With the first two components connected in orbit in late 1998, the ISS still lacked sufficient crew accommodations, propulsion for reboosts of the station to maintain or adjust its orbit, as well as sufficient life and electrical support systems. For that, the Russian Zvezda module was needed.

Originally a core element for Mir 2, like Zarya, the Zvezda module had been sitting around in various stages of completion as early as 1986.

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Zvezda, under construction around 1986. (NASA/Roscosmos)

For NASA’s ambitions, Zvezda was a vital element of the young station. There were no scheduled American elements of the station that provided what this Russian module would provide.

Complicating the importance of Zvezda was that the module was not insured, nor was there a backup module in case of launch failure. Without Zvezda, the early ISS would not be able to maintain station-keeping with the limited fuel resources of Zarya.

Just in case, NASA formulated backup plans. The first idea considered reviving a special device originally designed to assist in deployment of multiple classified military satellites.

The Interim Control Module would launch aboard a Shuttle Orbiter. Essentially a large box of fuel with thrusters, the ICM would dock to Zarya and maintain control authority of the station for up to 3 years.

The Interim Control Module, mated to the aft of Zarya, in this concept illustration. (NASA)

After the ICM’s use was completed, another special device, the Propulsion Module, would’ve been launched for long-term control of the station.

However, the ICM was still a bit in the skeletal stage of construction, never fully completed before being mothballed. So the Propulsion Module was the likely initial replacement as, due to development and funding issues, a functioning ICM would’ve flown without solar panels as shown in the illustration, relying on precious electrical power from Zarya itself.

Alternately, with more budget concerns and long-term control of the ISS, Boeing and NASA considered the use of a spare fourth ISS node placed in storage. While the node had a fault discovered during construction, it would be suitable (with two propulsion units on the port and starboard Common Berthing Mechanisms) as a permanent propulsion unit.

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The payload bay of Shuttle Atlantis and the double-sized SPACEHAB cargo modules. These stayed inside the Orbiter as crews entered the modules and transferred supplies to the ISS. (NASA)

On May 27, 1999, STS-96 was launched to the ISS. It carried more supplies to outfit the station, as well as an Integrated Cargo Carrier for the Russian Strela cranes, smaller but robust manipulator arms for the Russian modules. These would supplement the eventual Canadarm installation a few years later.

Zvezda would not be ready to launch for nearly two years after Zarya and Unity were joined in orbit. NASA turned its attention away from the ISS construction while Zvezda was in work during the rest of 1999 and part of 2000.

STS-93 launched July 23, 1999 with astronaut Eileen Collins as the first female Shuttle commander aboard Columbia, carrying the heaviest payload ever lofted by the Orbiter fleet: The Chandra X-Ray Observatory. The launch had serious engine and mechanical woes that fortunately did not end (at the least) in the ditching of the Orbiter.

On December 20, 1999, Shuttle Discovery returned to the Hubble Space Telescope on the STS-103 mission to make some critical repairs and upgrades to the venerable orbiting telescope. Shuttle Endeavour flew a fascinating radar topography mission on STS-99 on February 11, 2000.

Shuttle Atlantis returned to the ISS for yet more resupplies and equipment swaps, including another Integrated Cargo Carrier, on the STS-101 mission, launched May 19, 2000.

Finally, Zvezda was ready by July 2000. The module launched on July 12, 2000 on a Proton-K rocket with no complications. It docked to the aft of Zarya on July 26.

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Zvezda launches to the ISS on July 12, 2000. (Roscosmos/NASA)

The STS-106 crew arrived at the ISS after their September 8, 2000 launch on Atlantis, carrying several tons of additional supplies in their SPACEHAB double-pallet cargo modules (same as used on previous resupply missions) to outfit the station for the inaugural Expedition 1 crew, which would arrive at the station on November 2, 2000. The STS-106 crew made one spacewalk to complete data and power connections between Zarya and Zvezda.

Atlantis carried no ISS components for installation. It’s mission, in combination with a Progress supply craft already docked to Zvezda, was simply to get the ISS loaded for habitation with the final necessary supplies.

The ISS as seen from the STS-106 mission. A Progress M-1 cargo spacecraft, seen docked to Zvezda’s aft port, was also offloaded of additional supplies for use by the inaugural Expedition 1 crew (NASA)

With a loss of Zvezda, it’s not clear what would’ve been used as the central sleeping and living module for the ISS. It’s probable that the later-cancelled Habitation Module would’ve been completed and flown. The Habitation Module would’ve been the formal living quarters for the ISS crews, but over time, crews would simply sack out in smaller areas throughout Zvezda and later American segment modules.

With the fundamentals all aboard, Expedition 1 could arrive for their four-month shakedown stay aboard the new station in a few weeks time.

But the ISS had a long, long ways to go. The solar panels of Zarya and Zvezda provided a limited amount of power for life support. There was little room for experiments. Cooling would become a long-term problem, as would consumable storage. Station-keeping would also become a long-term issue without a non-propulsive supplement to Zvezda’s thrusters.

The next eleven Space Shuttle missions would quickly bring the ISS resources to a more usable state. Before more modules could be added, the station needed its power and cooling backbone.

Next: Assembly 3A.