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83 votes
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Do booster stages run out of fuel, or are they purposefully shut off?

First stages are generally run to depletion (though not complete depletion - I'll get to that later). First stage ascents often use a preprogrammed, open loop guidance system to get out of the ...
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74 votes
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Why is there a hole in solid rocket engines?

A bore in the solid propellant grain increases exposed surface area and allows for a higher burn rate to increase thrust. There might be several grain geometries used, to meet launch vehicle's ascent ...
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74 votes
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What "fuel more powerful than anything the West (had) in stock" put Laika in orbit aboard Sputnik 2?

Laika's magical mystery propellant was kerosene and LOX. Sputnik 2 was launched on the 8K71PS launcher. This was a modified R-7 ICBM, and like all the R-7 derived launchers, its RD-107 and RD-108 ...
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64 votes

Would it be practical to catch a rocket's exhaust to reuse it as fuel?

Like any perpetual motion machine, it won't work. In this case, there are two major reasons. First, your "send back fuel" arrow is pushing mass forward; every action has an equal and ...
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55 votes
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Using ozone as oxidizer

The book 'Ignition!' tells the history of propellant research and has this to say about ozone from page 112 available here For it has its drawbacks. The least of these is that it's at least as ...
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53 votes
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Why don't we use Cavea-B

Monopropellant systems such as catalyzed hydrazine thrusters are attractive at very small sizes, where the simplicity of a single propellant tank outweighs their relatively low performance. According ...
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48 votes

Pre-mixing cryogenic fuels and using only one fuel tank

To quote John D. Clark's great book Ignition! (Chapter 11: The Hopeful Monoprops): If Tannenbaum's mixtures were bad, that proposed at a monopropellant conference in October 1957 by an optimist ...
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  • 636
45 votes

Sending rockets to space will eventually consume all of our resources?

Most of the propellant expended in sending a spacecraft to Mars immediately returns to Earth -- the fuel and oxidizer are combusted, combining into (typically) water vapor, CO2, and other simple ...
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43 votes
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Why don't Raptor engines use CH3Cl instead of CH4?

They chose $\rm CH_4 + O_2$ because that is a much, much better fuel. $\rm CH_3Cl$ does burn with $\rm O_2$, producing: $$\rm 2CH_3Cl + 3O_2 \to 2CO_2 + 2H_2O + 2HCl + {\sim}1528\text{ kJ/mol energy}$$...
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40 votes
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Why did it take so long for methane to be used as a rocket propellant?

Or am I wrong and have there been attempts to build a methane rocket in the past? Well, if there were, I figured that John D. Clark's famous book Ignition! (1972, free online copy) would be the place ...
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40 votes
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What is the primary reason for SpaceX motion to have astronauts board Dragon before fueling up the rocket?

The Merlin-1D engines are now tuned to use the super cooled fuel and oxidizer. Thus you would be running the engines in an out of normal state, if not using it the same as all other launches with ...
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40 votes

Why can't cryogenic oxygen and cryogenic kerosene be "stored" together?

As Organic Marble hints, there is about 140 degrees Celsius between kerosene's freezing point and oxygen's boiling point; there's no temperature at which both are liquid. Even if the propellants were ...
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40 votes
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Why do the contents of the Space Shuttle External Tank not match the mixture ratio of the engines?

tl;dr as SF said in a comment "...they always packed a little more hydrogen than oxygen (for that ratio), so that at the end of combustion they wouldn't risk running oxygen-rich (and as result ...
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39 votes
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Ultimate fate of rocket propellant in space?

Presumably you are asking about engines that are used once a space vehicle has escaped the Earth's gravitational sphere of influence, or is close to that point. Rocket exhaust during launch becomes a ...
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38 votes

Why did it take so long for methane to be used as a rocket propellant?

The three main competitors for liquid fuel choices to date have been: Hypergolics - easiest to get started with Kerosene/LOX - Good thrust, low performance, but dense LH/LOX - Best performance, ...
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38 votes
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Reasons why liquid anhydrous ammonia fuel chosen for the X-15? Has it been used in other rocket engines?

