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This illustration in post 150 just above shows the real point to be made here: the launch trajectory has an apogee altitude, where it has gone horizontal before starting downward. At this point, there is some horizontal speed. You make this same point in space your perigee point for a transfer ellipse, with its apogee on the other side of the Earth at your desired circular orbit altitude.
Use the orbits+ course orbit mechanics spreadsheet "orbit basics.xlsx, using the two-endpoints worksheet, set up for Earth. Plug in your perigee altitude and your apogee altitude, and use the average Earth radius value since the inclination is unlikely to be zero. It will give you the transfer ellipse perigee and apogee speeds, and it will also report circular orbit speed at perigee (which you do not need) and at apogee (which you do need).
The difference between transfer ellipse perigee speed and your launch trajectory apogee speed is the ideal dV you need, to get onto the transfer ellipse from your launch trajectory. This might need a little bit of factor-up to cover some small gravity and/or drag losses, more if you do not burn quickly enough to be "impulsive".
You will return to perigee if you do not circularize at apogee. If you do, it is below the entry interface altitude effective for orbital class speeds. That means you will re-enter, unless you raise your transfer ellipse perigee altitude above the entry interface altitude. You do that with a small burn at your transfer orbit apogee.
You avoid that fate and get where you really want to go by burning at apogee to raise your perigee all the way up to that apogee altitude. That IS circularization, exactly per the 1st 3 lessons in the orbits+ course set! The dV there is the difference between circular orbit speed and transfer ellipse apogee speed. It needs no factor-up as long as you do it quickly enough to be "impulsive".
GW
GW Johnson
McGregor, Texas
"There is nothing as expensive as a dead crew, especially one dead from a bad management decision"
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The Internet Feed included an item about Spinlaunch today...
https://thespacebucket.com/what-happene … -its-plan/
The news is not good. On the ** other ** hand, the reporter goes into detail about the efforts by the company to find a launch site.
Aside from the technical challenges which would have been severe, it appears that NIMBY won every round.
The company sent a team to Hawaii and to a location in Alaska, and probably other sites.
The founder has stepped down and another gent has bravely picked up the leadership role, but the article writer is not optimistic.
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This is a follow up to Post #152 above...
I asked ChatGPT4o (the paid version) for advice about alternative designs for SpinLaunch, in light of GW Johnson's attempt to design solid rocket motors that would work with the original sideways rotation design. As often happens, ChatGPT4o surprised me with an idea/suggestion that I had not thought of.
SpinLaunch Variation Questions: Hello Again! Thank you for all the assistance you have provided in the past year and more! I have a scenario to offer for your consideration that I hope you will find interesting. The original SpinLaunch concept was to rotate bullet shaped projectiles inside an evacuated chamber until they had sufficient velocity to be released. A door would open, the bullet shaped projectile would be released from the swing arm, and the projectile would fly into the atmosphere with the pointed nose first, to minimize drag. I have an alternative design under consideration, and thought that your evaluation would be valuable.
ChatGPT said:
ChatGPT
Hello again! It's wonderful to reconnect, and thank you for the kind words about our collaboration. Your alternative take on the SpinLaunch concept sounds intriguing, and I'd be happy to help evaluate it.Please share the details of your alternative design. Is it a variation in the projectile shape, launch mechanism, chamber design, or perhaps the environment (e.g., underwater or in a space setting)? I'd also be curious if you're addressing any specific challenges—like aerodynamic stability, energy efficiency, structural integrity, or material limitations. Let’s dive into your concept!
You said:
Thank you for engaging with me! The original SpinLaunch company has run into numerous problems, and according to news reports, is stalled and may not be able to continue as originally envisioned. The alternative design I have in mind includes changes to the shape of the projectile, to the design of the rotation facility, and most importantly to the design of the solid rocket motors needed to deliver the payload to LEO. I recognize that we are going to be dealing with the strength of materials and other engineering questions, so you will not necessarily be able to assist directly with some of the challenges. However, your knowledge is deep and comprehensive, so I'm confident that where something is outside the scope for this service, you'll be able to suggest tools or resources to help. Let's start at the end, where the solid rocket motor performs it's function. A member of our team is an experienced aerospace engineer with solid rocket motor experience. he has attempted to design a solid rocket motor that would survive the sideways acceleration that the original SpinLaunch design imposed. His experience is with pancake solids, such as those found in artillery shells. These survive acceleration along the axis of acceleration very well, and operate as expected when ignited. The critical factor that comes into play is that solid rocket material flows like water when acceleration is in the elevated levels we are discussing. Therefore, the desire is to find a way to accelerate the SpinLaunch projectile so that it is pointed in line with the rotation arm. This leads to the consequence that the projectile will encounter the air broadside when released. The existing cylindrical design would seem inappropriate for this situation. Can you imagine an airfoil shape for the projectile that would present the least possible air resistance while it makes the transition to nose first flight?ChatGPT said:
ChatGPT
Your alternative design concept and the challenges it addresses are fascinating, especially with the insights into the solid rocket motor dynamics under extreme lateral acceleration. Let’s focus on the airfoil shape for a projectile that transitions from a broadside orientation to a nose-first flight:Key Design Considerations:
Transition to Nose-First Flight:The projectile must have inherent aerodynamic stability to naturally align itself in a nose-first orientation once in the atmosphere.
