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I'll open with a review of Iterative Design Principles written by Google's Gemini.
Specific design topics are created in the SSTO category for Carbon fuel and separately for LH2 fuel.
Iterative Rocket Design
Hi Gemini! Thank you for your help with numerous previous requests. A small group is studying design of a rocket to reach LEO using SSTO and carbon based fuel, such as RP1. We understand that successful rocket design is an iterative process. Does that assertion sound right to you, and if so, where do you think the process should start? Members have every kind of information that we can think of. The question I am asking (on behalf of the group) is how to start the iterative design process.
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Yes, the assertion that successful rocket design is an iterative process is absolutely correct. Rocket design is an incredibly complex undertaking, involving the interplay of numerous disciplines, constraints, and trade-offs. It's virtually impossible to get everything perfect on the first try, so an iterative approach is essential for refining the design, identifying potential issues, and optimizing performance.Given that your group has "every kind of information you can think of," the ideal starting point for an iterative SSTO (Single-Stage-To-Orbit) rocket design process using carbon-based fuel like RP-1 should focus on establishing the fundamental mission requirements and top-level constraints.
Here's a breakdown of where to start and why, leading into the iterative loop:
Starting Point: Defining Mission Requirements and Top-Level Constraints
Before any detailed engineering can begin, you need a clear target. This initial phase sets the boundaries for all subsequent design decisions.
Define the Payload:
What is the mass of the payload you need to deliver to LEO? (e.g., 1,000 kg, 5,000 kg, etc.) This is the single most critical input as it directly dictates the size and performance requirements of your rocket.
What are the dimensions of the payload? (Volume constraints for the fairing)
What are the environmental requirements of the payload? (e.g., maximum g-forces during launch, vibration limits, temperature ranges).
Define the Target LEO Orbit:
What is the target altitude of LEO? (e.g., 200 km, 400 km, etc.) Higher orbits require more delta-V.
What is the inclination of the orbit? (e.g., equatorial, polar, sun-synchronous). Inclination significantly impacts launch site selection and required delta-V due to Earth's rotation.
Establish Key Performance Goals:
Reliability Target: What is the desired success rate for launches? (e.g., 95%, 99%).
Cost Targets (if applicable): While perhaps not the very first design driver, having an idea of cost constraints can influence material choices and manufacturing processes down the line.
Launch Frequency (if applicable): How often will this rocket need to launch? This can influence manufacturing throughput and operational considerations.
Initial Fuel and Oxidizer Selection Confirmation:
You've specified carbon-based fuel (RP-1). This is a good starting point.
What oxidizer will you pair with it? For RP-1, Liquid Oxygen (LOX) is the standard choice. Confirming this early sets the stage for engine design and tankage.
Identify Major Constraints and Assumptions:
Launch Site: Where will the rocket be launched from? This impacts initial velocity from Earth's rotation and available azimuths.
Manufacturing Capabilities: Are there any pre-existing limitations on materials, fabrication techniques, or facility size?
Regulatory Environment: Are there any specific regulations or safety standards that must be met?
Why Start Here?
Delta-V Requirement: Once you have the payload mass and target LEO orbit, you can make an initial estimate of the total ΔV (delta-velocity) required for the mission. This is the single most important parameter determining the rocket's overall size and performance.
Mass Fraction: SSTO vehicles are incredibly sensitive to mass fraction (the ratio of propellant mass to total vehicle mass). The payload mass directly influences the required dry mass and, consequently, the overall vehicle size needed to achieve the necessary mass fraction.
Engine Thrust and Isp (Specific Impulse): Knowing the required ΔV and having an initial idea of the propellants allows you to start considering the characteristics of the propulsion system needed (thrust, specific impulse).
Iterative Loop Foundation: These initial parameters provide the baseline against which all subsequent design iterations will be measured. Without them, you're designing in a vacuum.
The Iterative Loop (After the Starting Point):
Once you have these initial requirements, the iterative process can begin. A simplified loop might look like this:
Conceptual Design & Initial Sizing:
Based on ΔV and payload, make a first guess at rocket mass, dimensions, and engine thrust. Use the Tsiolkovsky rocket equation as a fundamental tool.
Consider different propulsion cycles (e.g., gas generator, staged combustion) and their impact on performance.
Estimate initial propellant mass, tank volumes, and structural mass.
