Interior Spectroscopic Investigation of the Propellant Energy Modes in an Arcjet Nozzle
Abstract : Internal emission spectroscopy measurements were performed in the nozzle expansion region of a 26 kW class ammonia arcjet. A series of three optical access ports (0.020-inch diameter) were equally spaced along the center line of the expansion nozzle. Atomic and ionic excitation temperatures of H and NII were determined through the use of Boltzmann plots. Electron density measurements were also taken based upon Stark broadening of the hydrogen beta Balmer transition. It is believed that a change in the mechanism governing the electron density occurred just downstream of the constrictor between the first two access ports lending evidence that arc attachment is occurring in this region. Although the trends for excitation temperatures and electron density were similar to those previously observed in 1 kW arcjets, the temperature values were found to be significantly less. In addition, vibrational and rotational temperatures of NH were measured and appeared to be frozen throughout the expansion nozzle.
Numerical Simulation of Nonequilibrium Species Diffusion in a Low-Power Nitrogen–Hydrogen Arcjet Thruster
Species distributions in a low-power arcjet thruster are investigated using a two-dimensional thermal and chemical nonequilibrium numerical model that incorporates the self-consistent effective binary diffusion coefficient approximation treatment of diffusion. Plasma flows in arcjet thruster with different input mole ratios of nitrogen to hydrogen are modelled. It is found that species separation due to nonequilibrium chemical kinetic processes occurs mainly in the regions where the dissociation and ionization of nitrogen and hydrogen species take place. The enrichment of nitrogen molecules at the fringes of the arc and hydrogen molecules near the anode wall of the thruster occurs mainly because the recombination processes of these two gases occur in different temperature ranges. In the expansion portion of the thruster nozzle, the gas residence times are of the same order as some chemical kinetic processes. Comparison between the nitrogen and hydrogen species profiles at the constrictor and thruster exit shows that the recombination of hydrogen ions and atoms are dominant kinetic processes near the thruster centreline, while the chemical reactions of nitrogen species are almost frozen in the high speed flow. The effects of temperature and pressure gradients on the species diffusion inside the arcjet thruster are also presented, with thermal diffusion found to have a much larger influence than pressure diffusion.
STUDIES ON TERRESTRIAL CONTAMINANTS OF METEORITES
During t h e l a s t ha l f d e c a d e a n unpara l le led upsu rge h a s t aken p l ace in t h e s tudy of meteor i tes , e s p e c i a l l y t h e ca rbonaceous chondr i tes . S c i e n t i s t s from all ove r t h e world, employing t h e newes t a n d most s e n s i t i v e an a1 y t i c a l t ec hni q u e s , i n v e s t i g a t e t h e ch e m i c a l composition of t h e o rgan ic mate t ia l found in t h e s e meteor i tes . In t h i s way they a r e trying to de te rmine t h e phys ica l c o n s t a n t s of t h e meteor i tes and e s t a b l i s h , on t h e b a s i s of minera logica l and petrolog ica l s t u d i e s , t h e cha rac t e r i s t i c s of t h e environmental condi t ions f r o m which t h e s e s t o n e s or ig ina ted and to desc r ibe and ident i fy cer ta in mic ros t ruc tu res which abound in s o m e of t h e s e ca rbonaceous chondr i tes . A l l of t h e s e research i n t e r e s t s a r e d i rec ted towards o n e pa r t i cu la r problem, t h e def in i te so lu t ion of which may indeed have revolutionary e f f e c t s o n ou r c o n c e p t s of t he universe. T h e ques t ion is whether or not t h e s e meteor i tes conta in t r a c e s of ex t ra t e r r e s t r i a l l i fe , t hus proving tha t some kind of biota eve r e x i s t e d o ther t han on t h e ear th , o r if a l l of t h o s e f ea tu res tha t t end to subs t a n t i a t e t h e prev ious ly mentioned h y p o t h e s i s a r e only t h e r e s u l t of contaminat ion by te r res t r ia l matter. T h e impor tance of t h i s problem w a s emphas ized by Berna l (1961: 130) in t h e following way: “ T h e v i t a l ques t ion cou ld be s e t t l e d o n c e and for a l l if s p e c i f i c molecu le s s u c h a s porphyrins o r nuc leo t ides were found. A counter ind ica t ion a t t he moment is t h e extremely low phosphorous conten t of t h e meteorite.” S ince tha t s t a t emen t w a s made, porphyrins (Hodgson & Baker, 1964) a n d poss i b l y nuc leo t ides (Nagy et al., 1963a) have been ident i f ied f r o m t h e Orgueil meteor i te , but s t i l l t he q u e s t i o n of t h e e x i s t e n c e of extrat e r r e s t r i a l life is far from be ing proven. I t is clear from the a b o v e tha t o n e of t h e b a s i c problems tha t o n e faces in t h e s tudy of meteor i tes is tha t of contamination. In order t o e s t a b l i s h unques t ionably t h e e x i s t e n c e o r p a s t e x i s t e n c e of ex t ra te r res t r ia l l i f e through t h e s t u d i e s of meteor i tes , two primary q u e s t i o n s h a v e to b e dea l t with s imul taneous ly . O n e h a s to d e c i d e