Poll

When will full-scale hot-fire testing of Raptor begin?

Component tests - 2017
3 (0.7%)
Component tests - 2018
20 (4.8%)
Integrated tests -  2017
16 (3.8%)
Integrated tests -  2018
232 (55.8%)
Integrated tests -  2019
110 (26.4%)
Raptor is not physically scaled up
29 (7%)
Never
6 (1.4%)

Total Members Voted: 416


Author Topic: The evolution of the SpaceX Raptor engine (Super Heavy/Starship Propulsion)  (Read 421550 times)

Offline Lars-J

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Moved my post here from the update thread:

Pics of the bells and the bottom of a fin. Taken on 1-8-19 during the fit test excitement.

Using BocaChicaGal's photo, focusing on left 2 Raptors: Enhanced to show additional Raptor components through gap in the leg.

Note**  that the left bell and expander section are mismatched in O.D. ... whereas center is much smoother transition.

Peeking around leg, we can see part of the thrust chamber and lack of plumbing. This confirms EM's statement that thee were not flight ready units but development test articles being used as boiler plate fit check and alignment units...

Thanks for the great work BCG/Nomadd/Austin... and many others..

Yep, great images. Those clearly show (IMO) that the top part is a real engine part. But the larger nozzle looks welded on.

Could it still be a dual nozzle engine? Eh.. It's possible, but the likelihood just dropped even further. The rough look of that transition (and how it differs from engine to engine) makes it seem like a temporary thing.

EDIT: Attached image being discussed.
« Last Edit: 01/14/2019 04:22 pm by Lars-J »

Offline livingjw

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How are Raptors turbopumps bearings lubricated?
What's the cold start process regarding that lubrication?

I think they are hydrodynamic bearings which use the cryo propellants.

John
I suspected that too but then I have more questions:
1. How do they start? Hydrodynamic bearing has to have some static pressure untill it  it transits to hydrodinamic mode.
2. Cryo proppelants are fluid, but also low pressure. How's the sealing to between the bearing and hot, high pressure side of pump? How do cryo fluids in bearings don't start to boil?

Does anyone have any rocket turbopump cross section? I dissassembled large turbines with additional pumps for hydrostatic or hydrodynamic bearings but how does this work without additional pump?

The pumps are bathed in propellants prior to start (pre-chill), bearings probably also. Remember, you have 3 bar of pressure in the tanks.

This little paper outlines some of the problems and solutions:
https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19910009666.pdf

John

Offline envy887

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Is there any informed opinion that Raptor has hydrodynamic bearings, or is this entirely speculation? We know BE-4 has them, though Blue called them hydrostatic bearings:

https://twitter.com/blueorigin/status/950365085091811330

Quote
Latest BE-4 engine test footage where we exceeded our Isp targets. We continue to exercise the deep throttling of our full scale 550,000 lbf BE-4, the reusability of our hydrostatic pump bearings and our stable start/stop cycles. More to follow from ongoing tests. #BE4 #NewGlenn

Offline Robotbeat

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Is there any informed opinion that Raptor has hydrodynamic bearings, or is this entirely speculation? We know BE-4 has them, though Blue called them hydrostatic bearings:

https://twitter.com/blueorigin/status/950365085091811330

Quote
Latest BE-4 engine test footage where we exceeded our Isp targets. We continue to exercise the deep throttling of our full scale 550,000 lbf BE-4, the reusability of our hydrostatic pump bearings and our stable start/stop cycles. More to follow from ongoing tests. #BE4 #NewGlenn
Hydrodynamic bearings have rubbing until the speed is high enough, thus they have a lot of wear with start/stop cycles. Using a hydrostatic bearing pump means you can eliminate the rubbing before start-up, eliminating that source of wear and tear from start/stop cycles, increasing the cycle life.

