24

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 ...


23

The shuttle external tank held the propellants for the shuttle main engines. It was filled from spherical tanks positioned at the perimeter of the launch pad. Insulated lines ran from the spheres, through the Mobile Launcher, and into the Orbiter through two tombstone-shaped Tail Service Masts. Then through the Orbiter Main Propulsion System plumbing into ...


22

No, the previously used External Tanks (ETs) disintegrated in the atmosphere before they fell into the sea. Notably, Buzz Aldrin and others proposed different ideas for reuse of the tank in orbit, and allegedly NASA said that they would be willing to take external tanks to orbit if a private company would use them. No private effort ever stepped up to the ...


20

It's possible, but not as easy in real life as it is in KSP. To maintain proper tank pressurization, the crossfeeds have to be pump-driven; the fuel and oxidizer crossfeed lines have to be pretty large to move the required amount of propellant (i.e. on the order of the same power as the core section's engine turbopumps). All this increases weight and ...


20

It's theoretically possible to collect fuel from near empty space, the bussard ramjet is an example of an engine designed to do just that. The principle is that you use magnetic fields to collect and concentrate hydrogen atoms from the near vacuum of space, and then a fusion rocket would turn some of this into propulsion for speed and a fusion reactor would ...


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 ...


17

I don't have a great reference for this, but it was to reduce cost on the throw-away External Tank. By using the same interface into the Orbiter used to supply propellants to the main engines, the cost and complexity of adding a dedicated loading interface to the tank was avoided. It was not a tremendous complexity hit to the Orbiter Main Propulsion system ...


16

To produce a valve operating electric motor involves a very large number of parts to turn high speed low torque continuous rotary motion into short limited throw high torque motion. Every one of these parts is a potential failure that needs to have time and money spent to investigate and mitigate. They are also hard to test once fitted since once tank is ...


14

No reuse, but... NASA did not at any point actually reuse an external tank in any way. However... They made plans to allow reuse in orbit. NASA did have tentative plans for utilization of the tanks in orbit. These plans were scrapped, however. The primary factors being (1) decreased payload capacity to stable orbit †, (2) risk of insulating foam falling off ...


9

To answer the question, 'is Cassini running out of fuel': As you'd expect, NASA has monitored Cassini's fuel levels. In 2014 JPL published a study, 'Ensuring Cassini’s End-of-Mission Propellant Margins': With three years left and only 2.5% of its loaded bipropellant and 37% of its loaded monopropellant remaining, the Cassini project actively manages the ...


8

I'm not convinced that they (all) do. This other answer mentions a use case were open-loop hydraulics can be useful. I can also imagine some cases where you don't want to use electronic signals due to potential sparks with nasty consequences. However, I found this report evaluating pneumatic actuators versus electric torque motors for the new shuttle ...


8

A big issue with boosting the tank to orbit, would be the foam insulation. It was believed it would come off in chunks, like popcorn, causing immense amounts of orbital debris, potentially in the orbit you wished to store it at. Which could be really bad news.


7

Ariane 5: the Vulcain first stage engine is started using a small solid rocket motor. Shuttle SSME: after chilldown, the propellant valve is opened, allowing LH into the engine. This expands, driving the turbopump enough to fill the gas generators. The mixture in the gas generator is ignited and this drives the turbopump to operational speed. When a start ...


7

As a rule of thumb, no rocket fuel (or oxidizer) will ever be able to detonate on its own. For the simple reason that the maximum flame front propagation through it needs to be slower than the fluid speed through the injectors, otherwise the flame would propagate back into the tanks. NO, no-one has ever managed to pump flammable fluids faster than their ...


6

It would in principle produce a small amount of thrust; compressed-gas systems with no combustion are sometimes used for very small attitude control thrusters. Specific impulse is generally poor -- under 100 seconds as opposed to ~300 for hypergolic bipropellants and ~200 for catalyzed hydrazine monoprops. High-expansion ratio upper stage nozzles in ...


6

Even with hydrogen, the tank weight is quite small compared to the content weight. For some examples, you can look here (you may need to do some math to get the actual numbers): http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19750004950.pdf You are right that the heat loss is less of a problem for larger tanks, but structural integrity, especially ...


