A Pioneer Continues to Break New Ground

American Heritage of Invention & Technology, Winter 2001, Cover Story: "The Spacecraft That Will Not Die"

The latest issue of "Invention & Technology" contains a behind-the-scenes history of the famous first probe to Jupiter that was launched in 1972.  It describes the dedicated team that constructed and managed Pioneer 10 under tight cost, weight, and time constraints. Astonishingly the dedication continues to this day -- even though the project achieved its major science objectives in 1973 and officially ended on its 25th anniversary (1997!) year.

Simplicity was a factor in meeting the Spring 1972 launch window after the 1969 go-ahead.  Legendary project manager Charles F. Hall and TRW design engineer Herb Lassen strove to utilize proven electronics to achieve the probe's science objectives.  But this first mission past the orbit of Mars faced an original problem: power.  Solar energy received at Jupiter's range has only 1/27 the intensity at Earth orbit -- solar panels to power spacecraft systems would be massive at that distance.  Proven models of compact radioisotope thermoelectric generators (RTGs) available at the time were not considered reliable enough for the length of the mission.  But, like many technological milestones, the Pioneer mission was forged at a time when critical technology were maturing in its favor: the Atomic Energy Commission informed the Pioneer designers of the new long-life "SNAP-19" model RTG from Teledyne Corporation.  The mission even saved on prototype costs because Teledyne was anxious to put the new hardware on a spacecraft.

Part of the low-weight and simplicity of the probe was due to its lack of onboard computer.  It may seem surprising -- considering the computer and artificial intelligence systems that are de rigueur for current probes -- to imagine a spacecraft sans computer.  But Pioneer 10 could store only 5 commands to execute when not processing direct instructions from Earth.  This made it vital for the probe to stay in contact with ground controllers for updated real-time instructions.  Lack of computer sophistication was made-up for by designing critical systems to switch to redundant back-up hardware in case of primary failure.  Neither did Pioneer 10 have a real camera.  Images were obtained with a light-sensitive phototube that scanned sequential swipes of the target as Pioneer 10 rotated on its axis. This system was necessitated because the craft was spun to save the weight of a 3-axis stabilization system.  In the end NASA got a ship that weighed only 570-lbs and is still sending back data after almost 30-years of space flight.

Pioneer image of Jupiter and moon. NASA-Ames

When launched in March 1972 it was the fastest (32,000- mph) probe to leave Earth and the first to reach Solar System escape velocity.  Science gathering commenced soon after leaving our planet when the probe proved that the zodiacal lights were a Solar System phenomena.  Another important experiment was to count meteoroid impacts as it crossed the asteroid belt.  It was Pioneer that determined an asteroid belt crossing would not pose much risk to future craft.  More risks awaited Pioneer when it reached Jupiter in November 1973.  At the time it was not certain a craft could survive penetrating the massive planet's magnetic-field generated radiation belts.  But it did.  The craft also pioneered the use of the gravity boost technique when it swung past the large planet.  

For the general public the most memorial aspect of Pioneer may be the widely publicized gold plaque it bears. Designed by Carl Sagan and Frank Drake -- two scientist with an interest in exobiology -- the gold-anodized aluminum rectangle is attached to support struts behind the communications antenna.  It depicts, in line drawings, a man and woman standing in front of a representation of Pioneer 10 (for scale), the position of our system in the galaxy based on the location of pulsars, a stylized depiction of our system and Pioneer's path thought it, and other information that an intelligent race of beings can decipher.  Thus Pioneer will depart the Solar System as a cosmic "message-in-a- bottle" on its 2-million year crossing to another star system. 

Detail of Pioneer 10 plaque depicting the craft's passage from Earth to Jupiter.

Pioneer 10s post-Jupiter mission was to find the heliopause -- where particles from outside the Solar System encounter particles from the Sun.  The probe passed the orbit of Pluto in 1990 and is fast approaching twice that distance without having found this zone.  With budget priorities elsewhere, NASA officially cancelled the Pioneer project in 1997. But a dedicated group of people managed to maintain contact with Pioneer 10.  First as a training exercise for the Lunar Prospector project controllers and now in an experiment to develop new techniques for faint signal data extraction.  This small team at NASA-Ames keeps an  ancient DEC PDP 11-14 computer in repair to communicate with the probe though the Deep Space Network.  But software changes to the network means that in the next few years contact will have to be lost with Pioneer 10.

