Rakaydos
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Posts posted by Rakaydos
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Am I the only one noticed that the starships payload bay is just big enough for a full size electron? Plenty of room and mass for launch equipment.
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11 hours ago, Wjolcz said:
Ok, so it seems I was wrong. It just seemed very unorthodox to do things this way. The question now is: why won't more spacecraft be built this way? Cygnus probably could be. I guess it all depends on manufacturing techniques.
Btw, the Starship crawler is crawling.
Anything with a heat shield, need to protect that heat shield more than the docking ring, and generally the docking ring needs to be in the opposite side.
For disposable cargo I don't know, perhaps it's just design habit.
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Just now, tater said:
Zubrin gets into the weeds on plume-regolith interactions, and he love his "mini-starship idea (which is garbage, IMO). The only benefit of "mini Starship" for lunar (or small Mars) interactions is... 1 engine landing vs 3, maybe? They could just as well make a lunar SS with a single vacuum Raptor in the middle as a bespoke lunar vehicle (now it has exactly the same plume interaction as any SpaceX lunar vehicle would ever have, since they won't be using Merlin for this, ever). The landing legs? Yeah, I agree, a problem. Simple enough to make the lunar version have F9 legs writ large on the sides for a wide, wide stance. The first few vehicles are not meant to come back, they deliver cargo and are expended (or used as a hab). The cargo includes equipment for making a proper landing pad. Same could be true for Mars. A series of cargo vehicles (note that I am note a Mars colonization person, I think it's kooky, but I'll play along) has very wide stance F9 booster legs for "rough field" conditions. Initial cargo includes robots to lay out solar farm (required anyway), and for the creation of a landing pad.
My preferred "first survey/site prep" mission is a Starship with an Apollo 10 type profile (getting within a few hundred meters of the surface on a landing profile, than abort to orbit before plume interactions become a concern) but deploying a few dozen Cybertrucks with Superdraco Skycranes for "last mile" landing. The trucks would then do site survey and build a pad capable of a Starship landing.
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I want to know how cheaply Tesla could do a hypothetical "cyber coup"- 2 door and hatchback, single motor, rear facing back seats, 300 mile range, steel and glass from the cybertruck.
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20 minutes ago, ThatGuyWithALongUsername said:
Wait, I thought the header tanks were suppose to use the nosecone as a bulkhead? Did the design change again?
Room for further optimization.
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More than a lack of orbital mechanics, Star Wars operates under Luminiferus Aether (an old theory long since debunked for our own universe, but still interesting from a fictional standpoint) EXCEPT when an author tries to get "realistic" for a moment. In addition, there appears to be a neutral plane in space that less maneuverable ships will naturally align with, with a natural sense of "Up" and "Down" that isn't aligned with any celestial body. More maneuverable ships can Dive or Climb relative to this neutral plane, but it takes maneuver force to do so. Less maneuverable ships can "trim" their altitude slightly, presumably with the same tech that lets speeders float in a planetary gravity well.
There also appears to be a scaling factor on the interface between a planet and space- launching from great distances apart will put you close together once you reach space. This also generally seems to put all travelers on the same "side" of the planet.
What does this mean for a blockade?
First things first, you can float in space outside the planetary reference frame, no need for an orbit, Second, you only need to cover the neutral plane above where ships transition.
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7 hours ago, mikegarrison said:
Historically, the trigger for the anti-trust laws that prevent airplane manufacturers from running airlines came about when Boeing refused to sell 247s to TWA because they were reserving them all for their own airline, United. This had two consequences: TWA convinced Douglas to build the DC-1 and Boeing had to sell United (and also Pratt & Whitney). I suppose the same thing would be if somebody else wanted to run a P2P rocket business and tried to buy rockets from SpaceX, but SpaceX refused to sell them any in order to protect their own P2P business.
Except that wouldn't be the reason, the reason would be because Rocketry technology is ITAR protected.
If spaceX makes sympathetic noises while blaming the military, the military will protect SpaceX's monopoly.
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3 minutes ago, Wjolcz said:
Rivets sound like a bad idea though. Every single one of them seems like a good way to start a crack that will eventually rip the tank.
Works fine for submarines, doesn't it?
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2 hours ago, Wjolcz said:
Do you guys think they will be able to shear off 80t of materials from the Starship? Mk1 was about 200t and they want it to be 120t. Also, what about the heatshield tiles? They will need some sort of structure/grid to hold them in place. That sort of thing will only add weight.
