Kosmos-2499: Is it a spy or an assassin... or both?

Following its launch in May 2014, the mysterious Kosmos-2499 satellite, possibly also designated 14F153, performed a complex orbital dance. In November 2014, the spacecraft came ever closer to its apparent target in space and to a possible climax of its secret mission. Space observers around the world held their breath in anticipation!


A Rockot booster launches Kosmos-2499 along with three "ordinary" payloads on May 23, 2014.


The perigee (the lowest point in orbit) for a mysterious Object 2014-028E (or simply Object E) went down quickly in July and August (light blue line) allowing the spacecraft to catch up with an inert Briz-KM stage (dark blue line), which originally delivered it into orbit on May 23, 2014. Then, at the end of October, Object-E sharply climbed back seemingly aiming to intercept the Briz. What is going to happen next is anybody's guess. Credit: The online forum of the Novosti Kosmonavtiki magazine


Difference in longitudes of orbital nodes (the Equator crossing points) known as Right Ascension of the Ascending Node or RAAN, over time for an inert Briz-KM upper stage (dark blue) and a mysterious Object 2014-028E (or simply Object E), both launched on May 23, 2014. Credit: Online forum of the Novosti Kosmonavtiki magazine

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Mysterious launches

On December 25, 2013, at 04:31:54 Moscow Time, a Rockot booster lifted off from Russia's Northern launch site in Plesetsk on a seemingly routine mission to replenish the Rodnik communications satellite constellation, which has been operating in orbit since 2005.

However, unlike previous six launches, which had carried a trio of small Rodnik satellites each, this rocket also released a fourth object into orbit. Surprisingly, in a note to the United Nations dated May 5, 2014, the Russian government announced the launch of four satellites instead of three. They received designations Kosmos-2488, -2489, -2490 and -2491. It obviously meant that the fourth object was not a piece of space junk as originally believed but a functioning satellite. However, the biggest surprise came from following radar observations revealing that a mysterious fourth object had made orbital maneuvers! On Dec. 3, 2014, a Dutch amateur radio enthusiast Cees Bassa detected an S-band signal from Kosmos-2491 during its pass over Europe.

The story repeated itself on May 23, 2014. According to official Russian media quoting a representative of the Russian Air and Space Forces, VKO, Aleksey Zolotukhin, a Rockot booster lifted off from Plesetsk Cosmodrome, at 09:27:54 Moscow Time, carrying a cluster of military satellites. Shortly after the launch, ISS Reshetnev, the company which developed Rodnik-type satellites and its civilian version -- Gonets -- announced that three of its payloads had successfully reached their orbits and had established communications with ground control.

The three satellites were designated Kosmos-2496, -2497, -2498. However, as in the previous launch on December 25, 2013, the fourth unidentified object was detected orbiting the Earth a few kilometers away from "routine" Rodnik satellites.

Moreover, an analysis of orbital elements from a US radar by observers showed that the "ghost" spacecraft had made a maneuver between May 29 and May 31, 2014, despite being identified as "debris" (or Object 2014-028E) in the official US catalog at the time. On June 24, the mysterious spacecraft started maneuvering again, lowering its perigee (lowest point) by four kilometers and lifting its apogee by 3.5 kilometers. Object E then continued its relentless maneuvers in July and its perigee was lowered sharply, bringing it suspiciously close to the Briz upper stage, which had originally delivered all four payloads into orbit in May.

It is not a bird, it is not a plane

Ground observations indicated that the mystery satellite had not exceeded 0.3 meters in size. Previously, two Rockot launches with trios of Rodnik/Strela-3M launches also carried Yubileiny (a.k.a. MiR) experimental satellites with a reported mass from 48 to 100 kilograms. As with the previous launch, observers were at a complete loss about the possible purpose of the satellite, but such roles as inspection, robotic refueling, repairs and even anti-satellite missions are all within a realm of possibilities for this type of orbital behavior. Eneterprising observers looking at signals quickly recognized information about the electric current in the satellite battery and on its solar panels as well as data about temperatures of various onboard systems such as transmitter and navigational avionics.

Final encounter?

At the beginning of August, Object E descended to a 1,121 by 1,491-kilometer orbit, just below the Briz-KM stage, which by then was circling the Earth in a 1,150 by 1,505-kilometer orbit. Two objects were around one fifth of a revolution away from each other, however, thanks to its lower (and shorter) orbit, Object E was catching up with its "target" at a rate of around 0.045 of a revolution per day, observers estimated. Two objects also had around a three-degree difference in their orbital ascending node (the location where their orbits cross the Equator from the Southern to the Northern Hemisphere).

