totm nov 2023 SpaceX Discussion Thread

[magnemoe]

51 minutes ago, Wjolcz said:

Wouldn't surprise me if they skipped one or two of them and built the booster from their parts instead.

If the two currents are MK 1 and 2, next generation is 3 and 4. Assuming they will be build with the larger full diameter plate rings we seen in Florida. 
This sounds a bit weird to me, the first flight tests is to 20 km attitude. They can launch with 33-40% of fuel load, should not have much problem reaching space falcon 9 first stage style. 
It will give useful data for handling in space and reentry.
This should be doable without an heat shield I think since its can handle more heat than falcon 9 first stage and you can also adjust how high you go. 

If we assume 3 and 4 get heat shield, its require an high number of bolts for one so kind of doubt they do it on 1 and 2 I don't see why they should not test orbital runs on them. 
Kind of pointless to make more starship versions than tests. 

[Xd the great]

Can someone teach me about air augmented nozzle? I see this has popped up a lot in this thread.

[ThatGuyWithALongUsername]

2 minutes ago, magnemoe said:

Kind of pointless to make more starship versions than tests. 

Until one of them inevitably blows up and they can turn around and modify a starship they've already built and continue testing instead of having to wait a few extra months to build another one.

[sevenperforce]

11 minutes ago, magnemoe said:

If the two currents are MK 1 and 2, next generation is 3 and 4. Assuming they will be build with the larger full diameter plate rings we seen in Florida. 
This sounds a bit weird to me, the first flight tests is to 20 km attitude. They can launch with 33-40% of fuel load, should not have much problem reaching space falcon 9 first stage style. 
It will give useful data for handling in space and reentry.
This should be doable without an heat shield I think since its can handle more heat than falcon 9 first stage and you can also adjust how high you go. 

Yeah, less heating than a Falcon 9 re-entry, actually.

11 minutes ago, magnemoe said:

If we assume 3 and 4 get heat shield, its require an high number of bolts for one so kind of doubt they do it on 1 and 2 I don't see why they should not test orbital runs on them. 
Kind of pointless to make more starship versions than tests. 

They are building two for the 20 km test in case they lose one, but ferocitering on with Mk3 and Mk4 because they want to be ready for the orbital attempt once they are confident about skydive and turn-burn.

11 minutes ago, Xd the great said:

Can someone teach me about air augmented nozzle? I see this has popped up a lot in this thread.

Air-augmented rocket engines are the lazy big brother of air-breathing rocket engines, also known as "Rocket Combined Cycle" engines (RCC). An RCC engine takes in air and burns it with fuel for at least the first part of the burn, reducing the amount of oxidizer (usually LOX) the vehicle must carry. Examples of this include SABRE and LACE, and a turbo/ramjet (the P&W J58 on the SR-71) or scramjet (X43A, X51) is the airbreathing-without-pure-rocket-mode version. It's much more propellant-efficient than a pure rocket, because you take your oxidizer from the air, but you run into problems as you accelerate faster and faster because you have less air and it is more difficult to slow it down, cool it, combust it, and get useable thrust out of it.

Even hydrogen-fueled airbreathing engines cannot operate in airbreathing mode much beyond Mach 10 or 11, even theoretically, because the amount of air you need and its inlet speed gets too high to generate positive thrust. SABRE, with its novel dump-cycle-hydrogen precooler, shuts off the inlet just past Mach 5 and goes to pure-rocket mode because the thrust drops too low.

An air-augmented rocket, on the other hand, recognizes that trying to burn air is a losing battle and so it doesn't even try. Instead, it does the same thing that a turbofan engine does: pull in and mix a bunch of inert air with the hot exhaust. Because kinetic energy is proportional to the square of exhaust velocity while momentum is proportional to exhaust velocity, "spreading out" the kinetic energy with more reaction mass (e.g., not just the exhaust, but the captured ambient air) produces greater thrust for the exact same amount of propellant use. 

If a duct is placed around the exhaust nozzle of a rocket engine, with an inlet at the front, air flowing into the inlet will mix with the supersonic exhaust and "push" against the walls of the duct, producing greater thrust:

The only disadvantage is the weight of the duct. You get significantly more thrust with no added propellant consumption.

[Xd the great]

8 minutes ago, sevenperforce said:

An air-augmented rocket, on the other hand, recognizes that trying to burn air is a losing battle and so it doesn't even try. Instead, it does the same thing that a turbofan engine does: pull in and mix a bunch of inert air with the hot exhaust. Because kinetic energy is proportional to the square of exhaust velocity while momentum is proportional to exhaust velocity, "spreading out" the kinetic energy with more reaction mass (e.g., not just the exhaust, but the captured ambient air) produces greater thrust for the exact same amount of propellant use. 

