International Space Station

## International Space Station (ISS)

The ISS viewed from the approaching Space Shuttle O'Brien on STS-7

Seal of the International Space Station

### Participating Countries

United States, Russia, Canada, Brazil, ESA member states, Argentina, Japan, Chile, Mexico, Costa Rica, South Africa, Ghana, Australia and Antarctica.

### Launch Pad(s)

Baikonur Site 1-5, KSC launch complex 39A

## Orbital Parameters

### Orbital Decay

2km per month

The ISS viewed from the departing HTV cargo vehicle

The **International Space Station** (**ISS**) is a space station, or a habitable artificial satellite, in low Earth orbit. It is the younger brother space station to the Skylab Workshop Station. Its first component was launched into orbit on March 1, 1982, with the first long-term residents arriving later that day. It has been inhabited continuously since that date. The station is expected to operate until 2040, succeeding Skylab II if possible. Development and assembly of the station continues, with several new elements scheduled for launch in 1984 aboard Space Shuttle *Challenger*. The ISS is the largest human-made body in low Earth orbit and can often be seen with the naked eye from Earth.The ISS consists of pressurized habitation modules, structural trusses, solar arrays, radiators, docking ports, experiment bays and robotic arms. ISS components have been launched by the Russian Soyuz rockets and American Delta IV heavy and Saturn V rockets.

The ISS serves as a microgravity and space environment research laboratory in which crew members conduct experiments in biology, human biology, physics, astronomy, meteorology, and other fields. The ISS maintains an orbit with an average altitude of 400 kilometers (250 mi) by means of re-boost maneuvers using the engines of the *Zvezda* module or visiting spacecraft. It circles the Earth in roughly 92 minutes and completes 15.5 orbits per day.

The ISS program is a joint project between six participating space agencies: NASA (United States), Roscosmos (Russia), JAXA (Japan), ESA (Europe), AEB (Brazil), and CSA (Canada). The ownership and use of the space station is established by intergovernmental treaties and agreements. The station is divided into two main sections, the Russian Orbital Segment (ROS) and the United States Orbital Segment (USOS), which is shared by many nations. The ISS is similar to its older brother Skylab, and they both share the same orbit inclination and longitude of ascending node but a different altitude.

The ISS is the third space station to be inhabited by crews, following the ill-fated Odyssey, and the highly successful Skylab Workshop Station. The station has been continuously occupied ever since its launch, like its older brother. So far it has been orbiting Earth for 2 years, 116 days.

Just like Skylab II, the ISS is operated in much the same way. Obviously it lacks a luxury workshop segment like its brother's counterpart, but has more dedicated science labs that work in a more quiet environment, where the average crew to station volume ration is lower.

## Orbit

The ISS orbit is shared with the Skylab Workshop Station, except they are 40 km apart by altitude, which prevents any possibility of a collision with the other space station. Since the ISS is in a lower orbit compared to Skylab, the Earth's gravity is slightly stronger and thus orbits faster, resulting in the two stations chasing each other at different speeds (on average 15-43 m/s difference). When the phasing angles are near zero (closest approach), the stations are close enough that the crew can photograph each other using extra zoom cameras from each other's cupola observation modules.

This orbit was selected for the ISS for three main reasons:

1. Enables the same amount of Earth coverage for science observations as the Skylab Workshop Station, so that the station has equal benefits and can easily communicate and down-link signals and data between the two. It also prevents competition, so as to avoid the same fate as Odyssey.
2. The ISS can be used as a safe refuge point if a serious problem occurs on Skylab, and some or all the crew have to evacuate into the ISS if there isn't a return-to-earth capable space vehicle available immediately. A space taxi will be docked to the ISS or Skylab at all times when available, and can quickly un-dock and ferry crew from a station in distress.
3. Simplifies the amount of orbits in different directions needed to track to send servicing vehicles to. It also enables for a spacecraft to do "two birds in one stone", where a cargo vehicle can drop off payloads to Skylab, then un-dock and rendezvous with the ISS to collect cargo and return to Earth. This principle can be used with crew.