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#1140
by
RoboGoofers
on 04 Jan, 2019 17:47
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Is there some heuristic to rule out RCS on the fins/legs? Wouldn't those be ideal / what outweighs such a superior location?
'ideal' depends on what type of movement you want to make. there is no one ideal spot for all movements.
the wingtips might be good for z rotation but since they are far aft of the COM they might also induce a
precession. might be good for pitch or yaw but since there's only three wings you need to fire two at once which will create some error between expected motion vs actual. it's a bad location for translation moves.
they also need to be plumbed from the main tank (assuming they're methalox) which gets a bit tricky since two of the wings move.
The wings are also going to flex a bit, especially with the bang-bang type of action of RCS. i'd assume they'd need to model and control resonances.
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#1141
by
holmstar
on 04 Jan, 2019 17:48
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A little flag repair was needed as half was missing this morning.
Probably needed to be removed to weld the seam strip in place. It appeared that the flag was initially added before the strip was applied.
Edit: Johnnyhinbos beat me to it.
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#1142
by
RDMM2081
on 04 Jan, 2019 17:55
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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)
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.
I guess I shot myself in the foot by putting two completely disparate statements in my post. I haven't been right about anything yet, but I hadn't seen the "simple hole" theory stated very clearly yet so thought it needed a voice.
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#1143
by
magnemoe
on 04 Jan, 2019 17:56
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not 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.
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#1144
by
RotoSequence
on 04 Jan, 2019 18:08
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not 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?
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#1145
by
holmstar
on 04 Jan, 2019 18:14
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located in the least disruptive position for the vehicle's reaction control system?
*if it even has an RCS at all.
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#1146
by
RotoSequence
on 04 Jan, 2019 18:16
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located in the least disruptive position for the vehicle's reaction control system?
*if it even has an RCS at all.
The Hopper probably doesn't need RCS, but it will need bleed valves for the tanks.
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#1147
by
Johnnyhinbos
on 04 Jan, 2019 18:20
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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...
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#1148
by
holmstar
on 04 Jan, 2019 18:35
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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.
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..."
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#1149
by
JonathanD
on 04 Jan, 2019 18:49
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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.
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..."
Given the design, it seems to be primarily a Raptor test bed more than anything. There are definitely some aesthetic considerations involved also, for which I don't think Elon can help himself.
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#1150
by
Slarty1080
on 04 Jan, 2019 18:51
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not 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?
Perhaps the're drain holes for the toilets?
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#1151
by
RotoSequence
on 04 Jan, 2019 18:56
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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.
Since they could be actively cooling the structure and tankage by sinking the heat of entry into some of the onboard propellants, they'll have some pretty significant gas outflow to keep the ullage pressure from being too high. If these valves serve that purpose, they're probably pointing up and away from the already complex and dynamic reentry heating environment.
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#1152
by
DistantTemple
on 04 Jan, 2019 18:58
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Inside there is a suite for NSF commentators to get a first hand experience. The holes are for ventilation of hot air.
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#1153
by
bocachicagal
on 04 Jan, 2019 19:01
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#1154
by
50_Caliber
on 04 Jan, 2019 19:09
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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...
Definitely! Elon has provided the vision and money for this process, but the engineers and techs behind the scenes have designed and built these things. They're the ones that have literally given blood,sweat and tears to make a lot of this happen.
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#1155
by
ejb749
on 04 Jan, 2019 19:09
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So close. It almost fit.
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#1156
by
Johnnyhinbos
on 04 Jan, 2019 19:10
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Two moves in one day!
Oh my!
So - can people perhaps see a simple explanation for internal ventilation now?
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#1157
by
Cinder
on 04 Jan, 2019 19:10
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Very slightly behind NSF discussion in terms of questions and answers/hypotheses.
in and it seems to me that these are just the nozzles, the engines themselves are not mounted
You 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...
visible at +- 1m52s above
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#1158
by
Wudizzle
on 04 Jan, 2019 19:25
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Two 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.
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#1159
by
Johnnyhinbos
on 04 Jan, 2019 19:28
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Two 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.
Agreed - however allowing ambient air to pass in/out during ascent/descent of hop tests would be useful to prevent over/under expansion due to ambient pressure changes.
