~ Pergamon www.elsevier.com/locate/actaastro Acta Astronautica Vol.48, No. 5-12, pp 353-362, 2001 © 2001 ElsevterScienceLtd. All rights reserved Printed m Great Britain Pll: S0094-5765(01)00047-9 0094-5765•01 $- see front matter NITROUS OXIDE AS A ROCKET PROPELLANT Vadim Zakirov* and Prof. Martin Sweeting: Surre) Space Centre, University of Surrey. Guildford, Surrey, GU2 7XH, United Kingdom Tel: (44) 1483 259278. Fax: (44) 1483 259503. E-mail: m.sweeting@eim.surrey.ac.uk lnternet: http://www.sstl.co.uk Timothy Lawrence § and Jerry' Sellers • European Office of Aerospace Research and Development London, NW I 5TH, United Kingdom Abstract Nitrous oxide is introduced as a multi-purpose propellant for spacecraft. Potential space applications of this propellant are given. Based on comparison to conventional systems, a multi-mode nitrous oxide propulsion concept is expected to deliver higher performance. Main features of a self-pressurising, nitrous oxide storage system are described. A nitrous oxide catalytic decomposition technique is suggested for restartable spacecraft propulsion. Up- to-date experimental results are presented. A conclusion describes the long-term feasibility of novel nitrous oxide propulsion option concepts. © 2001 Elsevier Science Ltd. All rights reserved. I. 0 Introduction Nitrous oxide t (N:O) offers many inherent advantages as a small satellite propellant. It is a colourless, non- toxic, liquefied gas with a slightly sweet taste and odour. It is non-corrosive and may be used with common structural materials. Nitrous oxide is stable and comparatively unreactive at ordinary temperatures, e.g. to ozone, hydrogen, the halogens, the alkali metals, etc. ~ It is decomposed into nitrogen and oxygen by heating above 520°C. : Chemical composition of the decomposition products (36.3%0: + 63.7%N2) is akin to that of air. The decomposition reaction can be accelerated by a catalyst. At elevated temperatures nitrous oxide supports combustion and oxidises certain organic compounds, the alkali metals, etc. ~ Nitrous oxide is classified by the Department of Transportation as a non-flammable, compressed gas and is shipped with the required "Green Label". t Three basic properties of nitrous oxide make it attractive as a multi-purpose rocket propellant: • Can be stored as a liquid (-745kg/m a) with a vapour pressure of-52bar (at 20°C) • Decomposes exothermically with adiabatic decomposition temperature reaching - 1640°C t Ph.D. student Prof., OBE § Major, Ph.D. • Lt.-Col., (s) Ph.D. I also known as "'laughing gas", dinitrogen oxide, or dinitrogen monoxide • Free oxygen available by decomposition can be combusted with a wide variety of fuels Taking advantage of these properties, especially the exothermic catalytic decomposition, space propulsion applications of nitrous oxide may be extended to: • cold-gas propulsion for attitude control of a spacecraft • monopropellant thruster for spacecraft station- keeping and small orbit manoeuvres • bipropellant thrusters for large orbital manoeuvring • power-generation on-board spacecraft or launch vehicle • oxygen generation on board spacecraft Since the whole range of propulsion functions can be covered by one self-pressurising propellant, multi- mode propulsion systems can be envisioned to satisfy a wide variety mission requirements. Such systems would employ different types of thrusters fed by nitrous oxide from a single, simply designed storage tank. Nitrous oxide is not new to the propulsion community. Previously, the American Rocket Company (AMROC) used nitrous oxide as an oxidiser for its hybrid rocket motors. 3 However, it has yet to be officially recognised as a rocket propellant, nitrous oxide is also 353