Quote from: RDMM2081 on 01/04/2019 04:15 pmHere's a really dumb idea about the portholes: they're literally just temporary access holes poked through the side of this structure because they can.As many have said, this is very clearly NOT the final orbital design, just a test article with crazy margins and design/construction techniques. Maybe they needed some access holes, so they just cut some holes, and intend to "patch them up as good as needed" for the test hops.(I also think they are more probably for RCS (new methalox thrusters, not draco/superdraco) or possible even fin/canard/brakeron/gridfin thing attachment points)I was going to like your post, but I disagree with the last statement. I find it really unlikely that they will be RCS ports / attachments points. They're set up for ventilation, and either will stay that way, or be patched up later.
Here's a really dumb idea about the portholes: they're literally just temporary access holes poked through the side of this structure because they can.As many have said, this is very clearly NOT the final orbital design, just a test article with crazy margins and design/construction techniques. Maybe they needed some access holes, so they just cut some holes, and intend to "patch them up as good as needed" for the test hops.(I also think they are more probably for RCS (new methalox thrusters, not draco/superdraco) or possible even fin/canard/brakeron/gridfin thing attachment points)
Quote from: RoboGoofers on 01/04/2019 04:48 pmnot if they're for X-Y translation or rotation about Z axis. those you would want near the COM.The center of mass is going to vary depending on fuel load. If the hopper has an RCS system (and I doubt it will for version 1), it would make the most sense to have a set of thrusters on the far ends of the ship. It can then account for whatever the current center of mass might be. With thrusters at the center it only works it's only optimized for a particular fuel load.Edit: technically a central set of RSC thrusters would work regardless of COM, but is probably less optimal due to a smaller lever arm.
not if they're for X-Y translation or rotation about Z axis. those you would want near the COM.
Quote from: holmstar on 01/04/2019 04:52 pmQuote from: RoboGoofers on 01/04/2019 04:48 pmnot if they're for X-Y translation or rotation about Z axis. those you would want near the COM.The center of mass is going to vary depending on fuel load. If the hopper has an RCS system (and I doubt it will for version 1), it would make the most sense to have a set of thrusters on the far ends of the ship. It can then account for whatever the current center of mass might be. With thrusters at the center it only works it's only optimized for a particular fuel load.Edit: technically a central set of RSC thrusters would work regardless of COM, but is probably less optimal due to a smaller lever arm.They could if pointed in all directions. Think lunar lander upper stage used this setup. That would be the top part during decent and landing. You can also use moving thrusters but nobody used this outside of deep space and you will not use it for BFS who is planned to be manned during an landing. But putting them on the ends makes a lot more sense.
located in the least disruptive position for the vehicle's reaction control system?
Quote from: RotoSequence on 01/04/2019 06:08 pmlocated in the least disruptive position for the vehicle's reaction control system?*if it even has an RCS at all.
I think people are getting a bit too wild in the speculation department. This is a Phase I hopper (see thread title). So it's KISS (Keep It Simple, Stupid). There is so much to be learned by SpaceX through a simple (relatively speaking) BFH.
Quote from: Johnnyhinbos on 01/04/2019 06:20 pmI think people are getting a bit too wild in the speculation department. This is a Phase I hopper (see thread title). So it's KISS (Keep It Simple, Stupid). There is so much to be learned by SpaceX through a simple (relatively speaking) BFH.This! I'm also guilty of the Elon thing. He's the defacto face of SpaceX, though Gwen makes quite a few appearances also. Much of the info we get comes from Elon, so it's easy to fall into the trap of "Elon said..."
Quote from: magnemoe on 01/04/2019 05:56 pmQuote from: holmstar on 01/04/2019 04:52 pmQuote from: RoboGoofers on 01/04/2019 04:48 pmnot if they're for X-Y translation or rotation about Z axis. those you would want near the COM.The center of mass is going to vary depending on fuel load. If the hopper has an RCS system (and I doubt it will for version 1), it would make the most sense to have a set of thrusters on the far ends of the ship. It can then account for whatever the current center of mass might be. With thrusters at the center it only works it's only optimized for a particular fuel load.Edit: technically a central set of RSC thrusters would work regardless of COM, but is probably less optimal due to a smaller lever arm.They could if pointed in all directions. Think lunar lander upper stage used this setup. That would be the top part during decent and landing. You can also use moving thrusters but nobody used this outside of deep space and you will not use it for BFS who is planned to be manned during an landing. But putting them on the ends makes a lot more sense. We're still well and truly in the dark on the reason why SpaceX punched big holes in the vicinity of the tankage volume, I think. I'm leaning towards the flag and holes side being the "top," which would suggest RCS of some kind, but that location seems to make for a terrible moment arm. Perhaps they're tank-bleed valves for the tanks, deliberately located in the least disruptive position for the vehicle's reaction control system?
I am all for the equalization venting theory. It's simple, straightforward, and is logical. There's no thrust structure to speak of in this section (as far as we can tell). That section is being attached to the much more robust water tank section via metal tabs and holes on the top of the water tank. The holes aren't perfectly aligned in a horizontal line - if they were going to be backed by a rigid thrust structure you would expect higher precision fidelity when making the holes.
