Dear JHZR2:

I've read that the resolution of the images received from Spirit is so high that they still can show very sharp and crisp detail when blown up to the size as big as a movie screen! The resolution of images from Viking 1 must absolutely be no match for those from Spirit or Opportunity.

The current highest resolution professional digital (SLR) camera is the Kodak DCS Pro 14n with 14 megapixel resolution (4,536 x 3,024 pixel). I think each of the eight cameras on Spirit may have a resolution as high as 20 megapixels or higher, and may use Wavelet compression (using Discrete Wavelet Transform) instead of regular JPEG compression (using Discrete Cosine Transform). Wavelet compression is used in the newest JPEG2000 specification. I really do not know what compression NASA actually uses for compression of the digital image data from Spirit, even though I feel quite sure that NASA uses Wavelet compression because it's currently the most advanced and superior technique (so much better than DCT used in old JPEG). There is also a compression technique called Fractal Geometry compression, but it is not as mature and efficient as Wavelet compression.

Mr. Volosong please enlighten us more about it.

The Cassini, Galileo, Viking and Voyager spacecraft missions all used Radioisotope Thermoelectric Generators (RTGs) to power its devices and equipments. I remember that around summer 1999, news of Cassini spacecraft being on its way to pass the Earth at a relatively low altitude of about 700 miles caused quite a stir because Cassini (and its attached Huygens probe built by the European Space Agency) carried some RTGs, and there was a probability (quite small) that any slight error in its trajectory calculations or changes in cumulative gravitational force (due to many factors) would make Cassini fall towards the Earth instead of passing it while gaining more "free" speed. If Cassini fell towards the Earth, the atmosphere would burn it and its radiactive nuclear material would be scattered and dispersed over a large area. Fortunately, it passed the Earth without any hiccup and is still continuing along its journey towards Saturn. It will reach Saturn in this mid-summer 2004 and enter an orbit around Saturn; it will then send its Huygens probe to the surface of Titan, one of Saturn's biggest moons, for scientific studies.

All long interplanetary missions (especially to far outer planets like Saturn, Jupiter, Neptune etc...) require nuclear powered generators because the Sun light is extremely weak (due to extremely long distance) for efficient functioning of solar powered panels. These long distance spacecrafts may carry some solar panels but I think they are only there to power some low wattage devices.

NASA has been spending money on a new nuclear power technology called Stirling Radioisotope Generators (SRG). These generators are much more efficient than RTG, and require only as little as 1/4 of the radiactive nuclear material needed by RTG.

Fuel cells and SRG are miracles of science and technology.

Eric