SpaceX (general discussion)

An excellent discussion of Starship & BFR weights and mass fractions.

View: https://www.reddit.com/r/spacex/comments/d9gkuj/starship_mk12_200t_dry_weight_goal_to_reduce_to/


200 metric tons empty / 1400 metric tons full, that's a 0.86 propellant mass fraction.
Lower that to 120 metric tons and the PMF goes to near 0.92.

With methalox at 380 seconds, the second variant is tantalizing close from a SSTO,a 9100 m/s ballpark.
Except this is the VACUUM specific impulse, the ground-level one is 340, 350 best case. And thus, no SSTO - it would need 0.93 or above...

I'm interested by these numbers as realistic ones with present state of the art; for my own pet peeve: suborbital refueling.

In the end, even if it fails going into orbit alone, with such delta-v - 6, 7 or 8 km/s - Starship could make pretty large suborbital hops with a decent payload.
With 6 km/s it is possible to jump over the Atlantic, all 3500 miles / 5800 km of it.
With 8 km/s horizontal distance grows to 10 000 km or more.

Would be enough for a Paris - La Réunion much faster than those goddam Air France 777 taking 12 hours and only by night... in this peculiar case it would really shrinks the world and change people lives. Provided the ticket would be affordable, of course.
 
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The 0.86 mass fraction is probably a function of using stainless steel, and not a particular good one, in a semi monocoque structure. It was why Atlas went for a ballon tank to literally squeeze out every last pound(kilogram) out of the structure. Space X will recover some of the mass when the switch to the stronger stainless allowing the skin to thin down. As to if they can take 80 tons out of 200 remains to be seen, but I would be doubtful. You can get a very rough order of magnitude from just comparing the UTS’s (I’m guessing the grades) which suggests 30-40T is more practical. Anyway it’s a cracking effort nevertheless.

The other thing with these early prototype is there’s no payload? Or do they include ballast?
 
https://twitter.com/x/status/1369379914139451406
View: https://twitter.com/elonmusk/status/1369379914139451406


SN10 engine was low on thrust due (probably) to partial helium ingestion from fuel header tank. Impact of 10m/s crushed legs & part of skirt. Multiple fixes in work for SN11.
Click to expand...

https://twitter.com/x/status/1369380834772475906
View: https://twitter.com/nasaspaceflight/status/1369380834772475906


This is a tricky one given that I believe said helium pressurization was added to the CH4 header tank to mitigate what happened with SN8.

That's why it's a test program, of course.
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https://twitter.com/x/status/1369382210894237705
View: https://twitter.com/elonmusk/status/1369382210894237705


Fair point. If autogenous pressurization had been used, CH4 bubbles would most likely have reverted to liquid.

Helium in header was used to prevent ullage collapse from slosh, which happened in prior flight. My fault for approving. Sounded good at the time.
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https://twitter.com/x/status/1369383194248814607
View: https://twitter.com/erdayastronaut/status/1369383194248814607


Are there baffles in future designs to prevent slosh?
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https://twitter.com/x/status/1369438991943151620
View: https://twitter.com/elonmusk/status/1369438991943151620


There were baffles, but one may have acted like a straw to suck bubbles in from above liquid/gas level.

Something similar happened on an early Falcon 1 flight, resulting in unexpectedly high liquid oxygen residuals at main engine cutoff.
Click to expand...
 
https://twitter.com/x/status/1370222228701392896
View: https://twitter.com/thejackbeyer/status/1370222228701392896


I'm curious what this green flash is, if it were Falcon 9 the no brainer answer would be TEA-TEB - but Raptor just uses spark ignitors. It was visible during engine ignition for SN10's flip maneuver, specifically when the third and final engine lit. @elonmusk @NASASpaceflight
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https://twitter.com/x/status/1370224669261971456
View: https://twitter.com/elonmusk/status/1370224669261971456


Green flame in this context means engine is burning internal components made of copper. This is usually followed by a RUD (Rapid Unscheduled Disassembly).
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The big re-usage commercial saving kicks in at flight ten and beyond. With Space Shuttle the man rating aspect dictated a very deep level of overhaul between flights which made it hopelessly uneconomic. I think SpaceX is going for minimum maintenance intervention in between flights and that’s the answer to the “So what question”.