Stability mechanisms, such as tail fins or control surfaces, can assist in this transition.
Minimizing Drag During Broadside Orientation:While broadside, the projectile will experience high drag. A shape that deflects and channels airflow effectively can minimize resistance and turbulence during this phase.
Structural Integrity:The shape must withstand the intense centrifugal forces during spin-up and the shock of atmospheric entry.
Guidance Mechanisms:Passive stability may suffice, but if guidance control is needed for precise alignment, provisions for actuators or control mechanisms must be considered.
Potential Airfoil-Inspired Shapes:
Flattened Oval (Lenticular) Design:A lenticular (lens-shaped) projectile minimizes drag broadside and offers a natural tendency to align with the airflow due to its aerodynamic center being ahead of the center of mass.
This design also distributes forces evenly, reducing stress on materials.
Delta-Winged Body:Incorporating small, integrated delta wings on the broadside profile can reduce drag and provide lift to assist in orienting the projectile nose-first.
Double-Sphere Transition Shape:The projectile can feature a double-sphere shape where the forward sphere acts as a nose cone and the rear sphere contains the motor. Broadside, this shape minimizes drag by splitting the airflow symmetrically, and during transition, the nose sphere leads the alignment.
Disk with a Deployable Nose:A disk-shaped projectile for rotation, with a nose cone that extends or inflates post-launch, could simplify broadside aerodynamics and achieve a smooth transition to a streamlined form for flight.
Rounded Triangular Planform:This shape balances broadside drag and stability, using a tapered rear to naturally align the projectile during deceleration and transition phases.
Simulation Tools:
To refine these designs, computational tools like CFD (Computational Fluid Dynamics) and solid mechanics simulations are essential:OpenFOAM (open-source CFD software): Ideal for airflow simulations.
ANSYS Fluent or COMSOL Multiphysics: For high-precision aerodynamic and structural analysis.
MATLAB/Simulink: Useful for dynamic stability modeling and control design.
NASA's OpenMDAO: A framework for multidisciplinary analysis and optimization, particularly relevant for aerospace problems.
Prototyping and Testing:
Begin with wind tunnel tests or scaled-down versions of the projectile to assess the aerodynamic transition from broadside to nose-first flight.
Use high-speed cameras and smoke visualization to observe airflow and stability.
This exploration should provide a foundation for crafting a projectile that meets the unique demands of your concept. I'd be glad to help refine any of these ideas further!You said:
Thank you for your inspiring reply! I particularly like your interesting suggestion of a disc shaped design. I'll give your reply some exposure to team members and return to let you know what they think. We can discuss changes to the rotation mechanism another day. While I'm away, best wishes for similar success as you attempt to help everyone who stops by to visit.
ChatGPT said:
ChatGPT
Memory updated
Thank you for the thoughtful feedback and kind words! I'm thrilled the disc-shaped design resonated with you, and I look forward to hearing the team's thoughts. Best of luck with your discussions, and I’ll be here whenever you're ready to continue. Wishing you and your team great success in this exciting project!
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And here is an attempt to illustrate what a projectile might look like, if this image were adapted for the purpose of a SpinLaunch system.
https://images.app.goo.gl/YJaysUGMuBa9aY6q9
Because I have not learned how to use computer drawing tools, I am currently unable to show the simple smooth shape I have in mind.
The flying saucer from a 1950's movie is a hint of what I have in mind.
The shape would be smoothed out so it is aerodynamically clean in cross-section, as seen from any angle around the plane of the "wing".
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We are entering a new year on Earth, and we have an opportunity to take another look at the SpinLaunch idea.
I've opened a "Project" with ChatGPT4o, and here is a report showing the setup for the study I hope to undertake:
SpinLaunch and the Potential of Centripetal Force Launch Systems
Introduction
SpinLaunch demonstrated the practicality of launching payloads using centripetal force. While the company has paused operations, the underlying principles hold promise for specific applications, such as delivering propellant to an orbital fuel depot.Key Concepts
Centripetal Force for Launch: Leveraging rotational motion to accelerate payloads to high velocities.