That's why I assume the payload to LEO to be about 100t or less. At the same time I'm fully aware that they have done magic to F9. It's insane how much that rocket evolved and how much its capabilities changed.
Mark 1 was a battleship, overthick everywhere. They might not hit 120, but sub 150 is entirely reasonable.
The structure to hold the tiles is three rivits per tile. really not that heavy, all things considered.
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Why not ask the professionals?
http://www.psfc.mit.edu/sparc/faq
"
Why are the magnets so important?
To make fusion work, the fuel must be heated to temperatures above 100 million degrees. Matter in that state is called a plasma – where the particles have net electric charge. To be kept hot, this plasma must be very well insulated from ordinary matter. Fusion devices use magnetic fields to provide the thermal insulation that is required. The stronger the magnetic field, the stronger the confining force on the charged particles in the plasma, the better the insulation, which enables a much smaller, better performing fusion device"
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6 hours ago, Pds314 said:
We should however remember that Orion pulse units are shaped charge devices. The intent is to redirect >80% of the energy into a ~25-degree cone centered on the ship. So that reflector is hardly terrible in efficiency the way it would be with a raw fission or fusion explosive with no shaped charge system.
It's more complex. For one thing, the mean collision distance of particles in rocket exhaust is tiny. Whereas that of light in a flashlight is huge (light doesn't work that way at reasonable energies). For another, we also need to remember that there's a hole at the back for a combustion chamber, and that too rapid expansion early on would likely cause significant loss of energy. The optimal rocket bell is supposedly about 3% more efficient than a 12-degree cone though, so it's hardly a massive difference, if not a totally insignificant one considering the tyranny of the rocket equation.
40+%, not 80+%. Half the energy goes the opposite direction and doesn't interact with the plate. That's just how Conservation of Momentum works.
A combustion chamber catches that extra 50%, and squeezes it through a nozzle to reach maximum efficiency. But Orion is too powerful for any combustion chamber we can build.
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47 minutes ago, mikegarrison said:
Ah yes, corporations: "We're not laying you off. But your job is moving to an entirely different state. If you actually have a life here, you can choose to either give it up or lose your job. Have a nice day!"
If you're a single 25-yr-old renting an apartment, this might be an adventure. If you're a billionaire CEO, you can have houses or condos everywhere and fly back and forth at will. If you have a spouse and/or kids and a house, you're screwed.
This is SpaceX. They actively target the single 25yo.
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50 minutes ago, mikegarrison said:
Rocket exhaust is not made of light. It is a fluid, and subject to fluid mechanics.
Rocket nozzles are also material things, which must resist tremendous heat and force while still being as low-mass as possible.
And as @kerbiloid mentioned, the exhaust does not come from a point source at the focal point of the parabola but rather the entire throat of the nozzle. (The combustion chamber behind the throat doesn't really matter, though, if the throat is sonic, as it usually is.)
All of these are reasons why a simplistic analysis claiming they should all be built in a perfect parabolic shape is too simplistic.
Your 1st and 3rd points cancel each other out. While your second point remains true, a parabola remains the optimum shape for a bell to turn pressure into thrust. Other considerations, like the SSME avoiding flow separation despite it's expansion ratio, call for a non-optimum bell structure, reducing the theoretical vacuum thrust.
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In a vacuume, an infinite length parabolic nozzle is the most efficient.
In variable pressures, ignoring thermal management and combustion efficiencies, an aerospike is theoretically the best possible nozzle type. (practical concerns mean we use staged optimized parabolic nozzles instead.)
An orion pusher plate is very inefficient as a nozzle, but allows the use of a "combustion efficiency" orders on magnitude beyond any chemical engine while keeping the "thermal management" survivable. In effect, the combustion is so powerful it reduces the need for efficiency.
An Orion-Medusa Sailcraft combines Orion and a parabolic nozzle- a magsail that catches the detonation at a safe distance and directs the products backward, with the actual spacecraft suspended by tethers.
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15 hours ago, Raven Industries said:
Solid fuel alone is apparently 11 of the 25 launches. That stuff is heavy.
And not actually nessesary for lunar launch. The core stage should have plenty of TWR on the lunar surface, it doesn't need boosters.
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1 minute ago, kerbiloid said:
A related but maybe offtopic question on the reusability.
A docking port holds a several-tens-up-to-hundred tonnes of mass, withstands compression, bending, etc.
Is it known if the docking ports are actually reusable?
