Optical Clock and Drag-Free Requirements for a Shapiro Time-Delay Mission

TL;DR

This paper discusses the design requirements for an optical clock and drag-free system to improve measurements of the Shapiro time delay, testing general relativity with high precision using spacecraft near the Sun-Earth L1 point.

Contribution

It proposes a novel mission concept utilizing optical clocks and drag-free technology to achieve highly precise Shapiro delay measurements, surpassing current accuracy levels.

Findings

Achievable measurement accuracy better than 1 part in 100 million.

Design specifications for optical clock stability and drag-free systems.

Feasibility of using laser phase travel-time measurements in space.

Abstract

In the next decade or two, extremely accurate tests of general relativity under extreme conditions are expected from gravitational wave observations of binary black hole mergers with a wide range of mass ratios. In addition, major improvements are planned in both strong and weak equivalence principle tests; clock measurements based on the ACES program on the ISS; more accurate light-bending measurements; and other new types of tests. However, whether these tests are all consistent with general relativity or not, it still appears desirable to proceed with a much improved measurement of the Shapiro time delay. A suggested approach is based on using a high-quality optical clock in a drag-free spacecraft near the sun-earth L1 point and a smaller drag-free transponder spacecraft in a two-year period solar orbit. Laser phase travel-time measurements would be made between the two spacecraft over a period of 10 or 20 days around the time when the line of sight passes through the Sun. The requirements on the optical clock stability and on the drag-free systems will be discussed. The accuracy achievable for the time-delay appears to be better than 1 part in 100 million.