Pioneer 10

Specifications: Prime contractor  TRW Operator  NASA Mass at launch  250 kg Dry Mass   kg Dimension  1.45 long - 2.75 dia Basic shape  Hexagon + dish Solar array   Stabilization   Lifetime  Indefinite

Description:

The Pioneer 10 mission was the first to be sent to the outer solar system and the first to investigate the planet Jupiter, after which it followed an escape trajectory from the solar system. The spacecraft achieved its closest approach to Jupiter on December 3, 1973, when it reached approximately 2.8 Jovian radii (about 200,000 km). 

Pioneer 11 was the second mission to investigate Jupiter and the outer solar system and the first to explore the planet Saturn and its main rings. Pioneer 11, like Pioneer 10, used Jupiter's gravitational field to alter its trajectory radically. It passed close to Saturn and then it followed an escape trajectory from the solar system.

Fifteen experiments were carried to study the interplanetary and planetary magnetic fields; solar wind parameters; cosmic rays; transition region of the heliosphere; neutral hydrogen abundance; distribution, size, mass, flux, and velocity of dust particles; Jovian aurorae; Jovian radio waves; atmosphere of Jupiter and some of its satellites, particularly Io; and to photograph Jupiter and its satellites. Instruments carried for these experiments were: 

• Asteroid/Meteroid Detector (non-imaging telescopes with overlapping fields of view to detect sunlight reflected from passing meteoroids)
• Meteroid Detector (sealed pressurized cells of argon and nitrogen gas for measuring the penetration of meteoroids)
• Helium Vector Magnetometer (HVM)
• Infrared Radiometer
• Imaging Photopolarimeter (IPP)
• Trapped Radiation Detector (TRD)
• Plasma Analyzer (PA)
• Charged Particle Instrument (CPI)
• Cosmic Ray Telescope (CRT)
• Geiger Tube Telescope (GTT)
• Ultraviolet Photometer (UV)

The spacecraft body was mounted behind a 2.74-m-diameter parabolic dish antenna that was 46 cm deep. The spacecraft structure was a 36-cm-deep flat equipment compartment, the top and bottom being regular hexagons. Its sides were 71 cm long. One side joined a smaller compartment that carried the scientific experiments. The high-gain antenna feed was situated on three struts, which projected forward about 1.2 m. This feed was topped with a medium-gain antenna. A low-gain omnidirectional antenna extended about 0.76 m behind the equipment compartment and was mounted below the high-gain antenna. Power for the spacecraft was obtained by four SNAP-19 radioisotope thermonuclear generators (RTG), which were held about 3 m from the center of the spacecraft by two three-rod trusses 120 deg apart. A third boom extended 6.6 m from the experiment compartment to hold the magnetometer away from the spacecraft. The four RTG's generated about 155 W at launch and decayed to approximately 140 W by the time the spacecraft reached Jupiter, 21 months after launch. There were three reference sensors: a star sensor for Canopus which failed shortly after Jupiter encounter and two sun sensors. Attitude position could be calculated from the reference directions to the earth and the sun, with the known direction to Canopus as a backup. Three pairs of rocket thrusters provided spin-rate control and changed the velocity of the spacecraft, the spin period near the end of the mission being 14.1 seconds. These thrusters could be pulsed or fired steadily by command. The spacecraft was temperature-controlled between minus 23 deg C and plus 38 deg C. A plaque was mounted on the spacecraft body with drawings depicting a man, a woman, and the location of the sun and the earth in our galaxy. The design engraved into a gold-anodized aluminum plate, 152 by 229 millimeters, attached to the spacecrafts' antenna support struts to help shield it from erosion by interstellar dust.

Communications were maintained via 

• the omnidirectional and medium-gain antennas which operated together while connected to one receiver and 
• the high-gain antenna which was connected to another receiver. 

These receivers could be interchanged by command to provide some redundancy. Two radio transmitters, coupled to two traveling-wave tube amplifiers, produced 8 W at 2292 MHz each. Uplink was accomplished at 2110 MHz, while data transmission downlink was at 2292 MHz. The data were received by NASA's Deep Space Network (DSN) at bit rates up to 2048 bps enroute to Jupiter and at 16 bps near end of the mission.

Mission details:

• Passed 130400 km behind Jupiter on 1973 Dec 4.10
• Exceeded solar escape velocity. Expected final path apex near RA 04:33, declination 16.42°N.
  
