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  • 摘要:

    The formation of deuterated molecules is favoured at low temperatures and high densities. Therefore, the deuteration fraction D$_{frac}$ is expected to be enhanced in cold, dense prestellar cores and to decrease after protostellar birth. Previous studies have shown that the deuterated forms of species such as N2H+ (formed in the gas phase) and CH3OH (formed on grain surfaces) can be used as evolutionary indicators and to constrain their dominant formation processes and time-scales. Formaldehyde (H2CO) and its deuterated forms can be produced both in the gas phase and on grain surfaces. However, the relative importance of these two chemical pathways is unclear. Comparison of the deuteration fraction of H2CO with respect to that of N2H+, NH3 and CH3OH can help us to understand its formation processes and time-scales. With the new SEPIA Band 5 receiver on APEX, we have observed the J=3-2 rotational lines of HDCO and D2CO at 193 GHz and 175 GHz toward three massive star forming regions hosting objects at different evolutionary stages: two High-mass Starless Cores (HMSC), two High-mass Protostellar Objects (HMPOs), and one Ultracompact HII region (UCHII). By using previously obtained H2CO J=3-2 data, the deuteration fractions HDCO/H2CO and D2CO/HDCO are estimated. Our observations show that singly-deuterated H2CO is detected toward all sources and that the deuteration fraction of H2CO increases from the HMSC to the HMPO phase and then sharply decreases in the latest evolutionary stage (UCHII). The doubly-deuterated form of H2CO is detected only in the earlier evolutionary stages with D2CO/H2CO showing a pattern that is qualitatively consistent with that of HDCO/H2CO, within current uncertainties. Our initial results show that H2CO may display a similar D$_{frac}$ pattern as that of CH3OH in massive young stellar objects. This finding suggests that solid state reactions dominate its formation. .

    来源机构: 康奈尔大学 | 点击量:119
  • 摘要:

    Rosetta's comet has been seen changing colour and brightness in front of the ESA orbiter's eyes, as the Sun's heat strips away the older surface to reveal fresher material.

    Rosetta's Visible and InfraRed Thermal Imaging Spectrometer, VIRTIS, began to detect these changes in the sunlit parts of Comet 67P/Churyumov-Gerasimenko – mostly the northern hemisphere and equatorial regions – in the months immediately following the spacecraft's arrival in August 2014.

    A new paper, published in the journal Icarus, reports on the early findings of this study, up to November 2014, during which time Rosetta was operating between 100 km to within 10 km of the comet nucleus. At the same time, the comet itself moved along its orbit closer to the Sun, from about 542 million km to 438 million km.

    VIRTIS monitored the changes in light reflected from the surface over a wide range of visible and infrared wavelengths, as an indicator of subtle changes in the composition of the comet's outermost layer.

    When it arrived, Rosetta found an extremely dark body, reflecting about 6% of the visible light falling on it. This is because the majority of the surface is covered with a layer of dark, dry dust made out of a mixture of minerals and organics.

    Some surfaces are slightly brighter, some slightly darker, indicating differences in composition. Most of the surface is slightly reddened by organic-rich material, while the occasional ice-rich material shows up as somewhat bluer.Even when Rosetta first rendezvoused with the comet far from the Sun, ices hidden below the surface were being gently warmed, sublimating into gas, and escaping, lifting some of the surface dust away and contributing to the comet's coma and tail.

    VIRTIS shows that as the 'old' dust layers were slowly ejected, fresher material was gradually exposed. This new surface was both more reflective, making the comet brighter, and richer in ice, resulting in bluer measurements.

    On average, the comet's brightness changed by about 34%. In the Imhotep region, it increased from 6.4% to 9.7% over the three months of observations.

    来源机构: 欧洲航天局 | 点击量:39
  • 摘要:

    April 11th, 2016

    Artist’s rendering of the skCUBE in space. Image Credit: SOSA

    Slovakia is gearing up to launch its first satellite to orbit with the aim of demonstrating the country’s ability to carry out scientific experiments in space. The pocket-sized one-unit CubeSat, named skCUBE, is currently slated for liftoff in June atop SpaceX’s Falcon 9 rocket from the Cape Canaveral Air Force Station in Florida. The central European state is one of the last countries on the continent to have its own satellite.

    Weighing about 2.2 lbs. (1 kg), skCUBE is a 4-inch (10-centimeter) cube that will carry an onboard computer, a communications system and a small camera to conduct experiments when orbiting Earth. The main goal of this project is to demonstrate that Slovakia is capable of doing highly sophisticated space research.

    “We see the development of skCUBE as a first spark of light in showing the world that Slovakia belongs to countries with a potential in space science and industry. We want to show, that Slovakia has excellent universities, science institutions and companies which innovate and make our country a good name around the world and going to prove it through our first satellite Made in Slovakia,” Lucia Labajova, Marketing Manager of the Slovak Organization for Space Activities (SOSA), told Astrowatch.net.

    SOSA, founded in 2009, is a non-governmental entity developing the skCUBE project. The organization was established to popularize space research and to increase general awareness about the importance of space industry. It is also actively promoting the entry of Slovakia to the European Space Agency (ESA).

    SkCUBE is also backed by the government and could serve as an example of cooperation between universities, students, companies and other supporters. The Ministry of Education, Science, Research and Sport and the Ministry of Transport, Construction and Regional Development dedicated to the satellite about $102,000 (€90,000) in total. Many Slovak companies support the project with their know-how, qualified employees and also financially.

