"We estimate that 20 million people will view these images within the first 24 hours," says Kirk Goodall, who is responsible for the mirroring of the Pathfinder website . As clients of commercial Internet providers can attest, such a large increase in the number of people trying to gain access to the Internet can severely tax the resources of most Web servers.
To prevent long delays for people eager to see the first pictures of Mars, Goodall and coworkers at JPL are installing mirror websites at NCSA and several other computing centers from California to Moscow. As the name suggests, each mirror site is an exact reproduction of the main site at JPL.
The Web server at each mirror site must handle millions of hits-per-day and exchange information with the other computers on the network at more than 100 million bits-per-second. Although extremely high bandwidth connections like these may be widely available on the upcoming information superhighway, at present only a few computer centers, including NCSA, possess the needed hardware.
"NCSA has a long history of collaborating with NASA, and we're glad to be able to participate in this exciting new venture," says John Towns, team leader of the Consulting Services Group.
Scientists chose the Ares Vallis, an ancient Martian flood plain, as the landing site for Pathfinder. Great floods inundated this site eons ago, smoothing the surface and mixing together rocks and soil from many different parts of the Martian landscape. Researchers hope that antediluvean Ares Vallis is a geological grab-bag where a wide variety of materials will be within the grasp of Pathfinder.
Pathfinder carries several instruments that photograph the Martian landscape, analyze material from the planet's surface, and determine its composition. Scientists plan to use these instruments to study the geology and surface morphology of the Ares Vallis, the properties of Martian dust, soil and rocks, atmospheric conditions, and even the orbital dynamics of the planet. From the point of view of a net surfer, the most interesting instrument may be the one that takes panoramic stereoscopic images of the Martian surface -- the Imager for Mars Pathfinder, or IMP.
After Pathfinder lands on Mars, the IMP will survey the surrounding landscape and take photographs. These digital images will be downloaded to the Web page as soon as they arrive at JPL, allowing anyone with a modem and a browser to watch them appear at the same time as the scientists at JPL.
Pathfinder is also carrying a small rover, nicknamed "Sojourner," that will ramble about the Martian surface taking pictures and analyzing soil and rock samples. Information from Sojourner is sent back to Pathfinder and then transmitted to Earth. These images will also be posted on the home page as they arrive.
To preserve the consistency of the mirror sites, Goodall has written a program that automatically scans files in the main site and checks for any changes. Altered files are sent to mirror sites every fifteen minutes.
True to its name, the primary goal of the Mars Pathfinder mission is to demonstrate a simple low-cost method for delivering a scientific payload to the surface of Mars and to test the mobility and usefulness of a microrover. Future missions to Mars will benefit from Pathfinder's trailblazing efforts.
Pathfinder and Sojourner are expected to remain operational for at least a month and, hopefully, much longer. Solar cells power both instruments, providing an unlimited source of energy. However, the surface temperature of Mars swings by hundreds of degrees during the Martian day and this places immense stress on the instrument's electronics, eventually causing them to fail.
By that time, Pathfinder will have dramatically increased our understanding of the Red Planet and laid the groundwork for upcoming missions, such as the Mars Global Surveyor, scheduled to enter Martian orbit in September 1997, and begin mapping the surface in unprecedented detail in March 1998.
Mark Sincell is a freelance writer and a postdoctoral student in physics at The University of Illinois.