totm nov 2023 SpaceX Discussion Thread

[tater]

I should add that this is just a hopper. It's not a real spacecraft, but it's cool to see it moving forward.

[CatastrophicFailure]

40 minutes ago, StrandedonEarth said:

They seem to be treating it like a seaship instead of a spaceship

Starship. 

[Spaceception]

43 minutes ago, StrandedonEarth said:

Yeah, like, even kerbals build their rockets indoors. 

They seem to be treating it like a seaship instead of a spaceship

At least they can know it's rugged.

[cubinator]

1 hour ago, tater said:

 

*click*

[sevenperforce]

49 minutes ago, cubinator said:

*click*

Elon got his subassembly right and the attachment node connected!

1 hour ago, tater said:

I should add that this is just a hopper. It's not a real spacecraft, but it's cool to see it moving forward.

I would disagree, since Elon has talked about suborbital hops in 2019 (though, again, Elon Time)...but without articulation on the finlegs, I don't see how this does anything other than lawn-dart on re-entry.

Then again, Elon has hinted that there are radical changes for the stainless steel StarShip. Who knows -- maybe articulating finlegs is a bridge too far and the SpaceX aerophysics team has come up with a way to effect multiplanetary hypersonic lifting-body reusable re-entry sans moving parts. 

[Mad Rocket Scientist]

I wonder how much this is costing to build. If the raptors are real, that's probably more than 50% of the build cost.

[sevenperforce]

6 minutes ago, Mad Rocket Scientist said:

I wonder how much this is costing to build. If the raptors are real, that's probably more than 50% of the build cost.

I will bet hard money that the raptors are 100% real.

But yeah, this is ridiculously cheap construction.

I am thinking that some intern at SpaceX was like "Hey, look -- if we build this out of sheet metal then it will do the same job and be 10% the cost" and Elon was like "OKAY EVERYBODY LISTEN UP"

14 minutes ago, sevenperforce said:

Then again, Elon has hinted that there are radical changes for the stainless steel StarShip. Who knows -- maybe articulating finlegs is a bridge too far and the SpaceX aerophysics team has come up with a way to effect multiplanetary hypersonic lifting-body reusable re-entry sans moving parts. 

Someone who has more free time than me should take the quoted thrust of the Raptors, the estimated mass of stainless steel in the visible configuration, and look at what kind of dV the existing hopper can expect to achieve.

[sh1pman]

5 minutes ago, sevenperforce said:

I am thinking that some intern at SpaceX was like "Hey, look -- if we build this out of sheet metal then it will do the same job and be 10% the cost" and Elon was like "OKAY EVERYBODY LISTEN UP"

“This guy! This guy right here is now a Production manager! ”

[Ultimate Steve]

14 minutes ago, sevenperforce said:

22 minutes ago, sevenperforce said:

 

Someone who has more free time than me should take the quoted thrust of the Raptors, the estimated mass of stainless steel in the visible configuration, and look at what kind of dV the existing hopper can expect to achieve.

There's a few problems. We don't know how thick the stainless steel is, how much else is inside the rocket, and how big the fuel tanks will be. I'm pretty sure that the main body is not cryogen-tight and they will only have small tanks inside the hopper for tests, but I'd like to be wrong.

[sevenperforce]

15 hours ago, sh1pman said:

“This guy! This guy right here is now a Production manager! ”

Aaaaaand then everyone around him resents him, sets out to f*** him over, and he ends up quitting in tears after 2 weeks.

14 hours ago, Ultimate Steve said:

There's a few problems. We don't know how thick the stainless steel is, how much else is inside the rocket, and how big the fuel tanks will be. I'm pretty sure that the main body is not cryogen-tight and they will only have small tanks inside the hopper for tests, but I'd like to be wrong.

With only three engines, there is probably a hard limit on liftoff mass (TWR>1) before any structural limitations on the steel superstructure or volumetric limitations on tankage.

By my MSPaint magic, the engine bells are 87:608 pixels (in one image) which comes to 0.1466:1, which comes to 1.32m diameter on these raptors if the body diameter is the expected 9 meters.

These are full-size Raptors.

2 MN each.

6 MN total liftoff thrust.

Maximum takeoff mass 204 tonnes.

Wait, where the heck did I get 204 tonnes? 6 MN / g = 611 tonnes!

Edited January 5, 2019 by sevenperforce

[Ultimate Steve]

Just now, sevenperforce said:

Aaaaaand then everyone around him resents him, sets out to f*** him over, and he ends up quitting in tears after 2 weeks.

With only three engines, there is probably a hard limit on liftoff mass (TWR>1) before any structural limitations on the steel superstructure or volumetric limitations on tankage.

