Author Topic: Starship Launch Mount / Pad / Table Discussion  (Read 270381 times)

Offline edzieba

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Re: Starship Launch Mount / Pad / Table Discussion
« Reply #820 on: 05/30/2023 07:48 am »
I'm thinking that this idea got baked in at that point in time and then maybe people didn't return to it as a consideration with the thought "they already tried this and it wasn't practical"
Or more to the point - for most every other launch vehicle, it simply isn’t necessary.
Bingo. Everyone is happy to use watercooled (and not evaporative cooled in the vast majority of cases) diverters for engine test stands, but it's (thus far) not been needed for launch mounts.

Offline tntnt

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Re: Starship Launch Mount / Pad / Table Discussion
« Reply #821 on: 05/30/2023 12:28 pm »
I'm thinking that this idea got baked in at that point in time and then maybe people didn't return to it as a consideration with the thought "they already tried this and it wasn't practical"
Or more to the point - for most every other launch vehicle, it simply isn’t necessary.
Bingo. Everyone is happy to use watercooled (and not evaporative cooled in the vast majority of cases) diverters for engine test stands, but it's (thus far) not been needed for launch mounts.

My question here was going to be "What does the B-2 test stand at Stennis use for the 8 minute SLS tests?" as that's all I am aware of with comparative levels of craziness. As always, the internet provideth:

https://www.nasa.gov/sites/default/files/atoms/files/b-stand-poster.pdf

Quote
More than 32,500 5/32-inch holes in the B-2 Test Stand flame
deflector direct more than 240,000 gallons of water a minute to
cool rocket engine exhaust during a hot fire test. About another
92,000 gallons of water per minute will be sprayed through 92
nozzles to provide vibro-acoustic suppression protection during
Space Launch System core stage testing. This also will help to
shield the stage from radiant heating and other thermal effects.

                                                         The water system now
is capable of delivering 335,000 gallons per minute to the B-2
stand via 96-inch pipes

Also video of a flow test, link starts at the diverter portion of the test:


Offline InterestedEngineer

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Re: Starship Launch Mount / Pad / Table Discussion
« Reply #822 on: 05/30/2023 03:11 pm »
My question here was going to be "What does the B-2 test stand at Stennis use for the 8 minute SLS tests?" as that's all I am aware of with comparative levels of craziness. As always, the internet provideth:

https://www.nasa.gov/sites/default/files/atoms/files/b-stand-poster.pdf

Quote
More than 32,500 5/32-inch holes in the B-2 Test Stand flame
deflector direct more than 240,000 gallons of water a minute to
cool rocket engine exhaust during a hot fire test. About another
92,000 gallons of water per minute will be sprayed through 92
nozzles to provide vibro-acoustic suppression protection during
Space Launch System core stage testing. This also will help to
shield the stage from radiant heating and other thermal effects.


Converting that to MKS that's 15tons/sec of water.

Say 150t of water per launch.
« Last Edit: 05/30/2023 03:12 pm by InterestedEngineer »

Offline alugobi

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Re: Starship Launch Mount / Pad / Table Discussion
« Reply #823 on: 05/30/2023 03:57 pm »
I'd like to jump through that into a swimming pool below.

Offline zubenelgenubi

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Re: Starship Launch Mount / Pad / Table Discussion
« Reply #824 on: 05/31/2023 03:53 am »
Moderator:
I split/merged some recent posts to the "I risk sending the thread off topic" thread.
https://forum.nasaspaceflight.com/index.php?topic=53586.0
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Offline Proxa

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Re: Starship Launch Mount / Pad / Table Discussion
« Reply #825 on: 06/22/2023 03:00 pm »
I have a couple of questions concerning the stagnation layer above the steel plate of the Starship OLM that I hope you can help me with. So the way I understand it is, spewing water up through the steel plate will do two things: it keeps the plate cold to prevent an internal steam explosion and it creates a stagnation layer of steam above the steel plate that pushes most of the rocket exhaust to the sides away from the steel plate. Effectively this means that the steam stagnation layer does most of the job of protecting the launch surface and not the steel plate, right?

So my question is, if the steel plate doesn’t really do much, why not just remove it and build a simpler and safer system in the form of a deep pool of water? In both cases, the rocket exhaust would flash-boil water to create the steam stagnation layer that protects the launch surface. In the case of a pool we just don’t pump it up to meet the rocket exhaust. We just need to make sure that the pool holds at least the same amount of water as we are pumping up through the steel plate so that the stagnation layer doesn’t disappear.