6

RP-1 Was Adopted By The Military Because It's Storable, Temperature-Insensitive, and Similar To Jet Fuel According to Clarks' Ignition, the adoption of RP-1 rocket kerosene as the standard fuel for hydrocarbon rockets was very much a result of military concerns, including logistics, but it was a bit more complicated than you described. To summarize Clark: ...


5

The issue is that the collection mechanism tends to produce more drag than thrust. Robert Zubrin and Dana Andrews showed that this makes most Bussard Ramjet-type starship propulsion impractical. In fact, this sort of mechanism is so good at producing drag, it actually does function well for decelerating a starship once it reaches its destination, meaning ...


5

A cryogenic geyser occurs when a volume of cryogenic liquid inside e.g. a pipe suddenly boils, propelling the liquid/gas mixture through the pipe and into its destination at high speed. The pipe can then refill (potentially causing a water hammer), and the process may repeat. If it does, you have cryogenic geyser cycling. So it's not so much a filling ...


5

What you are describing are the header tanks, that were present in the SN8 vehicle and should be in all Starship vehicles going forward. A header tank is a smaller tank, that holds fuel or oxidizer. The Starship's CH4 header tanks is roughly a sphere, buried in the middle of the common dome (divider between LOX tank at the bottom, and CH4 tank on the top), ...


4

I performed a feasibility study for a Soyuz launch site on Christmas Island many years ago in support of the Asian Pacific Space Center. One of their press releases talking about the project is here: https://www.aerospace-technology.com/projects/christmas/ As part of that investigation I discussed the feasibility of adding enough refrigeration capacity to ...


4

There are lots of factors in KSP's simulation model which make "asparagus" staging viable and beneficial. The big one is the weak drag model (at least in early versions): the penalty for making the rocket wider isn't too bad. Conversely, the weak coupling between rigid components in KSP causes very tall rockets to "wobble", and the overpowered and under-...


4

tl;dr: The September 15, 2017 end for Cassini is part of the second mission extension (XXM, or Solstice Mission) proposed in 2009. The plan was approved. above: "Choosing the XXM Tour: Cassini project manager Bob Mitchell demonstrates the features of the Cassini spacecraft to the XXM senior review panel at JPL on February 10th 2009, watched by project ...


3

If you refer to page 25* of this Space Shuttle Main Engine orientation you will see that the LOX enters the engine at -297 deg F (-183 C) and the LH2 enters at -423 deg F (-253 C), whilst the main combustion chamber runs at a toasty 6000 deg F (3316 C). You ask specifically about the tank temperatures; if I recall correctly, there was a small temperature ...


3

As far as I know they vent any remaining propellants after landing for safety reasons so I would assume most of the helium would end up being vented along with that. So my assumption is no they don't recapture it. Would it be worth it? I doubt it. 20k might sound like a lot but when you are talking about a 60M a mission it ends up being 0.03% of the cost of ...


3

Once the tanks are no longer full, there's no point in keeping the propellants subcooled. When you start the engines, you just have to control the rate at which the tank and propellant warm up, to keep the pressure below its limit. The warm gas you inject into the headspace to pressurize the tank will start warming up the surface of the liquid. You'll ...


3

tl;dr: I see that comments below the question by the OP argue against this being a deal-breaker problem but I'm going to point it out anyway as a partial answer. Any engine using "sand" as a reaction mass will have to avoid any significant production of silica nanoparticles so large that they are not accelerated in the nozzle. Assuming a perfect, ...


3

Some rockets (especially hybrids) use nitrous oxide oxidizer, which exothermically decomposes into nitrogen and oxygen and is capable of detonation. This is not just a theoretical hazard, Virgin Galactic experienced an explosion during a cold-flow injector test in 2007 that killed 3 people and injured 3 more. Acetylene is typically handled as a solution in ...


2

The Falcon Heavy cores are essentially 3 Falcon 9 first stages, with only a few minor differences to distinguish them. If an explosion somehow resulted from any circumstances, all 3 cores would explode, likely causing an explosion about 3x from the AMOS-6 incident.


2

The Helium per se does not explode. What happened in the AMOS-6 incident is that when fueling the upper stage which has Helium COPV (Carbon Overwrap Pressurized Vessels) that are submerged in the subcooled LOX. The Helium as it was being pumped in, faster than usual, cooled even further and they think caused oxygen to solidify and work its way into the ...


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