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New Star in Orbit

By Christian Feichtinger, MSM Programme Representative in Moscow
ESA On Station newsletter 2

Station Assembly Resumes

The Zvezda (“star”) Service Module will be the first fully Russian contribution to the International Space Station and will serve as the early cornerstone for the first human habitation of the complex. Zvezda’s “brain” is ESA’s Data Management System (DMS-R) which, ultimately, will perform overall control of all Russian station elements, and guidance and navigation for the whole Station.

Zvezda’s launch is planned for 8-14 July on a Proton booster from the Baikonur Cosmodrome in Kazahkstan. It will be the third Station infrastructure element to reach orbit, docking with the Zarya/Unity pair that has been flying since December 1998 at an altitude of about 400 km. At the time of Unity’s docking, Zvezda’s launch was expected for July 1999 but funding difficulties on the Russian side and two Proton launch failures in 1999 combined to create a year’s delay.

Zvezda is similar in layout to the core module of Russia’s Mir station – indeed, the design was originally intended for the Mir-2 complex planned in the late 1980s. It will provide the Station’s early living quarters for the crew of three, life support system, electrical power distribution, data processing, flight control, propulsion and a communications system that includes remote command capabilities by ground controllers. Although many of these systems will be supplemented by later Station components, Zvezda will always remain the structural and functional centre of the Russian Segment.

The module is 13 m long and spans 30 m across its solar arrays. Its three pressurised sections begin with the 1.35 m-diameter spherical Transfer Compartment at the forward end, followed by the long, cylindrical main Work Compartment, and completed by the 2.0 m-diameter cylindrical aft Transfer Chamber. An unpressurised Assembly Compartment wraps around the Transfer Chamber to house external equipment such as propellant tanks, thrusters and communications antennas.

Zvezda’s four docking ports are divided between one aft and three in the spherical node: forward, up and down. The probe and cone docking mechanism of the aft port (see On Station #1 pp.20-22 for a description) will receive the Russian manned Soyuz and Progress ferry and ESA’s Automated Transfer Vehicle (ATV). Its Kurs (“course”) automatic rendezvous and docking system has long been used in Mir operations, and special ESA laser retroreflectors have been added on the aft end for use by ATV for rendezvous and docking. The forward docking ports all carry hybrid docking mechanisms for attachment to Zarya (forward-facing), and the later additions of Russia’s Science and Power Platform (up) and Universal Docking Module (down).

Like Mir, Zvezda’s living accommodation provides two personal sleeping quarters, a toilet and hygiene unit, a galley with a refrigerator-freezer and a table for securing meals while eating.The 14 windows offer direct viewing of docking activities, the Earth and other Station elements. Exercise equipment includes a treadmill and a fixed bicycle. Cosmonauts wearing Orlan-M spacesuits will venture out using the Transfer Compartment as an airlock. Zvezda also provides data, voice and TV links with mission control centres in Moscow and Houston.

Once in orbit, pre-programmed onboard commands will activate Zvezda’s systems and deploy the solar arrays and antennas.The module then acts as the passive target while Zarya/Unity perform the rendezvous and docking via ground control and the Kurs automatic system. After docking, Zvezda’s guidance and propulsion systems take over those functions from Zarya, which then becomes the Station’s propellant depot and the passageway between Unity and Zvezda.

The Schedule

Since it was delivered to the Baikonur integration and test facility in June 1999, Zvezda has been undergoing final integration and intensive electrical and vacuum chamber testing. The 60-day launch preparation sequence begins in May:

DMS-R: the European Heart of Zvezda

ESA, together with a European industrial consortium headed by DASA in Bremen (D) and including Belgian, Dutch and French partners, was responsible for the design, development and delivery of Zvezda’s DMS-R core data management system. Columbus and ATV will use similar systems, thereby reducing their development costs. ESA provided DMS-R in return for Rosaviakosmos supplying two flight unit docking systems for the Agency’s ATV, so that both sides receive important elements with no exchange of funds.

DMS-R provides system and subsystem monitoring and control for Zvezda, including real-time computing for guidance, navigation and control of the whole Station. It is based on a modular architecture with a two-failure tolerant philosophy applied to safety critical and essential functions. DMS-R consists of two Fault Tolerant Computers (FTCs), each of three identical Fault Containment Regions (FCRs), with each FCR in a separate box to facilitate onorbit exchange. The three FCRs are interconnected and perform continuous voting on the input and output data for automatic fault detection and fault masking. One FTC assumes the role of the Central Computer (CC), while the other is the Terminal Computer (TC).

In addition, two Control Post Computers (CPCs), connected to dedicated Laptops, can be configured to support different applications in parallel.This feature will be used during operation of the European Robotic Arm (ERA), which uses a CPC/Laptop chain as the man-machine interface when controlled from inside Zvezda. All FTCs and CPCs are interconnected via MIL-standard 1553 busses; the CPCs are connected to ERA via a dedicated 1553 bus. Some of the busses are linked to the US Segment via Zarya, as well as to the ATV when the supply vessel is docked to Zvezda.

The two FTCs installed in Zvezda have undergone intensive integrated testing at Baikonur. Zvezda will be sent into orbit without the two CPCs because of the need to keep the launch mass down and delays with the man-machine interface software. They will be delivered aboard the first Progress supply vehicle to the Station at the end of July 2000 for installation by cosmonauts.

GTS: Zvezda’s First Experiment The European Global Time System (GTS) experiment on Zvezda will be the Station’s first externally-mounted experiment, broadcasting accurate timing and data signals to multiple users on Earth. It is a European pilot project and, just as important, it is a commercial project in a joint venture with industry. ESA is paying for the launch and initial 2 years of operations in orbit, while the experiment itself is funded by DLR (50%), DaimlerChrysler (37.5%) and Fortis Uhren GmbH (12.5%). Management and development of GTS is by the technology transfer company Steisbein Transferzentrum Raumfahrt of Reutlingen. Subcontractors are the Institute for Spaceflight Systems at the University of Stuttgart and the TimeTech company.

GTS will transmit high-performance and -accuracy timing signals, as well as coded data, to assess the signal quality and data rates and to measure disturbances such as multi-path reflection, Doppler shifts, shadowing and elevation.The Station’s orbit means that small ground receivers anywhere within 70°N/S of latitude can pick up these signals during 5-7 periods of 5-12 minutes each day.

The signals are generated by a highly stable oscillator and broadcast at 400.1 MHz UHF by four electronically-scanned phased array antennas, and at 1.4 GHz L-band by a crossed dipole antenna. A wide-angle UHF receiving antenna picks up information from the ground. The same accurate timing signals can be sent via dedicated connectors to any scientific experiment running in the Station’s Russian Segment, making GTS just as useful onboard.

The GTS antenna unit was fitted to Zvezda in December 1998 and the transmitter hardware will be delivered by a Progress ferry in late 2000 or early 2001 for installation by the crew to begin the 2-year demonstration. After accurate time reception and location determination by ground users has been proved, the pilot service could be transformed into a fully commercial Station service, providing world-wide automatic time correction of clocks with built-in radio receivers.

Zvezda Principal Characteristics

Linked from Service Module Zvezda