T. J. Stubbs, D. A. Glenar, A. P. Jordan, Y. Wang, R. R. Vondrak, M. R. Collier, W. M. Farrell,

M. I. Zimmerman, N. A. Schwadron, and H. E. Spence

Annual Meeting of the Lunar Exploration Analysis Group NASA Goddard Space Flight Center, October 22–24, 2012.

Interplanetary Conditions during the Apollo Missions: Implications for the State of

the Lunar Environment

Motivation and Objectives

Obtain a comprehensive overview of the interplanetary conditions during the Apollo missions, and assess the possible effects on the state of the lunar environment.

Determine how the conditions during the Apollo era, and the Apollo

missions, compare with typical conditions during the Space Age.

Determine the implications for the conditions experienced on the lunar surface by the Apollo

astronauts, and the scientific observations made during the missions.

The Dynamically Coupled Lunar Environment Solar Energetic Particles (SEPs)

Solar wind Plasma

Solar UV & X-rays

Galactic Cosmic Rays (GCRs)

Plas

ma

Shea

th Surface

Electric Field

+ + + + + + + + +

− −

−

−

− − −

− −

Exos

pher

e

Ar He Na K

H2O Iono

sphe

re Ar+

He+ Na+

K+

O+

Cha

rged

Dus

t

+

+

−

Magnetic Anomalies

Coronal Mass Ejections (CMEs)

Hot & Tenuous Magnetospheric

Plasmas

Meteoritic Flux

Outgassing Ejecta Weathering Sputtering Topography Composition

Solar Flares

Spacecraft and Instrumentation Used OMNIWeb data: 27-day, 1-day and hour averages of interplanetary conditions at 1 AU stitched together from 25 missions and data centers (King and Papitashvili, 2005).

Missions used during Apollo era (1968–1972): IMP 4–8, AIMP 1 & 2, HEOS 1 & 2, OGO5, LANL VELA.

F10.7 index Daily proxy for solar ultraviolet (UV) intensity.

|B| Interplanetary magnetic field (IMF) magnitude – indicative of solar activity and structures in the solar wind (e.g., CMEs).

n Solar wind density. Moments relevant to lunar environment, etc. Tproton Solar wind proton temperature.

V Solar wind bulk flow velocity.

F (> 1 MeV) Flux of energetic protons with energies > 1 MeV. Best used for characterizing solar energetic particle (SEP) events. GRAY.

F (> 10 MeV) Flux of energetic protons with energies > 10 MeV. Less prone to magnetospheric contamination than F (> 1 MeV). RED

KP index 3-hr planetary index for geomagnetic activity – useful proxy for solar wind conditions in the absence of plasma moments.

Space Age Overview Parameters are averaged over a 27-day solar rotation.

: average.

: standard deviation.

Solar Cycle modulation is seen in all parameters (to some extent).

Apollo missions flew during Solar Cycle 20 – not as active as later cycles.

Apollo missions flew during Solar Maximum – peak through declining phase – yet to be repeated by any subsequent missions …

Apollo Era Overview Parameters are averaged over 1-day.

Fortuitously, the Apollo missions mostly flew during relatively quiet conditions.

Minor exceptions. Apollo 12: High solar UV Apollo 16: Energetic protons

Conditions appear far more erratic on these timescales.

Declining phase of the Solar Cycle evident in F10.7, but not in any other parameter.

Apollo 17 Conditions Parameters are hour-averaged.

Solar UV fluxes increase to moderate values.

Coronal mass ejections: intervals of enhanced |B|, n, Tproton and |V|).

Increased energetic particles fluxes in later CMEs (> 10 MeV).

Activity level reflected in the magnetospheric response.

Mission Phase LH: Launch LOI: Lunar Orbit Insertion LD: Lunar Landing LO: Lunar Lift-off TEI: Trans-Earth Injection SD: Splashdown

Anticipated lunar response: Enhanced surface charging, dust transport and exospheric activity.

Apollo 17 Boundaries

The lunar environmental response depends on location: solar wind, magnetosheath or magnetotail.

