SpaceX abandons floating platforms!

Oldfart1939 · 2023-02-16 09:01:05

SpaceX COO Gwen Shotwell announced that the company has sold the 2 floating platform oil rigs, and is putting their plans "on the black burner."
The focus is now on the orbital test flights.

Link: https://www.youtube.com/watch?v=-ujjyzBVxhc

tahanson43206 · 2023-02-16 09:23:28

For OF1939 re #1

Thanks for creating a topic for this news!

The platform idea was an attempt to decrease risks on shore.

Now it's clearly up to the US government agencies to deal with the risks of staying on shore.

There ** is ** another possibility ... the buyer(s) of those two platforms may have decided to take the risks involved in developing them.

They were a good idea and (from my perspective) they still are a good idea.

If anyone in the NewMars forum has the time to investigate further, please add your discoveries to this topic.

(th)

GW Johnson · 2023-02-18 11:15:28

Haven't seen much about this in the news. All I have seen in the more-or-less public media is that they want to launch Starship/Superheavy maybe in March, with success defined as not blowing up the launch pad and facilities. With almost twice the propellant tonnage of a Saturn-5, that is a hell of a risk. And it is exactly why NASA has become reluctant to let them launch Starship/Superheavy from Pad 39A at Canaveral. Somebody at NASA must have looked in the history books at what they found way back then looking at Nova designs.

From a safety standpoint, offshore platform launch makes sense, both from the explosion risk standpoint, and the lethal launch noise standpoint. The problem here, as near as I can tell, is that they are still defining what they need and want to do, when launching one of these things. For one thing, they're still betting they can catch a Superheavy with those same arms that they are using to stack the vehicle on the pad. I rather doubt that sort of landing will really work, and that outcome very heavily impacts the tower and facilities that you build.

Even assuming arm capture at landing will work, that tower and those arms, plus all the support faculties, are probably just too much to put onto a reworked oil platform or two. Such platforms will likely need to be custom-designed and built-from-scratch. An artificial island built on a remote reef would probably be a better choice, with a lot more room. But we'll see. Point is, they don't yet really know what they need to build on any such platform, and I think they have finally realized that.

GW

Last edited by GW Johnson (2023-02-18 11:18:50)

kbd512 · 2023-02-18 12:04:01

Vertical landing is exceptionally difficult to do, even if it's technically feasible. That was why the Space Shuttle landed on a conventional runway. China's aerospace engineers came up with a biplane hypersonic vehicle design, so that the wings could be shorter / stiffer / lighter.

Chinese hypersonic biplane design:
M2PSMNWUWNMBLUF6L34F7XQVSM.jpg?auto=webp

Thus far, nothing revolutionary has happened by using LCH4 as the fuel source. RP-1 is 2X the density of LNG, even if LNG provides a ~30 second Isp increase. I'm having a hard time accepting that we're going to colonize another planet tens of millions of miles from home, but the technology to make jet fuel is a bridge too far, when we already do that here on Earth at scale using solar power. They've had fire after fire on the pad while using LNG, because it's not a whole lot less flammable than H2. I anticipate no fires on the moon or Mars, but you have to get to orbit first. Even after you get to your destination, you still have to store the oxidizers and fuels on the moon or Mars. I think storing HTP and RP-1 will be considerably easier than storing LOX and LCH4, never mind the LH2 that NASA wants to use.

If you really want or need an Isp bump, then LH2 is the most obvious fuel to use.

As far as cleaning and inspecting engines goes, I think that will be required regardless of the engine technology used.

Would we relight a RS-25 on the moon without inspecting the turbopumps first?

I kinda doubt it.

Anyway, I wish SpaceX good fortune with Starship and Raptor and hope we get to see its maiden flight later this year.

GW Johnson · 2023-02-19 11:17:27

The "Chinese hypersonic biplane design" cannot work. Not hypersonically. Shockwave impingement happens with the shock wave off one wing hitting the other and other structures, and vice versa. The enhanced heating (by factor 5 to 10) at the shock wave impingement locations will cut the craft to pieces, in a matter of seconds, from about Mach 6 on up. We saw that experimentally at Mach 6.7 with the X-15 in 1967.

