AERO 4730 Space Mission Design               
 

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AERO 4740

Space Mission Design Lecture 6

What's happening in space:

 

Check out the new Space Link Page at Space Links Page

This link shows the ISS passing the Sun - a harsh environment???

http://science.nasa.gov/spaceweather/swpod2003/22aug03/Stalder1.avi

The Space Environment

 Read chapter 3 of text

Environmental effects or hazards in space:  Microgravity, vacuum, plasma, radiation, thermal, non-ionized atoms (atomic oxygen), MMOD, self contamination

Microgravity

•Effects

–< 10-6 g

–Physiological

–Loads

–Thermal (convection)

•Design considerations

–Human factors

–Launch loads vs on orbit

–Fluid flow

•Minimizing effects

–Artificial gravity

–Exercise equipment

–Pharmaceuticals

–On orbit assembly

–Pumps, fans, capillary action

 Vacuum

•Effects

–10-11 atm at 400 km

–Thermal (convection, conduction)

–Solar ultraviolet degradation

–Contamination

–Cold welding

•Design considerations

–Materials

–Operations

–Margins

Vacuum – Solar UV

•0.3 ΅m wavelength radiation

•Normally atmosphere absorbs it

•Severs molecular bonds

•Surface degradation

–Reduces emissivity → Temperature increase

•Sunburn

•Minimizing effects

–Material selection

–Coatings

–Plan margins (power, thermal)

–Window filters

Vacuum - Contamination

•Molecular

•Particulate

•Minimizing effects

–Material selection

–Bake out, allow time for outgassing

–Choose venting/thruster directions wisely

–Use protective covers/deflectors

Nonionized atoms

•Effects

–Atomic Oxygen chemical erosion

–Drag

–Sputtering physical erosion

–Glow

•Design Considerations

–Material susceptibility to AO and molecular impact erosion

–Sensor degradation

–Altitude

 Nonionized atoms – atomic oxygen

•Chemically reactive

•AO flux (Ф) and experimentally determined reaction efficiency (RE) determine rate

•Minimizing effects

–Material selection   Aluminum is very good RE=0

–Plan margins

–Coatings

Nonionized atoms - Drag

•Effects

–Orbital decay

–Mass (fuel) and propulsion system driver

•Design considerations

–Drag coefficient

–Orientation

–Altitude

–Solar cycle

Nonionized atoms - Drag

•Minimizing effects

–Go higher

–Use most aerodynamic orientation

 Plasma

•Most of the universe is plasma – charged particles with low kinetic energy (eV–keV)

•Spacecraft surfaces become charged to high potential due to high velocity

•Normally use negative ground

Plasma - Effects

•Arcing

–Surface damage

–Dielectric breakdown

–EMI

•Floating potential changes

–LEO w/o solar arrays ~ 1 V

–LEO w/ solar arrays `function of array voltage

–GEO ~kV potential possible

Plasma - Design Considerations

•Balance surface currents

–Use surface coatings

–Use plasma contactors

•Design in uniform surface conductivity

•Avoid electrostatic discharge

–Tie to common ground

–Shield and filter electronics

–Use thick, conductive surfaces

 Radiation

•High energy (>MeV) objects that deposit their energy in materials

–Particles (electrons, protons, neutrons)

–Electromagnetic (gamma, x-ray, UV, etc)

•Bad – can’t see, touch, predict or define exactly (material dependent)

•Hard to design for or protect

Radiation - Sources

•Solar particle events

–Sun coronal mass ejections

–Highest during solar max (11 year solar cycle peak)

–Very energetic so hard to shield against

•Galactic cosmic rays

–Highly energetic, mostly H and He ions

–Reduced during solar max

•Secondary radiation

Van Allen belts

•Doughnuts of trapped radiation

•Peak electron flux ~ 6000 km and 25000 km

•Peak proton flux ~ 16000 km

Radiation – South Atlantic Anomaly

•Charged particle flux up to 100 times average

•As low as 200 km

Radiation - Effects

•Deposits energy

•Solar cells

•Mechanical, electrical and thermal properties

•SPEs can harm humans, degrade sensors and materials, limit communications

Radiation – Quantifying effects

•Depends on type radiation and material

•Absorbed dose – deposited radiation energy / mass of irradiated material

                                    Gray = 1 J/kg

                                    Rad = .01 J/kg

•Relative biological effectiveness

–Quality factor

•NASA uses 2.5 for LEO during solar max

–Depends on type radiation

            Sievert = Gy x Q

            Rem = Rad x Q

Radiation – Design considerations

•Define environment with tools/computer programs

•Estimate part failure/ upset with tools

•Shielding

–Base on mission and analysis of environment

–Dependent on energy level – one material can’t do it all

–Liquid Hydrogen best, water is very good

–Upmass drives ability to shield

•Minimize effects through

–Materials/ system component selection

–Redundancy

–Error detection and correction

More than anyone ever wanted to know about radiation:          http://www.umich.edu/%7Eradinfo/introduction/natural.html

 Micrometeoroids and orbital debris

•Micrometeoroids – natural matter

•20,000 tons per year reach Earth

•Orbital debris – from other spacecraft

•8500 objects bigger than baseball tracked by the Air Force Space Command

•Estimate 40,000 golf ball sized and millions smaller objects

MMOD - Effects

•High velocity impacts

•Penetration of pressurized volumes, external systems or devices  Degradation of external surfaces, sensors or windows 

MMOD - Design Considerations

•Materials

–ISS – aluminum alloy 

–Spacehab - Kevlar material 

•Shielding

•Choice of orbital altitude 

•External systems and window placement

•Vehicle orientation

 Thermal

•It’s hot

•It’s cold

•Outside

–radiation primary heat transfer method

–Severe thermal differences and cycles

•Inside

–Conduction, convection, radiation

•Characterized by

–Direct solar radiation

–Earth reflected radiation (albedo)

–Earth IR

–Radiation to deep space

•Function of surface material, location, area

Thermal - Design Considerations

•Temperature sensitive elements:

–Propellant, water, tanks, lines, electronics, crew compartment, hydraulics, structure

•Maintain suitable temperature range

–Outside: material limits, thermal expansion, liquid freezing/boiling point

–Inside: Atmospheric temp: 18–28ΊC,  RH: 25-70%, surface temp: 4-45ΊC

•Affect mass, power, volume (Table 16-7)

Thermal – Minimize effects

•Reject heat from electronics, systems, crew

•Control inside temperature and humidity

•Heat walls to avoid condensation

•Insulate coolant lines to avoid condensation

•Passive thermal control

–Materials, insulation, coatings

•Active thermal control

–Heaters, Heat sinks, radiators, cold plates, air flow, shades, Heat pumps, heat exchangers

–Working fluids, noise

Self induced environment

•Contamination/degradation

–Off-gassing

–Thruster firings

–Fluid dumps

•Noise

•Effects

–Reduced effectiveness of sensors/ solar arrays, radiators

–Obscured windows

–Human performance/hearing loss

•Design Considerations

–Materials

–Coatings

–Thrusters

•Minimizing effects

–Locate/orient thrusters properly

–Locate/orient  thrusters properly

–Inert propellants

–Use closed cycles for fluids

–Design properly/insulate/dampen noise producers

 

A generic space information and news link:  http://space.com