On August 12, the mystery satellite descended further to a 998 by 1,498-kilometer orbit and on August 20, it entered a 925 by 1,489-kilometer orbit. While the difference in orbital inclination between it and Briz-KM was slowly closing, the satellite remained passive. Then, around October 28, as orbital inclination of two objects nearly matched, the mysterious spacecraft "leaped" ever closer toward the stage, by raising its perigee. The rendezvous between two objects was now looked all but inevitable as soon as first days of November.

By the end of October, the US officially re-classified Object E as "payload" instead of a "fragment" and finally cataloged it as Kosmos-2499 (with a "translated" spelling "COSMOS 2499"). The US military was now rechecking orbital parameters of the mysterious satellite three or four times a day! Following a maneuver between October 27 and October 28, the rendezvous rate between two vehicles slowed down to just 0.014 degrees per day pushing their encounter to around November 12. Their orbital period had just 1.16-difference at the time. It was taking the Briz-KM stage 112.2 minutes to complete a single revolution around the Earth thus bringining it back into the close proximity to Kosmos-2499 every 100 revolutions or eight days.

A weekend rendezvous


Russian ground controllers likely had a busy weekend, as a secret military satellite finally "intercepted" its target. Between Saturday, November 8, and Sunday, November 9, Kosmos-2499 (a.k.a. Object E) climbed from its 1,053 by 1,495-kilometer orbit, first to a 1,108 by 1,498 kilometer orbit and then to a 1,152 by 1,503-kilometer orbit, matching its apogee and perigee with those of the Briz-KM stage that had delivered it into orbit in May. The latest maneuvers coincided with the moment when orbital planes of two objects had also matched.

Estimates made by observers at the Novosti Kosmonavtiki magazine indicated that at 11:24 Moscow Time on November 9, two spacecraft came within 3.1 kilometers from each other with a relative velocity of 6.3 meters per second.

An analysis of orbital elements for Kosmos-2499 and Briz-KM measured a day before and a day after their closest encounter showed that the inert upper stage did not change its orbit, while the maneuverable satellite came as close as 0.76 kilometers to its target on November 9, at 08:48 Moscow Time with a relative speed of 4.6 meters per second.

By November 14, Kosmos-2499 was trailing around 38 kilometers behind Briz-KM, but due to the mystery satellite's slightly lower orbit, it was gradually closing in on its target once again. By November 16, Kosmos-2499 made it within 30 kilometers from Briz-KM even though radar data did not register significant recent maneuvers by the satellite.

November 25 encounter, new moves, transmissions

The mysterious Kosmos-2499 made another close pass near Briz-KM on November 25, 2014. The subsequent modeling of the pair's motion by Russian observers based on available orbital elements data indicated that Kosmos-2499 had come within 526 meters from Briz-KM at a relative speed of just 0.064 meters per second at 05:54 Moscow Time. The spacecraft spent most of the day maneuvering at a distance from a half a kilometer to one kilometer from its target.

After several days of orbiting the Earth at an average altitude from 20 to 30 meters below Briz-KM, Kosmos-2499 climbed few dozen of meters above the stage on November 29, 2014, estimates showed. A day later, to the surprise and delight of the amateur radio enthusiasts around the world, the mystery satellite started transmitting telemetry in Morse code under a call sign RS-47, a Russian amateur radio enthusiast Dmitry Pashkov reported. (Pashkov first detected mysterious signals that he had eventually traced to Kosmos-2499 in the summer of 2014.)

This radio-signature was typical of all satellites based on the Yubileiny platform -- another evidence of the similarity between Kosmos-2499 and its potential civilian cousins.

New maneuvers in 2015

On December 15, 2014, speaking at a year-end press-conference, the head of Roskosmos Oleg Ostapenko said that Kosmos-2491 and Kosmos-2499 were not "killer satellites." According to Ostapenko, the satellites were developed in cooperation between Roskosmos and the Russian Academy of Sciences and were used for peaceful purposes including unspecified research by educational institutions. "They completed their mission," Ostapenko said without elaborating what that mission had been.

In the meantime, after seven and a half months in operation, Kosmos-2499 have remained active at the beginning of 2015. Tracking data indicated that the spacecraft was slowly returning back toward a Briz-KM upper stage, which had delivered it into orbit on May 23, 2014, observers on the web forum of the Novosti Kosmonavtiki magazine said. As of January 3, the distance between two objects was estimated at 98 kilometers.