If we use the numbers that InterestedEngineer estimated we can get a feel for how large and deep a pool would have to be:


We can estimate the thermal energy of the exhaust, and this gives us an upper limit on the amount of water needed to dissipate that energy.   Probably not going to get to that upper limit, but a ceiling is nice.

The exhaust kinetic energy rate is 650kg/sec * 33 * 0.5 * 332502= 113GW.

We know that the engines are about 59% efficient in converting the chemical energy to kinetic energy, so this leaves us with 41/59 * 113GW = 78GW of thermal energy in the exhaust stream.

The heat of vaporization of water is 2.25 MJ/kg.   Thus to absorb all the thermal energy would require a flow rate of 78GW/2.25MJ/kg = 35t/second, or 35m3/sec.   (I'm not including the heat required to heat water from 20->100C because I'm looking for orders of magnitude here)

Note this is the upper limit.  Most the heat is escaping in the exhaust stream that is bouncing off of the stagnation layer, and that stream is moving so fast it's going to not have very much time to turn the water into steam below the exhaust mount.  I suspect 3.5t/sec would be more than sufficient.


So, the heat from the rocket exhaust will at most evaporate ~35m3 of water every second when we assume that no part of the exhaust is pushed away. For a pool with a diameter of 13m (The OLM legs are 16m apart) that means the booster would vaporize ~0.3m of water every second. For a launch like the first orbital flight test of Starship, where the booster fired for ~8s before lift off, we’d need a pool at least ~2m deep to not empty the pool but that's feasible to build.

Then there is of course the pressure from the rocket exhaust. Because we are not pumping the water up to meet the rocket exhaust, some of the rocket exhaust must always be in contact with the water surface to create the steam stagnation layer. This contact is obviously quite violent so additional water will be blasted away compared to the steel plate solution.

I find it difficult making a good conservative estimate on how much water is blasted away as this effect is a careful balance between creating steam from the rocket exhaust, and steam preventing the exhaust from reaching the water. Perhaps some of you smart people have an idea for a good estimate?

My gut feeling is that the total water removal rate from vaporizing water and blasting it out of the pool is less than what the heat from the rocket would remove if all of it was used to vaporize water (the 35m3/s mentioned above). If so, a pool concept would be a viable alternative to the steel plate solution SpaceX is building, but gut feeling ain’t much to build on.

Offline KilroySmith

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Re: Starship Launch Mount / Pad / Table Discussion
« Reply #826 on: 06/22/2023 03:22 pm »
AIUI, the stagnation layer doesn't get rid of the downward force from the thrust; there's still 75,000 kN of force that will be trying to toss the water in your pool into Mexico.  What the stagnation layer does do is reduce the amount of insanely hot, insanely fast gases that would otherwise scour whatever surface is resisting the thrust. 

Offline steveleach

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Re: Starship Launch Mount / Pad / Table Discussion
« Reply #827 on: 06/22/2023 03:38 pm »
My (very) limited understanding of all this is that there are several very difficult problems being addressed here:-

1. Dealing with all the thermal energy in the exhaust
2. Dealing with all the kinetic energy in the exhaust
3. Dealing with all the acoustic energy in the exhaust

Any attempt to understand the solution without looking at all of these (and probably many more besides) is going to be challenging.

Offline DanClemmensen

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Re: Starship Launch Mount / Pad / Table Discussion
« Reply #828 on: 06/22/2023 03:43 pm »
AIUI, the stagnation layer doesn't get rid of the downward force from the thrust; there's still 75,000 kN of force that will be trying to toss the water in your pool into Mexico.  What the stagnation layer does do is reduce the amount of insanely hot, insanely fast gases that would otherwise scour whatever surface is resisting the thrust.
But that's true for steam from a pool or steam from a fountain. The ideal steam bubble would evenly distribute the force across the whole pool. the pool would still feel the entire force and would need the same heavy and deep foundation that the steel plate needs. Of course, designing a pool whose shape forces all the splashed water to stay in the steam bubble may be impossible.

I think the plate has two main advantages. First, it forms a work surface that you can drive equipment on. Second, it's simpler to analyze where the water will end up, especially since the exhaust plume is is not an abstract ideal uniform thrust.

Offline meekGee

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Re: Starship Launch Mount / Pad / Table Discussion
« Reply #829 on: 06/22/2023 04:53 pm »
I have a couple of questions concerning the stagnation layer above the steel plate of the Starship OLM that I hope you can help me with. So the way I understand it is, spewing water up through the steel plate will do two things: it keeps the plate cold to prevent an internal steam explosion and it creates a stagnation layer of steam above the steel plate that pushes most of the rocket exhaust to the sides away from the steel plate. Effectively this means that the steam stagnation layer does most of the job of protecting the launch surface and not the steel plate, right?

