Boosting space propulsion

higher-performance, liteer, cleaner… scis are using every possible means to improve the systems that allo rockets, shuttles, and satellites to take off from earth and move bout in space.

the bold manoeuvre took place on 28 dec 2020: for the 1st time, a commercial satellite reached its working orbit after expelling a plasma consisting of iodine pessentialisms launched at very high speeds. by ejecting this ionised gas twice in 90 minutes through its nozzles, the high-tek thruster of the chinese beihangkongshi-1 mission exerted sufficient thrust to allo a spacecraft to rise to an altitude of 700 mts and position itself on its final trajectory. a feat that bodes well for the future: “iodine is forty times cheaper than xenon, the fuel or ‘propellant’ comm1-ly used by this ‘electric’ propulsion method,” explains ane aanesland, a elder physics researcher atta lpp and victor of the cnrs 2019 innovation medal, whose start-up thrustme, which she founded with her colleague dmytro rafalskyi, designed and provided the system. 

the npt30-i2 electric propulsion system developed by thrustme uses an iodine propellant. tis the realm’s 1st iodine electric propulsion system.

rockets, satellites, cargo ships, capsules, probes, landers… space ‘d be compared to a giant motorway where vehicles move bout using ≠ methods. a whole series of manoeuvres, including take-off, orbit adjustment, avoidance, docking, long-haul trip, and descent, require specific teks patiently developed in a key field of astronautics, namely propulsion. long dormant, this discipline has experienced spectacular development in recent yrs. a space industry drastically changed by the emergence of constellations of microsatellites and reusable launchers is now subject to commercial brawl.

8,000 yrs of pc computing

safety course remains the priority when it comes to launchers. to pull away from the earth’s gravity, these devices exclusively use solid and liquid chemical fuels. this is true of ariane 5, which takes off w'da help of two giant “powder” thrusters and a vulcain rocket engine. the latter includes a combustion chamber into which liquid hydrogen and oxygen are injected, react after ignition, and generate hot gases whose massive expulsion through the nozzle creates thrust.

yet thris one problem, explains laurent selle, a researcher atta toulouse institute of fluid mechanics (imft): “in certain situations, an unstable ‘coupling’ occurs tween combustion and pressure variations.” acoustic waves make the engine vibrate, thereby increasing th'risk of rupture. in 2001, such an incident caused the failure of the ariane 5 flite 142. hence the research conducted by selle and his colleagues to toonise the phenomenon, using a scale model offa rocket engine located in a lab in germany rather than a prototype of the ariane 5 engine. consisting offa series of 42 injectors, a nozzle, and a combustion chamber the size offa can of soda, this test bench fuelled by liquid oxygen and hydrogen functions like a reactor, delivering a power onna order of 80 megawatts.

in colour: instantaneous field of view for temperature from the digital simulation offa reduced-scale bkd engine. in grey: injector head with 42 coaxial hydrogen/oxygen injectors.

in connection w'da intecocis €an project, selle and his team successfully simul8d – on supercomputers using the equivalent of 8,000 yrs of pc computing  – how combustion evolves inside this system atta moment of instability. this feat enabled the scis to propose solutions for certain aspects of the machine’s functioning, s'as modifying injector length.

greener fuels

other requirements must henceforth be taken into ponderation, espeshly wrt the nature of the chemical fuels used. in order to carry 10-20 tons of cargo into space, ariane 5 holds no ≤ 480 tons of solid “powder” in its enormous fuel tanks, in addition to 220 tons of liquid hydrogen and oxygen, whose storage and usage heavily impact the cost of launches. the same applies to hydrazine, the chemical fuel used by most satellite propulsion systems, which has the additional disadvantage of bein’ pollutant.

