New Molecule Could Lead To Better Rocket Fuel

MithrandirAgain writes "Trinitramid is the name of the new molecule that may be a component in future rocket fuel. This fuel could be 20 to 30 percent more efficient in comparison with the best rocket fuels available today, according to researchers (abstract). The discovery was made at the Royal Institute of Technology (KTH) in Sweden. 'A rule of thumb is that for every ten-percent increase in efficiency for rocket fuel, the payload of the rocket can double. What's more, the molecule consists only of nitrogen and oxygen, which would make the rocket fuel environmentally friendly. This is more than can be said of today's solid rocket fuels, which entail the emission of the equivalent of 550 tons of concentrated hydrochloric acid for each launch of the space shuttle,' says Tore Brinck, professor of physical chemistry at KTH."

Comments

No hydrogen = poor exhaust velocity

[damburger]

By the rocket equation, mass fraction is determined by velocity and exhaust velocity is driven two things; the mass of the molecules being put out and the pressure/temperature of the combustion chamber. The latter is limited, as once you get to about 100 atmospheres and 3000K you start to run out of materials to make the combustion chamber out of. Thus, molecule mass is the real driving factor - which is why despite the truly horrific engineering problems it entails, liquid hydrogen is a highly valued rocket fuel.

In fact, because molecular mass is so important, H2/O2 rockets are run fuel rich, sacrificing some combustion efficiency in order to leave some unburned hydrogen in the exhaust and reduce its average molecular mass.

So it doesn't matter how much energy you can get out of this new compound. It will only spit out oxygen, nitrogen and nitrous oxides, all far more massive than the hydrogen and water vapour you get from rockets in use at the moment. Sure, breaking down this molecule in optimal conditions might yield enough energy that the reaction products would have more velocity than the exhaust of a H2/O2 rocket, but there is a reason chemists don't build rockets; these researchers aren't taking into account the kind of unobtanium combustion chamber walls you would need to utilise such an inferno.

Shuttle SRBs are neither cheap nor reliable

[EccentricAnomaly]

Most modern solid-fuel rockets use pretty much the same fuel as the shuttle SRBs. It's cheap, stable and reliable but it does produce a lot of goop and the ISP could be better. If this stuff is stable it might make an excellent replacement for ammonium perchlorate oxidizer.

Shuttle SRBs are more expensive and less reliable than equivalent liquid boosters. This is the main reason why SpaceX is only using liquid engines in the Falcon-9. ULA uses solid boosters for extra thrust on the Atlas V, but these solids are cheaper and more reliable than Shuttle SRBs. In addition, based on recent conference papers, I think they want to get away from solids in their next generation of rockets.

So why is NASA planning on using boosters based on the lower performing, more expensive, and less reliable Shuttle SRBs in their new Heavy lift rocket? This is because the Utah Congressional delegation is lobbying heavily for the company that makes the SRBs. The Utah senators inserted text into the continuing resolution that NASA is currently operating under that they claim prevents NASA from even doing trade studies to consider any alternatives to using the Shuttle SRBs.

Solids might have made sense in the 60s, but with current technology they are no longer needed except in a few specialized applications for robotic planetary exploration spacecraft.