APPENDIX E

ANALYSIS OF ARCING POTENTIALS AT REDUCED PRESSURE

It has been postulated that the Ranger 6 TV Subsystem failure was due to high voltage breakdown in the transmitter power supplies resulting in their destruction. Two conditions could facilitate such breakdown, if suitable potentials existed within those units:

1)

2)

Reduction of internal pressures through critical regions due to venting
to atmosphere.

Reduction of breakdown voltages due to contamination of the internal environ-
ment by outgassing of materials contained in the units.

The ambient pressure-altitude profile is shown in Appendix D. It is apparent that the Agena shroud pressure virtually coincides with ambient beyond 90,000 feet altitude, and it is assumed from the mechanical design that the internal pressures of the TV Subsystem units lag the shroud pressure by about one order of magnitude. Material outgassing and the breakdown mechanism are discussed in the following paragraphs.

An experimental program was undertaken at JPL to determine the transient pressure rise in a typical volume with a known vent area as a result of heating samples of materials used in the Ranger TV Subsystem. Preliminary results indicate that for the types and quantities of materials used inside the "black boxes" and the amount of existing box venting, outgassing is not of sufficient magnitude to raise the pressure into the critical range and cause corona discharge. Additional specific tests are being run to confirm in detail this general conclusion.

Paschen's law states that, for a given gas and specified electrode geometry, the breakdown potential is a function of gas pressure and electrode separation. A breakdown of potential between two electrodes may be caused by electrons which are accelerated in the electric field between the electrodes. When there is a gas present between the electrodes. the acceleration of electrons causes a formation of ionized particles. The electrons collide with the gas atoms, and lose kinetic energy with each collision; then between collisions they gain kinetic energy from the electric field. If sufficient energy is gained between collisions, ionization takes place. A minimum amount of energy is required to ionize an atom. If ionization occurs, the number of electrons is multiplied by a factor of 2 for each collision,

The number of

so there is an avalanche of electrons created. The electric field is proportional to the voltage and inversely proportional to the distance between the electrodes. collisions is proportional to the pressure. This means that the breakdown voltage will be a function of the pressure multiplied by the distance between the electrodes. If there is a high vacuum, with few atoms available, there will be less chance that the negative electrons liberated from the cathode will collide with an atom, and no breakdown will occur unless the voltage is extremely high. If the pressure is too high, the electron will suffer too many collisions, and will not gain sufficient energy between collisions to ionize. As a result, there is a minimum breakdown voltage for an intermediate pressure.

The gaps between possible electrodes in the TV Subsystem transmitter power supplies range from 0.1 to 2.0 inches. The maximum steady state voltage in the power supplies is 1000 volts, with turn-on transients ranging to perhaps 1500 volts. Figure E-1 illustrates Paschen's law for the two gap distance extremes in air.

10

A.

INTRODUCTION

APPENDIX F

RA-6 DYNAMIC ENVIRONMENT DURING BOOST

The various subsections and illustrations described in this appendix are intended to describe in some detail the dynamic environment of Ranger 6 from launch through first Agena burn cutoff, and to compare the actual environment with previous data compiled on RA-1 through RA-5.

Figures F-1 through F-9, F-17 and F-18 are actual data analysis records as obtained from the magnetic tapes telemetered from the launch vehicle.

Figures F-10 and F-11 are photographs of a typical Block I and II flight vibration monitoring point and the actual flight monitoring point for RA-6, respectively.

Subsections B through F describe in detail the dynamic difference between the flight monitoring point for vibration for Ranger Blocks I and II and Block III (Ranger 6 configuration).

B.

EFFECT OF DIAPHRAGM AND MOUNTING BLOCK CHANGES ON THE MEASURED
FLIGHT VIBRATION OF RA-6 AS COMPARED TO RA 1-4

1. Introduction

The large increase of measured vibration on RA-6 over that measured on RA 1-4 is explained by the effects of changing and slightly moving the accelerometer mounting block on RA-6, and to a lesser extent by removing the sterilization diaphragm. These effects were measured and the RA-6 data corrected for comparison with RA 1-4.

Measured vibration levels from the RA-6 flight were significantly higher than those measured on the previous Ranger flights (Blocks I and II). There were two changes on the RA-6 configuration which might account for this increase in measured vibration:

1) The sterilization diaphragm flown on RA 1-5 was removed on RA-6.

2) The accelerometer mounting block used on RA 1-4 was modifed and relocated for RA-6.

#Ranger RA-5 had no high frequency measurement.