Astrodynamical Space Test of Relativity Using Optical Devices I (ASTROD I)—A class-M fundamental physics mission proposal for Cosmic Vision 2015–2025

Abstract

ASTROD I is a planned interplanetary space mission with multiple goals. The primary aims are: to test general relativity with an improvement in sensitivity of over three orders of magnitude, improving our understanding of gravity and aiding the development of a new quantum gravity theory; to measure key solar system parameters with increased accuracy, advancing solar physics and our knowledge of the solar system; and to measure the time rate of change of the gravitational constant with an order of magnitude improvement and the anomalous Pioneer acceleration, thereby probing dark matter and dark energy gravitationally. It is an international project, with major contributions from Europe and China and is envisaged as the first in a series of ASTROD missions. ASTROD I will consist of one spacecraft carrying a telescope, four lasers, two event timers and a clock. Two-way, twowavelength laser pulse ranging will be used between the spacecraft in a solar orbit and deep space laser stations on Earth, to achieve the ASTROD I goals. A second mission, ASTROD (ASTROD II) is envisaged as a three-spacecraft mission which would test General Relativity to 1 ppb, enable detection of solar g-modes, measure the solar Lense-Thirring effect to 10 ppm, and probe gravitational waves at frequencies below the LISA bandwidth. In the third phase (ASTROD III or Super-ASTROD), larger orbits could be implemented to map the outer solar system and to probe primordial gravitational-waves at frequencies below the ASTROD II bandwidth.

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

“…ASTROD I during the superior solar conjunctions to measure the Shapiro delay of light and with continuous laser ranging of 1 mm accuracy to improve the determination of relativistic parameters is such a mission proposal. [31][32][33] BepiColombo to be launched in 2017 is an ESA-JAXA mission under implementation.…”

“…65 During this period, MESSENGER measured the gravity of Mercury and the state of the planetary core by utilizing the spacecraft's positioning data.) and ASTROD I (a mission proposal having a Venus swing-by for gravity assistance and for improved measurement of Venus gravity/multipole moments, with laser ranging of accuracy about 1 mm for improvement on the parameter determination of planets and asteroids) [31][32][33] are such examples. For laser-interferometric GW detection without fast Doppler tracking (e.g., using optical combs), nearly equal arm lengths are required; LISA-like mission concepts and ASTROD-GW-like mission concepts are examples.…”

“…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.…”