Effects of the Space Plasma Density Oscillation on the Interspacecraft Laser Ranging for TianQin Gravitational Wave Observatory

Abstract

The TianQin space gravitational waves (GW) observatory will contain three geocentric and circularly orbiting spacecraft with an orbital radius of 105 km, to detect the GW in the milli‐hertz frequency band. Each spacecraft pair will establish a 1.7 × 105 km‐long laser interferometer immersed in the solar wind and the magnetospheric plasmas to measure the phase deviations induced by the GW. GW detection requires a high‐precision measurement of the laser phase. The cumulative effects of the long distance and the periodic oscillations of the plasma density may induce an additional phase noise. This study aims to model the plasma induced phase deviation of the interspacecraft laser signals, using a realistic orbit simulator and the Space Weather Modeling Framework model. Preliminary results show that the plasma density oscillation can induce the phase deviations close to 2 × 10−6 rad/Hz1/2 or 0.3 pm/Hz1/2 in the milli‐hertz frequency band and it is within the error budget assigned to the displacement noise of the interferometry. The amplitude spectrum density of phases along three arms become more separated when the orbital plane is parallel to the Sun‐Earth line or during a magnetic storm. Finally, the dependence of the phase deviations on the orbital radius is examined.

Effect of Earth-Moon’s gravity on TianQin’s range acceleration noise. II. Impact of orbit selection

“…This is our sixth paper of the concept study series on TianQin's orbit and constellation [10,11,[17][18][19]. For progress on other space environmental effects on Tian-Qin, one may refer to [20][21][22][23][24]. This article is structured as follows.…”

Plasma noise in TianQin time-delay interferometry

“…For typical values of the involved quantities, i.e. N e ∼ 10 cm −3 at an altitude of ∼ 10 5 km and the armlength 1.7 × 10 5 km, we arrive at s ij ≈ 1 pm [25]. This motivates us to look further into the frequency domain behavior, and the single-link displacement noise requirement (preliminary) for plasma is given by…”

“…In this paper, we first obtain two sets of plasma noise data with the time resolutions of 60 s and 5 s using the SWMF model [25][26][27][28] and the PPMLR-MHD model [44], respectively. Then the frequency domain characteristics of the plasma noise along single links are analyzed, and it is shown that the noise behavior can be approximated by a Kolmogorov spectrum in the frequency range of 10 −4 − 1 Hz.…”

“…Details on the simulation procedure can be found in Refs. [25,27]. Due to the short light travel time between two satellites (∼ 0.5 s), the difference between s ij (t) and s ji (t) is very small (cf.…”

“…Recently, Ref. [25] has calculated the optical path length fluctuations caused by the solar wind plasma along single arms. The results indicate that the impact is close to the displacement noise requirement of TianQin and constitutes a noticeable noise source.…”