Between January 17 and January 20, Kosmos-2499 made a slight climb, in a possible effort to accelerate its approach to Briz-KM, the NORAD data indicated. However any further moves of the satellite were apparently too small to be destinguished by a ground-based radar. As of January 22, the spacecraft was around 40 kilometers from its target. Kosmos-2499 made a rendzvous with Briz-KM three days later and ended up 10 kilometers behind. On January 26, the restless spacecraft made a two-kilometer dive, mostly lowering its apogee. The lower orbit allowed it to overtake Briz by 400 kilometers in just two days, but on January 28, the satellite "jumped" again to the target's altitude and continued orbiting the Earth ahead of the stage.


Average orbital altitude of a dormant Briz-KM stage (blue) and that of Kosmos-2499.

Developments in 2016

After being motionless from February 2015 to March 2016, Kosmos-2499 suddenly made a braking maneuver on March 25, 2016, observers at the Novosti Kosmonavtiki magazine reported. At the time, the spacecraft was around 2,000 kilometers behind its Briz-KM stage, which had delivered it into orbit. The resulting lower (and shorter) orbit than that of the Briz, caused the spacecraft to begin a slow chase of the target cutting a distance between the two by around 10 kilometers a day.

In the meantime, Kosmos-2504 remained in the close proximity of its target without visible maneuvers since January 2016.


Average orbital altitude of a dormant Briz-KM stage (blue) and that of Kosmos-2499 as of June 7, 2016.

Developments in 2017

Kosmos-2499 resumed maneuvering at the beginning of 2017, in parallel with its counterpart Kosmos-2504.

A relatively small size of the mysterious Kosmos-2499 satellite combined with a great deal of its maneuvering in orbit made some observers wonder about the type of the propulsion system employed in the mission. Unsubstantiated claims were made on the Internet that the spacecraft could carry some super-efficient ion engines to perform its complex orbital dance.

According to estimates, all the maneuvers by Kosmos-2499 that have been detected from the ground over a six-month period resulted in an estimated velocity change (or delta V) totaling 190 meters per second. Assuming that the spacecraft had a mass of around 50 kilograms, like its potential civilian cousin, Yubileiny satellite, and the specific impulse of its engine was around 300 seconds, almost half of its "content" would have to be propellant, one observer of the mission on the online forum of the Novosti Kosmonavtiki magazine estimated. However with a specific impulse of 2,100 meters per second only 10 percent of its mass would have to be dedicated to propellant, Igor Lisov, the editor at Novosti Kosmonavtiki estimated.

Most importantly, short-duration maneuvers reaching 30 meters per second separated by hours of passive flight observed during the flight of Kosmos-2499 betray the action of a traditional liquid propellant engine onboard the spacecraft, rather than the work of ion-electric engines, which produce low but continuous thrust. As a result, Kosmos-2499 likely made its spectacular performance with traditional rocket engines, Lisov said.

Kosmos-2499 breaks up

On Oct. 23, 2021, the US military detected a breakup event associated with Kosmos-2499. According to the 18th Space Defense Squadron, 18 SDS, the spacecraft degenerated 22 detectable fragments.

At the beginning of 2023, 18 SDS reported another disintegration event associated with Kosmos-2499, which likely took place on Jan. 4, 2023, at around 03:57 UTC. By February 6, a total of 85 fragments originating from this incident in a 1,169-kilometer orbit had been tracked.

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Article and photography by Anatoly Zak

Last update: September 20, 2023

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A scale model of a Soviet maneuverable spacecraft, which could be used as an anti-satellite weapon or a missile interceptor, likely developed by Nudelman's design bureau within the Naryad, 14F11 project. Compare to the American EKV anti-satellite below. Copyright © 2001 Anatoly Zak


A 1:2 model of an early version of the Exoatmospheric Kill Vehicle, EKV, developed by Hughes (later Raytheon) to intercept long-range ballistic missiles beyond the dense Earth atmosphere in a direct "hit-to-kill" collision. EKV would be launched by the Ground-Based Interceptor, GBI, missiles deployed in Alaska and California. Copyright © 2011 Anatoly Zak


A possible target: Briz-KM stage? Copyright © 2011 Anatoly Zak


A Rockot booster lifts off with a trio of Rodnik satellites on Dec. 25, 2013. As it turned out, it also carried a secret maneuverable object. Credit: Zvezda TV Channel


A Rockot booster launches a trio of Rodnik satellites on May 23, 2014. Unknown to general public, a manueverable spacecraft was also onboard. Credit: Zvezda TV


The Yubileiny experimental satellites carried as "piggybacks" on Rockot missions could give a clue about the size and mass of the mysterious Kosmos-2491 and Kosmos-2499. Click to enlarge. Copyright © 2009 Anatoly Zak