Zvezda joins the ISS
On July 25, 2000, space officials around the world had a collective sigh of relief after several years of uncertainty, as the uninhabited International Space Station, ISS, linked up with the freshly launched Zvezda Service Module. The successful automated docking opened the door to an avalanche of assembly missions during much of the following decade, none of which could have proceeded without the flight control, propulsion and habitation capabilities provided by the Russian-built Zvezda.
The Zvezda deploys its solar panels shortly after reaching orbit.
Zvezda's post-launch operations
After the successful ride to orbit of the the Zvezda Service Module on July 12, 2000, the Russian mission control still had two weeks of very tense work to guide the precious spacecraft to a docking with the International Space Station, which at the time was comprised of just two elements — the Zarya FGB Control Module and the Node 1 Unity module, flying in a single stack since December 1998. Neither of the three vehicles involved had a crew onboard.
The orbital life of the service module started just 12 seconds after its separation from the third stage of the Proton-K rocket, which delivered it into orbit right after 8:00 in the morning Moscow Time. At that point, the command and control system aboard Zvezda was activated and it began deploying a pair of solar arrays, so that they could immediately follow the sun and re-charge onboard batteries. In parallel, the pre-programmed command sequence was activating onboard systems.
As the module completed its first orbit around the planet and re-appeared over the Russian ground stations for a communications window from 09:25 to 09:48 Moscow Time, mission control downlinked its telemetry and confirmed the activation of key systems onboard. The controllers also activated angular velocity sensors, ORT, while a more accurate gyroscopic velocity vector sensor, GIVUS, from the flight control system, was put in operational back-up mode. Mission control then commanded Zvezda to enter propellant-saving spin-stabilization mode with its solar panels pointed at the sun and tested the orientation of the module for an orbit-boosting maneuver.
After yet another orbit, the module was within range of ground stations from 10:58 to 11:16 Moscow Time, giving the mission control a chance to confirm that its solar panels were tracking the sun as planned.
The communications session during the third orbit lasted from 12:32 to 12:46 Moscow Time, during which time engineers switched the GIVUS sensor to the primary mode and put ORT sensors into active reserve.
The final communications session of the launch day started at 14:06 Moscow Time and lasted just eight minutes, giving mission control another opportunity to download the telemetry from the spacecraft.
The only minor problem detected in the data was the incomplete deployment of the docking target on the transfer compartment, PO. All the maneuvers of the day expended around 13.6 kilograms of propellant.
Engine test misfires
On the second day of the flight, July 13, 2000, ground control returned the spacecraft into active orientation mode in order to perform the first test of orbit-correction engines aboard Zvezda. The exercise ensured that the module was ready for a series of maneuvers designed to bring it to an altitude matching the orbit of the ISS.
The sequence for the two small trial engine firings was uploaded to the module during the first communications window of the day from 01:51 to 02:01 Moscow Time. As it turned out, an error in the commands started both maneuvers one orbit earlier or 1 hour 34 minutes 16 seconds ahead of schedule, proving the wisdom of starting with only minor orbit adjustments and fuel expenditures, amounting to just 0.99 meters per second in velocity change each:
The measurements performed during Orbit 17, after the completion of the firings showed that the Zvezda ended up in a 182.2 by 349.4-kilometer orbit. There were also indications that the engines were producing 15 percent more thrust than had been anticipated in ballistic calculations.
During the communications window from 10:56 to 11:05 Moscow Time, mission control adjusted the time settings aboard the module. Flight control specialists also tested the BINS inertial navigation system operating via BOKZ star trackers. Mission control also discovered that the heaters of the ONA high-gain antenna were off, while telemetry transmitters continued working (and consuming power) due to a missing command. During the next radio contact, the controllers activated the antenna heater and turned off the transmitters.
On July 14, in preparation for the first major orbit-correction maneuver of the Zvezda module, the specialists activated the BINS navigation system at 02:26 Moscow Time, first feeding it with data from infra-red sensors, IKV. Then, during the window from 03:47 to 04:52, they tested BINS operations based on data from the BOKZ star trackers. Finally, during the window from 06:12 to 06:31 Moscow Time, the module was put into a nose-first orientation for the two pre-programmed maneuvers. During the maneuvers, ground stations in Dzhusaly, Kazakhstan, and Ulan-Ude in the Russian Far East had some communications problems, but engine firings were completed as planned. The post-maneuver measurements once again showed that the engines had outperformed their projected thrust by around 15 percent:
Measurements made during the 34th orbit showed that after the maneuvers, the Zvezda had climbed to a 294.1 by 375.9-kilometer orbit.
In order to factor-in the real-life specifications of the Zvezda's propulsion system, mission control cancelled a single engine firing planned for the 48th orbit of the mission on July 15, 2000, while ballistic experts were re-calculating the rendezvous parameters. In any case, the module was now high enough above the dense atmosphere for mounting a rescue expedition aboard a Soyuz spacecraft under most contingency scenarios. The module's solar panels were again allowed to begin tracking the sun.
Regul calls home
During an early communications window on July 15, 2000, from 02:00 to 02:04 Moscow Time, the mission control conducted a test of the first set within the Regul communications system. Two orbits later, during the window from 04:58:49 to 05:12:06 Moscow Time, mission control activated flight control mode, allowing the BINS navigation system to receive periodic corrections from the BOKZ star tracker.
