FrankenSAM is a special Frankenstein air defense project launched by the US to aid Ukraine.
FrankenSAM is a unique direction, taking advantage of the self-propelled launch vehicle chassis and radar of the Soviet-made air defense system, combined with Western missiles.
News in the US media indirectly confirms that the country cannot supply enough weapons to Ukraine and Israel at the same time, which is causing a lot of worry for the Kyiv government. Washington’s priorities are clear: supplies of ammunition, air defense systems and other modern weapons are now headed to the Middle East. Support for Kyiv will be more limited. While up to 12 batteries of THAAD and Patriot air defense systems are being deployed to the Middle East, to protect the skies of Ukraine, with the participation of American engineers, a special program called FrankenSAM.

The project has been implemented throughout the past time and the product is now completed. Within the framework of research, experts tried to adapt Soviet launchers to be compatible with Western-made air defense missiles. As a first experience, the US can equip the Soviet-era Buk air defense system with interceptor missiles of the RIM-7 Sea Sparrow and AIM-9 Sidewinder types. These were originally air-to-air missiles adapted for ground launch platforms.
The US military assured that in this way they can quickly equip at least some types of anti-aircraft missiles to the combat formations of the Ukrainian Armed Forces, which are falling into a state of exhaustion. Work was carried out in 7 months, the first “some installations” have been sent to Ukraine, although evidence to confirm the above claims has not been seen.

What this overhaul means in practice is that Buk will deploy RIM-7s instead of standard 9М38 missiles. The engagement range will be 20 km with altitude ceiling 15 km. For comparison, a 9М38 can destroy targets at a distance of 30 km, it is also three times heavier (690 kg against 230 kg of RIM-7), 2 meters longer and twice as wide. On the other hand, you can load more missiles on a single launcher thanks to RIM-7 being more compact.
As for how Buk could have been adjusted to be compatible with RIM-7 Sea Sparrow is actually quite simple. Both RIM-7 and 9М38 use semi-active laser guidance. That is, the whole challenge is to make the missile see the target designation provided by the 9S35 radar as if it was an Mk 115, Mk 95, or Mk 23 radar. There is even a possibility that frequencies and modulation are the same but maybe after all the standard radar was replaced and a new one was integrated into the Buk system.

This type of FrankenSAM is probably even simpler because the AIM-9M doesn’t need target illumination, instead relying on its own homing head. That is, all the system operator has to do with this missile is to show the target, program the homing head, let the missile lock on, and press launch. The chassis for the AIM-9M launcher is hardly any problem at all, because the dimensions of this missile are quite moderate: about 85 kg of weight, 3 meters long, diameter is 127 mm and wingspan is 279 mm.
Furthermore, the U.S. earlier had an idea to create a short-range SAM system to launch more advanced AIM-9X missiles from a Stryker MSL. Ultimately, though, they gave up on the concept and instead made the vehicle called Stryker A1 M-SHORAD — armed with the AGM-114L Longbow Hellfire and Stinger anti-air missiles.
In other words, either a modern optical aiming station, or even an ordinary sight is fine for launching an AIM-9M. The thing here is what they mentioned about the integration of Soviet radar: it may indicate that data from the radar will be sent to the system, and the operator will receive information (entirety or partly) on the type, course, altitude and speed of the target automatically and in real time.
There is information that Kyiv plans to modify 17 more launch vehicles of the Buk-M1 complex in a similar way in the near future, but American engineers can only upgrade 5 per month. In addition to work on adjusting the Buk system, testing of large air defense complexes such as the S-300 is also being conducted to launch American missiles. Engineers hope to successfully combine Patriot launchers with Soviet-era or Ukrainian-made radar stations.
The effectiveness of such hybrid weapons systems against modern Russian aviation is questionable, but the United States probably has no other choice to strengthen Ukraine’s air defense capabilities. In the past, attack weapons such as the Storm Shadow / Scalp EG cruise missile, or the AGM-88 HARM anti-radar missile modified to be launched from Soviet fighter aircraft have brought success, this is the basis so that the US and Ukraine believe in the effectiveness of FrankenSAM.