The invention disclosed is directed to a method and apparatus for an arcjet starter. The invention discloses a method of moving an arc from the subsonic region of the thruster to the supersonic region by introducing a pressurized propellant into the casuty of the anode

Curran, Francis M.

Sankovic, John M.

NASA Technical Reports Server

US005540046A 
United States Patent [191 [ i l l  Patent Number: 5,540,046 
Sankovic et al. [451 Date of Patent: Jul. 30, 1996 
[54] METHOD AND APPARATUS FOR PRESSURE 
PULSE ARCJET STARTING 
[75] Inventors: John M. Sankovic, Brecksville; 
Francis M. Curran, Avon, both of 
Ohio 
[73] Assignee: The United States of America as 
represented by the Administrator of 
the National Aeronautics and Space 
Administration, Washington, D.C. 
[21] Appl. No.: 236,855 
[22] Filed: May 2, 1994 
[51] Int. Cl.6 ................................ F03H 1/00; H05H 5/00 
[52] U.S. C1. .............................................. 60/203.1; 60/204 
[58] Field of Search ............................... 60A39.141, 202, 
60/203.1, 204 
[561 References Cited 
U.S. PATENT DOCUMENTS 
4,577,461 311986 Cam ...................................... 60/203.1 
4,800,716 111989 Smith et al. ........................... 60/203.1 
4,805,400 211989 Knowles ................................ 60/203.1 
4,907,407 311990 Simon .................................... 601205.1 
5,076,051 121991 Naff ....................................... 601203.1 
5,111,656 511992 Simon .................................... 601203.1 
OTHER PUBLICATIONS 
AIAA-87-1951, Low Power Arcjet Thruster Pulse Ingnition 
Charles Sarmiento and Robert P. Gruber, propulsion Con- 
ference Jun. 29-Jul. 2, 1987. 
Primary Examiner-Louis J. Casaregola 
Attorney, Agent, or  Fim-Vernon E. Williams; Kent N. 
Stone 
[571 ABSTRACT 
The invention disclosed is directed to a method and appa- 
ratus for an arcjet starter. The invention discloses a method 
of moving an arc from the subsonic region of the thruster to 
the supersonic region by introducing a pressurized propel- 
lant into the casuty of the anode. 
4 Claims, 14 Drawing Sheets 
r2,0 
250-\ 
\ 
260 
https://ntrs.nasa.gov/search.jsp?R=20080004873 2019-08-30T02:54:28+00:00Z
U.S. Patent Jul. 30,1996 Sheet 1 of 14 
0 14 
5,540,046 
U.S. Patent Jul. 30,1996 Sheet 2 of 14 5,540,046 
. -  
-150 110 
FIG. 2 
U S  Patent Jul. 30,1996 Sheet 3 of 14 5,540,046 
FIG. 3 
U.S. Patent Jul. 30, 1996 Sheet 4 of 14 5,540,046 
FIG. 4 
U.S. Patent Jul. 30, 1996 Sheet 5 of 14 5,540,046 
FIG. 5 
U.S. Patent Jul. 30, 1996 Sheet 6 of 14 5,540,046 
L 
260 
270 d 
FIG. 6 
U.S. Patent Jul. 30, 1996 Sheet 7 of 14 5,540,046 
330 
31 0 J 
FIG. 7 
U.S. Patent Jul. 30,1996 Sheet 8 of 14 5,540,046 
370 J 400 
FIG. 8 
U.S. Patent Jul. 30, 1996 Sheet 9 of 14 5,540,046 
STATE OF THE ART 
I 
20 
TIME, s 
FIG. 9 
U.S. Patent Jul. 30,1996 Sheet 10 of 14 5,540,046 
PRESSURE PULSE TECHNIQUE 
20 
TIME, s 
FIG. 10 
U S .  Patent Jul. 30, 1996 Sheet 11 of 14 
200 
W- 
0 > 
STATE OF THE ART 
5,540,046 
4 
20 40 x IO -3 
TIME, s 
FIG. 11 
U.S. Patent Jul. 30, 1996 Sheet 12 of 14 5,540,046 
PRESSURE PULSE TECHNIQUE 
TIME, s 
FIG. 12 
U.S. Patent Jul. 30, 1996 Sheet 13 of 14 
200 
l i r  
STATE OF THE ART 
5,540,046 
T - T  
TIME, s 
FIG. 13 
U.S. Patent Jul. 30,1996 Sheet 14 of 14 5,540,046 
PRESSURE PULSE TECHNIQUE 
’ 200 
wi u 
F 100 
0 > 
I 
20 4ux 
TIME, s 
FIG. 14 
5,540,046 
1 2 
METHOD AND APPARATUS FOR PRESSURE 
PULSE ARCJET STARTING 
DESCRIPTION OF THE RELATED ART 
U.S. Pat. No. 4,577,461 the present invention relates to 
increasing the thrust efficiency of arcjet thrusters by sepa- 
ORIGIN OF THE INVENTION rating the gas flow into two flows, one of which is applied 
to the arc chamber and the second of which is used to cool 
The invention described herein was made by employees the chamber prior to recombination of the flows. U.S. Pat. 
