SpaceX successfully test fires all six engines on Starship prototype #24
Capitalism in space: SpaceX yesterday successfully completed for the first time an eight-second-long static fire test of all six engines on Starship prototype #24.
I have embedded video of the test below. The amount of power exhibited is quite impressive. In fact, it was so powerful it likely melted the concrete below the rocket, sending hot debris flying that caused a major brushfire.
Most likely, eight long seconds of blast-furnace conditions melted the top layer of surrounding concrete and shot a hailstorm of tiny superheated globules in almost every direction. Indeed, in almost every direction there was something readily able to burn, a fire started. In several locations to the south and west, brush caught fire and began to burn unusually aggressively, quickly growing into walls of flames that sped across the terrain. To the east, debris even made it into a SpaceX dumpster, the contents of which easily caught fire and burned for hours.
Eventually, around 9pm CDT, firefighters were able to approach the safed launch pad and rocket, but the main fire had already spread south, out of reach. Instead, they started controlled burns near SpaceX’s roadblock, hoping to clear brush and prevent the fire (however unlikely) from proceeding towards SpaceX’s Starbase factory and Boca Chica Village homes and residents.
The rocket itself came though the test unscathed, a major milestone on the path to its first orbital flight.
During a launch, the rocket would have quickly lifted off, and thus caused far less stress to the concrete on the ground. Nonetheless, this test suggests SpaceX needs to do more pad preparation for any tests of Superheavy prototype #7, which has 33 engines at its base.
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In 2020 when the world panicked over COVID I wrote that the panic was unnecessary, that the virus was apparently simply a variation of the flu, that masks were not simply pointless but if worn incorrectly were a health threat, that the lockdowns were a disaster and did nothing to stop the spread of COVID. Only in the past year have some of our so-called experts in the health field have begun to recognize these facts.
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Capitalism in space: SpaceX yesterday successfully completed for the first time an eight-second-long static fire test of all six engines on Starship prototype #24.
I have embedded video of the test below. The amount of power exhibited is quite impressive. In fact, it was so powerful it likely melted the concrete below the rocket, sending hot debris flying that caused a major brushfire.
Most likely, eight long seconds of blast-furnace conditions melted the top layer of surrounding concrete and shot a hailstorm of tiny superheated globules in almost every direction. Indeed, in almost every direction there was something readily able to burn, a fire started. In several locations to the south and west, brush caught fire and began to burn unusually aggressively, quickly growing into walls of flames that sped across the terrain. To the east, debris even made it into a SpaceX dumpster, the contents of which easily caught fire and burned for hours.
Eventually, around 9pm CDT, firefighters were able to approach the safed launch pad and rocket, but the main fire had already spread south, out of reach. Instead, they started controlled burns near SpaceX’s roadblock, hoping to clear brush and prevent the fire (however unlikely) from proceeding towards SpaceX’s Starbase factory and Boca Chica Village homes and residents.
The rocket itself came though the test unscathed, a major milestone on the path to its first orbital flight.
During a launch, the rocket would have quickly lifted off, and thus caused far less stress to the concrete on the ground. Nonetheless, this test suggests SpaceX needs to do more pad preparation for any tests of Superheavy prototype #7, which has 33 engines at its base.
Readers!
Please consider supporting my work here at Behind the Black. Your support allows me the freedom and ability to analyze objectively the ongoing renaissance in space, as well as the cultural changes -- for good or ill -- that are happening across America. Fourteen years ago I wrote that SLS and Orion were a bad ideas, a waste of money, would be years behind schedule, and better replaced by commercial private enterprise. Only now does it appear that Washington might finally recognize this reality.
In 2020 when the world panicked over COVID I wrote that the panic was unnecessary, that the virus was apparently simply a variation of the flu, that masks were not simply pointless but if worn incorrectly were a health threat, that the lockdowns were a disaster and did nothing to stop the spread of COVID. Only in the past year have some of our so-called experts in the health field have begun to recognize these facts.
