A HERO for General Relativity
Abstract
HERO (Highly Eccentric Relativity Orbiter) is a spacebased mission concept aimed to perform several tests of postNewtonian gravity around the Earth with a preferably dragfree spacecraft moving along a highly elliptical path fixed in its plane undergoing a relatively fast secular precession. We considered two possible scenarios—a fast, 4h orbit with high perigee height of 1047km and a slow, 21h path with a low perigee height of 642km. HERO may detect, for the first time, the postNewtonian orbital effects induced by the mass quadrupole moment J2 of the Earth which, among other things, affects the semimajor axis a via a secular trend of ≃4–12 cmyr‑1, depending on the orbital configuration. Recently, the secular decay of the semimajor axis of the passive satellite LARES was measured with an error as little as 0.7cmyr‑1. Also the postNewtonian spin dipole (LenseThirring) and mass monopole (Schwarzschild) effects could be tested to a high accuracy depending on the level of compensation of the nongravitational perturbations, not treated here. Moreover, the large eccentricity of the orbit would allow one to constrain several longrange modified models of gravity and accurately measure the gravitational redshift as well. Each of the six Keplerian orbital elements could be individually monitored to extract the GJ2/c2 signature, or they could be suitably combined in order to disentangle the postNewtonian effect(s) of interest from the competing mismodeled Newtonian secular precessions induced by the zonal harmonic multipoles Jℓ of the geopotential. In the latter case, the systematic uncertainty due to the current formal errors σJℓ of a recent global Earth's gravity field model are better than 1% for all the postNewtonian effects considered, with a peak of ≃10‑7 for the Schwarzschildlike shifts. Instead, the gravitomagnetic spin octupole precessions are too small to be detectable.
 Publication:

Universe
 Pub Date:
 July 2019
 DOI:
 10.3390/universe5070165
 arXiv:
 arXiv:1906.05728
 Bibcode:
 2019Univ....5..165I
 Keywords:

 general relativity and gravitation;
 experimental studies of gravity;
 experimental tests of gravitational theories;
 satellite orbits;
 General Relativity and Quantum Cosmology;
 Astrophysics  Earth and Planetary Astrophysics;
 Physics  Space Physics
 EPrint:
 LaTex2e, 35 pages, 9 tables, 4 figures