ofthe United States Government and may be manufactured No. 4,800,716 this patent relates to a means of decomposing 
and used by or for the Government for governmental pur- the propellant gas prior to arching, a means of repositioning 
Poses Without the Payment Of mY royalties thereon Or 1o the cathode to reduce current at startup, and a means of 
therefore. lowering the startup pressure to reduce chamber erosion. 
U.S. Pat. No. 4,805,400 this patent relates to a means of 
varying the pressure flow to effect arc erosion of the thruster 
mechanism. U.S. Pat. No. 4,907,407 this patent relates to a 
The present invention is directed to a method and appa- 15 means of reducing arc jet erosion by specifying the geom- 
ratus for pressure pulse arcjet starting. etry of the cathode and anode. 
Arcjet starting has primarily gained prominence as a U.S. Pat. No. 5,076,051 this patent relates to the cathode 
research area because of the role of an arcjet in the propul- and anode as a vortex flow causing dispersion which reduces 
sion system of a geosynchronous body. For example, in most erosion effects during firing. U.S. Pat. No. 5,111,565 this 
satellite systems geosynchronous orbit is maintained by 20 patent relates to an arcjet nozzle geometry which increases 
frequent firing of on-board propulsion systems. Without the efficiency of an arc jet thruster by reducing losses in a 
propulsion system readjustment of these satellites, they recombinant collet following diffusion. 
would be susceptible to north south drifts and therefore lose 
their geosynchronous orbit. One of the keys to propulsion 
system readjustment is the frequent firing of a propulsion 25 
system is the arcjet starter. 
The geosynchronous stationkeeping of the normal com- 
FIELD OF INVENTION 
SUMMARY OF THE INVENTION 
The present invention is directed to a method of increas- 
ing the starts of an arcjet thruster. 
munication In the present invention a steady state flow of propellant 
looO times during the lifetime Of the 'peration' As a result* 3o gas is introduced in an area between the anode and cathode 
may require that an arcjet start Over 
it is critical that these systems remain resilient during the of an arcjet thruster. Before ignition of the arcjet a high 
pressure propellant housed upstream of the nozzle is loo0 start lifetime. 
pulse released. The pressurized gas causes a quick step increase in 
to ignite the arc discharge. Propellant is then released in the the region between the anode and the cathode of the arcjet 
region between the cathode and the anode and heated as it thruster as a series of pulses is initiated. the pressure and 
flows past the arc. The arc is struck between a cathode and 35 gas flow monotonically decreases, the pressure becomes low 
an anode. When the arc is initially struck it attaches to a enough to allow the ignition ofthe arcjet. since the 
Point On the anode upstream Of the throat in a is still higher than the steady state pressure, the arc is quickly 
similar to arc welding. This is a highly destructive undesir- blown downstream into the supersonic region of the anode, 
able situation, because the high energy concentration into a where it is distributed around a larger area in the anode. 
small point erodes the anode W'all. After ignition, gas 40 a result there is less destruction to the arcjet nozzle, thereby 
dynamic drag forces will push the arc into a supersonic enabling more starts throughout the life of the thruster. 
portion of the nozzle where the arc becomes diffuse, there- 
fore, it attaches evenly azimutually over an axial length of 
several millimeters of the anode. Since this is over a large 
surface area of the anode this mode of operation is not 45 
destructive to the anode. Therefore, the sooner the gas 
dynamic drag forces of the system can push the arc down- 
stream, the less destruction to the anode and the longer the 