Your help allows me to do this kind of intelligent analysis. I take no advertising or sponsors, so my reporting isn't influenced by donations by established space or drug companies. Instead, I rely entirely on donations and subscriptions from my readers, which gives me the freedom to write what I think, unencumbered by outside influences.
You can support me either by giving a one-time contribution or a regular subscription. There are four ways of doing so:
1. Zelle: This is the only internet method that charges no fees. All you have to do is use the Zelle link at your internet bank and give my name and email address (zimmerman at nasw dot org). What you donate is what I get.
2. Patreon: Go to my website there and pick one of five monthly subscription amounts, or by making a one-time donation.
3. A Paypal Donation or subscription:
4. Donate by check, payable to Robert Zimmerman and mailed to
Behind The Black
c/o Robert Zimmerman
P.O.Box 1262
Cortaro, AZ 85652
You can also support me by buying one of my books, as noted in the boxes interspersed throughout the webpage or shown in the menu above.
As I understand it, burning grass releases more nitrogen into the environment than the burning of wood, and Nitrogen is the most important ingredient for growing new grass.
Push the button marked “Unwad Panties”.
Who’s not into renewable resources?
There’s also the issue of the literal dumpster-fire on the occasion of molten concrete being tossed into there.
I tend to agree that the fires should be flowing from the nozzle into something that can handle them, not blowing manmade lava 1500 meters into the bushes and porta-potties. I mean, come on.
I guess next time they will just hose it down like NASA launches.
The fact that the concrete had noticeable spalling in the heat needs to be dealt with.
As my engineer father once told me, “If we knew what we were doing, it wouldn’t be called research” I think he and Elon Musk would have understood each other perfectly
David Ross
“…blowing manmade lava 1500 meters into the … porta-potties.”
No ‘porta-potty contents’, Sherlock.
RZ has ruined our ability to make a joke in it’s intended manner.
Something is not right with the Universe.
Deescalation requires referring to Origin as “The Big Poof”.
}8^D
How about a flame trench to redirect the exhaust out to the Gulf.
Seems like a functional ablative heat shield. Might not be standard concrete. On the Saturn V pad the water was for breaking up and absorbing sound waves. Best way to flame proof a large area is a pre burn. Libun gamur.
Shouldn’t it just be called “search” not research?
Michael McNeil asked: “Shouldn’t it just be called “search” not research?”
I think ‘research’ refers to finding new things from previously gathered data. If you are gathering new data, it’s ‘experimentation’.
“During a launch, the rocket would have quickly lifted off, and thus caused far less stress to the concrete on the ground.”
That is true, but it is not Starship that is lifting off the pad, it is the booster with 30-odd engines not 6. So I think the jury is still out on how much pad damage there will be during liftoffs. I recall Elon saying one time that no flame trench “may be a mistake”.
Jeremy, AL: SH has a factor of 6 more engines than SS, but it’s more than a factor of 10 higher above the ground on the Orbital Launch Platform. SpaceX surely did the analysis to determine the height of the OLP before it was built based on many assumptions, not the least of which is plume attenuation as a function of nozzle downstream distance. If they weren’t conservative enough, they’ll find out and correct it soon. Soon being the key operative word. If this were NASA, they’d still have an army of engineers working on it and all we’d have at this point is a beautiful video of a launch base concept at Boca China, maybe even rendered in HD format.
Boca China—LOL—fat finger Freudian slip. It feels like China with all the government interference, even in the Republic of Texas.
Yes, I was about to make the launch platform height argument, and have also made the argument in the past that the thrust / weight ratio of the Starship as a whole will allow it to accelerate quickly upward, reducing the effect. I do NOT claim I can prove this, but I do claim that SpaceX engineers probably can.
