GPS World

Tag: Surrey Satellite Technology

  • ESA studies lay path to navigating the moon

    ESA studies lay path to navigating the moon

    Illustration of side-lobe signals from GPS satellites. (Image: ESA)
    Illustration of side-lobe signals from GPS satellites. (Image: ESA)

    Two European Space Agency studies found that the signal from navigation satellites orbiting Earth could be used to navigate the moon’s surface.

    News from the European Space Agency (ESA)

    To pinpoint a location accurately, a receiver — in smartphones or on a spacecraft — needs to collect and combine signals from at least four navigation satellites. The receiver determines its distance from each of the satellites by measuring the time that it takes for the signal to travel from the satellite to the receiver.

    Navigation satellites aim their antennas directly at Earth. Satellites orbiting above the navigation (GPS in this image, but Europe’s own navigation system is Galileo) constellation could only hope to detect signals from Earth’s far side. Now spacecraft can make use of signals emitted sideways from navigation antennas, within what is known as “side lobes.” Just like a torch, they shine energy to the side as well as directly forward.

    Navigation satellites orbit 22,000 kilometers above Earth’s surface. As they point in the direction of Earth, any spacecraft between them and Earth are served well by their signal. But around 10 years ago, engineers started demonstrating that spacecraft outside the orbit of navigation satellites could also navigate in space using “spill over” signal from the satellites.

    Then in 2012, two discovery and preparation studies explored a seemingly radical question: could this spillover signal even be used to navigate our way around the moon, and if so, what kind of receiver would we need to build to be able to use these signals?

    The studies found that the signal from navigation satellites orbiting Earth could be used to navigate the moon’s surface. But with the signal being so weak, they found that a new type of receiver would need to be built, and at the time there was no clear application for this.

    Eight years later, ESA invested in the development of such a receiver, and is exploring whether it could be demonstrated on the Lunar Pathfinder mission. ESA is collaborating with Surrey Satellite Technology Ltd. and Goonhilly Earth Station on this mission, which will provide exciting new opportunities for science and technology demonstration. In particular, it will help lay the groundwork for providing navigation services around the moon, currently studied through two ESA NAVISP activities and culminating in the Moonlight initiative.

    “We have now accurate simulation results that show that navigation signals may be used at moon orbit and provide good performances,” said Dr. Javier Ventura-Traveset, head of the Galileo Science Office and in charge of coordinating all GNSS moon activities for ESA’s Navigation Directorate. “And with an innovative receiver in Lunar Pathfinder, we could have the first ever experimental evidence of this.

    Artist’s impression of the Lunar Pathfinder mission. (Image: SSTL)
    Artist’s impression of the Lunar Pathfinder mission. (Image: SSTL)

    “Furthermore, we are also studying how existing navigation constellations may be complemented by additional moon-orbiting satellites, providing additional ranging signals for an optimal navigation service including moon landing and moon surface operations. This is being done as part of the ESA NAVISP program and through the ESA Moonlight initiative.”

    “The discovery and preparation studies have been eye-openers and they are currently being followed up by a NAVISP activity aiming to develop the highly sensitive spaceborne navigation receiver planned to fly on board Lunar Pathfinder,” said ESA Radio Navigation Engineer Pietro Giordano. “This technology will enable improved performances and much more cost-effective ways to navigate and operate missions to and around the moon.”

  • First of Batch 3 Galileo payloads delivered with evolved clocks

    First of Batch 3 Galileo payloads delivered with evolved clocks

    Galileo is on the march with a new generation of satellites bearing improved atomic clocks. The first of the Batch 3 navigation payloads was delivered in June by Surrey Satellite Technology (SSTL) in the UK to OHB System AG in Bremen, Germany.

    SSTL’s payload for Batch 3 is a recurrent build of the existing FOC payload, with an evolution of the atomic clocks to incorporate advances made under the European GNSS Evolution Programme. The earlier SSTL Galileo FOC payload comprised different units including European-sourced atomic clocks, navigation signal generators, high power traveling wave tube amplifiers and antennas.

