If Rockets Were Transparent [video]

https://www.youtube.com/watch?v=su9EVeHqizY

by vdfs • 6 years ago

239 121 6 years ago

Very cool! For someone who knows absolutely nothing about rockets, this makes it look so much more primitive for some reason. Just these tubes filled with fuel.

amelius• 6 years ago

Yes, we'll have to find a new phrase for "rocket science" :)

munchbunny• 6 years ago

That's pretty much what rockets are: massive fuel tanks and a ton of hardware to keep the resulting explosion under control.

The really hard part is keeping the explosion intentional and pointed where you want it to go.

Ididntdothis3• 6 years ago

Fundamentally the purpose of a rocket is to throw mass behind it very quickly. The idea is pretty simple but the implementation turns out to be quite complex.

dotancohen6• 6 years ago

As someone who knows quite a bit about rockets, they really are for the most part this primitive. Just these tubes filled with fuel, with a few volts of angry pixies at the top controlling a few degrees of gimbaling at the bottom.

pjc502• 6 years ago

Almost all the engineering magic and weight is at the bottom: nozzles to handle very high temperatures, high-pressure high-speed turbopumps, and so on. The falling Falcon stages have the aerodynamic stabilisation of a shuttlecock, and their low center of gravity helps them be stable on fairly small legs.

twicetwice3• 6 years ago

As others have said, that's basically the case. Most of the complexity, though, is at the bottom, in the engines. Absolutely incredible machines designed to withstand—and control—incredible forces. Turbopumps spinning at tens of thousands of revolutions per second. Insane amounts of heat that need to be cooled so the engine bell doesn't melt. Handling cryogenic fuels (liquid oxygen is very, very cold!) at very high pressures, moving them at very high speeds.

One failure mode, out of the many many possible failure modes, that's particularly interesting to me is that if the pressure in the pipes going into the turbopumps (which push the fuel into the combustion chamber fast enough to keep the explosion going) is too low, then you'll get cavitation on the back of the turbopump blades, and the forces from that will destroy the turbopump in under a second. Kaboom.

Oh, also, these pumps have to spin so fast that they themselves are driven by essentially little mini rocket engines.

For a visual depiction of the complexity of rocket engines, check out SpaceX's Raptor engine, arguably the most advanced engine being produced right now: https://imgix.bustle.com/uploads/image/2020/4/6/c1349369-162...

I'm no rocket scientist, though, just an interested amateur. Real rocket scientists please correct me if I got anything wrong!

lutorm3• 6 years ago

Turbopumps spinning at tens of thousands of revolutions per second.

This is actually not true. These turbopumps are quite large and spin fairly slowly. The design RPM on the F-1 turbopump appears to have been 5500 RPM, for example. (That's not to say they aren't complicated, because they were using 55,000 horsepower to push the propellants into the engine.)

SwiftyBug3• 6 years ago

What's the purpose of the plane-like rocket? It looks like something that was built to fly in an atmosphere, but it's designed to be in space. Does it eventually re-enter the atmosphere, thus the need to be able to fly in it?

CarVac• 6 years ago

The Space Shuttle was designed to be able to steer itself during reentry to a large extent, over 2000 kilometers. This is why it has such large wings.

The military wanted to launch it in a polar orbit, gather intelligence, and then land back where it started in a single orbit, which moves 2000 km east of where it was at launch.

SwiftyBug3• 6 years ago

So it just falls gracefully rather than actually fly?

9999px• 6 years ago

I got very excited to see someone who hasn't heard of the Space Shuttle. It's quite the feat of engineering.

https://en.wikipedia.org/wiki/Space_Shuttle

https://www.theatlantic.com/photo/2011/07/the-history-of-the...

g3e03• 6 years ago

Relevant xkcd https://xkcd.com/1053/

But I also have to admit I cannot fathom how someone could have not heard of the space shuttle? It was only retired in 2011?

dotancohen6• 6 years ago

And I got to feel that I've very old.

My four year old plays almost daily with his model of Atlantis. Both his older sister saw Atlantis at the KSP museum after watching a Falcon 9 launch.

macksd• 6 years ago

https://en.wikipedia.org/wiki/Space_Shuttle

There's a few things that led to this. Culturally, the American space program has tended more towards the ideal of the "hero" astronaut than others, and there's been some tension between the technical/automated approach and the pilot-astronaut approach to things. I see this as an extension of that. They even considered having pilots manually control the pitch, etc. of the rockets on their way to orbit with the pilots hand on a joystick just following a "recommended" course to orbit.

NASA had explored various ideas for very precise landings, believing that to be useful especially for rapidly-reusable aircraft. There was very serious consideration to having Gemini capsules land with a glider and the astronauts facing forward similar to an aircraft: https://en.wikipedia.org/wiki/Advanced_Gemini#Gemini_Paragli....