Use Shue et al. (1998) magnetopause and modified Howe and Binsack (1971) bow shock model to estimate the plasma regime at the Moon.

Models dependent on solar wind pressure, IMF Bz and flow vector.

Subsolar magnetopause/ bow shock location varying by a few RE.

LOI–TEI spent in the solar wind (briefly in magnetosheath, which is similar to solar wind at ~60 RE).

Location of the Moon during the Apollo Missions

Plasma Regions A8 A10 A11 A12 A13 A14 A15 A16 A17 LH – LOI SW SW SW SW SW SW SW SW SW

LOI – LD / LOI –TEI SW SW SW SW SW SW SW SW SW

LD – LO − − SW MSH − MSH SW / MSH

SW / MSH SW

LO – TEI − − SW MSPH − MSH MSH / MSPH MSH SW /

MSH

TEI – SD SW SW SW MSPH SW / MSH MSPH MSPH MSPH MSH /

MSPH

All Apollo missions occurred when the Moon was on the dusk flank of the Earth. “Morning-time” on the lunar surface.

SW Solar Wind MSH Magnetosheath MSPH Magnetosphere

August 1972 Event Apollo missions were fortunate to avoid extreme interplanetary conditions – especially the August 1972 solar flares and CMEs.

Timeline indicated for an “Apollo 17-type” mission.

Moderate solar UV, but strong |B| and high KP (hit maximum on several occasions).

Highest energetic proton fluxes in OMNIWeb database for the entire Space Age. Most of the Cycle 20 “dose” was delivered during this event.

Apollo Radiation Hazards Average radiation measured by passive dosimeters. Apollo

Mission Skin Dose, [rads (rem)]

8 0.16 10 0.48 11 0.18 12 0.58 13 0.24 14 1.14 15 0.30 16 0.51 17 0.55 August 1972 ~400!

Max. operational dose (MOD) limit was set to 400 rads for skin and 50 rads for blood-forming organs during Apollo.

August 1972 event would have caused moderate Acute Radiation Sickness (ARS) without effective shielding and medical counter-measures (Hu et al., 2009).

LRO: No additional shielding provided by the magnetosphere at lunar orbit (Case et al., 2010).

Established IAU Meteoroid Streams during Apollo Apollo

Mission LOI–TEI

Solar Long. Established

Stream ZHR Peak

Solar Long. ZHR Peak Rate [ /hr ]

Velocity VG [ km/s ]

8 273.0–273.8 Ursids Geminids

271.0 262.1

12 92

33 34.6

10 60.9–63.4 Daytime Arietids η Aquariids

76.7 46.9

54 28

35.7 66

11 117.1–119.5 S. δ Aquariids Perseids

125.6 140.2

18 93

40.5 59.4

12 235.9–239.7 Leonids 1969 235.3 400 70.9 13 24.3–25.0 – – – – 14 315.1–317.9 α Centaurids 319.4 7.3 58.2

15 126.3–131.3 Perseids S. δ Aquariids

140.2 125.6

93 18

59.4 40.5

16 30.1–35.2 April Lyrids 32.4 12.8 47.1 17 259.1–265.4 Geminids 262.1 92 34.6

Meteoroid streams enhance exospheric species (Wilson et al., 1999) and perhaps dust as well – saltation mechanism (Glenar et al., 2011).

Summary and Conclusions

The Apollo missions are, so far, the only missions to have flown during a solar maximum … (although Solar

Cycle 20 was not as active as later cycles).

The Apollo mission fortuitously managed to avoid any truly extreme interplanetary conditions, such as the

solar flares and CMEs during August 1972.

Apollo missions did coincide with disturbed conditions at the Moon, which would have resulted in enhanced

surface charging, dust transport and exospheric activity.

Some Apollo missions encountered strong meteoroid streams (Apollo 12, 15 and 17), which likely had a

significant effect on the abundance of neutral species and dust in the lunar exosphere.

Apollo Comparison Statistics calculated using hour-averaged data.

: average and standard deviation.

: minimum.

: maximum.

Apollo era statistics look similar to those for the Space Age.

All the Apollo mission appeared to experience very quiet interplanetary conditions.