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QUBE Mission Update: First Year of Operation of a 3U CubeSat for Quantum-Key-Distribution Experiments

Petermann, Timon, Elsner, Lisa, Schmidt, Benedikt, Pearson, Dominik, Datar, Tanuja, Mammadov, Ilham, Jäger, Eric, Chopra, Chaitnya, Unnikrashnan, Malavika, Dauner, Johannes, Nagalingesh, Vijay, Krauss, Markus, Haber, Roland, Schilling, Klaus, Rödiger, Benjamin, Rüddenklau, René, Bayraktar, Ömer, Pudelko, Jonas, Vermeer, Joost, Marquardt, Christoph, Auer, Michael, Baliuka, Adomas, Birkhold, Moritz, Freiwang, Peter, Steinberger, Michael, Rosenfeld, Wenjamin, Weinfurter, Harald, Knips, Lukas

Published Oct 4, 2025• 0 citations
OpenAlex

Abstract

The QUBE-I mission is a technology demonstrator mission for novel building-blocks for satellite-based quantum-key-distribution (QKD). The mission aims to test three highly integrated optical payloads, a quantum random number generator and two transmitters for polarization and phase encoded quantum states as a precursor mission for the first QKD demonstration from a CubeSat. The QKD sources are connected to, and are integrated together with the Optical Space Infrared Downlink System (OSIRIS) for QUBE (O4Q) in a 3U CubeSat. One of the mission's primary challenges is achieving a precise and accurate pointing of the O4Q with an error margin of less than 1° towards the optical ground station (OGS). Additionally, conducting the experiments presents several operational challenges, such as the need for precise orbital elements to track the satellite with the OGS and safety mechanisms to protect the Sunsensitive components of the satellite. Following the launch on 16th August 2024, we conducted an extensive commissioning phase to test all subsystems, payload components, and operational procedures. This paper provides insights and results from QUBE-I's first year in orbit, highlighting lessons learned from integrating multiple complex payload systems into a 3U CubeSat platform. Starting with communication establishment, we present the ground segment and operations capabilities. We elaborate on the use of flexible on-board scripting and recording mechanisms provided by the satellite's flight software stack for operations. An effective review, test, and deployment procedure was established to balance risk mitigation and agile operation planning. We present results of extensive tests conducted for the crucial attitude determination and control system (ADCS), including actuator verification, spin-up and detumbling tests, in-orbit sensor calibration procedures, and the evaluation of various pointing modes, such as the fine pointing mode required for the experiments. Besides that, we give insights in the actual performance of the experimental and scientific payloads after their commissioning. A big milestone marked the successful test of the operational procedure for the QKD experiments. This includes the timely provision of precise orbit determination to the OGS for tracking. In addition, the ADCS needs to prepare the fine pointing mode accordingly and the experiment needs to be started autonomously before actual contact. Flexibly selectable on-board recordings can be downloaded after the experiments for evaluation. As expected, the technical complexity of the QUBE-I mission resulted in a challenging first year of operation. With this paper, we aim to share our experiences and contribute our insights to the space community.