life of the arcjet thruster. Starting power is very low, 
compared to steady-state power. To increase the perfor- 
mance W h i l e  maintaining the Same power level, the flow rate 
in an arcjet must be decreased. Decreasing the flow rate 
causes the gas dynamic drag forces pushing the arc down- 
stream into the supersonic region after ignition, to decrease. 
As a result, the time the arc remains in the destructive spot 
attached to the anode is increased, which in turn will cause 
an unacceptable failure of the engine. 
It is therefore an object of the present invention to 
increase the number of starts in an arcjet. 
It is another object of the present invention to increase the 
gas dynamic drag forces pushing the arc downstream con- 
sidering the limited power constraint of the spacecraft. 
It is still another object of the invention to increase the 
mass flow of the propellant during ignition and then 65 
decrease to a steady-state operating flow rate once the arc is 
blown into the supersonic region. 
The state Of *e art arcjet Wtem uses a high 
BRTEF DESCRIPTION OF THE DRAWINGS 
FIG. 1 displays a schematic view of the prior art arcjet 
FIG. 2 displays a view of the node and cathode region of 
FIG. 3 displays a view of the anode and cathode region of 
FIG. displays a picture of the drag force pushing the arc 
FIG. 5 displays a picture of the arc after it has been moved 
FIG. 6 displays a schematic of the pressure pulse arcjet 
thruster. 
the thruster. 
the arcjet immediately after ignition. 
down stream. 
downstream. 
55 
60 
starting mechanism. 
arcjet starter technique. 
tation of the arc jet starter. 
44.8 mg/s. 
pressure pulse technique at a flow rate of 44.8 mg/s. 
FIG. 7 displays a schematic of a flight system using the 
FIG. 8 displays an alternate flight system for implemen- 
FIG. 9 displays a state of the art thruster at a flow rate of 
FIG. 10 displays a graph of an arcjet thruster using the 
5,540,046 
3 
FIG. 11 displays a state of the art thruster at a flow rate of 
FIG. 12 displays a graph of an arcjet thruster using the 
FIG. 13 displays a state of the art thruster at a flow rate 
FIG. 14 displays a graph of an arcjet thruster using the 
33.0 mg/s. 
pressure pulse technique at a flow rate of 33.0 mg/s. 
of 21.3 mg/s. 
pressure pulse technique at a flow rate of 21.3 mg/s. 
DESCRIPTION OF THE PREFERRED 
EMBODIMENT 
The preferred embodiment of the present invention is 
displayed in the schematic diagram of FIG. 1. In the arcjet 
displayed in FIG. 1, current is provided to the thruster 
through a power conditioning unit 10. Power is transmitted 
through a power cable 20 to the cathode 30. The power 
crosses to the anode 33 in the form of an arc an then returns 
through the body wall of the electrode assembly 37. 
Propellant is supplied to the system through a fluid 
restrictor 40. The resistor 40, regulates the flow rate and the 
thruster operating pressure by creating a large pressure drop 
between the spacecraft propellant fluid system and the 
thruster. The thruster control valve 50 is a solenoid actuated 
dual redundant seat valve which controls propellant flow to 
a gas generator 60 which runs in an ordoff mode. In the 
preferred embodiment hydrazine decomposition gases flow 
from the gas generator 60 through a delivery tube 65 to the 
annular passageway defined by the anode 37. 
FIG. 2 displays an enlarged view of the electrode appa- 
ratus. The 15 anode 70 is defined by a subsonic region SO a 
constrictor region 90 and a supersonic region 100. Inserted 
in the subsonic region is a cathode 110. The area 140 defines 
the distance between the anode 70 and the cathode 110. In 
the preferred embodiment gas flow 150 is usually introduced 
in the annular area of the anode, in the subsonic region 80. 
After travelling through the constrictor 90, the gas 160 is 