  
  
• Occulted by Jovian satellite Io on 1973 Dec 04.11.
• Crossed the orbit of Neptune and left solar system on 1983 Jun 13.
• On 1990 Sep 22 became first spacecraft to reach 50 AU from the Sun, heading towards Aldebaran at 2.7 AU per year.
• As of Jan 1, 1997 Pioneer 10 was at about 67 AU from the Sun near the ecliptic plane and heading outward from the Sun at 2.6 AU/year and downstream through the heliomagnetosphere towards the tail region and interstellar space.
• At GMT 17:27:30, Saturday, 28 Apr 2001, the signal from Pioneer 10 was received at station 63 in Madrid, the first time since August 5/6 of 2000. So it appears that Pioneer 10 has life, albeit in another mode - i.e., only in a two-way coherent mode. We have been listening for the Pioneer 10 signal in a one way downlink non-coherent transmission mode since last summer with no success. We therefore conclude that in order [for Pioneer 10] to talk to us, we need to talk to it. This means from now on, we need two-way round-trip light time (RTLT) passes to allow the Deep Space Network (DSN) to send up a strong stable signal to lock up with a coherent downlink signal.
• Pioneer 10 had another successful track on 9 Jul 2001 - exactly one year after the last pointing maneuver. The original results back on 9 Jul 2000 - weak signal - seemed to indicate that the maneuver may have failed. The signal strengths from the latest tracks, however, indicate that last year's weak signal was probably due to the onboard one-way oscillator. Therefore, we conclude that the maneuver did work, and another pointing maneuver will not be necessary until first quarter 2002.
• Situation on 5 Feb 2002:
  Pioneer 10 distance from Sun : 79.66 AU (1AU=149 598 000 km)
  Speed relative to the Sun: 12.24 km/sec (27,380 mph)
  Distance from Earth: 11.84 billion kilometers (7.36 billion miles)
  Round-trip Light Time: 21 hours 56 minutes
• On Aug 2006 Pioneer 10 is at 91.2 AU.

Questions:

• How far will Pioneer travel and on what path?
  Pioneer 10 will be in galactic orbit for billions of years. It is moving in a straight line away from the Sun at a constant velocity of about 12 km/sec. Until Pioneer 10 reaches a distance of about 1.5 parsec (309,000 AUs) - about 126,000 years from now - it will be dominated by the gravitational field of the Sun. After that Pioneer 10 will be on an orbital path in the Milky Way galaxy influenced by the field of the stars that it passes.
• Why and how is Pioneer 10 being maneuvered?
  The Pioneer spacecraft is spin-stabilized, spinning at approximately 4.28 rpm (Revolutions Per Minute), with the spin axis running through the center of the dish antenna. If a person were to sit in the spacecraft, looking through a hole in center of the dish antenna with a telescope, he would see the Sun traveling very slowly to the left. The Earth's path would describe a very narrow ellipse (the orbit is seen nearly edge-on) around the Sun. In July the Earth is near the right hand edge of the ellipse, and 6 months later will be near the left hand edge of the ellipse. The angle to the spacecraft between the left edge of the ellipse and the right edge is less than 2 degrees. In order to communicate with the spacecraft, the Earth has to be within 0.8 degrees of the boresight of the spacecraft antenna. Since the Earth moves by almost 2 degrees, the spacecraft has to be re-aimed at the Earth about twice a year. This is done by a "CONSCAN (conical scan) precession maneuver" executed by the spacecraft. The radio signal transmitted from an antenna on Earth is focused and reflected by the spacecraft dish antenna toward a small feed horn located on a tripod which is centered in front of the spacecraft dish antenna, and then conducted to a receiver in the spacecraft. During a CONSCAN maneuver, the feed horn is physically moved by 8 inches to one side. A ground command turns on a heater in a bellows filled with liquid Freon. The Freon boils, the bellows expands, and moves a mechanical piston and cam attached to the feed horn mounting plate against a mechanical stop. A micro switch cycles the heater power on and off to keep the feed in the offset position. With the feed in the offset position, the radio signal from the tracking station is seen by the spacecraft receiver as varying sinusoidally in amplitude (amplitude modulated). This error signal contains amplitude and phase information on the pointing angle between the spacecraft spin axis and the Earth and the direction to the Earth during the spin cycle. The minimum amplitude occurs during the spin cycle when the antenna points to the Earth, whereas the maximum occurs when the antenna dish points away from the Earth. The frequency of the modulation is equal to the spacecraft spin rate (4.28 rpm). The error signal is processed on board the spacecraft to calculate the timing requirements for firing the jets at the appropriate instant in the spin cycle to precess the spin axis towards the Earth. The CONSCAN processor averages the modulation over two revolutions of the spacecraft. On the third revolution, it orders two hydrazine thrusters (mounted 180 degrees apart on the rim of the dish antenna) to fire a short pulse of 0.0312 seconds duration. This moves the spacecraft spin axis a tiny amount toward the minimum amplitude value, i.e., the Earth, reducing the amplitude of the modulation by a small amount. This process is repeated each three revolutions, each time reducing the pointing angle error and the modulation amplitude. When the pointing angle is within 0.3 degrees of boresight, the processor terminates the maneuver automatically. Typically, about 20 to 28 pulses are fired. A ground command then executes to turn off the power to the feed offset heater, the gaseous Freon recondenses to pull the mechanism back to the normal centered position, and the maneuver is completed.
  (Ref: http://spaceprojects.arc.nasa.gov/Space_Projects/pioneer/PNStat.html )