Say, Shuttle is known to be reassembled from flight to flight, and some parts (say, engines) were replaced or sometimes exchanged between the shuttles.
Did they reuse the docking port part or replace it?The same about Dragon, CST (wannabe), etc.
I mean, does it make actually sense to have it integrated and return from orbit rather than jettison it like presumably unreliable on deorbiting?
Static loads are easy, the trick is to manage the shock loads of the docking itself, without using RCS near the other. Lots of careful trajectory management to softdock at relative speeds below what the docking collar can handle.
Starship refueling is going to say "But what if we COULD use RCS, both of us, as long as we don't actually spray each other." This gives them a lot more ability to manage their momentum and orientation.
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1 hour ago, Lukaszenko said:
Not sure I follow the logic here
The missing step is, reusable rockets are cheaper to fly.
So it's really, you make cheaper rockets, you get less money for them.
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On 11/3/2019 at 3:01 PM, Dragon01 said:
Presumably you start accelerating into another dimension.
As I said, that's the problem with tachyons. We don't know what imaginary mass/thrust/acceleration even are. Or if they are anything at all (likely not).
Cathrine Asaro had a science fiction setting with that as her plot-tech. Because technically, the lighspeed barrier is only a point in complex vectorspace, and so a rocket that can generate an imaginary component to their thrust can accelerate past lightspeed if they do it with a partially imaginary (complex is the mathematical term) velocity. Also they stored fuel in complex-space pockets they called Klein bottles.
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7 hours ago, kerbiloid said:
Was this estimation based on some numbers?
I'm not aware of Texan salaries, but currently Space-X has 7000 employees (wiki), and if the Starship personnel is, say, 1 000 people with 2 000 USD/month, it's already 2 mln/month.
And as far as I can understand, it will be the main source of money for the company in whole.By launching 3 times a day to distribute those fixed costs among 90 flights a month.
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On 11/6/2019 at 10:41 AM, farmerben said:
Maybe if Bill Phil specified one specific energy, people here could give rough estimates about it.
The magnets at CERN are about 8 T. But there is another type of magnet that can go up to 45 T. https://en.wikipedia.org/wiki/Bitter_electromagnet
The energy comes from Electric fields parallel to the particle's velocity. The reason to have a ring is to cause the particle to fly through the same electric potential thousands of times.
Laser Wakefield acceleration has taken over for electron boosting. It is now able to accelerate electrons to over 4 GeV in a few centimeters. Adapting this technology for positrons may be possible. For protons and ions the wakefield is not generated in the same way. Still anything that lets you generate crazy electric fields means you don't need to worry about the strength of your magnets or the size of your ring as much.
There was a talk about "linier partical accelerator around the circumference of the moon", that offhandedly mentioned that, if we REALLY wanted to, a particle accelerator around the track of Neptune's orbit would be able to reach Plank Energy.
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9 hours ago, Raven Industries said:
"Our project has not found a way to prevent detection of a large object reentering the atmosphere, but instead of writing off the whole thing, here's a way to send hundreds of 500 million dollar dummy Starships into the same area so that the enemy doesn't know which is the real one."
"Arnt real starship only 1/5 that price?"
"They're really good decoys."
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21 minutes ago, mikegarrison said:
Anywhere that had a landing pad. And a refueling center. And launch facilities. Or else, of course, your reusable Starship just turned into a one-time-use Starship.
And I'm not sure there are many conflicts that can be won by a couple of platoons.
Depends on the platoons. Seal team 6 was a lot fewer than two platoons.
As for it being a one way trip... sometimes, that's acceptable. Usually base to base, but sometimes you need to land it in a field.
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7 hours ago, satnet said:
Another negative impact of the square-cube law is that expander cycle rockets are limited to ~300 kN of thrust. This is because the surface area over which you can extract heat grows slower than the volume you need to fill with fuel and at some point you can't extract enough to run the pumps to fill the volume.
Anexceptio to that would be expander cycle aerospikes. Aerospikes have the opposite problem, where it has more throat that needs cooling per unit thrust, which is normally a problem, but solved the expander cycle problem.
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Note that packing efficiency (the proportion of engine thrust to area to rocket thrust to area) improves with larger engine clusters. A wider rocket can also be slightly taller, just from reducing inefficiency.
As I said, that's the problem with tachyons. We don't know what imaginary mass/thrust/acceleration even are. Or if they are anything at all (likely not).
SpaceX Discussion Thread
in Science & Spaceflight
Posted
Would be better on a cybertruck.