Ps. If you look at the legs of the orbital towers in Boca Chica and Cape Canaveral, you will note that the Texas tower legs have a kink, while the Florida tower legs are slanted but straight. I suspect that’s because somebody recalculated during the construct of the first tower that additional ground clearance was needed, but the legs were already set in place. Since the legs already narrowed to the minimum desired diameter for the launch platform, in order to raise the platform there was no choice but to extend them straight up!
Concerned: thanks for pointing that out, it had not occurred to me that the Booster stand was that much higher off the ground. And I was going to add that there are no doubt remediations available if it turns out to be necessary.
Ray Van Dune wrote: “If you look at the legs of the orbital towers in Boca Chica and Cape Canaveral, you will note that the Texas tower legs have a kink, while the Florida tower legs are slanted but straight. I suspect that’s because somebody recalculated during the construct of the first tower that additional ground clearance was needed, but the legs were already set in place.”
That is exactly what happened.
“ … and have also made the argument in the past that the thrust / weight ratio of the Starship as a whole will allow it to accelerate quickly upward, reducing the effect.”
If you think the Space Shuttle leapt off the pad compared to the Saturn V, Starship should make the Shuttle seem lazy. By my calculation, the Shuttle (weight ≈ 4.5 million pounds, thrust ≈ 6.5 million pounds) leapt off the pad at ½ G (Saturn V was about ¼ G — 7.5 million pound thrust and 6 million pounds weight at liftoff). (SLS should be about 0.6 G, 8.8 million pound thrust and 5.5 million pound weight.) Super Heavy thrust is in the neighborhood of 16 million pounds, and the weight is in the neighborhood of 8 million pounds. The math suggests that the acceleration should be in the neighborhood of 1 G, or 32 feet (10 meters) per second per second. Starship should clear the tower in about 5.2 seconds. I also calculate that it will go from zero to 120 miles per hour (190 km/h) in that 5.2 seconds. That is a pretty darned good sports car!
It should be quite a sight to see.
So, given that Super Heavy has 5-½ times as many engines as Starship, that it is much farther off the concrete blast non-deflector, that the exhaust should be almost entirely pointed down — thus the full amount of heat and energy impinges the concrete — given the damage done by Starship’s eight-second test, and that Super Heavy will take at least a second on the pad revving up its engines before beginning its climb out of the gravity well, how well do we think that the concrete will do against Super Heavy’s blast off (and “blast off” certainly seems like the right term for this launch)?
Being old fashioned and skeptical, my bet is that there will have to be some redesign of the pad. Having seen SpaceX in action, doing what engineers have considered unlikely or outright impossible, I also bet that any damage won’t be too bad.
By the way, if Starship accelerates so fast, when does it reach max Q, at what speed, and what is the force? I haven’t tried searching for these answers, because I assume they aren’t readily available.
Thrust / weight ratio of 2:1! Holy smokes! I have read that a high thrust / weight ratio is more efficient for a fully reusable rocket, but I cannot recall the logic.
Anyway, I guess now we know why Elon is already speculating about Starship growing bigger! There is apparently already muscle to spare, not to mention expected growth in Raptor 2 (3?) thrust and ISP!
Shuttle was side mount, parallel staged—so it looks the fastest. SS/SuperHeavy may be faster, but being taller might make look in between STS and the Saturns.
Edward–
Great stuff!
Are you able to give me the Readers Digest version of what goes into “max-Q?”
GaryMike–
–>ref Nitrogen:
Molecular nitrogen in the air is chemically/biologically “inaccessible to most organisms,” and has to be converted into ammonia or other nitrogenous compounds before being utilized.
As I see it, max Q refers to dynamic pressure, basically the aerodynamic drag the rocket experiences as it ascends. This value is proportional to the density of the air and (I believe) the square of the velocity of the rocket. There is no dynamic pressure on the rocket as it sits on the pad as it is not moving, and there is no dynamic pressure in space as there is no air for the rocket to push out of the way. So zero on the ground, and zero in space, and some positive value as the rocket moves through the air. Therefore there is a max value somewhere along the flight.
Andi-
yeah, I get that.
