Hot answers tagged

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 ...
  • 18.1k
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, ...
40 votes
Accepted

Why did it take so long for methane to be used as a rocket propellant?

Or am I wrong and have there been attempts to build a methane rocket in the past? Well, if there were, I figured that John D. Clark's famous book Ignition! (1972, free online copy) would be the place ...
38 votes

Why did it take so long for methane to be used as a rocket propellant?

The three main competitors for liquid fuel choices to date have been: Hypergolics - easiest to get started with Kerosene/LOX - Good thrust, low performance, but dense LH/LOX - Best performance, ...
  • 77.5k
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 ...
  • 77.5k
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 ...
  • 363
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 ...
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 ...
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 ...
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 ...
  • 147k
17 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, ...
  • 1,296
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 ...
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 ...
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 ...
  • 47.9k
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 ...
12 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 ...
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 ...
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 ...
10 votes

Why did it take so long for methane to be used as a rocket propellant?

Methane, while a high ISP fuel that is relatively easy to work with, does have it's share of difficulties. The hardest thing about working with methane is it requires an ignition source, as methane ...
  • 120k
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....
  • 120k
9 votes

Why did it take so long for methane to be used as a rocket propellant?

In the past, the options were the optimal high tech option (Hydrogen) or the commodity option (RP1, basically kerosene.) Methane is certainly much easier to handle than hydrogen, with a boiling point ...
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 ...
  • 6,254
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 ...
  • 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 ...
  • 122k
7 votes

Why did it take so long for methane to be used as a rocket propellant?

Aside from being, essentially LNG, Methane burns Cleanly. Kerosene produces coking and polymerization within the engine. This does not matter if you use the engine only a few times. If you want to ...
  • 87
7 votes

Why is SpaceX considering Methane as fuel for their next engine, the Raptor?

SpaceX is not shooting at the moon, SpaceX is shooting at Mars. Logistically, I’m not sure there are viable choices besides methane / LOX and Hydrazine / Tetroxide. The return shot requires fuel ...
  • 71
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-...
  • 15.6k
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 ...
  • 7,733
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 ...
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 ...

Only top scored, non community-wiki answers of a minimum length are eligible