Okay. Lunar Reactor, again, "chasm room".

Note: Actually, during the time I was typing this in, something came up that has radically simplified how I imagined this setup to play out. I will still type in everything I initially intended to, and I will leave the new development to the postscript.

Anyway.
Following ventilation shaft from the crusher room, you emerge on the ledge (1), the crusher closes your way back. You dispose of a turret, a single trooper,  and then notice someone is shooting you from below. You look down, notice ledge (2) lit with a blue light, that has three enemies shooting from it. You  dispose of them. You explore ledge (1), possibly find a secret, containing some ammo and a medkit for 30hp.

Hopefully, this setup reminds you of the similar looking setup from Fusion Station. Similarly to how you managed to save steroids for the jump THERE, you  managed to save a bottle of steroids (the only one in the level, no less) all the way from the bathroom, through the encounter with battlelord, crew quarters,  even the room with the crusher possibly even going for that secret with the two atomic health, all the while resisting the urge to use the damn thing already.  Now is clearly the time to pop it open just like that time on a Fusion Station.
There is a discrepancy though. On Fusion Station, you had to look down all by yourself, and to notice the platform with the jetpack all by youself. Here,  however, your attention was drawn to this ledge (2), it is closer, and brightly lit, making it easier to notice. Everything about this seems like a repetition  of setup from Fusion Station, just in a more primitive manner. Still, on Fusion Station you did have to look down all by yourself. What if you look down all  by yourself here, I mean, even more down than you are already looking.

So, you get right to the edge of the ledge (1), you look down as hard as you can, and you notice that way below, the rockface has some sort of opening. Firing  your weapon discloses, that that opening happens to have a floor to it too. We'll call that opening (3). By the way, please, do notice the protrusion on a  rockface, separating ledge (2) and opening (3). Due to that protrusion, anything about opening (3) isn't visible in any way from any point on ledge (2).

You steroid-jump to the ledge (2) (Note: or maybe you don't, see the postscript, however the way I describe is a continuation of what Fusion Station  introduced, it makes more sense to me personally as of this moment), there is ammo, there is yellow keycar, steroid timer keeps ticking down. You think "that  opening (3) was afar from ledge (2) all the way around that protrusion, it might just be that just walking towards it would end up being not enough, and I  don't know whether I'll manage to find another bottle of steroids further in the level, so it would make sense to use this opportunity". So, while steroids  are still ticking down, you steroid-jump again, or maybe not jump, just move under steroids, around that protrusion (you have air control that allows for  that), and you land on its lip. There is a cave with a Luke Skywalker gag. In that cave there is a shrinker, picking of which up spawns three octobrains that  immediately fly into the cave from the outside and get disposed of. The far wall of the cave seems a bit strange, you try to open it up, it opens, there is a  teleporter, you take that teleporter, you emerge in a closet, there is a teleporter presumably back and there is a button on its wall, you push it, door  opens, you find out that closet is situated on the ledge (1), so you are currently on the ledge (1) again. Difference is, now you don't have that pack of  steroids still ticking down.

So, now you have a choice. You can either exit the closet from a door, the door closes behind you, it won't open from the outside, there are no more steroids  on the level, provided you don't run, the opportunity is gone (or not, see the postscript below). Or you can think that there is something still off about  this situation, and it's not a given you'll be able to return from this closet from the outside or to the cave the way you did the first time around, so you  turn around, get back to the teleporter, and emerge back in the cave. By that time, the shrinker is picked up, shrinker ammo is also picked up and the  octobrains all somehow disposed of. You get back to the opening, you get right to the edge and take a look down, on a whim. You see nothing but the perfectly  vertical rock walls. Then you say "fuck it", crouch at the lowest point of the opening and jump down. Provided you have 61 or more hp (less if you have some  armor) you miraculously survive (you can get by with 58 hp provided enough savescumming, but 61hp guarantees your survival) and you are now at the bottom of  the chasm, where you find the jetpack. If you jump from ledges (1) or (2), you die even when having 200hp/100armor.

Now, let's talk numbers. Ledge (1) has a medkit for 30hp and the way back is closed by the crusher. Let us suppose that after using this medkit, if need be,  you end up having 100 hp, 0 armor, just for the argument's sake. Now, let's see whether this is enough to survive all the way down to the bottom of the chasm.  You have 100 hp, by jumping (walking under steroids isn't enough to make it to ledge (2)) to ledge (2) you lose 12/16hp (provided you don't land exactly on  the edge, which is a bug anyway), which leaves you with 84/88hp (86hp on average). Walking under steroids from (2) to (3) costs you another 26/30hp, which  leaves you with 54/62hp (58hp on average). If you jump, that number will be higher, so don't. And jumping down to the bottom of the chasm relieves you of  57/60hp (56/60 would make more sense, but whatever, maybe I just didn't luck out for that) leaving you with (-6)/5hp (-0.5 on average). Will you survive from  100hp/0armor? Short answer: fuck knows. Longer answer: depends on a system timer.

Now, to the POSTSCRIPT: you can just walk to the opening (3) from ledge (1) and get to it without either running, jumping OR EVEN USING STEROIDS. You end up,  provided you start with 100/0, with 60hp at worst, probably like 62 hp. If you have 60, you can still die from the jump to the bottom of the chasm, you have  any more than that, you are guaranteed to live. The difference between this case and the aforementioned is in that jumping required to get from ledge (1) to  ledge (2) costs you something like 2hp. Also, having an extra fall introduces one more +/-2 random factor to the mix. Regardless, that this course of actions  is possible, might be an overlook, might not be an overlook, I have no way of knowing. All I know, is that the first course of actions I describes maked sense  to me in the context of the levels arguably preceding this one, and the one from this postscript - doesn't really.

And this sense I was talking about, goes something like this. Dark Side: any aspect of perceived reality is always more complex than you currently imagine it  being, no worldview is exhaustive and nobody is infallible. Fusion Station: what the leads to is that from time to time you will grossly miscalculate through  no fault of yours simply due to overlooking something that ends up being crucial in your situation, due to a simple lack of relevant experience in your past.  Due to that it might, among other things, just pay off to always be ready for the worst thing LIKELY to happen in your current circumstances. Lunar Reactor:  that having been said, if you start to systematically grossly miscalculate, it is because the things around you don't really interact in the way you imagine  to, so in order to get your feet back to the ground, you sometimes just HAVE to experiment, knowing full well that the end result of your actions will NOT be  what you will imagine it being. As such, any experiment has an inherent risk connected to it, something, even if not immediately apparent, being put at a  stake, and you better be okay with the possibility of losing that stake for good. That having been said, IF you are experimenting at a given moment, you just  might follow it ALL. THE WAY. DOWN. provided that the stake stays roughly the same. Halfassing your experiment, you don't do yourself any favors, you just  squander an opportunity to learn something the previous omission of which necessitated the experiment in the first place. If you go off the beaten (for you  and for anyone else) track and start r&d-ing, you might just as well try to wring absolute maximum possible information out of it (even if that means putting the SAME stake under MORE possible risk).