Propulsion System Design (Initial Pass):
Select preliminary engine type(s) and estimate performance (Thrust, Isp).
Determine number of engines.
Consider thrust-to-weight ratio for liftoff and throughout the ascent.
Structural Design (Initial Pass):
Estimate tank masses, interstage structures, fairing, and other non-propellant masses.
Consider material choices (e.g., aluminum-lithium, carbon fiber composites).
Aerodynamics & Flight Mechanics:
Perform preliminary aerodynamic analysis to estimate drag.
Simulate initial trajectory to verify ΔV requirements and identify potential issues (e.g., maximum dynamic pressure, re-entry heating for an SSTO).
Mass Budget Refinement:
Combine all the initial estimates into a refined mass budget: Payload + Dry Mass (structure, engines, avionics, etc.) + Propellant Mass.
Check the mass fraction. For SSTO, this will be extremely high (meaning a very large percentage of the rocket's mass is propellant).
Performance Analysis & Verification:
Does the current design meet the ΔV requirement with the refined mass budget?
Is the thrust-to-weight ratio sufficient for liftoff and throughout the flight?
Identify Discrepancies & Iterate:
If the rocket is too heavy, doesn't have enough ΔV, or is otherwise unfeasible, identify the biggest drivers of these issues.
Example Iterations:
If not enough ΔV: Increase propellant tank size, improve engine Isp, reduce dry mass.
If too heavy: Optimize structural design, explore lighter materials, reduce subsystem mass.
If thrust-to-weight is too low: Add more engines, increase individual engine thrust.
If too much drag: Refine aerodynamic shape.
Trade Studies:
Throughout the process, conduct trade studies on key design choices (e.g., number of engines vs. size of engines, material selection for tanks, different re-entry profiles for SSTO).
This iterative process continues, with each loop providing more refined data and leading to a more optimized and feasible design. Good luck to your group!
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Thank you! I think your thoughtful listing of steps will be helpful.
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You're most welcome! I'm glad to hear that the steps are helpful for your group. Designing an SSTO is an incredibly ambitious and rewarding challenge, and a structured, iterative approach is truly the only way to tackle it effectively.If you have any further questions as you delve deeper into the design process, don't hesitate to ask. Good luck with your rocket design!
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I asked Google's Gemini to put together a checklist for NewMars members to use in preparing designs for various rocket missions
Conversation with Gemini
Iterative Rocket Design Checklist - Hello Again Gemini! Thank you for our thoughtful responses to numerous questions and requests. In another session, we discussed how members of a small group of forum members might approach Iterative Design of a Rocket system for a specific application. In that previous discussion, you suggested defining the mission and constraints as completely as possible, to help participants as they consider the many options that have to be selected to achieve the desired result. So far we have defined:All three options:
Objective is LEO at 300 km
Launch is at the equator facing due East
Mode is SSTO
Option 1 of 3: Carbon fuel
Payload: 100,000 kg (50 metric tons)
Option 2 of 3: LH2 fuel
Payload 100,000 kg (50 metric tons)
Option 3 of 3: LH2 Orbital RV
Payload 1 metric ton separate from vehicle plus the vehicle itself
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Given this start, please prepare a checklist for participants to complete
Please prepare the checklist in BBCode format
***Certainly! Here's an iterative rocket design checklist in BBCode format, designed to help forum members systematically approach their rocket development. It builds upon the mission and constraint definitions you've already established.
Iterative Rocket Design Checklist
For LEO 300 km, Due East Launch from Equator, SSTO Mode
Phase 1: Mission and Core Requirements (Completed - Review and Confirm)
Objective Confirmation:
Target Orbit: LEO at 300 km
Launch Site: Equator, Due East
Mode: Single-Stage-To-Orbit (SSTO)
Option 1: Carbon Fuel (High Payload)
Payload Mass: 100,000 kg (50 metric tons)
Option 2: LH2 Fuel (High Payload)
Payload Mass: 100,000 kg (50 metric tons)
Option 3: LH2 Orbital RV (Low Payload + Vehicle becomes habitat)
Payload Mass: 1 metric ton (separate from vehicle)
Vehicle: Itself (implies reusability on orbit as a living space)
Phase 2: Initial Concept & Design (For Each Option)
Propulsion System Selection:
Fuel Type (Confirm based on option: Carbon, LH2)
Oxidizer Type (e.g., LOX, NTO, etc.)
