Developing the BFS - Phase 1 - StarHopper - Discussion - THREAD 3

[Chris Bergin]

Thread 3 for the discussion of Starship Hopper. Keeping BFH just for housekeeping and some familiarity. Starting it now as Thread 2 is huge and could use a new thread and there's going to be some major milestones coming in the life of this Thread 3!

Resources:

Discussion Thread 1:
https://forum.nasaspaceflight.com/index.php?topic=47022.0

Discussion Thread 2:
https://forum.nasaspaceflight.com/index.php?topic=47113.0

UPDATES ONLY Thread:
https://forum.nasaspaceflight.com/index.php?topic=47120.0

L2 SpaceX Boca Chica Photos/Videos Update Thread (now a new standalone thread out of L2 SpaceX Pads and Facilities due to the surge in content with different views of the ongoing work):
https://forum.nasaspaceflight.com/index.php?topic=47107.0

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Remember the rules. Civil at all time. Make sure you post is useful. Want to crack a joke about shiny things, use the party thread. Be on topic. Start a new thread if you want to discuss splinter topics. Now, I'll let you get on with your business

[guckyfan]

https://forum.nasaspaceflight.com/index.php?topic=47113.msg1905773#msg1905773

@Norm38

Just getting caught up. The tank section with the dome top suddenly looks flight worthy for short hops. Just like the old Grasshopper.
Without the windstorm I would have flown it combined. But why wait?
I’d do every sub 100ft hop as is.

Elon gave a repair time of ~2 weeks, probably shorter than the time to build the pad and finish the hopper. They may change their plans and abandon the fairing, however.

[JonathanD]

More importantly, they don't have the engines yet.

[meekGee]

https://forum.nasaspaceflight.com/index.php?topic=47113.msg1905773#msg1905773

@Norm38

Just getting caught up. The tank section with the dome top suddenly looks flight worthy for short hops. Just like the old Grasshopper.
Without the windstorm I would have flown it combined. But why wait?
I’d do every sub 100ft hop as is.

Elon gave a repair time of ~2 weeks, probably shorter than the time to build the pad and finish the hopper. They may change their plans and abandon the fairing, however.

I don't think he said they'll repair the fairing, but rather the hopper as a while.  Given how fast it was to build it, I'd expect a new fairing to be built...

But as people are pointing out, there's no rush.  They can even do it on the pad and assemble it there.

[OneSpeed]

Upper manhole center is about 1.2m from the top edge, if this hole is indeed at the mid point of the LOX tank that gives LOX tank height at 2.4m, dome height is ~2.6m, dome volume is about 80m^3, total LOX tank volume is 311m^3, which is 355t of LOX.

Mixture ratio is 3.6, so methane mass would be ~99t, which gives methane tank height ~3.7m, total hopper height is 12m, so distance between lowest point of the methane tank to lower edge of the hopper is 12 - 2.4 - 3.7 - 2.6 = 3.3m

Total propellant load is 454t, still seems high, since first prod Raptor may not reach 200t thrust. Maybe they'll just let it thrust for a while on the pad until T/W is high enough for liftoff, I think Soyuz uses this method.

Perhaps we should also subtract the volume of the triangular support structure inside the LOX tank?

I measure them as 1mØ tubes, giving a volume of about cos(30°) * 8.875 * 3 * Π * 0.5^2 = 18m^3 for a total of 311 - 18 = 293m^3. As well, LOX ullage is typically about 6%, so the actual volume of LOX might only be 293 * 0.94 = 275m^3. I'm not sure how cryogenic the propellant will be for the StarHopper, but assuming a density of 1,141 kg/m^3, that would be 275 * 1.141 = 314t of LOX. For a LOX:CH4 mass ratio of 3.6, that would be 314 / 3.6 = 87t of CH4, for a total of 314 + 87 = 401t of propellant. Even if the StarHopper is on the heavy side, say 100t dry, 3 Raptors at 200t thrust would give an initial T/W of 600/501 = 1.2.

I'm not sure of the likely ullage requirement for liquid methane, but guessing 5%, and density of 424kg/m^3, the volume would be 87 * 1.05 / 0.424 = 215.5 m^3, which would correspond to an additional 3.5m for the methane tank. In cross section it might look something like this:

[Zephyrox]

Upper manhole center is about 1.2m from the top edge, if this hole is indeed at the mid point of the LOX tank that gives LOX tank height at 2.4m, dome height is ~2.6m, dome volume is about 80m^3, total LOX tank volume is 311m^3, which is 355t of LOX.

