Molecular sink facility and 25-foot space simulator have been used to distinguish nature of exhaust plumes from nozzles with relatively large internal boundary layer flow. Plume density has been measured by electron beam/photomultiplier system

Herrera, J. G.

Stephens, J. B.

English

NASA Technical Reports Server

March 1973
	
B73-10137 
NASA TECH BRIEF 
NASA Pasadena Office
	 4r 
NASA Tech Briefs announce new technology derived from the U. S. space program. They are issued to encourage 
commercial application. Tech Briefs are available on a subscription basis from the National Technical Information 
Service, Springfield, Virginia 22151. Requests for individual copies or questions relating to the Tech Brief program may 
be directed to the Technology Utilization Office, NASA, Code KT, Washington, D.C. 20546. 
Rocket Plume Properties Measured in Space Simulators 
Methods for determining the dynamic properties of 
rocket plumes emanating from small nozzles in a 
vacuum are, of course, extremely important because 
the results make possible an evaluation of the inter-
action of the plumes with spacecraft surfaces; how-
ever, the methods developed for aerospace purposes 
may also be of importance for terrestrial applications 
such as the design of diffusion pump jets for multiple 
stage vacuum pumps. 
Characterization of the nature of exhaust plumes 
from nozzles with relatively large internal boundary 
layer flow has taken place in a 25-foot space simulator 
facility and in a molecular sink facility. The molec-
ular sink facility provides means for performing tests 
at pressures as low as 10 torr with a continuous flow 
of about 0.07 mole of gas per second, or an equivalent 
altitude of 160 km at 0.01 mole of gas per second. 
Plume density has been measured by an electron 
beam/photomultiplier system. 
Study of rocket nozzle plume flow fields as they 
would occur in space requires that the plume be un-
disturbed either by the chamber wall or by the meas-
uring instruments. The first requirement was accom-
plished by a 20°K wall of the chamber because it 
captured virtually all of the gas molecules on first 
encounter. The second was met by means of an elec-
tron beam/photomultiplier system and an array of 
quartz-crystal microbalances located away from the 
nozzle. 
The electron beam system is based on use of a 
collimated beam of electrons which is projected into 
the plume, resulting in an illuminated path whose
intensity and spectral characteristics are related to 
gas density, composition, and temperature. The fluo-
rescence of the beam is measured by a photomulti-
plier whose output is normalized by the electron 
beam current; the photomultiplier/electron beam sys-
tem is calibrated against known gas density. Move-
ments of both the beam and the photomultiplier 
allow determination of the density at any desired 
point in the plume. 
Measurement of the mass-flow per unit area (nitro-
gen) has been effected by means of twelve 5-MHz 
quartz-crystal microbalances utilizing quartz crystal 
sensors mounted in various locations on the walls of 
the chamber. The quartz crystals are frequency sensi-
tive and can detect changes in mass. 
Notes: 
1. Quartz-crystal microbalances have also been used 
in biological studies; see Tech Brief B72-10243. 
2. Requests for further information may be directed 
to:
Technology Utilization Officer 
NASA Pasadena Office 
4800 Oak Grove Drive 
Pasadena, California 91103 
Reference: TSP 73-10137 
Source: James B. Stephens and Joseph C. Herrera of
Caltech/JPL
under contract to

NASA Pasadena Office 
(NPO-1 1608) 
Category 03 
This document was prepared under the sponsorship of the National 	 Government assumes any liability resulting from the use of the 
Aeronautics and Space Administration. Neither the United States 	 information contained in this document, or warrants that such use 
Government nor any person acting on behalf of the United States 	 will be free from privately owned rights.
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Rocket plume properties measured in space simulators

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