58 votes

How much has fuel efficiency increased in rockets since the Apollo missions?

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 ...
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54 votes

How much has fuel efficiency increased in rockets since the Apollo missions?

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 ...
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  • 65.6k
25 votes
Accepted

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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25 votes
Accepted

Is Asparagus Staging Possible

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 ...
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23 votes

How was the space shuttle fuelled?

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, ...
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21 votes
Accepted

Can we use interstellar hydrogen as a fuel for interstellar travel?

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 ...
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  • 18.9k
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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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

Why is the Space Shuttle's External Tank fuelled through the Orbiter's main engine plumbing system?

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 ...
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16 votes

Why do rocket engines use nitrogen actuators to operate the fuel/oxidiser valves instead of electric servos?

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 ...
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10 votes

How much has fuel efficiency increased in rockets since the Apollo missions?

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 ...
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  • 109
9 votes

Is Cassini running out of fuel?

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 ...
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  • 122k
9 votes

Have any rocket fuel systems actually been explosive, and could have detonated proper?

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 ...
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9 votes

What novel tank designs and ideas are out there to prevent fuel in a rocket tank from "sloshing around"?

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 ...
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  • 65.6k
9 votes

How much has fuel efficiency increased in rockets since the Apollo missions?

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 ...
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  • 47.3k
8 votes

Why do rocket engines use nitrogen actuators to operate the fuel/oxidiser valves instead of electric servos?

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 ...
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  • 12.4k
8 votes

Why can’t cryogenic propellants be storable, at least on the ground, via refrigeration?

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: ...
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  • 2,159
7 votes
Accepted

How is a rocket engine started?

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 ...
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  • 122k
6 votes

With pressure-fed engines, is any measurable thrust generated by venting the pressurant out the engine bell after flameout?

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 -- ...
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6 votes

How much does a hydrogen tank weigh compared to the hydrogen in it?

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/...
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6 votes
Accepted

What was the influence of the military in the decision to use kerosene as fuel for LOX?

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 ...
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  • 8,421
5 votes

Can we use interstellar hydrogen as a fuel for interstellar travel?

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 ...
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5 votes

Autogenous pressurization with sub-cooled propellant

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 ...
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  • 122k
5 votes
Accepted

Filling of LOX tanks - 'cryogenic geyser cycling'

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 ...
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  • 122k
5 votes

Can Starship use dedicated smaller auxiliary landing fuel tanks?

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. ...
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  • 76.7k
5 votes
Accepted

Have any rocket fuel systems actually been explosive, and could have detonated proper?

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 ...
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5 votes

How much has fuel efficiency increased in rockets since the Apollo missions?

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 ...
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4 votes

Is Asparagus Staging Possible

Asparagus staging is possible, but not viable. Mainly because pumping fuel around at the speeds and volumes needed for launch is a really big job, but also partially because the actual tank dry mass ...
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4 votes

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

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 ...
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  • 458
4 votes

Is Cassini running out of fuel?

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 ...
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  • 148k

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