    SkCUBE satellite being presented at a press conference on Jan. 7, 2016. Photo Credit: SOSA

    “SkCUBE is developed and built by Slovak engineers and scientists as a national project demonstrating an excellent cooperation of our state, universities, students, companies and other supporters, such as astronomy fans,” Labajova said.

    The tiny spacecraft is fitted with an electricity supply system, a sensory system and an orientation control instrument. The camera onboard the satellite will be capable of taking images with a resolution of 750 x 480 pixels. Its angle of view is 60 degrees and it contains infrared and neutral density filters.

    SkCUBE will focus on ham radio experiments that will include connection of two amateur radio operators via the satellite, sending of basic telemetry data via Morse code for easy listening and high speed data and image transmission via the 2.4 GHz band.

    Labajova noted that radio amateurs from all over the world will have the possibility to receive a picture, which will be marked with the skCUBE name, the call sign OM9SAT and a timestamp. It will only contain information in accordance with amateur radio regulations. Transport Protocol and possibilities for signal reception will be published in advance on the project’s website.

    The ham radio research will also include a VLF receiver with frame magnetic loop antenna, which allows recording of radio signals in the range 3 to 30 kHz, spectral analysis and data transmission to the ground. The data will be public, and can be used to further scientific analysis.

    Other technological experiments will see studies such as attitude control of the satellite in space using magnetic coil actuators or checking radiation resistance of critical technology components (DC-DC converters, current measurers, switching transistor, RAM, FRAM, FLASH memory).

    Jakub Kapus, the chairman of SOSA is leading the skCUBE effort. The project team consists of scientists from the Zilina University, the Slovak technical university in Bratislava and the Faculty of Aeronautics at the Technical University Kosice.

    “In the beginning when SOSA was founded we had a goal to achieve something almost unimaginable for such a small group of people. We were connected by our passion for space and new technologies and wanted to push the Slovak space science and technology another step forward to later eventually become a full member of ESA,” Labajova said.

    “History is formed by brave and stunning acts. Today we are happy to present SOSA as a group of capable young scientists, engineers and people who want to push the boundaries forward towards a new frontier,” she added.

    SkCUBE satellite being presented at a press conference on Jan. 7, 2016. Photo Credit: SOSA

    Slovakia signed the European Cooperating State Agreement with ESA in February 2015. The nation has been actively involved in space physics research and in astronautics, having two cosmonauts, the Czechoslovak Vladimír Remek (flew in space in 1978) and the Slovak citizen Ivan Bella, who spent nine days onboard the Mir space station in 1999.

    Although Czechoslovakia has already sent its first satellite into space, Magion 1, in October 1978, Slovakia, as an independent country, hasn’t yet put its homegrown spacecraft in orbit around Earth.

    The launch of skCUBE was initially scheduled to be launched on Apr. 16 but that was postponed and is now planned for June. However, the exact date is yet to be decided. Currently, SpaceX aims to conduct two orbital missions in June.

    Labajova said that at this moment everything is on track for the June liftoff and the team can focus on the arrangements for the launch. However, in the beginning it was a long and difficult bureaucratic process as the skCUBE will be the first Slovak object in space.

    来源机构: 航天飞行 | 点击量:50
  • 摘要:

    An Atlas V 401 rocket, carrying Orbital ATK’s S.S. Rick Husband Cygnus spacecraft, flies from Space Launch Complex 41at 11:05 p.m. EDT (03:05 GMT on Wednesday, March 23) with the OA-6 cargo resupply mission to the International Space Station. Photo Credit: Jacques van Oene / SpaceFlight Insider

    CAPE CANAVERAL, Fla. — A ULA Atlas V rocket, in the 401 configuration, caused windows to rattle and car alarms to go off for miles around the Space Coast as the booster and S.S. Rick Husband Cygnus spacecraft ferried an estimated 7,756 lbs (3,518 kg) of cargo on its way to the International Space Station – the largest payload the spacecraft has sent aloft so far.

    Orbital ATK and United Launch Alliance sent the fifth mission – under the $1.9 billion Commercial Resupply Services contract Orbital ATK has with NASA – on its way in spectacular fashion in the late evening hours of Tuesday, March 22.

    This was the second, and final, planned launch of the Cygnus spacecraft atop a ULA Atlas V 401 rocket from Cape Canaveral. Photo Credit: Jared Haworth / We Report Space

    The mission got underway promptly at 11:05 a.m. EDT (03:05 GMT), at the very opening of a 30-minute launch window. The weather conditions at the Cape simply could not have been more ideal. Mostly clear skies and a light breeze welcomed the Atlas V and its precious cargo as the rocket left the launch pad and slowly climbed into the moonlit skies above SLC-41.

    “Today’s successful launch continues our great progress and momentum under the CRS contract with NASA,” Frank Culbertson, President of Orbital ATK’s Space Systems Group said via a release issued by the company. “I applaud the numerous professionals at NASA, ULA and Orbital ATK for their hard work and dedication. While we are still early in this mission, everything is tracking well. We now eagerly await Cygnus’ berthing with the ISS and conducting scientific experiments onboard the spacecraft for the first time.”

    Forecasts had predicted a 90 percent chance of favorable launch conditions – by liftoff, it was clear that those conditions had reached 100 percent. Chilly temps had crept into the area yesterday, with highs only reaching the mid-60s during the day. That trend continued throughout today.

    As noted, Tuesday’s launch was watched over by a full Moon, the light from which was unfettered by a smattering of clouds.

