[FPSPACE] Pioneer 6 still transmitting after 35 years in space!

[Larry Klaes]

http://spaceprojects.arc.nasa.gov/Space_Projects/pioneer/PNStat.html

STATUS UPDATED: 13 December 2000 

Pioneer 10 

Launched 2 March 1972

Distance from Sun (1 December 2000): 76.61 AU 
Speed relative to the Sun: 12.24 km/sec (27,380 mph) 
Distance from Earth: 11.31 billion kilometers (7.025 billion miles) 
Round-trip Light Time: 20 hours 56 minutes 

There was a successful contact of Pioneer 6 for about two hours on 
8 December 2000 to commemorate its 35th anniversary.

The control room at NASA Ames Research Center in Mountain View, CA, 
was manned by Project Manager: Larry Lasher, Flight Director: Dave 
Lozier, Chief Flight Controller: Ric Campo, and Flight System Engineer; 
Larry Kellogg, with Network Operations Project Engineer: Ida Millner 
at JPL. 

Some 35 years from the launch date of 12/16/65, Pioneer 6 telemetry 
data were received expeditiously as spacecraft lockup occurred on the 
first attempt on Day 344 UT 0000:45 (local time 4:00:45 PM PST) at 
DSS-14 at Goldstone. 

Pioneer 6 was 83 million miles distant from Earth. The track lasted 
approximately 2.5 hours. The Signal-to-Noise Ratio (SNR)=9 dB and 
signal strength (AGC)=-164 remain at approximately the same levels 
as the last previous contact in October 6, 1997 demonstrating the 
stability and durability of NASA's oldest extant spacecraft. 
Viva la Pioneer! 

http://spaceprojects.arc.nasa.gov/Space_Projects/pioneer/PNhist.html

Pioneer 6 will be featured on the Star Date radio broadcast by the 
University of Texas McDonald Observatory on December 16 - the 35th 
anniversary of its launch. Pioneer 6 is the oldest NASA spacecraft 
extant. 

http://stardate.utexas.edu/

Pioneer 10 - "The Spacecraft That Will Not Die" - is featured in the 
Winter 2001 issue of the American Heritage of Invention & Technology 
magazine. The article written by Mark Wolverton follows the concept 
of the spacecraft born in the 1960s through its enduring legacy to 
this day and into the future. 

http://www.americanheritage.com/

"Pioneer Lives up to its Name" was a lead article about Pioneer 10 in
the Baltimore Sun in its December 10 issue written by Michael Stroh. 

http://www.sunspot.net/content/archive/story?section=archive&pagename=story&
storyid=1150520209023

The latest Pioneer 10 activity was on September 10, when DSS 63 tracked
the spacecraft. The station was not able to acquire the downlink. 
However, there was a report of two momentary receiver glitches at the 
Pioneer 10 frequency. This report was encouraging, since it means that 
the spacecraft signal is there, but it is still off Earth point. The 
Earth lookangle (ELA) is estimated to be over 1.4 degrees. The downlink 
signal strength drops off rapidly after 1.0 degree. The Earth is just 
starting to go back towards the PN 10 spin axis. As the year continues, 
the Earth will be closer in alignment with the spacecraft pointing and 
the tracking stations should be able to regain lock. We anticipate this 
to be about the middle of December. Our latest calculation of the 
ephemeris yields: 

Right Ascension = 76.27 degrees, Declination = 25.91 degrees. 

Since Pioneer 10 is over 75 AU distant and its telemetry signal is 
virtually at the limit of overall communication system's link margin, 
the spacecraft was chosen as a convenient test vehicle for the new 
methodology of Chaos theory. Chaotic.com has been testing the 
applicability of new methods in semi-blind signal estimation and 
noise reduction using Pioneer 10 signals. From the latest progress 
report by Richard. R. Holland of chaotic.com, there are two main 
areas of development: algorithm development and data analysis. 
Currently NASA and JPL are working with chaos.com to resolve issues 
regarding the data analysis. Keep tuned to this web-site for future 
progress reports on chaos theory and Pioneer 10. 

Larry Lasher, Pioneer Project Manager 


Pioneer 10 will continue into interstellar space, heading generally for 
the red star Aldebaran, which forms the eye of Taurus (The Bull). 
Aldebaran is about 68 light years away and it will take Pioneer over 
2 million years to reach it. 


Pioneer 11 

Launched 5 April 1973 

The Mission of Pioneer 11 has ended. Its RTG power source is exhausted. 

The last communication from Pioneer 11 was received in November 1995, 
shortly before the Earth's motion carried it out of view of the spacecraft 
antenna. 

The spacecraft is headed toward the constellation of Aquila (The Eagle), 
Northwest of the constellation of Sagittarius. Pioneer 11 may pass near 
one of the stars in the constellation in about 4 million years. 


Question: 
How far will Pioneer travel and on what path? 

Answer: 
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. 

Question: 
How much has Pioneer been eroded? 

Answer: 
All the wear, pitting, and erosion that Pioneer 10 has sustained are 
probably over now. The asteroid belt and the severe conditions of Jupiter 
have already been experienced. Now, Pioneer is in the vacuum of space 
where the average spatial density of molecules is one trillionth the 
density of the best vacuum we can draw on Earth. We expect Pioneer to 
last an indeterminate period of time, probably outlasting its home planet, 
the Earth. In 5 billion years, the Sun will become a red giant, expand,
envelop the orbit of the Earth, and consume it. Pioneer will still be out 
there in interstellar space. Erosional processes in the interstellar 
environment are largely unknown, but are very likely less efficient 
than erosion within the solar system, where a characteristic erosion 
rate, due largely to micrometeoritic pitting, is of the order of 1 
Angstrom/yr. Thus a plate etched to a depth ~ 0.01 cm should survive 
recognizable at least to as distance ~ 10 parsecs, and most probably to 
100 parsecs. 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. 

Question: 
Why and how is Pioneer 10 being maneuvered? 

Answer: 
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. 

Question: 
If the spacecraft are leaving the Solar System, why does the distance 
from Earth sometimes get shorter? 

Answer: 
It is a matter of a hyperbolic escape trajectory, geometry, and relative 
velocity vectors. The distance from the Sun is always increasing. However, 
since the Earth travels around the Sun faster than the spacecraft moves 
away from the Sun, the spacecraft-Earth distance decreases for a few 
months, and then rapidly increases again. 

Project Manager: Dr. Lawrence Lasher (e-mail:llasher@mail.arc.nasa.gov)