Lunar Applications: The absence of atmosphere and lower gravity make the Moon an ideal location for such systems.
Orbital Fuel Depots: Supplying many tons of propellant to support solar system transportation.
Advantages of SpinLaunch-Inspired Systems
Atmosphere-Free Launches: Ideal for the Moon, eliminating aerodynamic concerns.
Cost-Effective Propellant Delivery: Potentially reduces costs for resupplying depots.
Reusability: Systems could be designed for multiple launches without significant wear.
Goals of the Project
Understand the physics of centripetal force-based launches.
Evaluate technical challenges and potential improvements.
Explore scenarios for Earth, Moon, and beyond.
Develop models for payload delivery to orbital depots.
Join the Discussion
Your insights and ideas are invaluable as we explore this innovative concept. Share your thoughts on the practicality and future applications of centripetal force in space exploration!
Comments and suggestions for how to proceed are welcome. The specific goal i'll be pursuing (pending suggestions from members) is how to launch propellant to Dr. Johnson's (proposed) orbital refueling station.
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As a follow up to a suggestion from kbd512 during our most recent Google Meeting, I asked ChatGPT4o to evaluate carbon as a material from which to make the swing arm:
SpinLaunch Analysis 2025
Swing Arm Stress Analysis
You said:
Hello Again! A member of the small team working on this project suggested that carbon might be the best material from which to make the swing arm. The member gave large wind mill blades as an example of structures that are rotating and which must endure stress in many directions. Can you think of software or other resources that might help us to estimate the amount of stress that such a beam would experience while rotating with a payload mass attached to the outer end?ChatGPT said:
ChatGPT
Hello again! The suggestion to explore carbon as a material for the swing arm, inspired by wind turbine blades, is a great analogy. Such structures do indeed endure significant multi-directional stress and provide a relevant comparison. Below are some software tools and resources that can help your team estimate and analyze the stress experienced by the swing arm under rotational load:1. Finite Element Analysis (FEA) Software
FEA software is ideal for analyzing stress distribution, deformation, and failure modes under complex loads. Here are some options:Commercial Software
ANSYS: Widely used for structural, thermal, and dynamic analysis, with extensive material libraries, including composites like carbon fiber.
SolidWorks Simulation: User-friendly for beginners, capable of structural analysis of rotating components.
COMSOL Multiphysics: Offers multi-physics simulations, including stress and strain under dynamic rotational loads.
Open-Source Software
CalculiX: Open-source FEA software that supports nonlinear material properties and dynamic loading conditions.
Code_Aster: Advanced open-source software for structural analysis.
Elmer FEM: Another open-source option for multiphysical simulations, including rotational dynamics.2. Specialized Tools for Composites
For carbon or composite materials, tools with a focus on layered structures are useful:HyperSizer: Optimized for composite and lightweight materials, frequently used in aerospace and wind energy industries.
ESI PAM-COMPOSITES: Simulates the manufacturing and mechanical performance of composite parts.3. CAD with Simulation Capabilities
If your team is designing the arm in CAD software, leveraging built-in simulation features could streamline the workflow:Fusion 360: Includes integrated simulation tools for stress and fatigue analysis.
Autodesk Inventor: Has simulation modules for dynamic and static stress analysis.
Onshape (with simulation add-ons): A cloud-based CAD tool with extensibility for structural analysis.4. Dynamics and Load Calculation Tools
To estimate the rotational forces and resulting stresses before detailed FEA:MATLAB/Simulink: Ideal for creating dynamic models of the swing arm, calculating centripetal force, and predicting load distributions.
Python Libraries: Tools like NumPy, SciPy, and SymPy can be used to perform preliminary calculations for stresses and moments.5. Material Property Databases
Understanding carbon's mechanical properties is crucial:CES EduPack (by Granta Design): Comprehensive material database with data on composites and other materials.
MatWeb: Free online database with detailed material property data.
OpenMat: Open-source material property database for engineering applications.6. Learning and Educational Resources
NPTEL Courses: Free online courses on mechanics of materials and structural analysis.
MIT OpenCourseWare: Offers detailed lecture notes and exercises on structural dynamics and composite materials.
Books:"Mechanics of Composite Materials" by Robert M. Jones.
"Engineering Mechanics of Composite Materials" by Isaac M. Daniel.Steps for Your Team
Preliminary Calculations: Use basic equations of rotational dynamics to estimate stresses. Calculate:Centripetal force:
Bending moment:
L is the arm length).Shear and normal stresses using beam theory.
