NOSS Double and Triple Satellite Formations

Naval Ocean Surveillance System

Program Poppy
First Generation
Second Generation
Third Generation
China's NOSS-Like Triplets
Informational Links


One of the interesting sights in the night sky are the Naval Ocean Surveillance System (NOSS) satellite formations, each having two or three satellites in close proximity to one another. Normally these satellites are relatively dim to the unaided eye, but on occasion they brighten sufficiently to be easily seen in a dark sky.

NOSS satellites locate and track ships at sea by detecting their radio transmissions and analyzing them using the TDOA (time-difference-of-arrival) technique.

The recently de-classified Program Poppy launched NOSS precursors. The final launch, in 1971, orbited two pairs of satellites operating within the same orbital plane. Neither pair remains in formation today.

Eight 1st generation NOSS triplets were orbited between 1976 and 1987, one of which remains in formation.

Three 2nd generation NOSS triplets were orbited between 1990 and 1996, one of which remains in formation.

The 3rd generation NOSS are the first to employ only two satellites. They made their debut in September 2001, followed by launches in December 2003, February 2005, and June 2007.

The U.S. Government ceased publishing the orbits of NOSS satellites in June 1983, but they have been tracked ever since by hobbyists, who make thousands of precise positional observations each year, like these by Peter Wakelin, which they use to compute their orbital elements.

Anyone can become a skilled positional observer, with practice. The basic methodology is described here.

The initial operational NOSS orbits are approximately circular, about 1110 km in altitude, and inclined 63.4 degrees. Generally, their orbits become more elliptical over time, due to the perturbing effects of the odd zonal harmonics of Earth's gravity field on orbits inclined near 63.4 deg. This perturbation came as a surprise to the NOSS program, as revealed in the 1978 U.S. Navy paper, Perturbations in Perigee and Eccentricity at the Critical Inclination, which concluded that, "the cluster configuration remains unaffected by the large orbital perturbations, and the mission appears safe."

This effect is mitigated somewhat by launching into an initial orbit of argument of perigee near 180 deg, which causes the eccentricity to initially decrease. In the case of the 3rd generation NOSS, their initial 1000 x 1200 km orbit becomes nearly circular at 1100 km, about four years after launch. By that time, the argument of perigee will have precessed to about 90 degrees, whereupon the eccentricity begins to increase, such that the initial 1000 x 1200 km orbit is restored about eight years after launch. In this way, the orbit naturally remains within 100 km of circular for eight years, which presumably is the approximate design life of the satellites.

Operational NOSS satellites maintain their individual formations, and they also maintain nearly identical orbital periods across all three generations of NOSS, yet detectable re-boost manoeuvres have been rare.

A possible clue as to how this is accomplished is the observation that the entire operational constellation appears to decay at the same slow rate. One line of speculation is that this may be accomplished by varying the ballistic coefficient of each satellite, perhaps by changing the orientation of one or more panels facing into the direction of motion, to increase or decrease cross-sectional area.

During the solar-maximum period of the early 2000's, hobbyists who routinely track the NOSS, detected occasional orbit re-boost manoeuvres by the NOSS 1-6 and 1-7 formations, indicating the use some sort of thruster. Since they were the oldest operational NOSS, perturbations had caused their perigee to decrease to an altitude where the atmospheric density at solar-maximum may have resulted in a greater rate of decay than that of the overall constellation, even at the lowest ballistic coefficient achievable using the aforementioned panels.

Program Poppy

The recently de-classified Program Poppy, launched NOSS precursors seven times during the 1960's and early 1970's. The final four satellites were launched in December 1971, aboard a Thorad rocket, from Vandenberg AFB. They operated in pairs, within the same orbital plane.

Object 1971-110C trailed 1971-110A by about 30 s, and 1971-110E trailed 1971-110D by a similar time interval. The pairs were separated in time by about 50 minutes. Neither pair remains in formation today. They are the only Poppy objects for which official 2-line elements are not available (having been classified in 1983 June); however, they are reliably tracked by hobbyists.

Under favourable circumstances, these satellites reach magnitude +8 to +9, making them difficult to observe even with 11x80 binoculars.

The Agena D upper stage is readily visible, reaching magnitude 5 under favourable circumstances.

