The launch of Delta IV Heavy rocket is pushed back yet again to a 2019 date. The schedule is scrubbed four times after experiencing a series of technical and weather-related issues.

The Delta IV Heavy rocket will try again to launch early January next year from Space Launch Complex-6 at Vandenberg Air Force Base in California.

The rocket's launch is scheduled no earlier than Sunday, Jan. 6. The exact time of the liftoff has yet to be announced. The major reason for postponing the launch was that there were "indications of elevated hydrogen concentrations within the port booster engine section."

Delta IV Heavy Rocket Mission

The United Launch Alliance will use Delta IV Heavy rocket to launch the (NROL-71) mission for the United States National Reconnaissance Office (NRO). The NRO is the organization in-charge of United States fleet of reconnaissance and intelligence-gathering satellites using a different type of spacecraft and surveillance techniques to support national defense and security.

Regardless of the classified nature of their operations, however, the nature and purpose of different satellites were made known from combined information from NRO itself and other government sources, leaks, and observation of the satellites' orbits.

Also, an analysis of hazard areas is published for maritime and aviation safety ahead of each launch including a comparison of the type of rocket to be used to those that have orbited previous satellites. By having this information, most NRO satellites can be identified before they lift off into space.

For example, prior to the release of the details of the launch and hazard regions for the NROL-71 mission, satellite enthusiasts believed it was a safe bet that the launch would add a new member to the NRO's fleet of Crystal imaging satellites.

KH-11 Spacecraft

Key Hole 11 (KH-11) spacecraft, formerly codenamed Kennen, also collect high-resolution images of the Earth's surface and send them back to the ground for analysis.

The KH-11 was originally developed in the 1970s and have been upgraded since. It is one of the biggest satellites the NRO operates. Delta IV Heavy, one of the most powerful rockets of the United States, had placed the mentioned spacecraft into orbit.

The Delta IV rocket has served the country's top-priority U.S. Air Force and National Reconnaissance Office space programs since 2002. It also launched NASA's Orion capsule on its initial orbital test flight and sent the Parker Solar Probe on its journey navigating through the sun's atmosphere.