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55 votes

Why aren't rockets built with truss structures inside their fuel & oxidizer tanks to increase structural strength?

There's almost nothing to be gained by a truss. The load being applied is along the axis of the tank. A simple hoop of material is very strong in this orientation. (Try it with a piece of paper, ...
Loren Pechtel's user avatar
32 votes

Why aren't rockets built with truss structures inside their fuel & oxidizer tanks to increase structural strength?

Because they don't need to be. Clearly the current design of rockets can be successful. So adding truss structures to the current design would add weight for no reason and take away from the payload ...
Organic Marble's user avatar
32 votes
Accepted

Will some rockets really collapse under their own weight?

Sure, here's a video. May 11, 1963. Pressure-stabilized tanks work better...with pressure. There's a writeup on the specific failure here. During fueling, a gas ...
Organic Marble's user avatar
30 votes
Accepted

What does "stirring tanks" mean?

There was no "slush" in the Apollo cryo tanks. The O2 and H2 in the tanks were stored at conditions that made them supercritical fluids. The critical pressure for O2 is ~ 730 psi, the Apollo tanks ...
Organic Marble's user avatar
28 votes
Accepted

What are SpaceX's Starship's header tanks?

This has been answered before, but I chose not to just mark it a duplicate because there is one new reason for the header tank unique to Starship. In a Reddit AMA in 2017 where Elon Musk answered ...
Dan Hanson's user avatar
  • 2,218
27 votes

Why do cryogenic fuels want an extra pressure tank?

Rocket fuels are pumped into the rocket engines. Pumping a liquid near or at its vapor pressure is a very good recipe for cavitation. Pumps don't like cavitation. They lose a great deal of efficiency ...
fraxinus's user avatar
  • 2,519
26 votes

Do larger rockets tend to have a better mass ratio due to the square cube law?

The walls of pressurized tanks in particular need to get thicker as the pressurized volume increases, so the tankage mass still increases pretty close to linearly with the tankage volume, and tankage ...
Russell Borogove's user avatar
22 votes

Why can't we use the same tank to hold fuel for both the RCS Thrusters and the Main engine for a deep-space mission?

One reason for separating the RCS and main tankage is the ullage problem; to maintain good flow into the engine inlets, you need to separate the remaining propellant from the pressurant gas in the ...
Russell Borogove's user avatar
20 votes
Accepted

What happens when supercritical fuel tanks deplete below critical point?

For the Shuttle, the flight rules cover these cases. The O2 and H2 tanks had quantity "redlines" defined - operation of the tank heaters below those quantities could cause the heaters to overheat. ...
Organic Marble's user avatar
19 votes

Why aren't rockets built with truss structures inside their fuel & oxidizer tanks to increase structural strength?

Most modern rockets do rely to some extent on tank pressure for strength. The tankage needs to be pressurized in any case to drive the turbopumps without risk of cavitation, so the structural strength ...
Russell Borogove's user avatar
18 votes

Will some rockets really collapse under their own weight?

According to this Ottawa Citizen article, this is a photo of an Atlas on display that lost pressure and collapsed in 1986. The article itself is about a recently intentionally dismantled Atlas ...
Russell Borogove's user avatar
18 votes

Why can't we use the same tank to hold fuel for both the RCS Thrusters and the Main engine for a deep-space mission?

Most deep space craft do in fact use a single propellant system for these sensible reasons. For craft that have higher thrust needs or where cryogenic propellants become possible the performance ...
GremlinWranger's user avatar
18 votes
Accepted

Why is the LOX header tank on Spacex Starship at the front of the vehicle?

The only official source we have is a tweet from Elon Musk: It’s mostly to balance the ship during entry. After delivering satellites, the front is light & back is heavy due to engines & ...
Jörg W Mittag's user avatar
14 votes
Accepted

Do larger rockets tend to have a better mass ratio due to the square cube law?

It doesn't really work that way, because a tank isn't just a volume; the tank itself is a structural member that needs to support the mass of the material contained inside it (and in most cases the ...
Darth Pseudonym's user avatar
13 votes

Why aren't rockets built with truss structures inside their fuel & oxidizer tanks to increase structural strength?

