I think this movie may be Star Command, also known as In the Fold, a 1996 UPN TV movie originally intended to be a television pilot.
A crew of freshly graduated space academy students find themselves in combat with opponents from breakaway Earth colonies after their training officers are killed in an attack.
A crew of space navy cadets on a training mission find themselves forced to fight an enemy fleet for real. They lose their senior officers in the opening battle, then through luck and guile try to defend a helpless colony.
ID question on external site that led me to this movie:
Well, this was shown on TV long, long, long ago- in the 90's(?). I can't recall the tittle, or actors that well.
It was a science fiction movie, spaced based. I think the "commanding officer" was a well known actor and the "XO" was on Knots Landing (female).
Any how, the plot goes like this. The ship, a corvet (spelling), gets a bunch of academy cadets for a cruise. But, they end up getting redirected to go investigate something, somewhere. (I know, sounds like Star Trek, but it's not). They travel by folding space or folding is what they called it. Any how, they end up in a battle, the XO is killed when the weapons pod she is in is blown off the ship. And the CO goes down the hall to do something and is killed, gets impaled in some wreckage. A cadet goes to find him, sees him dead and removes his command key (or what ever).
Well, this leaves the cadets in charge. One of the unlikely cadets ends up taking charge. During the battle, they have to land to make some repairs. While out on the ice planet/commet or what ever, one cadet chooses to try to take off, while others are in the exaust port making repairs. Well, they stop him, and hold a court marshal. Before they can pass sentance, the cadet charged hangs himself.
The corvett has to defend and outpost that is being attacked by other humans. The attackers want to claim and "colonize" the planet for them self, but can't do that since someone is there. They end up defending the planet by using 'odd' methods. One was by pulling asteroids/rocks and letting it go infront of the enemy ship. When they are down to one enemy ship left (the flag ship none the less), and the last missel they fire doesn't destroy it, the cadet in charge orders ramming speed. But before they can, the fleet arrives to save them.
Since it is damanged heavely, the fleet admiral suggests that the ship be sun scuttled. The cadets talk him out of it and a new CO is assigned. The new CO tells the cadet that it is hard to start taking orders once you've been use to giving them.....
Some Youtube movie clips.