Quantum communication is a prime space technology application and offers near-term possibilities for long-distance quantum key distribution (QKD) and experimental tests of quantum entanglement. However, there exists considerable developmental risks and subsequent costs and time required to raise the technological readiness level of terrestrial quantum technologies and to adapt them for space operations. The small-space revolution is a promising route by which synergistic advances in miniaturization of both satellite systems and quantum technologies can be combined to leap-frog conventional space systems development. Here, we outline a recent proposal to perform orbit-to-ground transmission of entanglement and QKD using a CubeSat platform deployed from the International Space Station (ISS). This ambitious mission exploits advances in nanosatellite attitude determination and control systems (ADCS), miniaturised target acquisition and tracking sensors, compact and robust sources of single and entangled photons, and high-speed classical communications systems, all to be incorporated within a 10 kg 6 litre mass-volume envelope. The CubeSat Quantum Communications Mission (CQuCoM) would be a pathfinder for advanced nanosatellite payloads and operations, and would establish the basis for a constellation of low-Earth orbit trusted-nodes for QKD service provision.
Quantum key distribution from satellites becomes particularly valuable when it can be used on a large network and on-demand to provide a symmetric encryption key to any two nodes. A constellation model is described which enables QKD-derived encryption keys to be established between any two ground stations with low latency. This is achieved through the use of low earth orbit, trusted-node QKD satellites which create a buffer of keys with the ground stations they pass over, and geostationary relay satellites to transfer secure combinations of the keys to the ground stations. Regional and global network models are considered and the use of intersatellite QKD links for balancing keys is assessed.
Deployable optics promise a revolution in the capability of observing the universe by delivering drastically reduced mass and volume needs for a desired level of performance compared to their conventional counterparts. However, this places new demands on the mechanical and thermal designs of new telescopes, essentially trading mass and volume for structural and control complexity. We compile the thermomechanical challenges that should be taken into consideration when designing optical space systems, as well as summarize 14 projects proposed to address them. Stringent deployment repeatability requirements demand low hysteresis, whereas stability requirements require high stiffness, proper thermal management, and active optics.
Deployable optics can bring major cost reductions to the field of Earth Observation. One of the key challenges in the development of a deployable optical system, however, is making sure that it can meet its performance targets following its deployment. In this paper, a novel active correction system for a deployable telescope is described. The correction system co-aligns and phases the primary mirror segments and subsequently corrects remaining aberrations using a deformable mirror. A novel phasing sensor called PistonCam can bring telescope segments into phase while the telescope is staring at extended scenes. By only sampling segment boundaries, PistonCam is able to isolate piston and tip/tilt errors which allows the errors to be corrected more effectively. After phasing process has been completed, a moving scene sharpness optimization technique is used to correct the remaining aberrations with a deformable mirror, The technique does not require a constant scene, unlike existing sharpness optimization techniques. As such, the telescope does not need to track a ground scene during the correction process. The technique can also be used for continuous correction of telescope deformations. The active optics system offers robust aberration correction, is computationally inexpensive and requires limited additional optical hardware.
A 6U CubeSat for Earth observation in 230–350 km orbits with sub-meter resolution is presented. The proposed Stable and Highly Accurate Pointing Earth-Imager (SHAPE) system’s attitude determination and control system (ADCS) is composed of a single momentum bias wheel with magnetic bearings at rotational speeds of 6000–7000 rpm and refined magnetorquers. Reaction wheels as instability source are absent. The ADCS stabilizes the spacecraft attitude by counteracting the torques from external disturbances in the thermosphere down to < 1° pointing accuracy and < 0.1° instability. The momentum wheel was sized to an angular momentum of 1 Nms based on the worst-case atmospheric density of the next solar cycle. The 0.5 Am2 magnetorquer dipole moment provides with low power consumption, mass and cost, high reliability and sufficient torque. The ADCS initialisation study revealed three stable start-up modes, while the all-spun state is achieved using a set of thrusters. De-tumbling analysis show that the magnetorquers reduce the tumbling rates with magnitudes of up to 35°/s to mean motion values in less than an orbit using a static gain B-dot controller. A 3U camera design capable of sub-meter spatial resolution at 230 km altitude is presented which complies with the SHAPE spacecraft system design. The instrument has a single deployable primary mirror enabled by a deployment hinge design with hysteresis < 0.5 μ. This payload combined with air-breathing electric propulsion technology at 230 km nominal altitude boosts the SHAPE system Earth observation potential down to sub-meter spatial resolution and enables tuning of the mission lifetime by orbit keeping.
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