    The new payload will be integrated aboard the satellite platform Galileo FOC FM23, named Patrick in honor of the winner of a drawing competition. Payload integration will be followed by a series of comprehensive test activities. Patrick and its next youngest sibling satellite of this series are scheduled to be ready for launch in autumn 2020.

    “We are looking forward to this first ‘marriage’ of a Batch-3-payload and platform and are ready to start Patrick’s test sequence soon,” said Lars Peters from OHB System AG, in charge of the Assembly Integration and Test for the satellites at eleven production islands where one satellite is completed every five weeks.

    “The ambitious schedule means that looking forward reserve satellites will be available both in orbit and on the ground,” added Dr. Wolfgang Paetsch, a member of the OHB System AG Management Board responsible for navigation, Earth observation and science.

    Paetsch received a PNT Leadership Award from GPS World magazine in 2017. At that time, Paul Verhoef of ESA, accepting on behalf of Paetsch, stated:

    “Of course we are waiting a bit to see what the real lifetime of the satellites is going to be. We don’t know that yet but we will find out in the next couple of years. Obviously there is a lot of pressure for further innovation, for further improvements. The user community over the last couple of years has become more outspoken about what they want and what they expect, which is nice. Obviously we need to take care of the legacy users, and we are having to see what new technology would allow us to do.”

    OHB System AG has contracted to deliver a further twelve satellites of this Batch 3 for Galileo. This will bring to 34 the number of Galileo satellites being supplied by the SSTL-OHB partnership. Of these, 14 are already in orbit.

    Feature photo: The satellite Patrick, first of Galileo’s Batch 3, will eventually travel from OHB to ESA’s ESTEC technical centre (shown here) in Noordwijk, the Netherlands for rigorous testing in simulated space conditions. (Photo: European Space Agency)

  • Surrey Satellite GPS receiver to navigate NASA OCO-3 mission

    Colorado-based Surrey Satellite Technology US LLC has delivered an SGR-20 space GPS receiver to NASA’s Jet Propulsion Laboratory to be integrated as part of the pointing control system for NASA’s Orbiting Carbon Observatory—3 (OCO-3) mission.

    OCO-3 will collect spaced-based measurements of atmospheric carbon dioxide and solar-induced fluorescence.

    Once launched, OCO-3 will be installed and operated on the International Space Station (ISS) Japanese Experiment Module-Exposed Facility (JEM-EF).

    Surrey’s SGR-20 is a single-frequency, multiple antenna GPS receiver designed as a spacecraft orbit determination subsystem for small satellite low-Earth orbit applications. The OCO-3 mission will use the Surrey SGR-20 for positioning information (to an accuracy of better than 20 meters) and velocity data (to an accuracy of better than 0.25 meters per second). The SGR-20 features four front ends with antennas, allowing more flexibility and redundancy for the selected mission.

    According to Eugene Hockenberry, project manager at Surrey Satellite, “The SGR-20 receiver is part of a highly proven range of GPS receivers that Surrey Satellite offers. Our receivers are currently active on twenty-four Surrey satellites and have accumulated over 700 years of on-orbit experience. With this mission we will see another first for Surrey: this receiver will be our first space hardware onboard the ISS.”

    Surrey Satellite delivered the receiver to JPL three months ahead of schedule. OCO-3 is scheduled to launch in 2018.

  • NASA launches micro satellites with GNSS receivers for remote weather sensing

    NASA launches micro satellites with GNSS receivers for remote weather sensing

    Surrey Satellite Technology’s Space GNSS Receiver Remote Sensing Instrument (SGR-ReSI) is the primary payload onboard NASA’s CYGNSS constellation, launched today, Dec. 15, from Cape Canaveral Air Force Station in Florida.

    The Cyclone Global Navigation Satellite System (CYGNSS) mission is part of the NASA Earth System Science Pathfinder Program that aims to improve extreme weather prediction by studying how tropical cyclones form.