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•Oct 14, 2026•0 citations
The QUBE-I mission is a technology demonstrator mission for novel building-blocks for satellite-based quantum-key-distribution (QKD). The mission aims to test three highly integrated optical payloads, a quantum random number generator and two transmitters for polarization and phase encoded quantum states as a precursor mission for the first QKD demonstration from a CubeSat. The QKD sources are connected to, and are integrated together with the Optical Space Infrared Downlink System (OSIRIS) for QUBE (O4Q) in a 3U CubeSat. One of the mission's primary challenges is achieving a precise and accurate pointing of the O4Q with an error margin of less than 1° towards the optical ground station (OGS). Additionally, conducting the experiments presents several operational challenges, such as the need for precise orbital elements to track the satellite with the OGS and safety mechanisms to protect the Sunsensitive components of the satellite. Following the launch on 16th August 2024, we conducted an extensive commissioning phase to test all subsystems, payload components, and operational procedures. This paper provides insights and results from QUBE-I's first year in orbit, highlighting lessons learned from integrating multiple complex payload systems into a 3U CubeSat platform. Starting with communication establishment, we present the ground segment and operations capabilities. We elaborate on the use of flexible on-board scripting and recording mechanisms provided by the satellite's flight software stack for operations. An effective review, test, and deployment procedure was established to balance risk mitigation and agile operation planning. We present results of extensive tests conducted for the crucial attitude determination and control system (ADCS), including actuator verification, spin-up and detumbling tests, in-orbit sensor calibration procedures, and the evaluation of various pointing modes, such as the fine pointing mode required for the experiments. Besides that, we give insights in the actual performance of the experimental and scientific payloads after their commissioning. A big milestone marked the successful test of the operational procedure for the QKD experiments. This includes the timely provision of precise orbit determination to the OGS for tracking. In addition, the ADCS needs to prepare the fine pointing mode accordingly and the experiment needs to be started autonomously before actual contact. Flexibly selectable on-board recordings can be downloaded after the experiments for evaluation. As expected, the technical complexity of the QUBE-I mission resulted in a challenging first year of operation. With this paper, we aim to share our experiences and contribute our insights to the space community.
In a world of global satellite communication networks, it is crucial to ensure the security of these data links. QUBE is a project that will develop and launch a CubeSat for the downlink of strongly attenuated light pulses, with encoded quantum information, which can be used for the exchange of encryption keys. This 3U Pico-Satellite will be built using the UNISEC-Europe standard, which has been proven to provide a robust framework for increased reliability for CubeSat missions. In addition to advanced reaction wheels for precision pointing, the satellite will be carrying the DLR-OSIRIS optical downlink system as well as dedicated payloads for testing components required for quantum key distribution. A miniaturized quantum random number generator (QRNG) will create a sequence of numbers, which can be used to set the quantum states of the light. The light pulses will then be downlinked to the optical ground station at DLR in Oberpfaffenhofen, Germany, which is equipped with the corresponding components for receiving the quantum states. Additionally, the random numbers will partially be made available via an RF downlink. This will allow evaluating the link loss as well as the noise and errors in the transmission of quantum signals. In QKD, due to the underlying quantum mechanics, any attempt of reading the quantum states will alter them, which makes interceptions easily detectable. The quantum communication experiments will evaluate whether secure communication links are possible even on a CubeSat scale. A major challenge for building the required CubeSat is the attitude determination and control system that will provide precise pointing. This work will outline detailed mission requirements as well as the chosen subsystems for tackling these challenges in order to deliver a successful mission.
Free-space optical communication is an inherently secure and robust method to transfer information over large distances. To increase the level of secure communication even further, it marks the base for quantum key distribution, a tap-proof encryption method based on the principles of quantum mechanics. The ever-increasing number of small spacecrafts and the growing global threats require secure communication channels, robust against jamming, spoofing, and eavesdropping. Classical radio-frequency communication is, due to its physical properties and its wide-angled beacons sensitive for unwanted interceptions. The technology transfer of laser communication to small satellites like CubeSats provides solutions to overcome the limitations of classical communication, but it comes with the necessity of very precise and accurate pointing. To demonstrate quantum key distribution technologies on a CubeSat, the project QUBE has the goal to verify two experimental quantum sources which signals are transmitted over an optical link from a 3U CubeSat. Two quantum sources, developed by the Ludwig-Maximilian University of Munich and the FriedrichAlexander University in Erlangen, are coupled into the laser communication terminal OSIRIS4QUBE, an evolution of OSIRIS4CubeSat developed by the German Aerospace Center. These systems are integrated into the 3U CubeSat QUBE built by the Center for Telematics. Establishing an optical connection between the laser terminal and the optical ground station requires precise and accurate pointing of the satellite. This task is handled by a high-precision attitude determination and control system. This paper presents the first results of the launch and early orbit phase of the QUBE mission. It highlights the achievements of the attitude determination and control system and the commissioning of the OSIRIS4QUBE terminal. The paper focuses on these two topics and explicitly excludes the results of the experimental quantum payloads.
