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72 votes
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How did the Apollo Lunar Module ascent engine prevent gas bubbling through fuel?

The ascent engine was normally fired when the LM was sitting on the moon's surface, so the tankage was subjected to about 1/6 $g$, more than sufficient to separate the dense liquid fuel from the ...
Russell Borogove's user avatar
21 votes
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What is the advantage of using Helium over Nitrogen when used for pressurising LOx?

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 "...
TooTea's user avatar
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20 votes

Have light gases like hydrogen or helium been explored for ion propulsion?

(Top edit: The Question asserts "Xenon and krypton are popular despite their heavy mass" and asks about exploring H or He ion propellants for improved Isp. This answer shows that lighter is not ...
Bob Jacobsen's user avatar
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19 votes
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Why did the Herschel Space Telescope need helium coolant?

Imagine your telescope optics looked like this red-hot glass! Herschel's instruments look at the world in the wavelength range of 55–672 µm. When plotted as a function of wavelength, the thermal ...
uhoh's user avatar
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18 votes
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Why does the Falcon 9 use turbopumps as well as helium pressurisation system?

Pumps are great at creating positive pressure, hundreds of bars. But with tank at ~1 bar, atmospheric pressure, they can only create a grand total of 1 bar of suction - can't go more vacuum than ...
SF.'s user avatar
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17 votes
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Why does the Falcon 9 require a helium pressurization system?

The shuttle propellant tanks required pressurization. Prelaunch, the tanks were pressurized by helium, supplied from the ground support equipment. After Space Shuttle Main Engine ignition, the ...
Organic Marble's user avatar
16 votes

Is it correct that the Saturn V RP1 tank was pressurized by high pressure helium and the LOX tanks were pressurised by oxygen?

Helium was used to pressurize the RP-1 tank to save weight. Nitrogen is much cheaper but its density is 1.250 kg/m$^3$, helium is 0.1785 kg/m$^3$, so 1.071 kg is saved for every cubic meter of emptied ...
Uwe's user avatar
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16 votes
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Other than He and N as pressurizing gases

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 ...
Ilmari Karonen's user avatar
14 votes
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Is this explanation for the SpaceX 1-Sept-2016 anomaly plausible?

Edit Jan 2, 2017: Well, it was a COPV bottle after all. There were buckles in some liners where super-cooled liquid oxygen pooled. From NASAspaceflight article, quoting the results of the ...
kim holder's user avatar
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14 votes

Is it correct that the Saturn V RP1 tank was pressurized by high pressure helium and the LOX tanks were pressurised by oxygen?

Because all you have to do to get gaseous oxygen is take liquid oxygen and warm it up a bit. That means just tapping off a little gas from the engine and routing it back to the tank to keep the ...
Tristan's user avatar
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13 votes

Why did the Herschel Space Telescope need helium coolant?

Herschel was an infrared space telescope. According to this paper, the performance is expected to be not far from background-noise limited, with sensitivities (5σ in 1h) of ∼ 4 mJy or 3 − 20 × $10^...
DrSheldon's user avatar
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13 votes

In what ways is helium used on modern launch vehicles?

Helium is used as a pressurant and purge gas. While no longer a "modern" launch system, the Space Shuttle made extensive use of helium to pressurize various systems and can perhaps serve as ...
Organic Marble's user avatar
12 votes

Why does the Falcon 9 require a helium pressurization system?

Thanks, that much is clear; the question is more why can they not make do with out the helium? Because the shuttle didn't need it and the MCT reportedly also won't need it, so why the falcon? All ...
Surf's user avatar
  • 131
12 votes

In what ways is helium used on modern launch vehicles?

If there is a rocket using cryogenic hydrogen tanks, you need helium for it. Liquid hydrogen should not be mixed with air, oxygen or nitrogen. A mixture with oxygen is explosive and should be avoided ...
Uwe's user avatar
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10 votes
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Why Use Helium?

Bottom line: like so many things in rocketry, it's a design trade, usually at the system level. The book Pressurization Systems for Liquid Rockets goes into great detail on this. I highly suggest ...
Organic Marble's user avatar
8 votes
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How does tank pressurization work?

