On the 4th of July 1997 the Mars Pathfinder landed on Mars and so completed a long journey that had started on the 2nd of December 1996. One of the important aspects of the mission was completed with the landing - namely getting the pathfinder to Mars. Just think about this task for a while. The job of the navigation team was to get the lander from Earth to Mars, but both Earth and Mars are continuously moving, not only around the Sun but indeed on their own axes as well. To further complicate the task consider the fact that the mission scientists were very specific about where the lander should land on Mars! However, unlike driving a car from a starting point to some destination, or flying an aeroplane from one airport to another, the Mars Lander is not powered, certainly it has small rockets used to make trajectory corrections but for the large part of the journey the lander must travel along an orbit determined by the forces of the solar system.
Stated simply the task of the navigation team was to get the Mars lander from one object (Earth) moving in some orbit around the Sun to another object (Mars) moving in a different orbit around the Sun using its own orbit around the Sun.
(Photo copied from MPF Trajectory Data (Technical) - see link below)
In the image above the blue footprint illustrates the predicted landing site at the time of launch, "the red ellipse on this image represents a navigation solution using all tracking data from February to July 4, 1997 at 15:30 UTC (just prior to atmospheric entry). It represents our best navigation solution to date" (Robin Vaughan, Mars Pathfinder Navigator)
Some interesting links that you may want to visit to get a better feeling of exactly what was involved in the navigation aspect of the Mars Pathfinder mission:
Click the orbit icon to meet Pieter Kallemeyn,
the Navigation Team Leader, and read some of his journal
entries for the mission. It is particularly interesting to note
how he contrasts the reality of the pathfinder's route and the navigation
teams model (or plan) of the journey.
Robin Vaughan, one of the Mars Pathfinder Navigators has maintained a fascinating and more technical but no less interesting record of the navigation task. Visit two pages maintained by Robin Vaughan: MPF Trajectory Data, and MPF Trajectory Data (Technical), the latter has many very interesting diagrams of the trajectory and photos such as the one above.
Click the orbit icon to access a beautiful QuickTime video that
animates the travels of the pathfinder from Earth to Mars. For more Mars
Pathfinder related QuickTime videos visit the CNN
QuickTime video page. For a color slide that clearly illustrates
the the paths of Earth, Mars and the Mars Pathfinder with respect to the
Sun click
here.
The problem of landing the Mars Pathfinder on Mars is really not unique, similar problems are dealt with in space travel on a regular basis. When space shuttles travel around the earth and rendezvous with satellites or with the Mir space station, or, in years to come, with the new international space station, the problem is really fairly similar (if maybe on a smaller scale) - objects moving in orbits around other objects must meet at predictable times and places.
Have you ever wondered why shuttles are launched at peculiar times like 2:02 pm (STS 94 - 2 July 1997) instead of say at 2:00 pm? There is no single answer and you may wish to visit the NASA webb page (or if that is busy - and it often is- try the Kennedy Space Center page) and search for some discussion of launch windows. One of the factors that influences the launch time is the mission controllers desire that the shuttle (or rocket etc..) should avoid a rendezvous with some debris or other space craft already in orbit around the Earth.
We continue to talk about these orbits but what are they and why are they the shape that they are? These and related questions will form the basis of our next unit.
Having spent time reading the various journals (of Pieter Kallemeyn), the records by Robin Vaughan and visited some of the other related and sites.
Write a two page paper in which you:
Go to unit 2, return to welcome page.
