structural design practices - university of...

Structural Design PracticesENAE 483/788D - Principles of Space Systems Design

U N I V E R S I T Y O FMARYLAND

Structural Design Practices• Payload interfaces to launch vehicles• Examples of structural design approaches from

past space vehicles• Examples of recent structural concepts for

Constellation vehicles and other human lunar programs

© 2014 David L. Akin - All rights reservedhttp://spacecraft.ssl.umd.edu

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Shuttle Payload Restraint Configurations

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3 or 5 points of support. Orthogonal directions of support, doubled up in the case of Fx / Fz. 3 legged stool example



Orbiter Active Latches – Deployable Payloads

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Active latches used for payloads meant to be deployed from SS. Notice surrounding support structures and placement, like longeron (not solid piece of metal, but reinforced where it’s needed.) Trunion sticking off of payload fits into the latch hook.



Orbiter Passive Latches – Non-deployable Payloads

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Passive latches for fixed payloads that aren’t going to be deployed. Bridges are like reinforced hard points for attachments. Again, notice trunion coming off payload. Which directions is this latch constraining motion in?



Atlas V Payload Fairing Configuration

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Configurations of some tried and true attachment strategies. From last time, launch loads are likely to be the limiting cases for your S/C. So, protect it from these. Fairings protect from aerodynamic/acoustic loads. Payload adapter contains network of struts to alleviate random vibe and shock from staging events. Notice they’re at an angle (not straight up) because random vibe occurs along all axes. BTW, your CAD solid models should be at least this detailed, probably more.



Delta IV Bolted Payload Attach Fitting

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Actual attachments come in a few flavors: bolted (Here 18 bolts with pads/washers) Metal to metal contact is BAD. Why? No damping. Good example of the kinds of design drawings you can include for PDR/CDR.



Delta IV Pyro Payload Attach Fitting

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Pyro bolts – much more reliable than mechanical mechanisms. Only 4 of them, fewer chances of getting stuck. Notice this negotiable payload envelope. Could be used for storing lander legs, antennae, etc. Problem with pyrotechnic attachments? BOOM -> explosive, high acceleration/shock during separation, could damage sensitive equipment. Can find loads from pyro attachments in reference books.



Delta IV Marman Band PAF

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So, what to do about sensitive payloads? Clamp with a Marman band. Basically seat two smooth faces next to one another, wrap a band around them and clamp down from outside. -> Release the clamp, gently separate the two pieces. All of these attachment systems usually aided by spring-loaded devices to push pieces away from each other. Marman band invented in 1930’s by Zeppo Marx, 1/5 Marx Brothers (Groucho). Used by US military to tie down cargo, like atomic bombs. He made millions.



Orion/CEV Payload Fairing

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What kind of release system is shown here? Why would you use pyro bolts in this case?



Saturn V First Stage (S-IC) Cutaway

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Notice a few things. Oxidizer tank on top, fuel on bottom. Thin-walled pressure vessels have hoop stress -> so, circumferential reinforcement strengthens the tanks. Why on inside instead of outside? SI-C produced ~7.5 million lb thrust, essentially applied to a stack of tin cans. Stringers run longitudinally to add strength in this direction. “Orthogrid” – ortho meaning different in each direction. Cruciform thrust structure (huge beams to mount the engines to) SI-C produced ~7.5 million lb thrust, essentially applied to a stack of tin cans. Stringers run longitudinally to add strength in this direction. “Orthogrid” – ortho meaning different in each direction. Cruciform thrust structure (huge beams to mount the engines to)



Saturn V S-IC Intertank Fairing

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SI-C produced ~7.5 million lb thrust, essentially applied to a stack of tin cans. Stringers run longitudinally to add strength in this direction. Intertank fairing didn’t contain pressure, just needed strength to withstand thrust force.



Saturn V S-IC Intertank Assembly

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Having said that, part of assembly is done horizontally, so pieces had to withstand the crush from their own weight when laying sideways. Recall last lecture on design loads… maybe assembly loads is a critical issue in your design?



Saturn V S-IC Ground Handling

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Why not assemble the whole rocket on it’s side? Because you have to point it up eventually. What happens when you start to do this? BENDING MOMENT. M = F*rcostheta -> right when you remove the horizontal support of the floor, maximum bending moment is applied and you might buckle the structure. So, reduce r by assembling shorter pieces horizontally, then stack them.



Saturn V S-II Stage Stacking

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Then stack them.



N-1 Ground Handling

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Or… don’t remove the support while you’re lifting it. Russia’s answer to the Saturn V (or is it the other way around?) Can see fuel tank domes connected by these strut rings.



Buran Ground Handling

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Buran is Russian version of SS. Sticking with the horizontal assembly. External fuel tank has to support Buran’s weight here, whereas external fuel tank wasn’t designed (strengthened, made heavier) by this assembly method, relied on vertical assembly. Buran flew, btw, remote control.