    While concerns about cumulus clouds had been raised, the Launch Readiness Review cleared the Atlas V booster to be rolled from the adjacent Vertical Integration Facility (VIF) to SLC-41 on Monday, March 21, with the booster traversing the short distance between the two structures starting at 10 a.m. EDT (14:00 GMT).

    The cargo for this mission included an array of science experiments. Technology demonstrators such as Gecko Grippers to look into how artificial gecko setae (the hairs on the small reptiles’ feet) could aid robots sent on orbit or to distant planetary destinations.

    The Additive Manufacturing Facility or “AMF” is being launched on behalf of California-based Made in Space to serve as a permanent platform at the space station from which to print parts, experiments, and other needed items that would otherwise require a separate launch to get to orbit.

    Strata-1, meanwhile, will focus more on the physical locations that astronauts might be sent to such as an asteroid, the Moon, and Mars. Various regolith simulators will help researchers gain a better understanding of how actual regolith behaves in the microgravity environment.

    After about 55 days, with its cargo transferred to the ISS and it has been unberthed from the orbiting laboratory, Cygnus will spend an additional eight days on orbit. During this time, scientists will conduct the Saffire-1 experiment. Contained within its own compartment and away from the used experiments, waste, and trash that the Expedition 47 and 48 crews will have loaded the Cygnus spacecraft with, the experiment will ignite the largest purposely-set fire on orbit that has been lit today. It is hoped the experiment will provide a better understanding of flame propagation on orbit.

    The Atlas V booster is well-suited to handle sending Cygnus to orbit as the rocket is described as having the ability to send some to 21,600 lbs (9,800 kg) low-Earth orbit and 10,470 lbs (4,479 kg) to a geostationary transfer orbit. The rocket was launched for the first time on Aug. 31, 2002; the 401 configuration of the rocket has flown 31 times since then.

    The March 22 launch was greeted by a full Moon. Photo Credit: Michael Seeley / We Report Space

    Shortly after it left the pad, the Atlas V booster conducted a pitch, yaw, and roll maneuver so as to maintain the correct ascent profile as well as to minimize aerodynamic loads on the vehicle.

    One minute and twenty-three seconds into the flight Atlas was traveling Mach 1 – the speed of sound. Eleven seconds later and the vehicle entered the region of maximum dynamic pressure or “max-Q”. At this part of the flight, the rocket’s speed along with the density of the atmosphere conspired with one another to place the rocket and its precious cargo under the greatest amount of stress.

    At booster engine cutoff (BECO), the RD-180 was burning its fuel of RP-1 (a highly refined form of kerosene) and liquid oxygen at the impressive rate of about 1,350 lbs per second – and moving at a speed of 10,000 miles (16,093 kilometers) per hour.

    At this point in the flight, the rocket and payload were some 80 miles in altitude (Atlas was about 170 miles down range).

    Four-and-a-quarter minutes after it had left the pad at SLC-41, Booster Engine Cutoff took place, with separation between the first stage and the Centaur upper stage taking place about six seconds after that.

    A little more than four-and-a-half minutes into the flight, the first burn of the Centaur upper stage (MES-1) took place. The burn lasted approximately 37 seconds, ending at 18 minutes and nine seconds after liftoff.

    Having completed its primary mission of shielding Cygnus through Earth’s atmosphere, the Payload Fairing or “PLF” was jettisoned some eight seconds later.

    About a second-and-a-half under 21 minutes after it had left the pad far below, the S.S. Rick Husband separated from Centaur, unfurled its two solar arrays and began the final leg of its journey to the ISS.

    “This was our second mission on an Atlas V rocket after our very successful OA-4 mission which we launched last December,” Orbital ATK’s Vice President of Advanced Programs in the Space Systems Group at Orbital ATK, Frank DeMauro told SpaceFlight Insider. “The Cygnus team has been very busy with both tonight’s mission, as well as the return-to-flight on Antares for this summer, 2016.”

    来源机构: 航天飞行 | 点击量:46
  • 摘要:

    Astronomers have made great strides in discovering planets outside of our solar system, termed "exoplanets."

    In fact, over the past 20 years more than 5,000 exoplanets have been detected beyond the eight planets that call our solar system home.

    The majority of these exoplanets have been found snuggled up to their host star completing an orbit (or year) in hours, days or weeks, while some have been found orbiting as far as Earth is to the sun, taking one Earth year to circle. But, what about those worlds that orbit much farther out, such as Jupiter and Saturn, or, in some cases, free-floating exoplanets that are on their own and have no star to call home? In fact, some studies suggest that there may be more free-floating exoplanets than stars in our galaxy.

    This week, NASA's K2 mission, the repurposed mission of the Kepler space telescope, and other ground-based observatories, have teamed up to kick-off a global experiment in exoplanet observation. Their mission: survey millions of stars toward the center of our Milky Way galaxy in search of distant stars' planetary outposts and exoplanets wandering between the stars.

    While today's planet-hunting techniques have favored finding exoplanets near their sun, the outer regions of a planetary system have gone largely unexplored. In the exoplanet detection toolkit, scientists have a technique well suited to search these farthest outreaches and the space in between the stars. This technique is called gravitational microlensing.