So my question is, if the steel plate doesn’t really do much, why not just remove it and build a simpler and safer system in the form of a deep pool of water? In both cases, the rocket exhaust would flash-boil water to create the steam stagnation layer that protects the launch surface. In the case of a pool we just don’t pump it up to meet the rocket exhaust. We just need to make sure that the pool holds at least the same amount of water as we are pumping up through the steel plate so that the stagnation layer doesn’t disappear.

If we use the numbers that InterestedEngineer estimated we can get a feel for how large and deep a pool would have to be:


We can estimate the thermal energy of the exhaust, and this gives us an upper limit on the amount of water needed to dissipate that energy.   Probably not going to get to that upper limit, but a ceiling is nice.

The exhaust kinetic energy rate is 650kg/sec * 33 * 0.5 * 332502= 113GW.

We know that the engines are about 59% efficient in converting the chemical energy to kinetic energy, so this leaves us with 41/59 * 113GW = 78GW of thermal energy in the exhaust stream.

The heat of vaporization of water is 2.25 MJ/kg.   Thus to absorb all the thermal energy would require a flow rate of 78GW/2.25MJ/kg = 35t/second, or 35m3/sec.   (I'm not including the heat required to heat water from 20->100C because I'm looking for orders of magnitude here)

Note this is the upper limit.  Most the heat is escaping in the exhaust stream that is bouncing off of the stagnation layer, and that stream is moving so fast it's going to not have very much time to turn the water into steam below the exhaust mount.  I suspect 3.5t/sec would be more than sufficient.


So, the heat from the rocket exhaust will at most evaporate ~35m3 of water every second when we assume that no part of the exhaust is pushed away. For a pool with a diameter of 13m (The OLM legs are 16m apart) that means the booster would vaporize ~0.3m of water every second. For a launch like the first orbital flight test of Starship, where the booster fired for ~8s before lift off, we’d need a pool at least ~2m deep to not empty the pool but that's feasible to build.

Then there is of course the pressure from the rocket exhaust. Because we are not pumping the water up to meet the rocket exhaust, some of the rocket exhaust must always be in contact with the water surface to create the steam stagnation layer. This contact is obviously quite violent so additional water will be blasted away compared to the steel plate solution.

I find it difficult making a good conservative estimate on how much water is blasted away as this effect is a careful balance between creating steam from the rocket exhaust, and steam preventing the exhaust from reaching the water. Perhaps some of you smart people have an idea for a good estimate?

My gut feeling is that the total water removal rate from vaporizing water and blasting it out of the pool is less than what the heat from the rocket would remove if all of it was used to vaporize water (the 35m3/s mentioned above). If so, a pool concept would be a viable alternative to the steel plate solution SpaceX is building, but gut feeling ain’t much to build on.
In the case of a thin and replenished layer of water, the normal force is provided by the steel and concrete below.

In the case of a pool, there's no structural strength below, so the exhaust will "dig" into the pool and empty it in a microsecond.

As a poor analogy, consider hydroplaning your car on the freeway vs. trying it on a swimming pool.  Which is more fun?

--

Edit:  as an aside, consider taking off above the ocean.  How large must the body of water be, compared to the volume of excavated water, to maintain the water crater while the rocket is taking off?  That's how large your pool needs to be.  Plus whatever volume of water is evaporated or thrown clear of it.
« Last Edit: 06/22/2023 04:59 pm by meekGee »
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Offline Hog

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Re: Starship Launch Mount / Pad / Table Discussion
« Reply #830 on: 06/22/2023 06:54 pm »
I'm thinking that this idea got baked in at that point in time and then maybe people didn't return to it as a consideration with the thought "they already tried this and it wasn't practical"
Or more to the point - for most every other launch vehicle, it simply isn’t necessary.
Bingo. Everyone is happy to use watercooled (and not evaporative cooled in the vast majority of cases) diverters for engine test stands, but it's (thus far) not been needed for launch mounts.

My question here was going to be "What does the B-2 test stand at Stennis use for the 8 minute SLS tests?" as that's all I am aware of with comparative levels of craziness. As always, the internet provideth:

https://www.nasa.gov/sites/default/files/atoms/files/b-stand-poster.pdf

Quote
More than 32,500 5/32-inch holes in the B-2 Test Stand flame
deflector direct more than 240,000 gallons of water a minute to
cool rocket engine exhaust during a hot fire test. About another
92,000 gallons of water per minute will be sprayed through 92
nozzles to provide vibro-acoustic suppression protection during
Space Launch System core stage testing. This also will help to
shield the stage from radiant heating and other thermal effects.

