Space & Astronomy/Space and Astronomy (October 1993).iso/mac/TEXT/JPLNEWS1/0414.PR

Text File | 1993-04-21 | 7KB | 137 lines

OFFICE OF PUBLIC INFORMATION
JET PROPULSION LABORATORY, CALIFORNIA INSTITUTE OF TECHNOLOGY
NATIONAL AERONAUTICS AND SPACE ADMINISTRATION
PASADENA, CALIFORNIA.  TELEPHONE [phone]

                                 September 30, 1966

                      SURVEYOR II MISSION
         The National Aeronautics and Space Administration's
Surveyor II spacecraft impacted the moon near the crater Coper-
nicus on September 22, 1966.
         Its propellants depleted, power consumed and in an out-
of-control tumble, the spacecraft--second in a series of seven--
failed in its mission objective to soft land on the lunar
surface.
         Surveyor II was to land in the Central Bay area near
the exact center of the moon as seen from Earth and repeat the
performance of Surveyor I which transmitted 11,150 lunar
surface photographs of the Ocean of Storms during June and July
of 1966.
         Five more Surveyors are planned for 1967.  They are
built for NASA by the Hughes Aircraft Company under contract to
the Jet Propulsion Laboratory who has Surveyor Project manage-
ment responsibility.
         Earth communications with Surveyor II was lost at 2:35
a.m. Pacific Daylight Time Thursday, September 22, 45 hours and
three minutes after it was launched from Cape Kennedy.
         For more than 24 hours, engineers at the Jet Propulsion
Laboratory attempted to correct the out-of-control tumbling con-
dition which began during the midcourse trajectory correction. Z

                              -2-
         Surveyor Project officials said the tumble was caused
by the failure of one of three vernier (throttleable) rocket
engines to develop thrust during the thrust phase of the mid-
course maneuver at 10:00 p.m. PDT September 20.
         Flight control engineers at JPL first tried to
stabilize the spacecraft with small nitrogen gas jets, part of
Surveyor's attitude control system, but abandoned the attempt
because the rapid tumble was beyond the correction capability
of the jets.
         In order to stabilize the spacecraft, it was necessary
that all three vernier rocket engines fire simultaneously.  The
same three-engine firing is required to perform a controlled
landing.
         A total of 38 attempts to fire the engines at various
thrust levels and durations were made beginning a few hours
after the maneuver.  In each case, only two engines ignited.
         The final attempt, at 1:05 a.m. on September 22, was
commanded from the Canberra, Australia, tracking station of
NASA's Deep Space Network and called for a full-thrust motor
burn for 20 seconds.  While a proper three-engine firing might
have corrected the 92-rpm tumble, the partial, off-center thrust
increased the tumble rate to 136 rpm.
         Because the tumble prevented the spacecraft's solar
panel from locking onto the sun, Surveyor was operating on
battery power alone.  Knowledge that the battery life was  V

                              -3-
nearing an end prompted project officials to conduct experiments
in an effort to obtain as much engineering data as possible
before the mission ended.
         Commands were transmitted from the Canberra station to
vent helium gas used to pressurize the vernier engines, erect
the solar panel, turn on the radar altimeter and doppler velo-
city sensor normally used during the final descent phase of
Surveyor flight and fire the main retro engine.
         Activation of the radar system gave engineers important
data on the capability of a weakened spacecraft battery to
provide electricity to a system with large power requirements
and the capability of the RADVS to function under abnormally
low battery voltage.
         Helium venting provided information on the reliability
of a possibly faulty telemetry pressure sensor to aid in
determining the cause of the failure of the vernier engine.
         Because of centrifugal force of the tumbling, the
solar panel was not able to follow the commands it received.
In addition to the possibility of obtaining some solar energy,
it was hoped that movement of the panel would provide mechanical
data.
         The main retro motor was ignited at 29 seconds after
2:34 a.m.  Planned as the last event in the mission of Surveyor
II, it was recognized that firing of the 10,000-pound-thrust
engine under the tumbling conditions might terminate communica-
tions with the spacecraft. V

                              -4-
         The retro was fired to provide valuable engineering
information on the command ignition circuitry and the ignition
and burning of a large solid fuel motor in the vacuum of space
when it became apparent that Surveyor II's mission objectives
could not be achieved.
         The Canberra station was able to track Surveyor during
30 seconds of the 40-second-duration firing.  Loss of radio
lock occurred at 2:35 a.m.
         Up to the time of loss of contact, despite the tumbling
motion of the spacecraft, there was no evidence of further
failure in the Surveyor beyond the failure of vernier engine
number 3 to fire upon command.
         Helium tank depressurization increased the tumble rate
from 136 rpm to 146 rpm.  At the time of communications loss
during retro fire, the tumble slowed to 116 rpm.
         Whether or not the spacecraft was intensely damaged
structurally by the large stresses from retro firing under the
tumbling condition was not known.  However, there is no reason
to believe that there was any wholesale breakup of the space-
craft.
         Prior to mid-course maneuver, all launch vehicle and
spacecraft events occurred normally.
         The countdown on September 20 was interrupted several
times by minor problems with both stages of the Atlas-Centaur
launch vehicle.  Liftoff was scheduled for 4:56 a.m. PDT with a
window extending 36 minutes until 5:32 a.m. X

                              -5-
         At T-minus-two-minutes, a liquid oxygen pressurization
problem in the Atlas first stage caused a hold and a recycling
of the count which resulted in a liftoff less than a fifth of a
second before the end of the window.  Liftoff occurred at
5:31.824 a.m. PDT at an azimuth of 114.361 degrees.
         Accuracy of the Atlas-Centaur on the Surveyor II
mission outdid the excellent performance of its predecessor in
boosting Surveyor I toward the moon.  Surveyor II would have hit
the moon within about 25 miles of the aiming point on a direct
ascent launch from Earth without a mid-course maneuver.
         A maneuver, however, was required to put Surveyor down
at the desired location, a smooth portion of the moon's Central
Bay.  The failure of one of the three vernier engines became
known during the thrust phase of the maneuver.
         Surveyor II's impact point and time of impact--8:18
p.m. PDT September 22, 1966--was predicted from trajectory data
obtained from the spacecraft prior to loss of radio communica-
tions.


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