I’m just fuzzy on the factors that go into max-Q; this is a speed, cross-section, and sound-barrier thing’ correct?
Anyway….
Always enjoy the night launches. (This never really gets old; we’re living in the Future.)
Wayne: all of the aerodynamic forces and torques scale linearly with dynamic pressure. The vehicle structure is built to withstand those forces and, equally or more importantly, the controllability of the rocket is directly affected by those forces. The forces and stresses on those systems are maximum at max-q. It’s no coincidence that that is the point in flight that Space Shuttle Challenger not so much exploded, but essentially broke up due to the near-maximum aerodynamic forces that helped rip the malfunctioning Solid Rocket Booster from its External Tank attachment point.
Wayne: Also the other factors you mention are also important. The aero forces and torques also scale linearly with the vehicle’s characteristic area and length. In the case of an axisymmetric rocket, it’s usually cross sectional area and diameter. The lift, drag, and rotational forces and torques can also drastically change with Mach number, so going supersonic (Mach > 1) is as important a milestone in ascent as max-q; the faster acceleration of Super Heavy means Mach 1 will occur much sooner than max-q compared to other big rockets.
Concerned-
thanks for the factoids. (not an aviation or math guy, but I can follow along pretty well.)
–what is the relationship between the speed of sound and max-Q?
check the clip below, cued to the event:
The shock wave produced is from exceeding the speed of sound, correct?
Space Shuttle Booster(s): Up & Down in 400 seconds
https://youtu.be/527fb3-UZGo?t=70
(8:31 total)
wayne asked: “what is the relationship between the speed of sound and max-Q?”
There is not real relation between these two. Sometimes max-Q occurs before mach 1 and sometimes after (it seems to be more often after, though).
Speed and air density are two important factors in max-Q. The cross sectional area is a factor for the total force acting on the front of the fairing and thus on the interface of the fairing with the rocket. Keep in mind that pressure and force (drag) are two different things. As Andi said, dynamic pressure is proportional to the density and it is proportional to the square of the speed. Double the speed, quadruple the Q. Halve the density, halve the Q.
The reason that the dynamic pressure begins to decrease (I suspect this was your question, because it was mine, some years ago) is that at some point in the flight the density decreases faster than the rocket speeds up. As a thought experiment, think of a rocket that is traveling straight up at 500 meters per second and has burned enough fuel to be accelerating at one G. In the next second it will be traveling at 510 meters per second, a 2% increase, but the air density over that 510 meter distance has finally decreased by 4%, which is the same as the 4% increase in V^2. Here max-Q has been reached. Dynamic pressure drops after this, because the density is decreasing much faster in time than the rocket is speeding up. The density drops so fast, because the rocket is gaining altitude much faster than it is accelerating.*
My numbers were not randomly chosen, but I did round them out a bit. The last SpaceX launch in which I paid attention to the speed and increase in speed at max-Q were close to this (~450 m/s, ~1.5 G, and just about 14 km altitude), but pitch over had begun some time before, so it was not traveling straight up, as in our thought experiment.
The drag on a rocket is similar to drag on an airplane. In addition to the frontal cross sectional area, there is some drag from friction with the sides of planes and rockets, and planes have drag created by the reaction of the airflow over (and under) the wings. Fairings get some drag from the skin friction, and if the fairing diameter is larger than the body of the rocket there is a vacuum where the fairing narrows down to the rocket diameter. These also factor into the forces on the fairing and its interface with the rocket body (often an upper stage).
Starship will have a large drag, considering that the cross sectional area is a diameter of 9 meters (~64 square meters or ~700 square feet). This is similar to the Saturn V second and first stages.
One final point about traveling through the atmosphere: like the SR-71 (or A-12), the rapid travel through the air heats up the fairings, not just the front, but the sides, too.
