It has been my habit in this column to try to explore aspects of a particular mission or topic in some detail rather than attempt a synoptic coverage of all that is happening. If this works at all it is partly because space missions, especially the interplanetary missions which are JPL's special forte, tend to have long routine periods punctuated by occasional bursts of activity. However, since the last column so much has happened that it seems impossible to treat anything at length. So this month I will have to be content with little more than headlines. As a bonus, I will also give WWW URLs for most of the missions I have discussed here or previously.
The construction of the International Space Station (ISS) appears to be off to a fine start. Although most of you will have been following the story, yet the launch of the first elements is such a landmark event that I cannot omit it entirely. The first module, Zarya (also known as the "Functional Cargo Block" or FCB) was launched by a Russian Proton booster on 19 November. Approximately 13 days later, the Unity module was launched on the shuttle Endeavour, on STS-88. The mating of the two parts was accomplished over the next 12 days, and went with a smoothness that must have been very gratifying to those directly involved. To my mind the biggest single justification for the station is that it seems to be the only way humans can acquire the nitty gritty experience needed to allow us to work more routinely in space. Until we do this basic technological homework, all large-scale space projects, whether scientific, industrial, or exploratory, will be like a cavalry charge -- risky, expensive, and unusual, to be undertaken only as a last resort. No doubt many difficulties lie ahead during the years of construction still to be accomplished. Nevertheless, one must regard the good beginning as promising for the overall success of the project. The first permanent crew, of three occupants, is scheduled to take up residence in January 2000, just one year from now. Further information may be found at http://centauri.larc.nasa.gov/issvc97/material.html#elements.
Meanwhile, the first of the "Mars '98" missions, Mars Climate Orbiter (MCO) was successfully launched on 11 December, and is now en route to a 23 September, 1999 arrival in Mars orbit, where it will spend 2 years mapping and collecting data on Mars' atmosphere and weather, and then three more years as a data relay station for other missions yet to be launched. As of this writing all spacecraft systems are still being turned on and checked out as the mission settles down to interplanetary cruise, but everything seems in good health so far. The sister mission, Mars Polar Lander (MPL), remains scheduled for launch about the time you receive this, on 3 January 1999. It will arrive on 3 December 1999 for a landing at the edge of the South Polar Cap, along with two "microprobes" which will impact about 200 km from the main lander and return information from a depth of about 2 meters. Both of the Mars '98 missions were discussed here in more detail last September. A collection of links to further Mars mission information is at http://www.jpl.nasa.gov/marsnews/.
Deep Space 1, which we discussed in July, was successfully launched on a Delta II on 24 October. The ion drive, which is the centerpiece of this technology development mission, gave everyone a good scare when it shut down after just 4.5 min operation on 11 November and refused to restart. The ion engine accelerates xenon ions between two grids only about 0.6 mm apart, charged to a relative potential of up to 1280 volts. Small bits of dust or other contamination are liable to short the grids and make the engine inoperable until they are somehow cleared. Such problems have been observed in ground tests and in space (smaller ion thrusters have been used for attitude and station-keeping on communications satellites) before, and methods, akin to electric "bug zappers", exist for clearing faults of this kind. Thus no one was ready to despair. Nevertheless it was a great relief that the engine operated normally when it was tried again, 12 days after its earlier failure. Since that time it has been thrusting happily away, and has already substantially exceeded the pre-defined criteria for success. In fact, despite some minor glitches, all of the new technologies (at least those that have been tried so far as of this writing; there are a total of 12 on board) appear successful. The DS1 home page is at http://nmp.jpl.nasa.gov/ds1/.
