1 / 63

Loads, Structures, and Mechanisms Design Project

Loads, Structures, and Mechanisms Design Project. Team C4 Jason Burr, Rebecca Foust, Samantha Johnson, Kiran Patel, and Dennis Sanchez. Mission Objectives. Structural Analysis: Crew Vehicle Lunar Landing Vehicle Crew Vehicle Earth Launch Pressurization Loads Docking Loads

carver
Download Presentation

Loads, Structures, and Mechanisms Design Project

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Loads, Structures, and Mechanisms Design Project Team C4 Jason Burr, Rebecca Foust, Samantha Johnson, Kiran Patel, and Dennis Sanchez

  2. Mission Objectives • Structural Analysis: • Crew Vehicle • Lunar Landing Vehicle • Crew Vehicle • Earth Launch • Pressurization Loads • Docking Loads • Lunar Landing Loads • Earth EDL • Landing Vehicle • Basic design • Inert mass: 2199 kg • Propellant Mass (N2O4/MMH): 9914 kg • Payload: 12,110 kg • Landing Gear Analysis • Touchdown velocity 3 m/s vertical, 1.5 m/s horizontal

  3. Crew Capsule Selection • Jason’s crew capsule was selected because it has no external elements like radiators or solar arrays • It also has the highest mass margin, so we have the most mass available for our structural design

  4. Crew Vehicle

  5. Pressurization Stresses in a Conical Head “Analogous to the maximum stresses in the cylinder, there are maximum stresses in the conical head…However, in contrast to the cylinder, it is not possible to establish simple expressions for the three stress indexes…” Stresses in a Pressure Vessel With a Conical Head For this reason we will model our cone as a cylinder to find pressurization loads.

  6. Pressurization Loads • Cabin Pressure throughout mission = 59.77kPa • Hoop stress on cabin = 1.067 MPa • Longitudinal stress on cabin = 533 kPa • Hoop stress will cause the structure to fail before longitudinal stress can cause failure Total Pressurization Stress = 1.067 MPa Pressurization stress will occur at all times and is added into all total stress values

  7. Earth Launch • Use Falcon Heavy to launch to LEO • Can carry 53,000 kg to LEO • Max Thrust = 11,200 kN • Force at payload = 587 kN • Stress from thrust = 538 kPa • Random Vibrational Stress = 181 kPa

  8. Temperature Variation in Atmosphere

  9. Earth Launch • Thermal loading occurs as payload travels through different layers of the atmosphere. • Max temperature difference = 80 K • Thermal stress = 122.5 MPa Total Stress at Launch = 124.3 MPa

  10. Lunar Landing Loads • Maximum G force that our capsule will undergo is 1.125g • This is determined from the maximum G force the astronauts can undergo while standing • Force from Lunar Landing = 186 kN Total Lunar Stress = 1.24 MPa

  11. International Docking System Standard (IDSS) Maximum force exerted during seal closure Total Docking Stress = 1.16 MPa

  12. Earth EDL - Heat Shielding • AVCOAT ablative heat shield • Total Thermal Loading: 2597.9 MPa • Used on Apollo crew modules • Will diffuse heat into the air as opposed to the structure

  13. AVCOAT Shielding • Will withstand total thermal loading for EDL • Epoxy resin in fiberglass honeycomb matrix • Above – before EDL • Below – after EDL

  14. Earth EDL • Maximum G force that our capsule will undergo is 7.19g • Force during EDL = 493 kN • Thermal Stress = 122.5 MPa • This is from fluctuations in the atmosphere. The heat shield takes all of the thermal stress during EDL Total Stress during EDL = 126 MPa

  15. Safety Factors NASA Technical Standard: STRUCTURAL DESIGN AND TEST FACTORS OF SAFETY FOR SPACEFLIGHT HARDWARE Need a safety factor of at least 1.25 to fall under NASA standards

  16. Highest Stress on Lander • During EDL the stress reaches 126 MPa • Based off of the yield stress of different materials, aluminum will be the best material for our structure • With a safety factor of 1.25 the stress is still well under the yield strength of aluminum, 386 MPa

  17. Yield Stress vs. Density

  18. Total Stresses MOS is based off of case of maximum load

  19. Landing vehicle

  20. Lander Strut Configurations • Three Distinct Design Possibilities • Rigid Structure • Spring and Damper Attenuation • One-Time Energy Dissipation

  21. Lander Strut - Rigid Structure • Advantages • Simple analysis • Re-usable • Easy deployment • Disadvantages • Large loads • “Crash” landing scenario • Large magnitude accelerations • Potentially fatal to astronauts

  22. Lander Strut – Spring and Damper • Advantages • Re-usable • Adjustable maximum accelerations • Disadvantages • Complicated analysis • Challenging deployment technique • Springs act to move the struts to their equilibrium positions

  23. Lander Strut – Energy Dissipation • Advantages • Relatively simple analysis • Easy deployment • Comparable to rigid strut • Low accelerations • Disadvantages • One-time use

  24. Design Choice – Energy Dissipation • Honeycomb Energy Dissipation • Wide range of strengths available • Constant force during crushing • Reliable energy dissipation

  25. Honeycomb – Energy Dissipation • Energy Conservation • Kinetic Energy to Crushing Work • Lcrush is the total length of Honeycomb required to dissipate all of the energy from landing • Acceleration increases with decreasing stroke length

