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Elon Musk Announces That Raptor Engine Test Has Set New World Record (space.com)
Iwastheone shares a report from Space.com: A test fire of SpaceX's newest engine reached the power level necessary for the company's next round of rocket designs, CEO Elon Musk said on Twitter. "Raptor just achieved power level needed for Starship & Super Heavy," he tweeted on Feb. 7, four days after he shared a photograph of the first test of a flight-ready engine. [Musk added: "Raptor reached 268.9 bar today, exceeding prior record by the awesome Russian RD-180. Great work by @SpaceX engine/test team!"
The Raptor engine is designed to power the spaceship currently known as Starship as part of the rocket assembly currently known as Super Heavy (previously dubbed the BFR). The first Raptor test fire took place in September 2016, when the company was targeting an uncrewed Mars launch in 2018. Three Raptor engines like this one are built in to the Starship Hopper, which has been under construction in Texas and which SpaceX will use to begin testing the rocket technology in real life. Eventually, SpaceX plans to assemble 31 Raptor engines into the Super Heavy rockets, with another seven Raptors on the Starship itself.
The Raptor engine is designed to power the spaceship currently known as Starship as part of the rocket assembly currently known as Super Heavy (previously dubbed the BFR). The first Raptor test fire took place in September 2016, when the company was targeting an uncrewed Mars launch in 2018. Three Raptor engines like this one are built in to the Starship Hopper, which has been under construction in Texas and which SpaceX will use to begin testing the rocket technology in real life. Eventually, SpaceX plans to assemble 31 Raptor engines into the Super Heavy rockets, with another seven Raptors on the Starship itself.
This Shits Looking all to real... :)
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The RD-181 has the record for the highest chamber pressure for a flown engine. (And the RD-180 is only a few psi behind, so I'm not going to slam Elon for mixing them up.)
But the Raptor is currently a test-stand engine, and the record for tested engines is over 300 bar.
Testing an engine at a higher pressure than it flies in order to demonstrate a safety margin is of course completely normal. Aerospace uses a lot smaller margins than the factor of 2 used in a lot of civil engineering, but I expect a test at at least 110% of flight pressure.
So while this is an impressive demonstration worthy of praise, it is not any sort of record.
If I read de Laval nozzle equation correctly an increase in the combustion chamber pressure has minimal impact on the exhaust velocity (going from 260 Bar to 300 Bar has less than 1% improvement).
Combustion chamber temperature is a far better indication of efficiency of the engine and has a far more direct impact of exhaust velocity than pressure.
Credit where credit due - design requires 170 metric tonnes of force, test fire got 172 metric tonnes (design works as expected).
Chamber pressure is correlated to both thrust (higher chamber pressure = higher mass flow rate) and efficiency (and thus ISP, see here).
AFAIK, thrust density is the more key factor here, at least for Super Heavy (the first stage). There's a sort of "maximum height" to a rocket stage which relates to the thrust density. Your ability to pack more engines into the rocket corresponds to the rocket's cross section at the base. These engines in turn have to lift a column of liquid sitting above them; each engine can be viewed as having to lift the portion of the column of liquid directly above it (in addition to dead mass and payload). Eventually you get to a height where the mass of liquid (plus overhead) above each engine equals the thrust, and you don't move at all. The higher the thrust density of your engines, the taller you can realistically make that stage, the more fuel it can carry, and - for a given ratio of lower stage mass to upper stage mass - the heavier the payload it can launch (for a given dV). Other options to increase rocket upper stage masses come with disadvantages, such as making the rocket higher diameter (more air resistance) or adding strap-on boosters (more air resistance, more complexity, more work in recovery for reuse).
Thrust density is primarily of importance for lower stages (which is why you don't see many hydrolox lower stages without boosters), and why strap-on boosters (incl. very high thrust density solid rocket boosters) are commonly added to the first stages of large rockets. Thrust density limits are also why small rockets tend to be shaped like pencils (very high aspect ratio) while large rockets tend to be fatter, particularly at the base. For upper stages, ISP is of greater importance.
Also, for a rocket of a given (constant) height, improving its engines' thrust density comes with another advantage: they burn through their fuel faster and deliver the stage's dV faster. While there are limits to how fast you want to do this in the lower atmosphere, once you're past max-Q, more thrust is better (up to the G-force limits of your payload/passengers), as it means lower gravity losses.
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The Saturn V's first-stage engines were crude and inefficient due to problems scaling up the engineering of smaller rocket motors, with bodges added to solve difficulties with the flow of oxidiser and fuel into the engine. The Soviet solution was to use multiple smaller injection systems in separate combustion chambers.
