Megarocket

[kangaroota]

NASA are about to test fire 4 RS25 engines together producing 7 megatons of thrust.
My question is, how do you hold the assembly down and prevent damage to the engines straining against the thrust?
I doubt a couple of ratchet trailer tiedowns would cut the mustard.

[Winemaker]

NASA are about to test fire 4 RS25 engines together producing 7 megatons of thrust.
My question is, how do you hold the assembly down and prevent damage to the engines straining against the thrust?
I doubt a couple of ratchet trailer tiedowns would cut the mustard.
7 Megatons? Perhaps you mean 7 million pounds..... I was a kid in Huntsville, Alabama back in the moon days; they static tested Saturn F1 engines all the time and they were pretty loud.

[rans6andrew]

A short lived rocket blast! Seems that something went out of kilter about 1 minute in and caused a shutdown of all 4 engines. I was watching the live broadcast and it was good while it lasted.

Rans6...................

[Cpt_Pugwash]

The live commentary mentioned an MCF anomaly on the No.4 engine, but they continued and then went into shut down just before the gimbal cycling part of the test.

[tdracer]

7 Megatons? Perhaps you mean 7 million pounds..... I was a kid in Huntsville, Alabama back in the moon days; they static tested Saturn F1 engines all the time and they were pretty loud.

If memory serves, they had to carefully watch the weather conditions before they ran the F1 engine tests - if the conditions were correct, the sound would break windows in Huntsville.
Do you know if they are using the same test stand that was used for the F1 engines (upgraded to modern standards)? Or did destroy the old stand and have to start over?

[yellowtriumph]

I think is the NASA coverage of the event.

https://www.youtube.com/watch?v=ELHOXi2t3lk

[wiggy]

NASA are about to test fire 4 RS25 engines together producing 7 megatons of thrust.
My question is, how do you hold the assembly down and prevent damage to the engines straining against the thrust?
I doubt a couple of ratchet trailer tiedowns would cut the mustard.

Million pounds I'd suggest.

FWIW the Saturn V (first stage 5 X F-1 engines) totalling 7.5 million pounds of thrust was held down for several seconds on the launch pad prior to being released.
That was done by four relatively small, retractable hold down arms at the base of the vehicle so I'd expect the engineers these days could rig up something to hold down something with a bit less thrust..:}

There is video here of the first test firing of the Saturn V first stage (sorry for the breathless commentary):

https://www.youtube.com/watch?v=ouYoF9cQI44

There's video here with a much better commentary which gives the hold down arms a mention:

https://vimeo.com/4366695

Edit to add: For clarity in the bottom video the hold down arms are hidden under the "small" quadrant shaped covers. The much large "levers" that swing up are the tail service masts that provided electrical connections, electrical power and other consumables etc to the first stage prior to launch.

[NineEighteen]

7 Megatons? Perhaps you mean 7 million pounds.....

39,100,000 Newtons of thrust at launch apparently. I’m afraid I don’t understand imperial units of mass/force 😬.

Roughly equivalent to thirty eight 777’s at full power?

...edited to clarify that 39.1 MN thrust when joined by two solid fuel SRB’s.

[treadigraph]

Isn't it right that the Saturn V created the loudest sustained noise ever made by humans thus far?

Watched a Shuttle launch from the beach by Patrick AFB, about 25 miles south, that seemed pretty loud! Love to have seen a Saturn go...

[TURIN]

You think thats loud?
Wait until you hear 27 Raptors fire for the launch of the SpaceX Super Heavy Starship booster.

https://www.youtube.com/watch?v=4KcxC4IBCsU

That video is a bit out of date now, this one is more recent.

https://www.youtube.com/watch?v=rzJ7F7iFxAE

[NineEighteen]

STS-121 Launch audio

I'd imagine not nearly as impressive as the Mighty Saturn V but...pretty awesome nonetheless.

[Winemaker]

Million pounds I'd suggest.

FWIW the Saturn V (first stage 5 X F-1 engines) totalling 7.5 million pounds of thrust was held down for several seconds on the launch pad prior to being released.
That was done by four relatively small, retractable hold down arms at the base of the vehicle so I'd expect the engineers these days could rig up something to hold down something with a bit less thrust...
Ah, but don't forget that there is the weight of the rocket itself holding it down; the arms only have to hold against the delta between thrust and weight.

[Saintsman]

If only we had dilithium crystals. They would be so much quieter.

But probably much less fun to watch.

[wiggy]

Ah, but don't forget that there is the weight of the rocket itself holding it down; the arms only have to hold against the delta between thrust and weight.


You're right - in the Saturn V case you'd be looking at the hold down arms dealing with about 1.5 million pounds (not tonnes :}) of excess thrust over mass...of course unlike a static test rig with engines etc potentially bolted in place in the Saturn V launcher case all four hold down arms had to be able to release their "grip" simultaneously ...even almost 60 years down the road still a pretty impressive piece of engineering IMHO.

https://www.hq.nasa.gov/office/pao/History/SP-4204/ch13-4.html


On 17 May 1965, engineers tested the ability of the first hold-down arm to sustain a vertical thrust of 725,747 kilograms.