After a quiet Sunday limited to telemetry downloads, mission control resumed testing of the module on July 17. At 00:52:03 Moscow Time, engineers initiated a sequence cycling the module's power batteries. At 05:16:16 Moscow Time, mission control switched the BINS system to navigational data from a solar sensor, but at 07:01:07, the navigator was switched back to a celestial sensor. Two orbits later, during a communications session from 09:59 to 10:06 Moscow Time, controllers activated a forward-looking TV camera (-X axis, where the Zarya FGB was expected to berth), however the flow of digital data from orbit was interrupted and the similar activation of the camera along the +X axis was postponed pending an investigation of the problem. (912)
Throughout Zvezda's autonomous flight, controllers also tested the ability of the module's solar panels to rotate in darkness and measured their efficiency in providing power. (914)
Kurs is ready for a rendezvous
After an uneventful day on July 18, 2000, mission controllers successfully tested equipment of the Kurs rendezvous system on both axial docking ports of the Zvezda module on July 19. The passive version of the rendezvous system on the Zvezda, known as Kurs-P, was designed to give the module an ability to aim its front docking port toward the approaching active spacecraft, which would be responsible for all the maneuvering during the final approach and docking.
The second set of the Regul communications system aboard Zvezda was also tried on July 18. A new orbit correction with a single engine firing was scheduled for July 20, 2000, but when mission control sent synchronization signals to the spacecraft during the window from 00:02 to 00:16 Moscow Time, the onboard timer was found to be lagging by four seconds. Still, ballistic experts cleared the mission for the maneuver. The module oriented itself with engines along the direction of the flight and fired at 05:47:38 Moscow Time, adding 4.99 meters per second to its velocity. The post-maneuver orbit measurements performed during Orbit 127 found the module in a 302.1 by 373.2-kilometer orbit.
Just few minutes later, at 05:59:22 Moscow Time, thousands of kilometers away, the Zarya FGB Control Module also fired its engine to begin its rendezvous with Zvezda. The five-second maneuver added one meter per second in velocity to the station. Another similar maneuver took place at 07:25:12 Moscow Time.
Zvezda performed the final orbit correction before its scheduled docking with the ISS in early hours of July 24, 2000, during the module's 189th orbit. The spacecraft fired its engines at 03:20:14 Moscow Time climbing to a 351.8 by 381.5-kilometer orbit.
In turn, the ISS performed its orbit correction less than half an hour later, at 03:48:42 Moscow Time, entering a 364.2 by 373.3-kilometer orbit, or just a dozen of kilometers above Zvezda. (912)
A day before the rendezvous, Zvezda was put into its docking orientation and mission control tested the rotation of solar panels edge-first, while monitoring the input to the onboard batteries. That position was designed to minimize the impact of thruster exhaust on sensitive elements of the panels during the final approach. (914)
Everything was now set for a final rendezvous.
Artist rendering illustrating the Zvezda Service Module (left) and the Zarya FGB module docked in orbit.
In the early hours of July 26, 2000, Moscow Time, Russian mission controllers uploaded flight program to the ISS for its upcoming docking with the Zvezda module. At 03:38:42 Moscow Time, the ISS began maneuvering for a rendezvous in a fully automated mode but under the careful monitoring of mission control in Korolev.
During a communication session with the two objects from 02:02 and 02:24 Moscow Time, mission control activated the respective Kurs rendezvous equipment first on Zvezda and then on Zarya.
The critical final approach of the ISS to Zvezda was timed to coincide with a communications window with Korolev from 03:35 to 03:59 Moscow Time on July 26.
After a complex but seemingly flawless series of acceleration and braking maneuvers, the 33-ton stack of the Zarya FGB module and the Unity Node successfully docked with the nearly 20-ton Zvezda Service Module on July 26, 2000, at 03:44:44 Moscow Summer Time (00:44:44 UTC). It was still July 25 at US mission control in Houston, Texas.
At the time of their linkup, the two vehicles were in a 351.5 by 379.9-kilometer orbit. The mechanical docking process, including the closure of multiple hooks on the periphery of the docking port lasted around 25 minutes. The Zarya FGB spent around 400 kilograms of propellant for the rendezvous and docking.
On July 26, 2000, the two original elements of the ISS had already completed 9,300 revolutions around the Earth since their own docking in December 1998. At the same time, Zarya had made 9,605 orbits and Zvezda 220 orbits. Originally, Zarya and Zvezda were expected to dock just five months after the launch of the first element, but in reality, Zvezda arrived more than 1.5 years (20 months) later. (915)
Once the successful docking was confirmed, ground control gradually switched the primary functions of the station's control from the Zarya FGB to the Zvezda. (914)
Summary of the Zvezda maneuvers before docking with the ISS in July 2000:
The configuration of the Zvezda Service Module soon after separation from the launch vehicle. Click to enlarge. Credit: NASA
Artist rendering of the Zvezda Service Module deployed in orbit. Click to enlarge. Credit: NASA
The Zvezda fires its attitude control thrusters in this artist rendering. Click to enlarge. Credit: NASA
Artist rendering of the Zvezda Service Module performing an orbit-correction maneuver. Click to enlarge. Credit: NASA
View of the service module's rear docking port provided by a camera onboard approaching Soyuz TM-31 spacecraft in November 2000. Photo by Anatoly Zak via TsUP TsNIIMash