Debris has long been a hazard for in-orbit satellites and spacecraft - and that problem will not have been diminished when a Russian Briz-M upper stage from a failed launch exploded on 16 October.
The US Air Force says the blast created at least 80 large pieces of debris, and probably many more fragments too small for its powerful radars to pick up. There are concerns this debris field could pose a risk to the International Space Station.
The Briz-M in question arrived in its elliptical orbit during the 6 August failed launch of Telkom-3 and Ekspress-MD2, communications satellites destined for geostationary transfer orbit (GTO) for clients in Indonesia and Russia. The Proton rocket lifted off without a hitch from its Baikonur, Kazakhstan launch pad, and although the Briz-M made three successful burns - standard practice for GTO-bound satellites - the fourth and final did not occur. The satellites were declared total losses. In 2011, another Proton-launched Briz-M failed between its fourth and fifth burns.
While launch vehicles normally become more reliable as early mistakes are ironed out, the Proton's accident rate has remained steady. The Flightglobal Ascend SpaceTrak database reveals the launcher, as a whole, has an accident rate of more than 10%. However, that number is a little unfair to its current operators, and during the past five years the loss rate has hovered around 7.5-8.5%, a trend that began with the first International Launch Services missions in the mid-1990s.
Two Soyuz-launched payloads were lost in 2011 after malfunctions of the third stage. One Rockot using the Briz-KM upper stage put a satellite into an incorrect orbit from which the satellite did not recover.
All incidents were thoroughly investigated, and the requisite fixes found. Certainly, the introduction of new advancements and modifications shows the will of International Launch Services (ILS), which markets the Proton, to move forward and remain highly competitive.
The successful 14 October launch of Intelsat 23 marks Proton's 379th launch, according to SpaceTrak, and the 59th Proton/Briz-M stack. Another launch is scheduled for 2 November, carrying one commercial and one Russian government payload. However, even the lower accident rate compares unfavourably with that of the Proton's big competitor, Ariane V, which has a failure rate of little more than 6%, with no accidents since 2002.
Although United Launch Alliance has essentially priced its Delta IV and Atlas V vehicles out of the commercial market, their launches tell a similar story with even lower losses. So successful are they that the slightest deviation from the norm attracts scrutiny: the USAF recently convened a major accident investigation into the successful orbit of a GPS satellite after a minor issue with the rocket's Centaur upper stage.
In Russia, things are different. The recent string of launch failures, although not particularly different from normal operations, have brought rare public criticism from the country's leadership.
Vladimir Nesterov, head of space manufacturing powerhouse Khrunichev, majority owner of ILS, quit in response. Quality control among component suppliers was mooted as a reason for some failures.
Reliability is often cited as the primary factor in choosing a launch vehicle, and Proton and Briz-M are certainly dependable enough - they have little trouble finding commercial customers, including the big four communications satellite operators.
ILS has more than 20 satellites in its backlog, and is negotiating for at least two more. On top of the commercial launches, the Russian government uses the vehicles to place its own large payloads into orbit.
Proton - as well as Rockot, Dnepr and several other launch vehicles - are slated for replacement by the Angara family, designed around a single common core that can be combined with others depending on the payload and required orbit. Angara's upper stage will be a Briz-M.
Angara has yet to fly but some of its major components - the Briz-M, for instance - have. The common core module has flown twice as the core stage of the Korean Space Launch Vehicle - although both launches failed, the first for unrelated reasons, but the second under somewhat more confused circumstances. A third KSLV launch has been delayed because of a faulty seal on the Russian stage.
ILS has exclusive rights to the commercial marketing of Angara, and is holding capability briefings for potential customers in anticipation of the scheduled 2015 first flight.