We learned analytically and experimentally more than half a century ago that you may NOT have parallel-mounted structures and fly hypersonically! Yet people still persist in proposing this kind of nonsense. I presume that is out of ignorance of what it really takes to fly that fast, whether steady or transient.

It's not a driving temperature increase, it's an increase in the heating rate driven by the same temperature (basically an extreme magnification of the heat transfer coefficient). The material soaks out almost instantaneously to the full driving temperature, which from about Mach 6 or 7 on up is unsurvivable with ALL known materials!

A first-order estimate is the effective total temperature of the oncoming airstream, which is increasingly mis-predicted by standard compressible flow methods above about Mach 7, due to ionization into-plasma effects. Standard compressible flow methods fundamentally assume ideal gas behavior, when ionizing plasma is most definitely not an ideal gas!

To about 10% typical error, you can estimate the effective total temperature from T, deg K ~ V, m/s. Mach 7 is about 2100 m/s corresponding to about 2100 K. Mach 10 is about 3000 m/s corresponding to about 3000 K. Etc. The kinetic energy of the oncoming stream shows up as heat (measured as temperature) and ionization. The faster you fly, the more ionization there is.

There might be a super-ceramic that will survive 2000+ K, but it will be nearly isothermally soaked out, because high density IS high thermal conductivity! Just exactly how and with what are you going to hang onto a super-ceramic part that hot? See the problem? THAT is what I am talking about when I say that you have to have a feasible heat protection solution to fly that fast!

Which is EXACTLY why I am known to say "if you don't have a feasible heat protection solution, then you don't have a valid hypersonic flight concept, no matter the propulsion solution".

Steady flight at such speeds is quite different from entry, which is a short transient. All known entry schemes are fundamentally heat-sinking solutions that take advantage of the shortness of the transient. Heat not carried away into the surroundings conducts inward, and must be captured into something acting as a heat sink. PERIOD! END OF ISSUE!

For steady flight, you cannot carry a large enough heat sink. One way or another, all the heat conducting into the structure MUST be somehow collected and sent out the tailpipe! The usual means conceived is to dump it into the fuel to be burned in the engine. But there are definite limits on that concept! You can only let the fuel get "so hot", and you are only using that fuel at a relatively low rate! That sharply limits how much conducted heat you can deal with. Which in turn is your speed limit.

Ugly little facts of life. Materials may change, but those facts of heat transfer do not!

GW

Last edited by GW Johnson (2023-02-19 11:37:36)

kbd512 · 2023-02-19 14:06:14

GW,

This design has been successfully tested by the Chinese in a wind tunnel and is now in flight testing, along with the new engines. They have published research papers on this as well. The design is called an "I-plane wing". There's a link to the paper from Popular Science's website.

How probable do you think it is that this design could get to the flight testing stage if it was known to be fundamentally unworkable?

Since the Chinese have space capsules that routinely reenter successfully and operational hypersonic glide weapons, do you think they're totally unaware of stagnation point heating?

Look at the shape of that upper wing. Notice how far it is from the lower wing. The upper wing also has a very particular shape to it, with a scallop over the area where it sits above the engine outlets. It's not simply two triangular wings stacked on top of each other. If it's on the scale of a passenger airliner, then those wings could be 5 meters apart.

Putting all ego and ideology aside for a moment, is it possible that they could produce a biplane design wherein the shockwave doesn't impinge upon the fuselage or parallel wing surface?

At least read the research paper before making blanket assertions:
Hypersonic I-shaped aerodynamic configurations by Prof. Kai Cui, Dr. Ying-Zhou Xu, Dr. Guang-Li Li and Dr. Yao Xiao of the Institute of Mechanics at the Chinese Academy of Sciences

GW Johnson · 2023-02-20 10:57:57

Kbd512:

The shock waves are there whether anybody wants them to be there or not. Nobody knows any ways to delete bow wave shocks at any supersonic speed. Where the shock from one structure impinges against another, heat transfer rates (but not the driving temperature) get amplified by factors of 5 to 10, for speeds in the Mach 5+ range. This causes the material affected to soak-out almost immediately to the driving temperature, which is what establishes local thermal equilibrium at net zero heat flow.

