NOSS Double and Triple Satellite Formations
Naval Ocean Surveillance System
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.
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
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
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.
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.
NOSS 3-5, launched on 2011 Apr 15, replaced the NOSS 3-1 pair, which ceased to orbit in formation shortly after 2011 Nov 07. The Centaur stage was de-orbited into the Pacific Ocean shortly after it deployed its payload.
NOSS 3-6, launched on 2012 Sep 13, replaced the NOSS 3-2 pair, which ceased to orbit in formation shortly after 2013 May 21.
NOSS 3-7 was launched on 2015 Oct 08.
NOSS 3-8, launched on 2017 Mar 01, entered a plane roughly between those of NOSS 3-6 and NOSS 3-7. The Centaur stage was de-orbited into the Pacific Ocean shortly after it deployed its payload.
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. Ceased formation flight with 2001-040C / 26907 soon after 2011 Nov 07.
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. Ceased formation flight with 2003-054C / 28097 soon after 2013 May 21.
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)
NOSS 3-7 (A) 40964 2015-058A NOSS satellite
NOSS 3-7 r 40978 2015-058Q Centaur upper stage
NOSS 3-7 (R) 40981 2015-058R NOSS satellite (officially reported as debris)
NOSS 3-8 (A) 42058 2017-011A NOSS satellite
NOSS 3-8 (B) 42065 2017-011B NOSS satellite (officially reported as debris)
The U.S.A. officially catalogued only one payload from each of the NOSS 3 launches. However, anyone with a tracking capability can readily detect two payloads, because of the manoeuvres they make during the first few months after orbital insertion. Hobbyists routinely observe two payloads from each launch.
The U.S.A. also officially catalogued a single piece of debris from each launch, always as the final piece from the launch, which is described has having been shed by the payload. However, hobbyists have not found any evidence of debris from these launches, using binoculars and cameras.
Since two payloads have been proven to exist, and no evidence of payload debris has been found, it seems likely that the catalogued payload debris object is in fact the uncatalogued second payload. This could be due to an error, but it seems more likely to be a clumsy effort to deceive. Therefore, hobbyists have designated the second payload as the debris object, as shown above.
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
Yaogan 20A 40109 2014-047A Chinese NOSS-like satellite
Yaogan 20B 40110 2014-047B Chinese NOSS-like satellite
Yaogan 20C 40111 2014-047C Chinese NOSS-like satellite
Yaogan 25A 40338 2014-080A Chinese NOSS-like satellite
Yaogan 25B 40339 2014-080B Chinese NOSS-like satellite
Yaogan 25C 40340 2014-080C Chinese NOSS-like satellite
Yaogan-31 A 43275 2018-034A Chinese NOSS-like satellite
Yaogan-31 B 43276 2018-034B Chinese NOSS-like satellite
Yaogan-31 C 43277 2018-034C Chinese NOSS-like satellite
Yaogan-31 D 47532 2021-007A Chinese NOSS-like satellite
Yaogan-31 E 47533 2021-007B Chinese NOSS-like satellite
Yaogan-31 F 47536 2021-007E Chinese NOSS-like satellite
Yaogan-31 G 47691 2021-014A Chinese NOSS-like satellite
Yaogan-31 H 47693 2021-014C Chinese NOSS-like satellite
Yaogan-31 J 47695 2021-014E Chinese NOSS-like satellite
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.