Reading the history of the Pioneer 10 mission brings the realization that the "faster, better, cheaper" mantra the space agency invented in the 1990s was an attempt to capture the "can-do" attitude of an earlier NASA.  James Van Allen, one of the principal investigators on Pioneer, states in the article: "As far as I'm concerned, NASA just rediscovered the principal."

Mars Beckons: Research at NASA-Langley

Spaceviews.com; Nov 29, 2000; News: "Mars Probes Take On Tough Challenges"

Aeroshell. NASA-Langley.

NASA-Langley in Hampton, Virginia, is conducting research on improved ways to land spacecraft on the planet Mars.  Wind tunnel and computer studies are being conducted to determine how the Martian atmosphere can be used by probes to assume orbit or land on the planet.  Many of the technologies under development will be employed on Mars-bound craft that NASA will be launching in upcoming years.

One technology being studied is aerocapture: a method of diving a craft deep into the atmosphere of Mars in order to slow it down and obtain a desired orbit around the planet.  Atmospheric induced drag is also employed in aerobraking -- a method tested by the Mars Global Surveyor -- to gradually dip a vehicle into the upper atmosphere over a period of time to influence the orbit.  Sensors monitor heat build-up so the maneuver does not to harm the craft.  These methods must contend with the changing nature of the of Martian atmosphere.  Both techniques save spacecraft weight by not requiring extra fuel be carried to obtain a desired orbit. 

The flight profile thought the Martian atmosphere for airbag-bundled lander/rovers is also being studied.  Akin to the Mars Pathfinder method of landing, airbag shrouded landers will deposit improved rover vehicles to the Martian surface in future mission.  For these new missions vehicle mass and trajectory will differ from that of Pathfinder. 

Langley is defining a "smart lander" that aerobrakes and maneuvers through the Martian atmosphere on its way to a pin-point landing.  The lander will need to compute glides and banks in real-time to arrive at the target area.  Here the goal is to reduce the landing zone from the current 100-km to 200-km wide swath to just a 3-km long zone.  Various "aeroshells" are being considered for the lander to conduct this "aero-maneuvering."

It is hoped that demonstrating each of the these technologies over several missions will help prepare for the ultimate goal: a sample return mission that will bring coveted pieces of the Red Planet back to Earth for study.

Where Has All the Matter Gone?

University of Hawaii Institute for Astronomy; Nov. 8, 2000; MACS Press Release: “Scores of Newly Discovered Galaxy Clusters Have Broad Implications for Cosmology”

Galaxy Cluster

"MACS been mind-bogglingly successful at finding the elusive massive, distant galaxy clusters," states Dr. Harald Ebeling of the Massive Cluster Survey.  Much as stars can be gravitationally bound into clusters, so can galaxies form associations with thousands of members.  Detecting these galaxy clusters, the largest structures bound by gravity, broadens our understanding of the history and future of the Universe.  In this case data from MACS, on the number and distance of these clusters, challenges current understanding of how the Universes evolved.  Drs. Ebeling and J. Patrick Henry from Hawaii and Dr. Alastair Edge of the University of Durham, U.K., presented MACS findings at the High Energy Astrophysics Division of the American Astronomical Society meeting in Honolulu, Hawaii. 

Before MACS hundreds of clusters in our region of the Universe were known.  MACS's goal is locating more distant examples of these clusters.  The search is being conducted by studying archival All-Sky Survey data from ROSAT -- the German X-ray satellite.  ROSAT data is employed because the enormous quantity of hot gas in galaxy clusters, while invisible to optical telescopes, cause them to stand-out in the X-ray spectrum.  The MACS team revealed that one-hundred-one distant clusters have been discovered after analysis of three-quarters of the ROSAT data.  Large telescopes in Hawaii, radio telescopes in California, and the orbiting Chandra X-ray Observatory are conducting follow-up studies of some of the new cluster groups.

The great number of clusters detected is not the most important result of the study -- the distance is.  These clusters are billions of light-years away -- an indication that they formed when the Universe was half as old as it is today.  Prior studies had detected only a few clusters at great distance and concluded that galaxy clusters may have formed within the last 3-billion years -- less than the age of the Earth.  MACS data seems to indicate that much of the mass of the Universe was locked-up by these clusters long-ago.  Because clusters contain massive amounts of dark matter, they are important in determining the matter density of the Universe.  This quantity, known as omega, determines whether the universe will continue to expand.  A low value of omega means the universe will expand forever.  The MACS researchers expect to determine omega with high accuracy.

And that is where interpretation of the MACS results so-far challenges the accepted value range of omega.  "The analysis is not yet complete, but it is already clear that our observations are in conflict with a high value of omega," says  Dr. Edge.