Russian cubesats flying in formation

[B. Hendrickx]

Russia has been conducting some interesting experiments with maneuverable cubesats flying in formation. The satellites involved are 3U format cubesats built by the Special Technological Center (STTs), a company based in St.-Petersburg, some of them in collaboration with the Peter the Great St.-Petersburg Polytechnic University (SPbPU). The experiments have received little attention and may at least partially be intended for military purposes.

CSTP-1.1 / CSTP-1.2 / Polytech Universe 3

Three maneuverable 3U cubesats were launched along with Meteor-M N°2-3 in June 2023. These are CSTP-1.1 (2023-091AN/NORAD 57202) and CSTP-1.2 (2023-091W/NORAD 57186), both  products of STTs, as well as Polytech Universe 3 (PU-3) (2023-091AB/NORAD 57191), jointly built by STTs and SPbPU. The presence of an engine unit on all three satellites was acknowledged at the time of launch and it can be seen in an image of the three satellites released by STTs as well as in an illustration of PU-3 published by SPbPU (see position 6).

In October 2023 STTs reported on its Telegram channel that the three satellites had formed what it called a “cluster”. After having been separated by around 8000 km after launch, they had used their engine units to close that gap to around 200 km. STTs said the joint operation of the satellites would make it possible to conduct experiments “in the area of monitoring the electromagnetic spectrum”. 

More details on the joint maneuvers were published by STTs early this year in a technical journal of the Moscow Aviation Institute:
https://mai.ru/upload/iblock/112/zfwagla3uqgxbwghzylbhih3y0lo452l/18-BogatyrevDenisovMedvedevKovalchuk.pdf

This mentioned only CSTP-1.1 and PU-3, raising the question if CSTP-1.2 had been considered part of the cluster at all or had perhaps not managed to join the cluster. The formation of the CSTP-1.1/PU-3 cluster began in early September 2023 and was completed about two months later. The attached graphs from the article show how the distance between the two satellites gradually decreased during the “formation period" in September-November 2023 and how it evolved between November 2023 and September 2024.

According to the article, CSTP-1.1 and PU-3 were launched with a fuel supply of 338.8 g and 227.7 g respectively. Forming the cluster in Sep-Nov 2023 required significantly more fuel than maintaining it over the following 11 months. During the cluster formation period CSTP-1.1 performed 11 maneuvers, spending 14.3% of its original fuel supply. PU-3 made 3 burns during that period, spending 16.8 % of its original fuel supply. The only active satellite between November 2023 and September 2024 was CSTP-1.1,  which made 12 burns that consumed just 1.5 % of its fuel supply. There were periods of high solar activity in mid May 2024 and late June 2024 that caused the distances between the two satellites first to increase and then decrease naturally without any maneuvers being performed.
 
In June this year (on the occasion of the second anniversary of the launch) STTs gave another update on the three maneuverable satellites. It announced that a total of 87 maneuvers had been conducted, adding that CSTP-1.1 and PU-3 had been flying in formation for more than 1.5 years.

The group flight of the two satellites continues to this day. They are currently flying in the following orbits:
CSTP-1.1:  513x529,  97.56°
PU-3:        508x534 km, 97.55°

Their mean altitude is identical (521 km), as a result of which they stay relatively close to one another. PU-3 is currently trailing CSTP-1.1 by about 30 seconds, which at that altitude corresponds to a distance of roughly 200 km. Any maneuvers made in recent months seem to be beyond the detection range of Western tracking assets. In Celestrak graphs there are no obvious signs of maneuvers by CSTP-1.1 since January 2024 and by PU-3 since September 2023. However, this may require further analysis.

CSTP-1.2, which is clearly not part of the cluster, is in a lower 483x515 km orbit and made its last detectable maneuvers in late June.

CSTP-2.1 / CSTP-2.2 / Polytech Universe 4

More satellites of STTs and SPbPU rode to orbit with Ionosfera-M nr. 1 and 2 in November 2024, more specifically CSTP-2.1, CSTP-2.2, CSTP-2.10, CSTP-2.11, Polytech Universe 4 and Polytech Universe 5. CSTP-2.10 is an 8U cubesat for cosmic particle studies developed jointly with the Far Eastern Federal University in Vladivostok (which is why it is also called Vladivostok-1). CSTP-2.11 is a 12U cubesat with a remote sensing payload and all the others are of the 3U format. See the illustration of all six satellites below.

STTs has announced the presence of an engine unit only on CSTP-2.10 (2024-199S/NORAD 61751), which indeed made several small maneuvers last May. However, orbital data show that maneuvers have also been made by CSTP-2.1 (2024-199AU / NORAD 61777) and CSTP-2.2 ((2024-199AS / NORAD 61775) and that these are flying in formation with PU-4
(2024-199N/NORAD 61747). An engine unit can indeed be seen on both CSTP-2.1 and CSTP-2.2 in the illustration mentioned above, but is absent on PU-4. All three satellites are reported to be used for monitoring of radio sources and PU-4 also has a remote sensing camera. STTs has so far not reported anything on the new formation flight.

The current orbits of the satellites are:

CSTP-2.1: 455x477,  97.35°
CSTP-2.2: 454x478,  97.35°
PU-4:       459x473 km, 97.35°
 
The mean altitude of all three satellites is 466 km. The leading object is CSTP-2.1, with PU-4 trailing it by about 25 seconds (roughly 150 km) and CSTP-2.2 by just over a minute (over 400 km). Both CSTP-2.1 and CSTP-2.2 have been regularly adjusting their orbits in recent months, with the latest detectable maneuvers having taken place in July.