                                                         The water system now
is capable of delivering 335,000 gallons per minute to the B-2
stand via 96-inch pipes

Also video of a flow test, link starts at the diverter portion of the test:


The duration is long, but there's "just" 4 RS25s firing. Absent is 80% of the thrust in the 2 RSRMV.  then we figure that SH thrusts with double the thrust from its 33 engines.  The level of craziness isn't so comparable.
Edit
The 1st stage Saturn-V testing was much more impressive, though the ultimate burn duration is almost 3 times shorter, the thrust levels 3 times higher(2 million lbs thrust vs 7.5 million lbs. thrust for Saturn-V 1st stage(S1-C with 5 F-1 engines).

From the NSF.com thread listed at the bottom.

"the B-1/B-2 test stand was designed to support 11 million pound thrust loads, SLS mods now provide capacity to support 3 million pounds of thrust.
"On 13 February 1967 Corps of Engineers personnel completed construction of the S-IC B-2 test stand at MTF( Mississippi Test Facility)"

It appears that the very first test of all 5 F-1s in a cluster on March 3 1967 was 15 seconds.
A second test was March 17, 1967 lasting 60 seconds.

"Boeing personnel removed the S-IC-T from test stand B-2 on March 24, 1967, following post-static checkout, test stand refurbishment, and facilities modification."

From April 1967 through October 1970 12 S1-C flight stages were tested. S1C-4 through S1-C-15, with S1-C-14 and -15 never seeing space.
"The first tests were 15-16 seconds in duration with later tests increased slowly to a full-length firing time of 2.5 minutes."


Here's a bunch of facts about the B-2 test stand's history and the SLS mods

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

https://forum.nasaspaceflight.com/index.php?topic=53555.msg2494508#msg2494508
« Last Edit: 06/22/2023 07:06 pm by Hog »
Paul

Offline InterestedEngineer

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Re: Starship Launch Mount / Pad / Table Discussion
« Reply #831 on: 06/23/2023 05:58 pm »
AIUI, the stagnation layer doesn't get rid of the downward force from the thrust; there's still 75,000 kN of force that will be trying to toss the water in your pool into Mexico.  What the stagnation layer does do is reduce the amount of insanely hot, insanely fast gases that would otherwise scour whatever surface is resisting the thrust.

As you dig a hole in the pool (or the concrete as was recently done), the stagnation layer changes characteristics - all for the worse.   The digging rate accelerates, the rebound exhaust goes from horizontal to vertical, and the acoustic waves go more vertical.

Flat or convex good.  Concave bad

Offline FutureSpaceTourist

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Re: Starship Launch Mount / Pad / Table Discussion
« Reply #832 on: 06/26/2023 06:12 am »

Offline Lee Jay

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Re: Starship Launch Mount / Pad / Table Discussion
« Reply #833 on: 06/26/2023 02:00 pm »
So, more than 2 months after Elon said the repair was going to take 1-2 months, there's over 2 meters of exposed rebar under the OLM, we're waiting for concrete, and the steel plates and water system after that.

Am I the only one who's just completely sick of his entirely insane time estimates?  He's either the dumbest person on Earth (the evidence would indicate otherwise) or just lying about those time estimates.  Why?  Is it to push his people harder?

Offline mandrewa

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Re: Starship Launch Mount / Pad / Table Discussion
« Reply #834 on: 06/26/2023 02:30 pm »
So, more than 2 months after Elon said the repair was going to take 1-2 months, there's over 2 meters of exposed rebar under the OLM, we're waiting for concrete, and the steel plates and water system after that.

Am I the only one who's just completely sick of his entirely insane time estimates?  He's either the dumbest person on Earth (the evidence would indicate otherwise) or just lying about those time estimates.  Why?  Is it to push his people harder?

I'm very encouraged by what has happened.  I feel like a lot has been accomplished over the last two months.  I don't have any feelings of disappointment.

It feels to me like there's a decent chance that maybe they've finally solved the launch pad problem, which to my mind has been an issue for many years now.  Ie. there has always been concrete flying around.  And just maybe now we are approaching a point where that will no be longer be true.  Which, among other things, would mean they can do more frequent and longer static fires.