I am all for the equalization venting theory. It's simple, straightforward, and is logical. There's no thrust structure to speak of in this section (as far as we can tell). That section is being attached to the much more robust water tank section via metal tabs and holes on the top of the water tank. The holes aren't perfectly aligned in a horizontal line - if they were going to be backed by a rigid thrust structure you would expect higher precision fidelity when making the holes. I think people are getting a bit too wild in the speculation department. This is a Phase I hopper (see thread title). So it's KISS (Keep It Simple, Stupid). There is so much to be learned by SpaceX through a simple (relatively speaking) BFH.And this follows with a standard disclaimer - it's SpaceX - they never disappoint!One last comment. Everyone tends to say "Elon" when it's really "SpaceX". There are a LOT of really brilliant and creative thinking people at SpaceX. I remember talking to Stan Love when I was at the static fire for the SLS SRB QM-1 out in Promontory, Utah a few years ago and he couldn't stop talking about the amazing young brilliant engineers at SpaceX. They had blown his mind. Those are the people who are actually doing this design. Elon is a visionary and an amazing idea guy - but the execution is all because of those other people...
Two moves in one day!
Quote from: maximuvinal on 01/04/2019 02:01 pmin and it seems to me that these are just the nozzles, the engines themselves are not mountedYou can look through the cutout for one of the lower tubes of the legs in an earlier picture and see the curve of a turbopump exhaust manifold that is used for nozzle cooling (I believe). Highly doubt that would be there unless actual engines. I'd pull up the picture, but to be honest, this thread is so clogged with speculative posts (like this one), that the actual updates / images are fully buried...
in and it seems to me that these are just the nozzles, the engines themselves are not mounted
Quote from: bocachicagal on 01/04/2019 07:01 pmTwo moves in one day!Oh my! So - can people perhaps see a simple explanation for internal ventilation now?
Quote from: Johnnyhinbos on 01/04/2019 07:10 pmQuote from: bocachicagal on 01/04/2019 07:01 pmTwo moves in one day!Oh my! So - can people perhaps see a simple explanation for internal ventilation now?Sure, but unless there is a bulkhead in the way, not sure why said ventilation wouldn't be run through holes already present in the concrete jig? Seems a better option than drilling otherwise unnecessary holes (assumed in this premise) in your spacecraft.
Quote from: RobLynn on 01/04/2019 07:16 amA few observations:There is more than enough room in the lower, non-shiny thicker walled section of the hopper for fuel to stay aloft for 6minutes. that is something like 4km/s of deltaV, a lot of it at relatively low throttle settings, probably averaging somewhere between 300s and 320s rocket Isp through the flight. That implies a fuel to dry mass ratio of about 4:1 and with Raptors somewhere around 200tonnes thrust probably a little less than 400tonnes fuel and a little more than 400m³ fuel capacity (densified methalox about 930kg/m³). Fuel will need to be sub-cooled (densified) methalox for the Raptor turbopumps.Tanks will almost certainly be just domes welded into walls of lower hopper section between upper and lower leg frames, thick walls in that area make for forgiving assembly accuracy and welding requirements.Only need about 9-10m total tank length including spherical ends at Ø9m but the domes will be somewhat flattened - necessary as otherwise hard to achieve the LOX:CH4 volume ratio of 60:40. The larger volume 'squashed' sphere LOX tank will be above the lower volume CH4 tank, it's lower dome forming the upper dome of the CH4 tank so that it drains from it's lowest point in the middle.The shiny shell above the lower legged body is nothing but an aeroshell. No tanks, probably a little instrumentation and reaction control system stuff. Perhaps a frame of some sort to rigidify the aeroshell and perhaps provide an anchor point for some nose ballast.The aeroshell will likely be filled with vented oxygen with a pressure relief valve to provide some positive stiffening pressurisation.4km/s is enough to get pretty high and fast, but it is likely the hopper is only leading more sophisticated and lightweight stainless steel flight test articles by 6 months, and without movable forward and aft aero-surfaces it is unlikely that they can learn much from it above low transonic speeds. I very much like your summary of likely construction going forwards.Except I would be surprised if BFH or BFS used densified propellants. ISTM this would require a step too far for GSE employed initially on Mars. Seems right for SHB, though.
A few observations:There is more than enough room in the lower, non-shiny thicker walled section of the hopper for fuel to stay aloft for 6minutes. that is something like 4km/s of deltaV, a lot of it at relatively low throttle settings, probably averaging somewhere between 300s and 320s rocket Isp through the flight. That implies a fuel to dry mass ratio of about 4:1 and with Raptors somewhere around 200tonnes thrust probably a little less than 400tonnes fuel and a little more than 400m³ fuel capacity (densified methalox about 930kg/m³). Fuel will need to be sub-cooled (densified) methalox for the Raptor turbopumps.Tanks will almost certainly be just domes welded into walls of lower hopper section between upper and lower leg frames, thick walls in that area make for forgiving assembly accuracy and welding requirements.Only need about 9-10m total tank length including spherical ends at Ø9m but the domes will be somewhat flattened - necessary as otherwise hard to achieve the LOX:CH4 volume ratio of 60:40. The larger volume 'squashed' sphere LOX tank will be above the lower volume CH4 tank, it's lower dome forming the upper dome of the CH4 tank so that it drains from it's lowest point in the middle.The shiny shell above the lower legged body is nothing but an aeroshell. No tanks, probably a little instrumentation and reaction control system stuff. Perhaps a frame of some sort to rigidify the aeroshell and perhaps provide an anchor point for some nose ballast.The aeroshell will likely be filled with vented oxygen with a pressure relief valve to provide some positive stiffening pressurisation.4km/s is enough to get pretty high and fast, but it is likely the hopper is only leading more sophisticated and lightweight stainless steel flight test articles by 6 months, and without movable forward and aft aero-surfaces it is unlikely that they can learn much from it above low transonic speeds.
