WASHINGTON — International Launch Services confirmed Dec. 28 another delay in the return to flight of its Proton rocket, but said the latest delay is not related to a problem on the vehicle’s previous launch in June.

The launch of EchoStar 21, a 6,900-kilogram spacecraft for Colorado-based EchoStar, was previously scheduled for Dec. 22 before slipping to Dec. 28. On Dec. 23, Proton manufacturer Khrunichev announced another delay in order to perform checks on the launch vehicle. Moscow-based Khrunichev, which owns ILS, offered no additional details at the time regarding the delay.

In a statement released Dec. 28, ILS said there is no new date for the EchoStar 21 launch, which is now unlikely to happen in 2016. In response to SpaceNews inquiries, ILS spokesperson Karen Monaghan said that this latest delay is not related to a problem during the Proton’s last launch on June 9, during which the rocket successfully delivered the Intelsat 31 satellite to orbit but suffered a premature shutdown of one of its four second-stage engines.

Khrunichev said in a Dec. 26 statement that the company plans to continue testing the rocket. Barring an unlikely immediate resolution to the issue, Proton will have performed only three launches in 2016 — Eutelsat 9B, the ExoMars 2016 mission and Intelsat 31 — compared to eight in 2015 and 10 in 2014.

Caleb Henry is a former SpaceNews staff writer covering satellites, telecom and launch. He previously worked for Via Satellite and NewSpace Global.He earned a bachelor’s degree in political science along with a minor in astronomy from...