EXACT Mission Objectives

EXACT will pursue the following primary mission objectives:

• EXACT shall accurately time tag incoming photons from pulsars in order to get accurate time of arrival information for use in PNT calculations. 

EXACT will have the ability to use time of arrival information from pulsar signals which can be used in conjunction with models for the time of arrival of the same pulsar signal at a reference point (e.g. Earth or the  solar system).  By comparing the two signals, the time-difference of arrival (TDOA) of the signal on EXACT and the reference point can be established.  This, in turn, will allow determining the offset between the clock on EXACT and the one at the reference thereby synchronizing the two clocks..

• EXACT shall validate the performance of a simple, inexpensive PNT sensor. 

The development of the payload will allow it to become a pathfinder for a small, inexpensive spectrometer which could be replicated for other missions.. By developing a smaller, inexpensive detector which allows for proper time synchronization, the payload can be used by a spacecraft to supplement its PNT sensor suite thereby enabling a standalone time synchronization method to supplement atomic clocks for GPS/GNSS denied operations.

• EXACT shall measure its position in orbit with respect to a ground truth.

EXACT will measure its position in orbit using a ground truth to provide a reference to the TDOA calculations and to aid its attitude determination and control system.

EXACT will pursue the following secondary mission objective:

• EXACT shall measure the energies of individual hard X-ray photons from the sun in order to investigate flare-accelerated electron energy distributions on sub-second timescales.

It is not known how solar flares accelerate electrons and ions up to such high energies, but it is known that accelerated electron populations produce high-energy (“hard”) X-rays via the bremsstrahlung process.  These electrons are one of the most immediate indicators of energy release in the solar corona, and their resulting hard X-rays (HXRs) are therefore one of the best diagnostics of when and how energy release is taking place.  Measuring individual photon arrival times and energies allows the calculation of the energy distribution of flare-accelerated electrons over time, a dynamic that is closely associated with the acceleration of any related CME.  HXRs therefore serve a diagnostic tool for energy release and can inform space weather models of CMEs by explaining and exploring their origins.