Could be that the bearings are also hydrodynamic, it's just that they use the hydrostatic pump during start-up and spin-down.
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Offline DusanC

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Is there any informed opinion that Raptor has hydrodynamic bearings, or is this entirely speculation? We know BE-4 has them, though Blue called them hydrostatic bearings:

https://twitter.com/blueorigin/status/950365085091811330

Quote
Latest BE-4 engine test footage where we exceeded our Isp targets. We continue to exercise the deep throttling of our full scale 550,000 lbf BE-4, the reusability of our hydrostatic pump bearings and our stable start/stop cycles. More to follow from ongoing tests. #BE4 #NewGlenn
Hydrostatic and hydrodynamic bearings are different.
https://en.m.wikipedia.org/wiki/Fluid_bearing

I thought that Raptor uses hydrodynamic ones because I couldn't see the piping for hydrostatic bearings in that Raptor render from IAC.

Offline IntoTheVoid

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At that point, it's less "deep throttling" and more "prelighting" backup engines in case there is an engine failure during descent. By having a couple spare engines idling at >5%, they can be rapidly throttled up if needed, more easilly than doing a fresh turbopump ignition>Main chamber ignition>full power landing.
My recollection (which admittedly could be wrong) was that Elon's justification for landing on 3 engines at low throttle was to be able to land on 2 at higher throttle, if there was an engine issue. I therefore, wouldn't expect any 'idling' engines.

Offline Oersted

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Maybe the Super Heavy could have different-sized engine bells on different engines and direct fuel to them accordingly, to optimize performance durent ascent and descent. Just throwing the idea out there...

Offline DusanC

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More on bearings:

Quote
Yes, plenty of work has been done in that area. The best primer is probably the paper that kicked off the whole hydrostatic bearing discussion (this is what you mean by "some high pressure gas"), "Reddecliff and Vohr, 1969". A lot of work has been done since then. The French had a hydrostatic bearing test stand for the never-completed European staged combustion engine (TPX/TPTech). Pratt & Whitney wanted to replace the pump side bearing in one of the Space Shuttle turbopumps with a hydrostatic one, but nothing came of this either.

IHI, the Japanese rocket turbopump manufacturer, has released information about a turbopump that they want to sell overseas that uses hydrostatic bearings, so they are probably the furthest along. Unless of course SpaceX uses hydrostatic, but for all we know their bearings run on fairy dust.

Superconducting magnetic bearings have been studied as well.

Here are the three largest problems for these bearings:

    The stiffness is tiny compared to rolling element bearings. Hydrostatic bearings have at most a tenth the stiffness, magnetic bearings maybe only a hundredth or a thousandth. This means that rotordynamic instability is a huge development risk, since it can't be well predicted.
    They require an additional supply of propellant, which lowers the efficiency of the turbopump and increases the complexity.
    Rolling element bearings have made huge strides, so expendable and even some reusable rockets have really no need. Silicon nitride bearing balls together with induction-harded Cronidur steel races have made some other components in the Space Shuttle look really bad in terms of life time.

https://space.stackexchange.com/questions/14848/has-any-work-been-done-on-alternatives-to-rolling-element-bearings-in-rocket-tur

So with more reading from other sources I don't see any definite conclusion that Raptor has fluid bearings, and with compactness of bearing positions and absence of some  visible pressure source for fluid bearings I believe that it's more probable that Raptor uses advanced roller bearings especially as they don't need that high level of clean fluid as fluid bearings.

Offline philw1776

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Is there any informed opinion that Raptor has hydrodynamic bearings, or is this entirely speculation? We know BE-4 has them, though Blue called them hydrostatic bearings:

https://twitter.com/blueorigin/status/950365085091811330

Quote
Latest BE-4 engine test footage where we exceeded our Isp targets. We continue to exercise the deep throttling of our full scale 550,000 lbf BE-4, the reusability of our hydrostatic pump bearings and our stable start/stop cycles. More to follow from ongoing tests. #BE4 #NewGlenn

Wonder if it irks Elon that Bezos's methalox BE-4 has more thrust than Raptor?

