# Sun-Earth Lagrange reference for fundamental physics and navigation

## TL;DR

This paper proposes using the Sun-Earth Lagrange points as a natural reference frame for space-based fundamental physics experiments, including tests of relativistic effects, gravitational waves, and galactic magnetic fields.

## Contribution

It introduces a novel concept of positioning spacecraft at Lagrange points to perform high-precision measurements for fundamental physics and navigation in the solar system.

## Key findings

- Time of flight differences can measure Sun's angular momentum with <1% accuracy.
- Lagrange points can serve as artificial pulsars for relativistic positioning.
- Potential to detect galactic gravito-magnetic fields and gravitational waves.

## Abstract

The use of four Lagrange points of the Sun/Earth system for fundamental physics experiments in space is presented. L1, L2, L4 and L5 rotating rigidly together with the Earth form a natural reference frame at the scale of the inner solar system. The idea which is discussed in the paper considers the possibility of locating four spacecraft in the four cited Lagrange points and exchanging electromagnetic pulses among them. Including stations on earth, various closed paths for the pulses are possible. Time of flight measurements would be performed. The time of flight difference between right- and left-handed circuits is proportional to the angular momentum of the Sun and the detection of the effect would reach accuracies better than 1% depending on the accuracy of the clock. The four points could also be used as "artificial pulsars" for a relativistic positioning system at the scale of the solar system. Additional interesting possibilities include detection of a galactic gravito-magnetic field and also, using a global configuration as a zero area Sagnac contour, detection of gravitational waves. More opportunities are also mentioned.