* e.g. at 1000 m/s, a 1G acceleration is down to 1% increase each second, and air density decreases by about half every 5,500 meters, so at that speed and 1% acceleration, the density decreases more than 16%, going straight up. Rockets pitch over to 45˚ for a while, so the density may decrease only 10% at that speed. With this in mind, did anyone notice that my thought experiment does not fit reality for a straight up rocket? Yeah, me neither.
Edward: It is also my understanding that the shape of the rocket’s fairing or nosecone is critical. I know that in descent, a blunt shape is essential, as it produces a plasma envelope that actually protects the spacecraft or missile. A pointed shape heats up too much. These facts were learned in the 1950s.
On ascent I suspect a blunt nosecone is also advantageous, though of course I’d love to hear your analysis, since I am no engineer.
Robert,
Shape is especially important for supersonic speeds. You may notice that subsonic airplanes have rounded noses and rounded wing leading edges and pointy tails and pointy wing trailing edges. Supersonic planes tend to have pointy noses and sharper wing leading edges.
Your description is for reentry vehicles, and they were studied heavily in the 1950s. Sharper or pointier reentry bodies tend to pass through the upper atmosphere without slowing much. They are more like the pointy supersonic planes, and there isn’t as much resistance to passing through the air. They will tend to slow down more in the lower atmosphere, so you will see these on warheads from ballistic missiles.
The duller reentry bodies, the various manned capsules and the Space Shuttle, tend to have stronger reactions to the upper atmosphere, as the molecules don’t bounce as much out of the way, to the side. The molecules tend to accumulate in front of the blunt body and create a volume of compressed air. Compression heats the air to a great degree and it becomes a plasma during the hot parts of reentry, and this helps to carry away heat. Plasma is a fourth form of matter (solid, liquid, gas) in which the gas is heated so much that electrons begin to come off the atoms, so plasmas are ions. The solar wind is a plasma, as are coronal mass ejections.
One effect of the compressed plasma in front of the blunt heat shield is that the air/plasma contacting the heat shield is subsonic relative to the heat shield, so there is not as much frictional heating as would be expected, but heat shields still get really hot.
Most rockets we see tend to have sharper noses so that they get through the atmosphere more easily. The U.S. submarine launched rockets tended to be rounded, blunter, but that may have been to fit them into the submarine. By the time of the Trident II rocket, there was a probe that extended out from the nose in order to help create a shock wave in front of the rounded nose, so that the nose was not what was cutting through the supersonic air. Strangely, there was a pie-plate sized disk at the front of this probe, but I don’t remember why they had this blunt feature instead of a nice pointy needle feature. You may have noticed that Gemini also had a flat front on its nose.
So, how sharp or pointy should you design your rocket’s nosecone? I’m not sure, but some are somewhat rounded, like the Starship’s nose.
Edward: It seems to me that almost all new commercial rockets today have somewhat blunt nosecones or fairings. Though intuitively this appears to increase the stress at Max Q, I suspect overall it is an advantage, though I still would love to find out the pros and cons.
Edward-
Good stuff. (I’m actually able to follow along.)
referencing Andi above–
“…zero [dynamical forces] on the ground, and zero in space, and some positive value as the rocket moves through the air.”
Is there a generic idealized graph of this? (is this a smooth curve?)
Michael McNeil asked: “Shouldn’t it just be called “search” not research?”
Nah. You never get the answer on the first try.
If you do, then it is called “Search” but most scientific progress comes from repeated attempts and failures which is why we call it “Research”.
wayne – found this – contains a graph that seems to imply a bell-shaped generic curve.
https://carterkaplan.blogspot.com/2016/07/max-q.html
Andi-
Thanks!
wayne asked: “‘…zero [dynamical forces] on the ground, and zero in space, and some positive value as the rocket moves through the air.’ Is there a generic idealized graph of this? (is this a smooth curve?)”
It is the Laffer Curve, which was created to describe a similar concept for taxes. Somewhere between a zero tax rate and a 100% tax rate is a maximum income for government. No one has explored where that maximum is, because taxes are no longer about governmental income but about social engineering.