The significant pieces from the final Poppy launch are:

   Common     Catalog   International
    Name       Number    Designation    Comments
-----------   -------   -------------   --------
Poppy 7 (A)     5678      1971-110A     Poppy satellite
Poppy 7 r       5679      1971-110B     Agena D upper stage
Poppy 7 (C)     5680      1971-110C     Poppy satellite
Poppy 7 (D)     5681      1971-110D     Poppy satellite
Poppy 7 (E)     5682      1971-110E     Poppy satellite

First Generation NOSS

The initial three 1st generation NOSS were launched aboard Atlas F rockets; the final five, on Atlas H. All were launched from Vandenberg AFB. The NOSS were attached to a specialized upper stage, known as the MSD (Multiple Satellite Dispenser), which manoeuvred to release each NOSS satellite into its required orbit.

The MSD have been officially catalogued as payloads, but they did not maintain formation with the NOSS triplets, and it is unknown whether or not they hosted any payload that remained operational after deployment of the NOSS.

Two missions orbited an experimental satellite named LIPS (Living Plume Shield). (A third was lost in a launch failure.) They were built around the plume shield that protected the NOSS from the exhaust of the MSD's engine, converting an object normally ejected as debris, into a payload.

Normally, under favourable circumstances, the NOSS satellites and the MSD reach magnitude +7 to +8, observable with 11x80 binoculars. Rarely, they brighten to magnitude +2 to +4, readily visible to the un-aided eye.

The NOSS 1-7 triplet remained in formation into 2007, but by 2012 none of the first generation NOSS remained in formation.

The significant pieces from the first generation NOSS launches are:

   Common      Catalog   International
    Name        Number    Designation    Comments
------------   -------   -------------   --------
NOSS 1-1 MSD     8818      1976-038A     Multiple Satellite Dispenser
NOSS 1-1 (C)     8835      1976-038C     NOSS satellite
NOSS 1-1 (D)     8836      1976-038D     NOSS satellite
NOSS 1-1 (J)     8884      1976-038J     NOSS satellite

NOSS 1-2 MSD    10502      1977-112A
NOSS 1-2 (D)    10529      1977-112D
NOSS 1-2 (E)    10544      1977-112E
NOSS 1-2 (F)    10594      1977-112F

NOSS 1-3 MSD    11720      1980-019A
NOSS 1-3 (C)    11731      1980-019C
NOSS 1-3 (D)    11732      1980-019D
NOSS 1-3 (G)    11745      1980-019G

NOSS 1-4 MSD    13791      1983-008A
LIPS 2          13792      1983-008B    Living Plume Shield satellite
NOSS 1-4 (E)    13844      1983-008E
NOSS 1-4 (F)    13845      1983-008F
NOSS 1-4 (H)    13874      1983-008H

NOSS 1-5 MSD    14112      1983-056A
NOSS 1-5 (C)    14143      1983-056C
NOSS 1-5 (D)    14144      1983-056D
NOSS 1-5 (G)    14180      1983-056G

NOSS 1-6 MSD    14690      1984-012A
NOSS 1-6 (C)    14728      1984-012C
NOSS 1-6 (D)    14729      1984-012D
NOSS 1-6 (F)    14795      1984-012F

NOSS 1-7 MSD    16591      1986-014A
NOSS 1-7 (D)    16623      1986-014D    Manoeuvred to maintain formation in Nov 2005
NOSS 1-7 (E)    16624      1986-014E    Manoeuvred to maintain formation in Nov 2005
NOSS 1-7 (H)    16631      1986-014H    Manoeuvred to maintain formation in Nov 2005

NOSS 1-8 MSD    17997      1987-043A
LIPS 3          17998      1987-043B    Living Plume Shield satellite
NOSS 1-8 (E)    18009      1987-043E
NOSS 1-8 (F)    18010      1987-043F
NOSS 1-8 (H)    18025      1987-043H

Second Generation NOSS

All 2nd generation NOSS were launched aboard Titan 4 rockets; NOSS 2-1 from Cape Canaveral AFS, NOSS 2-2 and 2-3 from Vandenberg AFB. The NOSS were primary payloads, attached to a specialized upper stage, known as the TLD (Titan Launch Dispenser), which manoeuvred to release each NOSS satellite into its required orbit - a process that took 28 days after launch.

Each TLD permanently hosted a small experimental communications package called SLDCOM (Satellite Launch Dispenser Communications). There is some evidence, not fully confirmed, that experimental infrared telescopes called COBRA BRASS were also hosted on the TLDs, as discussed here and here.

