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50 votes
Accepted

If rocket engines only need fuel and oxidizer, then why there are so many pipe lines on the engines?

While an ideal engine would just ingest fuel and oxidizer and produce exhaust gas real world engines will have some combination of regenerative cooling, film cooling, turbine exhaust, hydraulic power, ...
GremlinWranger's user avatar
50 votes
Accepted

Why did Starhopper's exhaust plume become brighter just before landing?

Indeed it is due to contaminants — dust! — in the plume. Did you notice all the dust being kicked up around the landing site? Some of that dust cloud, a very small and low-dust-density part of it (so ...
Tom Spilker's user avatar
  • 18.3k
30 votes

Why doesn’t SpaceX sell Raptor engines commercially?

Wouldn't that be amazing for meteorology and weather prediction. You could launch them vertically... In addition to GremlinWranger's points, atmospheric science rockets don't need bleeding-edge ...
Russell Borogove's user avatar
29 votes

For the Starship SN8 flight, did they lose engines in flight?

Elon Musk posted a tweet on this topic: The Raptors were well below max thrust or the ship would have blown through the altitude limit. As we hit min throttle point, an engine would shut off. The ...
geoffc's user avatar
  • 79.9k
26 votes

For the Starship SN8 flight, did they lose engines in flight?

A couple days ago I watched this video which does a pretty good job of explaining the whole test. Basically: Take-off needed all three engines to reach enough altitude, so all three engines were ...
walen's user avatar
  • 365
25 votes
Accepted

How are vacuum optimized engines tested without disintegrating them?

Flow separation can occur in a rocket nozzle that is overexpanded. This can cause quite severe turbulence and thus buffeting of the rocket nozzle. The SSME used a special rocket nozzle shape to ...
CuteKItty_pleaseStopBArking's user avatar
21 votes
Accepted

Benefit of Raptor Engines

A few different factors contribute to the Raptor's higher thrust: The specific impulse -- force delivered per mass of propellant consumed -- of methane-LOX combustion is generally higher than ...
Russell Borogove's user avatar
20 votes
Accepted

What's so special about SpaceX's Raptor rocket engine with 300 Bar chamber pressure?

The Raptor is a full-flow staged combustion methalox engine. There is a lot of new technology in that sentence. Staged Combustion Fuel and/or oxidizer is ignited to run a turbine that spins a ...
T.J. Tarazevits's user avatar
20 votes

Why doesn’t SpaceX sell Raptor engines commercially?

In addition to the points raised by GremlinWranger and Russell Borogove, SpaceX sells launches. Why bolt whole logistics and sales and support and integration teams onto your company so somebody else ...
Erin Anne's user avatar
  • 12k
18 votes

Why is SpaceX's Raptor's design so simple in comparison to SSME?

I wouldn't draw any conclusions based on diagrams alone, SSME is very well-known to the public, so we have a more detailed diagram. That doesn't mean that the actual engine is more or less complex, ...
JohnEye's user avatar
  • 1,336
18 votes

Why did Starhopper's exhaust plume become brighter just before landing?

The bright yellow light from RP-1 burning engines is from carbon soot built up from already-complex carbon molecules in kerosene. However the single-carbon methane molecules quickly oxidize to CO2 and ...
uhoh's user avatar
  • 149k
16 votes

Why doesn’t SpaceX sell Raptor engines commercially?

There are a number of rocket science reasons why SpaceX has not tried to sell Raptor, but a practical one is simply that, with Super Heavy needing 33 engines each and ambitions to sustain launch rates ...
GremlinWranger's user avatar
15 votes

Why is SpaceX's Raptor's design so simple in comparison to SSME?

A lot of questions here, let's tackle these two first: 4.And last but not least, what's SpaceX's solution for the oxygen-rich environment at 377bar, 748K injector and 546bar, 811K pre-burner? 2.The ...
Level River St's user avatar
15 votes

New BFR Engine arrangement

This question was actually asked and answered in the announcement itself. Elon Musk: In order to minimize the development risk and cost we decided to commonize the engine between the booster and the ...
Jörg W Mittag's user avatar
13 votes
Accepted

Rocket Engine Plumbing: Still don't understand the Full Flow Staged Combustion Cycle

1) If oxidizer and fuel are both cryogenic, why is it only the fuel that gets pre-heated? I assume you are talking about the H2 that flows through the nozzle? You have it a bit backwards. This is ...
Organic Marble's user avatar
13 votes

How are vacuum optimized engines tested without disintegrating them?

