A novel emergency system for low earth orbit satellites using Galileo GNSS

Low Earth Orbit (LEO) satellites have a limited direct contact time with the stations of their ground segment. This fundamentally constraints a timeliness reaction of the mission control center in case of emergency situations onboard the LEO spacecraft. To enable such a rapid reaction to emergency situations onboard LEO satellites, it is proposed to use a Search and Rescue (SAR) beacon onboard that spacecraft to transmit an alert message via Galileo satellites which support SAR through the Cospas-Sarsat (C/S) system to the satellite mission control center. While SAR up to now is limited to terrestrial, maritime, and aviation user scenarios, this space user concept presents a novel emergency system which helps facilitating the valuable space assets which LEO satellites in many cases represent. However, such a space user system faces various technical, system, and business challenges as well as legal and regulatory issues. The frequency band assigned for the SAR system is limited to low power satellite emergency position-indicating radio beacons and is foreseen for earth-space transmissions only. The International Telecommunication Union (ITU) should agree on opening this band for space-space communication for space user distress beacons. The Distress Alerting Satellite System (DASS) and the SAR/Glonass system will also operate in this band and an agreement will be required for these as well. A visibility analysis is presented for LEO to Galileo satellites. Depending on the placement of the antenna of the distress beacon on the LEO spacecraft, between 6 and 21 Galileo satellites are visible. The space user beacon may cause interference to the current SAR system when it’s signals collide with those of Earth-bound users in time or overlap in frequency at the Galileo transponder. When they collide in time one of the signals might still be processed if one of the signal levels is significantly higher than the other. Upon sharing the same frequency, both signals could be lost in a worst case scenario. This overlap in frequency can be caused by Doppler shifts. Therefore, a Doppler analysis was performed and Doppler shifts of about ?11 kHz were identified. Next to frequency overlaps the traffic load in the adjacent channels can increase. Different methods to prevent these Doppler shifts were analyzed. To reduce system complexity and benefit from existing technology, the space user beacon could be similar to that of an Earth beacon. However, the repetition time could be increased and the frequency channel selected for the Doppler analysis is chosen such that the interference is minimal. A high level design of the SAR payload onboard the LEO satellite was performed and different protocol options were valuated.Space EngineeringAerospace Engineerin

Preliminary Analysis of a Novel SAR Based Emergency System for Earth Orbit Satellites using Galileo

This paper presents a preliminary analysis of a novel Search and Rescue (SAR) based emergency system for Low Earth Orbit (LEO) satellites using the Galileo Global Navigation Satellite System (GNSS). It starts with a description of the space user SAR system including a concept description, mission architecture and legal and regulatory aspects. This is followed by a visibility and interference analysis and a high level payload design will be presented.Space EngineeringAerospace Engineerin

Ventilation-induced plethysmographic variations predict fluid responsiveness in ventilated postoperative cardiac surgery patients

Background: It has been shown that ventilation-induced pulse pressure variation (PPV) is a better variable than central venous pressure (CVP) or pulmonary artery occlusion pressure (PAOP) for predicting cardiac output changes after fluid administration. The plethysmographic wave form measured with a fingertip pulse is very similar to the arterial blood pressure curve. Methods: We investigated whether this widely used, noninvasive instrument could predict fluid responsiveness by conducting an observational study in 32 patients who had undergone cardiac surgery. We compared PPV, CVP, PAOP, diastolic pulmonary artery pressure, and ventilation-induced plethysmographic variation (VPV) for predicting the cardiac output change after the administration of 500 ml, 6% hydroxyethylstarch. Results: We found a good correlation between cardiac output changes and both PPV and VPV (P < 0.05). Receiver operating characteristic analysis revealed an area under the curve of 0.937 for PPV and 0.892 for VPV. The optimal thresholds were a variation of 11.3% for both PPV and VPV in predicting a 15% increase in cardiac output. Conclusion: This study shows that VPV, like PPV, is a more reliable predictor of fluid responsiveness than CVP and PAOP

The Energetic Particle Telescope: First Results

The Energetic Particle Telescope (EPT) is a new compact and modular ionizing particle spectrometer that was launched on 7 May 2013 to a LEO polar orbit at an altitude of 820 km onboard the ESA satellite PROBA-V. First results show electron, proton and helium ion fluxes in the South Atlantic Anomaly (SAA) and at high latitudes, with high flux increases during SEP (Solar Energetic Particles) events and geomagnetic storms. These observations help to improve the understanding of generation and loss processes associated to the Van Allen radiation belt