Construction on-orbit of the 14.2 ton vehicle began on November 20, 1998 with the launch at 06:40:27 UT by Russia for the first element called the Zarya/USCM (US Control Module) on a Proton rocket (Flt. 1A/R). This put Zarya into the same inclined orbit as Mir but in a completely different orbital plane. This was originally proposed by Russia to allow adequate time for the Russian control center to reconfigure for communications between the two different vehicles.
Originally, this module would have provided propulsion storage, propulsion, guidance, and attitude control for subsequent launched elements for up to 400 days. Modifications were made to allow refueling from its nadir or lower facing port from Progress supply vessels. In addition, Zarya will have a power connection as the same nadir port to provide power to any visiting Progress or Soyuz vessel. The aft docking port is being modified to allow docking of the Interim Control Module . Thus, the USCM can provide attitude control to the Unity component for an extended period of time without the use of the Service Module. Zarya will be the active component in docking with the Service Module (SM) once the SM is put into orbit.
The second element, the Unity node, was launched on the shuttle Endeavour STS-88 (Flt. 2A). on December 4, 1998. Attached to either end of the pressurized connecting node, a Pressurized Mating Adapter (PMA) provides an androgynous peripheral docking interface between the Zarya and future orbiters.
According to Jonathan's Space Report No. 380, the PMA-1 and PMA-2 adapters are detachable from Unity. Endeavour will unberth Unity from the bay using the RMS arm, and dock PMA-2 to the Orbiter Docking System. After rendezvous, the axial +Y port of Zarya will be attached to PMA-1. PMA-2 will be used as ISS's main Shuttle docking port; it will be moved from Unity to the Lab module when that is launched.
Here's a view (178k) of Unity and one PMA without shielding and thermal insulation prior to pressurization testing in March, 1998.
The third element which was launched by Russia on July 12, 2000 at 0456 UTC smoothly docked with the ISS on July 26 at 00:44 UTC over northeastern Kazakhstan above the Russian Federation.
A Progress supply vessel (Progress M1-3) was launched on August 6, 2000 at 18:27 UTC and docked at the aft end of Zvezda on August 8 at 20:14 UTC. This docking (although only temporary) increased the length of the ISS to 43 meters and 67 tons. Propulsion fuels and supplies will be ferried by the modified Progress tankers for delivery to the Service Module.
The Zvezda (Star) Service Module has been the second and probably the most critical portion of the second launch mission provided by the Russians. Problems with shuttle scheduling and Proton second stage engine problems moved the expected launch date from Dec 1999-Jan 2000 to Feb 2000 and then to July 2000.
This module will allow permanent habitation of the orbiting station by crew members (an American and two Russians) to be launched on October 31, 2000 on a Soyuz TM-31.
The Service Module will provide long term propulsion and attitude control. This 21 ton module was first constructed in 1985 and is based on the Mir-2 core module with upgraded avionics and additional capabilities. The module is 43 feet long and 97 feet wide with the solar arrays extended. It has four docking ports, 13 windows, a waste water system that generates oxygen, crews quarters for three, a kitchen, a refrigerator and freezer, a toilet and exercise equipment.
The Interim Control Module (ICM) would have been a modified 210 million dollar version of the previously classified 12.5 ton bus that was originally designed for a shuttle launch. The bus was used to launch ocean surveillance satellites (Naval Ocean Surveillance System) from Titan IV rockets. It would provide the necessary propulsion (10000 pounds of fuel) and attitude control for approximately 12-36 months. Six months of training by the assigned shuttle crew would be needed to support a launch. The other option is to use the ICM to refuel the SM in place of Progress fuel ferries. The ICM would not provide habitation unlike the Service Module design for continual manning by three astronauts/cosmonauts.
Modifications to the NRL designed ICM would include use of a smaller propulsion engine, use of 3 inertial measurement units, utilization of 3-axis stabilization control and an attitude control system designed to maintain the attitude of a changing configuration.
Plans had the ICM delivered by the shuttle and docked to the Zarya module in 2001 as a backup propulsion module. NASA would have to purchase a pressure dome and docking port from Russian to accomplish this. NASA has now decided not to launch the ICM since the Service Module is in place and an adequate supply of Progress resupply vessels exist for at least the next year. NASA has issued a stop work order effective October 30, 2000. It would take an additional two years to see the ICM delivered to the ISS if work were to begin again. The uncompleted ICM will remain in storage.
Graphs of ISS's altitude over a period of time can be found at Heavens-Above. ISS has a maximum altitude limit of 460 km based on the design of the Zvezda module. The normal maximum limit is 425 km to allow Soyuz rendezvous missions and a minimum altitude limit of 278 km based on excessive atmospheric drag.
ISS Status Reports from NASA
The Public Broadcasting Corporation has a good graphical presentation on the ISS.
The revised schedule for station elements of the space station, along with graphics and videos can be found at the new NASA Human Space Flight home page.
Boeing has an information page on the ISS.
The ISS complex is in an orbit that was similar to the Mir complex, with an inclination of 51.6 degrees and an altitude ranging from between 361-425 km. It will be visible to observers between latitudes 60N and 60S. It is visible with the naked eye if the observer knows when and where to look with information supplied by Two Line Element sources.Observers can also find predictions for the ISS at Heavens-Above
U.S. Strategic Command (USSTRATCOM) has assigned the designation of the ISS as 25544/98067A. Frequently updated elsets for this object can be found at Celestrak.
Alpha's attitude is being maintained by the gyro attitude control system with the addition of the US Destiny Lab. The large P6 solar arrays are automatically tracking the sun now for optimum output. Reports have Alpha's visual characteristics at around magnitude -2 when fully illuminated (comparable to Jupiter).
Links: to the VSO Home Page, the observing guide itself, observing Mir, satellite predictions.