There are several test stands with altitude capability of up to 100 K ft (30.5 km or 8 Torr) for engine firings using the steam ejector system and up to 250 K ft (76 km) non-firing capability with ...
Uwe's user avatar
  • 49.2k
13 votes

Is a Raptor 2's thermal output really comparable to that of a nuclear power plant?

On average it isn't wrong as a "close-enough" analogy. All but one of Britain's 10 operating nuclear power stations are scheduled to close by 2023 and two of these are planned to close at ...
Organic Marble's user avatar
12 votes
Accepted

Is a Raptor 2's thermal output really comparable to that of a nuclear power plant?

Power is in units of "energy rate," joules per second, and thus it is relatively easy to estimate for a rocket engine: take the "energy rate" of the exhaust gases at the nozzle ...
BrendanLuke15's user avatar
11 votes

Why did Starhopper's exhaust plume become brighter just before landing?

Scott Manley comments in his video that it could be part of the engine has started to burn or erode, introducing new elements otherwise very pure rocket exhaust. Evidence for this (as opposed to ...
Robin Bennett's user avatar
10 votes

Why doesn’t SpaceX sell Raptor engines commercially?

In addition to the points brought up by others... I would assume one Raptor 2 engine could launch a small rocket to space. No. Given the size of the Raptor 2, even with a relatively high T/W ratio ...
Christopher James Huff's user avatar
9 votes

Benefit of Raptor Engines

I can answer the second question — engines are by and large fuel specific. There's plenty of complicated stuff that goes on in the combustion and the transition to supersonic flow that means you ...
Ingolifs's user avatar
  • 6,458
9 votes

New BFR Engine arrangement

The engines are all now sea level engines, they removed the vacuum ones from version 1.0 to reduce complexity. They did arrange things such that they can add in more engines if required for the future....
PearsonArtPhoto's user avatar
  • 121k
8 votes

How much methane to push Titan into Saturn?

Let's turn the question on its head and see what exhaust velocity we need to if Titan's entire (mostly nitrogen) atmosphere were used as a propellant. $\Delta v = v_e log(m_i / m_f)$ Wikipedia tells ...
user25972's user avatar
  • 421
7 votes

How much methane to push Titan into Saturn?

Let's do a Fermi estimate: Rockets bring about 2-5% of their start mass to orbital velocity. To cancel out Titan's orbital velocity, you're looking at two orders of magnitude more fuel and oxidizer ...
Hobbes's user avatar
  • 128k
7 votes

Does methalox fuel have a coking problem at all?

Methalox produces the least coking of any hydrocarbon rocket fuel. Coke is a compound of almost pure aromatic carbon rings, whose chemical structure resembles chicken wire. Coke is formed by the ...
Woody's user avatar
  • 22.4k
7 votes

Does Raptor rocket engine of SpaceX include a cracker or fuel conversion system to crack the hydrocarbon fuel into its constituents?

The Raptor is a full-flow staged combustion engine. The turbine exhaust gases go into the main combustion chamber. No. The fuel is burned without conversion. No conversion is necessary: the methane in ...
Hobbes's user avatar
  • 128k
6 votes

New BFR Engine arrangement

The bonus cargo capacity that two different engine types would allow wasn't worth the extra development time, money, and complexity for the initial version. It's designed that in later versions vacuum-...
Dragongeek's user avatar
  • 19.2k
6 votes
Accepted

What materials can withstand corrosive oxygen-rich hot-gas environments inside rocket engines?

Googled and found that the alloys mentioned below are available for purchase in Russia.... For example "Steel 12Х18НЮТ" - 195 000 rubles ($3036) per ton The main recommendations for the ...
A. Rumlin's user avatar
  • 7,863
6 votes
Accepted

Why do some rockets have closed boattails around the engines and others do not?

The "powerheads" of the shuttle's main engines were nicely sealed away to provide thermal and debris protection. Photo credit NASA - from STS-127 These diagrams from the KSC SSME System ...
Organic Marble's user avatar
6 votes
Accepted

SpaceX Starship: Could they use the Vacuum engines during landing in case of other engine failure?

No, they can't, for two reasons: When SpaceX recently test-fired the vacuum-optimized Raptor engine, they had to carefully manage the thrust and install additional bracing on the nozzle in order for ...
Jörg W Mittag's user avatar

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