    Artist's concept of one of the eight CYGNSS satellites in orbit. (Image: NASA/University of Michigan)
    Artist’s concept of one of the eight CYGNSS satellites in orbit. (Image: NASA/University of Michigan)

    The CYGNSS space segment consists of a constellation of eight micro satellites, each carrying the Surrey SGR-ReSI as the observatory payload in the form of a delay Doppler mapping instrument (DDMI). Making use of reflected global positioning signals, the DDMI collects ocean surface roughness data using a technique called GNSS reflectometry, providing CYGNSS with a new method for looking inside hurricanes. Wind speed will be estimated from this reflectometry data.

    “At the end of last year, we delivered the SGR-ReSI flight models, low-noise amplifiers, and antennas to Southwest Research Institute for final integration into the CYGNSS observatories — marking a significant hardware shipment out of our Englewood, Colorado, manufacturing facility,” said Clare Martin, vice president of programs at Surrey Satellite Technology U.S.. “All of us at Surrey are proud that our instrument is playing an integral role in this mission, and we will watch with great interest as the satellites are put to work.”

    The CYGNSS team is made up of the University of Michigan Department of Climate and Space Sciences and Engineering, Southwest Research Institute (SwRI), Surrey Satellite Technology and Sierra Nevada Corporation.

    Surrey Satellite Technology demonstrated the concept of GNSS reflectometry for the first time on its UK-DMC mission launched in 2003, and subsequently developed the SGR-ReSI, which is currently flying on Surrey’s TechDemoSat-1 mission.

    CYGNSS is NASA’s first Earth science small satellite constellation, designed to help improve forecasting hurricane intensity, hurricane tracks and storm surges.

    CYGNSS will measure previously unknown details crucial to accurately understanding the formation and intensity of tropical cyclones and hurricanes.

    “This is a first-of-its-kind mission,” said Thomas Zurbuchen, associate administrator for NASA’s Science Mission Directorate at the agency’s headquarters in Washington. “As a constellation of eight spacecraft, CYGNSS will do what a single craft can’t in terms of measuring surface wind speeds inside hurricanes and tropical cyclones at high time-resolution, to improve our ability to understand and predict how these deadly storms develop.”

    The CYGNSS mission is expected to lead to more accurate weather forecasts of wind speeds and storm surges — the walls of water that do the most damage when hurricanes make landfall.

    Using the same GPS technology that allows drivers to navigate streets, CYGNSS will use a constellation of eight micro satellite observatories to measure the surface roughness of the world’s oceans. Mission scientists will use the data collected to calculate surface wind speeds, providing a better picture of a storm’s strength and intensity.

    Unlike existing operational weather satellites, CYGNSS can penetrate the heavy rain of a hurricane’s eyewall to gather data about a storm’s intense inner core. The eyewall is the thick ring of thunderstorm clouds and rain that surrounds the calm eye of a hurricane. The inner core region acts like the engine of the storm by extracting energy from the warm surface water via evaporation into the atmosphere.

    The latent heat contained in the water vapor is then released into the atmosphere by condensation and precipitation. The intense rain in eyewalls blocks the view of the inner core by conventional satellites, however, preventing scientists from gathering much information about this key region of a developing hurricane.

    “Today, we can’t see what’s happening under the rain,” said Chris Ruf, professor in the University of Michigan’s Department of Climate and Space Sciences and Engineering and principal investigator for the CYGNSS mission. “We can measure the wind outside of the storm cell with present systems. But there’s a gap in our knowledge of cyclone processes in the critical eyewall region of the storm — a gap that will be filled by the CYGNSS data. The models try to predict what is happening under the rain, but they are much less accurate without continuous experimental validation.”

    The CYGNSS small satellite observatories will continuously monitor surface winds over the oceans across Earth’s tropical hurricane-belt latitudes. Each satellite is capable of capturing four wind measurements per second, adding as many as 32 wind measurements per second for the entire constellation.

    CYGNSS is the first complete orbital mission competitively selected by NASA’s Earth Venture program. Earth Venture focuses on low-cost, rapidly developed, science-driven missions to enhance our understanding of the current state of Earth and its complex, dynamic system and enable continual improvement in the prediction of future changes.