    来源机构: 空间参考 | 点击量:40
  • 摘要:

    This artist’s concept depicts the Bigelow Expandable Activity Module (BEAM), constructed by Bigelow Aerospace, attached to the International Space Station (ISS). Image Credit: Bigelow Aerospace

    Expandable space habitat manufacturer Bigelow Aerospace and launch provider United launch Alliance (ULA) issued a press release on Friday stating that the two companies would announce a new partnership at a news conference on Monday, April 11, at 4 p.m. MDT, at the 32nd Space Symposium in Colorado Springs Colorado. Both ULA CEO Tony Bruno and Bigelow Founder and President Robert Bigelow will be at the press conference which will be live-streamed on ULA’s website. The announcement comes just as a crucial on-orbit test of expandable habitat technology is about to begin.

    Expandable habitats are lighter and require less payload volume than traditional rigid structures. After being deployed in space, they can provide a comfortable area for astronauts to live and work inside. The habitats can also provide varying degrees of protection from solar and cosmic radiation, space debris, ultraviolet radiation and other conditions in space that are potentially harmful to humans.

    Image Credit: Bigelow Aerospace

    On Sunday, April 10, Bigelow’s Expandable Activity Module (BEAM) will arrive at the International Space Station (ISS) in the unpressurized aft trunk of SpaceX’s CRS-8 Dragon spacecraft. Five days later, the module will be removed and attached to the station using the station’s Canadarm2 robotic arm. Expansion of the module to its full size of 10 feet in diameter and 13 feet in length is scheduled to begin in late May.

    BEAM’s mass is approximately 3,000 pounds (1,360 kg). It consists of two metal bulkheads, an aluminum structure, and multiple layers of a Kevlar-like material, with spacing between the layers.

    BEAM should remain attached to the space station for about two years. During this time, ISS crew members will enter the module for a few hours several times a year to retrieve data from sensors and to assess how it is handling the rigors of space flight. It is hoped that this demonstration mission will help NASA to determine how well the habitat protects crews against solar radiation, space debris, and contamination.

    At the end of the two-year testing and evaluation period, astronauts will use the space station’s robotic arm again; this time, to detach BEAM from the orbiting lab. The module will then de-orbit and burn up during its descent through Earth’s atmosphere.

    Bigelow plans to produce a much larger habitat module in the future. The B330 is planned to be some 57 feet (17.3 meters) long and have 330 cubic meters (12,000 cubic feet) of usable internal space. The module is capable of providing living quarters for up to 6 astronauts and has an estimated lifespan of 20 years. B330 modules could be used for a number of purposes including orbital space stations, habitation modules for deep-space exploration, or surface habitats on the Moon or Mars. B330 habitats could be launched into space by the 552 variant of ULA’s Atlas V booster.

    来源机构: 航天飞行 | 点击量:42
  • 摘要:

    11 June 2013The module carrying the telescope and scientific instruments of ESA’s Euclid ‘dark Universe’ mission is now being developed by Astrium in Toulouse, France.

    Euclid will be launched in 2020 to explore dark energy and dark matter in order to understand the evolution of the Universe since the Big Bang and, in particular, its present accelerating expansion.

    Dark matter is invisible to our normal telescopes but acts through gravity to play a vital role in forming galaxies and slowing the expansion of the Universe.

    Dark energy, however, causes a force that is overcoming gravity and accelerating the expansion seen around us today.

    Together, these two components are thought to comprise 95% of the mass and energy of the Universe, with ‘normal’ matter, from which stars, planets and we humans are made, making up the remaining small fraction. Their nature remains a profound mystery.

    “Euclid will address the cosmology-themed questions of ESA’s Cosmic Vision 2015–25 programme with advanced payload technologies, enabling Europe to become a world leader in this field of research,” says Thomas Passvogel, Head of the Project Department in ESA’s Directorate of Science and Robotic Exploration.

    Astrium will deliver a fully integrated payload module incorporating a 1.2 m-diameter telescope feeding the mission’s two science instruments, which are being developed by the Euclid Consortium.

    The two state-of-the art, wide-field instruments – a visible-light camera and a near-infrared camera/spectrometer – will map the 3D distribution of up to two billion galaxies and the associated dark matter and dark energy, spread over more than a third of the whole sky.

    By surveying galaxies stretched across ten billion light-years, the mission will plot the evolution of the very fabric of the Universe and the structures within it over three-quarters of its history.

    In particular, Euclid will address one of the most important questions in modern cosmology: why is the Universe expanding at an accelerating rate today, rather than slowing down due to the gravitational attraction of all the matter in it?

    The discovery of this cosmic acceleration in 1998 was rewarded with the Nobel Prize for Physics in 2011 and yet there is no accepted explanation for it.

    By using Euclid to study its effects on the galaxies and clusters of galaxies across the Universe, astronomers hope to come much closer to understanding the true nature and influence of this mysterious dark energy.

    “We are excited that Euclid has reached this important milestone, allowing us to progress towards launch in 2020, and bringing us ever closer to uncovering some of the Universe’s darkest secrets,” says Giuseppe Racca, ESA’s Euclid Project Manager.

    Notes for Editors.

    Euclid is an ESA survey mission to investigate the nature of dark matter and dark energy. It was selected as the second Medium-class mission in ESA’s Cosmic Vision programme in October 2011 and formally adopted in June 2012. The mission will be launched in 2020 and will orbit around the Sun–Earth L2 point located 1.5 million km from Earth. Science and spacecraft operations will be conducted by ESA.

    More than 1000 scientists from over 100 institutes form the Euclid Consortium building the instruments and participating in the scientific harvest of the mission. The consortium comprises scientists from 13 European countries: Austria, Denmark, France, Finland, Germany, Italy, the Netherlands, Norway, Portugal, Romania, Spain, Switzerland and the UK. It also includes a number of US scientists, including 40 nominated by NASA.

