Table of Contents

Orbital Mechanics

Student Activity

Docking with the ISS

1. Consider the drawing below. The Space Shuttle is in exactly the same orbit as the International Space Station (not to scale), and behind it, travelling in the same direction.

   The objective is to dock the Shuttle to the ISS. The Shuttle, being the much more manoeuvrable vehicle, must fire its rocket engines to converge on the ISS and dock with it.

   Describe the procedure required to accomplish this. Note that all rocket burns change the orbit of the Shuttle.

   

   ANS: To rendezvous with the ISS the Shuttle must speed up. It can only accomplish this by moving to a lower orbit.
   
   The procedure would be:

   1. Fire rockets in the retro (reverse) direction. This slows the Shuttle down (away from the ISS) and it moves to a slightly lower orbit.

   2. In the (new) lower orbit it is now moving faster (having gained more kinetic energy than it lost in the retrofire). The ISS and the Shuttle begin to converge.

   3. As the Shuttle gets nearer the ISS it must execute a slight foward thrust of its engines. This causes it to move to a slightly higher, and therefore slightly slower orbit.

   4. A series of consecutively smaller and smaller orbital manoeuvers are undertaken until docking occurs.

   
   
   

2. Consider the drawing below. The Space Shuttle is in exactly the same orbit as the International Space Station (not to scale), and ahead of it, travelling in the same direction.

   The objective is to dock the Shuttle to the ISS. The Shuttle, being the much more manoeuvrable vehicle, must fire its rocket engines to converge on the ISS and dock with it.

   Describe the procedure required to accomplish this. Note that all rocket burns change the orbit of the Shuttle.

   

ANS: To rendezvous with the ISS the Shuttle must slow down. It can only accomplish this by moving to a higher orbit.

The procedure would be:

1. Fire rockets in the foward direction. This accelerates the Shuttle (away from the ISS) and it moves to a slightly higher orbit.

2. In the (new) higher orbit it is now moving slower (having lost more kinetic energy than it gained in the rocket thrust). Now the ISS and the Shuttle begin to converge.

3. As the Shuttle gets nearer the ISS it must execute a slight reverse thrust of its engines. This causes it to move to a slightly lower, and therefore faster orbit.

4. A series of consecutively smaller and smaller orbital manoeuvers are undertaken until docking occurs.