then ejected through the supersonic region 100. 
In FIG. 3 the gap 180 between the beginning of the 
constrictor 90 and the beginning of the arc 190 is defined. In 
FIG. 4 the arc 190 in FIG. 3 has extended as displayed by 
the gap 200 displayed in FIG. 4, as the arc 210 moves farther 
into the constrictor. Lastly, in FIG. 5 the arc 220 has been 
blown into the supersonic region 100 of the anode by gas 
dynamic drag forces. 
There are several methods to generate a pressure pulse in 
the arcjet starter described above, FIG. 6 illustrates one 
technique. In FIG. 6 a first valve 240, which controls the 
steady-state flow of the gaseous propellant source 230 to the 
arcjet thruster 250 is closed and a second valve 260 is 
simultaneously opened allowing propellant to fill an accu- 
mulator 270. The second valve 260 is then closed isolating 
the accumulator and the first valve 240 is opened allowing 
the normal operating flow to pass from the propellant source 
230 to the arcjet thruster 250, creating a first pressure in the 
arcjet thruster. A Pressure pulse is then created when the 
second valve 260 is opened. Opening the second valve 260 
generates a step increase in the pressure in the thruster 
carrying the thruster up to a second pressure. Once the 
accumulator has discharged its pressurized propellant, the 
pressure in the thruster is then allowed to monotonically 
decrease to a level between the second and first pressures 
which will allow an arc to be struck between the anode and 
lathode. 
Alternate Embodiments 
For a flight system using hydrazine as a propellant the 
embodiment displayed in FIG. 7 may be used. In FIG. 7 
4 
propellant from the space propellant feed system 280 is fed 
into the fluid resistor 290. Initially a first valve 300 is opened 
allowing propellant to flow to the arcjet 340 by way of a first 
gas generator 320. To achieve monotonically decreasing 
5 chamber pressure which is required to strike an arc in the 
arcjet 340 a second valve 310 is cycled open and close, 
thereby cycling gas to the arc jet 340 through a second gas 
generator 330. 
An alternate embodiment to the flight system presented in 
10 FIG. 7 is displayed in FIG. 8. In FIG. 8 the propellant 350 
is fed into a first fluid resistor 360 and a second fluid resistor 
370 simultaneously. A first valve 380 is opened allowing a 
steady state flow of propellant to pass through the fluid 
resistor 360 to the gas generator 410. The gas generator 410 
15 then processes the propellant fluid and delivers it to the 
arcjet thruster 420. A second valve 400 serially attached to 
the second resistor 370, is cycled open and close causing an 
extra surge of propellant and a sudden increase in the 
chamber pressure of the arcjet thruster 420. The chamber 
20 pressure then decreases monotonically to a pressure that 
allows an arc to be struck between the cathode and the 
anode. 
The initial pressure of the arcjet thruster, depends on the 
flow rate and the diameter of the nozzle used. In the present 
25 invention a 2:l nitrogenhydrogen mixture was used with a 
0.25” nozzle diameter. 
When the flow rates given below were applied, the 
following pressure resulted: 
_ _  
Flow rate, mg/s Pressure, psia 
45 
31 
30 
42.2 
34.3 
29.3 
JJ 
The pressure attained after a release of propellant from the 
accumulator is a function of the volume of the propellant 
system, initial pressure, and the thruster geometry. For the 
test detailed above, the pressure was 85 psia. 
The time required for the pressure to decrease to the 
ignition pressure is a function of the starting voltage pulse, 
the thruster throat diameter, the propellant flow rate; and the 
volume of the propellant system. For the apparatus used in 
45 the disclosed invention the time required for the pressure to 
decrease was 21 seconds. 
The number of high voltage pulses required for starting 