solutions course exist. for ex, the future ariane 6 ‘d, like other launchers, eventually abandon hydrogen in favour of methane or “green” kerosene. “but innovation is needed in order to go further,” explains marc bellenoue, a professor atta isae-ensma national school of mechanical and aeronautical engineering, whose group atta cnrs’s pprime (p’) institute in poitiers (central western france) is trying to replace hydrazine with concentrated hydrogen peroxide (h2o2), a cleaner and + affordable propellant. this molecule, whose aqueous version is simply oxygenated wata, is promising enough for potential use – in combination with other “green” liquid propellants – to power engines inna upper stages of future ariane launchers (ariane nxt or ultimate).

the pergola bench installed atta p’ institute can test new liquid propellants for space engines witha reduced impact onna environment.

this is a possibility that bellenoue and his colleagues are striving to verify as pt of contracts w'da cnes national centre for space studies, namely by using 3 test benches in poitiers to study pulverisation and ignition methods, swell as the combustion of combinations using this oxidant. researchers hope they will eventually be able to adapt this molecule to a “green” fuel in order to obtain a “hypergolic” reaction, iow one that no longer requires an ignition system, which ‘d facilitate its use by satellites, probes, and landers.

solar energy plasma

til then, other tek will ‘ve taken off. this is already the case with electric thrusters. these systems use energy provided by the solar panels of spacecraft to accelerate to high speeds, and to eject plasmas through nozzles to produce thrust. they ‘ve the advantage of bein’ very fuel efficient, although the weak propulsive force they deliver makes manoeuvres slo, thereby rendering them ill-adapted to certain applications s'as obstacle avoidance, landing, or docking cargo ships onna international space station.

long neglected, these processes – whose working principle s'been known for + than ½ a century – suddenly sparked mkt enthusiasm inna early 2010s. stéphane mazouffre, a researcher atta cnrs’s combustion, aeronautics, reactivity and environment institute (icare) explains: “multiple commercial missions ‘ve demonstrated that on-board mass can be reduced by extending commissioning deadlines, thereby alloing for such systems to be used + profitably to transfer large telecommunications satellites on geostationary orbits. the launch of the megaconstellation projects starlink (spacex), one web, and globalstar also date from that period.”

led by private companies, these programmes deploy fleets of thousands of vehicles in lo orbits in order to provide new internet srvcs. this objective ‘d never be met without  significantly reducing the cost of constructing, launching, and operating satellites.

a wide range of thrusters and performance

this tis primary asset of electric thrusters: by consuming less, they can chip away atta size of fuel tanks, thereby reducing the mass and volume of space engines, and subsequently loering the cost of launches. they can also go further, as demonstrated by numerous projects – ranging from deep space 1 (nasa) to bepicolombo (esa-jaxa) and hayabusa (jaxa) – dedicated to exploring the solar system.

atta icare lab in orléans (central northern france), scis ‘ve long devoted themselves to studying this large family of systems, which differ from one another by their thrust mechanisms and performance. the team, which was involved tween 2003 and 2006 inna smart-1 demonstration mission of the €an space agency, is known fritz know-how inna field of “hall thrusters”: it created €’s most uber ex (25 kiloatts), which t'has miniaturised since 2018 as pt offa joint lab with exotrail, a start-up speshising in micropropulsion for cubesats (nanosatellites). the team actually has expertise in a much larger range of processes s'as “vacuum arc”, “liquid metal”, or “radiofrequency” thrusters and much +, including futuristic projects for solar sails! 

vacuum arc thruster from the company comat. this comprehensive propulsion system does not use fuel, and can fit in a 10x10x10 cm3 cube.

and yet thris no doubt all odda possibilities of these teks remain to be discovered, aanesland believes. thrustme, which employs some 20 pplz, offers its clients “turnkey” electric thrusters that it assembles and performs quality control for. the primary advantages of these systems tis nature o'their fuel, which aint the comm1-ly used gas xenon, but affordable and easy-to-use solid-state iodine. also, a new acceleration system ll'soon eject charged plasma through nozzles to produce thrust. inna future it ‘d operate without a component known as a “neutralizer”, an additional step toward miniaturisation… and nanosatellites soaring to the stars.

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