Simple question. Is it ever explained how the Tet succeeded in destroying the moon ? I can't recall this being explained.
We are never given the official path to the moon's apparent destruction. We know the alien invaders are somehow responsible, mining the moon, apparently destructively, before turning their attentions toward invading the Earth.
The IMDb Oblivion synopsis provides us with:
In the year 2077, Jack Harper (Tom Cruise), is a drone technician living in a tower high above the clouds, with his assigned partner Victoria/Vika (Andrea Riseborough). They are the last people left on Earth after it was destroyed by aliens known as the Scavengers/'Scavs', who wanted Earth's resources. The Scavs destroyed Earth's moon for material resources, which caused a series of natural disasters and global devastation, then they invaded.
The destruction of sections of the moon was supposedly a prelude to the alien attack on the Earth.
Given the ability to destroy as much of the moon as they did, the resulting debris should have showered down upon the Earth creating fantastic devastation from earthquakes to tsunami rendering a good portion of the planet unpleasant to live on, at best, a nightmare of catastrophic proportions at worst. Humanity would be poorly equipped to resist an alien invasion with its most populous cities underwater or smashed by tidal waves from falling moon debris.
However, the movie's design artists fail to take account of the natural movement of matter in space, the remnants of the moon after sixty years should have taken up a ring like position around the planet.
Not to mention how the chunk of moon to the far left got there. An explosion would have sent such a fragment UNDER the moon from our perspective. The only way you get a piece over to the left was to hit the moon from the far right of the image implying an attack from OUT THERE somewhere.
I suspect the real reason for this element is to give a single, startling image that says "Toto, we're not in Kansas anymore." The goal of that blasted moon is to signify life as we knew it was over. If they had gotten the physics right, I would have been less put off by the picture.
It wasn't explained in the movie how or why. Further, I'm not sure the tidal disturbances supposedly caused by the moon's destruction really hold up. It was clear in the film that most of the moon was still in orbit around the Earth. If most of that mass is still basically in the same place, the tidal disturbances, if any, would be minimal.
It was most likely a deuterium-based fusion bomb.
This interview with Oblivion's Writer/Director describes the mission of the Tet aliens as being part of a scheme to steal Earth's seawater for it use in their fusion energy generators:
The notion of heavy hydrogen or deuterium existed in our seawater as being a very special thing in the universe. Heavy hydrogen is an element that exists in very trace amounts in our seawater, and it's used to create kind of the purest form of fusion energy. that's one thing that makes Earth valuable, that energy source.
and the film's draft script confirms that the element that really packs a punch is the Deuterium found in seawater. The aliens use it to power their ships and the drones:
The Gatherer is sucking up salt water, harvesting the elements essential to create DEUTERIUM, "Heavy Hydrogen.". At the top of the giant machine, Drones work tirelessly, ferrying containers of Deuterium energy up into the sky. Jack raises the Binocs, snaps a few photographs...
He turns to find that the ROVER is already there, a DEUTERIUM FUEL CELL sitting in its payload bay.
Under the circumstances, we could reasonably expect an alien civilisation with the ability to create fusion energy to generate power to also have the ability to generate a fusion explosion using much the same technology.