As for a true commercial operation they’re still screwed by chucking away the second stage, but that’s where Star Ship comes in.
 
Zoo Tycoon said:
The big re-usage commercial saving kicks in at flight ten and beyond. With Space Shuttle the man rating aspect dictated a very deep level of overhaul between flights which made it hopelessly uneconomic. I think SpaceX is going for minimum maintenance intervention in between flights and that’s the answer to the “So what question”.

As for a true commercial operation they’re still screwed by chucking away the second stage, but that’s where Star Ship comes in.
Click to expand...

Pretty sure the "commercial saving" kicks in a flight two. Because, you know, you don't have to build another first stage.
 
sferrin said:
Zoo Tycoon said:
The big re-usage commercial saving kicks in at flight ten and beyond. With Space Shuttle the man rating aspect dictated a very deep level of overhaul between flights which made it hopelessly uneconomic. I think SpaceX is going for minimum maintenance intervention in between flights and that’s the answer to the “So what question”.

As for a true commercial operation they’re still screwed by chucking away the second stage, but that’s where Star Ship comes in.
Click to expand...

Pretty sure the "commercial saving" kicks in a flight two. Because, you know, you don't have to build another first stage.
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It’s true that there’s a commercial saving a flight two but the saving just gets better and better with each successive reuse until about flight ten. Then it levels off at a new sustainable baseline. This new baseline is the basis for Elon’s publicly declared future costing.

Ref ICES -2018-81 “The recent large reductions in Space Launch Cost” by H W Jones NASA Ames Research Center.
 
current state at Boca Chica
View: https://www.youtube.com/watch?v=KOiiDOuSXsM


I have theory about SN2, SN7 and SN7.2
SN2 was not scrap but put on concrete ring and used for welding test for Aerodynamic covers of the flaps

SN7 and SN7.2 feature strutting on lower part that other SN not have
could it be that SN7 and 7.2 are more then test tanks for Starship but also for GSE-1 ?
they pour large concrete ring similar to those were SN6 sit on and once for MK1 before both were scrap
and that new installation is label GSE on Plans
 
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Flyaway said:
https://twitter.com/x/status/1370222228701392896
View: https://twitter.com/thejackbeyer/status/1370222228701392896


I'm curious what this green flash is, if it were Falcon 9 the no brainer answer would be TEA-TEB - but Raptor just uses spark ignitors. It was visible during engine ignition for SN10's flip maneuver, specifically when the third and final engine lit. @elonmusk @NASASpaceflight
Click to expand...

https://twitter.com/x/status/1370224669261971456
View: https://twitter.com/elonmusk/status/1370224669261971456


Green flame in this context means engine is burning internal components made of copper. This is usually followed by a RUD (Rapid Unscheduled Disassembly).
Click to expand...
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newinform.com

Опыт российских специалистов позволил повысить КПД ракетного топлива в 5 раз

Результат исследования показал, что медь увеличивает скорость горения топлива на 500%, цинк – на 130%, а бор – на 10%.
newinform.com newinform.com

Researchers have proposed an alternative component composition of solid fuels. As a fuel, experts used aluminum powder, a catalyst - nano- and microadditives of aluminum, boron, zinc, nickel, copper, molybdenum and their oxides. It turned out that the addition of copper nanoparticles to fuel would increase the speed of rockets by a factor of five. The result of the study showed that copper increases the burning rate of fuel by 500%, zinc - by 130%, and boron - by 10% "

Starship is a pretty heavy rocket, so high thrust of using copper is needed to control its landing to reposition itself?
 
