An innovative ESA-backed instrument to sample the space weather environment in-situ is set to join the International Space Station. Norway’s multi-Needle Langmuir Probe, m-NLP, due to be fitted to the European-made Bartolomeo platform on the ISS, a ‘front porch’ open to space, will map the ionospheric plasma surrounding the Station in unprecedented high resolution, performing almost 10 000 measurements per second continuously along its orbit.
Having passed its ESA acceptance review, the instrument has been passed to Altec in Italy to be prepared for launch to the ISS next March.
Meanwhile, another m-NLP is about to set off to the Moon aboard the United Arab Emirates’ Rashid lunar rover, scheduled to launch soon aboard Japan’s Hakuto-R lander on a SpaceX Falcon 9 rocket.
This m-NLP will survey the plasma environment immediately above the lunar surface, as the regolith interacts with sunlight, in the same way as the other will track the Station’s exterior plasma.
Plasma is sometimes called ‘the fourth state of matter’. Here on Earth it occurs only under special circumstances, for example in the form of lightning, polar auroras, or ‘sprites’ in the high atmosphere. Out in the wider Universe, however, the vast majority of matter takes the form of plasma, including our Sun and other stars, and the solar wind that streams from the Sun to interact with Earth, giving rise to ‘space weather’.
Numerous Langmuir probes have flown in space, used to measure plasma properties, and their design has scarcely changed since they were first invented back in 1924: a series of voltages is applied to the probe, and the collected currents are used to identify properties of the plasma, such as electron and ion density, as well as temperature.
“A standard Langmuir probe performs a voltage sweep from negative to positive to gather plasma parameters,” explains Tore André Bekkeng of Norway’s Eidsvoll Electronics. “But it takes time to perform such a sweep, typically from a half to two seconds. Operating at orbital velocities of around 7 km per second means you are limited to at most one sample per 3.5 km of space – which is far too coarse to capture those small ionospheric structures that are disturbing, among other things, satellite navigation signals and cause what is known as ‘signal scintillations’.”
He adds that the multi-needle Langmuir Probe (m-NLP) instead extends a quartet of miniature cylinders, each set to a different, but fixed, voltage, producing a much narrower spatial resolution – down to less than two metres.
“The idea dates back to the University of Oslo in the late 2000s, and was tested for the first time on a sounding rocket in 2008, flying up to the top of the atmosphere and down again to gain just around 10 minutes flight time,” Tore continues. “We continued on several sounding rockets, then progressed to flying MicroSats and CubeSats – Norway’s NorSat-1 and the Netherlands’ BRIK-II, whose operations continue to this day – although these versions of the m-NLP are performing 1000 and 4000 samples per second respectively, compared to the almost 10 000 per second achieved with our current design.”
The University of Oslo and Eidsvoll Electronics continued to work together on the m-NLP concept, and received shared funding to develop an ISS-ready version, through ESA Directorate of Science’s PRODEX programme supporting work on mission payloads and ESA’s Directorate of Technology’s General Support Technology Programme, preparing promising concepts for spaceflight and the open market.
In parallel the teams also worked on a rad-hard m-NLP version capable of operating at higher orbits, potentially as part of a space weather constellation currently under study. Eidsvoll Electronics designed and built the electronics, while the University took the boom system designed for NorSat-1 and enhanced it for improved performance.
Lasse Clausen from the University of Oslo explains: “Here in Norway – like other Arctic countries – we have always been fascinated by the auroras and their connection to space, and we are also operating a lot of aircraft and marine vessels in the northern regions.
“Accordingly, we are heavily reliant on Global Navigation Satellite Systems like GPS and Galileo. It turns out that aurora and other space weather phenomena cause significant ionospheric plasma variability which can seriously disrupt GNSS signals. So if it were possible to measure the ionospheric plasma state with multiple m-NLP instruments on board a fleet of satellites, we could develop a space weather forecast that predicts GNSS signal problems. Such a service would be highly valuable for society.”
Tore André Bekkeng adds: “PRODEX and GSTP support has been highly instrumental in developing both m-NLP versions, including allowing us to receive advice from ESA experts and make use of Agency Labs. And Eidsvoll Electronics has through the development of the m-NLP payload for the ISS acquired extensive system-level experience, and hired new project managers, system engineers, experts in electronics and software developers. The company is also in the procurement phase for a thermal vacuum facility capable of accomodating up to 16-unit CubeSats.
“Accordingly, this contract has significantly strengthened our position for future Norwegian and ESA-led payloads and missions.”
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