By chance, DS1's success comes just as the Cassini Saturn mission has performed a major midcourse trajectory correction (about 450 meters per sec, requiring a 90 minute burn of its main engine), near the aphelion of its great loop out into the inner asteroid belt before a close flyby of Venus scheduled for June. (I have reported on Cassini's progress here before, especially in October and November of 1997; we still need to say much more about its instruments, science, and various other aspects of the mission; but for Cassini at least we have a good deal of time before it reaches its goal in 2004! Meanwhile, the JPL home page is at http://www.jpl.nasa.gov/cassini/index_frames.html for those who cannot wait.) One other large burn of this engine is scheduled, that needed to place the spacecraft in orbit around Saturn. Some of you will recall Cassini's enormous launch mass of 5600 kgm, the largest US payload ever sent beyond the Moon. Over 3000 kgm of this was propellant needed for the burn just accomplished, and for the one to come at Saturn. All else being the same, an ion thruster might reduce the propellant needed by a factor of about 10 with potentially large savings in launch mass and the $400 million cost of the Titan IV. Although the electric power required for the drive -- especially at Saturn -- would certainly be a serious problem, various possible tradeoffs and solutions could not even be seriously considered, because no demonstrated ion drive existed. All that is now changed, and I suspect that the huge advantages in propellant mass offered by ion drives will prove irresistible to mission designers beginning in the near future.
A burn of similar magnitude (actually somewhat greater in velocity) is to be performed by the NEAR spacecraft less than 2 days hence (on 20 December) as it matches its velocity with the large Near-Earth Asteroid 433 Eros, prior to orbital capture. On 10 January 1999 NEAR should settle into its initial orbit, several thousand km out. A year from now our knowledge of this fascinating little body (a mere 1013 tons or so) will have been revolutionized. Again I have written of the mission here, as recently as November; but all that will soon be swept away as real knowledge replaces guess and speculation. For more on NEAR, see http://near.jhuapl.edu/.
After several years of waiting for flight, SWAS (Submillimeter Wave Astronomy Satellite), one of NASA's original Small Explorer Missions (SMEX; SWAS was selected in 1989) has finally been launched, on 5 December, into a 70° inclination 600 km circular orbit by a Pegasus air-launched booster. SWAS will study star formation in dense clouds by examining the emission of a variety of common intra-cloud species, such as water, O2, carbon monoxide, and atomic carbon. The ability of such clouds to cool effectively by radiation is a major factor controlling their subsequent collapse into stars, and the emission of these molecules is believed to be their major cooling mechanism. However, it is largely unobservable from the ground due to interference from the Earth's atmosphere. SWAS is a submillimeter wave telescope operating just on the borderline between the radio and the far infrared. At about 500 GHz (wavelength 600µ) it may be considered on the "radio" side largely because of its use of dual heterodyne 487 GHz-556 GHz radiometers and an acousto-optical spectrometer -- detecting techniques of radio astronomy rather than methods known in the IR. So far everything seems to be operating well, as the systems are checked out in orbit prior to the 1--2 year period of scientific observations. A URL with further links for SWAS is at http://pluto.harvard.edu/cfa/oir/Research/swas.html.
Another SMEX, known as WIRE, the Wide Field IR Explorer, is a mid-infrared telescope which has been proposed and developed here at IPAC, and is being prepared for launch on 26 February 1999. It is primarily intended to study the birth and evolution of so-called "starburst" galaxies, at distances where cosmological evolution is significant. Such galaxies contain regions of extremely rapid star formation, often harboring many massive, luminous young stars, but which are typically buried in dust so thick that visible light is largely suppressed, and only infrared from the warm dust escapes. It is based on a small 30 cm telescope operating at 12µ and 25µ, cooled by solid hydrogen to less than 7° K. It is expected that its objectives, including the observation of tens of thousands of starburst galaxies, can be fulfilled in only 4 months. The spacecraft is based on the SWAS design. More information may be found at http://www.ipac.caltech.edu/wire/.
Finally, also at IPAC, the first "sampler" data from the Two Micron All-Sky Survey (2MASS) have just been publically released. We discussed 2MASS here in March 1998. The 2MASS Sampler includes just one night of survey data, that taken by the northern observatory on 16 November 1997. It is remarkable that just this one night of 2MASS data exceeds that from the entire year of operation of the first IPAC mission, IRAS, the Infrared Astronomy Satellite, which was flown in 1982-1983. A larger data release is planned for the spring of 1999; for more information, see http://www.ipac.caltech.edu/2mass/.