Jack Beyer? For a moment I thought it said Jack Bauer, and was looking for the hidden nuclear warhead or other deadly McGuffin of the day. ;)
 
tequilashooter said:
newinform.com

Опыт российских специалистов позволил повысить КПД ракетного топлива в 5 раз

Результат исследования показал, что медь увеличивает скорость горения топлива на 500%, цинк – на 130%, а бор – на 10%.
newinform.com newinform.com

Researchers have proposed an alternative component composition of solid fuels. As a fuel, experts used aluminum powder, a catalyst - nano- and microadditives of aluminum, boron, zinc, nickel, copper, molybdenum and their oxides. It turned out that the addition of copper nanoparticles to fuel would increase the speed of rockets by a factor of five. The result of the study showed that copper increases the burning rate of fuel by 500%, zinc - by 130%, and boron - by 10% "

Starship is a pretty heavy rocket, so high thrust of using copper is needed to control its landing to reposition itself?
Click to expand...
The burning of copper is not intentional (the engine is conceptually aimed to be capable of being reflown 100 times); parts of the engine are made of copper, and that copper is being oxidised when too much LOX is being fed to the preburners and/or main chamber.

The Raptor engine used on Starship is a full-flow staged combustion engine, which means that you basically have two gas generators / preburners (practically rockets of their own), with one burning CH4-rich and the other burning O2-rich, and combining their exhausts into a central combustion chamber for burning the rest of the propellant. Each of the two preburners is responsible for capturing some thrust via a turbine to drive a turbopump, which is what keeps fuel flowing at an extreme flow rate and pressure (the turbopump outlet pressure has to be higher than every other part in the engine to prevent flow reversal).

This type of rocket engine has the advantage of turning 100% of the propellant it burns into thrust (others have gas generators that dump their exhaust overboard with minimal thrust gained out of it), but having to run one of the gas generators / preburners LOX-rich is difficult, and because one preburner spins a LOX turbopump, and another preburner spins a CH4 turbopump, with each individual turbopump feeding both preburners, if there's any issue with a preburner that affects a single turbopump's RPM, it affects the propellant ratio in both preburners and the main combustion chamber.

It's a complicated and somewhat fragile engine design, but SpaceX have done well with Raptor; they're trying to make it more reliable, but they're also still in the midst of trying to squeeze extra performance out of the engine, both in increased thrust, and in being able to throttle more deeply. When they're finally happy with its performance they can really try to nail down reliability, but in the meantime they can also attack the problem from the side of making Starship's propellant flow cleaner and more stable during the flip maneuver prior to landing.
 
Dragon029 said:
tequilashooter said:
newinform.com

Опыт российских специалистов позволил повысить КПД ракетного топлива в 5 раз

Результат исследования показал, что медь увеличивает скорость горения топлива на 500%, цинк – на 130%, а бор – на 10%.
newinform.com newinform.com

Researchers have proposed an alternative component composition of solid fuels. As a fuel, experts used aluminum powder, a catalyst - nano- and microadditives of aluminum, boron, zinc, nickel, copper, molybdenum and their oxides. It turned out that the addition of copper nanoparticles to fuel would increase the speed of rockets by a factor of five. The result of the study showed that copper increases the burning rate of fuel by 500%, zinc - by 130%, and boron - by 10% "

Starship is a pretty heavy rocket, so high thrust of using copper is needed to control its landing to reposition itself?
Click to expand...
The burning of copper is not intentional (the engine is conceptually aimed to be capable of being reflown 100 times); parts of the engine are made of copper, and that copper is being oxidised when too much LOX is being fed to the preburners and/or main chamber.

The Raptor engine used on Starship is a full-flow staged combustion engine, which means that you basically have two gas generators / preburners (practically rockets of their own), with one burning CH4-rich and the other burning O2-rich, and combining their exhausts into a central combustion chamber for burning the rest of the propellant. Each of the two preburners is responsible for capturing some thrust via a turbine to drive a turbopump, which is what keeps fuel flowing at an extreme flow rate and pressure (the turbopump outlet pressure has to be higher than every other part in the engine to prevent flow reversal).

This type of rocket engine has the advantage of turning 100% of the propellant it burns into thrust (others have gas generators that dump their exhaust overboard with minimal thrust gained out of it), but having to run one of the gas generators / preburners LOX-rich is difficult, and because one preburner spins a LOX turbopump, and another preburner spins a CH4 turbopump, with each individual turbopump feeding both preburners, if there's any issue with a preburner that affects a single turbopump's RPM, it affects the propellant ratio in both preburners and the main combustion chamber.

