Okay... Reading it now and making notes as I go along.
1)
INT. SPACECRAFT
--Even though your first opening scene takes place inside a spacecraft? You still need to let us know if it's NIGHT or DAY. I'm sure it'll be NIGHT (which simply means it's dark) but you still need to let us know.
2)
ASTRONAUT (35) sits in his space ship.
--This is redundant since you've already told us we're inside the SPACECRAFT. No need to tell us again.
3)
The astronaut reaches for the meal tray. He peels away
the aluminum foil.
--This could be even shorter... No need for "He." Just write something like: Astronaut reaches for the meal tray, peels away the aluminum foil. Or, the way I would personally do it:
Astronaut peels away the aluminum foil.
--Do we really need to see him REACH for it? If I was writing it? Nope. There's no RIGHT answer but I only mention it because it's little things like this that you can EASILY cut and LOSE NOTHING from your story and if you have sentences like these scattered all throughout the script? Might be wise to cut some of the fat.
4)
The astronaut takes a mouthful and chews. A blank look on
his face.
--Again, not really sure how this adds much to the story so since it doesn't FEEL like it does? Again, you could cut it down to something like this:
With a blank face, Astronaut chews his food.
Or
Astronaut chews his food with a blank face.
--Again, just showing you how you can cut this stuff way down to get your story to read much faster. If it's a good story and reads fast? The chances of it getting read ALL THE WAY THROUGH increase dramatically.
5)
In the distance, SPARKS dance about, emitting a faint GLOW.
An electric STORM replaces the black emptiness.
The astronaut stops eating, stupefied by the strange phenomenon.
--Okay... Well again, does your Astronaut need to actually stop eating? If he's stupefied by the strange phenomenon and then mutters to himself, hasn't he already stopped eating? I'll say this as I've said before in other posts/threads... If this is just a short you're writing to make yourself? No worries... Write it any way you want to write it because IN THE END? You obviously KNOW what YOU mean. But what I'm talking about here is more for those of us who write spec scripts. Maybe something like this:
As Astronaut stares into space, an electric storm catches his
attention. Sparks emit a faint glow.
ASTRONAUT
(muttering)
What the heck?
--Again, just showing how this can be trimmed down and still achieve what you want to depict.
6)
The lights and controls dim. The astronaut looks around.
Signs of distress evident within the space craft. Mild
shaking, items falling, sparking.
--To me? This paragraph is confusing which takes me out of the story for a moment. Why? For one thing, you've written: The astronaut looks around. Is he a character? Yes he is. So remember to Capitalize the first letter of his character name EVEN if you're now referring to him as just some astronaut because you've already introduced him to us. He's a character. Don't make him somebody else who's not important by now calling him "the astronaut." But that's NOT what I was confused by... Just mentioning it.
--What's confusing me is that you then write:
Signs of distress evident within the space craft. Mild
shaking, items falling, sparking.
--Signs of distress evident? No need to tell us that because NOW? Even though you followed up with "Mild shaking, items falling, sparking." -- You've set it up with signs of distress evident. I'm not an astronaut. I don't know what "signs of distress" actually are although, based on other movies, I could easily guess but that's what you're FORCING me to do here and hence, taking me out of the story for a moment so I can figure out what signs of distress are.
--I'm sure you've heard the old saying... "Show, don't tell." You're telling me first that signs of distress evident. No need for that. Just SHOW us what's going on inside the SPACECRAFT. Show us what's shaking. Show us what items are falling. Show us what's sparking. Make sense? Last but not least? You told us right at the beginning that we are inside a SPACECRAFT, not a space craft. A simple error but I point it out because in the end? Pick one way of spelling it and STICK with it throughout the script.
7)
--I'll mention this again... The Astronaut is your character. You don't have to always keep referring to him as "the astronaut." I assume he's your Protagonist, so you can dispense with the word, "the" and just call him Astronaut OR you could actually give him a better INTRODUCTION along with a NAME so we can identify with him a little more. Make sense?
--Since I'm reading a script and I keep seeing you refer to your Protagonist as "the astronaut," it takes me OUT of the story for an instant every time I see it because I know what I should be seeing is you refer to him as "Astronaut" or at the very least, "the Astronaut" instead of "the astronaut." Let's say you named this astronaut, JACK and then throughout the script, kept referring to him as "the astronaut." Do you see how that could be confusing? You've named this character, ASTRONAUT so when you then call him, "the astronaut," it's like you're now referring to his profession instead of his character. Confusing because it makes me WONDER WHY you're doing that when you should be referring to him by his actual character name. I know this may seem like I'm beating a dead horse but these comments are for EVERYONE, not just you... So I tend use longer explanations. Hope that makes sense.

The cabin goes dark -- warning lights and sounds fill the
space ship. A trickle of blood appears under the astronaut’s
nose.
--I actually like this except for "and sounds." What sounds? When you force us to come up with the sounds? It takes us out of the story for an instant because each one of us has to come up with our own idea of what sounds we might be hearing. This is YOUR WORLD, not ours. So because it's YOUR WORLD? It's up to YOU to show and tell us what sounds are filling the space ship... Or? Do you mean, spacecraft? LOL.
9)
The astronaut screams ... his eyes roll behind his head ...
he collapses and is out cold.
--I've never heard or read "his eyes roll behind his head" before. Are you saying his eyes are rolling back? That, I've heard. That, I've read. I know eyes cannot roll behind someone's head but I still got that visual when I read it and it stopped me cold. I know what YOU MEANT but you can't rely that we will ALL KNOW what you meant.
Astronaut screams. His eyes roll back and he collapses out cold.
--Your use of ellipses in your action sentence is confusing. The ellipsis usually signifies either a short pause or a truncated quote. I know you're not truncating a quote... I would think this is all happening quickly so I don't understand why you used them.
10)
Okay... You started doing the same thing with HUMANOID that you did with ASTRONAUT. You introduce him as HUMANOID, then immediately refer to him as "the humanoid." Same comment as above.
That's all I can do for now... This took over an hour. I'll get back to it when I have the time and continue on.
Good luck with it!