    来源机构: EUCLID | 点击量:33
  • 摘要:

    The New Horizons spacecraft sent back over three years worth of measurements of the solar wind the constant flow of solar particles that the sun flings out into space from a region that has been visited by only a few spacecraft.

    This unprecedented set of observations give us a peek into an almost entirely unexplored part of our space environment - filling a crucial gap between what other missions see closer to the sun and what the Voyager spacecraft see further out. A new study to appear in The Astrophysical Journal Supplement lays out New Horizons observations of the solar wind ions that it encountered on its journey.

    Not only does the New Horizons data provide new glimpses of the space environment of the outer solar system, but this information helps round out our growing picture of the suns influence on space, from near-Earth effects to the boundary where the solar wind meets interstellar space. The new data shows particles in the solar wind that have picked up an initial burst of energy, an acceleration boost that kicks them up just past their original speed. These particles may be the seeds of extremely energetic particles called anomalous cosmic rays. When these super-fast, energetic rays travel closer to Earth, they can pose a radiation hazard to astronauts. Further away, at lower energies, the rays are thought to play a role at shaping the boundary where the solar wind hits interstellar space - the region of our solar system that Voyager 2 is currently navigating and observing.

    Studying the Solar Wind

    Though space is about a thousand times emptier than even the best laboratory vacuums on Earth, its not completely devoid of matter the suns constant outflow of solar wind fills space with a thin and tenuous wash of particles, fields, and ionized gas known as plasma. This solar wind, along with other solar events like giant explosions called coronal mass ejections, influences the very nature of space and can interact with the magnetic systems of Earth and other worlds. Such effects also change the radiation environment through which our spacecraft and, one day, our astronauts headed to Mars travel.

    New Horizons measured this space environment for over a billion miles of its journey, from just beyond the orbit of Uranus to its encounter with Pluto.

    The instrument was only scheduled to power on for annual checkouts after the Jupiter flyby in 2007, said Heather Elliott, a space scientist at the Southwest Research Institute in San Antonio, Texas, and lead author on the study. We came up with a plan to keep the particle instruments on during the cruise phase while the rest of the spacecraft was hibernating and started observing in 2012.

    This plan yielded three years of near-continuous observations of the space environment in a region of space where only a handful of spacecraft have ever flown, much less captured detailed measurements.

    This region is billions of cubic miles, and we have a handful of spacecraft that have passed through every decade or so, said Eric Christian, a space scientist at NASAs Goddard Space Flight Center in Greenbelt, Maryland, who studies what's called the heliosphere the region of our solar system dominated by the solar wind but was not involved with this study. We learn more from every one.

    Since the sun is the source of the solar wind, events on the sun are the primary force that shapes the space environment. Shocks in the solar wind which can create space weather, such as auroras, on worlds with magnetic fields are created either by fast, dense clouds of material called coronal mass ejections, or CMEs, or by the collision of two different-speed solar wind streams. These individual features are discernible in the inner solar system but New Horizons didnt see the same level of detail.

    The New Horizons data show that the space environment in the outer solar system has less detailed structure than space closer to Earth, since smaller structures tend to be worn down or clump together as they travel outwards, creating fewer - but bigger - features.

    "At this distance, the scale size of discernible structures increases, since smaller structures are worn down or merge together," said Elliott. It s hard to predict if the interaction between smaller structures will create a bigger structure, or if they will flatten out completely.

    Subtler signs of the sun S influence are also harder to spot in the outer solar system. Characteristics of the solar wind including speed, density, and temperature - are shaped by the region of the sun it flows from. As the sun and its different wind-producing regions rotate, patterns form. New Horizons didn't see patterns as defined as they are when closer to the sun, but nevertheless it did spot some structure.

    Speed and density average together as the solar wind moves out said Elliott.But the wind is still being heated by compression as it travels, so you can see evidence of the sun s rotation pattern in the temperature even in the outer solar system.

    Finding the Origins of Space Radiation Hazards

    The New Horizons observations also show what may be the starting seeds of the extremely energetic particles that make up anomalous cosmic rays. Anomalous cosmic rays are observed near Earth and can contribute to radiation hazard for astronauts, so scientists want to better understand what causes them.

    The seeds for these energetic, super-fast particles may also help shape the boundary where the solar wind meets interstellar space. Anomalous cosmic rays have been observed by the two Voyager spacecraft out near these boundaries, but only in their final stages, leaving questions as to the exact location and mechanism of their origins.

    "The Voyagers can't measure these seed particles, only the outcome," said Christian. "So with New Horizons going into that region, this blank patch in the observations is being filled in with data."

    Filling in such a blank patch will help scientists better understand the way such particles move and affect the space environment around them, helping to interpret what Voyager is seeing on its journey.

    Comparing New Horizons to Observations and Models

    Since New Horizons is one of the very few spacecraft that has explored the space environment in the outer solar system, lack of corroborating data meant that a key part of Elliott's work was simply calibrating the data. Her work was supported by the Heliophysics Research and Analysis program.

    She calibrated the observations with pointing information from New Horizons, the results of extensive tests on the laboratory version of the instrument, and comparison with data from the inner solar system. NASA's Advanced Composition Explorer, or ACE, and NASA's Solar and Terrestrial Relations Observatory, or STEREO, for example, observe the space environment near Earth's orbit, allowing scientists to capture a snapshot of solar events as they head towards the edges of the solar system. But because the space environment in the outer solar system is relatively unexplored, it wasn't clear how those events would develop. The only previous information on space in this region was from Voyager 2, which traveled through roughly the same region of space as New Horizons, although about a quarter of a century earlier.

