PARIS — The February explosion of the upper stage of an International Launch Services Proton-M rocket in low Earth orbit created a debris field with an estimated 1,000 pieces large enough to be detected from ground radars, according to a preliminary NASA estimate of the event.

The event — one of the more serious debris-creating explosions in recent years — has been overshadowed by the even larger debris field created in January when the Chinese military intentionally destroyed a retired Chinese weather satellite with a ground-launched missile in a test of an anti-satellite system.

The Chinese action, whose consequences still are being assessed by NASA and the U.S. Defense Department’s Space Surveillance Network of ground radars, scattered an estimated 35,000 objects of at least one centimeter in diameter distributed between 200 kilometers and more than 4,000 kilometers in altitude, according to NASA’s latest estimate. Of these, more than half are orbiting at altitudes higher than 850 kilometers, guaranteeing that they will remain in orbit for decades.

The international space station, the U.S. space shuttle and numerous meteorological and other Earth observation and scientific satellites operate at these altitudes, and the danger posed to them increases with every new debris-creating event.

February was a particularly bad month, according to the NASA publication Orbital Debris Quarterly News.

A Chinese Bedou navigation satellite, intended to operate in geostationary orbit, suffered a partial failure Feb. 2, spewing 700-1,000 pieces of debris, distributed between 195 kilometers and 41,775 kilometers in altitude. The satellite at the time was in a transfer orbit after separation from its launch vehicle. China has not fully explained what happened with the satellite but its government press service has said the satellite survived the incident and has since climbed into operational orbit, where it is functioning.

Kira Abercromby, a spokeswoman for NASA Johnson Space Center, home to the agency’s orbital-debris analysis team, said the Chinese apparently “have managed to put the Beidou satellite into a geosynchronous orbit, but not a geostationary one. So there was a debris event, but apparently it did not totally disable the spacecraft.”

On Feb. 14, the upper stage from a Russian Proton rocket, which was a remnant left over from the November 1997 launch of a Russian government Coupon communications satellite, broke into 60 observable pieces while in an orbit of 260 kilometers by 14,160 kilometers. NASA said the likely cause is residual propellant in these Proton stages.

In the third debris-creating incident, the retired China-Brazil Earth Resources Satellite-1, CBERS-1, broke into about two-dozen pieces Feb. 18 at an altitude of between 770 and 780 kilometers.

The Proton-M event Feb. 19 caused the most serious debris after the Chinese anti-satellite test. The Proton-M’s Breeze-M upper stage had been abandoned following a February 2006 launch failure in which the Arabsat 4A telecommunications satellite was lost following the Breeze-M’s failure. The 2,370-kilogram Breeze-M stage, measuring 2.6 meters long and 4 meters in diameter, was in an elliptical orbit with a perigee of 495 kilometers and an apogee of 14,705 kilometers.

“The cause of the breakup is assumed to be related to the propellants remaining on board the stage after the engine failure,” NASA said in its assessment of the event. “As recommended by many national and international orbital debris mitigation guidelines, spacecraft and launch vehicle components should be passivated at the end of their useful lives. Even in the case of the Breeze-M malfunction, a backup command to vent unused propellants in the event of a system failure could have prevented the subsequent explosion.”

Abercromby said NASA is continuing to assess the extent of the debris field caused by the Breeze-M explosion. Fran Slimmer, a spokeswoman for International Launch Services of McLean, Va., which sells Proton vehicles commercially, said the company had no comment on the event. Breeze-M, like most of the rest of the Proton-M rocket, is built by Khrunichev State Research and Production Space Center of Moscow.

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