40

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 out into a highly elliptical earth orbit. Thus, the risk of recontact with the command module during entry would have been eliminated. However, on Apollo 8, 10 ...


32

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: But something more potent than alcohol was needed for the X-15 rocket-driven supersonic research plane. Hydrazine was the first choice, but it sometimes exploded ...


30

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 has any chance to transfer its heat into them. The exhaust gas primarily cools through adiabatic expansion - high pressure and high temperature both transformed ...


30

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 thaws out, there is more than can fit in the pipe, and it can burst. In the Space Shuttle's auxiliary power unit, hydrazine plumbing was allowed to sustain ...


30

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 chamber wall location and which occur at completely random intervals is called rough combustion. It's different from "combustion instability" defined as ...


26

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 tanks would need to be much larger and heavier - so they are commonly used in their condensed liquid form. For small engines gases have been used - both as ...


23

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 Umbilical". The system as implemented on Shuttle was complicated but caused major problems only once in the program (see below). There were two umbilical areas ...


20

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 boiloff rate and fluid feed lines to replace lost fluid while waiting on the pad. During flight the consumption rate outpaces any boiloff losses and it is not an ...


19

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 states of the hydrogen molecule, ortho and para. At room temperature, hydrogen is about 3/4 ortho. At liquid-hydrogen temperatures, the stable state is ...


19

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 temperatures. That means without having to burn the gases, in other words. (It achieves this by reducing the "activation energy" of the reaction as the question ...


19

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 "enriched air" instead of pure oxygen as the oxidizer degrades the performance of the engine: The transfer of liquid oxygen (LOX) from a storage vessel to a rocket engine ...


18

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 chamber but flows through the turbine, dropping in pressure there and in the ducting before it enters the main chamber. The preburners generally run at a lower ...


18

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 details.) This isn't a major issue with expendable engines, but it drives up costs when trying to reuse the engines. The BO New Glenn's first stage is planned to ...


18

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 reacts and produces H2O (water) as exhaust. Just because the exhaust is used to push the rocket forward that does not make it the propellant. The propellant is ...


17

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 fuel quickly is not easy. You need to stop pumping cleanly when the tank is empty (or risk a pump explosion when the pump runs dry), this is difficult: you ...


15

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, burning a small part of the fuel which spins the pumps and vaporizes the rest of the fuel. When they enter the combustion chamber they are both in gaseous form. ...


14

The main reason for this is the temperature. Depending on the actual fuel the temperature in the main combustion chamber can be above 3000K. However, in the gas generator the temperature is kept below 1400-1600K. These lower gas temperatures allow uncooled chamber construction and prevent melting or limit the erosion of turbine blades. Source: Sutton - ...


14

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 30% delta v advantage, ton for ton, which more than offsets the structural volume penalty. The drag penalty is mostly irrelevant for upper stages as long as ...


14

This is especially interesting considering that the Service Module and LM RCS used the same thruster hardware (Marquardt R-4D). The R-4D was originally designed for MMH and first flew on Lunar Orbiter 1: Marquardt experimented with a variety of liquid storable propellants. They selected NTO and MMH for their thrusters. However, government requirements led ...


14

A good pressurizing gas needs to satisfy a few basic properties: it needs to stay gaseous at the temperatures and pressures your fuel and oxidizer are stored at, so that it won't just condense out when injected into the tanks; it needs to be inert enough to be safe to mix with both the fuel and the oxidizer (since if you're going to have two different ...


14

The Rutherford engines produce much less vibration than SRB's. This is actually a major selling point for Rocket Lab, as pointed out by Peter Beck here after 31:03: In essence, the low vibration spectrum enables the customer to put more useful payload onboard the Electron, because they need less/lighter mechanical structure....


13

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 capable of running on these, the infrastructure for storage and manipulating them is out of range of amateurs. Even professionals like SpaceX avoid LH2 and run on ...


13

As noted by @asdfex, 440N and 22N are convenient round numbers in imperial units: 100 lb-f and 5 lb-f. The exact thrust values for small spacecraft maneuvering thrusters aren't usually critical to designs of those craft; if the thruster is a little larger or smaller, maneuvers will just take a little less or a little more time. Thus standardized, known-...


13

In addition to the "rough combustion" that Organic Marble mentions, liquid engines also characteristically suffer from pogo oscillation. This is the phenomenon in which the thrust causes acceleration of the rocket, which changes the flow of propellant in the lines fuel and oxidizer lines, which then causes a change in the thrust, which is now a loop. Pogo ...


12

You might be confusing it with the balloon tanks used by the original Atlas and the Centaur upper stage. The Shuttle external tank was not a balloon tank - it did not need to be pressurized to be structurally stable under its own weight - but the pressurization did contribute to its ability to withstand flight loads, as is the case for almost all liquid-...


12

It's not hypergolics per se that are super-desirable for ICBMs, but room-temperature-storable fuels. ICBMs have to stay ready for long periods of time and be launched on short notice, so that means they have to stay fueled up more or less constantly. In practice, that means solid fuels or something in the UDMH/NTO family. A cryogenic fuel ICBM would need ...


12

Unlike chemical rockets such as hydrazine (a monopropellant, which doesn't require separate oxidizer and fuel to burn), water is just the reaction mass — not the energy source. The Comet-1 thruster that the DSi Prospector series is using is electrothermal, so it requires a substantial electrical power supply in order to energize the water (presumably ...


12

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 collapse under its own weight (huge PDF). The stage had to be pressurized (or kept in a support jig) at all times. the Falcon 9 uses flight pressure stabilization....


11

Firstly, the image you provided is not of the BFR, but the BFS (Big F***ing Spaceship) or ITS (Interplanetary Transport System) spaceship (Musk is purportedly not happy with either name). Elon Musk answered a question in his Reddit AMA on r/SpaceX recently that describes the exact purpose of the spheres. Long story short, yes, they are propellant tanks. ...


11

TLDR: Yes, but probably no, well maybe. Fundamentally, the second law of thermodynamics is about entropy: If you create it, part of the energy budget of a running engine has to be spent on getting rid of it. Combustion processes create entropy as a result of creating heat, and the rest follows. To the extent that fuel cells (and human cells) avoid ...


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