5.338A In the frequency bands 1 350-1 400 MHz, 1 427-1 452 MHz, 22.55-23.55 GHz, 24.25-27.5 GHz, 30-31.3 GHz, 49.7 50.2 GHz, 50.4-50.9 GHz, 51.4-52.4 GHz, 52.4-52.6 GHz, 81-86 GHz and 92-94 GHz, Resolution 750 (Rev.WRC 19) applies. (WRC 19)
5.532AB The frequency band 24.25-27.5 GHz is identified for use by administrations wishing to implement the terrestrial component of International Mobile Telecommunications (IMT). This identification does not preclude the use of this frequency band by any application of the services to which it is allocated and does not establish priority in the Radio Regulations. Resolution 242 (WRC 19) applies. (WRC 19)
5.534A The allocation to the fixed service in the frequency band 25.25-27.5 GHz is identified in Region 2 for use by high-altitude platform stations (HAPS) in accordance with the provisions of Resolution 166 (WRC 19). Such use of the fixed-service allocation by HAPS shall be limited to the ground-to-HAPS direction in the frequency band 25.25-27.0 GHz and to the HAPS-to-ground direction in the frequency band 27.0-27.5 GHz. Furthermore, the use of the frequency band 25.5-27.0 GHz by HAPS shall be limited to gateway links. This identification does not preclude the use of this frequency band by other fixed-service applications or by other services to which this band is allocated on a co-primary basis, and does not establish priority in the Radio Regulations. (WRC 19)
5.536 Use of the 25.25-27.5 GHz band by the inter-satellite service is limited to space research and Earth exploration-satellite applications, and also transmissions of data originating from industrial and medical activities in space.
5.536A Administrations operating earth stations in the Earth exploration-satellite service or the space research service shall not claim protection from stations in the fixed and mobile services operated by other administrations. In addition, earth stations in the Earth exploration-satellite service or in the space research service should be operated taking into account the most recent version of Recommendation ITU R SA.1862. Resolution 242 (WRC 19) applies. (WRC 19)
5.536B In Algeria, Saudi Arabia, Austria, Bahrain, Belgium, Brazil, China, Korea (Rep. of), Denmark, Egypt, United Arab Emirates, Estonia, Finland, Hungary, India, Iran (Islamic Republic of), Iraq, Ireland, Israel, Italy, Jordan, Kenya, Kuwait, Lebanon, Libya, Lithuania, Moldova, Norway, Oman, Uganda, Pakistan, the Philippines, Poland, Portugal, Qatar, the Syrian Arab Republic, Dem. People’s Rep. of Korea, Slovakia, the Czech Rep., Romania, the United Kingdom, Singapore, Slovenia, Sudan, Sweden, Tanzania, Turkey, Viet Nam and Zimbabwe, earth stations operating in the Earth exploration-satellite service in the frequency band 25.5-27 GHz shall not claim protection from, or constrain the use and deployment of, stations of the fixed and mobile services. Resolution 242 (WRC 19) applies. (WRC 19)
5.536C In Algeria, Saudi Arabia, Bahrain, Botswana, Brazil, Cameroon, Comoros, Cuba, Djibouti, Egypt, United Arab Emirates, Estonia, Finland, Iran (Islamic Republic of), Israel, Jordan, Kenya, Kuwait, Lithuania, Malaysia, Morocco, Nigeria, Oman, Qatar, Syrian Arab Republic, Somalia, Sudan, South Sudan, Tanzania, Tunisia, Uruguay, Zambia and Zimbabwe, earth stations operating in the space research service in the band 25.5-27 GHz shall not claim protection from, or constrain the use and deployment of, stations of the fixed and mobile services. (WRC 12)
US258 In the bands 8025-8400 MHz and 25.5-27 GHz, the Earth exploration-satellite service (space-to-Earth) is allocated on a primary basis for non-Federal use. Authorizations are subject to a case-by-case electromagnetic compatibility analysis.

Wiki entries

Unlicensed Level Probing Radars

Proposed Use 24.05–29 GHz

The FCC has released a Notice of Proposed Rule Making that would allow downward-pointing, unlicensed level probing radars, for use both in tanks and outdoors, at 5.925-7.250, 24.05-29, and 75-85 GHz.

Proposed EIRP boresight emissions limits are:

5.925-7.250 GHz: -33 dBm/MHz average and +7 dBm across 50 MHz.
24.05-29 GHz: -14 dBm/MHz average and +26 dBm across 50 MHz
75-85 GHz: -3 dBm/MHz average and +34 dBm across 50 MHz

Proposed average emissions limits to the sides and upward are:

5.925-7.250 GHz: -55 dBm/MHz
24.05-29 GHz: -41.3 dBm/MHz
75-85 GHz: -41.3 dBm/MHz

Airport Body Scanners

Current Use 24.25–30 GHz Airport body scanners

Under an FCC waiver (link below) issued to SafeView, Inc., since acquired by L-3 Security & Detection Systems, full-body airport scanners can use repeated sweeps over the range 24.25-30 GHz to detect objects hidden underneath clothes. These units are referred to as millimeter wave scanners by the U.S. Transportation Security Administration (TSA), but don't actually operate in the millimeter wave band (30-300 GHz).

