46 votes
Accepted

How did sloshing prevent the Apollo Service Module from moving safely away from the Command Module and how was this fixed?

Let's start with the "Statement of Problem" in the anomaly report. ...the service module, upon being jettisoned on a lunar return flight, should have entered the earth's atmosphere, then skipped ...
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43 votes

Why can solid rockets be both the skinniest and most spherical launch vehicles while liquid fuel rockets have a more limited range of aspect ratios?

The squat end of the spectrum has little to do with solids versus liquids and everything to do with aerodynamics. Spherical tankage is most weight-efficient, so you'd expect squat stages in cases ...
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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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38 votes
Accepted

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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36 votes

Is it bad if hydrazine freezes on a spacecraft? Is it always kept as liquid, or can it be safely allowed to freeze and then thawed when needed?

At least for the Space Shuttle, freezing was OK, but thawing out was bad for piping. Hydrazine contracts when it freezes, so it can 'superpack' (more fluid flows in, then freezes, etc.)...then when it ...
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35 votes

Do the SpaceX Falcon-9 rockets use foam insulation similar to the Space Shuttle? Is it still a potential problem?

The Space Shuttle used liquid hydrogen, contained in the external tank along with liquid oxygen. While the Falcon rockets do use liquid oxygen, they do not use liquid hydrogen. Keeping the liquid ...
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  • 65.5k
32 votes
Accepted

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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  • 8,401
31 votes
Accepted

Do liquid propellant rocket engines experience thrust oscillation?

Yes, in liquid engines this phenomenon is called "rough combustion". Sutton (4th edition) says Combustion that gives pressure fluctuations greater than about +/- 5% of the mean pressure at a ...
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30 votes
Accepted

The principle behind regenerative cooling?

You are missing how heat is distributed in exhaust. Most of propellant ejected through the nozzle never makes contact with the nozzle surface or walls of the combustion chamber, and as result never ...
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  • 52.6k
28 votes
Accepted

Is it possible to use gases instead of liquids as fuel in a rocket engine?

Possible: yes. Feasable: not really (at least not for power applications). The main trick is energy density (per volume) - gases tend to be quite significantly less dense than liquids - and thus the ...
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  • 586
25 votes
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How was fuel crossfeed achieved, between the main tank and the Shuttle?

1) Can someone provide an overview of the crossfeed system - in particular the detachable joint that fed LOX to to the shuttle from the tank? The buzzwords to use for googling this topic are "ET ...
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24 votes

Using of the rocket propellant for engine cooling

Really, there is nothing particularly special about it. Any liquid flowing through pipes in the engine wall will carry heat away from the engine as it heats up. Obviously, some liquids will be more ...
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  • 8,401
22 votes

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

Because it will almost certainly go KABOOM. Intimately mixed fuels and oxidizers are pretty much indistinguishable from explosives, and in particular, LOX intimately mixed with flammable hydrocarbons ...
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  • 8,401
21 votes
Accepted

How do rockets keep their fuel in a liquid state?

As small amounts of LOX boil off heat is removed from the remaining volume. Boiloff actively cools the fluid and helps keep the remainder liquid. Rockets typically have vents to aid in managing the ...
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  • 6,377
21 votes
Accepted

What is the density of supercooled LOX at −206 °C, as SpaceX uses it

The US National Institute of Standards and Technology (NIST) is pretty useful for that. They offer a free tool that allows you to calculate a lot of useful properties of multiple interesting compounds ...
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  • 1,002
21 votes

Why is an inflatable balloon inside a fuel tank not used to prevent fuel from "sloshing around"?

They do! Many propellant tank, especially those required to work in zero-g environments, do use just such a bladder-inside-a-tank for the fuel. Typically monopropellants for thrusters. It completely ...
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20 votes
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Platinum Colloid in Liquid Hydrogen fuel to increase fuel efficiency

Short answer: no, it won't increase the performance of the rocket. Platinum (or other catalysts) can be used in fuel cells, where the purpose is to get a chemical reaction at (relatively) lower ...
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  • 5,168
20 votes
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What is the advantage of using Helium over Nitrogen when used for pressurising LOx?

As suggested by OrganicMarble in a comment, nitrogen is miscible with oxygen (you can thus make liquid air). According to NASA Technical Paper 2464, this is a major concern because using "...
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  • 1,380
20 votes

How easy is it to use liquid nitrogen dioxide as an oxidizer?

Not a good idea for amateurs; it can kill you without you realizing you're dying: 10–20 ppm can cause mild irritation of the nose and throat, 25–50 ppm can cause edema leading to bronchitis or ...
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19 votes

Why don't rockets drive the turbopump from the combustion chamber?

You've got it slightly incorrect. Staged combustion engines pre-burn the propellants at a higher, not lower pressure than the main chamber. The exhaust from the preburner isn't pumped into the main ...
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19 votes
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What is the ortho/para issue with LH2 as a fuel?

The problem is that the transition produces enough energy to boil the LH2. As explained on the old sci.space.history group: Skipping the gory quantum-mechanical details... there are two energy ...
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19 votes
Accepted

What is the MXP-351 storable bipropellant?

Until Masten Space Systems reveals the exact composition of the propellants, we can only speculate on the combinations they used. Based on what you have presented in question we can rule out options ...
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  • 2,173
18 votes
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Why does the BE-4 use methane as fuel?

Reusability is the big factor. Kerosene engines have issues with "coking", where solid carbon is deposited throughout the engine's pipes. (See this dissertation and its supporting research for more ...
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  • 1,908
18 votes

How was fuel crossfeed achieved, between the main tank and the Shuttle?

The crossfeed seen in KSP works by pumping fuel from one fuel tank to another, i.e. against tank pressure. To do this, you need pumps (independent of the engine turbopumps). Pumping large amounts of ...
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  • 122k
18 votes
Accepted

Is it correct to say that a LH2/LOX rocket uses water as propellant?

No, it is not. The exhaust is water, not the propellant. The propellant is a bi-propellant consisting of liquid H2 and liquid O2. The bi-propellant is injected into the combustion chamber, where it ...
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  • 6,800
18 votes

Do the SpaceX Falcon-9 rockets use foam insulation similar to the Space Shuttle? Is it still a potential problem?

The problem is not the foam breaking off per se, but the fact that the orbiter was below the fuel tank and got hit by the falling foam. The Dragon capsule is on top of the stack, it can't be hit by a ...
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17 votes
Accepted

Pros and Cons of LH2/LOX vs Other Fuels

It's not a "marginally higher" specific impulse. High performance hydrogen engines typically have a vacuum Isp of around 420-450 seconds, compared to 310-350 for hypergolics or kerosene. That's about ...
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17 votes
Accepted

Can we use liquid propellants in amateur rockets?

Liquid propellants like kerosene and hydrogen peroxide - that's risky, though doable. Cryofuels like liquid oxygen and hydrogen - no. Even if you manage to develop an amateur rocket motor that's ...
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  • 52.6k
17 votes

Is it possible to use gases instead of liquids as fuel in a rocket engine?

Yes, and it is currently being done on a few engines, notably SpaceX's Raptor engines. They run on liquid oxygen and liquid methane. These are run through turbopumps in two different mixture ratios, ...
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  • 461
16 votes
Accepted

Is the pressurization of propellant tanks necessary for structural integrity?

Pressure stabilization is used in some rockets, and to varying degrees. the Atlas and Centaur use 'full-scale' pressure stabilization. The tank walls were so thin, an unpressurized stage would ...
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  • 122k

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