Orbital ATK [OA] is designing a third stage to be integrated on United Launch Alliance’s [ULA] Delta IV Heavy rocket for a future NASA mission to study the sun’s atmosphere.

The companies announced a teaming agreement April 3.

Orbital ATK’s third stage will combine its STARTM 48BV rocket motor with avionics, inertial navigation, attitude control and separation systems used in on the company’s Pegasus, Minotaur, and Minotaur-C launch vehicles. The STAR 48 series has been employed in 130 missions since the first motor was introduced in the 1980s.

The newly-designed third stage will be critical for NASA’s Solar Probe Plus mission to send a spacecraft closer to the sun than ever before. The mission, scheduled to begin in 2018, will launch a craft into the sun’s outer atmosphere to study the energetic particles emanating from it. Johns Hopkins Applied Physics Laboratory is developing the spacecraft.

Once separating from the launch vehicle’s second stage, Orbital’s third stage motor will accelerate the spacecraft, propelling it into the corona. The flight computer and guidance system will direct it into an elliptical orbit around the sun even closer than the planet Mercury.

The third stage will be developed at Orbital ATK facilities in Virginia, Arizona and Maryland. The company estimates it will measure seven feet tall and four-and-a-half feet in diameter.