ESA-OSIP Alticube+ project in its final stage!

In autumn 2023 the ESA OSIP project “Alticube+ – An Aggregated CubeSats Swarm for Long Fixed-baseline Radar Altimetry” started as one of the seven studies selected from around 70 proposals. OSIP stands for Open Space Innovation Platform. This program offers the exploration of new ideas and may lead to activities with ESA to further develop the ideas technologically to new missions. Project participants consist of two NL-RIA members, i.e. TU Delft (lead) and ISISpace, and a Spanish company Comet (not an NL-RIA member).

The theme for this OSIP campaign is “Innovative Mission Concepts Enabled by Swarms of CubeSats”. The idea is to take advantage of increased performance of swarms. At the same time the relatively low cost of CubeSats will allow to realize a constellation of swarm systems to increase the much wanted spatiotemporal resolution. From all submissions in early 2023 seven ideas have been selected. One of them, the final winner, will be awarded with a session at ESA’s Concurrent Design Facility together with ESA experts. This is a first step towards an In-Orbit Demonstration (IOD). The selection will take place at the end of April 2024. Read more about OSIP at Our Idea can be found at

Two innovative ideas based on the Alticube altimeter have been worked out in the course of this study. The Alticube altimeter was designed in earlier projects under the NL-RIA financing of NSO and an ESA project. The ideas are MIMOSARAL and MiniSWOT.

MIMOSARAL is a MIMO altimeter system, consisting of 5-8 CubeSats, which – once in orbit – are connected by booms to form a single instrument of up to 10 meters wide, thus forming a large MIMO antenna that observes the oceans with high cross track resolution under 1 km over a width of 10 – 20 km. In along track direction SAR processing results in high resolution. Thus a high resolution swath observing altimeter is created.

Artist impression of MIMOSARAL

The second idea that was explored is the MiniSWOT. Inspired by the success of the very expensive SWOT mission an aggregated system of 5 CubeSats is foreseen as a miniaturised and lower cost version of SWOT. 4 CubeSats are equipped with Ku-band radars to form two interferometer pairs. The 5th unit is the central node to control the system and process and downlink the data. The two interferometer systems are used to look to the left side and the right side of nadir over a swath of 18 km at very small incidence angles (1-4 deg). The interferometers result in a height map of the imaged ocean swath and is crucial for the study of long ocean wavelength features, including eddies, etc.

MiniSWOT measures 8 meter wide, consisting of 4 radar nodes and a central unit.

After the exploration of these two ideas we selected MiniSWOT for further detailing and to analyse the technological possibilities of realising the systems in 16U CubeSat platforms. Space is tight, as we need to include in the 16U platform the boom, reflector antenna with feed, propulsion system, radar, GNC (Guidance, Navigation & Control), and so on.

More information:         Jian Guo, Faculty of Aerospace Engineering, TU Delft.
                                       Peter Hoogeboom, Faculty of Civil Engineering and Geoscience, TU Delft