Mixture ratio is 3.6, so methane mass would be ~99t, which gives methane tank height ~3.7m, total hopper height is 12m, so distance between lowest point of the methane tank to lower edge of the hopper is 12 - 2.4 - 3.7 - 2.6 = 3.3m

Total propellant load is 454t, still seems high, since first prod Raptor may not reach 200t thrust. Maybe they'll just let it thrust for a while on the pad until T/W is high enough for liftoff, I think Soyuz uses this method.

Perhaps we should also subtract the volume of the triangular support structure inside the LOX tank?

I measure them as 1mØ tubes, giving a volume of about cos(30°) * 8.875 * 3 * Π * 0.5^2 = 18m^3 for a total of 311 - 18 = 293m^3. As well, LOX ullage is typically about 6%, so the actual volume of LOX might only be 293 * 0.94 = 275m^3. I'm not sure how cryogenic the propellant will be for the StarHopper, but assuming a density of 1,141 kg/m^3, that would be 275 * 1.141 = 314t of LOX. For a LOX:CH4 mass ratio of 3.6, that would be 314 / 3.6 = 87t of CH4, for a total of 314 + 87 = 401t of propellant. Even if the StarHopper is on the heavy side, say 100t dry, 3 Raptors at 200t thrust would give an initial T/W of 600/501 = 1.2.

I'm not sure of the likely ullage requirement for liquid methane, but guessing 5%, and density of 424kg/m^3, the volume would be 87 * 1.05 / 0.424 = 215.5 m^3, which would correspond to an additional 3.5m for the methane tank. In cross section it might look something like this:

Can someone please explain to a frenetic kerballer how the Center of mass on that thing isn't going to make it do a u turn once in the air?

[Crispy]

Can someone please explain to a frenetic kerballer how the Center of mass on that thing isn't going to make it do a u turn once in the air?

It'll be dynamically unstable, just like any VTVL rocket, but the engine control is good enough to keep it balanced (unlike the Auto mode in Kerbal!)

[Semmel]

Can someone please explain to a frenetic kerballer how the Center of mass on that thing isn't going to make it do a u turn once in the air?

Many people here guess that the tinfoil hat is purely cosmetic. I challenge them for the exact reason you give. I think (speculation!) the tinfoil hat is as large as it is to make the hopper aerodynamically stable on the way down. The current design would have a strong tendency to head dive into the ground, active control or not. With the large hat though, the aero forces should right it up, o at least make the margin for errors much larger. I have no way o proving that though.

[magnemoe]

Can someone please explain to a frenetic kerballer how the Center of mass on that thing isn't going to make it do a u turn once in the air?

Many people here guess that the tinfoil hat is purely cosmetic. I challenge them for the exact reason you give. I think (speculation!) the tinfoil hat is as large as it is to make the hopper aerodynamically stable on the way down. The current design would have a strong tendency to head dive into the ground, active control or not. With the large hat though, the aero forces should right it up, o at least make the margin for errors much larger. I have no way o proving that though.

Yes, its affect aerodynamic on the way up and down, good point in that it will increase stability by moving center of drag up. it also make the hopper more like the final version aerodynamically giving better test data.

[ZChris13]

RE: the cylinders at the base of the hopper
there's no real way to tell what's in them, but the labels on them are green which I believe indicates inert gasses. Since they're all clustered together they're probably all homogeneous. Depending on the process they're using, the cylinders could be full of Argon, an Argon/CO2 mix, or maybe even some helium, although I doubt that.

[SpaceWoof]

The brown cylinders are Argon, the bluish green cylinders are oxygen. The cylinder cap doesn't always indicate anything but in this case do appear to be color matched to the cylinders. It also appears that there is one yellow or dirty yellow bottle there and that is normally breathable air. That is about all I can make out.

Thanks for the great site! This is my first post, but I have been following it closely from the beginning of the hopper construction. Nice to "meet" you all!

[georgegassaway]

Regarding BocaChicaGal's recent images of scaffolding going up around BFH:
https://forum.nasaspaceflight.com/index.php?topic=47120.msg1905755#msg1905755

Reminded me of Little Joe-I:

[Rei]

Very reminiscent.  I expect to soon start seeing lots of pictures of welders out there on the scaffolding turning those tacks into proper welds. 

You know, despite the wind disaster, I have a strong suspicion that something like this ("shipyard"-style construction) is going to end up how the final Super Heavy and Starship are built, rather than in pristine factory conditions.

