PARIS — Russia’s plans to have 24 healthy Glonass navigation satellites in orbit by the end of this year have been scrapped with the decision to delay the launch of the next three satellites, already postponed from September, until February, the Russian space agency, Roskosmos, announced Sept. 21.

The launch of the three Glonass-M spacecraft aboard a Proton rocket from Russia’s Baikonur Cosmodrome in Kazakhstan had been scheduled for late September but was canceled just before the launch following discovery of an unspecified defect in one of the three spacecraft.

The launch was rescheduled for late October. In its Oct. 21 statement, Roskosmos said additional work needs to be done to assure the reliability of the satellites.

It was not clear whether a planned December launch of three other Glonass spacecraft will remain on track or will be delayed for the same reason.

The current Glonass constellation features 18 operational satellites in medium Earth orbit. A fully operational constellation requires 24 satellites, a goal that Russia has been working toward for several years as it slowly rebuilds the system, which has suffered from neglect in recent years.

Roskosmos announced Oct. 22 that Russian companies continue to make progress in designing global navigation satellite system receivers capable of capturing signals from four satellite systems — Glonass, the U.S. GPS and the future European Galileo and Chinese Beidou/Compass constellations.

Peter B. de Selding was the Paris bureau chief for SpaceNews.