By the late 1960s the Isp figure for LOX/RP fuels was about what we can get today, 300s-plus at sea level for well-designed engines like the RD-170 derivatives (the F1's sea-level Isp was 263s by comparison). The big steps made in rocket engineering are design and materials. The structures are lighter but stronger since the CAD tools allow better understanding of where to add mass and where to remove it without lessening strength, rigidity, resistance to vibration, heat dissipation and other factors. The engines are modelled and tested in simulation a long time before any metal is bent or additively-fabricated, the shapes and structures can be more complex thanks to new manufacturing processes, new alloys and composite materials are available etc. etc.
My guess is not much, given that by the 1960s the physics has been worked out pretty well and the materials have not changed markedly.
We have much better ways of 3D modelling, much better materials (like single crystal nickel alloys), and also much improved manufacturing techniques. The basic physics were known in the '60, but you couldn't model an entire rocket engine, because of wide scale interactions between pressure, temperature, intermediate reaction products, pressure wave propagation and deformation of the engine.
See: https://www.youtube.com/watch?...
Also, some things may have been possible in the '60, like machining special alloys, or weird shapes, they have become much more practical and affordable now.
The it evolved to "always add Elon to the title and a negative slant". Getting an angry response from Elon is the lottery prize. But even without it, decent uptick in clicks.
Then it seems to be evolving to "drop the negative slant, the shorts have moved on. Just mention Elon".
What is it now? Seventh Elon story in three days?
sed -e 's/Chuck Norris/Rajnikant/g' joke > fact
I love the various hacks that have been used in rocketry over the years to deal with "difficult problems", which throw away a bit of performance in order to not have to deal with them. One of the most recent ones that springs to mind is that North Korea "dealt with" the stability problems on their missiles by adding a ring of stationary (no axial rotation, aka non-maneuvering) grid fins around the base. They deliberately increase the drag of the first stage in order to keep it stable (like a shuttlecock).
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In the early 2000's NASA published a lot of software allowing for better simulation and design of nozzles and reaction chambers, leading to much better design efficiencies. It was right after that that Musk, Bezos and Branson decided to invest in space programs
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I think you underestimated rather severely: Escape velocity is sqrt(2) * orbital speed, so you're right that it's about 4.3km/s from geostationary orbit - but that only gets you away from Earth - you'd still be in basically the same orbit as Earth around the sun, and need even more delta-V to reach the asteroid belt.
I *think* that would be equivalent to the difference in solar escape velocities from each, so Earth's orbit (30km/s * sqrt(2)) - asteroid belt orbit (25km/s *sqrt(2)) =~ 7km/s. If somebody knows for sure, please chime in - I could use a simple, reliable formula for required delta-V between orbits.
Why ship fuel from a planet though? 16 Psyche may not have the right raw materials to produce fuel, but lots of neighboring asteroids do, and the delta-V required to move things from one belt asteroid to another is tiny.
Also, why would you ship iron back to Earth? We've got plenty of iron here already - scrapheaps full of the stuff rusting away. We might ship back various rare elements that have a high market value on Earth, and negligible utilitarian value in space, but bulk materials like iron and "concrete" for radiation shielding are far more valuable where they're at.
You're right that a (beanstalk) space elevator on Earth is probably magical - multi-walled carbon nanotubes are strong enough for the job, but just barely, with only enough excess strength for something like a 10% safety margin as I recall. And no responsible engineer would consider making even an ordinary elevator cable with less than a 10x safety factor, much less something that's liable to kill millions of people all over the world if it fails. And sadly, carbon nanotubes are quite possibly approaching the strength limits of physical materials - the strength of the C-C bond, combined with the fact that carbon is the smallest/lightest element capable of making four bonds per atom, makes it unlikely that we'll ever be able to develop a material with an order of magnitude greater tensile strength-to-weight ratio.
However, there's other kinds of space elevators - the tumbling cable/spinning wheel variety for example. They're not quite as elegant for getting to and from the surface - you still need to fly out of the atmosphere on a suborbital trajectory by other means - but they're FAR smaller, and easily within the strength limitations of existing materials. And they have uses far beyond getting to and from a planet's surface.
They have the *very* useful property of serving as a 100% efficient momentum batteries, with no primary moving parts, so that you can use the momentum captured from incoming payloads to launch outbound ones, with no extra delta-V needed except for fine-tuning trajectories. Set up a spinning cable in Earth orbit, and another around Mars, or in the asteroid belt, or..., and you can send payloads back and forth with negligible net energy consumption, provided that the mass-flow is the same in both directions. And if it's not - they're an *excellent* candidate for ion drives (or magnetic drives, in Earth orbit) - you can build up excess rotational momentum at your leisure, and then discharge it over the course of a few minutes as you sling a payload toward its destination. (Or alternately, leisurely dissipate excess momentum captured from incoming payloads)
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