Correct, there are some hard limits we can use to estimate...

Assuming the Raptor is still the 2000kN one quoted on Wikipedia, that means the mass is capped at 600 tons. Not very helpful... But the FCC filing asked for, what, 5 minutes and 5km max? That's 5*60 = 300 seconds at ~10m/s^2, so a maximum 3 kilometers per second of Delta V is required, ish, using 330s for sea level Raptors, which might have changed, which would require the mass to be 40% structure and 60% fuel. However, I doubt that this hopper has that much Delta-V, the header tanks don't need to be that big. I don't think we have up to date dry mass numbers for Starship since the stainless steel update, let alone for the hopper, all we have is an old 85t estimate, and I'll roll with 100t to make the math easy and to account for the idea that they might build the walls thicker because they don't need this to be a high quality vehicle (it might be even higher still!). That means 150t of propellant for a 100 ton vehicle for 3 kilometers per second. The operational BFR is supposed to have around 1100 tons of propellant (last official number, probably pre-stainless), so that's a bit over 15% of the total Starship fuel mass. And the header tanks only need a few hundred meters per second of Delta-V for landing, but...

At least in the 2017 version it looks like the header tanks take up 1/14-ish of the volume. That's ~7% of the fuel, not 14%, meaning probably one of the following:

• Starhopper has full fuel tanks (doubtful given those welds)
• Starhopper has larger than normal header tanks for testing, a custom tank (this involves differing from the production design but it could be likely)
• The overall design has been changed for larger header tanks (doubtful, I don't see a place where you'd ever need 3 kilometers per second of Delta-V sitting around, although with a 150t payload that would only be 2.2km/s. Landing only requires a few hundred meters per second, unless you want to do a pre-entry burn or an entry burn.

Or my favorite and the most probable IMO:

• The application for the flight tests anticipates also hop testing with a production or at least near-production vehicle, the hopper can't go do that much.

 

...And this fits well with the application... I've been using the high altitude numbers this whole time, and the application also specifies parameters for low altitude tests - 500 meters and 100 seconds. 100 seconds at 10m/s^2 means 1km/s of Delta-V. That only requires the vehicle to carry ~40 tons of fuel based on 330s sea level isp and a 100 ton dry mass. 40 tons fits into our 7% number for the header tanks, which is about 77 tons assuming that it's actually 1/14, and looking at the (admittedly old) diagram it looks to be a bit less because of rounded edges.

 

TL;DR: Starhopper has approximately 1 kilometer per second of Delta V, probably a bit more, and probably only has header tanks installed rather than a cryogen-tight skin tank.

 

This also means that the thing only has a takeoff mass of ~140 tons, maybe more, meaning it doesn't need three Raptors. It could get away with one. But who knows, maybe they are testing different landing profiles, need roll control, will add dozens of tons of ballast to the hopper, or maybe all three.

[RedKraken]

wild guess for hopper dry mass :

If they use all 5mm stainless @ 8000kg/m3,

I get minimum 55 tonne for the steelwork we can see.

Body is about 35t, legs 5t, leg fill (fins) maybe another 5t?

Included is 5 tonnes of engines (3t) + plumbing, and 5 tonnes of bolted hexaweb.

[CatastrophicFailure]

It’s official. 

 

[CatastrophicFailure]

Aaaaaand now its early February.  Because politics. 

 

[MaverickSawyer]

8 minutes ago, CatastrophicFailure said:

Aaaaaand now its early February.  Because politics. 

Hey, at least they're being realistic and transparent.

[MinimumSky5]

And at least this isn't Elon time, it's *gets into a needless political rant*. 

But seriously, it makes me sad thinking of all the media outlets screaming that SpaceX has delayed again, when it has absolutely nothing to do with them. 

[KSK]

15 hours ago, tater said:

I can't express how much I love that this is happening.

We go from waiting for tweets, or IAC meetings... to watching crowd-sourced images of it being built in front of our eyes.

Its certainly one way of fielding any questions...

I'll get my coat.

[Green Baron]

At least it is not riveted :-)

Statler, let's go

Edited January 5, 2019 by Green Baron

[sevenperforce]

11 hours ago, RedKraken said:

wild guess for hopper dry mass :

If they use all 5mm stainless @ 8000kg/m3,

I get minimum 55 tonne for the steelwork we can see.

Body is about 35t, legs 5t, leg fill (fins) maybe another 5t?

Included is 5 tonnes of engines (3t) + plumbing, and 5 tonnes of bolted hexaweb.