Saturn V S-II LOX Tank Cutaway

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LOX tank detail. Two “hemispherical” halves mated and welded. Notice again the hoop and longitudinal ribs/stringers. INTERNAL, could double as slosh baffles to prevent contents from getting into a harmonic motion



Saturn V S-II Stage Engine Cluster

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Detail showing placement of pressure tanks, fuel lines



Saturn V S-II Thrust Structure Detail

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And the beefy cruciform thrust structure. Engines pointing upwards here. Notice how vertical loads are resolved through a few different paths. X structure, stronger in the thrust direction Center post attached to base of fuel tank, sending forces up through it. Radial members connecting center to outboard structure.



Saturn V S-II Interstage Jettison

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Pretty picture. Also notice the glowing rings on engines. Again, serving a structural function to contain pressure. (Also thermal, preheating the fuel, cooling the engine)



N-1 Launch Vehicle Interstages

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Struts on interstage adapters



Saturn V S-IVB/J-2 Thrust Structure

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Single engine, thrust forces resolved directly into the tanks



Mercury Spacecraft Layout

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Structural considerations when people are involved. Mercury didn’t have much in terms of comfort, basically in a sardine can. One important addition (problem) with humans is that they want WINDOWS, which are basically structural voids. So, make them small (think commercial aircraft).



Mercury Spacecraft Assembly

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Assembly forces not as great, simply because the weight was lower.



Gemini Spacecraft Equipment Arrangement

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Bigger, more capability. Also notice where support equipment is located – Outside of the crew area. (Control electronics in capsule, the only piece that persists the whole flight) .



Gemini Spacecraft Layout

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Support equipment located in the spaces too small to be occupied/useful by astronauts. I like the “Rockets and Pyrotechnics” right behind the astronaut’s heads. (Ejection seats)



Landing Gear - External Equipment Bays

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Can see this alternative landing method hanging in the Udvar-Hazy annex of the Air & Space museum. Eventually decided against it because landing on solid ground requires more energy absorbing equipment, heavier.



Soyuz Spacecraft Design

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Apollo Spacecraft Components

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Apollo spacecraft. For your reference later



Lunar Module Overall Configuration

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Strange shape used to cover most components from lunar dust environment. Also notice the RCS engine deflectors to keep exhaust from impinging on LM structure



Lunar Module Ascent Stage Structure

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Core structure, thin walls with support ribs. Also notice: windows. Angled for visibility.



Lunar Module Ascent Stage Structure

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Secondary structures



Lunar Module Descent Stage Structure

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Primary structure of LM descent stage. Attachments to ascent stage. Outrigger assembly is reminiscent of interstage struts. -> Bridge truss design could give good ideas, static analysis/optimization is pretty straightforward, given some known loads.



Lunar Module Descent Stage Structures

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Notice landing leg angles and outrigger positions -> stability, don’t want to tip over if you land with some horizontal velocity. Can calculate the max horizontal velocity that’s safe, given lunar gravity and COM of LM



Soviet Lunar Lander Concepts

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Vertical landing legs – What’s wrong with this configuration? Any side (shear) forces won’t be resolved in that direction



LK Lunar Landing Vehicle

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What’s wrong with this? Big window = heavy



LK Spacecraft on Moon

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But it looks cool



Project Constellation Structural Examples

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CLV Upper Stage Components

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Again, similar components and arrangement. Don’t reinvent the wheel (but don’t blindly copy, either)



CLV Upper Stage Structural Elements

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Each of these components are subjected to some of the same loads (thrust, random vibe) but some experience extra/different loads (Tank pressure). Must be designed as such.



Delta IV Heavy Configuration

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Atlas V 401 Configuration

http://www.spaceflight101.com/launch-vehicle-library.html

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Design Overview - CEV Crew Module

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Details of CEV/MPCV/Orion capsule



Pressurized Module Structural Details

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With explanations about structural reasons and orthogrid skin panel details.



Service Module Structural Design

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Launch Vehicle Adapter Structure

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FEA Load Cases

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Excellent example of piece parts analysis for entire mission profile. Could even include assembly/manufacturing loads, but maybe on a separate chart.



Crew Module FEA Sample Results

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Examples of FEM cases you can run with a high-fidelity CAD model



Descent Assisted, Split Habitat (DASH)

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DASH Lander Structural Components

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DASH Engine Support Truss Concepts

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Example of kinds of trade studies you should go through during your structural design iterations



Apollo Lunar Roving Vehicle

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LRV Suspension

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LRV Steering Assembly

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TURTLE Lunar Rover (2007)

Design modifications and rendering by Terrabuilder, Inc.

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