PLUTO

Objectives

The main objective is the in-orbit demonstration and operation of newly developed avionics components oriented towards high power density and high performance CubeSats. An enabling technology to support the mission is the deployment of a 100 W solar array based on a flexible substrate. The avionics to be demonstrated consists of several mission -critical components including a reconfigurable software defined radio, an onboard computer, a power system and an intra-spacecraft wireless network.

The reconfigurable SDR can be utilized for the reception of ADS-B signals, but at the same time can be reconfigured in space to demonstrate an experimental S-Band up- / and downlink.

The components shall be operated for at least 1 year to prove their reliability in orbit and to gain experience with their operation.

The sub-objectives can be summarized as:

• Demonstration of a flexible satellite communication payload with reconfiguration features in orbit, enabling
• Feasibility of a wireless sensor network based on ultrawideband for intra-spacecraft communication
• Operation of high-power density GaN-based power distribution and conditioning
• Investigation of ageing effects in Li-Ion batteries on cell level
• Evaluation of long-term radiation effects on high performance computing nodes
• Deployment and operation of a 100W flexible solar array
• In-Orbit Demonstration of the thermal stability during 100W power generation

The overarching challenge best concluding PLUTOs purpose is that of miniaturization. The goal is to demonstrate more sophisticated components designed for larger spacecraft and in larger formfactors (e.g. cPCI) on a low-cost CubeSat mission. On one hand this strengthens the capabilities of CubeSats and enhances their scope of application. On the other hand, it gives spacecraft component developers cost-effective access to space to gain flight heritage with their components. Also, it will allow to raise the technological maturity of the developments and thus in a broader context strengthen German and the European competitiveness as a whole.

System Overview

PLUTO is based on a 6U CubeSat structure with a deployable flexible solar array and a secondary internal structure to accommodate avionics components in a backplane architecture. The satellite is fully compliant with the CubeSat Standard Rev. 13 and thus does not require any interfaces to the launcher besides a generic 6U deployer. The internal structure allows the accommodation of components in a cPCI- and PC104 compatible formfactor. Due to the experimental nature of some components used in PLUTO, some components have been supplemented with proven backup systems.  The satellite is nominally powered by the 100W deployable flexible solar array, but body mounted panels provide power as a backup and during LEOP. Both systems are connected to two independent Array Power Regulators (APR) for maximum power point tracking. Electric energy is stored in a 90 Wh battery and distributed to all units via the Power Distribution Unit. The PDU also handles the protection of all outputs to isolate faults in any connected unit. Communications are handled either via a commercial UHF transceiver or the Generic Software Defined Radio (GSDR) in S-Band. Both systems are connected to the central reliable node of the onboard computer. The reliable node controls all operations of the satellite, collects telemetry and distributes telecommands. A CAN is used for internal communications between most components with low data rate while SpaceWire is used for high rate communication to the high-performance node and the GSDR. The satellites’ attitude will be determined via sun sensors and an IMU and controlled via magnet torquers. The necessary calculations and control signals will be implemented in the reliable node of the onboard computer. In addition, wireless communication within the spacecraft based on ultrawideband technology is planned.

Integrated Core Avionics as the main pillar of PLUTO

Integrated Core Avionics (ICA) explores the advantages of a holistic view on the central components of spacecraft avionics and their design processes. The current scope of the work includes communications, data handling, power conditioning and distribution as well as wireless connectivity. To enable a modular and customizable solution, the functions are implemented on separate modules connected by a backplane which handles power, data and control signals.

The current range of DLR research activities encompasses two distinctive mechanical design aspects. On one hand, there are the larger systems built around Eurocard-style PCBs, potentially compatible with SpaceVPX or CPCI Serial Space, enclosed in bespoke boxes and made for small satellites in the 50 — 300kg class. Due to the board size these systems cannot be used on CubeSats. On the other hand, there are the smaller systems following the CubeSat formfactor, which is widely used in academia and new space. CubeSats have also been identified as possible test vehicles for technology demonstration and in-orbit verification of new designs.

Here the reduced circuit board space can lead to an overhead for the interconnections when applied to larger systems. There is a strong incentive for ICA to bridge the gap between both approaches to achieve a versatile system that profits from low cost flight opportunities on CubeSat missions, but also readily enables the integration with commercial small satellite systems.

The resulting concept is called the Unified Module Framework (UMF) and includes specifications for a set of module types, their mechanical characteristics and their logical and electrical connections. The resulting avionics systems can be integrated in CubeSats and stand-alone enclosures while ensuring compatibility with full size CPCI Serial Space systems.

For more details to the flexible solar panel: see DEAR and CREAM.