Walker M.J.H.,SCISYS Deutschland GmbH |
Palmer J.B.,Logica |
SpaceOps 2012 Conference | Year: 2012
The Integral spacecraft, a Gamma, X-Ray and optical telescope operated by ESOC since 17/10/2002, is in a highly elliptical high inclination orbit and experiences a perigee passage through the Van Allen radiation belts every 3 sidereal days. As the high radiation experienced during these passages would damage the instruments, these are switched off. In addition to these periodic regular orbital events, there is significant long-term evolution of the orbital parameters, which also fundamentally affects the characteristics of the radiation belt crossings. To optimise the science return, it is necessary to be able to predict as accurately as possible when the instruments must be switched off, and when they can be safely switched back on. In this paper we explore the observation of a correspondence between the bi-annual geotail crossings, the eclipse seasons and the periodic variation in instrument activation and deactivation altitudes. The paper characterises the nature of these radiation belt passages and proposes a method of predicting their future trend as the orbit evolves. Our analysis will address the following: Variation of Radiation belt entry and exit altitudes over time. Precession of the orbital plane, in particular the rotation of the line of nodes and the corresponding effects on the bi-annual timing of eclipses and geotail crossings. How the motion of the line of apsides impacts the belt crossing altitude. Combination of all 3 of the above effects The presented method and our findings could assist other missions by offering an optimisation strategy for science operations by predicting the evolution of radiation belt crossings and as a result, allow any protective measures to be implemented in time. In particular a methodology for data analysis and reduction is defined. © 2012 by Michael John Havelock Walker. Source
When rockets and their satellites leap into the sky from Europe's Spaceport in Kourou, French Guiana, they typically head east across the Atlantic, rising higher and faster with every second. Some 50 minutes after launch, the new mission can be seen from Western Australia, rising up from the Indian Ocean horizon and then arcing high in the sky, already in space. By the time the satellite, travelling at some 28 000 km/h, separates to start its life in orbit, it will already be in radio range of the land down under. By early next year, a new radio dish will be working at ESA's existing New Norcia, Western Australia, tracking station, tracking station, ready to catch the first signals from new missions. New Norcia currently has a large, 35 m-diameter dish for tracking deep-space missions such as Rosetta, Mars Express and Gaia, typically voyaging in the Solar System several hundred million km away. Its size and technology are not ideal, however, for initial signalling to new satellites in low-Earth orbit. In contrast, the new dish, just 4.5 m across, will lock onto and track new satellites during the critical initial orbits (see Liftoff: ESOC assumes control), up to roughly 100 000 km out. It can also 'slave' the much larger dish, which can then receive ranging data and telemetry – onboard status information – from the new spacecraft. "For satellite signals, the new dish has a wider field of view than the 35 m antenna," says Gunther Sessler, ESA's project manager, "and can grab the signal even when the new satellite's position is not precisely known. "It also offers rapid sky searches in case the satellite's position after separation is completely unknown, which can happen if the rocket over- or under-performs." In addition to satellites, the new antenna can also track rockets, including Ariane 5, Vega and Soyuz. The upgrade was prompted by the need to move the capability that, so far, has been provided by the ESA tracking station at Perth, 140 km southeast of New Norcia. That station's location has become increasingly untenable through urban sprawl and radio interference from TV broadcast vans. The upgrade ensures that ESA's Estrack tracking network can continue providing crucial satellite services along the most-used trajectories. "With the closing of Perth station, ESA would have lost its capability in Western Australia, which is a critical location for most European missions," says Manfred Lugert, ground facilities manager at ESA's operations centre in Darmstadt, Germany. The antenna was designed for low maintenance and operating costs and can go into hibernation when it is not needed between launches. Perth station will remain in operation until the end of 2015, when it will be dismantled and many of its components reused at other ESA stations. Once testing is completed, the dish will enter service in early 2016 in time for Galileo navsat launches and the first ExoMars mission, in March.
