No abstract

Satellite networks are inevitable for the ubiquitous connectivity of M2M (machine to machine) and IoT (internet of things) devices. Advances in the miniaturization of satellite technology make networks in LEO (Low Earth Orbit) predestined to serve as a backhaul for narrow-band M2M communication. To reduce latency and increase network responsivity, intersatellite link capability among nodes is a key component in satellite design. The miniaturization of nodes to enable the economical deployment of large networks is also crucial. Thus, this article addresses these key issues and presents a design methodology and implementation of an adaptive network architecture considering highly limited resources, as is the case in a nanosatellite (≈10 kg) network. Potentially applicable multiple access techniques are evaluated. The results show that a time division duplex scheme with session-oriented P2P (point to point) protocols in the data link layer is more suitable for limited resources. Furthermore, an applicable layer model is defined and a protocol implementation is outlined. To demonstrate the technical feasibility of a nanosatellite-based communication network, the S-NET (S band network with nanosatellites) mission has been developed, which consists of four nanosatellites, to demonstrate multi-point crosslink with 100 kbps data rates over distances up to 400 km and optimized communication protocols, pushing the technological boundaries of nanosatellites. The flight results of S-NET prove the feasibility of these nanosatellites as a space-based M2M backhaul.

The compact form factor of nanosatellites or even smaller satellites makes them predestined for distributed systems such as formations, constellations or large swarms. However, when it comes to orbit insertion of multiple satellites, these ride share payloads have constrains in the deployment parameters such as sequence, direction, velocity and time interval. Especially for formation flight missions without propulsion, where the satellites should minimize their relative distance drift either passively or by atmospheric drag control, the initial ejection parameters must find a proper trade-off between collision probability and relative drift. Hence, this article covers short-term (first orbit) collision analysis, long-term (30 days) drift analysis and atmospheric drag control strategy for long-term distance control of multiple satellites. The collision analysis considers various orbit deployment parameters such as insertion direction and tolerance, orbital elements of insertion and time span. To cover the parameter space, a Monte Carlo simulation was conducted to identify the impact of these parameters. It showed that for collision probability the major factor is the time span between two ejections and the precision of the deployment vector. For long-term drift analysis, orbit perturbation such as atmosphere and J2 terms are considered. The result showed that for drift minimizing, minimizing the along-track variation is more substantial than reducing the time span between ejections. Additionally, a drag control strategy to reduce the relative drift of the satellites is described. The results have been applied on the S-NET mission, which consists of four nanosatellites with the task to keep their relative distance within 400 km to perform intersatellite communication experiments. The flight results for orbital drift show equal or better performance (0.1-0.7 km/day) compared to the worst-case simulation scenario, implying that orbit perturbation was chosen correctly and all orbit injection tolerances were within specified range. The drag control maneuver showed good matching to the flight results as well with a deviation for the maneuver time of approximately 10%.

Abstract

Am 14. Oktobcr 19% gab die Iioniglich Schrvedische Altadcinic dcr Wisscnscliaftcn ihl-en Beschlui\ bekannt, Rudolph A. Marcus, Professor a m Cdifornia Institute of Technology, den Chernie-Nobelpreis 1992 fiir seine Reitragc mi-Theorie der Elektroiienu berfiilirurigsreaktioncn in cheniischcn Systemen m verleihen.