FOV/Attitude

What Are We Imaging?• Lunar Atmosphere – interaction with S.W.

– What criteria should be applied?

• Magnetosheath – interaction with S.W.

– Primary driver for aspect selection criteria

• Heliosphere–interaction of neutral ISM with S.W.

– Sample region small

• X-ray Background

– A bonus, does not drive aspect selection criteria

Magnetosheath Model• Bowshock/Magnetosheath model of Spreiter,

Summers, & Alksne (1966)

• Scaled by nominal Solar Wind– ρ=2.0 cm-3

– v=400 km/s

• Exospheric Neutral Model– N(r)=25.0(10.0 RE/R)3 cm-3

• X-ray Emission proportional to– N(r)ρ(r,θ)[v(r,θ)2+3kBT(r,θ)/m]½

Magnetosheath Model• Distances/sizes to scale

• X-ray emission strength unnormalized

• MP~11.95RE

• BS~15.09RE

Baseline Instrument• Zenith telescope at selenographic (λ,µ)

=tilted telescope at some other (λ,µ)

• Incapable of pointing

• Field of view diameter of 10°

• Detector on at all times

Model FOV as f(t)Given (λ,µ)

Lunar Model• Lunar Orbit

– e=0.05490

– i=5.15° from the ecliptic

– a~384,400 km ~60RE

– dΩ/dt=19.35°/year (18.6 year precession period)

• Moon– Obliquity=6.87° from orbit, 1.54° from ecliptic

– ω=13.17635815 deg/day

Lunar ModelConsequences:

• Cis-lunar space is not scanned evenly

• LOS from moon can pass above/below the Earth-sun line

• LOS from moon has nearly constant ecliptic latitude

Lunar Model• Lunar Orbit

– e=0.05490

– i=5.15° from the ecliptic

– a~384,400 km ~60RE

– dΩ/dt=19.35°/year (18.6 year precession period)

• Moon– Obliquity=6.87° from orbit, 1.54° from ecliptic

– ω=13.17635815 deg/day

JPL DE405 ephemeris

IDL implementation by Markwardt

P.K.Seidelmann, IAU Working Group (2000)

LCaMD (JPL D-32296)

Lunar Model• Assumed telescope at lunar barycenter

• Width of MP-BS at subsolar point:3.14RE~3°

• Radius of bright subsolar “spot”: 8RE~7.5°

Model for (λ,µ)=(0°,0°)

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Model for (λ,µ)=(0°,0°)

Model for (λ,µ)=(0°,0°)

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10° FOV

Model for (λ,µ)=(0°,0°)

Over entire 18.6 year cycle

Model for (λ,µ)=(0°,0°)

Ecliptic Coordinates, FOV centers only

1.57°

Model for (λ,µ)=(0°,0°)

Ecliptic Coordinates, full FOV

Model for (λ,µ)=(0°,0°)

Galactic Coordinates, FOV centers only

Subsolar point appears uniformly along band

Model for (λ,µ)=(0°,0°)

Galactic Coordinates, entire FOV

Sel

enog

raph

ic L

atitu

de

Selenographic Longitude

“Conclusions”|µ|≥10° removes the

paths of both the sun and earth from the FOV

“Spot” remains in the FOV

MP-BS line on the edge of field

Tolerances are fairly tight!

Need sun/earth constraints.

Model for (λ,µ)=(10°,10°)

Galactic Coordinates, entire FOV