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Questions tagged [ullage]

Questions regarding the management and nature of gas is tanks otherwise filled with liquids.

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Starship maintaining tank pressure during reentry and landing

Starship relies on tank pressure to gain it's full structural strength. During reentry, the tank walls heat up, causing the ullage gas to heat up, causing pressure to rise. How will Starship prevent ...
Abdullah is not an Amalekite's user avatar
3 votes
1 answer
184 views

Why does the Vulcan-Centaur upper stage do ullage burns after engine shutdown?

During the livestream of the recent Vulcan-Centaur launch, the animation of the upper stage shows what appear to be extensive ullage burns (at least four minutes, at least three minutes, and at least ...
Mark's user avatar
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11 votes
1 answer
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How is hot staging of Starship expected to provide such a large (10%) increase in total mass to LEO?

there's a meaningful payload to orbit advantage with hot staging that is conservatively about a 10% increase (Elon Musk during Twitter Spaces interview on June 24th, 2023, timestamp 37:13) In a line ...
Ingolifs's user avatar
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8 votes
2 answers
448 views

How will Starship get ullage during launch?

All the Starship air-starts up to this point have been landing burns using small header tanks which gave less ullage requirements, but I can't recall any mention of how Starship settle it's propellant ...
Abdullah is not an Amalekite's user avatar
4 votes
3 answers
365 views

Starship deorbit process

It does not seem to me that SpaceX will use thrusters similar to Draco to deorbit Starship, and I think firing a Raptor would be too powerful. All I can imagine is that it will use ullage gases ...
Douglas Sutherland's user avatar
3 votes
2 answers
427 views

Can propellant tanks in a pressure-feed rocket be pressurized by burning the propellant inside those same tanks? Recipe for Ka-BOOM?

Pressure-fed liquid fuel rocket engines use pressurized propellant tanks to deliver propellant to the combustion chamber, rather than pumps. This eliminates the mass, cost and complexity of the gas ...
Woody's user avatar
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4 votes
1 answer
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Why did Apollo missions open the propulsive Hydrogen vents during the coast phase?

According to Figure 2-1 of the SA-503 flight manual the LH2 continuous vent was opened during the coast phase, and closed during the ullage stage of the S-IVB restart T_6 + 0:00:42.0 (but open for ...
Thomas Paulin's user avatar
3 votes
2 answers
544 views

Ullage control with single engine stage?

How does a single-engine upper stage, like that of Falcon 9, do ullage control before starting the engine? Does it fire its cold gas thrusters? Does it fire the engine at minimum throttle for a second ...
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Ullage control on stage shutdown?

Is ullage control a thing only engine startup? Would a rocket like the Saturn V or Falcon 9 leave an engine running for a second or two longer just for ullage control?
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7 votes
2 answers
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Why does the Falcon 9 use turbopumps as well as helium pressurisation system?

Falcon 9 first stage use turbopumps as well as helium pressurisation system. Isn't the turbopumps enough to pump in the propellants to the combustion chamber?
Ashvin's user avatar
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11 votes
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Why do Soviet and Soviet-derived rockets hot-stage instead of using ullage motors?

I am only aware of one US rocket that used hot-staging for maintaining proper ullage during stage seperation--the Titan family. Otherwise, US rockets tend to use reaction control systems or small ...
Anton Hengst's user avatar
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6 votes
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How (the heck) will SpaceX's Starship's future pressure-fed thrusters work at "any gee’s, any attitude"?

In the SpaceX video Starship Update at about 57 minutes Tim Dodd the Everyday Astronaut asks about how the Starship rotates from reentry orientation to landing (vertical) and Musk explains that in the ...
uhoh's user avatar
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13 votes
1 answer
6k views

What is and what isn't ullage in rocket science?

This comment and others below this answer address ullage. "Ullage" basically just means "the portion of the tank that isn't filled with liquid". The extended rocket-science implications of ullage ...
uhoh's user avatar
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3 votes
1 answer
305 views

Are these sliding ullage bulkheads in the OTRAG rocket? How do they seal?

This answer to Were there any non-state organizations to organize space flight and colonizations in the second half of the 20th century? mentions OTRAG and links to Astronautix's OTRAG page. The ...
uhoh's user avatar
  • 149k
9 votes
1 answer
688 views

Why did the S-IV-B refer to "jettison"ing its ullage?

This is based on a recent question about S-IV-B ullage motor shutoff timing, specifically something found in the Technical Information Summary AS-501, page 15: Ullage Jettison ~ 532. But why "...
A. P. Heiler's user avatar
9 votes
2 answers
601 views

Why did the ullage motors for the S-IVB TLI burn shut down prior to S-IVB ignition?

I found "Technical Information Summary AS-501: Apollo Saturn V Flight Vehicle" when looking for info about the Saturn V staging sequence. It contains a nice diagram on pages 14-16 showing the various ...
awksp's user avatar
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1 vote
3 answers
3k views

What do the terms milli-g and microgravity mean? How are they used?

I've seen the terms "milli-g" acceleration and microgravity in many questions and answers here, within the context of spaceflight. Does milli-g refer to accelerations between 0.001 $g_0$ and 1 $g_0$, ...
uhoh's user avatar
  • 149k
2 votes
1 answer
504 views

How might an internal combustion engine generate substantial external thrust?

This answer mentions the proposed use of an internal combustion engine (ICE) in ULA's ACES upper stage to extract energy from LH2/LOX in multiple forms for multiple uses, which is described further in ...
uhoh's user avatar
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