    "There are similar characteristics between what was seen by New Horizons and Voyager 2, but the number of events is different," said Elliott. "Solar activity was much more intense when Voyager 2 traveled through this region."

    Now, with two data sets from this region, scientists have even more information about this distant area of space. Not only does this help us characterize the space environment better, but it will be key for scientists testing models of how the solar wind propagates throughout the solar system. In the absence of a constant sentinel measuring the particles and magnetic fields in space near Pluto, we rely on simulations - not unlike terrestrial weather simulations - to model space weather throughout the solar system. Before New Horizons passed Pluto, such models were used to simulate the structure of the solar wind in the outer solar system. With a calibrated data set in hand, scientists can compare the reality to the simulations and improve future models.

    来源机构: 空间参考 | 点击量:34
  • 摘要:

    MIRI is the mid-infrared instrument for the James Webb Space Telescope and provides imaging, coronagraphy and integral field spectroscopy over the 5-28 micron wavelength range. MIRI is one of four instruments being built for the Webb telescope. It is being developed as a partnership between Europe and the USA - the main partners are ESA, a consortium of nationally funded European institutes, the Jet Propulsion Laboratory (JPL) and NASA's Goddard Space Flight Center (GSFC).MIRI - a versatile, mid-infrared instrument with wide-ranging capabilities

    MIRI has capabilities needed for the whole range of JWST science, covering every phase of cosmic history from the high redshift Universe through the formation of planetary systems to our own Solar System.

    .

    MIRI (wrapped in its aluminized thermal shield) integrated into the JWST Integrated Science Instrument Module (ISIM). Credit: NASA/Goddard Space Flight Center/Chris Gunn

    Schematic diagram of the MIRI instrument. Credit: University of Arizona

    The science goals of JWST require a versatile mid-infrared instrument covering the 5-28.5 μm wavelength range with a wide field of view for imaging through broad and narrow band filters, low resolution spectroscopy from 5-10 μm, moderate resolution spectroscopy with R ~ 3000, and high dynamic range coronography. MIRI is designed to provide all of these functions in a single instrument.

    The MIRI imaging mode has a plate scale of 0.11 arcsec/pixel, fully sampling the JWST point spread function at 5.6 μm, a field of view of 1.7 by 1.3 arcmin and 10 filters (see Table 1 of Wright et al., 2008 for details of the filters).

    The MIRI coronagraphy mode has four coronagraphs operating at wavelengths selected for the optimal study of exoplanets. (The coronagraph filter bands are given in Table 1 of Wright et al., 2008.)

    The MIRI medium resolution spectroscopy mode is an integral field spectrograph with R ~ 3000, covering 4.6-28.6 μm. This wavelength range has been divided into four channels with concentric fields of view on the sky, and each channel has three sub-bands with dedicated gratings, so that a complete spectrum of a 3.5 × 3.5 arcsec field of view can be obtained in three exposures. The details of spectral resolution, spatial resolution and fields of view for each of the spectrometer channels and the wavelength sub-bands are given in Table 2 of Wright et al., 2008. For low-resolution spectroscopy, the resolution is R ~ 100, with a five arcsecond slit.

    Instrument overview.

    Due to the need to operate at mid-infrared wavelengths, MIRI must be cooled to a temperature of 7 K, much lower than the rest of the instruments in the JWST observatory, which will be at a temperature of 40 K. The instrument is therefore the only one of the JWST instruments to be cooled by a dedicated cooler and is thus unique in its distribution across all three regions of the spacecraft. This brings additional challenges for the instrument development. The MIRI optical system and the MIRI cooler system have followed different development paths, to take account of the different maturity levels of the technologies being employed.

    The MIRI optical system

    The MIRI optical system includes the opto-mechanical system known as the optical bench assembly (OBA); the instrument control electronics (ICE) to drive the mechanisms, read temperature sensors and similar tasks; the focal plane control electronics (FPE) to drive the detectors; and the MIRI flight software which configures and controls the instrument and handles the data flow between the hardware and the JWST Integrated Science Instrument Module (ISIM) flight software.

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    MIRI optical bench assembly and key subsystems. Credit: University of Leicester, UK

    The instrument has a modular optical design and is an isothermal all-aluminium construction. The sub-assemblies have been designed to be testable in isolation. The optical bench assembly is both supported on, and thermally isolated from, the ISIM structure by a Carbon Fibre Reinforced Plastic (CFRP) hexapod. Isolation from the ISIM thermal environment is provided by custom designed Multi-Layer Insulation (MLI) blankets.

    Optically, the instrument is divided into two channels - an imager channel, with one detector array and a spectrometer channel, which is further subdivided into long and short-wavelength modules - each having its own detector array. Both the imager and spectrometer channels are fed by common optics from a single pick-off mirror placed close to the Webb telescope focal plane. A pick-off mirror in front of the Webb optical telescope assembly focal plane directs the MIRI field-of-view towards the imager. A small fold mirror adjacent to the imager light path picks off the small (up to 8 × 8 arcsec) field-of-view of the spectrometer. A second fold in the spectrometer optical path is used to select either light from the telescope or from the MIRI calibration system.

