In early March, the Ukrainian media announced that Russian forces are using an enhanced version of the Kometa GNSS receiver in the Ukrainian theatre.
The militarnyi website reported on 9th March that Russian air-to-surface ordnance equipped with the UMPK precision guidance kit are using a new variant of the Kometa system. UMPK kits are like the Boeing Joint Direct Attack Munition (JDAM) guidance system in use with US and allied militaries. Like JDAM, the UMPK kits adorn standard ‘dumb’ ordnance to improve precision. The guidance kits rely on Global Navigation Satellite System (GNSS) Position, Navigation and Timing (PNT) signals to improve precision. Russian sources say UPMK uses PNT signals transmitted by that country’s GLONASS GNSS constellation. GLONASS transmits PNT signals on frequencies of 1.201 gigahertz/GHz to 1.605GHz. Nonetheless, UMPK kits can probably use any GNSS signals transmitted on frequencies between 1.1GHz and 1.6GHz.
UPMK detects PNT signals with the target’s position being correlated with the bomb’s location as it flies. The guidance kit sends commands to a fin assembly mounted on the rear of the weapon. The fins move to correct the course of the weapon as it approaches the target. While UMPK helps to improve precision it can risk making a freefall weapon thus equipped vulnerable to jamming. GNSS PNT signals tend to be very weak by the time they have travelled from the satellites transmitting them to Earth. As previous articles have stated, the signals may be as weak as -127 decibels-per-milliwatt/dBm at the end of their journey. Comparatively weak jamming signals aimed at a UMPK kit maybe drown out the PNT signals used for guidance.
Kometa
Russian language technical papers discussing the baseline Kometa system, which the UMPK relies on, say the system provides ‘noise immunity’ to GNSS PNT jamming. Noise immunity levels of between 32 decibels/dB to 108dB are reportedly achievable with Kometa. It appears that Kometa detects abnormally high-power transmissions mimicking PNT signals using three radio receivers. These receivers detect and compare the spatial separation between the incoming PNT transmission and the more powerful jamming signal. Processing screens out the jamming based on its power levels and angle-of-arrival vis-à-vis the PNT signals. Weighing circa one kilogram (2.2 pounds), Kometa was designed to equip space-constrained platforms. Such attributes make it unsurprising that the apparatus has been employed in the UMPK equipment.
Kometa-M
The Ukrainian media reports in early March said Kometa has now been augmented with eight receivers with the new configuration known as Kometa-M. The addition of five PNT receivers is no doubt intended to improve the resistance of UMPK kits to jamming. By adding additional receivers, Kometa-M may be able to defeat more than three jamming sources. Additional radio receivers may improve the system’s discrimination between real and fake PNT transmissions. It is noteworthy that Kometa-M is also being used with Russian land forces tactical uninhabited aerial vehicles.
The enhancement of the baseline Kometa design shows that Ukrainian electronic warfare directed against Russian GNSS-dependent military systems is effective. It also shows that Russian electronic engineers can rapidly develop solutions to electromagnetically vulnerable systems. Expect similar innovations by both sides as the war continues.
by Dr. Thomas Withington
