Proceedings of AJCPP2012 Asian Joint Conference on Propulsion and Power March 1-4, 2012, Xi’an, China
AJCPP2012-039 A Study of the Effect of Input Power on Liquified-Gas Resistojet Performance Abdolrahim Rezaeiha and Faramarz Mankavi Sharif University of Technology, Tehran, Iran Email:
[email protected] Keywords: Space thruster, resistojet, experimental characterization; CFD
Abstract Low power resistojet thrusters are a type of electrothermal propulsion systems which are capable of producing a thrust up to 100 mN at power less than 50 W, specific impulse up to 100 s, feed pressure up to 10 bar, and operating temperature up to 500°C using most compressed- or liquified-gases as propellant. A liquified-gas resistojet thruster developed by SSTL was launched on ALSAT- 1 in 2002 and was able to deliver a typical specific impulse of about 80 s when using butane as propellant. Currently, with respect to the growing interest for smaller satellites, low power systems are of so much interest as they can offer many advantages compared to other potential systems of the same category. However, the performance of such a system is highly dependent on the input power to the system and investigation of this dependency is of great concern. Therefore, following the development of a laboratory model resistojet in Iran which is capable of operating at low powers ranging from 15 - 50 W using a liquified gas as propellant (Butane); a parametric study has been conducted to investigate the effect of input power on the thruster performance and the results of the study has been compared to numerical simulations and experimental results of other research centers. The results of the present study showed that increasing the power from 0 to 30 W, accelerates the exhaust velocity from 685 to 800 m/s while mass flow diminishes from 72 mg/s to 60 mg/s. Thrust proved to be independent of input power while the specific impulse which is supposed to increase directly with square of flow temperature, improved from 69 to 81 s. The paper briefly describes the present study. Introduction Resistojets are one of electrothermal thrusters which operate by passing the propellant in gaseous state around an electrical heater and increasing the temperature of propellant, then using a conventional convergent-divergent nozzle to accelerate the propellant to supersonic speed and produce thrust.1) The heating process can be made possible using direct
contact between the heating element and the propellant or indirectly, when thruster case is heated by the surrounding elements (the case could be heated radiatively from the outside). The heating of propellant reduces the gas flow rate at a given upstream pressure and a given nozzle area, thus leading to the familiar increase in specific impulse in relation with T .1) This is the main idea behind a resistojet which gives it advantage over a cold gas thruster as it can yield to a higher specific impulse compared to a cold gas thruster using the same propellant and on the same upstream condition through the same nozzle. However, thrust is independent of temperature at given upstream pressure and constant nozzle geometry. In case of propellant, any compressed or liquified gases can be used as long as they are compatible with high temperature nature of a resistojet. During the development of several low power resistojets by SSTL which were used on satellites including UoSAT-12 (1999) using Nitrous oxide, Alsat-1 (2002), UK-DMC, Nigeriasat-1, Bilsat-1 (2003), and Glove-A (2005); all using Butane, Beijing-1 (2005), Proba-2 (2007), and RapidEye (2007) using Xenon; it has been mentioned that the achieved thruster specific impulse will vary according to propellant, power input, firing duration and thrust levels. The maximum specific impulse values achieved during their test have included 55s with xenon, 99s with nitrogen and up to 100s with Butane at temperatures up to 500ºC.2-5) Therefore, following the development of a low power resistojet6) using a liquified gas as propellant and benefitting from previous experiences in operational testing and parametric study of electric thrusters (PPT)7,8) and cold gas thrusters9 in Iran; the laboratory model resistojet was put on test in a big-size 1 × 2.5 m vacuum chamber and the effect of input power on the thruster performance was studied and compared to the numerical results. The parametric study is briefly reviewed here. Resistojet System Background
Table 1indicates a list of some of the most important resistojets ever flown including the most recent low power resistojet systems as well as their launch year, performance parameters and the satellite they were used on. Table 1 List of space-qualified resistojets.2,10,11) Launch
Satellite
1967 19681969 1971
ATS-2&-3
1980 1983 1994 1965 1965 1967 1971 1981 1988 1997 1999 2002 2003 2003 2003 2003 2005 2005 2008 2009 2009
ATS-4&-5
Propellant Watt Experimental Ammonia 3.6 Ammonia
3.6
mN
Isp (s)
18
150
18
150
Sol Rad-10 Hydrazine
