Nanoengineered thrusters for the next giant leap in space exploration
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duction Can rockets be made of plastic? We show that the most massand volume-efficient (in terms of thrust and power) and highperformance “rockets” will be enabled by nanomaterials and nanofabrication and that such thrusters operate at room temperature utilizing electrically accelerated ions, in other words, yes, plastic rockets. For the past few decades, electric propulsion (EP) has been explored and used in an increasing number of space missions because of the important benefits it provides with its high specific impulse (Isp), or amount of thrust force produced per unit weight of propellant used, and the corresponding savings in total mass of the propulsion system relative to chemical thrusters.1 EP technologies work by creating and accelerating ion or plasma beams using a combination of electric and magnetic fields. The most successful of these technologies are ion engines and Hall effect thrusters, respectively. Ion engines are two-stage devices. The first stage is an ionization cavity where the ion-electron plasma is produced. The second stage is a pair of closely spaced grids biased at high voltage that accelerate ions in the plasma. A Hall thruster has no grids, but instead a magnetic structure that traps electrons, effectively producing the plasma and accelerating the ions in a single stage. Other promising technologies, such as the magnetoplasmadynamic (MPD) thruster,
variable specific impulse magnetoplasma rocket (VASIMR), and pulse inductive thruster (PIT), also have the potential to serve the needs of high-power EP. Different technologies are better suited for different applications (see Figure 1). Ion engines with Isp values in the 3000– 5000 s range are optimized for deep-space exploration or very long missions, such as orbital maintenance of large communications satellites for which propellant savings are paramount. Hall thrusters, on the other hand, cover better the requirements at higher thrust to power (hence lower Isp at fixed efficiency) in missions such as orbital raising operations and corrections, where emphasis is given to savings in power supply mass. Most of these technologies have been optimized for operation at a range of power levels that serve the needs of specific space missions. For example, a relatively large number of Hall effect thrusters range from ∼200 W in power level to several tens of kilowatts. Despite significant progress, there is still a lack of high-performance (adequately high Isp and highefficiency) EP devices operating outside this range, namely, at very low and very high power levels. It has long been recognized that materials research would strongly pace advances in EP, in particular, thruster lifetime and performance of Hall effect thrusters.2,3 Resistance to erosion and environmental effects of cathode materials, even at
Paulo C. Lozano, Massachusetts Institute of Technology, USA; [email protected] Brian L. Wardle, Massachusetts Institute of Technology, USA; [email protected] Padraig Moloney, Lockheed Martin Space Systems Company, USA; [email protected] Suraj Rawal, Lockh
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