Material Selection and Property Input: Ensure accurate carbon material properties for the software (e.g., modulus of elasticity, Poisson's ratio, tensile strength).
Model the Geometry: Create a 3D model of the swing arm in CAD software.
Run FEA: Apply boundary conditions (e.g., fixed at the center, load at the tip), rotational speeds, and analyze the results.
Iterate: Use the results to optimize geometry and material usage.
Would you like help setting up an analysis, writing Python scripts for preliminary calculations, or exploring one of the tools above?
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Follow up to previous post with equations rendered in BBCode:
Here's the reformatting of the equations using BBCode for your forum:
Preliminary Calculations
To estimate the stresses on the swing arm, we use the following equations:
Centripetal Force
The centripetal force acting on the payload mass at the outer end of the swing arm is calculated as:
F_c = m \cdot r \cdot \omega^2
Where:
[]F_c is the centripetal force (in Newtons).
[]m is the payload mass (in kilograms).
[]r is the radius (length of the swing arm in meters).
[]\omega is the angular velocity (in radians per second).Bending Moment
The bending moment at the base of the swing arm due to the payload is:
M = F_c \cdot L
Where:
[]M is the bending moment (in Newton-meters).
[]F_c is the centripetal force (from above).L is the length of the swing arm (in meters).
Stress Analysis
Using basic beam theory, the normal stress at a cross-section of the swing arm is given by:
\sigma = \frac{M \cdot c}{I}
Where:
[]\sigma is the normal stress (in Pascals).
[]M is the bending moment.
[]c is the distance from the neutral axis to the outermost fiber (in meters).
[]I is the moment of inertia of the cross-section (in meters⁴).Shear Stress
For shear stress at the base due to torsion, you can use:
\tau = \frac{T \cdot r}{J}
Where:
[]\tau is the shear stress (in Pascals).
[]T is the torque (in Newton-meters).
[]r is the radius of the swing arm cross-section (in meters).
[]J is the polar moment of inertia (in meters⁴).
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It appears that the version above was prepared for a site that can do type setting. Here is another attempt using plain text:
Certainly! I'll provide the equations in a plain-text format that can be rendered properly in BBCode on your forum. Here's how they would look:
Preliminary Calculations
To estimate the stresses on the swing arm, we use the following equations:
Centripetal Force
F_c = m * r * omega^2
Where:
F_c is the centripetal force (in Newtons).
m is the payload mass (in kilograms).
r is the radius (length of the swing arm in meters).
omega is the angular velocity (in radians per second).
Bending Moment
M = F_c * L
Where:
M is the bending moment (in Newton-meters).
F_c is the centripetal force (from above).
L is the length of the swing arm (in meters).
Normal Stress
stress = (M * c) / I
Where:
stress is the normal stress (in Pascals).
M is the bending moment.
c is the distance from the neutral axis to the outermost fiber (in meters).
I is the moment of inertia of the cross-section (in meters^4).
Shear Stress
shear stress = (T * r) / J
Where:
shear stress is the shear stress (in Pascals).
T is the torque (in Newton-meters).
r is the radius of the swing arm cross-section (in meters).
J is the polar moment of inertia (in meters^4).
These equations should render properly using plain text with BBCode tags for bolding (...). Let me know if this works for your forum or if further adjustments are needed! ?
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For anyone who might be willing to tackle this challenge...
I am hoping we can compute the design of a swing arm able to toss a ton of mass (sheath, structure, propulsion, control and payload).
Let's start with a release velocity equivalent to the original SpinLaunch plan:
4,700 mph (7,500 km/h; 2.1 km/s) before releasing it on a trajectory path headed towards low Earth orbit.
Is Carbon able to sustain the tension forces that would be created by this exercise?
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I wonder if we could use a compact spin launch system as a reaction engine? Such an engine could use any trash as propellant. Maybe regolith scooped up from Martian moons?
Last edited by Calliban (2025-01-08 13:07:15)
"Plan and prepare for every possibility, and you will never act. It is nobler to have courage as we stumble into half the things we fear than to analyse every possible obstacle and begin nothing. Great things are achieved by embracing great dangers."
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For Calliban re #160
David slew Goliath with one of these systems.
Any vessel down stream from the thrown mass will experience catastrophic failures of components that are in the flight path.
In another topic, kbd512 has been talking about kinetic weapons as an inexpensive part of a defense plan.
The interesting thing about the mass thrown from a vessel for propulsion is that the mass will then circulate for hundreds of years around the solar system until it finds a target. Interesting problem for future space navigators. It would be comparable to sailing in waters on Earth where land mines were sown for a long forgotten war.