After deploying its NOSS, the TLD manoeuvred to the SLDCOM's required orbit: 63.4 deg, 1200 km x 11600 km, with apogee permanently over the Northern Hemisphere. Years later, SLDCOMs 2 and 3 raised their perigee height to more than 2600 km. The TLD/SLDCOMs are the "A" objects of each launch, in the official satellite catalog.

Normally, under favourable circumstances, 2nd generation NOSS satellites reach magnitude +5 to +6, observable with 7x50 binoculars. Occasionally, they brighten to magnitude +2 to +4, readily visible to the un-aided eye.

Rarely, they outshine the brightest stars. One observer of such an event commented, "Imagine seeing Venus in formation with itself separated by less than 7 degrees, with Saturn trailing along; that's what the spectacle looked like."

Early in 2006, the NOSS 2-2 formation's C and D objects began to fall behind E, and by early 2007, they trailed it by more than 2 minutes. The formation of C and D is somewhat similar to those of the third generation NOSS, so it will be interesting to see whether or not they will eventually re-synchronize their orbital period with that of the operational NOSS, and operate as a pair. Meanwhile, object E has retained nearly the operational period, and leads the NOSS 3-3 formation, with which it is nearly co-planar, by a couple of minutes. It remains to be seen whether or not there will be any sort of cooperation among them.

More recently, the NOSS 2-3 formation's D object began to fall behind C and E, which by mid-2007, led by about 45 seconds. Subsequently, the NOSS 3-4 pair launched to within several degrees of the NOSS 2-3 plane, which suggests that they are intended to become the primary satellites in that plane, with NOSS 2-3 C and E assuming a secondary role.

On the NOSS 2-3 mission, in 1996, the TLD deployed TIPS (Tether Physics and Survivability Experiment). The tether faded rapidly after it was deployed, but remained observable using large binoculars or a small telescope, until it finally broke, in July 2006.

By 2012, none of the second generation triplets remained in formation, but a few of the satellites remain fairly close together.

The significant pieces from the second generation NOSS launches are:

   Common      Catalog   International
    Name        Number    Designation    Comments
------------   -------   -------------   --------
SLDCOM 1        20641      1990-050A     TLD plus experimental communications satellite
NOSS 2-1 (C)    20691      1990-050C     NOSS satellite
NOSS 2-1 (D)    20692      1990-050D     NOSS satellite
NOSS 2-1 (E)    20642      1990-050E     NOSS satellite

SLDCOM 2        21775      1991-076A
NOSS 2-2 (C)    21799      1991-076C     C and D began to fall behind E early in 2006.
NOSS 2-2 (D)    21808      1991-076D     As of early 2007, they trailed E by more than
NOSS 2-2 (E)    21809      1991-076E     two minutes.

SLDCOM 3        23893      1996-029A
NOSS 2-3 (C)    23908      1996-029C     C and E began to separate from D in 2007.
NOSS 2-3 (D)    23862      1996-029D
NOSS 2-3 (E)    23936      1996-029E
TIPS            23937      1996-029F     Tether Physics Survivability Experiment
                                         Tether broke in July 2006.

Third Generation NOSS

The first 3rd generation NOSS were launched on September 8, 2001, aboard an Atlas 2AS rocket. Satellite observers were surprised to find only two satellites, instead of three, leading to speculation that a third satellite had failed to separate from the Centaur upper stage.

The question was settled a few hours after the second launch, on December 2, 2003, when observers again saw only two satellites, as first reported by Jean-Paul Cornec, confirming that the new NOSS employ only two satellites.

Normally, under favourable circumstances, these satellites reach magnitude +5, observable with 7x50 binoculars. Occasionally, they brighten to magnitude +2 to +4, readily visible to the un-aided eye. Rarely, they rival the brightest stars, as reported on SeeSat-L by Sue Wheatley, and Ed Cannon.

NOSS 3-1 and NOSS 3-2 were launched from Vandenberg AFB on Atlas 2AS rockets; NOSS 3-3 and 3-4 were launched from Cape Canaveral AFS, on Atlas 3B-SEC and Atlas V 401 rockets, respectively.

