Besides the video game and Nine Inch Nails box set, what is HALO-IV? How does it relate to the testing of ICBM interceptors?

Question

Near the end of the Raytheon Technologies YouTube video Missile Defense Agency completes unprecedented homeland defense test can be seen what looks to me like thermal infrared footage of a ship-launched ICBM interceptor doing what it's supposed to do.

I thought I would search for "Halo-IV missile" or "Halo-IV space" but I keep getting sent to things discussing the video game Halo 4 or (occasionally) the Nine Inch Nails box set, neither of which (I assume) is directly related to what's happening here.

Question: Besides the video game and Nine Inch Nails box set, what is HALO-IV? How does it relate to the testing of ICBM interceptors?

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Screenshot of the linked video and information from the video's page:

As part of a historic Missile Defense Agency demonstration and for the first time ever, an intercontinental ballistic missile target was intercepted and destroyed outside Earth's atmosphere by an advanced SM-3® Block IIA ballistic missile defense interceptor made by Raytheon Missiles & Defense, a Raytheon Technologies business. Learn more: https://rtxdefense.co/38OWV0N (Video by Mark Wright, Missile Defense Agency)

Answer 1

Well, since I used to work for 'em (L3), I'll omit the argument about whether is this on-topic:

HALO stands for High Altitude Observatory. It's an airplane (several airplanes)

The existing contract requires L3 to maintain and operate a fleet of specialized Government-owned Gulfstream II-B (G-IIB) aircraft – HALO I, II, and IV – which are sensor-equipped to collect electro-optic and infared (sic) image data during MDA test events. Each of these sensor- equipped G-IIB aircraft comprises one complete High Altitude Observatory system.

High Altitude Observatory (HALO)

The High ALtitude Observatory (HALO) is an instrumented aircraft used as an airborne optical data collection platform supporting U.S. Missile Defense Agency’s Ballistic Missile Defense System (BMDS) tests. The system is currently based on Gulfstream IIB twin engine jet aircraft.

The system is used to collect missile test and evaluation data including photo documentation, characterization of target scenes, metric and radiometric characterization of systems, and missile plume phenomenology/signature data.

The HALO-I is an airborne system equipped with an infrared imaging system with high-speed visible and infrared photodocumentation. The large windows on the Gulfstream aircraft (replaced with optical windows) and enclosed, environmentally controlled optical benches make this aircraft an excellent choice for unique and experimental EO/IR systems.

The HALO-II and HALO-IV are airborne systems that operates at altitudes up to 13,716 meters (45,000 feet) that are equipped with visible and infrared photodocumentation and ultra high frequency satellite communication (SATCOM). They performs target acquisition and tracking. The EO/IR sensors are mounted in a pod on top of the fuselage (large dorsal fairing), enabling excellent azimuth field of regard (FOR) and horizon-to-horizon elevation viewing.

Press release

MDA = Missile Defense Agency