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See Table: SMAD p. 305 for directory to Spacecraft design constraints. Space Environment. Radiation (SMAD 214) UV Ionizing TID SEU Disturbances (SMAD 366 - 367) Gravity Gradient Magnetic Solar Pressure Aerodynamic Self-disturbances. Vacuum ( various ) Outgassing TVC

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## Space Environment

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**See Table: SMAD p. 305 for directory to Spacecraft design**constraints Space Environment • Radiation (SMAD 214) • UV • Ionizing • TID • SEU • Disturbances (SMAD 366 - 367) • Gravity Gradient • Magnetic • Solar Pressure • Aerodynamic • Self-disturbances • Vacuum (various) • Outgassing TVC • Vacuum welding • Heat transfer • Drag (SMAD 144, 209) • Atomic Oxygen (SMAD 211) • Debris (SMAD 840) • Natural • Synthetic Engin 176**Space Environment - i**• Vacuum • Outgassing http://epims.gsfc.nasa.gov/og/ • Max TVC in % is specified - usually 0.5% • Problems with outgassing: • Destroys materials (brittle, flaking, delamination, adhesives, colors) • Re-condense on sensitive surfaces (especially cooled ones - optics) • Disturbance torques (usually minor) • Vacuum welding • Zero lubricant or contaminant to separate surfaces Galileo: Vacuum Welded Engin 176**Space Environment - ii**• Vacuum • Outgassing • Vacuum welding • Heat transfer (see future lecture but for now…) • Heat balance is radiative only (sun, earth, space) • => periodic inputs in LEO, t = 1/r2, • All collected solar energy goes somewhere (solar panels as radiators) • No fluid convection - even in pressurized regions • Fans are suspect and often don’t help • Lightweight structures and adhesives (eg RTV) are poor conductors Engin 176**Space Environment - iii**• Drag • 1/2 rv2 x A x Cd (calc @ 300 km = STS / Station)= 0.5 x 10-11 kg/m3 x (7500) 2 m2/s2 x 22 m2 x 2 = 0.001 kg m / s2 (Newton) to 0.01 N for 10x r => Acceleration = F/m ~ 10-4 N = 10-5 g and Orbit lifetime 10 to 50 days (note Cd > 1 and dependence on ballistic coefficient) • Solar Activity • Roughly factor 10 variation over solar cycle • Atomic Oxygen • Only a factor with propulsion (otherwise you’ll deorbit first) Engin 176**Space Environment - iv**• Debris • Natural • Synthetic • Rockets and spacecraft are commonly debris controlled but accidents do (rarely) happen • Arthur Clarke “end of LEO” prediction • Collision mechanics, the cheese cutter and tethers Engin 176**Space Environment - v**• Radiation • UV: materials degradation problem - optics, adhesives, organics • Ionizing • SEU: EDAC, fast processing, hard storage, watchdogs & rebooting • SEL: Current detection, watchdogs & power cycling • TID: Accumulated damage, mainly from protons - well characterized and quantified - 10 krad is standard part tolerance - how do laptops work in STS? (LEO, low I, shield, short duration) Engin 176**Space Environment - vi**• Disturbances (SMAD 366 - 367) • Gravity Gradient • Magnetic • Solar Pressure • Aerodynamic • Self-disturbances (eg bearing noise, magnetics, crew motion & mechanisms) Engin 176**Environmental Torques**Torque Drivers Torque Magnitude Key Equation Assumptions (Newton-meters) Aerodynamic Area, Length, 2.5 x 10-4 T= 1/2rAV2(cp-cg) h=300 km; A=1m2 Orbit Altitude cp-cg = 0.1m Gravity Inertia ∆ 3.0x10 -6 T=3(w)2 x ∆I 100 minute orbit Gradient Orbit Altitude ∆I = 1 kg - m2 Stray Magnetic Current Loops 5.0 x 10-6 T = Dipole X Bfield LEO Bfield Magnetics 1A-t-m2 current loop Solar Pressure Area vs. CG 4.5 x 10-7 T=4.5x10-6 xAx (cp-cg) 1 m2 @ 0.1m Leaks / Leak rate, location 2.0 x 10-4 T=m’Ve(L-Cg) 0.1 gm/s, Ve=20m/s Outgassing L - Cg = 0.1m Torque Bearings 1.0 x 10-8 (Empirical) Manufacturer’s Noise Lubrication Specification Thermal Materials 5.0 x 10-1 T=dX/dt2 x M x (∆Cg) dX/dt = 1 m/s in 10s Flex 5kg, ∆Cg =1m Meteor Meteor Mass 10-1 T=Mm x Vm = ∆Cg Mm = 10-6 kg, non-spinner Vm = 106 ∆Cg = 0.1m Engin 176**For Next Week (Feb.6)**• 7 - Radio & Comms • 8 - Thermal / Mechanical Design. FEA • 9 - Reliability • 10 - Digital & Software • 11 - Project Management Cost / Schedule • 12 - Getting Designs Done • 13 - Design Presentations • 1 - Introduction • 2 - Propulsion & ∆V • 5 - Attitude Control & instruments • 4 - Orbits & Orbit Determination • 3 - Launch Vehicles • Cost & scale observations • Piggyback vs. dedicated • Mission $ = 3xLaunch $ • The end is near? • AeroAstro SPORT • 6 - Power & Mechanisms • Reading • SMAD 18 • SMAD 17 (if you haven’t already) • TLOM 16: Launch sites Engin 176**Homework Questions Review**• 2 - Trip to Phobos: Space Environment • Assume cubic spacecraft of 2m characteristic length • What is P(impact) with object of dimension 1 mm3 or larger during 4 year interplanetary cruise? • What is Total Ionizing Dose (TID) for the cruise? • What is largest disturbance torque during cruise? What might be #2 and #3? • 1 - Propulsion system for Phobos Landing • Requirements: • Electricity (~100W) (optional) • 1 km/s ∆V - 4 years post launch • Small bursts for ACS en route+ soft landing • 100N deceleration burns (pulse or vernier) • Pick a Propulsion System • Justify via (1 or more of these) • Calcs • Tradeoffs vs. alternatives • Qualitative (bullets?) advantages • Sketch major elements of system • Tanks, pressurization, fluid mgt. • Valves, nozzles, electrical • Thrust Vector Control Engin 176**Design Work and Reading**• Design Milestones: • Form teams (3 - 4 members) • Mission Statement • RequirementsDefinition • Reading for lecture #3 • SMAD 18 • SMAD 17 (if you haven’t already) • TLOM 16: Launch sites For your calendar: Feb 26; 2:00 PMEN 194 S07 (Entrepreneurship) Engin 176

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