The expected 13 November reentry of what is likely to be a rocket body poses very little risk to anyone but could help scientists improve our understanding of how any object – man-made or natural – interacts with Earth's atmosphere. Observing and studying the reentry will help improve orbital models and reentry prediction tools, and can be used by scientists studying near-Earth objects (NEOs), such as natural asteroids, or the orbital decay of artificial objects such as satellites. It was discovered by the Catalina Sky Survey in 2013 and has been observed several times since then by the same team, who have been sharing their data via the US-based Minor Planet Centre (MPC), the International Astronomical Union's official repository for such observations. As confirmed by experts at ESA's NEO Coordination Centre (NEOCC), ESRIN, Italy, the object, dubbed WT1190F, is thought to be a discarded rocket body; it is orbiting Earth every three weeks in a highly 'eccentric' – that is, non-circular – orbit. "NEO experts have used observational data to estimate the object's density, which turns out to be much less than that of the solid rocky material that comprises many asteroids," says Detlef Koschny, responsible for NEO activities at ESA's Space Situational Awareness (SSA) programme office. "This density is in fact compatible with the object being a hollow shell, such as the spent upper stage of a rocket body or part of a stage." It is now predicted to reenter Earth's atmosphere in a few weeks, around 06:19 GMT (11:49 local; 07:19 CET) on 13 November 2015. "The object is quite small, at most a couple of metres in diameter, and a significant fraction if not all of it can be expected to completely burn up in the atmosphere," says Tim Flohrer, from ESA's Space Debris Office at the ESOC operations centre in Darmstadt, Germany. Whatever is left is expected to fall into the ocean about 100 km off the southern coast of Sri Lanka. Its mass is not sufficient to cause any risk to the area, but the show will still be spectacular, since for a few seconds the object will become quite bright in the mid-day sky. Tim says this object is rather special as it is likely man-made, but was discovered by an NEO monitoring system and its orbit has many similarities with an NEO orbit. This enables ESA experts to predict the impact time and location quite precisely, well in advance, which is usually not possible in comparison with reentering space-debris objects. The more observations, the better During the next few weeks, the NEOCC will implement observational campaigns to collect as much data as possible on this object, explains Marco Micheli, as astronomer working at the NEOCC. "The first goal will be to better understand the reentry of satellites and debris from highly eccentric orbits," he says. "Second, it provides an ideal opportunity to test our readiness for any possible future atmospheric entry events involving an asteroid, since the components of this scenario, from discovery to impact, are all very similar." Astronomers who may wish to observe the object are welcome to contact ESA's NEOCC for further information. The objective of ESA's SSA programme is to support Europe's independent utilisation of, and access to, space through the provision of timely and accurate information and data regarding the space environment, especially regarding hazards to infrastructure in orbit and on the ground. In general, these hazards stem from possible collisions between objects in orbit, harmful space weather and potential strikes by natural objects, such as asteroids, that cross Earth's orbit.
At first glance, this scene may look like a reptilian eye or a textured splash of orange paint, but it is actually a fish-eye view of Saturn's moon Titan. It was acquired at a height of about 5 km as ESA's Huygens probe, part of the international Cassini–Huygens mission, descended through Titan's atmosphere before landing. In the late afternoon of 14 January 2005, engineers and scientists at ESA's ESOC operations centre in Darmstadt, Germany, waited anxiously for data to arrive from Huygens, which touched down on Titan at around 12:34 GMT – the most distant landing of any craft. Following its release from NASA's Cassini on 25 December, Huygens reached Titan's outer atmosphere after 20 days and a 4 million km cruise. The probe started its descent through Titan's hazy cloud layers from an altitude of about 1270 km at 10:13 GMT. During the following three minutes Huygens decelerated from 18 000 km/h to 1400 km/h. A sequence of parachutes then slowed it down to less than 300 km/h. At a height of about 160 km the probe's scientific instruments were exposed to Titan's atmosphere. Around 120 km, the main parachute was replaced by a smaller one to complete the descent. The probe began transmitting data to Cassini four minutes into its descent and continued to transmit after landing at least as long as Cassini was above Titan's horizon. The signals, relayed by Cassini, were picked up by NASA's Deep Space Network and delivered immediately to ESOC. The first science data arrived at 16:19 GMT. Huygens was humankind's first attempt to land a probe on another world in the outer Solar System. "This is a great achievement for Europe and its US partners in this ambitious international endeavour to explore Saturn system," said Jean-Jacques Dordain, then ESA's Director General. This image is a stereographic (fish-eye) projection taken with the descent imager/spectral radiometer on Huygens. Explore further: Cassini Returns to Southern Hemisphere of Titan
Drusch M.,European Space Agency |
Del Bello U.,European Space Agency |
Carlier S.,European Space Agency |
Colin O.,Earth Observation Directorate |
And 11 more authors.
Remote Sensing of Environment | Year: 2012
Global Monitoring for Environment and Security (GMES) is a joint initiative of the European Commission (EC) and the European Space Agency (ESA), designed to establish a European capacity for the provision and use of operational monitoring information for environment and security applications. ESA's role in GMES is to provide the definition and the development of the space- and ground-related system elements. GMES Sentinel-2 mission provides continuity to services relying on multi-spectral high-resolution optical observations over global terrestrial surfaces. The key mission objectives for Sentinel-2 are: (1) To provide systematic global acquisitions of high-resolution multi-spectral imagery with a high revisit frequency, (2) to provide enhanced continuity of multi-spectral imagery provided by the SPOT (Satellite Pour l'Observation de la Terre) series of satellites, and (3) to provide observations for the next generation of operational products such as land-cover maps, land change detection maps, and geophysical variables. Consequently, Sentinel-2 will directly contribute to the Land Monitoring, Emergency Response, and Security services. The corresponding user requirements have driven the design toward a dependable multi-spectral Earth-observation system featuring the Multi Spectral Instrument (MSI) with 13 spectral bands spanning from the visible and the near infrared to the short wave infrared. The spatial resolution varies from 10. m to 60. m depending on the spectral band with a 290. km field of view. This unique combination of high spatial resolution, wide field of view and spectral coverage will represent a major step forward compared to current multi-spectral missions. The mission foresees a series of satellites, each having a 7.25-year lifetime over a 15-year period starting with the launch of Sentinel-2A foreseen in 2013. During full operations two identical satellites will be maintained in the same orbit with a phase delay of 180° providing a revisit time of five days at the equator. This paper provides an overview of the GMES Sentinel-2 mission including a technical system concept overview, image quality, Level 1 data processing and operational applications. © 2012 Elsevier Inc. Source