It's a complicated and somewhat fragile engine design, but SpaceX have done well with Raptor; they're trying to make it more reliable, but they're also still in the midst of trying to squeeze extra performance out of the engine, both in increased thrust, and in being able to throttle more deeply. When they're finally happy with its performance they can really try to nail down reliability, but in the meantime they can also attack the problem from the side of making Starship's propellant flow cleaner and more stable during the flip maneuver prior to landing.
Click to expand...
Interesting. Shouldn't they bypass the pre-burner stage during the landing burn? They have 3 engines and something much lighter weight: efficiency margin is irrelevant.
 
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tequilashooter said:
Starship is a pretty heavy rocket, so high thrust of using copper is needed to control its landing to reposition itself?
Click to expand...

The article you posted was about copper in solid rockets. Starship is all liquid fuels so no, it is not intentionally burning copper. As Musk tweeted, if you see burning copper in Starship, that's the engine failing and usually about to blow up.
 
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TomcatViP said:
Interesting. Shouldn't they bypass the pre-burner stage during the landing burn? They have 3 engines and something much lighter weight: efficiency margin is irrelevant.
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And pump fuel with what, exactly? The only way to do that is with the pumps that are turned by the turbines that are powered by the preburners.
 
TomcatViP said:
Interesting. Shouldn't they bypass the pre-burner stage during the landing burn? They have 3 engines and something much lighter weight: efficiency margin is irrelevant.
Click to expand...
That's not possible; the preburners (which are basically combustion chambers with turbines in the exhaust) exist to provide the energy required to spin the turbopumps. A Raptor engine burns >600kg/s of propellant at full throttle, which means many megawatts of shaft power is required.

During start-up, a gas pressurised to some very high pressure is used to spin up the turbopump (I assume the gas is blown over the preburner turbine), but to operate the engine at its full throttle, you need the power of a rocket's exhaust being (partially) captured by a turbine to keep the turbopump running at the required RPM.

To use an analogy, Raptor is like a pair of turbojet engines where the turbopump is the fan / compressor stages (one turbojet breathes in oxygen, the other breathes in methane, and then bleed valves allow the engines to share their fluid with the other engine), the preburner is the combustion chamber / turbine, and the main combustion chamber is a reheater / afterburner section of tailpipe that's shared by both turbojet engines.

Most other rocket engines have the turbopumps powered by a single preburner (known as a gas generator in this case) which has less propellant flow through it and captures more energy with its turbine, but doesn't produce any meaningful thrust with its exhaust, wasting propellant.

To use the turbojet analogy again, this is like having a jet engine with a fan / compressor that's driven by an APU, and with the compressors feeding right into the afterburner.
 
Yes I know about turbines in rocket engine, obviously. Thank you. But a monoturbine H-1 type of geometry would alleviate metering disparity issues.
So bypassing the pre-burner stage would results in using one of the turbine only with a slight losses in output. But that won't really matters in that situation where you have an excess of engine and burn time is low.
 
[Deleted an earlier reply because I realised I had a false assumption in it and didn't have time to edit it properly]

Such a system would probably be feasible, but it would introduce additional mechanical complexity due to needing something akin to a transfer case to have the LOX and CH4 preburners / turbopumps all connected (the CH4 preburner / turbopump is situated off the side off the power head while the LOX preburner / turbopump is along the centreline, between the main combustion chamber and gimbal mount). Lightweight, megawatt-class gear systems aren't unprecedented (the F-35B's lift fan drivetrain is an example of one), but for a system that needs to be able to perform burns, then coast through space for several months, then perform a flawless landing burn without any inspections or maintenance, you want as few moving parts as possible - "the best part is no part" as per Musk's personal belief.

Halving the power delivered to the turbopumps will also require more engines to be lit during all types of landing (whether it be a Starship landing with no return payload, or one landing with a full 100 tonne payload), so that'd in-turn reduce the engine-out capability.

Ultimately though I don't think such a design change is necessitated at this point; other issues like gas pressurant reaching the engines appears to be more critical and is something that needs to be solved regardless. With proper baffles, valve control systems, etc managing propellant ratios seems plausible without adding more moving parts.
 
Raptor engine schem (wiki) :
1616435887380.png

@Dragon029 : great argumentation. My main point is that turbopumps and electrovanes are not that much heavy. That would have to be balanced against a bunch of full size baffles obviously...
 

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