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

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.  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

If you shoot the first Terrorship, the second is going to come 2w later. If you shoot the second Terrorship, the terror-site will not happen.

sub-ufo-c is empirically always 0 for Terror acts.

Retaliation

ufo-c	time-c	ufo-type
0/0	3d      s.Scout
0/1	?	s.Scout (unreliable, criteria for skipping not diagnosed...fast shootdown of predecessor suspected.)
1/0	?       m.Scout
1/1	?	m.Scout
2/0	?       l.Scout
2/1	?	l.Scout
2/2	?	l.Scout (unreliable, criteria for skipping not diagnosed...fast shootdown of predecessor suspected.)
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.

Shooting down a UFO immediately after it slows down "post-entry" [within the same half-hour block] schedules these fairly reliably. (At least, this is about the only time I see it. Empirical probability...somewhere under 50%, 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.