Aliens & Asteroids is a great, not over-large game focusing on combat-mission SF similar to movies such as ALIENS or STARSHIP TROOPERS. The game-system is named Inverse20, where you roll a d20 to get a number equal to or less than a Target Number (TN). Rolling a 1 (or the exact Target Number) is a Critical Success, rolling a 20 is a Critical Fail. Actions are sometimes taken with an Advantage, in which case you roll 2 d20s and take the most advantageous roll, or at a Disadvantage (roll 2 d20s and take the least advantageous roll). There can be only one Advantage or Disadvantage situation and, if you are somehow receiving both, they cancel out. This kind of scheme is familiar to players of D&D 5th-ed.

Characters are defined as belonging to the Dominion Space Forces. They have 7 basic physical and mental Attributes, determined by rolling 2d3 and adding 8. There are a few Secondary Attributes which are derived from the first ones. Characters also accumulate certain Traits, based on their planet of origin or career path. There are military soldier-type characters but also specialists in other careers who are essential to pulling off a successful mission. Soldiers get to go hog-wild with an assault-rifle, others get a handgun, but all may add special gear. Traits and gear may add to an Attribute-based roll or confer an Advantage. Not having the right gear, not having the right skill Trait, or situational problems might confer a Disadvantage to the roll. Damage is always figured in d3 or d6 rolls with modifiers, and some weapons have special effects. Armor resists damage, but if the Armor Resistance rating is overcome, Armor Points absorb the excess damage until the armor is worn away.

The Dominion setting and alien races are covered, and your characters are encouraged to read massive tomes on the Dominion's history and political structure, as they ride through a B.A.N.C.E. Gate to jump to the adventure. Okay, just kidding! Maybe all the characters care about is to be pointed to the right opposition and to fight it! Technology, drones (assorted robots), weapons and gear are covered, there is a chapter on Refereeing and guidelines to set up and run a set of missions, finishing missions, and levelling up. A few alien and creature stats are given with guidelines and tables on designing your own. There is finally a sample-adventure, "Graduation Day", where the graduation of a squad of fresh recruits graduating on Luna is interrupted, and they are asked to investigate strange goings-on nearby.

This is an effective, digest-sized 111-page book which does what it sets out to do. I managed to join an introductory teleconferenced game run by the main author, reconning a dead asteroid-base that stopped broadcasting, and our characters had a nervous exploration and restoration of the floors to find out the cause. Diverse character types meshed well, each playing their part. You get a lot of SF mileage from what the players put in, all the great stuff like gear and squad-banter from movies and TV shows.

So what are you waiting for, grunt? Crack open the airlock, drop the ramp, and let's have a Bug Hunt!