Saucer by Stephen Coonts 2002 Saucer & The conquest 

Saucer
A relic from the past. A bridge to the future.

After 140,000 Years...
Seismic Surveyor Rip Cantrell has made an exhilarating discovery-a flying saucer embedded in the Sahara sandstone. Buried for eons, it's not the invention of modern man. Computer-equipped, it can't belong to ancient man. Rip's betting his life on the only alternative. If the ship's memory bank holds the proof he needs, it's going to rock civilization, and make Rip a very famous man.

Its Time Has Come.
Once the secret's out, Rip's outwitted by an enterprising billionaire set to steal the saucer's profitable technology-and outnumbered by the Libyan army looking to lay claim to history. But it's in a skeptical UFO investigation team that Rip finds an unlikely ally: test-pilot Charlotte Pine. Together, they come up with a plan to protect the saucer's secrets.

But Where In The World Is It Going?
Under a hail of bullets, in an exhaust of white fire, Rip and Charlotte are off. Accelerating on a fantastic journey across continents and oceans, they're about to experience the mystery of what once was, and explore the possibilities of what could be, on an adventure 140,000 years in the making.

The conquest
Bestselling author Stephen Coonts took fans by surprise with the phenomenal and heart-pounding tale of Saucer. Now Rip Cantrell and Charley Pine are back for seconds with with Saucer: The Conquest.

Someone is using top-secret information about saucer technology, information that comes from the mysterious top-secret region in Nevada known as Area 51. Meanwhile, Charley takes up flying space planes to the moon for the French lunar base project. There she discovers a madman and a world-threatening antigravity beam…

When Charley sees how high the stakes are, she needs the kind of help that only Rip can bring her—by prying his saucer out of the hands of the U.S. Government and hurtling it toward the moon...

A furious duel is in the offing between a megalomaniac bent on the conquest of Earth and a handful of runaway heroes. As a plot that reaches back 50 years explodes, a horrific weapon is trained on the Earth's cities; humankind is dragged to the brink and offered a fearsome choice: surrender or death...