Saturn is New "Moon King"

Cornell University; Oct 26, 2000; Press Release: "Successful satellite-hunting team finds four new moons in the far reaches of the planet Saturn"

Hubble near Infra-red photo.

Four new moons around the planet Saturn were announced at the annual meeting of the American Astronomical Society in Pasadena, California.  Not much is known about the satellites: they all orbit at least 15-million km from the planet's surface and have estimated diameters, based on surface brightness, of 10-50-km.  Due to their great orbital distance and orbital circumstances (non-circular and inclined to the equatorial-plane) these moons are suspected of being captured asteroids.  

The moons were discovered and confirmed using telescopes to image the space around Saturn every hour.  Computers were programmed to compare the digital images and detect any object that moved between images.  The primary telescopes used were the European Southern Observatory's (2.2-m) telescope in Chile and the Canada-France-Hawaii (3.5-m) scope on Mauna Kea, Hawaii.  Other telescopes were used to confirm the moon's existence.  The technique was used by, the same team of scientists, to discover five new moons for Uranus in the past few years. 

The team notes that several suspect objects may turn out to be more moons of the planet.  Saturn now has 22 known moons and wrests the title of "Moon King" -- the planet with the most moons -- from Uranus by one moon.  But another contender, Jupiter -- the "King of Planets" and former "Moon King," may not mind since -- in mythology -- Saturn is the father of Jupiter.

NASA, Technical Support Package: JPL New Technology Report on: "Nesting-Hoop Solar Sail (NPO-20879)" 

NASA Tech Briefs, Sept 2000, Books and Reports: "Nesting-Hoop Solar Sail"

A JPL "New Technology Report" outlines the use of variable size "nested hoops" to form a solar sail. This system has the advantage of extremely compact storage and requiring less force to deploy. Sail material, just a few microns thick, would be stretched across hoops made of 0.3-mm diameter hypodermic syringe needle tubing. Hoops are bonded or held by springs to adjoining hoops with each hoop slightly smaller that its neighbor to allow them to "nest" within adjoining hoops when stored. Amazingly, a theoretical sail array of 64x64 (4096) disks would fold to only 6-cm thick. The stack would be constructed so that it unfolds a 64-disc "spine" from which 32-disc arrays would deploy to either side.

A problem with previously considered monolithic solar sail designs is the deployment force required to tense the material into a smooth sheet. In the hoop system, tensioning force at deployment is greatly reduced because the sail material is pre-stretched across each hoop. A smaller tensioning system in turn reduces the overall mass and complexity of the system. In fact, a stacked configuration could be slightly bent in a way to allow solar flux pressure to deploy the sails.

Prototype hoops of 0.3-m diameter, using hypodermic syringe needle tubing, have a hoop-to-wire diameter ratio of 1000:1 and a tubing mass of 0.39-gm. Sail material would add 5-gm-per-square-meter for a sail density of 10-gm-per-square-meter. The report notes that using alternative material for hoops can reduce the mass, but the hypodermic needle tubing used in the prototypes can be precision laser welded with commercially available equipment.

Deep Sixing Deep Space 1?

Aerospace America, Oct 2000, Features: “Refocusing Deep Space 1”

Unknown to the general public, political complications surround the first spacecraft of the "New Millennium" series.  Deep Space 1 was launched in October 1998 as an engineering technology demonstrator.  It incorporated -- for the first time -- an ion drive for main propulsion, artificial intelligence, silicone lenses embedded into the solar arrays, and many more new technologies

Most of the risky engineering technology demonstrated has borne fruit.  Because the ion drive operates over long periods of time, to gently thrust the craft, it has accumulated more operating time in space than any other engine.  It is now being considered as the baseline engine for other probes.  Previously communications engineers had feared that the ion plume would interfere with communications.  This electric engine requires constant power from the new, high-power, solar cells.  If the experimental cells failed there was no backup; on board power would only supply electricity for a few hours without them.  Other technologies successfully demonstrated new lighter-weight instruments and communications gear.  This would lead to cost/mass reductions on future spacecraft and on ground-receiving systems. 

While there is overall satisfaction with the mission, instrument and navigation failures have occurred since launch.  This can be expected with so much new technology riding on one craft.  Engineers have developed solutions to work around some of the problems.  One of the equipment failures involved proven technology that was not meant to be part of the engineering test. 

But the JPL managed project started planning scientific examinations of asteroids and comets -- which caught the eye of the White House budget office.  It accused NASA of short-circuiting its review process by proposing science projects for the experimental spacecraft.  The JPL project manager counters that the science objectives were added after the technology demonstration work was completed.  But in recent months NASA has turned back to operating the craft as an engineering experiment.  NASA officials still maintain that using a healthy spacecraft to perform science missions -- once the primary mission objectives are achieved -- makes sense.

Planets Pooh-Poohed

SpaceDaily.com; Oct. 29, 2000; Exo Worlds: "Many Exo Planets Are Probably Stars"

1997 Hubble Telescope near-infrared image of newborn binary system. Enlargement points to what was initially thought to be an ejected extrasolar protoplanet several times the mass of Jupiter.

A report presented at the Planetary Sciences division of the American Astronomical Society meeting in Pasadena, California, suggests that half of all extrasolar planets detected so far are actually brown dwarfs, double-stars, or small stars.  Preliminary data from the study found that only nine stars, of twenty-four with suspected planets, were likely to have planets in the 10-15 Jupiter- mass range.  The remaining were found to have companions too large to be considered planets.  Analysis of more stars with suspected planets is ongoing. 

A popular method of detecting planets outside the solar system is to measure changes in the radial velocity -- toward or away from Earth -- of a star.  These small changes are thought to be caused by the gravitational tug of an object around the star; yet this method can not determine the mass of the object: that would require knowledge of the shape of the orbit.  In this study, precise astrometric data from the European Space Administration Hipparcos spacecraft was combined with the radial velocity data to uncover more information about the orbit of the unseen bodies suspected to be extrasolar planets.  This new orbit information lead to mass estimates for these objects. 

The report also backs-up an earlier study that found no statistical difference between the distribution of orbital periods and eccentricities of the supposed extrasolar planets and those of binary stars.