Musk has a habit of doing things like this: trying some cheap, improvised approach for testing reasons or as a temporary cost savings measure, and then deciding that he likes it so much that it becomes the way forward from there on. For example, at Tesla they built GA4 (General Assembly 4) in a tent in order to get their production rates up on a very limited budget and tight schedule. Much of the line was built out of scrap they had lying around - for example, the conveyor belt that moves the cars was actually a scrapped parts conveyor (since the motor wasn't powerful enough to move whole cars, they simply jacked it up on one end so that gravity assisted it). It turned out that GA4 outperformed their fancy automated GA3 line on both labour cost and QA testing metrics.  Because it was a long tent, trucks just pulled up beside each workstation on the outside of the tent and unloaded the parts straight to the workstation, rather than into a central depot from which they had to to transport parts. Tesla now plans to make future GA lines follow this principle.

If Musk likes how quickly they can put together the hopper like this, and it manages to perform, I fully expect this sort of "shipyard assembly" to be the way Starship and Super Heavy get built as well.  Sure, it can complicate some things (LOX for example doesn't play nice with organic contaminants, you have potential corrosion problems, etc). But if they design for dealing with this... and it's a cheap, fast way to build...

[rcoppola]

Hopper is a test-bed anomaly hack. Not some new way forward for building the largest, most complex spaceship ever. There is no chance that an SS designed for Crewed Lunar and/or Mars missions will be constructed outside, exposed to the elements for the many months, years it will take to build.

...imo.

[OxCartMark]

Hopper is a test-bed anomaly hack. Not some new way forward for building the largest, most complex spaceship ever. There is no chance that an SS designed for Crewed Lunar and/or Mars missions will be constructed outside, exposed to the elements for the many months, years it will take to build.

...imo.

Or maybe not.

...imo

[jpo234]

This may be nothing but it caught my eye this morning. 

LOX pipe??

[Rei]

I really don't think corrosion is going to be an issue. Starship should be able to sit outside for centuries without corrosion.  The only concerns would be any exposed junctions between dissimilar metals.

Alumium is ostensibly also quite inert, but it's really prone to galvanic corrosion. And when in contact with a dissimilar metal, it's almost always the alumium which corrodes, not the other metal. Doesn't like salt, either; it ruins the protective oxide layer.

I really see no issues with the tankage (incl bulkheads) and fairing being built first out in the open - however long it takes - just like a ship. Once it's weathertight, with a closable opening for lowering hardware into the rocket - the rest of the work can be done from the inside or underneath. Again, very similar to building a ship. The only thing I see that requires a particular caution (apart from *cough* proper anchoring) is that they'd need to clean the LOX tank well (methane isn't particularly sensitive to contaminants).

I just don't see SpaceX making a new VAB.  Or engineering it to lay on its side during construction.

[JamesH65]

Hopper is a test-bed anomaly hack. Not some new way forward for building the largest, most complex spaceship ever. There is no chance that an SS designed for Crewed Lunar and/or Mars missions will be constructed outside, exposed to the elements for the many months, years it will take to build.

...imo.

Why? Every house, office block etc was built open to the elements until the roof is put on and they can be pretty complicated. As long as the crafts shell is water proof, the work inside can be as compicated as you want. It's already indoors....

Need the bottom kept dry? Attached a tent around the bottom. You can have covered passageways to small buildings where parts are kept.

I'd make proper one in two parts, just like this. That way you don't need to have lifts up the the top outside the craft.

[b.lorenz]

Hopper is a test-bed anomaly hack. Not some new way forward for building the largest, most complex spaceship ever. There is no chance that an SS designed for Crewed Lunar and/or Mars missions will be constructed outside, exposed to the elements for the many months, years it will take to build.

...imo.

Or maybe not.

...imo

My guess is that the competing needs for fast and cheap construction vs. clean and controlled environment will meet in the middle.
I can imagine that this would be a closed space, but more akin in its atmosphere to a sci-fi shipyard-- with sparks flying and cranes tossing around hull segments-- than the clean room environment present day deep space vehicles are usually assembled. (After all, Starship would be  a deep space vehicle, that is also half a launch vehicle and also a crewed ship)

I can also imagine, that this 'spaceshipyard' could unite the responsibilites of a factory assembling rocket stages (tanks, piping, wiring, mating engines) and those functions of the integration facility that are not meant to be performed on the pad (inspection, SS-SH mating). So they would ingest low-level components (test-fired raptors, electronics boxes, wires, hull panels) and put out a finished spaceship.

[Wargrim]

Perhaps they are going to enclose the sprung structure? Caught this load at the main gate this morning.

I might be wrong, but this looks like 2 rollgates on the truck. If they close up the sprung structure, they would have a wind-protected, debris protected area to do some work in. Unfortunately it would also stop us from looking.