Why are you using a "laser"? There are better ways to do space based weaponry. The below assumes that you are expanding the falling damage rules to be more inline with real physics.

Step 1: Turn etheral and head down under a mountain a ways.
Step 2: Cast a transdimensional disintegrate to make a cave. Cast disintegrate repeatedly until you have a 20x20x20 foot room.
Step 3: Fill a bag of holding with adamantium.
Step 4: Shapechange into a golem
Step 5: Use Fabricate to turn the adamantium into a hollow column that has a hollow section 15 meters long and 5 wide in the middle and walls 1 foot thick. 5 meters from the bottom should be a small shelf that sticks out an inch or so and runs around the entire column.
Step 6: Use greater teleportation to teleport the acceleration chamber, standing vertical, into its hole.
Step 7: Use Stone Shape to make a base that will hold the acceleration chamber firm.
Step 8: Create a small construct using the feat Rudimentary Intelligence to give in an Intelligence score.
Step 9: Cast Telepathic Bond on the construct.
Step 10: Make the bond permanent.
Step 11: Teleport the construct into the bottom of the acceleration chamber.
Step 12: Give the construct a ring gate on a 5 foot tall metal pole.
Step 13: Use Soverign Glue to glue a ring gate to the top of the acceleration chamber (not linked to the constructs gate, and so that items come out the end pointing down and from now on referred to as RG 2).
Step 14: Cast Teleportation Circle on the shelf, it should teleport to right below the top of the acceleration chamber.
Step 15: Make it permanent.

Ammunition:
Step 1: Create an adamantium missile that weighs less than 100 pounds.
Step 2: Use Animate Object to animate the missile.
Step 3: Make Animate Object permanent.
Step 4: Use Craft Contingent Spell to put a contingent Energy Immunity (Fire) spell on said object with an activation condition of "Touches air after the phrase "Arm Missile Number (Insert missile number here)" is spoken and then not touching air for at least 30 seconds.

Arming:
Step 1: Select a missile and speak its arming phrase.
Step 2: Drop the missile through the ring gate linked RG 2 one.

Firing:
Step 1: Place the ring gate linked to the one the golem has above your target
Step 2: Order the golem in the bottom of the acceleration chamber to raise his ring gate up through the teleportation circle.

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There you go. You can accelerate the missile up to significant fractions of the speed of light. If you want more shots per day just use missiles that weigh less.

Now if you aren't using expanded terminal velocity rules it is a lot easier.

Falling damage maxes at 20d6, and so does the damage something takes when being hit by a falling object.

Step 1: Create a frame that is 17 feet tall and can hold 4 ring gates. The 2 at the top are stacked on top of eachother with the side facing down being the active side. The 2 on bottom are also stacked on top of each other but with the side facing up being the active side. The 2 ring gates in the middle should be linked to eachother. The distance between the 2 in the middle should be 15 feet.
Step 2: Turn etheral and head down under a mountain a ways.
Step 3: Cast a transdimensional disintegrate to make a cave. Cast disintegrate repeatedly until you have a 20x20x20 foot room.
Step 4: Shapechange into a golem.
Step 5: Teleport the frame into space.
Step 6: Use Fabricate to create an airtight sheath for the frame.
Step 7: Teleport the acceleration chamber into the excavated chamber.
Step 8: Create a 1 pound ball of adamantium.
Step 9: Drop it through the ring gate linked to the very top gate in the acceleration chamber.
Step 10: Have the gate linked to the very bottom gate in the acceleration chamber pointed at your target.

There you go.
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Now if you want KEW platforms I will get into creating orbiting satellites in my next post.