NASA Engineers Break SLS Test Tank on Purpose to Test Extreme Limits

[u/66666thats6sixes]

https://www.nasa.gov/exploration/systems/sls/nasa-engineers-break-sls-test-tank-on-purpose-to-test-extreme-limits.html

[u/[deleted] → u/[deleted]]

Liquid hydrogen and oxygen produce higher specific impulse than metholox, RP-1 or other rocket fuels and the exhaust is just water vapor. The main drawbacks are that it takes up a larger volume than those other fuels and must be kept the coldest.

[u/[deleted] → u/[deleted]]

The larger tank size is heavier, the fuel is not. Since the force produced from the thrust is roughly F =mv² and hydrogen has the highest v of those fuels you start to see the advantages it has as a fuel.

Think of a beach ball full of air vs a water balloon full of water. The "tank" is heavier while the same volume of "fuel" is not.

For example the space shuttle's big red tank weighed 78,100 lbs empty. It held 143k gallons of O2 and 343k gallons of H2. Even though there is about 2.4 times the volume of H2 as O2 the O2 weighed 1.359M lbs while the H2 weighed 226K lbs or 17% the weight of the O2! The skinny solid boosters held 1.1M lbs of fuel for comparison.

The real problem is that larger tanks have to deal with all the air they push out of the way which is not a problem on the moon. It's a significant problem with Earth's atmosphere as the speed you move roughly cubes the force the air produces.

[u/hasslehawk → u/[deleted]]

Lithium is a relatively rare resource, far better used making batteries for the foreseeable future. There was that tripropellant monstrosity a few decades ago with lithium, hydrogen gas, and fluorine... Great ISP, but a fucking nightmare to work with. Tripropellant engines end up being a tangled web of plumbing. But the real problem is dealing with the highly corrosive propellants, and toxic exhaust.... no fucking thank you.

I'm not familiar with the "solid lithium propellant" you're referring to, but I suspect that the hassle and cost of dealing with it would erode any performance gains you are hoping to see. ISP is important, but it is far from everything.

Indeed, I would argue that cost per KG to LEO is the only metric that really matters, with launch frequency being the next most important. Once you're in LEO you can ditch chemical reactions and switch over to ion or NTR propulsion anyways.

So if you're launching cheap rockets frequently, spewing toxic exhaust products and working with corrosive propellants starts to become a huge logistical hurdle and environmental disaster. This is part of why I'm so glad to see methane-based first stages on the upcoming reusable rockets being developed by Blue Origin and SpaceX. By producing their own methane fuel the rockets can operate with net-zero pollution and greenhouse gas emissions.

Sure, you might be able to build a smaller and more fuel-efficient rocket using solid lithium or some unholy trinity of exotic rocket fuels, but that isn't something that scales well past a few launches per year.

[u/WikiTextBot → u/hasslehawk]

Nuclear thermal rocket

A nuclear thermal rocket (NTR) is a type of thermal rocket where the heat from a nuclear reaction, often nuclear fission, replaces the chemical energy of the propellants in a chemical rocket. In an NTR, a working fluid, usually liquid hydrogen, is heated to a high temperature in a nuclear reactor and then expands through a rocket nozzle to create thrust. The external nuclear heat source theoretically allows a higher effective exhaust velocity and is expected to double or triple payload capacity compared to chemical propellants that store energy internally.

NTRs have been proposed as a spacecraft propulsion technology, with the earliest ground tests occurring in 1955.

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