MarconISSta is a spectrum analyzer payload that we want to launch to the International Space Station in 2018. It will monitor parts of the frequency spectrum in VHF, UHF, L and S band in order to analyze current use and availability of bands for satellite communication.
The project is conducted by a team of researchers and students from Technische Universität Berlin with support of DLR, ESA and other partners.
Radiofrequency spectrum for satellite operation is a scarce resource. Along with the increasing number of launched and upcoming small satellites, the potential of harmful interference rises. In particular in UHF bands, small satellites are launched and operated at very low costs and therefore higher repetition rate than traditional systems. This evolvement puts pressure on existing allocations for amateur-satellite and space operation services. For this reason, a payload is introduced to measure the spectrum use in orbit and to assist in the identification of potentially free frequency allocations to ease the current coordination environment.
MarconISSta (from marconista, Italian for radio amateur) is an ISS experiment to measure spectrum use, interference potential and to support sharing studies in the crowded frequency spectrum allocated to satellite communication. The experiment is based on readily available COTS (Commercial Off-The-Shelf) hardware that is only slightly modified to withstand the space environment.
MarconISSta is proposed to be integrated into the existing ARISS setup and to use the ARISS antennas on the Columbus module. Any work in the experiment shall not negatively influence the incumbent amateur radio/ AIS activities. Since the results might be usable for ITU studies that shall be finished by 2019, it is planned to conduct the experiment during ISS expedition 56 in 2018.
- Analysis of spectrum use in UHF in the ranges 400.15-420 MHz & 435-438 MHz
- Analysis of spectrum use in VHF in the ranges 145.8-146 MHz & 150.05-174 MHz
- Analysis of spectrum use in L Band in the range 1260-1270 MHz
- Analysis of spectrum use in S Band in the ranges 2025-2120 MHz & 2400-2450 MHz
- Detection of interferers using algorithms based on received signal strength, attitude information, frequency Doppler shift information and antenna gain pattern
- Assessment of ARISS antenna radiation pattern
Since the ARISS antennas are pointing in nadir direction, the experiment will focus on terrestrial sources. However, LEO signals can be assessed as well, for example in LEOP phases of small satellite deployments from the ISS.
The main objective will be to monitor the spectrum use in different frequency bands. For this, the payload will measure the signal strength over a specified range of the spectrum (see objectives) over various orbits, calculate the maximum and average over time (e.g. one minute/ one hour). The measured data will be stored and then forwarded to the scientific user. Over time, a map of global spectrum use will be established .
In case of interference, a more detailed analysis of the region in which the interference occurred will be needed. In this case, a higher sampling rate and resolution per pass is required. These measurements will be relatively short (e.g. ten minutes in three consecutive orbits). Based on signal strength, Doppler shift and orbit/ attitude information, the interferer will be located.
An additional application of the experiment is the analysis of the radiation pattern of the ARISS antennas. Although the radiation pattern of the ground plane antennas is known, the influence of the Columbus structure is not known. Transmissions to the ISS will be measured and based on the terrestrial location of the signal, the received signal strength and the orbit of the ISS the radiation pattern will be constructed.
The measurements shall be taken with the ARISS Columbus antennas (VHF/UHF antenna and L/S band antennas). The measured RF data will be routed to the ARISS transceivers or to MarconISSta. For this, a switch must be integrated which is already planned by ARISS. This switch will most likely be a 4 to 1 mechanical switch for both the VHF/UHF and the L/S band cables. The experiment consists of an SDR (Software Defined Radio) and an SBC (Single Board Computer). The used SDR is the open source device LimeSDR. It is based on a field programmable RF chip (Lime Microsystems LMS7002M), an FPGA (Altera Cyclone IV) and a fast USB3.0 controller. It covers all frequencies between 100 kHz and 3.8 GHz and has two receivers and two transmitters. The receivers will be used to collect the RF data, which will be processed and then forwarded to the SBC via USB. The USB interface will also be used to power the SDR.
The main functions of the SBC will be to store and to forward the measured data. Luckily, we found out that ESA already has a very interesting SBC project on the ISS: The Astro Pi. The Astro Pi is a special Raspberry Pi that was designed to withstand the environment on the ISS while serving as a platform for educational projects. Its main mission was conducted during Tim Peake’s mission (ISS expedition 46 & 47) and shall now be available for new projects – like MarconISSta. We currently investigate the feasibility to use the Astro Pi and first results look very good! However, since the Astro Pi makes use of a first generation Pi, ARISS already plans to upload a newer version – the ARISS Pi. We might be able to use this one, which will definitely show besser performance.
In order to test the performance of MarconISSta with Astro Pi / ARISS Pi, we 3D-printed models of both and assembled them with all sensors that they also have on the station. With that, we are able to simulate their use for our experiment to a high level (thermal behaviour & radiation effects are of course neglected at the current stage).
Future work & milestones
What happens next? Well, the software is already at a quite advanced level, measurements can already be taken. We now have to finalize the design of the housing. Once this is done, we will do some EMC/ EMI testing of the device to see if there are any problems created by electromagnetic waves. Afterwards, the system (software & hardware) is send to ESA for review. In the meantime, we will prepare ourselves for the operation of the system and prepare the analysis of the data.
In parallel, a huge load of documentation will be prepared to assure ESA, NASA and others that the system can meet their high quality standards.