According to Clark's "Ignition!", German rocket scientists in WW2 had done the math on ammonia, and JPL had burned it with RFNA and WFNA oxidizers in 1949-1951. Regarding the XLR99, Clark says: ...
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38 votes
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Why was ramjet fuel used as hydraulic fluid during Saturn V checkout?

What a fascinating question! Turns out it's less flammable. Ground Supply Fluid—Because the flash point of RP-1 fuel, which supplies the system in flight, is 110 to 139° F, it is classified as ...
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35 votes
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Why would oxygen be stored as a super critical fluid?

The same system was used on Shuttle - allow me to discuss that, the design philosophy applies to Apollo as well (Shuttle deleted the fans though, and had a special Avoid-Apollo-13-circuit in the O2 ...
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35 votes

How do you reliably blow up a rocket that was built not to explode?

Well, I can refer you to the Range Safety Wikipedia entry: Two switches were used, ARM and DESTRUCT. The ARM switch shut down propulsion for liquid propelled vehicles, and the DESTRUCT ignited the ...
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34 votes

Why is there a hole in solid rocket engines?

It depends on the particular engine. Thrust from a solid rocket is approximately proportional to the burning surface area of the fuel (also called the grain). A long solid rocket motor with a ...
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34 votes
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What was the result of the propellant predictions in the last chapter of "Ignition!"?

Chemical rockets will never have more than 600 seconds specific impulse. Storing free radicals in propellant to defeat this limit is impractical. Validated. Chemical rockets in use top out at 450-460 ...
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34 votes

Pre-mixing cryogenic fuels and using only one fuel tank

In addition to what the other answer said, it would take very little provocation for such a situation to turn into a good way to test the blast resistance of nearby facilities.
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33 votes
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Do rockets deplete the oxygen on earth?

Let's start with a Fermi estimate: The atmosphere has a mass of about 5.15×1018 kg, 20% of that is oxygen. A rocket launch uses on the order of 106 kg of oxygen. To use up all the oxygen (and ...
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32 votes
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Why will Starlink satellites use krypton instead of xenon for electric propulsion?

It's the same reason SpaceX often does things differently: Krypton is a lot cheaper. The satellites are designed to control costs. For example, each will maneuver with Hall-effect thrusters—ion ...
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  • 121k
32 votes
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What actually is RP-1, and how is it different from any other hydrocarbon liquid fuel?

Most commercial commodity specifications for hydrocarbons such as gasoline, kerosene, Diesel fuel, jet fuel, naptha, mineral spirits, etc are fairly broad. RP-1 is kerosene that meets some particular ...
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31 votes
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Why is fuel ratio different for upper stage of a rocket?

The J-2 engine used on the second and third stages of the Saturn V has a "PU valve" (propellant utilization) on the oxidizer turbopump. Adjusting the mixture ratio with this valve primarily ...
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31 votes
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What is "anti-geysering" and why would you turn it off 70 seconds before launch?

Partial answer to What is "anti-geysering"... tl;dr Anti-geysering systems are intended to stop geysering, which is a phenomenon that can occur in long vertical pipes of cryogenic fluid ...
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30 votes
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Was there fuel consumption budgeting for Apollo 11 Lunar module?

The Apollo LM had three independent propellant supplies: tankage in the descent stage usable by the descent engine, tankage in the ascent stage for the ascent engine, and in the ascent stage for the ...
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30 votes
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Could a Mars rover go to Phobos or Deimos instead?

No, for a lot of reasons. The Mars rovers slow down based on aerodynamics, heat shields, and parachutes. None of that is available on one of the Moons, meaning that the fuel requirements are much ...
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  • 118k
29 votes

Why are hydrogen-fluorine fuels not used for rockets more frequently?

In addition to all the issues raised by TidalWave, you also need to consider the exhaust products. The space shuttle main tank carried about 730 tons of hydrogen and oxygen. Burning that produces ...
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