Compared to the industry in general, SpaceX moves fast.  They've demonstrated that again.

But at the same time, it takes longer than one would wish it would take.

Offline DanClemmensen

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Re: Starship Launch Mount / Pad / Table Discussion
« Reply #835 on: 06/26/2023 02:31 pm »
So, more than 2 months after Elon said the repair was going to take 1-2 months, there's over 2 meters of exposed rebar under the OLM, we're waiting for concrete, and the steel plates and water system after that.

Am I the only one who's just completely sick of his entirely insane time estimates?  He's either the dumbest person on Earth (the evidence would indicate otherwise) or just lying about those time estimates.  Why?  Is it to push his people harder?
At your company, do large projects ever get done on time? In my personal experience spanning about 50 years, The only projects that ever come in on time are those with absolute unchangeable deadlines, like theatre opening night, conventions, or election campaigns. Construction projects (custom homes, swimming pools) always seem to slip. So do hardware and software development project that are big enough to need more than one developer.

Offline meekGee

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Re: Starship Launch Mount / Pad / Table Discussion
« Reply #836 on: 06/26/2023 02:31 pm »
So, more than 2 months after Elon said the repair was going to take 1-2 months, there's over 2 meters of exposed rebar under the OLM, we're waiting for concrete, and the steel plates and water system after that.

Am I the only one who's just completely sick of his entirely insane time estimates?  He's either the dumbest person on Earth (the evidence would indicate otherwise) or just lying about those time estimates.  Why?  Is it to push his people harder?
Probably you and a couple other loud ones.

The rest of us accept that schedule estimates for R&D are often off by 100%, and what matters is how much is achieved over how much time.
« Last Edit: 06/26/2023 07:12 pm by meekGee »
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Offline greybeardengineer

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Re: Starship Launch Mount / Pad / Table Discussion
« Reply #837 on: 06/26/2023 02:35 pm »
So, more than 2 months after Elon said the repair was going to take 1-2 months, there's over 2 meters of exposed rebar under the OLM, we're waiting for concrete, and the steel plates and water system after that.

Am I the only one who's just completely sick of his entirely insane time estimates?  He's either the dumbest person on Earth (the evidence would indicate otherwise) or just lying about those time estimates.  Why?  Is it to push his people harder?

In that case you must have been physically ill from watching SLS, Orion, and JWST development. Given such a bad reaction to program delays why do you even follow aerospace at all? Or perhaps it is just one specific company (the one that ironically moves at warp speed compared to the rest of the industry) or just one person and it isn't really schedule slips that got your knickers in a knot.  ::)

Offline Coastal Ron

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Re: Starship Launch Mount / Pad / Table Discussion
« Reply #838 on: 06/26/2023 02:41 pm »
So, more than 2 months after Elon said the repair was going to take 1-2 months, there's over 2 meters of exposed rebar under the OLM, we're waiting for concrete, and the steel plates and water system after that.

Am I the only one who's just completely sick of his entirely insane time estimates?  He's either the dumbest person on Earth (the evidence would indicate otherwise) or just lying about those time estimates.  Why?  Is it to push his people harder?

As a scheduling professional, and a SpaceX fan, long ago I realized that when Elon Musk provides estimates they are "No Earlier Than" estimates, not "No LATER Than" ones.

I also think his public proclamations are partly for SpaceX personnel to understand the overall goals, and they also know that Musk's public proclamations are not based on well thought out estimates, but SWAG's (scientific wild ass guesses).

If you view his proclamations in this way, you never need to get emotional when the dates don't happen...  ;)
If we don't continuously lower the cost to access space, how are we ever going to afford to expand humanity out into space?

Offline tssp_art

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Re: Starship Launch Mount / Pad / Table Discussion
« Reply #839 on: 06/26/2023 03:24 pm »
So, more than 2 months after Elon said the repair was going to take 1-2 months, there's over 2 meters of exposed rebar under the OLM, we're waiting for concrete, and the steel plates and water system after that.

Am I the only one who's just completely sick of his entirely insane time estimates?  He's either the dumbest person on Earth (the evidence would indicate otherwise) or just lying about those time estimates.  Why?  Is it to push his people harder?

You may well be the "only one who's just completely sick of his entirely insane time estimates" (although a few others I can think of may chime in) - the rest of us just chuckle at "Elon time" and apply a factor of 2 to 20 to make it realistic. Life is too short to let yourself get "just completely sick" over a silly "estimate" from someone as clever as Musk. They are likely just overly optimistic rather than "completely insane".

Now this guy was clearly insane -

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