1) "do both stages need to pressurize the tanks, or only the upper stages?" In general all stages need pressurization. I am unaware of any counterexample. If the engine is pressure-fed, you need ...
Organic Marble's user avatar
6 votes

Is helium used to power the Falcon 9 grid fins?

Helium is a gas at any reasonable temperature, so a system using helium would be pneumatic. Pneumatic systems are less suited for exact position control than hydraulics: because gases are ...
Hobbes's user avatar
  • 128k
6 votes

Is helium used to power the Falcon 9 grid fins?

It was thought, initially that the grid fins used RP1 propellant as a hydraulic fluid, when it was using an open system (The fluid is ejected after use until you run out, which they did). After a ...
geoffc's user avatar
  • 79.9k
6 votes

Why does the Falcon 9 use turbopumps as well as helium pressurisation system?

In a turbopump feed system it is still necessary to pressurize the tanks slightly (10 to 50 lb/in2) in order to prevent pump cavitation. Rocket Propulsion Elements, Sutton, 4th edition, p. 223 ...
Organic Marble's user avatar
5 votes
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Role of ground-supplied helium in S-1C stage

To acheive full thrust of the first stage F-1 engines of the Saturn V only liquid oxygen should be pumped into the combustion chambers. A mix of gaseous and liquid oxygen would reduce the desired mass ...
Uwe's user avatar
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5 votes
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Liquid Helium (4.2K) sealed, then raised to sub-LOX temperature (~70K) - what is the new pressure?

We don't need to look into the phase diagram here, because it doesn't matter on which path we reach a certain end point. We can safely assume that we heat up the helium at constant pressure and then ...
asdfex's user avatar
  • 15.1k
5 votes

How did the Space telescopes lose their coolant helium?

The helium evaporated away, as it was intended to do, thereby helping to cool the critical parts of the telescopes' detectors. The difference between these telescopes and Hubble are the frequencies of ...
Steve Linton's user avatar
  • 19.6k
4 votes

Why does the Falcon 9 require a helium pressurization system?

The Merlin engines use Helium to purge before launch. At least in the Merlin 1C days, and you can see several aborts that were called because of Helium issues. For the upper stage it is used to ...
geoffc's user avatar
  • 79.9k
4 votes

Can carbon dioxide be distilled from a Helium/Oxygen atmosphere by using natural refrigeration?

It's possible, but not simple or cheap. This process is called air separation and is the primary method for producing (liquid) nitrogen and oxygen. Pure gases can be separated from air by first ...
Hobbes's user avatar
  • 128k
3 votes

Have light gases like hydrogen or helium been explored for ion propulsion?

I will write another complementary answer because the top one unfortunately has some unit and physics inconsistencies. First to answer the question: have light gases like hydrogen or helium been ...
grafo's user avatar
  • 255
3 votes

Other than He and N as pressurizing gases

There aren't many atomic or diatomic gases at room temperature: H, N, O, F, Cl and the noble gases. noble gases are expensive F and Cl are corrosive oxygen reacts with propellants, so can only be ...
Hobbes's user avatar
  • 128k
3 votes
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Cassini's main engines' burns "can be blow-down or pressurized (with Helium)" - why?

According to Sutton, both blow-down and conventional pressurization use a pressurant (like helium in this case). Conventional systems have a pressure regulator between a pressurant tank and fuel tank, ...
Russell Borogove's user avatar
3 votes

Does SpaceX recover and reuse tank pressurization helium?

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 ...
Evan Steinbrenner's user avatar
3 votes

What is the purpose of the helium and argon gas supplies on ISS?

Nitrogen Usage The Minus Eighty Degree Laboratory Freezer for ISS (MELFI) uses high purity nitrogen for its Brayton cycle, not helium (source). The nitrogen ISS uses for other payloads and ECLSS isn't ...
Doresoom's user avatar
  • 1,794
3 votes
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How did the Space telescopes lose their coolant helium?

The helium used for cooling was liquid helium, it slowly evaporated, the resulting gas has to be vented to space to avoid a very high pressure and to optimize cooling. Herschel used liquid helium ...
Uwe's user avatar
  • 49.2k

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