Bit of Administration ….Bit of Administration ….

• Lab 2Lab 2– New observation dates: March 22 - April 5New observation dates: March 22 - April 5

• No need to duplicate observations in hand!No need to duplicate observations in hand!

– New due date: April 9 at my officeNew due date: April 9 at my office

• HomeworkHomework

• ReadingReading– BSNV pp. 153 - 168BSNV pp. 153 - 168

• No office hours today No office hours today – Feel free to e-mail for later in weekFeel free to e-mail for later in week

AstronauticsAstronautics

• Interplanetary TravelInterplanetary Travel

• The Central Concept …The Central Concept …

The paths of interplanetary spacecraft areThe paths of interplanetary spacecraft are simply orbits around the Sun …simply orbits around the Sun …

And the spacecraft obey the same physical lawsAnd the spacecraft obey the same physical laws as do planets.as do planets.

AstronauticsAstronautics

• Transfer Orbit = Minimum Launch EnergyTransfer Orbit = Minimum Launch Energy

• Launch in the direction of motion of the launch platform.Launch in the direction of motion of the launch platform.

• Arrive at destination at aphelion ( for outer target) or Arrive at destination at aphelion ( for outer target) or perihelion (for inner target) of spacecraft orbit.perihelion (for inner target) of spacecraft orbit.

(Aphelion - point of orbit most distant from Sun(Aphelion - point of orbit most distant from Sun Perihelion - point of orbit closest to Sun)Perihelion - point of orbit closest to Sun)

Transfer Orbit for the MoonTransfer Orbit for the Moon

AstronauticsAstronautics

• Transfer Orbit = Minimum Launch EnergyTransfer Orbit = Minimum Launch Energy

• Launch in the direction of motion of the launch platform.Launch in the direction of motion of the launch platform.

• Arrive at destination at aphelion ( for outer target) or Arrive at destination at aphelion ( for outer target) or perihelion (for inner target) of spacecraft orbit.perihelion (for inner target) of spacecraft orbit.

(Aphelion - point of orbit most distant from Sun(Aphelion - point of orbit most distant from Sun Perihelion - point of orbit closest to Sun)Perihelion - point of orbit closest to Sun)

•Advantages - Fuel efficiencyAdvantages - Fuel efficiency

•Disadvantages - Long travel timeDisadvantages - Long travel time

AstronauticsAstronautics

• Gravity BoostsGravity Boosts

• Gain in energy due to gravitational “slingshot” aroundGain in energy due to gravitational “slingshot” around a more massive body.a more massive body.

• Note: More massive body loses energy, but in case of Note: More massive body loses energy, but in case of planet and spacecraft this is not a problem!planet and spacecraft this is not a problem!

AstronauticsAstronautics• Gravity BoostsGravity Boosts

In frame of JupiterIn frame of Jupiter

In frame of Solar SystemIn frame of Solar System

but Jupiter is moving …but Jupiter is moving …

AstronauticsAstronautics• Gravity Boosts - NASA missionsGravity Boosts - NASA missions

The Physics of LightThe Physics of Light• Light as a Wave = Light as a Wave = Electromagnetic RadiationElectromagnetic Radiation

• Wavelength (Wavelength () has units of length) has units of length• Frequency (Frequency () - number of crests passing per second) - number of crests passing per second - has units of cycles per second, or Hertz- has units of cycles per second, or Hertz• Speed - for light, c = 3x10Speed - for light, c = 3x1055 km/sec km/sec

Wavelength

3 x 105 km/sec

The Physics of LightThe Physics of Light• Light as a Wave = Light as a Wave = Electromagnetic RadiationElectromagnetic Radiation

• Wavelength (Wavelength () has units of length) has units of length• Frequency (Frequency () - number of crests per second) - number of crests per second• Speed - for light, c = 3x10Speed - for light, c = 3x1055 km/sec km/sec

Large wavelengthLarge wavelengthSmall frequencySmall frequency

Small wavelengthSmall wavelengthLarge frequencyLarge frequency

The Physics of LightThe Physics of Light

€

=c

λ

• Light as a Wave = Light as a Wave = Electromagnetic RadiationElectromagnetic Radiation

• Wavelength (Wavelength () has units of length) has units of length• Frequency (Frequency () - number of crests passing per second) - number of crests passing per second - has units of cycles per second, or Hertz- has units of cycles per second, or Hertz• Speed - for light, c = 3x10Speed - for light, c = 3x1055 km/sec km/sec

The Physics of LightThe Physics of Light

• Electromagnetic Electromagnetic SpectrumSpectrum

1 km = 1000 m1 km = 1000 m1 m1 m1 mm = 0.001 m = 101 mm = 0.001 m = 10-3-3 m m1 1 m = 10m = 10-6-6 m (“micron”) m (“micron”)1 nm = 101 nm = 10-9-9 m (nanometer) m (nanometer)

The Physics of LightThe Physics of Light• Electromagnetic RadiationElectromagnetic Radiation

• Light acts as an electric forceLight acts as an electric force

• Light acts as a magnetic forceLight acts as a magnetic force

- - - - - - - - - - --- -

S

N

N

SS

N

S

N

N

S

N

S

S

N

S

N

S

N

N

S

N

S

N

S

The Physics of LightThe Physics of Light• Electromagnetic RadiationElectromagnetic Radiation

--

-

-

-

-

-

-

-

AntennaAntenna

The Physics of LightThe Physics of Light• Doppler ShiftDoppler Shift

The Physics of LightThe Physics of Light

• Doppler ShiftDoppler Shift

• Source moving toward observer orSource moving toward observer or observer moving toward light source observer moving toward light source

Shorter WavelengthShorter Wavelength Higher FrequencyHigher Frequency BlueshiftBlueshift

• Light source moving away from observer orLight source moving away from observer or observer moving away from light source observer moving away from light source

Longer WavelengthLonger Wavelength Lower FrequencyLower Frequency RedshiftRedshift

The Physics of LightThe Physics of Light

• Doppler ShiftDoppler Shift

• Source across observer’s line of sight Source across observer’s line of sight

Same Wavelength as emittedSame Wavelength as emitted Same Frequency as emittedSame Frequency as emitted No ShiftNo Shift

The Physics of LightThe Physics of Light

• Doppler ShiftDoppler Shift

€

Δrest

=v

c

v = velocity of light source or observer (+ => toward each other)v = velocity of light source or observer (+ => toward each other) = rest wavelength= rest wavelengthΔΔ = change (shift) in wavelength= change (shift) in wavelengthc = 3 x 10c = 3 x 1055 km/sec km/sec