THE SMALLER THE BETTER
Nanosatellits really are the future. With their extremely low mass – up to 10 kg by definition – they are the cheapest way to access space, giving the opportunity to researchers, students and private companies to get involved in space activities.
With a maximum weight of 10 kg, nanosatellites have very reduced production time and costs, expecially if launched as piggyback payloads. Thus, they are an unparalleled means to offer students hands-on activities on a real space mission. The introduction of the Cubesat standard in 2003 boosted the exploitation of such smal satellites. Every year a large number of space missions based on nanosatellites are proposed, ranging from educational activities to technolgy demonstration and scientific research.
The limited onboard resources in terms of mass, volume and power available to the payload still prevent the exploitation of high performance scientific instrumentation, or demanding commercial payloads such as high gain antennas.
Optical communication is one of the most promising solutions for boosting the telecom capabilities of miniature satellites. In fact, laser links are characterized by a much narrower beamwidth and higher carrier frequency, which mean higher transmission gain. In other words, optical communication can realize higher data rate transmission with more compact and lighter devices. Moreover, optical links cannot be jammed or intercepted: they are secure channels.
So far so good? Nope. In fact, optical communication require very high pointing accuracy for the laser beams: typically, one tenth of the laser beamwidth, which means 1 to 20 microradians. Not only: the attitude control accuracy of nanosatellites is usually no better than 1-0.5 deg, which means they are “noisy” satellites.
STABILIZATION OF FLEXIBLE STRUCTURES
Highly flexible structures are widely used in various applications both in aeronautical and space fields. These structures are typically made of very thin layers of material, that have to be properly controlled and actuated in order to perform particular movements or to be kept in a determined position and/or attitude. This kind of structures can be found in miniaturized devices as well as in very large systems.
For what concerns space devices, flexible power subsystems are a promising technology, because of their advantages in terms of lower cost, superior radiation resistance and higher power density with respect to traditional bulk solar panels. Nevertheless, their extreme flexibility implies the employment of a control system to keep them deployed, avoiding undesirable instability conditions, in which power production and vehicle attitude are compromised. Dynamic analyses of the behaviour of thin-film solar panels subjected to typical disturbances in low Earth orbit have been performed through a multi-body software, both in uncontrolled and controlled conditions.
DIFFERENTIAL GPS ATTITUDE DETERMINATION
This project aims to develop an attitude sensor that uses differential phase measurements of the GPS carrier (DGPS). The innovative aspect resides in the small dimensions of the intended applications, such as miniature satellites (CubeSats) and drones. Using differential carrier phase measurement from three GPS antennas, mounted on a platform in a non-collinear fashion, the baseline vector of each pair of antennas can be precisely determined and the attitude of the platform reconstructed.
Previous DGPS attitude sensors used bulky electronic boxes and antennas that prevented their application on small platforms, it is possible to overcome these limitations by making use of the current progresses of the available GPS hardware, in terms of miniaturization of the GPS receivers and antennas.
Space users will benefit of the small impact of the sensor (both mass and volume use) while taking advantage of its potential use as an orbital position (standard GPS) and an attitude sensor (DGPS). Such system can be integrated with a standard Inertial Measurement Unit (IMU) platform to form a complete position and attitude determination suite. In atmospheric flight related applications the DGPS attitude sensor can be used as a reference sensor for IMUs, enabling the use of cheaper accelerometers and gyroscopes. The small dimensions of this sensor can make it useful for attitude determination in drones applications.