The communication layer for the OLFAR satellite swarm

Recently, new directions in astronomy are investigated as space observations tend to evolve from optical observations to the low-frequency domain. Ultra-long EM waves are the result of planetary emissions from outside and inside the solar system and of high-energy particle interactions. Exploring this band would create an image of our younger universe and uncover a lot of the so called astronomical dark ages(1)

Orbiting low frequency antennas for radio astronomy(OLFAR): Distributing signal processing

Recently, new and interesting science drivers have emerged in the ultra low frequency range of 0.3-30 MHz ranging from the epoch of re-ionization, exo-planets, ultra-high energy cosmic rays and studies of the astronomical dark ages. However at these wavelengths, ground based observations are severely limited due to ionospheric distortions below 50MHz, manmade interference, complete reflection of radio waves below 30MHz and even solar flares (1)

Frequency and management of maternal infection in health facilities in 52 countries (GLOSS): a 1-week inception cohort study

Background: Maternal infections are an important cause of maternal mortality and severe maternal morbidity. We report the main findings of the WHO Global Maternal Sepsis Study, which aimed to assess the frequency of maternal infections in health facilities, according to maternal characteristics and outcomes, and coverage of core practices for early identification and management. Methods: We did a facility-based, prospective, 1-week inception cohort study in 713 health facilities providing obstetric, midwifery, or abortion care, or where women could be admitted because of complications of pregnancy, childbirth, post-partum, or post-abortion, in 52 low-income and middle-income countries (LMICs) and high-income countries (HICs). We obtained data from hospital records for all pregnant or recently pregnant women hospitalised with suspected or confirmed infection. We calculated ratios of infection and infection-related severe maternal outcomes (ie, death or near-miss) per 1000 livebirths and the proportion of intrahospital fatalities across country income groups, as well as the distribution of demographic, obstetric, clinical characteristics and outcomes, and coverage of a set of core practices for identification and management across infection severity groups. Findings: Between Nov 28, 2017, and Dec 4, 2017, of 2965 women assessed for eligibility, 2850 pregnant or recently pregnant women with suspected or confirmed infection were included. 70·4 (95% CI 67·7–73·1) hospitalised women per 1000 livebirths had a maternal infection, and 10·9 (9·8–12·0) women per 1000 livebirths presented with infection-related (underlying or contributing cause) severe maternal outcomes. Highest ratios were observed in LMICs and the lowest in HICs. The proportion of intrahospital fatalities was 6·8% among women with severe maternal outcomes, with the highest proportion in low-income countries. Infection-related maternal deaths represented more than half of the intrahospital deaths. Around two-thirds (63·9%, n=1821) of the women had a complete set of vital signs recorded, or received antimicrobials the day of suspicion or diagnosis of the infection (70·2%, n=1875), without marked differences across severity groups. Interpretation: The frequency of maternal infections requiring management in health facilities is high. Our results suggest that contribution of direct (obstetric) and indirect (non-obstetric) infections to overall maternal deaths is greater than previously thought. Improvement of early identification is urgently needed, as well as prompt management of women with infections in health facilities by implementing effective evidence-based practices. Funding: UNDP–UNFPA–UNICEF–WHO–World Bank Special Programme of Research, Development and Research Training in Human Reproduction, WHO, Merck for Mothers, and United States Agency for International Development

Swarm-to-earth communication in OLFAR

New science drivers have recently emerged in radio astronomy for observation of low-frequency radio waves, below 30 MHz. Exploring this frequency requires a space-based radio telescope with a very large aperture that is impossible to realize in a monolithic fashion. A distributed system consisting of a swarm of 50 or more nano-satellites is used to realize such an instrument. Equipped with low-frequency antennas, the very small spacecraft provide the needed aperture to capture and sample ultra-long electromagnetic waves. The distributed low-frequency telescope has to fulfill multiple tasks in which drawbacks such as the size and the limited power available are overcome by the large number of satellites. Sending the processed data to a base station is one of these aforementioned tasks that is critical for the functionality of the system. In our paper we analyze the challenges of downlinking data from a swarm of nano-satellites to Earth and propose a diversity scheme that helps the system to achieve its mission

Swarm to earth communication in OLFAR

New science drivers have recently emerged in radio astronomy for observation of low-frequency radio waves, below 30 MHz. Exploring this frequency requires a space-based radio telescope with a very large aperture that is impossible to realize in a monolithic fashion. A distributed system consisting of a swarm of 50 or more nano-satellites is used to realize such an instrument. Equipped with low-frequency antennas, the very small spacecraft provide the needed aperture to capture and sample ultra-long electromagnetic waves. The distributed low-frequency telescope has to fulfill multiple tasks in which drawbacks such as the size and the limited power available are overcome by the large number of satellites. Sending the processed data to a base station is one of these aforementioned tasks that is critical for the functionality of the system. In our paper we analyze the challenges of downlinking data from a swarm of nano-satellites to Earth and propose a diversity scheme that helps the system to achieve its mission

Calibration approach of the OLFAR space based radio telescope

In recent years, science drivers have emerged for radio astronomy in the frequency range between 0.3 and 30 MHz. Due to strong man-made radio frequency interference (RFI) and opacity and scintillation in the ionosphere, this is not possible on Earth. For this reason the Orbiting Low-Frequency Antennas for Radio Astronomy (OLFAR) project aims to develop a space-based radio telescope, consisting of 50 or more nano-satellites in a location far away from Earth. These satellites will be flying in a swarm approximately 100 km in diameter to synthesize a large radio aperture. As with any radio telescope, OLFAR will need to be calibrated. However the satellite swarm concept brings along several unique challenges for the calibration, which are outlined in this paper. An approach is proposed for the calibration using known calibrator sources and an alternating least squares (ALS) approach which solves for the complex receiver gains, the array response matrix, direction dependent antenna gains towards the calibrator sources and the receiver noise power. This paper provides proof of concept of the proposed calibration approach by means of Monte Carlo simulations