Custom Crew Exploration Vehicle• CONCEPT• Custom Crew Exploration Vehicle spacecraft structure idea based on Apollo Command Module and Orion Crew Exploration Vehicle.
Custom Crew Exploration Vehicle 32.5 deg 5.5m Image Source: NASA’s Exploration Systems Architecture Study (ESAS) Final Report documents
Advantages• The CEV pressurized volume is 30.6 m^3 .It has almost three times the internal volume as compared to the Apollo Command Module(10.4 m^3).• The CEV was designed for the EOR–LOR (Earth Orbit Rendezvous- Lunar Orbit Rendezvous ), and volume reduction helps to reduce mass to that required for the mission.• This configuration provides 29.4 m^3 of pressurized volume and 12–15 m^3 of habitable volume for the crew during transits between Earth and the Moon.• The CEV operates at a nominal internal pressure of 65.5 kPa with 30 percent oxygen composition for lunar missions, although the pressure vessel structure is designed for a maximum pressure of 101.3 kPa. Operating at this higher pressure allows the CEV to transport crew to the ISS without the use of an intermediate airlock.NOTE: The above mentioned advantages are based on “CEV Overview and Recommendations” by NASA (SOURCE).
Spacecraft charging(Structural Element-Al)• Atomic number: 13.0• Photoelectric current: 4.000E-05 A m-2• Secondary yield for 1 keV protons: 0.244• Energy for maximum yield: 230.000 keV• Maximum secondary yield for electrons: 0.970• Energy for maximum yield: 0.300 keV• SEE formula: Katz• R1: 154.0 Å• n1: 0.800• R2: 220.0 Å• n2: 1.760
EQUIPOT Environment parameter as a function of energy (For structure material Aluminium)
EQUIPOT current as a function of time (For structure material Aluminium)
EQUIPOT Electron emission yields (For structure material Aluminium)
Patch Material (Kapton)• Relative permittivity: 3.000• Thickness: 2.500E-05 m• Conductivity: 1.000E-15 ohm-1 m-1• Atomic number: 5.0• Photoelectric current: 2.000E-05 A m-2• Secondary yield for 1 keV protons: 0.455• Energy for maximum yield: 140.000 keV• Maximum secondary yield for electrons: 1.900• Energy for maximum yield: 0.200 keV• SEE formula: Katz• R1: 70.0 Å• n1: 0.600• R2: 300.0 Å• n2: 1.750
EQUIPOT Environment parameter as a function of energy (For Patch Material Kapton)
EQUIPOT current as a function of time (For Patch Material Kapton)
EQUIPOT Electron emission yields. (For Patch Material Kapton)
Kapton can be used as Protective Shielding• The primary technique for meteoroid protection is placement of multi-layer insulation (MLI) blankets on critical areas of the spacecraft, such as propellant and helium tanks. MLI blankets are composed of layers of a Kapton polyamide .• MLI effectiveness in preventing damage to critical spacecraft subsystems depends on the:• Blanket material, location, and number of layers.• Meteoroid mass, impact velocity, density, and angle of impact.• Impacted structure material, thickness, temperature, stress level, and the number and spacing of the plates composing the structure and the subsystem package.
Critical mass (mc) for a double-wall structure• Critical mass (mc) for a double-wall structure where a blanket shields the exterior of a spacecraft structure (such as a propellant tank) or component (such as a cable along a spacecraft boom).
Critical mass (mc) for a double-wall structure• Where:• S = spacing between blanket and tank wall (cm)• tb = thickness of tank wall (cm)• sy = yield stress for the tank wall (47,000 lb/in2)• rm = meteoroid mass density (2.5 g/cm3)• rt = blanket mass density (0.3 g/cm3)• V = impact velocity (km/s) NOTE:Equation demonstrates that the critical penetration mass will increase and the probability of failure will decrease with increased spacing between the blanket and the shielded surface.
One of several tears in the outer layer of Hubbles multi-layer insulation blanket along the direct Sun-exposed side of the telescope. Credit: NASA
Hubbles multi-layer insulation blanket• Sixteen thin layers of dimpled aluminized Kapton material are covered by an outer aluminized Teflon shell , all together measure less than one-tenth of an inch thick.
Flammability Testing• Mercury and Gemini spacecraft operated with pure oxygen atmospheres at all times.• Flammability testing consists of purposely short-circuiting or overloading wires at strategic points throughout the spacecraft to start fires.• Once the fires are started, engineers study their self-extinguishing characteristics.• The spacecraft is normally tested prior to launch at a positive internal pressure of about 16 pounds to assure spacecraft sealing integrity. That is to overcome the 14.7 pounds of normal sea level atmosphere pressing on the spacecraft at launch.• In orbit , a cabin pressure of from five to six pounds is maintained in contrast to the zero pressure of outer space.
Conclusion• Crew Exploration Vehicle(CEV) should light weight.• To increase the volume of CEV , the outer diameter of CEV may be increased.• Sidewall angles can be decreased further to increase the volume of CEV, but it should increase the weight of CEV.• It can accommodate 4 to 6 crew to ISS or MOON.(as CEV volume increased due to increase in diameter and decreases the sidewall angle.