[{"command":"openDialog","selector":"#drupal-modal","settings":null,"data":"\u003Cdiv id=\u0022republish_modal_form\u0022\u003E\u003Cform class=\u0022modal-form-example-modal-form ecl-form\u0022 data-drupal-selector=\u0022modal-form-example-modal-form\u0022 action=\u0022\/en\/article\/modal\/7031\u0022 method=\u0022post\u0022 id=\u0022modal-form-example-modal-form\u0022 accept-charset=\u0022UTF-8\u0022\u003E\u003Cp\u003EHorizon articles can be republished for free under the Creative Commons Attribution 4.0 International (CC BY 4.0) licence.\u003C\/p\u003E\n \u003Cp\u003EYou must give appropriate credit. We ask you to do this by:\u003Cbr \/\u003E\n 1) Using the original journalist\u0027s byline\u003Cbr \/\u003E\n 2) Linking back to our original story\u003Cbr \/\u003E\n 3) Using the following text in the footer: This article was originally published in \u003Ca href=\u0027#\u0027\u003EHorizon, the EU Research and Innovation magazine\u003C\/a\u003E\u003C\/p\u003E\n \u003Cp\u003ESee our full republication guidelines \u003Ca href=\u0027\/horizon-magazine\/republish-our-stories\u0027\u003Ehere\u003C\/a\u003E\u003C\/p\u003E\n \u003Cp\u003EHTML for this article, including the attribution and page view counter, is below:\u003C\/p\u003E\u003Cdiv class=\u0022js-form-item form-item js-form-type-textarea form-item-body-content js-form-item-body-content ecl-form-group ecl-form-group--text-area form-no-label ecl-u-mv-m\u0022\u003E\n \n\u003Cdiv\u003E\n \u003Ctextarea data-drupal-selector=\u0022edit-body-content\u0022 aria-describedby=\u0022edit-body-content--description\u0022 id=\u0022edit-body-content\u0022 name=\u0022body_content\u0022 rows=\u00225\u0022 cols=\u002260\u0022 class=\u0022form-textarea ecl-text-area\u0022\u003E\u003Ch2\u003EGreener fuels to propel rocket launches into space\u003C\/h2\u003E\u003Cp\u003ESpace exploration may have given us pictures of our pristine, blue planet Earth and raised awareness to protect our environment, but that\u2019s no good if the rockets that get us to orbit are based on old, toxic propellants.\u003C\/p\u003E\u003Cp\u003EFor decades, the most common rocket propellant has been hydrazine, a toxic compound of nitrogen and hydrogen that is on the EU\u2019s list of substances of high concern. It is also the suspected cause of abnormally high rates of \u003Ca href=\u0022http:\/\/news.bbc.co.uk\/2\/hi\/health\/4169095.stm\u0022 target=\u0022_blank\u0022 rel=\u0022noopener noreferrer\u0022\u003Ehormonal and blood disorders\u003C\/a\u003E\u0026nbsp;around the Baikonur rocket launch site in Kazakhstan.\u003C\/p\u003E\u003Cp\u003EThat\u2019s why scientists at the German Aerospace Centre (DLR) in Lampoldshausen are working on new, greener fuels that can future-proof space exploration methods and make them environmentally friendly.\u003C\/p\u003E\u003Cp\u003EThe efforts are centred around a compound known as ammonium dinitramide (ADN), which when heated decomposes into only nitrogen, oxygen, and water.\u003C\/p\u003E\u003Cp\u003E\u2018ADN was an oxidiser salt first found in the Soviet Union, but was rediscovered in Sweden in the 1990s where they had the idea to develop it into a liquid propellant,\u2019 said Dr Michele Negri, leader of a space propulsion project called \u003Ca href=\u0022https:\/\/cordis.europa.eu\/project\/rcn\/193718\/factsheet\/en\u0022 target=\u0022_blank\u0022 rel=\u0022noopener noreferrer\u0022\u003ERHEFORM\u003C\/a\u003E.\u003C\/p\u003E\u003Cp\u003EThe problem is that ADN is a salt, so it is solid. While it can be dissolved into other fuels like methanol or ammonia, it takes a high temperature - \u003Ca href=\u0022https:\/\/www.sciencedirect.com\/science\/article\/pii\/S0094576518301152\u0022 target=\u0022_blank\u0022 rel=\u0022noopener noreferrer\u0022\u003Emore than 1500\u00baC\u003C\/a\u003E\u0026nbsp;-\u0026nbsp;to ignite it.\u003C\/p\u003E\u003Cp\u003E\u2018Hydrazine thrusters do not require pre-heating, if you just open the valves then they start firing. On the other hand, with an ADN thruster if you just open the valve the blend would come out in liquid form. It would not react,\u2019 Dr Negri said.\u003C\/p\u003E\u003Cp\u003EThe RHEFORM project looked at the ADN-based propellant LMP-103S used by a Swedish space company called \u003Ca href=\u0022http:\/\/ecaps.space\/\u0022 target=\u0022_blank\u0022 rel=\u0022noopener noreferrer\u0022\u003EECAPS\u003C\/a\u003E, which was a project partner and has already launched 13 propulsion systems based on the compound.\u003C\/p\u003E\u003Cp\u003E\u003Cblockquote class=\u0022tw-text-center tw-text-blue tw-font-bold tw-text-2xl lg:tw-w-1\/2 tw-border-2 tw-border-blue tw-p-12 tw-my-8 lg:tw-m-12 lg:tw--ml-16 tw-float-left\u0022\u003E\n \u003Cspan class=\u0022tw-text-5xl tw-rotate-180\u0022\u003E\u201c\u003C\/span\u003E\n \u003Cp class=\u0022tw-font-serif tw-italic\u0022\u003E\u0026#039;ADN was an oxidiser salt first found in the Soviet Union, but was rediscovered in Sweden in the 1990s where they had the idea to develop it into a liquid propellant.