[yellowtriumph]

Ah, but don't forget that there is the weight of the rocket itself holding it down; the arms only have to hold against the delta between thrust and weight.


I believe also, according to something I read a long time ago, that when the Saturn V engines actually ignited the total overall weight of the complete assembly is too heavy for them to lift it. During the first few seconds when the engines were getting up to full power sufficient fuel is burned off in that start up process that the overall weight of the complete craft is reduced such that the engines do then have the power to lift it. Sounds right somehow to this totally non expert.

[yellowtriumph]

If only we had dilithium crystals. They would be so much quieter.

But probably much less fun to watch.

... and what will Greta make of all this? Can Nasa designers come up with some electric equivalent that can be plugged in and charged up overnight?

[wiggy]

I believe also, according to something I read a long time ago, that when the Saturn V engines actually ignited the total overall weight of the complete assembly is too heavy for them to lift it. During the first few seconds when the engines were getting up to full power sufficient fuel is burned off in that start up process that the overall weight of the complete craft is reduced such that the engines do then have the power to lift it. Sounds right somehow to this totally non expert.

I'm not aware that was ever the case.

At lift off the five first stage engines generated a total of (nominal) of 7.5 million pounds of thrust ( 5 X F-1s at 1.5 million pounds each)

The nominal lift off weight was usually 6 million pounds, so there was about 1.5 million pounds of excess thrust at lift off.

The fuel burn was about 15 tonnes a second, so yes the weight was reducing rapidly..but OTOH they would still have been in serious ***** if an engine had failed on or just after liftoff.......

[yellowtriumph]

I'm not aware that was ever the case.

At lift off the five first stage engines generated a total of (nominal) of 7.5 million pounds of thrust ( 5 X F-1s at 1.5 million pounds each)

The nominal lift off weight was usually 6 million pounds, so there was about 1.5 million pounds of excess thrust at lift off.

The fuel burn was about 15 tonnes a second, so yes the weight was reducing rapidly..but OTOH they would still have been in serious ***** if an engine had failed on or just after liftoff.......

Well as I said I'm a total non-expert in this field, I am happy to be corrected.

[wiggy]

Do you know if they are using the same test stand that was used for the F1 engines (upgraded to modern standards)? Or did destroy the old stand and have to start over?

If this NASA article is to be believed it looks like at the core of the structure it's the original B-2 stand..

https://www.nasa.gov/sites/default/files/atoms/files/b-2_test_stand_v1.pdf

[tdracer]

Yellow, that's popular myth, but it was never actually true for any operational rocket.
Think about it - if you needed to burn off fuel to reach the liftoff weight - why not just reduce the starting fuel load?
Thanks wiggy - good to know some sanity remains at NASA. I'm still angry that we're spending tens of billions of dollars to re-create the heavy lift capability we had five decades ago and simply threw away.

[BirdmanBerry]

According to the BBC News (https://www.bbc.co.uk/news/science-environment-54583588)

The four RS-25s can generate 1.6 million lbs (7 Meganewtons) of thrust - the force that propels a rocket through the air.

[yellowtriumph]

Yellow, that's popular myth, but it was never actually true for any operational rocket.
Think about it - if you needed to burn off fuel to reach the liftoff weight - why not just reduce the starting fuel load?
Thanks wiggy - good to know some sanity remains at NASA. I'm still angry that we're spending tens of billions of dollars to re-create the heavy lift capability we had five decades ago and simply threw away.

As I say, I am happy to be corrected by those who do know about these things.

The myth seemed reasonable to my mind because I assume a rocket engine does not go from ‘zero power’ to stable state ‘top whack’ power instantaneously and that some time was require to go from one state to the other. Using unnecessary, overweight fuel during that power build up stage seemed plausible to me. I suppose a proper myth has to have a large degree of plausibility.

I’m surprised no-one has levered in the expression it isn’t rocket science yet in this thread!

[Hokulea]

I’m surprised no-one has levered in the expression it isn’t rocket science yet in this thread!
That's because it is rocket science!

[TURIN]

... and what will Greta make of all this? Can Nasa designers come up with some electric equivalent that can be plugged in and charged up overnight?

No need,
Hydrogen and LOX only exhaust steam.

Having said that, Methane and LOX produce steam and CO2, so Greta not so happy .

[ThomaJo]

Hmm. All manufacturers in the world: we can make engines smaller, fuel consumption is lower, and power is higher.
Rolls Roys and UK Space Agency: We will try to build a nuclear rocket engine to reduce the mass of the rockets.
NASA: we can connect 4 engines at once.

[tdracer]

The four RS-25s can generate 1.6 million lbs (7 Meganewtons) of thrust - the force that propels a rocket through the air.

Pretty big difference between "Meganewtons" and "Megatons"