I've got a scene in a science fiction screenplay that involves a battle in orbit above a planet.  One of the ships in orbit fires a barrage down towards the planet's surface.  We follow the volley of fire all the way down from orbit, though the atmosphere, until it strikes its target.  In my mind, I'm picturing this is one long shot, but I don't like putting any camera instructions in my screenplays.  I'd rather just imply it through action.  The scene is short, so I've pasted it below.  I think the opening slug line is fine, but I'm a little bit bothered that by the end of the scene we're on the planet surface.  Should I try to squeeze another slug line in there?  Any suggestions?

EXT. OUTER SPACE - LATER

A battle rages in orbit above a glistening green world.
Three enormous cruisers versus a pair of much smaller
frigates.  The two frigates are trapped between the planet
and the cruisers.  No escape.

Barrages of ENERGY BEAMS.  Deflector shields flicker and
GLOW as the two sides trade fire.

One of the cruisers repositions.  It's main guns aim past
the frigates.  It has a new target, something on the planet
below.  Engine's dim as full power is dumped into the energy
cannons.

A massive volley is unleashed.  PARTICLE BEAMS race towards
the planet, slicing through the atmosphere, streaking down
towards the target - a forested mountain.

In an instant the mountain is gone, annihilated by the
orbital bombardment.

A BLINDING FIREBALL takes its place, the nearby mountains
dwarfed by the rising MUSHROOM CLOUD.

I think you'd be better off writing another slug in there, as it's a shift of location.  

EXT. OUTER SPACE - LATER

Battle sequence.  As the ships fire on the planet --

EXT. MOUNTAINOUS FOREST

Blinding fireball levels the forest. Mushroom cloud rises, etc.

Then shift back to outer space or wherever the next scene takes place.  Always have a slug in there, even if you're inside, using mini-slugs as opposed to full slugs whenever the scene demands it.

In this case, I wouldn't use two scene headings and would leave it up to the director to figure out how exactly to shoot it. What you've written is clear enough... that's all you need.