\u0026#039;\u003C\/p\u003E\n \u003Cfooter\u003E\n \u003Ccite class=\u0022tw-not-italic tw-font-normal tw-text-sm tw-text-black\u0022\u003EDr Michele Negri, German Aerospace Centre, Lampoldshausen, Germany\u003C\/cite\u003E\n \u003C\/footer\u003E\n\u003C\/blockquote\u003E\n\u003C\/p\u003E\u003Cp\u003E\u003Cstrong\u003EEasy ignition\u003C\/strong\u003E\u003C\/p\u003E\u003Cp\u003ETo tackle the problem of easy ignition, the project looked at developing a better, more reactive catalyst so that the fuel could react at room temperature. Hydrazine followed the same path of early development.\u003C\/p\u003E\u003Cp\u003E\u2018At the very beginning in the \u201960s they were not able to fire at room temperature, but then they developed a catalyst that was good enough,\u2019 Dr Negri said.\u003C\/p\u003E\u003Cp\u003ESuch catalysts work by increasing the surface area for reactions to take place, making it easier for them to occur at lower temperatures, or possibly by adding in a compound like a metal to increase reactivity.\u003C\/p\u003E\u003Cp\u003E\u2018The catalyst in pellet form was composed only of a support (phase), which is the pellets themselves \u2013 typically a ceramic material with a high specific surface area,\u2019 he said. \u2018On top of that you can place an active phase, which is typically a metal.\u2019\u003C\/p\u003E\u003Cp\u003EAfter testing many materials, the rocket scientists found out that hexaaluminate would make the best base material.\u003C\/p\u003E\u003Cp\u003EBut what if simple pellets could be improved to have an even more ideal surface area to make them more reactive?\u003C\/p\u003E\u003Cp\u003E\u003Cstrong\u003E3D printing\u003C\/strong\u003E\u003C\/p\u003E\u003Cp\u003ETo find out, they used computer modelling and 3D printing to create complex honeycomb-like structures known as monoliths, and so increasing the surface area.\u003C\/p\u003E\u003Cp\u003E\u2018This basically was done in the automobile industry (in creating catalytic converters), replacing the pellets with a monolithic structure. With the know-how the of our project partner (3D printing company) LITHOZ, we were able to print very complicated structures in ceramic, and then use that as a catalyst,\u2019 Dr Negri said.\u003C\/p\u003E\u003Cp\u003EThe catalyst ceramics sit inside the thrust chamber on a rocket engine, which propellant is injected through before making its way out the engine nozzle during launch.\u003C\/p\u003E\u003Cp\u003E\u2018We were able to have them react under lab-scale, just above a temperature of 100 degrees,\u2019 he said. \u2018The ideal would be if they could start in normal environmental conditions, requiring no type of pre-heating.\u2019\u003C\/p\u003E\u003Cp\u003EDr Negri says that the next step for achieving room temperature ignition of ADN probably would be using propellants which do not contain water.\u003C\/p\u003E\u003Cp\u003EWater makes propellants more stable, and safer to ship, but it also makes them less reactive.\u003C\/p\u003E\u003Cp\u003E\u2018You can play a lot with the composition to find a good trade-off between different factors, for example performance, like specific impulse, storability, or explosivity,\u2019 he said.\u003C\/p\u003E\u003Cp\u003E\u003Cstrong\u003ECheaper\u003C\/strong\u003E\u003C\/p\u003E\u003Cp\u003EIn addition to being greener, ADN could also be cheaper. \u2018Fuelling a satellite with LMP-103S is a lot easier than hydrazine, since by the first launch you have spent just a third of the manpower needed for the more hazardous hydrazine,\u2019 he said. Even if the propellant is a little more costly, the total life cost could be lower, Dr Negri adds.\u003C\/p\u003E\u003Cp\u003EUS space agency NASA, which was not involved in the \u003Ca href=\u0022https:\/\/cordis.europa.eu\/project\/rcn\/193718\/factsheet\/en\u0022 target=\u0022_blank\u0022 rel=\u0022noopener noreferrer\u0022\u003ERHEFORM\u003C\/a\u003E project, agrees that there is a need for greener rocket fuels and is working on a safer-to-handle propulsion system.\u003C\/p\u003E\u003Cp\u003E\u2018While effective, hydrazine is highly toxic and requires special measures be taken for proper handling,\u2019 said Dayna Ise, programme executive of NASA\u2019s Technology Demonstration Missions.\u003C\/p\u003E\u003Cp\u003E\u2018Non-toxic, \u201cgreen\u201d propellant and compatible systems offer a safer and more efficient alternative for the next generation of launch vehicles and spacecraft.\u2019\u003C\/p\u003E\u003Cp\u003E\u003Cem\u003EThe research in this article is funded by the EU. 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