Deep Space Relay Architecture for Communications and Navigation

This paper discusses an evolvable deep space relay architecture that provides communications and navigation services for spacecraft in the Mars vicinity and in the inner-planets region. The deep space relay orbiter(s) are expected to be placed in strategic Mars heliocentric orbits that would mitigate the Mars superior conjunction problem for optical communications, and at the same time provide a good geometry for deep space navigation services. The study involves a multidisciplinary optimization of the relay architecture, such that the relays are optimal in their roles as both communication services provider and navigation services provider. One key objective of this paper is to investigate the deep space relay configuration that best improves the data return of optical communications with Mars users. Under the right geometric conditions, the relays will help to break up a long signal path into two shorter signal paths (2 hops), and to increase the Sun-Earth-Probe (SEP) and Sun-Probe-Earth (SPE) angles. This avoids long outages of the optical link during the Earth-Mars synodic period and helps to reduce the sky radiance noise that incidents onto the telescope, which in turn ensures that the pulse position modulated (PPM) optical link operates in a signal-power dominated, 1/range2 regime instead of a noise power dominated, 1/range4 regime, thus greatly improving the data return. On the navigation side, the deep space relay orbiters and Earth combine to form a space-based Deep Space Network (SDSN) with good geometric diversity for the space service volume that covers the Mars vicinity and the inner-planets region. This paper investigates the feasibility of using radiometric and/or optometric measurements between users at various locations within this space volume and the various assets in the SDSN for three-dimensional (3-D) kinematic positioning of the crewed or uncrewed user spacecraft.