Engin 176 Meeting #2: 1

Space EnvironmentVacuum (various)

Outgassing TVC

Vacuum welding

Heat transfer

Drag (SMAD 144, 209)

Atomic Oxygen (SMAD 211)

Debris (SMAD 840)

Natural

Synthetic

Radiation (SMAD 214)

UV

IonizingTID

SEU

Disturbances (SMAD 366 - 367)

Gravity Gradient

Magnetic

Solar Pressure

Aerodynamic

Self-disturbances

See Table: SMAD p. 305 for directory to Spacecraft design constraints

Engin 176 Meeting #2: 2

Space Environment - iVacuumOutgassing 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 weldingZero lubricant or contaminant to separate surfaces

Galil

eo:

Vacu

um

Weld

ed

Engin 176 Meeting #2: 3

Space Environment - iiVacuum

Outgassing

Vacuum welding

Heat transfer (see future lecture but for now…)

Heat balance is radiative only (sun, earth, space)

=> periodic inputs in LEO, = 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 Meeting #2: 4

Space Environment - iiiDrag

1/2 v2 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

=> 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 Meeting #2: 5

Space Environment - ivDebris

Natural

Synthetic

• Rockets and spacecraft are commonly debris controlledbut accidents do (rarely) happen

• Arthur Clarke “end of LEO” prediction

• Collision mechanics, the cheese cutter and tethers

Engin 176 Meeting #2: 6

Space Environment - vRadiation

UV: materials degradation problem - optics, adhesives, organics

IonizingSEU: 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 Meeting #2: 7

Space Environment - viDisturbances (SMAD 366 - 367)

Gravity Gradient

Magnetic

Solar Pressure

Aerodynamic

Self-disturbances (eg bearing noise, magnetics, crew motion & mechanisms)

Engin 176 Meeting #2: 8

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(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/sOutgassing 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

Environmental Torques

Meeting #2: 9Engin 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

Meeting #2: 10Engin 176

• 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

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?

Meeting #2: 11Engin 176

• Reading for lecture #3– SMAD 18– SMAD 17

(if you haven’t already)

– TLOM 16: Launch sites

Design Work and Reading

• Design Milestones:– Form teams

(3 - 4 members)– Mission Statement– Requirements

Definition

For your calendar: Feb 26; 2:00 PM EN 194 S07 (Entrepreneurship)