    The imager module has a combined field of view for the imager, coronagraph and low-resolution spectrometer modes. Coronagraph masks are placed at a fixed location on one edge of the imager field. The light is collimated and, at the pupil image formed by the collimator, a filter wheel holds the imaging filters, Lyot stops and filters for the coronagraph and a pair of prisms for the low-resolution, 5-10 μm spectroscopy. A camera then images the field (or spectrum) onto a single detector.

    The medium resolution spectrometer module is split into a short-wavelength (~5 to 12 µm) and a long wavelength (~12 to 28 µm) spectrometer each covering two of four wavelength channels split by dichroics. Each channel consists of an Integral Field Unit whose output is collimated and then dispersed by a dedicated first-order diffraction grating. The spectra from pairs of IFUs are combined by two cameras onto two detectors.

    The spectrometer optics fall naturally into two subsystems - a spectrometer pre-optics which consists of the system of dichroics and image slicers with associated fold and re-imaging mirrors, and a spectrometer main optics consisting of the gratings and camera systems for the two spectrometers. Only one third of the full spectral band covered by each channel is sampled in a single exposure. A pair of mechanisms (the Dichroic and Grating Assemblies, or DGA) is used to select gratings and dichroics matched to each of the three sub-spectra. A full 5-28 μm spectrum requires that three exposures are made, one at each of the three positions of the two DGAs.

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    The MIRI instrument during alignment tests. Credit: STFC/RAL Space

    The fields of view for imaging and spectroscopy are defined and separated in the input optics and calibration sub-assembly, which also provides a calibration source for flat-field illumination of the imager. For calibration purposes the blackbody radiation is produced by micro-miniature tungsten filament lamps and is rendered uniform by a diffusing surface within an optical concentrator. The light is then re-imaged to a pupil placed in the shadow of the secondary mirror. An identical calibration source is also included in the spectrometer channel. The imager optics are supported on one side of primary structure with the spectrometer optics on the other side, and all the mirrors and structures are of light-weight construction.

    There are three wheel mechanism assemblies, based on Infrared Space Observatory designs and heritage; one in the imager and one in each channel of the spectrometer. The imager wheel carries both the filters for imaging and the coronagraph masks/filters. Each spectrometer wheel mechanism assembly has a pair of wheels mounted on either side of the mechanism: a wheel with dichroics that define the sub-bands of the spectrometer, and a wheel with the matching set of gratings. There is also a contamination control cover; used to protect the MIRI detectors and optical chain from contamination in flight during the observatory cool down process. The cover is also used to protect the detectors from saturation during the process of centring bright stars accurately behind the coronagraph masks.

    The instrument control electronics (ICE), located in the warm spacecraft region, operates in cold redundancy and provides the capability for controlling the four mechanisms, processing mechanism position sensor and thermistor telemetry, and driving the calibration emitters. The ICE is connected to the ISIM Command and Data-Handling electronics (ICDH) by an MIL-STD-1553B bus, and responds to instrument configuration commands from the MIRI flight software.

    The imager and short and long wavelength spectrometer modules each have a Focal Plane Module (FPM) housing a single Sensor Chip Assembly (SCA) containing a 1024 × 1024 pixel Si:As detector array - with anti-reflective coatings applied to the detector to maximise the absorption for each instrument band - and readout electronics. The Focal Plane Electronics is a space-qualified electronics box located in a room temperature compartment on the ISIM, which responds to observation setup commands, produces the clocks and biases necessary to drive the detectors and read-out electronics, receives the analogue signals from the detectors, amplifies and digitises those signals, and transmits the science and housekeeping data to the ICDH. It receives setup commands for the individual FPM SCAs from the MIRI flight software, which is an instrument-specific application within the ICDH and its software hierarchy, communicating through a high speed SpaceWire interface. The FPE receives its power from the spacecraft Electrical Power Unit (EPU). The FPE also monitors and controls the temperature of each FPM and controls the detector annealing heaters, which may be used to help remove the effects of latent images.

    MIRI's unique cooling system.

    The MIRI cooler system uses a 6 Kelvin Joule-Thomson cooler, pre-cooled by a three-stage pulse tube cryocooler to provide 65 mW of cooling at the instrument. MIRI's 6 K cooling load, directly behind the primary mirror of JWST, is remote from the location of the compressors and pre-cooler. This distance, and the parasitic heat load on the refrigerant lines spanning it, is accommodated by the design. Design and construction of the cooler system is being carried out by Northrop Grumman Space Technology (NGST) under contract to JPL.

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    Cryocooler for MIRI. Credit: Northrop Grumman

    The Joule-Thomson compressor is based on a flight qualified High Efficiency Cooler (HEC) compressor. Reed valve modules have been added to the centre plate of the HEC compressor to produce a continuous flow of helium gas through the Joule-Thomson loop, producing 6 K cooling via the Joule-Thomson restriction.

    The pulse tube pre-cooler is based on the largest of NGST's product line of flight compressors, the High Capacity Cooler (HCC) compressor. The three-stage pulse tube cryocooler pre-cools the helium gas used in the Joule-Thomson cooling loop. Pre-cooling the helium gas for the Joule-Thomson cooler is achieved using three sections of recuperator and three thermal connections to the pulse tube cold head, one to the cold block of each of the stages of the cold head. The three sections span temperature ranges of 300-100K, 100-40 K, and 40-17 K.

    The pre-cooler recuperator section, including pulse tube cold head stages, recuperator stages, heat exchangers, thermal straps, the thermal radiation shield and mechanical supports was recognised as a particularly challenging part of the design. Simultaneously providing structural robustness to withstand launch vibration and low thermal parasitic loads required a careful balance to be achieved. Launch vibration and functional testing of the pre-cooler subassembly has demonstrated the successful design of this hardware.

