More Cracks

Four new cracks have appeared in the external tank of space shuttle Discovery. NASA says these cracks will be fixed using the same techniques applied to earlier cracks in the same tank.

This mission, the last for Discovery, was scheduled to go in early November, but weather problems, a gas leak, and the initial cracks in the tank delayed things. Launch is now scheduled for February 3, but that too might be pushed back.

Discovery seems in no hurry to go into retirement.

Galaxy 15 Back Under Control

Galaxy 15, the communications satellite that went out of control last April and began wandering through the constellation of communications satellites, threatening havoc, came back under control last week. Engineers think the battery powering the satellite finally went dry, whereupon the onboard computer reset, as it was designed to do in such circumstances, and began accepting commands from the ground again.

Intelsat, owner of the satellite, has put it in safe mode until all its systems can be thoroughly checkd out. After that, a decision will be made as to whether Galaxy 15 can be returned to service. Engineers still don't know what made the satellite malfunction in the first place.

Dextre Checks Out

Dextre, the robotic astronaut assistant aboard ISS, successfully completed its final check out last week. The first real task for the two-armed robot will be next month. A Japanese cargo vessel will arrive, and Dextre will unload it and place two suites of equipment in their permanent positions.

Dextre is stationed on the outside of ISS and is designed to do some of the routine maintenance tasks that have been done up to now by spacewalking astronauts, thus relieving them of some more dangerous duty and freeing them to spend more time on more productive projects.

Exploring Titan

Mission planners studying ways to explore Saturn's magnificent moon Titan within the next few years are looking at several possibilities. The big element guiding their work involves deciding whether to try to cover a large area to get a broad overview, or, alternatively, study a smaller area in more detail.

If they choose the latter approach, the obvious choice would be to send a lander partnered with a rover. We know how to do that, but pulling it off on Titan would be a real challenge. For one thing, because of the distance between Earth and Titan, a rover there would either have to move extremely slowly, or it would need to be able to navigate and make decisions largely on its own-- in what is likely a more dynamic surface environment than the one on Mars, for example.

Covering a large area would require using aircraft; Titan's thick atmosphere allows a range of options. Lighter-than-air vehicles could fly high, studying the atmosphere, or fly under the haze layer to map large tracts of the surface. Hot-air balloon-type craft could also be used. Even jets are a possibility. A jet aircraft might be able to circumnavigate Titan at relatively low altitude in several hours.

Combining those two basic options might also be possible. A blimp or a balloon, for example, could drag an instrument package along the ground as it flew, thus sampling both sky and surface. Deciding exactly how best to go after Titan's mysteries in an era of extremely limited budgets will be at once a difficult and a fascinating exercise.

Noticing Novae

Scientists using data from a satellite meant to study the Sun and the solar wind have discovered four novae in the early stages of their eruptions. Only two of the stars were picked up by other means. A nova is the explosion of a white dwarf star. Not only doesn't the explosion destroy the star, but a single star can go nova several times. A supernova, on the other hand, does destroy the star, sometimes leaving a black hole.

The study suggests the astronomical community is missing many such events even when a nova reaches naked-eye visibility, resulting in an underestimation of the frequency of nova events in the universe. Dedicating an astronomical satellite to doing an all-sky survey every orbit of the Earth could pick up more nova explosions. The locations of those events could then be relayed to ground-based observatories for more detailed study. This seems to be a case in which a relatively modest program could produce important results.

Indian Mishap

India's largest launch vehicle, the GSLV, malfunctioned Saturday shortly after liftoff and had to be destroyed. It was the second failed launch of the rocket this year.

The GSLV carried a huge communications satellite and had had to be modified to accomodate that size. Whether that modification contributed to the malfunction is not yet known. Whatever the cause turns out to be, the failure is a setback for the building space power. Historically, however, failures are relatively common in the development of new rockets. The Indians plan to push forward, though, on their emerging space program.

Alien Comets

A new study suggests that most of the comets now orbiting the Sun in fact originated in other star systems. The study tries to put a number on the comet population of the Oort Cloud, a huge shell around the Sun far beyond the orbit of Pluto, and comes up with 400 billion. Using the current model, which assumes virtually all comets are left over pieces from the formation of the Solar System, the number comes to only about 6 billion.

The huge discrepancy probably stems from the birth circumstances of the Sun, researchers say. Astronomers think the Sun developed in a loose star cluster that contained perhaps between one hundred and one thousand members. The cluster broke apart, of course, since the Sun now flies through space essentially alone, but while the stars were close, they could have traded comets, and the Sun could have acquired a huge retinue.

Astronomers generally argue that studying comets can tell us a lot about the early Solar System. If this new study is correct, studying comets could also shed light on the formation of other solar systems-- a remarkable bonus for science.