Quoting from the FCC waiver: "The SafeView SafeScout imaging device is a security portal that uses imaging technology to detect weapons or contraband carried on an individual’s person, including non-metallic objects or explosives, which might otherwise require intrusive manual searches or be missed entirely by existing metal detectors. A person to be scanned by the SafeView device steps briefly into a transparent, upright cylinder seven feet high by four feet in diameter. Two vertical antenna masts rotate around the person over a 2-second interval. Each antenna element in turn sweeps from 24.25 to 30 GHz, operating for approximately six microseconds per sweep. The device measures reflections of the radio signals from the subject and calculates an image that shows hidden objects."

NASA Tracking and Data Relay Satellite System (TDRSS)

Current Use 25.25–27.5 GHz Ka-band Single Access (TDRS receive)

According to NASA:

The Tracking and Data Relay Satellites (TDRS) comprise the communication satellite component of the Tracking and Data Relay Satellite System (TDRSS). TDRSS is a communication signal relay system which provides tracking and data aquisition services between low-earth orbiting spacecraft and control and/or data processing facilities. The system is capable of transmitting to and receiving data from spacecraft over at least 85% of the spacecraft's orbit.

The TDRSS space segment consists of six on-orbit Tracking and Data Relay Satellites located in geosynchronous orbit. Three TDRSs are available for operational support at any given time. The operational spacecraft are located at 41°, 174° and 275° West longitude. The other TDRSs in the constellation provide ready backup in the event of a failure to an operational spacecraft and, in some specialized cases, resources for target of opportunity activities.

The TDRSS ground segment is located near Las Cruces, New Mexico, known as the White Sands Complex. Forward data is uplinked from the ground segment to the TDRS and from the TDRS to the spacecraft. Return data is downlinked from the spacecraft via the TDRS to the ground segment and then on to the designated data collection location.

The Tracking and Data Relay Satellite (TDRS) Project is providing follow-on and replacement spacecraft necessary to maintain and expand the Space Network. The contract to build three additional TDRS spacecraft, known as TDRS K, L, and M, was awarded to Boeing Space Systems in December 2007. TDRS K launched January 30, 2013, and TDRS L launched January 23, 2014. TDRS M's launch readiness date is scheduled for 2015. The contract also has options for one additional spacecraft, TDRS N. In addition to building the TDRS K, L, and M spacecraft, the contract also includes the modifications to the White Sands Complex (WSC) ground system required to support these new spacecraft.

The TDRS Project, established in 1973, is responsible for the development, launch, and on-orbit test and calibration of TDRS spacecraft. There have been four procurements of TDRS spacecraft, which include the Basic Program (TDRS F1-F6), the Replacement Program (TDRS F7), the TDRS H,I,J Program, and the TDRS K,L,M Program. TDRS Flight 7 was a replacement for Flight 2, which was lost aboard Challenger in 1986. The first seven spacecraft (TDRS F1-F7) are referred to as the First Generation, the H,I,J series are called the Second Generation, and the K,L,M series are known as the Third Generation. TDRS F1-7 spacecraft were built by TRW (now Northrop Grumman) in Redondo Beach, CA. The TDRS F8-10 (H,I,J) spacecraft were built by Hughes (now Boeing) in El Segundo, CA.

The NASA Space Network consists of the on-orbit telecommunications TDRS satellites, placed in geosynchronous orbit, and the associated TDRS ground stations, located in White Sands, New Mexico and Guam. The TDRS constellation is capable of providing nearly continuous high bandwidth (S, Ku, and Ka band) telecommunications services for expandable launch vehicles and user spacecraft in low Earth orbit. Examples include: the Hubble Space Telescope, the Earth Observig Fleet and the International Space Station. The TDRS System is a basic agency capability and a critical national resource.

NASA Deep Space Network (DSN)

Current Use 25.5–27 GHz DSN K-Band Downlink (from spacecraft less than 2 million km from Earth)

According to NASA:

"The NASA Deep Space Network - or DSN - is an international network of antennas that supports interplanetary spacecraft missions and radio and radar astronomy observations for the exploration of the solar system and the universe. The network also supports selected Earth-orbiting missions.

"The DSN currently consists of three deep-space communications facilities placed approximately 120 degrees apart around the world: at Goldstone, in California's Mojave Desert; near Madrid, Spain; and near Canberra, Australia. This strategic placement permits constant observation of spacecraft as the Earth rotates, and helps to make the DSN the largest and most sensitive scientific telecommunications system in the world."