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 Mode 3
Vibrational Load Mode 4
Vibrational Load Mode 5
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