depends on the frequency of the pulse and the rate of 
pressure decrease. In the test using a 37 mg/s flow rate with 
50 a pressure decrease of 215 and a pulse frequency of 12 Hz, 
252 pulses resulted. 
The objective of the invention is to move the arcjet from 
“low mode” operation of 50 V to the high mode operation 
of 100 V or greater. At 50 v or below the arc is still in the 
55 subsonic reason, therefore, it is destructive. While in the 
“high mode” operation the arc has extended into the super- 
sonic region and therefore is not destroying the arcjet 
thruster. With the state of the art drawings, FIGS. 9, 11, and 
13, which represent flow rates of 44.8 mg/s, 33.0 mg/s and 
60 21.3 mg/s respectively. The arcs are still in low mode (250 
V) after 40 milliseconds. The graphs of the pressure pulse 
technique, FIGS. 10, 12 and 14 display the arcjet thruster 
performance at flow rates of 44.8 mg/s, 33.0 mg/s and 21.3 
mg/s, respectively. The graphs show that with the pressure 
65 pulse technique the arcjet thruster is operating in “high 
mode” (voltage greater than loo), almost as soon as the 
thruster ignites at time 0. 
40 
5,540,046 
5 
While several embodiments of the method and apparatus 
of the arcjet starter have been disclosed, it will be appreci- 
ated that various modifications may be made without depart- 
ing from the spirit of the invention and the scope of the 
subjoined claims. 
What is claimed: 
1. A method of starting an arcjet thruster, said thruster 
including an anode having a subsonic region and a super- 
sonic region, said method comprising the steps of: 
introducing a constant flow of propellant into said arcjet 
thruster thereby creating a first pressure in the subsonic 
region of said arcjet thruster, 
introducing additional propellant into said arcjet thruster 
whereby a pressure pulse is initiated thereby creating a 
second pressure which is higher than the first pressure 
in said arcjet thruster, 
initiating voltage pulses in said arcjet thruster whereby an 
arc is created in the subsonic region at a pressure higher 
than the f is t  pressure, and blown from said subsonic 
region of said anode to said supersonic region of said 
anode in less time, due to the higher dynamic forces on 
the arc, than would occur if the arc was created the 
subsonic region at the first pressure. 
2. A method as claimed in claim 1 wherein said voltage 
pulses are initiated as pressure in said arcjet thruster mono- 
tonically decreases from said second pressure to said first 
pressure. 
6 
3. A method of arcjet starting, said arcjet starter including, 
a power processing unit, a gas propellant source, an arcjet 
thruster, an accumulator, a first valve serially connected to 
said propellant source and the arcjet thruster, a second valve 
serially connected between said accumulator and the pro- 
pellant source, said method comprising the steps of: 
closing said first valve and opening said second valve, 
thereby filling said accumulator with propellant from 
closing said second valve and opening said first valve 
whereby gas flows from said propellant source to said 
arcjet thruster thereby creating a first pressure in said 
opening said second valve whereby gas flows from said 
accumulator through said first valve to said arcjet 
thruster thereby creating a second pressure in said 
arcjet thruster, 
utilizing said power processing unit to initiate a series of 
high voltage pulses in said arcjet thruster thereby 
starting said arcjet thruster. 
4. A method as claimed in claim 3 wherein said high 
voltage pulses are initiated as said second pressure mono- 
tonically decreases to said first pressure. 
IO said propellant source, 
15 arcjet thruster, 
2o 
25 
* * * * *  


Method and apparatus for pressure pulse arcjet starting

Abstract

Similar works

Full text

Available Versions

NASA Technical Reports Server