Some year´s ago Rocket Lab successfully tested a third stage for their electron rocket this was designed to put payloads into exactly the right orbit or to boost them higher up it also used a smaller rocket engine called Curie
but the most interesting part of this revelation was that it used a green mono propellant now of course when I say green I'm not talking about the color of the fuel I'm referring to the fuel being less hazardous than the fuel that is generally used for such things hydrazine in this case it's a lot less to do with protecting the environment as it is to do with making it easier for ground crews working with the satellite who have to get dressed up and protective gear with self-contained oxygen supplies I mean apparently it can cost over a hundred thousand dollars just for the fueling process for a small satellite the truth is that hydrazine is a horrific substance to work with I mean it's a rocket fuel so of course it has lots of energy in it but it's also corrosive carcinogenic and straight-up toxic to humans it will in tiny quantities it will attack the nervous system the liver and bleh all sorts of other essential organs so unsurprisingly getting a fuel which is greener than hydrazine is actually pretty easy monopropellant thrusters use a single fuel which can be decomposed to release exhaust gases and heat typically this means passing it over a catalyst bed with they're made of something like iridium or platinum and in the case of hydrazine this will decompose into hydrogen nitrogen ammonia and the exhaust gases will be as hot as a thousand degrees centigrade the nice thing about mono repellents is that since there's only one fuel you basically can control them by flipping one valve open and closed so it gives you a lot of advantages in terms of simplicity on the other hand monopropellant performances tend to be significantly lower than by propellants for example hydrazine has performance of about 220 seconds of specific impulse whereas when you use something like mono methyl hydrazine and dinitrogen tetroxide on the space shuttle that got you 330 seconds that's the 50% boost just by switching over to a bi propellant now some people would argue that hydrogen peroxide could be considered a green fuel because its exhaust products are water and oxygen to substances the human body works just fine with it's also well understood with a long history of use in the space programs but hydrogen peroxide still is nasty stuff to handle it'll happily corrode all sorts of things and truthfully its performance is pretty lousy similarly cold gas reaction control thrusters can be used these are actually used on Falcon 9 to control the first stage during its flip over before landing and of course cold gas thrusters are great you know it's just compressed gas which is completely inert the exhaust is completely inert there's actually as some footage of Elon musk and cedar it's and kind of walking around the wreckage of the grasshopper which had exploded minutes earlier it's still smoking and I'm gonna say that's fine with cold gas thrusters I would not do it if there had in hydrazine anywhere on that thing a more modern green fuel that's already been tested on a Swedish spacecraft called Prisma is codenamed lmp1 o3s it's mostly made of ammonium dye nitrate mind and it's dissolved in a mixture of water methanol and ammonia to balance out the combustion products and to stabilize its explosive tendencies when you try to put that many nitrogen atoms in a single Moloch who you just know that there's a lot of energy just wanting to get out so not only is it safer and easier to handle it actually gets superior performance about six percent better specific impulse over hydrazine and when you consider its higher density it gets a bit 30% better impulse overall if you just swapped out a hydrazine system with their lmp1 or 3s and that's even before you start considering the savings from being able to cut down on safety features which are less essential know that propellant isn't gonna poison people once it leaks so why isn't every spacecraft already switching over to this well aerospace is a notoriously risk-averse industry and changing an existing working design is understandably met with resistance when you can't service your spacecraft on-orbit it's easy to justify using the fuel which has worked on hundreds of missions previously anyway on this side of the Atlantic the US has been developing its own green mana probe in the guise of a fm3 15e developed by the Air Force Research Lab this is based about around something called hydroxyl ammonium nitrate on its own this molecule comes with lots of energy and a tendency to decompose when you look at it the wrong way but over the last couple of decades their force scientists have come up with the exact combination of fuels solvents and stabilizers so they could put 8gn in and get out a good monopropellant on paper its superior to lmp1 o3s with a specific impulse of 257 seconds and a density 45% higher than hydrazine however it yet to be flown on any test flight in space but we hope that we will see this happen soon the green propellant infusion mission is a NASA mission which is gonna ideally be flown on the second launch of the Falcon Heavy as part of the space test program I'll ride along with a bunch of other experimental satellites and hopefully we'll get to see that later this year I'm getting excited the gpim literature also mentions other advantages of this fuel mix it can be safely allowed to freeze in the tanks and later thawed out when it's needed whereas hydrazine subsystems are supposed to be kept heated to avoid potential damage due to pipe and pipe due to expansion and contraction the propellant is also less prone to leakage due to higher viscosity and the thrusters can't accidentally fire because it would decompose unless the catalyst beds are heated before before firing which does add a little bit of complexity to the design but overall it's considered a safety improvement however the exact fuel used by lock rocket lab and the Curie engine is still a secret as of now and there are plenty of other possibilities but there is a patent for an engine using something called a viscous mono probe which was awarded to rocket lab and it describes a different type of fuel from the two that I've been talking about perhaps this is what they've developed into their Curie engine at this time we can't really know and we'll be paying attention regardless so yeah green mana propellants aren't just a nod to the environment they are actually better propellants overall and that's real rocket science so we hope to find out what happens and we hope to see some future launches with this technology.