KineticLensman3• 6 years ago

The book Digital Apollo [0] is fascinating on this subject. It describes the tensions that had to be resolved in terms who had overall authority, e.g. mission control vs. the crew vs. automation.

[0] https://mitpress.mit.edu/books/digital-apollo

pjc502• 6 years ago

The Space Shuttle was massively handicapped by the Air Force giving it unreasonably difficult requirements. They were the ones who wanted it to be most plane-like. Especially the requirement to take off, capture a satellite (friendly or hostile), and land again at Vandenberg in a single orbit.

wayneftw• 6 years ago

I don't know anything about space or rockets, but...

Why is a car housed atop the third rocket? You can see it around 4 minutes after the housing is jettisoned - https://youtu.be/su9EVeHqizY?t=239

(I was just about to post this question when I decided to just look it up - I vaguely remember hearing something about this - https://en.wikipedia.org/wiki/Elon_Musk%27s_Tesla_Roadster )

OnlyOneCannolo• 6 years ago

Because Elon Musk launched his personal Tesla into space on the Falcon Heavy test flight.

https://youtu.be/A0FZIwabctw https://youtu.be/wbSwFU6tY1c

mannykannot2• 6 years ago

If only there were a teapot in the trunk...

https://xkcd.com/1866/

wondringaloud4• 6 years ago

Because billionaires with large egos exist in the wild.

nickik4• 6 years ago

Or because they had to do a test launch and launching a block of concert would be boring. Why not do something that gets some more media attention and thus exposes far more people and kids to Spaceflight.

But its defiantly just because of his ego, not thought went into it beyond then that.

KineticLensman3• 6 years ago

Nice. If I could change one thing it would be to rotate the different vehicles as they ascend to emphasise that they are trying to achieve high horizontal speed rather than just altitude. That means they are in orbit when the engines cut off, otherwise they would just drop back to Earth.

SlowRobotAhead• 6 years ago

Which to me is why it’s crazy these have so much fuel and burn so hard - while Virgin’s “plane” gets as high as it does.

Virgin isn’t trying to leave orbit, but it’s still really an interesting comparison to rockets.

KineticLensman3• 6 years ago

Virgin isn’t trying to leave orbit

It isn't even trying to reach orbit. As soon as the fuel is exhausted it cannot help but fall back to Earth because it hasn't achieved orbital velocity. The passengers get a few minutes at high altitude, enough to experience weightlessness and see the stars.

It's a suborbital lob, a much more polished version of the X-15 in the 1960s.

[Edit - clarity]

dotancohen6• 6 years ago

Orbit requires about 7.8 km/s. That an "s" on the end, not an "h". Orbital vehicles travel almost 8 kilometers every _second_ so as to miss the Earth when they fall.

You're right, Virgin's plane gets very high, about one quarter as high as the international space station. But some missions require actual orbit.

asciimike• 6 years ago

One of the most amusing books I've read on the subject is "Ignition! An Informal History of Liquid Rocket Propellants" (PDF: http://www.sciencemadness.org/library/books/ignition.pdf, Amazon link: https://amzn.to/2WXzWcp), which discusses how science used to be more fun and chemists basically just mixed lots of super dangerous chemicals together all the time to see what worked.

Related-ish: https://www.discovermagazine.com/environment/in-russias-spac... (again, most rocket propellants aren't exactly great for you).

tectonic• 6 years ago

Looks like you just submitted it to HN too: https://news.ycombinator.com/item?id=23192651 :) Love that book!

umvi• 6 years ago

which discusses how science used to be more fun and chemists basically just mixed lots of super dangerous chemicals together all the time to see what worked.

Reminds me of the book "Uncle Tungsten", which I highly recommend.

hoorayimhelping• 6 years ago

Red is kerosene, blue is liquid oxygen, orange is liquid hydrogen, the fuel that looks like fire is solid fuel (think compressed gunpowder).

Left to right: Saturn V, Space Shuttle, Falcon 9 Heavy, SLS (still under construction).

2:22, you hear Neil Armstrong say "inboard cutout," that is the center engine shutting off to limit the thrust, and therefore G-forces the astronauts felt. As fuel ran out, the rocket stack would weigh less and so the rocket would push harder. By the time the main engine cutoff, the Saturn V was pulling 4 and a half Gs.

Also, just noticed the SLS keeps its launch escape tower (the big needle on the top of the rocket - see this: https://www.youtube.com/watch?v=AqeJzItldSQ) - this wouldn't happen in a real flight. The flight plan calls for ditching than when it's not longer useful - you can hear the Apollo 11 call saying, "tower jettisoned."

NikolaeVarius3• 6 years ago

Wasn't sure why the SLS escape tower stayed on while the S5 was shown jetissoning it

_curious_• 6 years ago

Great info, thanks for adding, you are helping ;)

bfieidhbrjr2• 6 years ago

So the SRBs don't burn from the bottom up?