Engine Cycle (e.g., staged combustion, gas generator, expander cycle)
Thrust-to-Weight Ratio (TWR) at Liftoff (initial estimate)
Specific Impulse (I sp ) in Vacuum (initial estimate)
Number of Engines (initial estimate)
Vehicle Architecture:
Body Diameter and Length (initial estimate)
Tank Configuration (e.g., common bulkhead, separate tanks)
Materials Selection (e.g., aluminum-lithium, carbon composites for tanks, structure)
Aerodynamic Profile (nose cone shape, fin presence/absence for SSTO)
Landing does not apply for SSTO design
Mass Budget Estimation (Iterative Process):
Structural Mass (tanks, interstage, engine mounts)
Engine Mass
Propellant Mass (based on ΔV requirements)
Payload Adapter/Fairing Mass
Avionics & Guidance, Navigation, and Control (GNC) Mass
Reaction Control System (RCS) Mass
Power System Mass
Thermal Protection System (TPS) Mass (omit for the present series)
Dry Mass (sum of all non-propellant mass)
Wet Mass (dry mass + propellant mass)
Trajectory & ΔV Calculations:
Initial ΔV requirement to reach LEO at 300 km from the equator (consider atmospheric drag, gravity losses)
ΔV for orbital insertion
ΔV for de-orbit/re-entry if necessary)
Margin for maneuvers and contingencies
Disposal if not used on orbit
Re-entry & Safe Disposal Considerations
Phase 3: Subsystem Deep Dive & Optimization (Iterative refinement)
Structural Analysis:
Stress and strain analysis for launch and re-entry loads
Buckling analysis for tanks and airframe
Material property refinement based on selected materials
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Aerodynamics:
Drag reduction techniques
Lift-to-Drag ratio optimization (not applicable in this series)
Stability and control analysis (center of gravity vs. center of pressure)
Thermal Management:
Engine cooling
Avionics cooling
Propellant boil-off (especially for LH2)
Re-entry not applicable
Guidance, Navigation, and Control (GNC):
Sensor selection (IMUs, GPS, star trackers)
Actuator selection (gimbaled engines, RCS thrusters)
Flight control algorithms
Propellant Management:
Tank pressurization system
Propellant feed system design
Ullage control
Power System:
Battery sizing (for launch, orbit, re-entry)
Solar panels/RTGs (if extended orbital operations)
Manufacturing & Assembly Considerations:
Feasibility of fabrication for chosen materials and designs
Assembly sequences and tooling requirements
Cost of manufacturing (initial estimates)
Phase 4: Risk Assessment & Trade Studies
Failure Mode, Effects, and Criticality Analysis (FMECA):
Identify potential failure points and their impact
Develop mitigation strategies
Cost Analysis:
Estimate development costs (R&D, prototyping, testing)
Estimate recurring costs (per launch, maintenance)
Perform cost-benefit analysis for each option
Performance vs. Cost Trade-offs:
Evaluate how changes to design impact performance and cost
Identify optimal balance points
Technology Readiness Level (TRL) Assessment:
Assess the maturity of critical technologies used in the design
Identify areas requiring further R&D
Phase 5: Refinement and Documentation
Detailed Design Review:
Present and discuss detailed designs with the group
Incorporate feedback
Simulation and Modeling:
Refine and run high-fidelity simulations for all flight phases
Use CFD (Computational Fluid Dynamics) for aerodynamic analysis
Use FEA (Finite Element Analysis) for structural integrity
Documentation:
Maintain thorough records of design decisions, calculations, and trade studies
Create a technical design document for each option
This checklist provides a structured approach to the iterative design process. Remember that each item on this list will likely involve multiple sub-tasks and continuous iteration as new information and challenges arise. Good luck to your forum members!
Are there any specific areas within this checklist you'd like to expand upon or modify?
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Thank you for this list, and for the very nice BBCode formatting! I expect it will upload to our elderly forum as is.
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You're very welcome! I'm glad the checklist and the BBCode formatting are exactly what you needed. I hope it helps your forum members significantly in their iterative rocket design discussions and that it uploads perfectly to your forum.Is there anything else I can assist you with today as you refine this project?
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For readers who are not yet members, and who might be interested in following this rocket design initiative, GW Johnson is working on a concept for offering a learning exercise around the SSTO topic.
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