The NOSS 3-4 pair fell short of their planned intial orbit, due to the premature termination of the Centaur's second and final burn, during their launch in mid-June of 2007. The nominal vs achieved orbit was as follows:

                   Nominal  Achieved
Perigee, km         1000       842
Apogee, km          1200      1186
Arg Perigee, deg     180       150
Inclination, deg   63.43     63.35
Between mid-July 2007 and early February 2008, the pair made in excess of 50 corrective manoeuvres, which nearly made up the altitude shortfall. They had also corrected the small shortfall in inclination and manoeuvred to establish the operational planar separation between them. Their argument of perigee was about 143 deg, well short of the nominal 180 deg.

The Centaur of the NOSS 3-5 launch was de-orbited into the Pacific Ocean shortly after it deployed its payload.

The NOSS 3-1 and NOSS 3-2 satellites are no longer in formation.

The significant pieces from the third generation NOSS launches are:

   Common      Catalog   International
    Name        Number    Designation    Comments
------------   -------   -------------   --------
NOSS 3-1 (A)    26905      2001-040A     NOSS satellite
NOSS 3-1 r      26906      2001-040B     Centaur upper stage
NOSS 3-1 (C)    26907      2001-040C     NOSS satellite (officially reported as debris)

NOSS 3-2 (A)    28095      2003-054A     NOSS satellite
NOSS 3-2 r      28096      2003-054B     Centaur upper stage
NOSS 3-2 (C)    28097      2003-054C     NOSS satellite (officially reported as debris)

NOSS 3-3 (A)    28537      2005-004A     NOSS satellite
NOSS 3-3 r      28538      2005-004B     Centaur upper stage
NOSS 3-3 (C)    28541      2005-004C     NOSS satellite (officially reported as debris)

NOSS 3-4 (A)    31701      2007-027A     NOSS satellite
NOSS 3-4 r      31702      2007-027B     Centaur upper stage
NOSS 3-4 (C)    31708      2007-027C     NOSS satellite (officially reported as debris)

NOSS 3-5 (A)    37386      2011-014A     NOSS satellite
NOSS 3-5 (B)    37391      2011-014B     NOSS satellite (officially reported as debris)

NOSS 3-6 (A)    38758      2012-048A     NOSS satellite
NOSS 3-6 r      38770      2012-048N     Centaur upper stage
NOSS 3-6 (P)    38773      2012-048P     NOSS satellite (officially reported as debris)
The U.S.A. officially reports only one payload for the NOSS 3 launches. It does report a single piece of debris from all six launches, typically as the C object, which if it exists, is too faint to be seen using binoculars. Perhaps the second payload has been mistakenly listed as debris. In any case, anyone with a tracking capability can readily detect both payloads, because of the manoeuvres they make during the first few months after obrbital insertion. Hobbyists have designated the second payload as the debris object, as shown above.

China's NOSS-Like Triplets

In early 2010, China launched a NOSS-like triplet, into very nearly the identical orbital inclination and altitude of U.S. NOSS. Follow-up launches occured in 2012 and 2013. None of the U.S. NOSS triplets remain in formation, so the three Chinese triplets are the only intact examples in orbit today. They are readily visible in binoculars, and occasionally to the unaided eye. Like the U.S. NOSS, they sometimes brighten to rival the brightest stars and planets.
   Common      Catalog   International
    Name        Number    Designation    Comments
------------   -------   -------------   --------
Yaogan 9A       36413      2010-009A     Chinese NOSS-like satellite
Yaogan 9B       36414      2010-009B     Chinese NOSS-like satellite
Yaogan 9C       36415      2010-009C     Chinese NOSS-like satellite

Yaogan 16A      39011      2012-066A     Chinese NOSS-like satellite
Yaogan 16B      39012      2012-066B     Chinese NOSS-like satellite
Yaogan 16C      39013      2012-066C     Chinese NOSS-like satellite

Yaogan 17A      39239      2013-046A     Chinese NOSS-like satellite
Yaogan 17B      39240      2013-046B     Chinese NOSS-like satellite
Yaogan 17C      39241      2013-046C     Chinese NOSS-like satellite

Informational Links

Wide Area Surveillance Space Systems by

The U.S. Navy's "White Cloud" Spaceborne ELINT System from

More information on the NOSS groups from David Hastings' Military Space Page listed under "surveillance" for satellite types.

SPACEWARN bulletins 458 and 512

Paul Maley, who is an experienced satellite observer, has produced an excellent web site on satellite observing including pictures of a NOSS formation.

Additional information and observations related to the NOSS satellites, can be found in our archives.

Links: to the VSO Home Page, the observing guide, satellite predictions.

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