57

If this is true that today's rockets use half the fuel they used to? No. One might imagine that 60+ years of development must have produced large gains, but chemical rocket performance is fundamentally limited by the amount of energy in the chemical fuels, and the 1960s engines were already getting at least 2/3 of the maximum theoretically possible ...


54

My friend stated that today’s rockets use half the fuel of the rockets of those days, and can travel equal or further the distance. Your friend doesn't know what they are talking about. That is nonsense. That's not saying it right. It is utter nonsense. What SpaceX and other new space companies have done is to focus on massively reducing cost rather than ...


25

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 ...


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

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 ...


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 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 ...


18

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 ...


18

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 ...


10

David Hammen's answer is right, but I would also add that none of today's rockets have the payload capacity of the Saturn V. That's why they use half the fuel, because they are not launching humans to the moon.(With all the support equipment that requires.) Starship Heavy and New Glen are tomorrow's rockets, and they are every bit as large or larger as ...


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 ...


9

Sloshing is not a problem in zero-g conditions. A key challenge with regard to starting the firing of a thruster in a zero-g situation is to get the propellant flowing to the thruster, without any ullage gas also flowing to the thruster. This is the primary reason some spacecraft use bladdered tanks. Other spacecraft do not have bladders in their propellant ...


9

The J-2 engine of the Saturn V 2nd and 3rd stage had two successors, the J-2X and the HG-3 engines. All three engines used LH2/LOX and were designed for vacuum. The Shuttle engine RS-25 used the same propellants and there is vacuum data too. The RL-10B-2 is still used for the Delta III and IV rockets. LH2/LOX is used and there is a specific impulse for ...


8

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 ...


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.


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 ...


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 ...


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

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 ...


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), ...


5

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 ...


5

Specific impulse is indeed the main way that rocket engine efficiency is compared, as a rocket has to lift its own fuel. There's a table on the wiki page, but it also includes lots of non-rocket engines, and doesn't include any SpaceX engines. So here's a few I've collected for you: Saturn5 1st stage: 263s Saturn5 2nd and 3rd stage: 421s Space Shuttle RS-25: ...


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