On December 25, 2013, at 04:31:54 Moscow Time, a Russia launched Kosmos 2488 (Strela-3M-7/ Rodnik-S-7), Kosmos 2489 (Strela-3M-8, Rodnik-S-8), Kosmos 2490 (Strela-3M-9, Rodnik-S-9), and the mysterious Kosmos 2491. At the time, Russia was launching these satellites in groups of three, with its previous, failed attempt being Kosmos 2482/2483/2484 (Strela-3M-4/5/6, Rodnik-S-4/5/6) [1,2].
Figure 4: Historical Rodnik (Strela-3M) launches 
2005 Dec. 21
|Kosmos-2416 (Rodnik/Strela-3M), Gonets-1M|
2008 May 23
|Kosmos-2437, Kosmos-2438, Kosmos-2439 (Rodnik/Strela-3M), Yubileiny|
2009 July 6
|Kosmos-2451, Kosmos-2452, Kosmos-2453 (Rodnik/Strela-3M)|
2010 Sept. 8
|Kosmos-2467, Kosmos-2468 (Rodnik/Strela-3M), Gonets-M No. 12|
2012 July 28
|Kosmos-2481 (Rodnik/Strela-3M), Gonets-M No. 13, Gonets-M No. 14|
2013 Jan. 15
|Kosmos-2482, Kosmos-2483, Kosmos-2484 (Rodnik/Strela-3M)|
2013 Dec. 25
|Kosmos-2488, Kosmos-2489, Kosmos-2490 (Rodnik/Strela-3M); Kosmos-2491*|
2014 May 23
|Kosmos-2496, Kosmos-2497, Kosmos-2498, (Rodnik/Strela-3M); Kosmos-2499*|
Surprisingly, in a note to the United Nations dated May 5, 2014, the Russian government announced the launch of four satellites instead of three, after leading the world to believe for the previous several months that they had only launched three satellites . The interesting part as shown in the figure above is that the object known as Kosmos 2491 was originally treated as debris or a dead satellite, which was a reasonable assumption since the object was an oddity as a fourth satellite on what is normally a three-satellite manifest, and this object had remained inactive in a 1400 km x 1414 km, 82.6 degree orbit for some time as if it were dead. Soon after the note from Russia to U.N. the object began active, orbital maneuvers by dropping to an 1121 x 1491 orbit and apparently inspecting the Briz-KM upper stage that delivered it into orbit, and catching up to the Briz-KM that was at 1500 x 1500 km.
Radar data and historical data indicate the object is probably a 100 kg object with an RCS of 0.3 m and significant delta-V/ specific impulse (probably around 800 m/s delta-V with 200 Ns/kg Isp) [1,3].
- Russian Space Web: Kosmos 2499
- Gunter Space Web: Strela-3M
- Small Communication Satellite Mission for Enhancement of Antarctic Investigations, Dankov, P., et al. 2010.