Satellite-based Quantum Key Distribution (QKD) can be used to deliver information-theoretically secure keys for cryptographic applications, no matter where end-users are located. Several space missions using this concept have shown feasibility of systems and component technologies. The QUBE-II mission, with a planned launch in Spring 2026, uses an economic CubeSat platform to show the possibility of a global secure communication by simple means. This paper presents the optical system design of the QUBE-II laser communication terminal (LCT). It is based on the previous developments for the CubeL mission (launched in 2021), for CubeISL, and for the precursor mission QUBE-I (launched in 2024). The 2.5U LCT is integrated into an 8U CubeSat and serves as transmit system for two Alice modules operating at 850 nm and in optical L-band1, 2 respectively. At the same time, bi-directional classical links are used for link acquisition, tracking, and data transmission. With its 85 mm aperture and an 800 mm receiver telescope on the ground station, the antenna gain is sufficiently high enough to perform QKD links. The LCT’s optical system is designed based on a commercially available reflective telescope in combination with custom-designed lenses. It integrates several fiber-optical and electrical components for wavelength combination, wavelength splitting, tracking, and uplink data reception into a compact design. The Alice payloads are connected to the LCT by optical fibres allowing a flexible placement of the modules within the satellite bus. Collimators couple the light into free-space beams which are co-aligned and interfaced to the transmit telescope. In addition to the optical system design, this paper provides further information about the integration of the optical into the mechanical system, and the performed functional and qualification tests.
Laser communication technology, especially QKD (Quantum Key Distribution), is coming more and more into practical operations. It is a maturing technology that enables the distribution of cryptographic key between two remote parties [1][3] for secure communication even in presence of quantum computers[3]. To demonstrate this technology DLR is part of the QUBE project to have a precursor mission for QKD from CubeSats in orbit as well as hosting and operating the ground-based counterpart the Optical Ground Station Oberpfaffenhofen (OGSOP).The OGS is equipped with an 80cm primary mirror, a Coudé path with optical bench, adaptive optics system, fiber coupling and a single photon detector. The ground station already performed successful downlinks from low Earth orbit (LEO) (Flying Laptop, CubeL and others) and geostationary platforms (Alphasat, Project BayernQSat), as well as aircrafts (Project QuNET) [4][11][13].In the last year the ground station was upgraded from its basic configuration to adapt for multi-mission support and QKD experiments. Several features were integrated and upgraded at the telescope, in the Coudé path and on the optical bench. The focus of the upgrades was to connect the OGSOP (Optical Ground Station Oberpfaffenhofen) with the satellite QUBE. The target of compatibility could be achieved and improved from OGS side.Knowledge from ground-to-ground-tests were considered to rebuild the receiving setups in an improved and more operational way. The QUBE satellite contains an optical terminal designed and developed by DLR to transmit two experimental quantum signals over the optical link. These sources were developed by the Ludwig-Maximilian University (LMU) of Munich and the Friedrich-Alexander University (FAU) in Erlangen.On May the 2nd 2025 the OGSOP was able to catch the first light from QUBE and establish a link between both sides[2]. This started the optical communication commissioning phase of the satellite, including the classical communication terminal and the quantum light sources. This paper describes the entire setup, from satellite to ground detector, and presents the key achievements so far.
In 2017, the Micius mission [1] showed that satellite quantum key distribution (QKD) can surpass the range limit of fiber-based QKD [2]. Due to the high launch cost of satellites the cost of these systems would be reduced significantly if the size, weight and power of the satellites could be reduced. This requires the use of new integration technologies, like the miniaturized modules based on photonic integrated circuits (PIC) tested in the QUBE mission [3], [4]. Using the knowledge gained there, the QUBE-II mission aims to launch an 8U CubeSat(10×20×40cm3)(10\times 20\times 40\text{cm}^{3})(10×20×40cm3)with the goal of performing QKD between the cubesat and an optical ground station [5].
The Institute of Communication and Navigation at the German Aerospace Center (DLR) hosts the Optical Ground Station Oberpfaffenhofen (OGSOP). The station is operating with an 80cm primary mirror telescope, including a Nasmyth configuration. These were guiding light to several different experimental ports at the Ground Station itself, as well as a free space optical Coudé-Path, leading onto an optical table inside the laboratory below the station. After the commissioning of the OGSOP (2021 – 2023) various projects and free space laser communication experiments have been conducted. OGSOP approved operations including data downlinks from the low orbit satellites Flying Laptop, CubeL and QUBE. Experiments with Alphasat (GEO stationary platform) were also carried out as well as an aircraft link campaign in the frame of QuNET project. The gained experiences and lessons learned of all these missions led to further development and upgrades of the OGSOP, especially from classical laser communication towards the direction of Quantum Key Distribution (QKD). The upgraded OGSOP and its peripheric systems are a designated test bed for QKD [1][2]. The QKD precursor Missions QUBE-I (launch August 2024) is already in the phase of an ongoing linking campaign at OGSOP. From first light to scientific experiments, the OGSOP could already proof its capability to support this type of optical free space satellite communication missions. The receiving Coudé-Path and system PUMUQL (Prototyping Unit for Modulated User-data and Quantum Links) was integrated for the quantum light, as well as an adaptive optics system in development. The follow up mission QUBE-II is also already launched (May 2026) and currently in its finally LEOP phase, it will will go into first tests around autumn 2026 at OGSOP. The preparation for Eagle-1 is a main part of the work and development for the optical ground station. QKD up- and downlink path is redesigned, implemented and brought into operational service. The growth of the number of projects dropping into the OGSOP was one of the reasons to go from classical project-based time by time mission support to a matrix like solution for multi mission support and operations. An established configuration management, new commanding, booking and preparation processes are assisting the whole organization. Following an overview of the current status of the OGS, the ongoing projects (QUBE, Eagle-1, QuNET, and more) will be given. A description of the ground stations infrastructure and support facilities will be represented in relation to different project requirements and missions.