Per edit above, I have no idea where I got 204 tonnes. Three SL Raptors can lift 611 tonnes. If SpaceX wants a 1.5 TWR on liftoff, then GLOW is 407 tonnes. Your number comes to a dry mass of 110 tonnes, representing 29% mass growth over the composite 2017 IAC version (which was bigger and included a cabin) so that is conservative enough to cover any other issues. This will be mass-limited before it is volume-limited (since tankage volume is not significantly less than the full-size version).

Doing the math, that gives 4.2 km/s of dV. That's twice what you need to do a suborbital hop.

[tater]

https://twitter.com/CowboyDanPaasch/status/1081567268901928961

 

[sevenperforce]

7 minutes ago, tater said:

https://twitter.com/CowboyDanPaasch/status/1081567268901928961

 

It's a friggin' spaceship.

At 4.2 km/s (understand, that's if they top the tanks all the way to GLOW limits, rather than using small internal tanks), this thing can accelerate to over 100 km, then fire its engines all the way back down to a soft landing.

[tater]

 

[magnemoe]

14 hours ago, Ultimate Steve said:

Correct, there are some hard limits we can use to estimate...

Assuming the Raptor is still the 2000kN one quoted on Wikipedia, that means the mass is capped at 600 tons. Not very helpful... But the FCC filing asked for, what, 5 minutes and 5km max? That's 5*60 = 300 seconds at ~10m/s^2, so a maximum 3 kilometers per second of Delta V is required, ish, using 330s for sea level Raptors, which might have changed, which would require the mass to be 40% structure and 60% fuel. However, I doubt that this hopper has that much Delta-V, the header tanks don't need to be that big. I don't think we have up to date dry mass numbers for Starship since the stainless steel update, let alone for the hopper, all we have is an old 85t estimate, and I'll roll with 100t to make the math easy and to account for the idea that they might build the walls thicker because they don't need this to be a high quality vehicle (it might be even higher still!). That means 150t of propellant for a 100 ton vehicle for 3 kilometers per second. The operational BFR is supposed to have around 1100 tons of propellant (last official number, probably pre-stainless), so that's a bit over 15% of the total Starship fuel mass. And the header tanks only need a few hundred meters per second of Delta-V for landing, but...

At least in the 2017 version it looks like the header tanks take up 1/14-ish of the volume. That's ~7% of the fuel, not 14%, meaning probably one of the following:

• Starhopper has full fuel tanks (doubtful given those welds)
• Starhopper has larger than normal header tanks for testing, a custom tank (this involves differing from the production design but it could be likely)
• The overall design has been changed for larger header tanks (doubtful, I don't see a place where you'd ever need 3 kilometers per second of Delta-V sitting around, although with a 150t payload that would only be 2.2km/s. Landing only requires a few hundred meters per second, unless you want to do a pre-entry burn or an entry burn.

Or my favorite and the most probable IMO:

• The application for the flight tests anticipates also hop testing with a production or at least near-production vehicle, the hopper can't go do that much.

 

...And this fits well with the application... I've been using the high altitude numbers this whole time, and the application also specifies parameters for low altitude tests - 500 meters and 100 seconds. 100 seconds at 10m/s^2 means 1km/s of Delta-V. That only requires the vehicle to carry ~40 tons of fuel based on 330s sea level isp and a 100 ton dry mass. 40 tons fits into our 7% number for the header tanks, which is about 77 tons assuming that it's actually 1/14, and looking at the (admittedly old) diagram it looks to be a bit less because of rounded edges.

 

TL;DR: Starhopper has approximately 1 kilometer per second of Delta V, probably a bit more, and probably only has header tanks installed rather than a cryogen-tight skin tank.

 

This also means that the thing only has a takeoff mass of ~140 tons, maybe more, meaning it doesn't need three Raptors. It could get away with one. But who knows, maybe they are testing different landing profiles, need roll control, will add dozens of tons of ballast to the hopper, or maybe all three.

Agree with it probably only having header tanks, yes you could put two very short tanks in the bottom part as in full width header tanks but if you went to that work you could just as well make them full size and add the header tanks for an more realistic test. Its not tanks in the top or center part but might be other stuff. 
No RCS as I can see. 
And yes why three engines? It might be to test multi engine operations perhaps engine out.

Assumes this will be followed up by an full test rocket who can do suborbital jumps for testing everything outside or orbital reentry, but it will test aerodynamic.  the version 1 don't have foldable fins or canards so can not do the switch from aerobrake to vertical landing realistically. Saw an stainless steel starship image from spacex and it looks like same overall design as the dear moon version but shiny. 
Yes the second version could be an flight ready one but doubt it. 

 

[tater]

 

[Elthy]

I would assume they just stick some Falcon9-diameter tanks in the hopper, they allready have the tooling.