Greetings once again --

The stately progress of our endeavor continues, and indeed much has happened in space and astronomy since my last column for Canopus. Mars Global Surveyor has been quietly revolutionizing our knowledge of the Red Planet, and a follow-up mission, Mars Odyssey 2001, is more than half way to its October arrival. NEAR rests in peaceful bliss, safe on the surface of Eros, the largest near-Earth asteroid. The near-infrared 2 Micron All Sky Survey (2MASS, on which I happen to have been working for the past several years at IPAC, Caltech's Infrared Processing and Analysis Center) has now finished its observing phase and just begun a final uniform processing of the 25 Terabytes of data collected by the two observatories, with the final data release expected in about a year. The Chandra X-Ray Observatory (nee AXAF) has been returning marvelous new images and spectra for two years, continuing the trail blazed by HST over the past decade. The Space Infrared Telescope Facility, SIRTF, has been assembled and awaits integration with the spacecraft; launch is officially scheduled for less than a year. JPL's Cassini/Huygens Saturn mission has passed far beyond Jupiter and is now well over half way there, both in distance and in time since launch. Deep Space 1's revolutionary ion drive is still quietly thrusting away towards its planned rendezvous with comet Borrelly in September, two years after the formal mission objectives were accomplished. The MAP and Genesis missions have been launched and are well on their ways, while the construction of the International Space Station continues.

It is indeed a ponderous process: we wait eagerly, and at times impatiently. Yet one does not need to look back too far to notice the vast distances we have covered, and to realize that we truly are in a Golden Age for both astronomy and space exploration.

Deep Space 1

The first thing you have to understand about DS-1at this point is that the Comet Borrelly encounter due on September 22 is a long shot, way beyond reasonable expectations for what was, after all, a technology development mission, only intended to get some real flight experience with an ion drive and wring out some new instruments and mission operations concepts for the future. Essentially all of the nominal mission objectives were accomplished during the "primary mission" by September 1999, but shortly thereafter the startracker (used to orient the spacecraft accurately) failed, seriously complicating the ability of controllers to point the MICAS camera and near infrared spectrometer. Up until the event, this had been considered a mission-terminating contingency, since it also made it impossible to point the high gain antenna or the ion drive propulsion unit in the way that had been planned. By a fairly heroic software development effort, DS-1's computers have been re-programmed to use the MICAS images to replace the missing startracker data. Since MICAS has less than 0.1 of the angular field-of-view of the star tracker (about 0.7° vs almost 9°) and can only reliably detect 6th mag stars, this was not a simple undertaking. Nevertheless, it was achieved with remarkable success.

A major complication for the comet rendezvous is that the nucleus is small enough that even the HST could not identify it on its last pass through the inner solar system, so its exact position is unknown. (The comet's coma, or outgassing atmosphere, is of course enormous compared to the nucleus -- very roughly ~100,000 km vs ~10 km -- and much brighter.) DS-1 will pass through the coma at a relative speed of 16.5 km per second. So the trick is to use MICAS to locate the nucleus shortly before the flyby and accurately measure its position. To do this it has to try to recognize the faint point-like nucleus in the image against the confusing background of the coma using onboard recognition software, estimate where it will appear a few hours later at closest approach, and then use the gyros to try to point the spacecraft at that critical instant. Clearly a sporting proposition. (How can we resist to try?) A plasma experiment, PEPE, will measure the composition, density, and temperature of ions and electrons in the comet's coma. PEPE is relatively insensitive to precise orientation, and should obtain good results regardless of the success of the imaging endeavor. Because the mission is virtually over, the www pages have little recent news beyond an entertaining and informative series of reports by mission scientist Marc Raymond at his Mission Log Page,

http://nmp.jpl.nasa.gov/ds1/mrlog.html

which I recommend for anyone with an adventuresome spirit. For much more funky technical detail, try the mission papers at

http://nmp.jpl.nasa.gov/ds1/papers.html

Some previous background material about the DS-1 mission can be found in my own Canopus columns from 1999 at

http://www.wwheaton.com/waw/canopus/index.html

MAP

The Microwave Anisotropy Probe, launched on June 30, is on its way to the L2 Sun-Earth Lagrange point, in the antisolar direction about 1.5 million km from the Earth. Most readers of Canopus know that the cosmic microwave background (CMB) is the actual light of the Big Bang, the veritable flash of creation, released when the Universe first cooled enough to become transparent, about 300,000 years after the beginning. At that time the temperature was about 3000 K, but the cosmic expansion has since redshifted this primaeval photospheric light by a factor of about 1000, to the 2.73 K we now observe. MAP follows on the enormously successful Cosmic Background Explorer (COBE) mission, launched into Sun-synchronous polar orbit in November 1989, which first clearly revealed tiny ripples in the CMB, by which it deviates from perfect uniformity. These fluctuations, less than 0.1% of the temperature of the CMB itself, reveal a great deal about conditions at those earliest times, and about the present cosmos as well. Recent observations from balloons seem to demonstrate that the large-scale geometry of the Universe is very nearly flat (ie, Euclidean), though at least three distinct kinds of unknown dark matter may be needed to account for the total inventory that appears to be required when all the different kinds of evidence are considered. This will clearly all have to wait for a future column (while I brush up on my cosmology, for one thing), but I at least have space and time here to say that the L2 point from which MAP will observe, being far from the Earth and having all major heat sources (that is, Sun, Earth and Moon) on one side, can be shielded from confusing light and heat much better than any previous mission, and will be able to map the CMB over the entire sky with a sensitivity and angular resolution previously unachievable. In fact, L2 seems destined to become the premier site for space astronomy in the next few decades; keep your eye on this space.

The launch was perfect, and so far, all is well; details can be found at the MAP Homepage at:

http://map.gsfc.nasa.gov/index.html

Bill Wheaton