CSTP-4.1 / CSTP-4.2 / CSTP-4.3 / CSTP-4.4

Four more 3U cubesats of STTs were launched with Ionosfera-M nr. 3 and 4 in late July. They are designated CSTP-4.1, 4.2, 4.3 and 4.4 and are also intended for radio monitoring. STTs released a picture of them before they were shipped to the Vostochny cosmodrome and they seem to have an engine unit as well, so we should expect to see these satellites make maneuvers and, possibly, fly in formation in the coming weeks and months.

PROPULSION SYSTEM

In 2023 STTs published an article on two types of cubesat propulsion systems it was working on.
https://mai.ru/upload/iblock/384/0pzncidf2kw1c21kjbxcnuwubor2f5he/16-BabaninaGasanbekovProkhorenko.pdf

One (designated DUBk) is intended for 3U cubesats and the other (designated RDUG) for 12U cubesats. Three types of freon propellants had been evaluated (Freon R-236fa, R-227ea and RC-318), but it was not specified on which of those the choice had eventually fallen. Although the article did not specifically link DUBk to the CSTP satellites, a freon-based propulsion system is known to be on board PU-3, leaving no doubt that the CSTP satellites carry the same system.

The DUBk propulsion unit is no larger than a 1U cubesat and has an overall mass of around 1.4 kg. It has a peak energy consumption of no more than 17 W.  The total thrust impulse is given as about 138 N.s and nominal thrust as 15 mN. The delta V for a 5.6 kg nanosat is 24 m/s.  The propellant is stored in liquid form and turned into gaseous form by a heater.

MISSION GOALS

In its press releases on the cubesat missions, STTs has revealed little about the exact purpose of the CSTP satellites that are involved in these group flights apart from the fact that they are being used for radio monitoring. The payloads of the satellites have not been described anywhere. SPbPU has been more forthcoming with information on the PU satellites, although it does not mention their joint operations with the CSTP satellites. Among the tasks given for PU-3 and PU-4 is geolocation of radio sources. For this purpose, PU-3 carries four antennas capable of picking up signals in four different frequency ranges (0.1-0.8 GHz, 0.8-6 GHz, 6-10 GHz and 10-18 GHz). The same overall frequency range (0.1-18 GHz) has been given for PU-4, one objective of which is given as “correcting errors and increasing the accuracy of ground-based geopositioning systems”.

The tandem flights are apparently needed to pinpoint the location of radio sources with the help of the time-difference-of-arrival (TDoA) technique, which is also employed by several clusters of American and Chinese electronic intelligence satellites. According to a press article published in November last year, the three satellites launched in June 2023 had been involved in an experiment to determine the location of an American meteorological station.
https://www.fontanka.ru/2024/11/08/74315492/

One objective may be to practice ways of locating the source of interference on satellite communication channels. One joint conference paper by STTs and SPbPU in 2022 described the use of TDoA to achieve that goal.
https://elibrary.ru/item.asp?id=44422074

Three satellites would be needed for this. One would be the satellite at which the interference signals are aimed. The other two orbiting in its neighborhood would pick up the side lobes of the interference signals and relay these to multiple antennas at a satellite ground station, allowing the coordinates of the interference source to be determined. As can be seen in a ground track map posted by STTs, one of the ground stations for the CSTP satellites is operated by a company called OOO Komin. The location matches that of an antenna field that the company has at its headquarters in Pargolovo (a suburb of St.-Petersburg) and which could well be used for that purpose. STTs has also done research on what it calls “anti-geolocation”, which is aimed at preventing space-based geolocation systems from finding radio sources by masking the signals they emit.

Considering these potential applications, it is perfectly possible that the formation flights of the CSTP and PU satellites at least partially serve military purposes. Also pointing in that direction is the fact that two specialists of STTs presented a paper on the results of their cubesat missions at a conference on the military uses of space organized last year by the Mozhaiskiy Military Space Academy. It should be pointed out that STTs mainly carries out orders for the Russian Ministry of Defense. Among other things, it builds military drones and is also involved in several electronic warfare projects, including the space-related Tobol project.

[B. Hendrickx]

CSTP-4.1 / CSTP-4.2 / CSTP-4.3 / CSTP-4.4

Four more 3U cubesats of STTs were launched with Ionosfera-M nr. 3 and 4 in late July. They are designated CSTP-4.1, 4.2, 4.3 and 4.4 and are also intended for radio monitoring. STTs released a picture of them before they were shipped to the Vostochny cosmodrome and they seem to have an engine unit as well, so we should expect to see these satellites make maneuvers and, possibly, fly in formation in the coming weeks and months.

These four CSTP satellites are indeed flying in close formation, as can be seen in the screenshot below taken from a recent Russian television report. They are not mentioned by name in the USSPACECOM catalog, but tracking information indicates they are the following objects:
-2025-155G (NORAD 64882) : 489x497 km
-2025-155H (NORAD 64883) : 489x497 km
-2025-155J (NORAD 64884) :  488x497 km
-2025-155V (NORAD 64895) : 490x497 km

According to the TinyGS website, CSTP-4.1, 4.2, 4.3 and 4.4 correspond to objects V, H, G and J respectively, but it is not entirely clear on what that is based.
https://tinygs.com/satellites

Object J made a few small orbit corrections in October, as indicated by the black SMA (semi-major axis) line in the Celestrak graph. The other three have not yet made any detectable maneuvers.