ASTROD I: Mission concept and Venus flybys

Abstract

ASTROD I is the first step of ASTROD (Astrodynamical Space Test of Relativity using Optical Devices). This mission concept has one spacecraft carrying a payload of a telescope, five lasers, and a clock together with ground stations (ODSN: * Corresponding author. Purple Mountain Observatory, Chinese Academy of Sciences, Nanjing, 210008, China. Optical Deep Space Network) to test the optical scheme of interferometric and pulse ranging and yet give important scientific results. These scientific results include a better measurement of the relativistic parameters, a better sensitivity in using optical Doppler tracking method for detecting gravitational waves, and measurement of many solar system parameters more precisely. The weight of this spacecraft is estimated to be about 300-350 kg with a payload of about 100-120 kg. The spacecraft is to be launched with initial period about 290 days and to pass by Venus twice to receive gravity-assistance for achieving shorter periods. For a launch on August 4, 2010, after two encounters with Venus, the orbital period can be shortened to 165 days. After about 370 days from launch, the spacecraft will arrive at the other side of the Sun for the determination of relativistic parameters.

Gravimagnetic effect of the barycentric motion of the Sun and determination of the post-Newtonian parameter γ in the Cassini experiment

“…The translationally-invariant gravimagnetic field can be measured more accurately in space missions LATOR [22] and ASTROD [23]. The space inter-ferometer SIM [24] and ground-based Square Kilometer Array [25] can also achieve this goal [26].…”

Solar-system tests of the relativistic gravity

“…They predict that the determination of γ can reach 2×10 -6 . ASTROD I is envisaged as the first in a series of ASTROD missions [78,[156][157][158][159]. ASTROD I mission concept is to use one spacecraft carrying a telescope, four lasers, two event timers and a clock with a Venus swing-by orbit.…”

Gravitational wave detection in space

“…With this accuracy and extended ranges of 20 AU, the capability of probing the fundamental laws of spacetime and mapping the solar system gravity will be greatly enhanced. [32][33][34][35] The basic principle of spacecraft Doppler tracking, of spacecraft laser ranging, of space laser interferometers, and of pulsar timing arrays (PTAs) for GW detection are similar. In the development of GW detection methods, spacecraft Doppler tracking method and pulse laser ranging method have stimulated significant inspirations.…”

“…23 The mission study shows that the precision of testing relativistic gravity in the solar system is achievable to 10 −9 -10 −8 in terms of Eddington parameter γ, which is more than three orders of improvement over the present precision, with accompanying improvement in other aspects of relativistic gravity. [31][32][33][34][35] Early in 2009, responding to the call for GW mission studies of CAS (Chinese Academy of Sciences), a dedicated mission concept ASTROD-GW (ASTROD optimized for Gravitational Wave [GW] detection) for GW detection with 3 S/C (spacecraft) orbiting near Sun-Earth Lagrange points L3, L4 and L5 respectively with nominal arm length of 260 million km was proposed and studied. 3,[36][37][38][39][40] A schematic of ASTROD-GW orbit configuration with inclination is shown in Fig.…”