If a duct is placed around the exhaust nozzle of a rocket engine, with an inlet at the front, air flowing into the inlet will mix with the supersonic exhaust and "push" against the walls of the duct, producing greater thrust:

The only disadvantage is the weight of the duct. You get significantly more thrust with no added propellant consumption.

Thanks for the explanation! *Like

[tater]

 

[magnemoe]

1 hour ago, ThatGuyWithALongUsername said:

Until one of them inevitably blows up and they can turn around and modify a starship they've already built and continue testing instead of having to wait a few extra months to build another one.

I agree he is also playing Texas and Florida against each other. Still waiting until 5 to go orbital imply he assumes he will burn trough 4 ships before he goes orbital. This might be true with an intensive test program. 
On the other hand we hear 20 km then orbit, something who require superheavy and lots of engines. Now making 5 and 6 cargo versions even with reduced capacity because of still beta makes more sense.  
You can still use them for testing and you can use them to launch starlink then done. 
 

[tater]

https://www.nasa.gov/johnson/HWHAP/the-spacex-dragon

Direct link to listen (also on podcast players, obviously):

https://www.nasa.gov/sites/default/files/atoms/audio/ep111_spacex_crew_dragon.mp3

 

[Jacke]

5 hours ago, Wjolcz said:

Wouldn't surprise me if they skipped one or two of them and built the booster from their parts instead.

Considering it's going to have multi-engine plumbing much more complex than the Saturn I S-I stage and the Saturn IB S-IB stage, about as complex as the Russian N1, Super-Heavy is a tad more complex to get right.  If they get it wrong, well, N1 had four launches all fail, with that plumbing thought to contribute to the failures.

[Geonovast]

Just now, Jacke said:

Considering it's going to have multi-engine plumbing much more complex than the Saturn I S-I stage and the Saturn IB S-IB stage, about as complex as the Russian N1, Super-Heavy is a tad more complex to get right.  If they get it wrong, well, N1 had four launches all fail, with that plumbing thought to contribute to the failures.

If I'm not mistaken, at least one of the failures was due to the computer shutting down the wrong companion engine after a failure.  Also, didn't they only test something like 1 out of every 6 of those engines before sticking them on the rocket?

[KSK]

14 minutes ago, Jacke said:

Considering it's going to have multi-engine plumbing much more complex than the Saturn I S-I stage and the Saturn IB S-IB stage, about as complex as the Russian N1, Super-Heavy is a tad more complex to get right.  If they get it wrong, well, N1 had four launches all fail, with that plumbing thought to contribute to the failures.

I think we've been through most of these comparisons before Falcon Heavy flew.

[tater]

 

[tater]

Next launch I think is a Starlink in a week or two.

I'm wanting some cool rocket landings... hopefully Mk1 does the 20km test this year, that'd be cool. BTW, in February 2018 (presser from after the first FH launch), Musk said “If we get lucky, we’ll be able to do short hopper flights with the spaceship part of BFR maybe next year.”

He says "it's conceivable we do our first test flight in 3-4 years." He's referring to the BFR stack, so in current lingo, SS/SH. That's 3-4 years from February 2018, so 2021-2022. If they can get skydiver to work in 4 tries (since they are building 4 of them for testing right now), Mk5 is absolutely on track for next year, the only question would be SH available for an orbital test. Elon time seems to not really be a thing, actually, if anything they will beat his aspirational goals.

[RCgothic]

I feel sorry for the pad used for a full duration static fire of superheavy!

[tater]

 

[insert_name]

SpaceX has been contracted to launch a commercial lunar lander. Interesting that they will be supplying metholox to the lander until shortly before launch

https://spaceflightnow.com/2019/10/02/intuitive-machines-selects-spacex-to-launch-commercial-lunar-lander/

Edited October 4, 2019 by insert_name

[mikegarrison]

7 hours ago, sevenperforce said:

Instead, it does the same thing that a turbofan engine does: pull in and mix a bunch of inert air with the hot exhaust. Because kinetic energy is proportional to the square of exhaust velocity while momentum is proportional to exhaust velocity, "spreading out" the kinetic energy with more reaction mass (e.g., not just the exhaust, but the captured ambient air) produces greater thrust for the exact same amount of propellant use. 

If a duct is placed around the exhaust nozzle of a rocket engine, with an inlet at the front, air flowing into the inlet will mix with the supersonic exhaust and "push" against the walls of the duct, producing greater thrust:

Kind of. Turbofan get efficiency in two ways. 1) They move more air, but slower. This increases propulsive efficiency. 2) The turbine makes use of heat energy that would otherwise be wasted. This increases thermodynamic efficiency.

This is actually an "eductor". It does try to improve the propulsive efficiency by using the same "move more air but slower" trick. However, it doesn't capture the lost heat energy.