Robert noted: “It seems to me that almost all new commercial rockets today have somewhat blunt nosecones or fairings. Though intuitively this appears to increase the stress at Max Q, I suspect overall it is an advantage, though I still would love to find out the pros and cons.”
So, I did a little more research on the topic (research, because I half-heartedly searched for these kinds of answers a few years back) and found three things about rounded nosecones on rockets.
1) Flow separation. With pointed noses, the airflow tends to remain in contact with the cylindrical portion of the fairing and the rocket body. This is where a lot of the heating comes from. Rounded noses throw the airflow away from the cylindrical portion. This is counterintuitive to me, as the Coanda effect tends to keep the flow attached to the body, as happens with the pointy conical nosecones.
https://en.wikipedia.org/wiki/Coandă_effect
You can try this at home with a spoon under a faucet or watch it in action in this short video:
https://www.youtube.com/watch?v=1JWjLly6xNE (1 minute)
2) Different shock wave shape and behavior. A sharp nose creates a shockwave that is attached to the rocket body for some distance, generally the distance of the conical part of the nose or fairing. It then propagates away in a straight line, whose angle is related to the rocket’s speed and the speed of sound. The shockwave is a region in which compression takes place (the sonic boom is a compression wave), and compression heats the air. Since it is attached (the air flow makes direct contact) to the rocket, that portion of the rocket is heated by the compressed air.
https://en.wikipedia.org/wiki/File:Schlierenfoto_Mach_1-2_Pfeilflügel_-_NASA.jpg
The rounded nose creates a shockwave that is more rounded and separated from the body. The rounded shockwave keeps the compressed, heated air farther away from the body, so less heat is transferred to the nose.
https://en.wikipedia.org/wiki/Bow_shock_(aerodynamics)
3) Fewer vibrations. With the shockwave farther from the rocket or fairing, there is less vibration that is caused by the shockwave and its compression pressure. Remember the problems they were having breaking the sound barrier? There was a lot of vibration and weird things happening, as depicted in the book and movie “The Right Stuff.” Some of the vibration came from the developing shockwave at the nose of the aircraft, and some came from the developing shockwave on top of the wings, where the airflow speed increases to create the lift via Bernoulli’s principle.
Finally, here is a tidbit on the pie plate disk at the nose of the Trident II missile (called an aerospike, which is not to be confused with the rocket engine, also called aerospike). The answer is that it accomplishes much of the three solutions listed above.
https://space.stackexchange.com/questions/35523/what-are-the-pros-and-cons-of-aerospike-nosecones
So, why don’t all rockets use aerospikes? *Sigh* That is a research (search?) project for another day.
Speaking of max-Q, New Shepard, today, had a failure of an unmanned launch, right around the max-Q portion of the launch, when stresses are high on parts of the structure. Coincidence? Maybe. It could have just been (and looked to me like) an engine problem and not a structural problem. We will have to keep an eye out for the incident report. Meanwhile, Robert has a post on this incident:
https://behindtheblack.com/behind-the-black/points-of-information/blue-origin-suborbital-flight-aborted-during-ascent/
Edward: Your research about nosecones fits (and revives) my memory of the 1950s research. It also explains why modern rockets have blunt ends at their top.
Edward-
Great stuff!
Ray Van Dune wrote: “Thrust / weight ratio of 2:1! Holy smokes! I have read that a high thrust / weight ratio is more efficient for a fully reusable rocket, but I cannot recall the logic.”
Goodness graciousness. I had intended to respond to this, too. Tim Dodd, the Everyday Astronaut, has a bit to say about this, too. I have this 45-minute video cued up to explain gravity drag, which many of us may already understand:
https://www.youtube.com/watch?v=BqJ5bKuApbs#t=752
I have this part cued up father along, to gravity drag as it works against launch:
https://www.youtube.com/watch?v=BqJ5bKuApbs#t=1266
The rest of the video is fun, too. Dodd explains Falcon 9’s hover slam and Starship’s belly flop.