Online Slarty1080

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Snip...
Wonder if it irks Elon that Bezos's methalox BE-4 has more thrust than Raptor?
I suspect it probably does. Although this is probably moderated by the fact that Blue have not reached orbit yet.
The first words spoken on Mars: "Humans have been wondering if there was any life on the planet Mars for many decades well ... there is now!"

Offline gongora

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Wonder if it irks Elon that Bezos's methalox BE-4 has more thrust than Raptor?

BE-4's thrust has nothing to do with Raptor.  If SpaceX cared about having a bigger engine they'd build one.

Offline matthewkantar

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SpaceX set out to build a cheap reliable Mars transportation system. The size of the engines was determined by the engineering trades made in the (apparently ongoing) design process. If they were dumb enough to get into a pissing match over engine size, they would have the biggest engine powering a more expensive or less capable or incapable spacecraft.

Matthew

Online Slarty1080

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SpaceX set out to build a cheap reliable Mars transportation system. The size of the engines was determined by the engineering trades made in the (apparently ongoing) design process. If they were dumb enough to get into a pissing match over engine size, they would have the biggest engine powering a more expensive or less capable or incapable spacecraft.

Matthew

Of course they are! And I have every hope that they will succeed. Of course they wouldn't be so dumb as to have some stupid engine size competition. But that still wouldn't stop Elon being irked by the size of Jeff's rocket engine at some level.
The first words spoken on Mars: "Humans have been wondering if there was any life on the planet Mars for many decades well ... there is now!"

Offline RobLynn

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Wonder if it irks Elon that Bezos's methalox BE-4 has more thrust than Raptor?

Cost to orbit and ISRU on Mars are the only metrics Space X cares about.  High Isp and high thrust to weight with low maintenance are the major goals.  Bigger engines have worse thrust to weight due to longer fluid flow paths.  They also reduce failure redundancy and mass-production advantages, and get more expensive and difficult to manufacture and assemble (larger heavier components that can't be easily man-handled).
The glass is neither half full nor half empty, it's just twice as big as it needs to be.

Online Lemurion

Any degree of irk that Elon may feel from the size of BE-4 will likely vanish should Raptor fly first, which it should do within the next 60-90 days at the outside-- especially since the reference to deep throttling tests indicates that Blue may not have achieved full design thrust yet anyway.


Online Stan-1967

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Wonder if it irks Elon that Bezos's methalox BE-4 has more thrust than Raptor?

As OT as how much Bezo's is probably irked by how comparatively cheap Musk got off in his first & second divorces.

Offline meekGee

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Wonder if it irks Elon that Bezos's methalox BE-4 has more thrust than Raptor?

As OT as how much Bezo's is probably irked by how comparatively cheap Musk got off in his first & second divorces.
Finally, an answer worthy of the question :)
Well played.
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Offline RobLynn

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Are there any facilities other than Arnold Engineering Development Complex that can altitude test a vacuum expansion nozzle on a Raptor?  Was their ~2.4MN thrust limit a deciding factor in sizing the Raptor?
The glass is neither half full nor half empty, it's just twice as big as it needs to be.

Offline matthewkantar

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Are there any facilities other than Arnold Engineering Development Complex that can altitude test a vacuum expansion nozzle on a Raptor?  Was their ~2.4MN thrust limit a deciding factor in sizing the Raptor?

Yes. The other facility will be economical soon, the entirety of outer space.

Edited 01.15.19, added "be"
« Last Edit: 01/15/2019 03:36 pm by matthewkantar »

Offline mme

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Are there any facilities other than Arnold Engineering Development Complex that can altitude test a vacuum expansion nozzle on a Raptor?  Was their ~2.4MN thrust limit a deciding factor in sizing the Raptor?
My recollection is that modeling showed that using more smaller engines counterintuitively resulted in a better T/W even including all of the plumbing.
Space is not Highlander.  There can, and will, be more than one.

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