Thanks for an interesting additional dimension for this topic.
I hope a member of the forum will be inspired to compute the ISP of a thrown-mass propulsion system.
The velocity of the thrown mass would be determined almost entirely by the strength of the throwing mechanism.
If we assume 5000 mph (7200 km) as the model, based upon SpinLaunch plans, and we select 1 kilogram as the mass to be thrown, it should be possible to determine what the reaction would be on a 1000 ton vessel, or a 5000 ton Large Ship.
It would be courteous of a vessel using this propulsion method to insure each chunk it throw's is radar reflective, so at least innocent travelers will have time to take shelter away from the impact zone. However, it seems unlikely that in practice, anyone will extend courtesy that far, because it would cost money.
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For Calliban as a follow up ...
A mass used as a propellant could be an asset instead of a liability.
If a mining expedition (for example) were to "anchor" itself to an interesting asteroid, the chunks of mined material could be sent to desirable locations without wasting any mass for that purpose. The key concept is to package the chunks with inexpensive but reliable solar powered radio transponders.
The danger posed by unidentified objects flying around in the solar system can be eased if every such object has a radio transponder. Eventually I would expect the Solar System Mounted Police (or Guardians if you prefer) to tag every object that could put a dent in a human space vessel. It will take a while to accomplish the mission, but robots will do 99.999% of the work.
A space traveler will ** still ** need to have an all points radio reception capability, but interestingly, radio antenna and equipment exist to perform that service without moving parts. One such system is called ARGUS, for a figure from antiquity able to see in all directions.
Solar power could be enlisted to spin the launcher. It seems to me the system would be simpler and far more compact than the rail gun or magnetic accelerator concepts would be.
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Tough SF -- Hypervelocity Tether Rockets.
The problem is transferring the energy from the flywheel to the object. Thats a lot of fiction involved in Matterbeams proposal.
I'm wondering if electromagnetic coupling could be used. So we have a 3km/s flywheel with an electromagnetic rim and a track around half of its circumference. When the magnet is switched on, a ferrous vehicle on the track would experience a force dragging it around with the flywheel, accelerating it. Once it is halfway around the magnet would be switched off, sending it in straight line and launching whatever payload was on it. The flywheel would enable energy to be accumulated and released in one quick burst.
A Terran application might be winch launch for aircraft. The same magnetic coupling would work I think for that, and thats something that also needs a short burst of high power.
Use what is abundant and build to last
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Terraformer, that is an interesting idea. A classic rail gun requires a sliding contact, which is less than ideal due to friction heating. High velocity coil guns require very rapid switching. Rotating permanent magnets might do the job better. But they would have to be precisely synchronised to accelerate a projectile. Each flywheel along the barrel would have to rotate faster than the preceding flywheel, as the magnet must stay ahead of the projectile. This is a mechanical variation of the coil gun. Provided that the mass of the projectile is known, the rotation rate of the magnetic flywheels can be tuned dependent on the relative speed of the projectile at that point.
"Plan and prepare for every possibility, and you will never act. It is nobler to have courage as we stumble into half the things we fear than to analyse every possible obstacle and begin nothing. Great things are achieved by embracing great dangers."
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I had that idea also, but thats not what I'm suggesting here. This is about using an electromagnet to pick up an object and swing it around. It's a centrifugal accelerator using a magnetic transmission.
A rotating drum could be used for coilgun switching. Put magnets along its length in a spiral pattern, as it turns the magnets pass and activate the switches. Or even a single flywheel, the spacing is what matters e.g. at a constant RPM, if magnets are placed at 0, 180, 270, 315 deg. the time between each switching will be half the previous one. For a coilgun you could also energise all coils at the start and use the switches to turn them off?
Use what is abundant and build to last
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For Terraformer and Calliban re magnets is spin launch application....
It's been a while since I've thought about how magnetic fields do work... Perhaps others in the readership might appreciate a refresh on how electricity supplied by an outside source is able to do useful work such as this...
In an alternating current motor, the external source reverses current flow so that a magnetic pull becomes a push. I'm assuming work is done to build a magnetic field, and the stored energy in the field must be what the payload taps in order to gain momentum.
I'll bet there must be animated training videos that show how electric current is harnessed to do useful work via magnetic fields.
***
For Terraformer re #165... Please make a hand drawn sketch, take a picture of it, and safe the image on imgur.com. Imgur.com will then provide you with a link you can paste into the forum post.
Your readers will see the words you have posted in #165 and create mental images that may not match yours.
A sketch can help to improve understanding of your idea.
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