Table of Contents

Phase 4 - Docking Challenge

Teacher Backgrounder

International Space Station

Artist’s representation of ISS in its completed form

The International Space Station (ISS) represents the largest and most advanced international scientific and engineering program ever built. In addition to the Canadian Space Agency (CSA), the ISS counts on the partnership of international space programs including the National Aeronautics and Space Administration (NASA), Russia's Federal Space Agency (Roskosmos), Japanese Aerospace Exploration Agency (JAXA), and the European Space Agency (ESA). The ISS, located 400 kilometres above the Earth, is powered by solar arrays and contains laboratory and habitation modules. Upon completion, it will support a permanent international crew of seven astronauts and their experiments. It will serve as a platform to observe both Earth and space and will lead to new materials and medicines that can be developed only in micro gravity. A total of over 50 missions and 160 spacewalks will be required to transport and assemble all the ISS components. The expected date of completion for the ISS estimated to be 2010.

Mobile Servicing System (MSS)

The Mobile Servicing System’s external components

Canada's Space Program contributed the Mobile Servicing System (MSS) to aid in the assembly and maintenance of the International Space Station. By contributing the Mobile Servicing System (MSS) to the International Space Station (ISS), Canada acquires rights for the use of the Space Station for scientific and technological research.

The components that comprise the MSS include the Space Station Remote Manipulator System (SSRMS or Canadarm2), the Mobile Base System (MBS), the Special Purpose Dexterous Manipulator (SPDM or Dextre) and the Mobile Transporter (MT), all of which are Canadian except the MT, which was provided by NASA.

Canadarm2

This 17.6-metre robotic arm was the first component of the MSS to be delivered to the International Space Station during mission STS-100 with Canadian astronaut, Colonel Chris Hadfield in April 2001. This manipulator, consisting of two symmetrical booms, has the capacity to handle large ISS payloads with a maximum mass of 116,000 kg. It is currently used to assemble the Station, but in the future it will be used to capture and berth spacecrafts to the ISS and perform routine maintenance tasks. The Canadarm2, has 7 degrees of freedom (3 shoulder joints, 1 elbow joint, 3 wrist joints), which give it flexibility in movement. Due to its two Latching End Effectors (LEEs), the Canadarm2 can relocate itself like an inchworm on the International Space Station as it "walks" along the Station from one grapple fixture to the next.

The Mobile Base System (MBS)

The Mobile Base System or MBS was the second MSS component to be launched in June 2002. It serves as a work platform, equipped with four grapple fixtures that provide a base to accommodate both the Canadarm2 and Dextre, a smaller two-armed robot. It is in turn mounted on the Mobile Transporter, which moves along the entire width of the Station.

Dextre

The third Canadian component is the Dextre, scheduled for launch to the ISS in 2007. Dextre is a dual-arm robot that acts like a pair of robotic "hands" and performs intricate maintenance and servicing tasks such as the removal and replacement of smaller components on the exterior of the Station. Much like the Canadarm2, each of Dextre's arms has a total of seven joints, which gives it great flexibility of movement when performing tasks. Only one arm can be moved at a time in order to avoid self-collision and for greater stability. It is capable of loading and unloading payloads, and using robotic tools. Dextre can either be attached to the end of the Canadarm2 or be based on one of the MBS grapple fixtures.

Docking

After the Space Shuttle leaves Earth’s atmosphere and enters the space environment it takes approximately 2 days before it reaches the International Space Station. In order to successfully dock the Space Shuttle to the ISS, the spacecraft must first intersect the orbit of the ISS. It generally takes many orbits to maneuver the Shuttle to within docking distance of the Space Station. Thus steering the shuttle to the ISS requires orbital maneuvering by making a series of consecutively smaller orbital adjustments using the shuttle’s onboard thrusters and maneuvering engines (called the Orbital Maneuvering System). The onboard Reaction Control Systems located at the nose and tail sections of the Space Shuttle are used to change speed, orbit and attitude. Once the Space Shuttle stops within 50 metres of the ISS, and clearance is given by Mission Control, the Reaction Control Systems are activated and the Space Shuttle moves in on the ISS.

The docking target must be kept clearly in view and the alignment of the Space Shuttle must be fine-tuned with the docking target using a large black cross called the Stand-off-Cross. A series of hooks are then engaged latching the Shuttle to the station.

Docking is a slow process. After the Shuttle gets into range, it takes about 90 minutes to complete docking.

To learn more about the ISS and how to manoeuvre a spacecraft to dock with the ISS please visit the following resources:

• Docking with the ISS: Driving a Spaceship
  
  
• The International Space Station