AIAA 99-2434

DEVELOPMENT AND STATE OF ARCJET PROPOLSION SYSTEM FOR ORBIT CORRECTION AND ORIENTATION OF

LOW POWER SATELLITES.

Andriy V. Loyan, Andriy A. Rubakov

SCIENTIFIC AND TECHNOLOGICAL CENTER OF SPACE POWER AND ENGINES AT KHARKOV AVIATION INSTITUTE, UKRAINE.

35th AIAAlASME/SAE/ASEE Joint Propulsion Conference and Exhibit

20-24 June 1999 Los Angeles, California

For permission to copy or to republish, contact the American Institute of Aeronautics and Astronautics, 1801 Alexander Bell Drive, Suite 500, Reston, VA, 20191-4344.

DEVELOPMENT AND STATE OF ARCJET PROPOLSION SYSTEM FOR ORBIT CORRECTION AND ORIENTATION OF LOW POWER SATELLITES

Andriy V. Loyan, Andriy A. Rubakov

SCIENTIFIC AND TECHNOLOGICAL CENTER OF SPACE POWER AND ENGINES AT KHARKOV AVIATION INSTITUTE

Address: 17, Chkalova st. Kharkov, 3 10070, Ukraine;

tel.: +380 (572) 44-2599;

fax: +380 (572) 44-1131;

e-mail: lovan@ai.kharkov.ua

The mass of fuel of usual propulsion systems (PS) makes up to 60 % from total mass of a satellite. Therefore, one of the major problem of the developers PS of correction and orientation of a space flight vehicle on orbit is the increase of specific impulse. Gas flow system do not meet the requirements of today. Today some types of electric jet engines permitting to receive specific impulse up to 10000 s. They are in various stages of development. Arcjet engines, having specific impulse for easy working gas, such as NH3 400 - 900 s and efficiency 35 - 40 %, take an intermediate position between liquid-propellant jet engines and electric jet engines. Beside the arcjet is the most expedient replacement gas flow system. Arcjet has a number of advantages on a comparison with other types electric propolsion, including small risk of development and capability of application of systems created earlier, that allows essentially to reduce the cost of the project. In STC SPE KhAI the activities on creation of the arcjet engine of low power are conducted. An experimental bench for tests for arcjet the power up to 1 kW on the basis of an existing vacuum system created. The experimental bench includes the vacuum system, gas feed system,

power supply and measuring equipment (fig.1). Volume of the vacuum chamber about 1,7 Mu. The vacuum pumping system is arranged with allowance for specifities of the arc engine - with necessity of maintenance of a chamber pressure at a level of 10-3 torr when gas flow up to 50 mg/s.

fig. 1. Vacuum camera

The bench is arranged with two systems of storage and submission of a working gas which can ensure simultaneous input in channel of the engine. Created for gaseous feed (ammonia, methane, argon) sypply allow to regulate and to measure the mass consumption in range 0.3 - 200 mg/s with accuracy not worse 1 %. Engine is installed in the chamber on assembly desktop. The power supply includes the

unit of initialization of discharge and basic power source of a current and provides start-up and operation of the engine in range of powers up to 1000 W. The measuring equipment allows to measure all electrical parameters of discharge. For measurement of the characteristics of a jet

the water calorimeter and thrust measurement supply are used . Four engine modifications by power from 150 up to 500 W was created and tested. The general view of base version arcjet is shown in a fig. 2

1 I I

\

Fig 2. Design of the electric arc engine

Main singularity is an application hollow cathode, that has allowed considerably to reduce thermal losses and to increase efficiency of engine. The special feed system provided optimum conditions of start-up arcj et, reliable activity in microaccount operational mode and fast exit on a nominal thrust. The acceleration of gas implements in the

nozzle (l), made from graphite. The given material is easily treated and has high work temperature (up to 2600 K), permitting to achieve high operation temperatures. The nozzle (1) is soldered to a corpus (4). The heating of gas implements in a dielectric channel of the shaper (2), made from ceramics. The shaper is inserted into a corpus and is fixed in an axial direction by the nozzle (1). The dielectric canal surface of the shaper will allow to increase a voltage drop in an arc, that in turn will increase total bringed power.

The emission implements from emitter m made from a porous tungsten, impregnated salts of barium and calcium, that allows to reduce barrier with 4,5 eV up to 2,1-2,2 eV. The barrier reducing allows to a drop of operation temperature of a surface, that reduces thermal loses and erosion of a material of the cathode. The tablet (6) is inserted into the capsule (5) and is covered with the diaphragm from a tungsten (3), which is soldered to the capsule (5). The capsule (5) is made from a molybdenum having high heat resistance. Inside it the channel of gas is drilled. The capsule (5) is soldered to a handset (20), that provides a good electrical contact and necessary strength permitting to withstand pressure up to 0,7 MPa . The thermal screen (7), made from a molybdenum is welded by dot welding on the capsule (5). The corpus (4) is made of a molybdenum, that is explained in high operation temperatures and provides hermetic sealing of a discharge cavitny, electrical contact between the nozzle (1) and anodic current input (19), thermal screening of the cathode. The voltage on the cathode moves through cathode input 18 on a details 9 and further through a handset 20 on a body of the capsule 5.

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The results of tests arcjet D500.01 were describes in [ 11. Arcjet worked on argon, the basic characteristics obtained in experiments have made: a thrust 25 - 30 mN, specific impulse 290 -300 s, efficiency 25 - 30 %. The engine also worked on nitrogen, but the efficiency has shown lower outcomes. The hydrogen is optimum gas from a point of view of obtaining of maximum specific impulse. But, taking into account the requirements to working gas presented at long duration storage onboard, for further researches the ammonia is selected. It has small mean weight of yields of a dissociation and allows to use already existing elements of gas feed system. By results of activity above the engine arcjet D 500.01 the modification (fig. 3) was created it. Galvanic outcome of the nozzle (1) from a body of the engine differs from a base model. The intermediate electrode has allowed to simplify a procedure of initialization of a primary breakdown and it further steady activity.

Fig.3 A modified part of the electric arc engine.

The further studies of conditions of start- up arcjet D500.02 have allowed to be convinced, that the voltage of the unit breakdown 400 V, current of a short-

circuit 0,25 A. It reduction weight of propulsion system as a whole. By activity with modification D500.02 was detected, that destruction a ceramics 2 because of high thermal loads and low heat conducting. Therefore, the design of a flowing part was upgraded (fig. 4)

1 2 34 5

Fig. 4. The following engine modification.

The main discharge is between the cathode 1 and nozzle - anode 5. Breakdown happens between the cathode 1 and body 2 connected electric with former 3. The electrical outcome happens through ceramics 4. The impregnated tungsten, as an emitter had worked good on argon. Also, as an emission material the tungsten with 2 % Th was applied. Also was tested instead of hollow cathode the rod cathode. Thus volt-ampere characteristic was dropping, at change of a current from 3 A up to 10 A the voltage has falled with 46 V up to 33 V. For hollow cathode at change of a current from 4 A up to 15 A voltage remained practically to constant at a level 25 V. The length of a flowing part 3 have been increasing. It was made for increasing discharge voltage with a constant current with the purpose of more discharge power but voltage remained in quasi constants level. The in-depth numerical outcomes of experiments will be shown in future.

Reference

1. Nikolaiy V. Belan, Niklaiy N. Koshelev and others. Arcjet Thruster for Station Keeping and Orbit Repositioning. Proc. Second European Conference, 27-29 May, 1997 (ESA SP-398, Aug. 1997).

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