Felix:Anyway, UNSC ships aren't designed(I don't know how many times I can that) to fly in atmosphere, as they don't have anti-gravity.
Halo 3 Marine conversation- The Ark: "Is the Dawn rated for atmosphere?"
"I don't know, but we'll sure as hell find out."
This indicates that the UNSC has a rating system for whether a ship, Frigate, or Marathon Class Cruiser is able to survive and operate in a given planet's atmosphere. Even the Forward Unto Dawn was able to remain "airborn" in the Ark's atmosphere. To add onto this:
Cortana and Captain Jacob Keyes:
Cortana: "While you do what, go down with the ship?"
Captain Keyes: "In a manner of speaking. The object we found, I'm going to try and land the Autumn on it."
Keyes was known to have outlandish maneuvers that sometimes worked, but if he had intention to land on an object similar to Earth's atmosphere, then he would have had to know that it could be done.
Now, on the point of the Spirit of Fire.
We all know that ships have artificial gravity, allowing the occupants to move naturally in a Zero-G environment. This is probably done magnetically for ships in the Halo Universe, 500 years from now. So, what if, on the considerably sizable belly of the Spirit, was a series of gigantic generators that produced a magnetic field opposite to that of the planet surface beneath them?
The UNSC has already mastered space travel, high levels of space maneuverability, space-to-planetside ship reentry (as seen with Pods Shortswords, Longswords, and Pelicans) and lightspeed travel. Don't tell me that stabalizing a magnetic field to allow a ship- even one as large as the Spirit- the ability to hover above land. The field could be strengthened or weakened to attain different levels of height, and would keep the Spirit (and any other UNSC ship) well susspended above the ground.
On a side note- just something that I've noticed- nobody complains and groans when Star Wars or Star Trek does something like this.
Current Fan Fictions in the Library:ODST: Hellbound
The Interrogation of Ellen Anders
Halo: Archangel