The final Titan rocket to fly from Cape Canaveral, originally scheduled for this past weekend, is searching for a new launch date after encountering trouble with balky ground equipment.

Liftoff of the Lockheed Martin Titan 4B booster from Complex 40 carrying a classified national security payload was supposed to happen sometime between 8 and 10:30 p.m. EDT Sunday. But difficulties loading storable propellants into the first and second stages earlier this week forced delays to Monday, then Tuesday and now the Air Force has no official target date selected.

Problems cropped up when technicians were preparing to pump Aerozine 50 fuel -- a mixture of hydrazine and unsymmetrical dimethyl-hydrazine -- and nitrogen tetroxide oxidizer into the two stages. But gremlins in the ground equipment scuttled the timeline.

"We've had a couple of hardware issues with our ground support equipment that has just caused us some delays," Ben Dusenbery, Lockheed Martin's director of Titan launch operations at Cape Canaveral, said in an interview last week.

The first and second stages have since been filled with the Aerozine 50 propellant. However, problems with the hardware used for loading the nitrogen tetroxide have persisted.

Officials noted that the glitches reside in the pad systems and not the Titan 4 rocket itself.

"It is amazing -- the rocket sits there and it is darn ready to go, but we have a couple of ground issues we have to work through," Lt. Col. Jimmy Comfort, commander of the 3rd Space Launch Squadron at the Cape and the Air Force launch director, said in an interview.

"The good news is it is not flight hardware," Comfort added. "It is actually our propellant loading unit on the ground we are trying to work through."

"Pretty minor items but aggravating (when) trying to maintain a schedule," Dusenbery said. "The customer has been very understanding. They want us to when we are ready to go -- no sooner, no later. They are not pressing us hard, they are trying to be very understanding and cooperative."

This launch will place a secret cargo into space for the U.S. National Reconnaissance Office, which is the government agency responsible for the country's classified intelligence-gathering spacecraft.

The rocket features no upper stage kick booster, such as a Centaur or Inertial Upper Stage that were used in many past Florida flights. It will take just 9 minutes, 30 seconds for the vehicle to propel its clandestine payload into a highly-inclined orbit on the combined power of the liquid-fueled first and second stages and a pair of strap-on solid rocket boosters.

The $411 million rocket will be the 27th and final Titan 4 to launch from Cape Canaveral and the 168th overall in the almost 50-year history of the Titan family dating back to the Titan 1 intercontinental ballistic missile.

California's Vandenberg Air Force Base plays host to the planned July 10 liftoff of the last-ever Titan 4, which will send the Titan name into retirement. That mission carries an NRO spacecraft, too.

As the most advanced and powerful of the Titan program, the Titan 4s have been around since 1989, lofting hefty military and spy satellites and even NASA's Saturn-orbiting Cassini spacecraft.

The Evolved Expendable Launch Vehicles now in service -- Lockheed Martin's Atlas 5 and Boeing's Delta 4 -- were built to replace Titan 4 as the primary way to launch large payloads into orbit. The new rockets are meant to be far more affordable.