  26. Honeycomb – Acceleration Limits • Maximum Acceleration – 1.125g • Limit imposed on elevators • Provides low enough acceleration that astronauts can remain standing in lunar descent • Maximum Stroke Length – 1.75 m • Limit to easily store struts in descent stage • Assume all energy is dissipated in a single strut (worst case) • Results in minimum acceleration of 0.328g

  27. Honeycomb – Strength Selection • Various Honeycombs of different strengths and densities • Performing the worst case landing, we can determine the Honeycomb mass and diameter to meet our constraints

  28. Strength Selection Continued • Optimum Honeycomb:p=8.1 lb/ft3Pcrush=750psi • Note: All designs from this point on use this Honeycomb

  29. Honeycomb – Landing Scenarios • Three likely scenarios to arise are: • Landing on a single strut • Landing on extremely uneven surfaces (rock) • Landing on a constant incline • Assumed smooth planar surface • Landing on a flat surface • Specific type of incline

  30. Case 1: Uneven Landing

  31. Landing Scenario – Single Strut • Worst case – all energy dissipation is in a single strut • As before, the length of the crushed section is:

  32. Case 2: Sloped Landing

  33. Landing Scenario – Sloped Landing • More complicated • Total length required for energy dissipation remains the same • Maximum crushing occurs in the “leading strut” of the lander, minimum in the “trailing” one Assumptions: • Lander remains horizontal to the surface during descent • Maximum landing slope is determined where the trailing leg does not need to absorb any additional energy

  34. Sloped Landing – First Pass *Maximum crushing occurs in the “leading strut”. It never reaches the maximum crush length because the two struts between the leading and trailing one absorb some of the energy. Note: assume the landermust make contact with all four struts – any other configuration is unstable! (This is the cause of the curves ending)

  35. Sloped Landing – Refined Pass • Considering only the data points that maximize the slope at any given acceleration, we can produce the following plot: • Possible landing slope is maximized at the lowest acceleration, 8.07ᵒ and 0.328g’s, respectively

  36. Case 3: Zero-Slope Landing

  37. Landing Scenario – Flat Surface • Subset of the previous scenario where the slope is equal to 0 • Energy is dissipated evenly between the four struts – thus the crush length is as well

  38. Summary of Landing Crush Lengths The following table represents the worst crush lengths for the three main landing scenarios: *Honeycomb Mass= 2.62 kg/strut Where: a = 0.378g’s Pcrush = 5.17 kPaAcrush= 0.011 m2 m = 16905 kg Lcrush = 1.75 m ρcrush= 130 kg/m3

  39. Landing Strut Analysis • Source of loads on the landing struts: • Earth launch loads • Lunar landing loads • Thermal loads • Landing struts are 6 m long before crushing • Minimum of 4.25 m after crushing • Model the struts as hollow tubes • Design varied to minimized margin of safety • Neglect joint forces

  40. Strut Analysis – Earth Launch • Stress due to launch forces and moments • Iteratively solved to minimized mass with: ax = 8.5g ay = 5.8g az = 4.85g L = 6 m

  41. Strut Analysis – Lunar Landing • Stress due to landing force and moment • Assumed the landing force is purely axial and purely rotational • Physically impossible to occur at once, but creates an extreme-upper bound on loading • Iteratively solved to minimized mass with: a = 0.328g L = 6 m

  42. Strut Analysis - Thermal • Rapidly changing temperatures while during Earth launch • Greatest temperature variation ~80 K • Iteratively solved to minimized mass with: ΔT = 80 K L = 6 m

  43. Strut Analysis – Combined Loading • Consider Earth and thermal loading combined, as well as lunar landing and thermal loading • All cases use factors of safety (SF) of 1.4 • Iteratively design with various radii to minimize mass and the margin of safety or Depending on which is the limiting (lower) value

  44. Strut Analysis – Analyzed Materials • Consider the following metals for our struts: • These materials are used with the preceding formulas to find the optimum strut design that • Minimizes strut mass • Keeps an external strut diameter below 20 cm • Has a MoS= 0

  45. Strut Analysis – Optimization Titanium appears to be the best metal, but…

  46. Strut Analysis – Optimization Cont. When we consider the constraint of less than 20 cm (external) diameter, we see that Steel 300M at this point is 68.24 kg/strut, whereas titanium at an external diameter of 20 cm is 72.78 kg/strut

  47. Strut Analysis – Summary • Landing Strut • Total length 6 m • Outer radius 10 cm • Inner radius 9.5 cm • Material Steel 300M • MoS 0 • Strut Mass 68.24 kg/strut • Honeycomb • Max crush length 1.75 m • Min crush length 0 m • Honeycomb Mass 2.62 kg/strut

  48. Strut Storage and Articulation • The landing struts are divided into three 2-meter segments: two hollow tubes and one honeycomb piston • During launch, the three segments are stored side by side as shown here • Rotary actuators at the joints align the segments and lock them into place for lunar descent

  49. Actuators • The landing struts will be stored folded into 3 sections during launch • Before lunar descent, the landing struts will deploy using the space-rated rotary actuator shown below • This actuator was chosen because it can produce high torque at low speeds. Lower speeds will reduce vibrational loads on the spacecraft

  50. Supplemental Ladder • The honeycomb piston is designed for worst-case scenario loading, so a best-case load would result in significantly less compression • Because of this, a supplemental ladder is attached to the end of the second segment on the ladder strut • The ladder will deploy in all scenarios, but will only be critical for light load cases where the astronauts would otherwise be unable to perform EVAs

More Related