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https://ntrs.nasa.gov/search.jsp?R=19850007496 2020-07-30T12:01:52+00:00Z

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ION THRUSTER PROJECT

G. E. Pe rche

Translation of "Proieto de um r-ro-3ulsor lonico",Instituto de Pesquisas rspaciais, Sao Jose dos.Campos (Brazil), Report I1PE-2803-PRE/363, July,1983, pp. 1-16.

NATIONAL AERONAUTICS AND SPACE AD=gISTRA'"IONWASHINGTON D.C. 20546 SEPTEMBER 1984

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IL s.»I..m.4a NowTranslation of 'Projeto de um Propulsor Ionico", Instit-uto de Pesquisas Espaciais, Sao Jose dos Campos (Brazil) ,Report INPE-2803-PRE/363, July, 1983, pp 1-16_(N84-11?0S)

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The mercury bombardment electrostatic ion thruster isthe most successful electric thruster available today.A 5 cm diameter ion thruster with 3,000sb,,ecific impulseand 5mN thrust is described. The advantages of electricpropulsion and the tests that will be performed arealso presented.

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TABLE OF CONTENTS

1. Operation 1

2. Application 1

3. Characteristics of Project

4

4_ Experimental Part 5

iii

I. Operation

The specific impulse MO is the quantity of thrust (F) generated

in a rocket per unit of emptying in Freight of propellant (mg). /1*

This value is directly proportional to the velocity of exhaust

of the gases (v) and is limited to 300 s for chemical rockets:

I s = F/69 - V/9

The ionic thruster by electrostatic acceleration is capable

of producing a specific inpulse of up to 10, 000 s and a thrust on

the order of 10 mN. In the thruster (Figure 1), the vaporized propel-

lant (Hg, Cs, Ar, or others) is injected into an ionization chamber

where it is bombarded with electrons with an energy of approximately 50eV

(in case the propellant is mercury). The impact between the particles

gives rise to a plasma of density N = 10 12 /cm3 and a temperature

of KTe = 5eV. The ions created are extracted and accelerated by

the electrical field existing between the separation of stage and

that of acceleration, near the chamber outlet. The final velocity

of the ions is controlled by the potential of the separation stage,

and, to maintain the neutrality of the spacecraft, some electrons

are emitted together with the ion beam. The primary electrons are

obtained by thermionic emission and the path of the electrons from

the cathode to the anode is increased by creating an axial magnetic

field inside the chamber.

2. Application

Change of Orbit

A thruster is capable of carrying two or three times more payload

from an orbit of 300 Km to a geostatzonary orbit than the thruster

using hydrazine (Figure 2).

*Numbers in margin indicate foreign pagination.

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(1500,' hi0(^Cv)

Figure 1. Schematic operation of an ionic thruster.

Key: 1) Ionization chamber; 2) Cathode; 3) Anode; 4) Coilsof the magnetic field; 5) Trajectory of the primaryelectron; 6) Separation stage; 7) Acceleration stage;8) Neutralizer.

Key: A) Hg tank; B) Hg vaporzier; C) Hg flow control; D) Hgvapor; E) Hg plasma; F) Hg+ beam; G) Neutralized Hg+ beam.

Latitude Correction

The thruster is capablF of increasing by 300 Kg the payload

of a geostationary satellite of 2,000 Kg with a useful life of 7

years (Figure 3).

2

l^l

oe

Figure 2. Trajectory for change of orbit used by an ionicthruster.

Figure 3. Operation of the thrusters to maintain the correctlatitude of a satellite.

Mobile Satellite

The total pulse provided by an electric thruster is nearly

twice as large as the one provided by chemical rockets of the same

weight (Figure 4).

Figure 4. Alteration of the position of a satellite in space.

3

!9

Interplanetary Missions

The electrical thrusters are capable of carrying more scientific

equipment on board and causing the spacecraft to have a higher velo-

city (Figure 5) .

Figure 5. Satellite entering into interplanetary space.

3. Characteristics of the Proiect

Thrust 5 mN

Specif is impulse 3,000 s

Propellant Hg

Ionization chamber: Reverse Flow

Design: Modular

Dimensions

Potential of the separation stage 1,500 V

Potential of the acceleration stage 12 v

Separation of the stages 1.4 mm

Thickness of the separation stage * mm

Thickness of the acceleration stage 1.0 mm

Current density through the stages 116 A/m2

Diameter of the outlet cross section: 100 mA

Diameter of the gaps of the stages 1.4 mm

Length of the ionization chamber 10 cm

Magnetic field in the center of the chamber: 60 GDiameter of the outlet 5 cm

Power supply sources

Vaporizer 10 V/5A

Cathode heater: 10 V/5A

Cathode discharge 80 V/8A

Magnetic field: 10 V/5A

* Illegible4

i

Separation stage 1,500/100 mA

Acceleration stage 1,500/100 mA

Heater of the neutralizer 10 V/5A

Neutralizer: 1OV/100 mA

The first model of the ionic thruster may be seen on Figure 6.

4. Experimental Part

Figure 7 shows a photo

thruster, which consists of:

separation and acceleration s

Each of the components of the

without altering the others.

each of the components of the

of the first model of the ionic /7

Hg tank, vaporizer, ionization chamber,

tages, magnetic field and neutralizer.

thruster may be modified separately,

Thus it is possible to optimize simply

thruster.

To simulate the conditions found in space, the test chamber

of the thruster must be large enough not to interact significantly

with the ion beam, maintain a pressure of 10 -6 torr at maximum,

and have a system which assures that all the mercury expelled by

the thruster should not interfere with the beam. The ion beam will

be studied in a chamber of 85 cm diameter by 120 cm length and with

cryogenic cooling. The thruster will be installed in a smaller

chamber connected with the first one by a valve of the pendulum

type, which allows the smaller chamber to be opened and closed without

any loss of the vacuum in the main chamber.

It is intended to carry out tests of thrust, propellant consumption,

specific impulseand other operating conditions at the beginning

of 1984, while by 1985 it is expected to have sufficient data to

build a second improved model.

5

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7