We played our first game in around 13-15 years with aerospace a couple of weeks ago. We have an ongoing RPG campaign in which the PCs are mercs in a 'Mech unit, like you do. A returning player from years ago asked if he could play an Aerojock. He created the character, got himself a fighter, and wingman in a matching fighter, and the company commander had the unit purchase four Mechbusters to deploy once in atmosphere. We decided we would use the "Radar Map" rules.
To keep things simple for the first game, the scenario was a surprise attack on an outlying outpost where the Kurita defenders didn't have time to scramble any air cover in response. It was on its way when the scenario ended. Due to the rules for movement on the radar map, starting the fighter's approach on the outer ring, the aerospace forces got two passes before the PCs pulled out, having accomplished their objective of hitting the outpost hard enough to force the Kurita defenders to send more forces to garrison it later.
Those two passes went like this: ASFs strafed, and missed. Two Mechbusters, all they brought in, leaving the other two back in the cargo hold, executed a strike. One miss, one hit... and rolled a 12 for location. BOOM. Headshot. This made all the PCs sit up and take notice of what enemy air power could do to them if and when it showed up. The funky rules on counterfire meant the one Kurita anti-air 'Mech, a Rifleman, was unable to hit the fighters as they flew over due to it being on the other mapsheet, and altitude adding to range.
After they turned around for another pass, the fighters all missed their attacks, but the Rifleman scored a hit with a single AC/5 thanks to the Anti-Air quirk. The 5 points was above the threshold, the pilot made his pilot check, failed, and rolled for altitude loss. LAWN DART. The PCs now took notice that even hitting most aircraft with a relatively light smack could immediately end them. The PC involved burned an edge point to re-roll, but the point was made to the players.
Our consensus after this trial game was that aerospace added a lot to the feel of the battle, but did take a bit of emphasis off 'Mechs. This was counterbalanced by the fighters being just as fragile as they were hideously effective when they actually hit. We discussed how things could have been more complicated by enemy aircraft, underwing ordnance, etc. and how the full-on mapsheet-for-fighters game would have worked. We talked about anti-air, and how to try to defend against fighters. The fighter player brought up fuel expenditure and loiter time over the battlefield, which he found shockingly limited for an ASF, but adequate for the air-breathing Mechbusters. I need to re-read these rules myself.
The debrief resulted in the players wanting to keep aerospace as part of our games, but stick to the radar map to keep the rules overhead as light as possible. The fighter player agreed.
I'd say the lack of popularity is more due to the rules complexity, and fragility of aerospace for the person playing them. If you want to be low enough to strafe or strike, you're risking being a lawn dart if anything bigger than an SRM hits you in most locations. The rules are also scattered, and in some cases make little sense, like the hex you count range to if you're not in the line of flight if you're conducting ground-to-air fire.
We had fun, but man, it's taking a while to knock all the rust off the rules.