SAI_Peregrinus2• 6 years ago

Nope, inside out. They're hollow, and the top section has a star cross section rather than cylindrical. The goal is to keep an overall constant pressure for the entire burn time.

Sharlin2• 6 years ago

Nope, they burn from the inside out! The propellant does not constitute a solid cylinder but has a hole in the center going through the whole thing. Ignition happens at the top and the burning (very rapidly) spreads from there to the whole inner surface.

clarkmoody2• 6 years ago

Fun fact: the shape of the propellant determines the thrust curve as it burns, as thrust is proportional to the surface area burning. And as material burns away, the surface area changes according to the pre-burn geometry.

StackExchange pictures and discussion: https://space.stackexchange.com/questions/4153/could-3d-prin...

205guy2• 6 years ago

Other comments have already mentioned the various patterns. What hasn't been mentioned is that end-burners (as they're called) are possible, but have the downside of heat on the casing and change in center of gravity.

Coming from model rocketry myself, I had the same question, so I went straight to wikipedia to find out: https://en.wikipedia.org/wiki/Solid-propellant_rocket

Somehow I thought that the combustion of the propellant had to be inline with the thrust, but TIL there is a combustion chamber, and it's the ejection of the combusted gases through the nozzle causes the thrust.

I like hearing other people's experience with model rocketry. It's interesting because I experienced it more as model building (assembling and decorating) with a fun day of launching and running after them. I never got into the physics of the flights (other than lighter==higher) or even thought of investigating propellant properties--geometry and chemistry--as amateur rocketry does. I guess nobody told me "you can make your own engines if you want," but even then I'm not sure I would've pursued it.

SAI_Peregrinus2• 6 years ago

In the video SLS keeps its launch escape tower until 8:13, then jettisons it. I do think that's too long, I wonder where they got that. If it does stay for so long, I wonder why.

sandworm1013• 6 years ago

It was likely kept longer than needed/useful because they didn't want to run into it. If the rocket is still accellerating it could theoretically catch up to the ejected tower. The probably kept it until they knew its velocity after release would be greater than the capsule's orbital velocity.

CydeWeys2• 6 years ago

I think they're retaining it until just after the final stage separation, i.e. it will be used if that stage separation goes poorly.

g3e03• 6 years ago

This really makes it easy to see that the SLS (far right) is derived from the space shuttle, with the orbiter removed and the payload placed on top instead.

0xffff2• 6 years ago

It totally does. I knew this fact already in the abstract, but the imagery in the video really drives home at a more intuitive level just how similar they are.

dotancohen6• 6 years ago

I'm sure that helped reduce the costs and timeframe associated with developing and building it, then.

d883kd8• 6 years ago

Very interesting for me to see how much shuttle legacy is present in the planned SLS. I knew it was using the same engines but based on the timing here it seems to follow a very similar flight plan with the boosters jettisoned at the same time and the 1.5 stage running out around the same time too.

LordHeini• 6 years ago

Time to play Kerbal Space Program again :)

unnouinceput• 6 years ago

This animation doesn't do enough credit to Saturn V. Tell me again off them 4, which one carried people to the moon and back?

NikolaeVarius3• 6 years ago

None of them. The Saturn 5 was discarded after launch.

dotancohen6• 6 years ago

The S-IVB performed the TLI maneuver.

And by any definition, the Saturn V carried the entire stack into orbit. From orbit you're halfway to anywhere.

dotancohen6• 6 years ago

That is not the purpose of the video. I worship the Saturn V as much as anyone, seriously not a week goes by that my kids don't hear a story out of me featuring that rocket, but the video does it's purpose.

If you really to give more (rightfully deserved) credit to the Saturn V, then in fact you can see how much more payload and propellant is on top of the still-firing S-IVB at the end of the video.

marmshallow• 6 years ago

I'd also love to see a comparison of the rockets' altitude & velocity thru the launch

onemoresoop• 6 years ago

I enjoyed this with my 2yo son. He loves rackets and calls them Kiko. Surprisingly he had the patience to watch the video till the end:)

Thinking back, I was quite fascinated by rackets and only when I was 7-8 did I get across a book on rockets with very colorful fold out posters in it. I think it’s great to have all this educative material on youtube, I will curate some cool playlists for him to watch and learn things.

ardy42• 6 years ago

The Saturn V and SLS engines burn for significantly longer than the Falcon 9 Heavy's. What's the significance of that? I assume it means they can lift more into higher orbits, but I'm not sure.

oconnor663• 6 years ago

The Saturn V and the SLS are as big as they are because they're designed to carry astronauts to the Moon (or farther). I don't think the Falcon Heavy can do that without using multiple launches and meeting / refueling in orbit.