Because it would be an inefficient way to handle the loads. Let's say your rocket is a simple cylinder with engines at the bottom (no strap-on boosters or fins that might actually need extra ...
TooTea's user avatar
  • 1,765
13 votes

Why can't we use the same tank to hold fuel for both the RCS Thrusters and the Main engine for a deep-space mission?

Where the OP asks "why can't we..." it indicates a starting assumption that "this doesn't happen so far". Whilst the other answers to this question have suggested valid reasons ...
Puffin's user avatar
  • 9,654
12 votes

What does "stirring tanks" mean?

From this NASA pdf: At 46:40:02 Mission Elapsed Time during the Apollo 13 mission, both oxygen tank fans were powered on, hopefully to get a more accurate reading of the tank pressure. In fact,...
Uwe's user avatar
  • 49.2k
11 votes
Accepted

How does tankage mass really scale?

NASA TM-78661 TECHNIOUES FOR THE DETERMINATION OF MASS PROPERTIES OF EARTH-TO-ORBIT TRANSPORTATION SYSTEMS agrees with the "proportional" method Main propulsion system tank mass, if non ...
Organic Marble's user avatar
10 votes
Accepted

Why the shape of header tank is the way it is?

A simple cylinder with flat circular sheets at both ends is less stable and would be heavier than a cylinder with hemispherical or elliptical ends. A sphere has the best ratio of volume to surface ...
Uwe's user avatar
  • 49.2k
10 votes

Will some rockets really collapse under their own weight?

Rockets such as the Atlas-Agena rely on pressurized gas to maintain their structure. In the 1962, Atlas-Agena depressurized, thus imploded and broke apart on the launchpad. Here is the footage:
Star Man's user avatar
  • 5,928
10 votes

Why do cryogenic fuels want an extra pressure tank?

It is true that warming cryogenic propellants will increase the gas pressure in the headspace. But this will take some time to achieve if left to sunlight or even if left to electrical heating. In ...
Slarty's user avatar
  • 9,720
9 votes

Are there liquid fueled rocket boosters having coaxial fuel/oxidizer tanks?

For large rockets, you end up with more structure, not less. If you keep the length and radius of the tankage the same, i.e. don't change the shape of the rocket, you still need the same amount of ...
Bob Jacobsen's user avatar
  • 12.7k
9 votes
Accepted

Are there active (as of 2020) developments in liquid-fuel tank technology?

The in-development Prime launcher from Orbex has an uncommon arrangement: One key aspect of propane is that it remains liquid at cryogenic temperatures. That enabled a “coaxial tank” design for ...
Bob Jacobsen's user avatar
  • 12.7k
9 votes

Why are balloon tanks used by so few rocket designs?

Balloon tanks aren't used because they require many precautions to work with. The pressure stabilizes the tanks, so the moment the pressure drops, the tank collapses. Not very convenient to work with....
Anonymous Person's user avatar
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 ...
David Hammen's user avatar
9 votes

In Apollo hardware, why were sump tanks needed?

I'm not sure if a definite answer can be given by anyone except the original design engineers, but here's an educated guess. The Apollo Lunar Surface Journal website hosts two excellent documents: &...
Ludo's user avatar
  • 14.4k
8 votes
Accepted

Are rocket tanks being filled up until the last seconds before liftoff?

Neither Ariane nor the Space Shuttle are refueled while the engines are running. I don't know of other launch vehicles that have extended periods where the engines are running before liftoff. The ...
Rikki-Tikki-Tavi's user avatar
7 votes
Accepted

What are common rocket fuselage designs?

Normally the tank is the wall is the structure. This minimizes weight. There are usually cylindrical regions connecting the different propellant tanks - sometimes called "intertanks". This portion ...
Organic Marble's user avatar
7 votes
Accepted

How are oxygen and nitrogen replenished in the storage tanks on the ISS?

The original ISS design called for High Pressure Gas Tanks (HPGTs) to be delivered by the shuttle. With the cessation of shuttle flights, a system called Nitrogen Oxygen Resupply System (NORS) was ...
Organic Marble's user avatar

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