[tater]

SS/Sh simulation with 150t cargo using numbers recently given about stack mass, etc.

https://www2.flightclub.io/result/2d?code=STAR

[Nothalogh]

3 hours ago, mikegarrison said:

However, it doesn't capture the lost heat energy.

Sure it does, it heats the air in the duct.

Same way a thermal ramjet does.

[mikegarrison]

21 minutes ago, Nothalogh said:

Sure it does, it heats the air in the duct.

Same way a thermal ramjet does.

Yes, this happens somewhat, and does get turned into thrust by the nozzle. But not terribly efficiently.

The point is that any heat coming out the back end of the nozzle is wasted energy. Ideally you want all the energy to be mass flow, not heat. With a turbofan, the turbine extracts heat from the core flow and converts it to energy to drive the fan, which then creates mass flow (and some heat due to inefficiency). This is a much more effective way to turn what would be wasted heat energy into mass flow. This is why afterburners/augmentors are so fuel-inefficient.

But it does come with a weight and complexity penalty.

Edited October 5, 2019 by mikegarrison

[Nothalogh]

6 minutes ago, mikegarrison said:

Yes, this happens somewhat, and does get turned into thrust by the nozzle. But not terribly efficiently.

The point is that any heat coming out the back end of the nozzle is wasted energy. Ideally you want all the energy to be mass flow, not heat. With a turbofan, the turbine extracts heat from the core flow and converts it to energy to drive the fan, which then creates mass flow (and some heat due to inefficiency). This is a much more effective way to turn what would be wasted heat energy into mass flow. This is why afterburners/augmentors are so fuel-inefficient.

But it does come with a weight and complexity penalty.

Also, you are defining a turbofan solely by the design scenario of a high bypass turbofan, and that is not the reality of the design at all

[mikegarrison]

37 minutes ago, Nothalogh said:

Also, you are defining a turbofan solely by the design scenario of a high bypass turbofan, and that is not the reality of the design at all

High or low bypass, turbofans have the same thermodynamic cycle. The idea remains the same.

The propulsion tradeoffs get a little different, that's all. Low bypass turbofans work better at higher airplane speeds and take less frontal area, getting better thrust/weight and lower drag, but worse fuel efficiency.

Anyway, I'm sorry. We're moving pretty far from air-augmented rockets.

Edited October 5, 2019 by mikegarrison

[IncongruousGoat]

8 hours ago, Geonovast said:

If I'm not mistaken, at least one of the failures was due to the computer shutting down the wrong companion engine after a failure.

Surprisingly, no. Only the first failure was due to the flight computer (even then, only partly; the first stage was also on fire), and the failure mode in that case was a lot more complicated than the computer shutting down the wrong engine (which didn't happen). Basically, the electrical engineering was really shoddy and caused the computer to believe a whole bunch of things that weren't true, and also the booster was on fire.

The second failure was caused by Engine #8 exploding (this is the one that fell back onto the pad), the third was an uncontrolled roll due to funky aerodynamics at the base of the rocket that led to gimbal lock, and the fourth was caused by a fire that started after several fuel lines ruptured from a hydraulic shockwave after the 6 center engines were shut down to reduce Max-Q. And also an engine exploded.

[AVaughan]

On 10/1/2019 at 4:28 AM, tater said:

A 100t (wet) lander with a single Vac Raptor could do a round trip from LLO with 37t of cargo (I'm calling the lander 9t dry). You can drop the cargo mass slightly and take the lander all the way back to Gateway (if anyone cares to do that).

Can a single Vac Raptor throttle low enough for that landing?  (I'm too short on time atm to do the math.  I'm only have enough time to skim through a weeks worth of posts in this thread).  They could do a hoverslam, (zero all velocity 0.5 m above the surface, cut the engine and just drop), but a controlled hover and landing is probably preferable.  They might also be able to build a smaller Raptor, but that would take up valuable design and testing time.  Alternatively would a cluster of hot gas (methane/oxygen) rcs engines have enough thrust for the actual touch down?

[Xd the great]

54 minutes ago, AVaughan said:

Can a single Vac Raptor throttle low enough for that landing?  (I'm too short on time atm to do the math.  I'm only have enough time to skim through a weeks worth of posts in this thread).  They could do a hoverslam, (zero all velocity 0.5 m above the surface, cut the engine and just drop), but a controlled hover and landing is probably preferable.  They might also be able to build a smaller Raptor, but that would take up valuable design and testing time.  Alternatively would a cluster of hot gas (methane/oxygen) rcs engines have enough thrust for the actual touch down?

No. 1 raptor has a thrust of 2000kN.

1 starship mass is 110 tonnes.

Moon gravity is 1/6th of that of earth.

Weight of empty starship is about 180kN.

Raptor min throttle is about 50%. Or 1000kN. (Might be lower, I forgot).

Edited October 5, 2019 by Xd the great