It Keeps on Ticking! 

NASA Pioneer Home Page; April 29, 2001; Mission Status

70-m DSN dish of the type that recovered Pioneer 10. - NASA

"The report of my death was an exaggeration" -- a quote by mark Twain -- appears appropriately on the Mission Status page of the Pioneer spacecraft website. As reported here recently (NewsNotes: 04.15.01 Longer Lived Than Some Rock-Stars), the Pioneer 10 spacecraft was presumed lost after several failed attempts to contact it. But on April 28th contact was made with the probe using the 70-meter Deep Space Network (DSN) antenna in Madrid, Spain. Prior to this, the last contact with the historic Pioneer 10 was eight months ago in August of 2000.

Communications with the spacecraft can only take place in "two-way coherent mode." This requires a strong tracking signal be broadcast to the craft before it can reply. Pioneer's 11.74-billion km distance from Earth creates a 21.75-hour time-delay between tracking transmission and ground-station reception of a reply. Unfortunately the DSN is shared with other missions (Galileo, Cassini, and Ulysses are the major ones) and Pioneer 10's unique communications needs will cause it to be allocated less time on the system. Every data download from the spacecraft is important because it may turn out to be the last: the limited output power and the small size of Pioneer's dish antenna may doom communications in a few years as the craft gets farther from Earth.

The Pioneer Mission Status page contains details on how the aging Pioneer goes about "locking up" the signal from Earth so that it can reply. This feat is accomplished during a "conical scan precession maneuver" (CONSCAN). The maneuver works because the spacecraft spin axis passes through the Sun-facing dish antenna. To begin, the spacecraft's antenna feed horn -- the part that receives signals bounced off the dish antenna -- is offset to one side through mechanical means. A steady radio signal from Earth gets weaker and stronger as the spinning antenna rotates the feed horn toward and away the signal reflected from the dish. The spacecraft notes this change in signal strength and fires brief thruster pulses to orient the entire spacecraft inline with the radio signal. Amazingly, 29-years after launch, the craft still has enough hydrazine fuel to fire thrusters to accomplish this task.

Pioneer 10 and friends head toward the edge of the solar system -- NASA

Pioneer 10 carries the famous gold plaque, designed by Carl Sagan and others, which depicts humans and gives directions to locate Earth. The little ship is thus Earth's "message in a bottle" to the stars and should survive the relatively benign environment of interstellar space for an unimaginable length of time. Possibly far longer than the Earth can. Theories of stellar evolution predict the Sun will expand into a red giant star and obliterate the Earth in 5-billion years. The Pioneer Home Page uses this theory to proudly boast: "Accordingly, Pioneer 10 and any etched metal message aboard it are likely to survive for much longer periods than any of the works of Man on Earth."

Has the Bubble Burst for Space Mirror Concept?

University of Arkansas; April 22, 2001; Press Release: "A wrinkle in space may ground lightweight mirrors" 

A University of Arkansas assistant professor of mechanical engineering, Bob Reynolds, has found a new wrinkle -- a bad one -- concerning proposals to build giant, inflatable space-based telescope mirrors.  His findings were presented at the recent American Institute of Aeronautics and Astronautics Annual Structures, Structural Dynamics and Materials Conference in Seattle.

While the Hubble Space Telescope has greatly extended our understanding of the Universe, its mirror size -- therefore its "reach" -- was dictated by the confines of the Space Shuttle cargo bay and the lifting capacity of that vehicle.  Some studies to create larger space telescopes proposed using inflatable mirrors.  These lightweight and space-saving alternatives to hard mirrors would stay folded until deployment.  Researchers proposed constructing miles wide telescopes using this technique.   

"Because the collective impact of the wrinkles would be a serious deformation of the size and shape of the overall structure, this is an significant limitation in the use of these films in devices such as mirrors, where precision is critical." -- Bob Reynolds, University of Arkansas Engineering Professor

Reynolds subjected polymer membranes of two thicknesses to folding, compression, and tensile loading as would be experienced by a deploying space mirror.  Wrinkles in the inflated structure were counted using an optical device above the surface of the membrane.  He found that wrinkle size decreased rapidly after the first two hours of inflation.  But after 24-hours 50 to 80% of the wrinkles remained in the membrane.  

