Nanotechnology for University Nanosatellites Flying in Formation: Prototype Design and Test

The goal of the research program is to develop a prototype of a satellite constellation consisting of four Nanosatelites flying in a formation, having on board a stereoscopic imaging experiment for the analysis of the Earth surface. A camera is on-board each of the four nanosatellites, and images of the Earth are taken from all the satellites at the same time. A space debris mitigation experiment is also scheduled, de-orbiting the launch adapter by an inflatable balloon. Use of recently developed and not yet space flight tested nanotechnology devices is a key point of the research program, in order to save weight and volume for the system. Each University Institution participating in the Project develops its own nanosatellite, according to prefixed standards, including the mechanical, electrical, communications interfaces and the co-ordinated orbital control strategy for the formation maintenance. Exchange of information and know-how among all the participating Universities is also one on the project goals, based on the experience gained in previously financed programs, in which the same Universities have been involved in the development of a common project. The nanosatellites are launched together in a single launcher adapter. After the launch adapter separates from the launcher the nanosatellites are released from the adapter one at a time at regular time intervals. The adapter is also exploited to perform a space debris mitigation experiment. After the last nanosatellite has been released, an inflatable balloon installed on the adapter is inflated, de-orbiting the adapter. The adapter itself is an active satellite, equipped with a battery, and a telemetry system, downloading the balloon pressure measured on-board. The nanosatellites are 10cm to 15 cm cubes, weighting less than 5 kg. They are three axis stabilised and have a propulsion system for orbit and attitude control. Orbit determination and relative formation geometry measurements are achieved either using GPS receivers, or by cross radio links among the satellites. The formation control requirements and the relative geometry determination algorithm is agreed among all of the participants in the first three months of the program. Every satellite is equipped with at least two radio transmitters and two receivers in the UHF and VHF band. One of radio channel is devoted to communication with the ground station. The other is used for cross link among the satellites. This gives both exchange of information (commands, data…) and a measurement system for the relative geometry of the satellites. Terrestrial components adapted to be operated in the space environment will be used whenever possible, in order to keep the system cost down. Based on the UNISAT-1 and UNISAT-2 experience at Università di Roma “La Sapienza”, this proved to be an effective way to approach the problem of budget constraints, leading to systems capable of one year operation in orbit at reasonable cost. On the other hand, nanotechnology devices seem to be a key point for the research program feasibility, allowing to keep down weight, power and volume for on-board components, such as attitude sensors and propulsion system. Nanotechnology based sensors have been recently proposed, including magnetoresistive magnetometers, weighting few grams and few centimetres size, while nano-optical devices could be used to build sun sensors in a square centimetre surface. Propulsion systems based on “micronozzles”, giving 100 microNewton thrust have been recently developed and ground tested. These devices are going to be flown on UNISAT-2 next year. These could be a basis for future developments, including miniaturisation of the control valves, reducing the overall weight of the propulsion system to the gas and tank weight, with nozzle and valve built on a single silicon chip.