I'm about to run a session tonight (fingers crossed) set on a dilapidated space station. I'm fairly certain that one of my players will at one point in time attempt to throw grenades in a zero gravity environment. I'm definitely going to put in a healthy number of setback dice to the attempt, but I'm wondering if the maximum range of the throw can be increased?

Depends how complicated you want to make it. A zero-g environment could certainly justify increasing the range, but there are complications as well. If you set the grenade to go off on a timer, how do you make sure it's going to be close to the target? You can't just bounce it to a stop, so you'll gave to try and throw it at just the right speed to go off as it passes the target, and if you get the timing wrong then who knows where it'll go off? Or you can set it to go off on impact, but if the target's not close to a convenient surface you can throw the grenade against, then you've got to hit the target directly. Shenanigans, either way.

I don't see why not given that it only works in that specific environmental hazard. Sounds like a fun thing. I might treat it like the talent Sniper Shot; increase the difficulty by one, give him an extra range band, otherwise follow the rules for zero-g; adding 2/3 setbacks.

My follow-up question is what do you do with a high gravity environment if it comes up later? Does the range decrease? If he's going from Short to Engaged, that's going to basically invalidate his grenades for the encounter unless he's got really specific talents. That question makes me rethink allowing an increased range in zero-g.

Great question!

Nah, I wouldn't increase the range. Zero-G is a different animal: there would be no arc, no bounce, only an extremely precision throw which increases exponentially in difficulty the farther out you get. Use the rules as written, and if they wanna try for a long-range throw, there's either the Strong Arm talent, the Sniper Shot talent, or the "impossible task" rules (spend a Destiny Point to make a Formidable check). Any way you slice it, the rules have you covered.

Upgrade and/or add some setback dice and use any Threat to have unpleasant things happen; for example, grenade goes this way, you go that way, hitting the wall face-first hurts.

I would just make it an automatic Upgrade, no Destiny Point flipped. If that Despairs shows up, they didn't throw it fast enough to get it out of their range, or maybe they did, but in the zero g, the shrapnel moves farther and the blast effect is larger than they anticipated, and they get hit too. Maybe decrease the advantage needed to activate blast by one.

I'd let them increase the range, with the understanding that you're adding Red's instead of Purples for difficulty dice....because bouncing grenades are fun.