Space environmental study for ASTROD I Zhang Qingxiang Wangli Shi Wanglin Hou Xinbin Song Zhenji Deep Space Exploration & Space Science Technology Division Research & Development Center，CAST

Outline Introduction Space environment for ASTROD1 Preliminary space environment effect analysis Suggestion for space environment monitor onboard ASTROD1 Conclusion

1. Introduction 2004.10---- CAST setup Deep Space Exploration & Space Science Technology Division at R&D center to promote space science missions. 2006.3 ----- DESSTD began to work together with ASTROD team 2006.6 -----DESSTD took parting in a ASTROD workshop at Purple Mountain Observatory ...

ASTROD 1(Mini -ASTROD) Two-Way Interferometric and Pulse Laser Ranging between Spacecraft and Ground Laser Station Testing relativistic gravity 3-order-of-magnitude improvment in sensitivity; Astrodynamics & solar-system parameter determination improved by 1-3 orders of magnitude; Improving gravitational-wave detection compared to radio Doppler tracking (Auxiliary goal). Wei-Tou Ni(1,2) and Diana N A Shaul(3) Solar, COsmic Ray and Environmental physics for/with ASTROD and ASTROD I

ASTROD 1 Orbit For ASTROD I the distance from the Sun is 0.5 AU to 1.04 AU; The orbit of ASTROD I is out of magnetosphere of Earth ASTROD and ASTROD I: Progress Report

Key technology for ASTROD 1 Tree dimensions sensing capacitive proof masses μN proportional thrusters （Electric Propulsion thrusters ） lasers and optics （5 lasers onboard ASTROD 1 ） …… longevity and reliability of these technologies in the space environment is vital to success for ASTROD I.

2. Space environments for ASTROD1 Galaxy Cosmic Ray Solar event particles Solar wind Solar electromagnetic radiation

Galaxy Cosmic Ray All Elements in Periodic Table Energies in GeV Found Everywhere in Interplanetary Space Omnidirectional Mostly Fully Ionized Cyclic Variation in Fluence Levels Lowest Levels = Solar Maximum Peak Highest Levels = Lowest Point in Solar Minimum Single Event Effects Hazard Model: CREME96 Janet Barth: Radiation Environments

GCR energy and LET spectrum at 1AU calculated with CREAM96

GCR Gradients in the Heliosphere Basd on data from IMP, Voyage and Pioneer, GCR flux increased with distance form Sun. The gradient magnitude is 10% per AU at 1AU 4%per AU at 5AU Difference between GCR flux at 0.5AU and 1AU will be less 10%, Using external radiation fluence at 1AU for ASTROD1 is conservative.

Solar event particles CME Solar Flares Increased Levels of Protons & Heavier Ions Energies Protons - 100s of MeV Heavier Ions - 100s of GeV Abundances Dependent on Radial Distance from Sun Partially Ionized - Greater Ability to Penetrate Magnetosphere Number & Intensity of Events Increases Dramatically During Solar Maximum Models Dose - SOLPRO, JPL, Xapsos/NRL Single Event Effects - CREME96 (Protons & Heavier Ions) CME Solar Flares Janet Barth: Radiation Environments

Proton Event Spectra - Cycle 22 time φ0 k α r 1972.8.4 2.45×1010 0.0236 1.108 0.996 1989.8.12 1.622×1011 1.166 0.4015 0.994 1989.9.29 3.631×1010 0.877 0.3841 0.998 1989.10.19 1.230×1012 2.115 0.2815 1991.3.23 1.660×1011 0.972 0.4410 0.993 Total Integral Proton Fluence Janet Barth: Radiation Environments

SEP energy and LET spectrum at 1AU calculated with CREAM96

SEP Gradients in the Heliosphere The gradient in peak intensity was found to be about R-3, and the total fluence gradient as R-2(NASA) a 1/r+ heliocentric scaling is used for SPE, whilst no scaling is used for heliocentric distances greater than 1AU.(ESA) Recommendations of NASA Sun-Solar System Connections(2005) Radiation Exposure and Mission Strategies for Interplanetary Manned Mission – REMSIM(2004) The SEP peak intensity at 0.5AU is 8 times of that at 1AU, total fluence at 0.5AU is 4 times of that at 1AU.

Solar wind Stream of Charged Particles from Sun’s Corona electrons, protons, heavy Ions Magnetized Plasma Detected Out to 10 billion km from Earth by Pioneer 10 Velocity ~ 300 - 900 km/s Energy ~ .5 - 2.0 keV/nuc

Solar wind plasma parameter Electron Density e temperatureTe Ion Velocity vi Ei/Ti density i Debye Lengh 0.5AU(A) 4.27cm-3 10.6eV 702km/s 2573 eV 6m 0.5AU(B） 13.1 cm-3 68.2 eV 863 km/s 3888 eV 17m A:come from Feldman, high speed solar wind environment scaled to 0.5AU B: data from the SWOOPS(Solar Wind Observations Over the Poles of the Sun) instrument onboard Ulysses

Solar electromagnetic radiation Solar electromagnetic radiation diffuses with distance from the sun at a rate of 1/R2.

3 Preliminary space environment effect analysis Total dose effect Displacement damage Single Event Effect Optical darkening and thermal property changes Optical contamination

Total dose effect

The Solar Orbiter will go into the inner heliosphere to 0.21 AU, For a nominally shielded (4mm Al) silicon component is epected to receive a dose of 48 krad over the entire mission(5 years) The effect of Total dose to microelectronic is not very serious for ASTROD1.

Displacement damage CCD and laser LED may be degraded at very low proton fluence by displacement damage. Allan H. JohnstonDisplacement Damage and SpecialIssues for Optoelectronics

Single Event Effect Microelectronics are likely to occur different SEE.

Detectors will be flooded with “noise”. Single event effect will be a major concerns for ASROD1 , especially during large SEP. SOHO/LASCO Images

Effect to exposed material optical darkening and surface thermal property changes due to synergistic effects between radiation, UV, thermal cycling, vacuum and contamination.

4 Suggestion for space environment monitor onboard ASTROD1 */ The space environment definition is not very certain because we don’t have enough data. It’s proposed that space radiation instrument onboard ASTROD1 satellite: To space environment safety management of satellite and charge management of test materials. Collect environment data in inner heliosphere It’s proposed to add space environment measurement as one of the scientific objects of ASTROD1

5.conclusion Studying the space environment and it’s effect as early as possible are very important for space mission success. It’s proposed to add space environment measurement as one of the scientific aims of ASTROD1.

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