Robotbeat4• 6 years ago

Falcon Heavy could do a single-launch loop around the Moon with Dragon.

lutorm3• 6 years ago

The animation of the FH appeared to show that the Mvac on the second stage cut out really early. I don't think that's accurate, SECO on the FH demo flight with Starman was at about T+9 minutes.

mr_toad2• 6 years ago

It’s easier to recover the boosters when they are moving slower.

Nokinside• 6 years ago

Saturn 1 (SA-5) Camera Inside Kerosene Tank https://www.youtube.com/watch?v=fL-Oi9m2beA

shadowgovt• 6 years ago

It's fascinating to observe how little fuel is left in the Falcon Heavy lower stages when they're jettisoned. That reentry profile really gets to take advantage of atmospheric drag to sink all that kinetic energy.

SergeAx• 6 years ago

Solid rocket boosters of Space Shuttle and SLS are quite similar indeed:

https://en.m.wikipedia.org/wiki/Space_Shuttle_Solid_Rocket_B...

https://www.northropgrumman.com/space/nasas-artemis-program/

gorgoiler2• 6 years ago

This is wonderful.

I’ve never really understood how solid fuel boosters work. Are they filled with something granular like sand, that empties down the rocket tube?

The video makes it seem as if the entire tube is on fire at the same time.

It’s also fantastic that an asymmetric vehicle like the Space Shuttle was ever built. What an outlier it seems, amongst the more, I suppose traditional looking rocket designs in this video.

A very poetic leap, as well, to think that the same orbiter that climbs under so much power is the same vehicle that glides into land without power, all the way back from orbit!

franzb• 6 years ago

As I understand it, the solid propellant is hard and hollow on the entire length: https://en.wikipedia.org/wiki/Solid-propellant_rocket. Also check this wonderful Applied Science video: https://www.youtube.com/watch?v=TLPWqCMb7DE

nickik4• 6 years ago

Its not really like sand, its more like toothpaste that is dried up. Its essentially a rocket fuel where the fuel and the oxidizer is premixed in the same 'paste'. This makes clear why its a pretty dangerous substance. You need to be very careful manufacturing those, as they can explode pretty easily.

The way it works, is that it burns from the insight out, like a hollow candle. The trajectory of the booster is basically molded into the hole in the middle. Once you light in on fire, the booster is gone fly its trajectory whatever you do.

Here you can see all that pretty well:

https://www.youtube.com/watch?v=k_JULlA_9Mo

akincisor• 6 years ago

If you've ever used a firecracker rocket it has solid fuel in exactly the same way. It just burns from the inside out (I think) to ensure that the rocket's center of gravity doesn't change as the burn progresses.

PostOnce• 6 years ago

This is my all time favorite animation of how a solid rocket works https://i.imgur.com/E7J8pxF.mp4

so yeah it is all burning at the same time

In the OP's video, it looks like the fire is magically coming out of thin air... it'd be hard to do the animation style I linked at the distance in OP's video though, so I'm not sure how they could better animate a solid fuel rocket

gorgoiler2• 6 years ago

Aha! Very nice! So this is why solid fuel boosters are ejected before they’ve burned out - because they will eventually burn out to the edges of the tube and the whole thing will start to glow?

mr_toad2• 6 years ago

traditional looking rocket designs

It’s ironic how much Starship resembles a 1930’s pulp-fiction rocket.

deanCommie• 6 years ago

Always a good reminder, what people think about as "rockets" is really mostly fuel tanks.

I mean intellectually people know that. Rocket = "Engine" + "Fuel tank".

But I still think that when people are imagining the awe-inspiring power of a massive rocket carrying humans into space, they're not dwelling on the fact that the majority is just a big cavernous vessel for fuel.

apatheticonion• 6 years ago

Are reusable rockets more cost effective than disposable (or recoverable by parachute) solid rockets?

205guy2• 6 years ago

And another TIL from reading the comments on the video:

"Question: Are inertial forces required, and incorporated into the designs of rockets, in order to keep liquid fuel at the bottom of each tank?"

Reply: "They are in constant acceleration except when staging or after a shutdown before a re-start. They use ullage motors to accelerate the rocket just enough to settle the fuel (either small solid rockets or reaction thrusters) when they are in zero g."

Reply 2: "Apart from Ullage Motors you can also do "Hot Staging" where you light the next Stage while the current one is still burning. That's why a lot of Russian Rockets don't have this open Interstage Sections where you can see the Engines instead of Interstage Fairings."

https://en.wikipedia.org/wiki/Ullage_motor

ashtonkem• 6 years ago

Some rockets also pressurize their fuel tanks with Helium for similar reasons I believe, including the Saturn V.

boublepop• 6 years ago

Content like this and the amazing contributing comments here is what I love most about the internet. When I woke up this morning I did not expect to spend hours reading and watching videos about space rockets, but here I am all the merrier for it. Thank you!

If Rockets Were Transparent [video]

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