preliminary design review: loads, structures, and...

Preliminary Design Review:

Loads, Structures, and

Mechanisms

Michael Cunningham, Shimon Gewirtz, Rajesh

Yalamanchili, Thomas Noyes

Crew Cabin Structure

• Height of ~3.7m from heat shield to top of

the cone

• Internal pressure of 60 kPa

• Power, Propulsion, and Thermal systems

mass of 1853 kg

o However, all following calculations use a gross mass

of 4795 kg

• Chosen because it had the fewest external

structures previous to the following design

Choice of Shell Material

• Considered aluminum, high strength steel,

low strength steel, and titanium.

Material Density

(lb/in3)

σu/ρ

Aluminum 0.1 420

High strength

steel

0.29 390

Low strength

steel

0.28 204

Titanium 0.16 906

Choice of Shell Material

• All materials would be able to withstand the

stresses that they would undergo at a 0.1m wall

thickness with a reasonable safety factor

• Chose aluminum because the only

consideration left is mass, and aluminum is the

least massive

• Specifically, chose aluminum alloy 7075 T6

because it is the strongest of all aluminum

alloys

Load Analysis

Pressurization loads

• Cabin pressure of 60 kPa

• Max pressurization load occurs in a vaccum

• This max stress is 5.26 MPa

• Pressure is maximized along the edges and

at the bottom of the capsule

Pressure Loads

Docking Loads

• Assume a Δv of 0.10 m/s, a damping

coefficient of 2000 N-s/m and a Δt of 2.1131

sec based on research

• Use a damper to absorb the force

• This means there is a max force of 800 N

acting on the craft.

Vibrational Loads

• Used SolidWorks to compute resonant

frequencies

Mode Frequency (Hz)

1 138.04

2 224.1

3 242.62

4 242.72

5 244.04

Vibrational Load Mode 2

Vibrational Load Summary

• Mode 1 did not produce any meaningful

displacement

• Modes 4 and 5 produced large

displacements (27.78 mm and 33.10 mm

respectively) at high frequency and would

very likely result in complete structural failure

Earth Launch Acceleration Force

• Assumed max acceleration of 4.8 g's based on

notes

• Assumed Pressure force and propulsive thrust act

on the craft

• Max acceleration force is 87165 N

• Due to 25° half cone angle, this force breaks down

into:

o Axial force of 78998 N

o Lateral force of 36838 N

Deformation Due to Launch Force

Earth EDL Deceleration Force

• Assumed max deceleration of 10 g's because

research indicated that this is near the upper limit

for safe re-entry

• Based on research, assumed a temperature of 176

Celsius reaches the capsule

• Max deceleration force is 181594 N

• Assumed Pressure load, thermal load, and frictional

deceleration force all act on capsule

Earth EDL Deceleration Force

Velocity at Impact with Water

• Will deploy parachute at Mach 2

• Deploying at Mach 2 will give the craft

sufficient time to decelerate to terminal

velocity.

• Assumptions: o Radius of parachute = 8.08 m

o Cd = 0.62

o γ = -30 degrees

Velocity at impact with water

calculation

• Used following formulas:

o β = m/(Cd*A)

o V = sqrt(-2*g*β*sin(γ))

• Velocity at impact is 32.9698 m/s

• Assumed a max g load of 6.2 g's at

splashdown based on loads during Apollo 11

Stress at Impact with Water

Stress at Impact with Water

• Max stress felt by craft during splashdown is

6.05 MPa

• Stresses are concentrated along the bottom

of the craft

• Max displacement is under 0.3 mm

Basic Design of Crew

Propulsion Stage

Engine and Nozzle Design

• We determined that if we were to generate a

thrust of 1.5 MN we would have a nozzle

diameter of 0.9322 m^2 with an area ratio of

~46.68.

• In addition the diameters of the two paired

spherical fuel and oxidizer tanks are 1.57 m

and 1.61 m respectively. The tanks are

distributed around the nozzle with the nozzle

protruding from the center.

Landing Structure

Landing Gear Key Designations (in mm)

Landing Gear

• The landing structure is a truss with a

telescoping foot

• The foot is surrounded by honeycomb

material to attenuate landing loads and

bounce. It ensures that the maximum

acceleration the astronauts feel never

exceeds one-and-a-half earth gravities

Landing Gear • For our cross section we chose a bending

moment of inertia and generated a contour of

the radius ratios

Landing Gear

• The landing structure was analyzed for the

critical buckling load (Pcrit) in both the foot

and main compressive truss member.

• Pcrit for the foot = 1.6 MN

• Pcrit for the main truss member = 294 kN

Landing Gear Deployment

• The main leg member is stowed by having

joint C initially unattached and members AD

and BD bent along their lengths to retain

contact with point D in the retracted

configuration.

• To deploy member CD is pyrotechnically

actuated downward to lock node C in, where

node C is attached at point C with a ball

socket joint, and locked in to the node by the

tension in AD and BD.

Leg Cant Angle

• The main leg strut was canted at a 45o angle

based on the desire to keep the maximum truss

member force, Fcd= 63 kN (C) , lower down and

retain stability of the craft to withstand tipping.

This graph varies force

applied through cant

angles to get Feffective.

Fig. A gives forces

resultant from this.

Figure A

Member and Reaction Forces

(Truss) (For the worst case of landing on one leg)

Reactd = 2.5595e+004

Reactc = 5.3500e+004

Reactb = 1.3953e+004

Reacta = 1.3953e+004

Fab = 9.6002e+003

Fac = 3.6811e+004

Fad = 3.5896e+004

Fbc = 3.6811e+004

Fbd = 3.5896e+004

Fcd = 8.3231e+004

Safety Factor

• The landing gear calculations were done

with a 1.2 Factor of safety to ensure

conservative estimates for safety, while not

adding too much to the initial launch and

lunar launch masses.

Impact Attenuation

• We used honeycomb cylinders designed to

crush at a designated pressure,Pcrush= 800

psi, to control our rate of compression of the

honeycomb.

Impact Attenuation

• The honeycomb acts like a crumple zone to

extend the maximum time over which the

total impulse (Itotal= 62113 N-s) of impact is

integrated (tcrush=~0.25 s )

• This decreases the transmitted acceleration

(to Atransmit= 1.49*gearth), which is calculated

by dividing the transmitted force by the

mass, Mtot=16905 kg, of the craft.

References

http://www.faa.gov/other_visit/aviation_industry/designees_

delegations/designee_types/ame/media/Section%20III.4.

1.7%20Returning%20from%20Space.pdf

http://www.aerospaceweb.org/question/spacecraft/q0218.s

html

http://www.braeunig.us/space/comb-NM.htm

http://www.hexcel.com/Resources/DataSheets/Brochure-

Data-Sheets/Honeycomb_Attributes_and_Properties.pdf

References

http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19720

018253_1972018253.pdf

http://www.structsource.com/analysis/types/beam.htm

http://www.astronautix.com/craft/lmlggear.htm

http://www.hq.nasa.gov/alsj/alsj-LMdocs.html

http://history.nasa.gov/ap11fj/26day9-reentry.htm

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