-c time-c ufo-type 0 1w s.Scout 1 1w m.Scout 2 2w l.Scout 3 3d Abductor 3/1 3d Abductor 4 1h Battleship
Infiltration
ufo-c time-c ufo-type 0 2w s.Scout 1 2w m.Scout 2 2w m.Scout 3 2w l.Scout 4 3d l.Scout 5 1h Terrorship 6 1h Battleship 7 1h Supply 8 1h Battleship
after this, the mission does not end, but starts again with ufo 0 again.
Base
ufo-c time-c ufo-type 0 1w s.Scout 1 1w m.Scout 2 1w l.Scout 3 1h Supply 3/1 1h Supply 4 1h Battleship
if you shoot down the supplys the battleship will not come for several weeks and a retaliation mission is started.
Terror
ufo-c time-c ufo-type 0 2.5h* m.Scout 1 1w l.Scout 2 1w Terrorship 3 1w Terrorship
Each Terrorship will cause one terror mission, if it is not shot down before it lands.
sub-ufo-c is empirically always 0 for Terror acts.
Retaliation
ufo-c time-c ufo-type 0/0 50h* s.Scout 1/0 ? m.Scout 1/1 32h* m.Scout (add 146.5h* if 1/0 shot down at first turning point) 2/0 ? l.Scout 2/1 ? l.Scout 3/0 ? Battleship 3/1 ? Battleship
Zaimoni: Don't have exhaustive information on how these get initiated, yet. Per NKF, hyperwave detection capability can trigger this even without other X-COM activity. Before hyperwave detection, these aren't scheduled out of thin air. 0/0 time-c is for retaliation acts scheduled in response to shooting down UFOs.
Unlike the others, the onset times for these are not measuring as random at all. There may be variance between games, or other factors, but certainly no random variation for a given UFO.
Shooting down a UFO immediately after it slows down "post-entry" [within the same half-hour block] schedules these unreliably. (At least, this is about the only time I see it. Empirical probability...somewhere around/under 10%, don't have a large enough sample to be more precise.) The time that can elapse while still triggering this is not fully known, and may depend on prior BattleScape results and/or various aspects of the scoring system.)
Using the information
You might find that may small scouts appear at 2:30 on the first of a month. This is due to a often found count of 5 with the first ufo on a new terror mission for the month.
To make use of this knowledge might be difficult. But say, if you see a supply ship at a location without an alien base at the end of the third week of a month, it might be on a base mission. Then you should expect a second supply ship and a battleship somewhere close. If it is on infiltration you might see two battleships. If you see a first harvester/abductor, watch out for a second within three days. With a hyperwave decoder you might have more use from the mission sketches.