Our SpaceFlight Heritage: Departing the safe harbor – the flight of Pioneer 10
CAPE CANAVERAL, Fla — Thirty-two years ago, on June 13, 1983, NASA’s Pioneer 10 spacecraft crossed the orbit of Neptune and left the Solar System for points unknown, venturing from the confines of our tiny portion of the cosmic backyard and into the vast, unexplored regions of the galaxy. With its mission to explore the gas giant Jupiter complete, it was left to fly ever outward, a messenger for humanity in the icy cold void.
With a launch mass of about 569 lbs (258 kg), Pioneer 10 was the first mission to be sent to Jupiter as well as the first vehicle to achieve the escape velocity required to leave the Solar System.
Managed by NASA’s Ames Research Center in California, the spacecraft was built on a hexagonal-shaped bus by TRW. Pioneer 10 was equipped with a 9 foot (2.74 meter) diameter parabolic dish high-gain antenna, which was made from aluminum honeycomb sandwich material.
The spacecraft was kept in constant rotation at 4.8 rpm about an axis that was parallel with the axis of the antenna, thereby ensuring that it was kept orientated toward the Earth. The spin-rate was maintained by six 4.5 N hydrazine thrusters mounted in three pairs: pair one sustained the spin, pair two managed the forward thrust, and pair three controlled the attitude.
Pioneer 10’s power was provided via four SNAP-19 radioisotope thermoelectric generators which, at launch, imparted 155 watts, but had decayed to 140 watts by the time of the Jupiter encounter – the spacecraft required 100 W to power all of its systems. The SNAP-19 RTGs were required to provide power for at least two years in space – this was greatly exceeded throughout the mission.
Although the plutonium-238 that powers RTGs has a half-life of 87.74 years, steady degradation of the thermocouple junctions led to rapid deterioration in the spacecraft’s RTGs electrical generation; therefore, by 2001, the total power output was just 65 W – insufficient to maintain power to the spacecraft’s transmitter and systems.
At the behest of Carl Sagan, NASA had agreed to place a pair of gold-anodized aluminum plaques – measuring 152 mm by 229 mm (6.0″ by 9.0″) – featuring a pictorial message from mankind on board the 1972 Pioneer 10 and the 1973 Pioneer 11 spacecraft.
Both of the plaques depict nude figures of a human male and female along with several scientific symbols which are designed to provide information about the origin of the spacecraft to any extraterrestrials that may intercept either one of them at some distant future. The plaques were attached to the two spacecraft’s antenna support struts in a position that would provide some shielding from erosion by interstellar dust.
The path-finding spacecraft’s journey began more than a decade earlier when it was launched on March 3, 1972, by an Atlas-Centaur expendable vehicle from Cape Canaveral Air Force Station in Florida. Pioneer 10 was the first spacecraft to travel through the asteroid belt from July 15, 1972, and February 15, 1973. The craft began photographing Jupiter in Nov. 1973, reaching its closest encounter with the Jovian planet on Dec. 3, 1973.
At closest approach, reaching a velocity of 132,000 km/h, the spacecraft came within 132,252 km above the Jovian cloud tops; the probe captured some 500 images during the encounter and beamed them back to Earth. Pioneer 10 would greatly increase humanity’s understanding of Jupiter, the asteroid belt, the solar wind, and other aspects of the outer Solar System.
Radio communications with Pioneer 10 ceased on Jan. 23, 2003, due to its radio transmitter losing electric power. At this point in the mission, the vehicle was some 12 billion kilometers (80 AU) from Earth. Further attempts to establish contact with the spacecraft were unsuccessful. A final attempt was made on March 4, 2006, the last time when the spacecraft’s antenna was correctly aligned with Earth, but no response was received. NASA had deemed that the RTG units had probably degraded below the power threshold necessary to operate the transmitter; therefore, no further attempts at contact were made.
Now Pioneer 10 silently cruises interstellar space as a ghost ship, heading in the general direction of the red star Aldebaran, 68 light-years distant, in the constellation of Taurus (the Bull) – a destination which will take it more than 2 million years to reach.
Jason Rhian spent several years honing his skills with internships at NASA, the National Space Society and other organizations. He has provided content for outlets such as: Aviation Week & Space Technology, Space.com, The Mars Society and Universe Today.