The material strength and melt-point then sets a speed limit. I did note in the Chinese paper that they were looking at Mach 5 flight, and investigated with CFD codes their shapes at Mach 5, 6, and 7. The X-15A-2 bird set its Mach 6.7 speed record at just about 100,000 feet, while carrying a scramjet test article as a parallel nacelle mounted to the ventral fin stub. At Mach 6.7 the driving temperature was enough to very quickly destroy Inconel-X (exceeding the melting temperature limit by over 1000 F while subjected to serious wind pressures). That driving temperature is 4077 R = 3617 F = 2265 K = 1992 C.

Mil Handbook 5 says (I am quoting my copy) Inconel X-750 (the “Inconel-X” used for the X-15) is useful for high-strength parts to 1000 F, for high creep resistance to 1500 F, and for low-strength requirements to 1900 F. That last is 1900 F = 2360 R = 1311 K = 1038 C. According to manufacturer's data on the internet, the melting point is 2540-2600 F, which is 1393-1427 C.

It should be absolutely no surprise that the vertical fin stub and underside of the fuselage tail suffered very severe (very nearly fatal) damage during that flight. The white ceramic heat-resistant paint actually made the problem worse, by reducing skin radiation emissivity, precisely because it was white! That paint was missing from all the hotter locations after that flight. There some overheating damage there, too.

If you want to see pictures of the damage to the X-15A-2 from that flight, I have posted some on my "exrocketman" site, as the article titled "Shock Impingement Heating Is Very Dangerous", dated 12 June 2017. That's too old for scrolling down to be practical. Use the fast navigation tool on the left side of the web page. Click on the year 2017, then the month of June, and you are there. It is the only article I posted that month.

For this kind of thing to be accurately predicted by a CFD code, requires that a proper shock impingement heating model be incorporated within that code. Not many would have that. Running the code in this situation without such a model gets you bad results even with good inputs. Computers process data without regard as to whether the data is good or bad, and without regard as to whether what they are doing with it is good or bad. Ugly little fact of life.

As for the speed limit effect, consider this: at "only" Mach 5 and 100,000 feet, the driving temperature is 2452 R = 1992 F = 1362 K = 1089 C. That is actually right on the edge of the recommended max service temperature of 1900 F for Inconel X-750, for low-strength applications. You could soak out to this in only seconds with shock impingement heating, and still survive intact! 309 and 310 stainless would also survive at 1900 F. There are other high-temperature alloys listed as 1800 F service (Waspalloy and Nimonic 75 are two), that would likely survive shock-impingement heating at only Mach 5. It's very speed-sensitive, because Mach 6.7 is only a little faster, yet over 1600 F hotter!

What I am talking about here is the real reason why no entry spacecraft has ever had parallel-mounted nacelles or other structures. It is also the reason why I think the Brit's "Skylon" airframe design CANNOT survive entry, no matter whether its "Sabre" engine ever really works adequately or not.

It's not about ego. It's about physics, numbers, and data. Hypersonics is really tough. There’s a lot more to it than just stagnation-point heating.

GW

Last edited by GW Johnson (2023-02-20 10:59:50)

SpaceNut · 2023-02-20 11:24:51

Seems that Mach 5 throttle back for a period of time to stabilize is part of the shock wave solution.

with the most recent post in the solar fuel by MIT it would seem that a solution was to have a much bigger presence for making a launch from the oil platform is required for such a large spaceship that space x was and is trying to achieve.

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#1 2023-02-16 09:01:05

SpaceX abandons floating platforms!

#2 2023-02-16 09:23:28

Re: SpaceX abandons floating platforms!

#3 2023-02-18 11:15:28

Re: SpaceX abandons floating platforms!

#4 2023-02-18 12:04:01

Re: SpaceX abandons floating platforms!

#5 2023-02-19 11:17:27

Re: SpaceX abandons floating platforms!

#6 2023-02-19 14:06:14

Re: SpaceX abandons floating platforms!

#7 2023-02-20 10:57:57

Re: SpaceX abandons floating platforms!

#8 2023-02-20 11:24:51

Re: SpaceX abandons floating platforms!

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