This means that conventional material may not be able to form the mirror-smooth surface required for astronomical work.  "Because the collective impact of the wrinkles would be a serious deformation of the size and shape of the overall structure, this is an significant limitation in the use of these films in devices such as mirrors, where precision is critical," says Reynolds.

"Planetary" Woes Build for Pluto

Academic Press; April 19, 2001; Daily InScight: "Distant Comet Tangoes With Satellite"

Sky & Telescope; April 20, 2001; News: "A Distant Double in the Kuiper Belt"

Binary nature of 1998 WW31 revealed -- Veillet (CFHT)

More fuel was poured on the "Is Pluto a planet?" debate when a known Kuiper Belt body was re-imaged and found to be a double object.  The Kuiper Belt consists of asteroid-size objects that orbit beyond Neptune.  Many of these are recent discoveries made by new imaging technologies.  Some astronomers argue that if Pluto were discovered today it would be regarded as the largest of these objects -- not a "planet" like the Earth.   

The discovery was made when a team at the 3.6-meter Canada-France-Hawaii Telescope (CFHT), on the extinct volcano Mauna Kea in Hawaii, were imaging a Kuiper Belt "supercomet."  This object, designated 1998 WW31, surprised them when it resolved into two objects separated by about 40,000-km: a tenth the distance from Earth to the Moon.  Estimates indicate that objects in this binary system are 150 and 200-km across.  There were plans to search for such binary Kupier Belt objects with the Space Telescope, but the CFHT finding was surprising.  "I think that probably nobody really thought that you could actually see one from the ground on a medium-size telescope," says imaging team leader Christian Veillet.

Binary Kuiper Belt objects may be a common result of collisions between objects.  This gives credence to those astronomers that see Pluto as one of many such distant binary objects.  Benny Peiser of Liverpool John Moores University points out that, "Those who argue that Pluto is 'different' because it has a satellite need to think again." 

Old Idea Will Create Our Star Trek Future

Space.com; April 25, 2001; Astrobiology: "Seeking Life's Chemical Fingerprints with the 'Raman Effect'"

Devices that detect the chemical composition of an object at a distance are a staple of science fiction television and movies.  The most famous portable example being the tricorder from Star Trek.  Mr. Spock, on an away-mission, could use this book-sized device to analyze samples and detect alien life hiding behind the rocks.  

Star Trek devotees know that the tricorder had many functions besides chemical analysis.  But it is satisfying to know that current technology is duplicating at least part of what that versatile tool could do.  Science teams are currently working on devices that can quickly detect the mineral composition of alien surfaces and even find alien life signs.  

The new devices will be miniaturized versions of Raman spectrometers currently used in medicine for analyzing genes and microbes, among other things.  The theory of Raman spectroscopy was formulated by Chandrasekhra Venkata Raman of the University of Calcutta, India.  He won the 1930 physics Nobel Prize for discovery of this effect.

Raman, the real Vulcan? -- Nobel Foundation

What Raman discovered was that a tiny fraction of light photons hitting an object -- as little as 1-in-a-trillion photons -- reflect back at a different wavelength than the arriving photon.  The wavelength shift is equal to the vibration frequency of the material reflecting the arriving light.  Each type of molecule has its own shifted wavelength signature.  The development of the pocket laser and computer miniaturization will allow small versions of this instrument to be carried to other worlds and deployed by land and submarine vehicles.

Small Raman devices have been able to detected amino acids, DNA, protein, ancient bacteria, and fossilized planet pigments on Earth.  Astrobiologists hope to put such a device on one of the next planned Mars rover missions.  A laser probe at the end of a rover arm will scan rocks for chemical signatures that indicate life, the remains of life, or detect minerals indicating conditions conducive to life.  Scientists believe this last possibility the most likely.  Future missions to Jupiter's ice moon Europa may release a probe that will melt its way down into a postulated subsurface ocean.  There, a Raman probe will study the water for mineral content and possible life.  The versatile devices may also be used to prevent contaminating microbes from hitching a ride on spacecraft traveling to and from our planet. 

I think any Mr. Spock wanabe would be fascinated at the possibilities of this device.