ISS communications

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During the early days of the ISS, the Russian communication system was the only one available. With the arrival of the U.S. modules, the main system used is the American one: S-band (audio) and the higher-rate Ku-band (audio and video). Russia still prefers to use its own system, though, for up- and downlinking experiment data, and controlling Progress and Soyuz flights. TsUP can utilize the NASA communications systems via a phone link between the two control centers.

Communications can essentially be divided into two types: internal (within the modules) and external (air-to-ground and vice versa, as well as during spacewalks and between spaceships). All are controlled via the «Восход-М» СТТС, Voskhod-M STTS, Telephone-Telegraph Signal System, whose antennae are on the outside of Zvezda. (Some of this I am not quite sure about, or have sketchy information on.)

Internal

The communication system between the Russian modules is analog; the equivalent U.S. system is digital. The Russian Audio Interface Unit in Zarya enables 2-way comm between both audio systems (converts Russian copper analog data to IAS fiber optical digital data, and back). There are six STTS PAs, comm panels, throughout Zvezda.

External

Communications with TsUP are through the VHF (Very High Frequency)-1 «Регул», Regul radio link. They are usually channeled through Russian ground stations, which are only available for a portion of each orbit, from around 5 minutes to 20 minutes depending upon the ground track of a particular pass. (This varies due to orbit precession: the ISS orbits eastward, and the Earth is also turning eastward. The ISS, at an average height of 400 km, takes around 92 minutes. At this height, the ISS’s ground track moves backwards, or westwards, by 22.5 degrees each pass.) A communications relay satellite called «Молния», Molniya is sometimes available to augment comm, but channels on this are shared with the Russian military.

TsUP do not have their own dedicated satellites like NASA’s 3 TDRS (Tracking and Data Relay System) satellites. The original plan was to replenish the Luch, «Луч» satellite relay network that provided communications to the Mir space station and there was one satellite that had been kept in storage ready for launch. But upon inspection it was found that it was damaged beyond repair. The Lira antenna was flown in any case (it is the large projection at the rear of Zvezda that looks like a giant lollipop – see photo below), but the radio system was not taken into orbit.

For spacewalks (VKD, ВКД), each Orlan spacesuit has a «Транзит-А», Tranzit-A system, contained in the «Корона», Korona radio set. This relays radio signals to the Tranzit-B telemetry monitoring hardware in Zvezda; the latter converts the data into a form that can interface with Zvezda’s БИТС-2-12, BITS-2-12 system, which relays signals to TsUP and back when in range of ground stations. Alternatively, comm can be transmitted through an umbilical attached to the spacesuit. Spacewalkers can also talk directly to engineers in TsUP via UHF (Ultra-High Frequency), though there is some interference from other users on Earth (air traffic control, ham radio, etc.). When not in the range of Russian sites, communications can also be routed through the U.S. S-band (both control centers are permanently linked).

Television and video are similarly up- or downlinked via ground stations. Signals are SECAM/PAL (which are incompatible with the American NTSC system). The equivalent of the U.S. Ku-band (voice and video) is the «Лира», Lira system.

Ship-to-ship communications are by UHF. The «Курс», Kurs antenna (mounted on the rear of Zvezda) transmits approach-and-docking radio signals between the Russian segment and an approaching or undocking Progress supply ship or Soyuz. The ТОРУ, TORU equipment in Zvezda’s Work Compartment enables a crewmember to remotely monitor and (if necessary) take over the automated Progress docking; a TV camera mounted on the Progress provides him with visual input.

An extract from Chris van den Berg’s ISSCOM 038 (25 August 2003):

Communications:
Mainly these are handled on the American Ku- and S-bands so via the American TDRS-es. An amount of traffic from and into the Russian segment is routed via the Russian systems Regul and Voskhod-M (so VHF-1 on 143.625 mc). Originally Regul had been designed to be used with the old Russian geostationary comm. satellites of the Luch-type (so the Altairs). Such satellites are no longer operational, but Regul still has some alternatives. Regul can communicate directly with a number of Russian tracking stations. For telemetry the Russian comm. satellites Molniya can be used. 2 Transponders of these satellites are allocated for the handling of telemetry traffic directly from the Service Module Zvezda. The orbit of this type of satellite is elliptical with a perigee of approx. 400 KM and an apogee of approx. 40 000 KM. To make communications between Zvezda and Molniya possible a radio bearing procedure is necessary. In fact the main purpose of the Molniya is the relay of traffic like TV, Radio, etc. via the system Orbita to enable the Russians to cover the most northern parts of the Russian territory. These satellites are also used for the communications between point-to-point stations, for instance between Russian tracking stations for manned space flight and MCC-M (TsUP-M). (There is no need for the tracking station Shcholkovo to use Molniya due to the short distance with TsUP and the existing line network.)

Telemetry signals of the so called BITS-2 system can also be transmitted directly to the tracking stations (NIP-s). Regularly these transmissions can be monitored during passes of the ISS within reach of the Netherlands. (I suppose that this monitoring also is possible in some regions of the U.S.A. for some American tracking stations are able to receive signals like that.) The main stream of the Zvezda module transmits on 630.125 mc, the secondary stream on 628.125 mc. The main stream of the FGB (Zarya module) transmits on 633.850 mc.

Diagrams

Communications (external link, 250 KB). Page illustration from the Reference Guide to the International Space Station PDF.

~ Page last updated: 21 January 2007

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