    来源机构: JWST | 点击量:16
  • 摘要:

    At approximately 4:52 p.m. EDT (20:52 GMT), SpaceX successfully carried out a landing on the “Of Course I Still Love You” Autonomous Spaceport Drone Ship positioned out in the Atlantic Ocean. Image Credit: SpaceX

    CAPE CANAVERAL, Fla — The hits kept right on coming for SpaceX today as the NewSpace firm successfully returned their Dragon spacecraft to service and carried out the first completely successful ocean landing in the company’s history when at approximately 4:52 p.m. EDT (20:52 GMT) the Falcon 9’s first stage successfully touched down on the “Of Course I Still Love You” Autonomous Spaceport Drone Ship (ASDS) positioned out in the Atlantic.

    SpaceX launched the CRS-8 mission to the International Space Station (ISS) on April 8, at 4:43 p.m. EDT (20:43 GMT). The launch site for the mission was Cape Canaveral’s Space Launch Complex 40 (SLC-40) in Florida. The flight should see some 7,000 lbs (3,175 kg) worth of cargo, crew supplies and experiments arrive at the ISS on Sunday, April 10.

    Liftoff occurred at 4:43 p.m. EDT (20:43 GMT) from Cape Canaveral’s Space Launch Complex 40 in Florida. Photo Credit: Michael Howard / SpaceFlight Insider

    This afternoon’s launch marked the first time that SpaceX’s Dragon has taken to the skies since the June 2015 CRS-7 mishap that saw another Dragon and the Falcon 9 v1.1 rocket explode in the skies above Kennedy Space Center some 139 seconds after it had lifted off of the pad.

    SpaceX has already returned the Falcon 9 launch vehicle to flight. In fact, a mere six months had elapsed between the CRS-7 anomaly and the rocket’s return to flight (the Dec. 22, 2015 launch of Orbcomm OG2). Two more flights of the rocket followed in January and March of this year (2016). However, today’s flight was all about the Dragon.

    NASA has spent considerable energy highlighting the experiments and technology demonstrators that roared aloft with the Falcon 9 FT.

    Included in the payload for this mission was the Veg-03, Micro-10, Genes in Space and an array of other scientific investigations that will join the 250 or so that are already being carried out on the ISS.

    “The cargo will allow investigators to use microgravity conditions to test the viability of expandable space habitats, assess the impact of antibodies on muscle wasting, use protein crystal growth to aid the design of new disease-fighting drugs and investigate how microbes could affect the health of the crew and their equipment over a long duration mission,” said NASA’s Deputy Administrator Dava Newman via a statement issued by the agency.

    There’s little doubt that the payload that has “expanded” interest in the mission the most is the Bigelow Expandable Activity Module (BEAM). This technology demonstrator will further studies that have been and are underway into the concept of inflatable habitat modules—something of keen interest to NASA who is hoping to get back into the business of sending astronauts far beyond the orbit of Earth.

    In terms of the crew on board the space station, they will spend very little time in BEAM. NASA and Bigelow Aerospace have stated crews will only enter the habitat about three times per year during the its planned two year stint attached to the outpost. Although it is possible that astronauts on the ISS might spend more time in the hab, at present, they’re only slotted to spend three to four hours in the module during each visit.

    As is the case with any research done on orbit, mission planners first have to get their experiments out of Earth’s gravity well. That took place under mostly-clear skies which granted a 90 percent chance of favorable conditions for launch.

    Photo Credit: Jared Haworth / We Report Space

    “The rodents on our experiment will stay on the station for about six weeks, coming back with the CRS-8 Dragon,” NASA Ames Research Center’s Dennis Leveson-Gower told SpaceFlight Insider. “It’s thrilling to see your experiment go up, our team has been really been working hard on this … it’s really exciting to see it go off on the first day that it was scheduled.”

    On the afternoon of Thursday, April 7, Dragon was loaded with what is known as “late load” cargo in preparation for the launch attempt.

    Some 38 minutes before the launch was scheduled to take place, the launch conductor carried out a readiness poll. This was followed three minutes later with the fueling of the Falcon 9 FT began. The two-stage rocket is fueled by a mixture of RP-1 (a highly-refined version of kerosene) and liquid oxygen (LOX). The RP-1 is loaded first, which is then followed about 20 seconds later by the LOX (fueling was completed about a minute and-a-half before T-0).

    With just about 10 minutes remaining before launch, the Falcon 9 Ft entered into an engine chill, this was followed about three minutes later by the Dragon spacecraft being switched over to internal power.

    Eight minutes later, SpaceX’s Launch Director confirmed that the mission was ready to get underway with the 45th Space Wing’s Range Control Officer verifying that the Eastern Range was ready to support the launch about 30 seconds later.

    At just one minute prior to launch, the rocket’s command flight computers began final pre-launch checks. SLC-40’s sound suppression system, dubbed “Niagara,” was activated during this time. Twenty seconds after that, the rocket’s flight tanks were pressurized and the stage was set for flight.

    Three seconds before launch, the engine controllers directed the engine ignition sequence to start.

    As the new countdown clock in front of the Turn Basin at Kennedy Space Center ticked down to zero, the nine Merlin 1D rocket engines in the Falcon 9 FT’s first stage came alive with fire and thunder—announcing their fury to the residents of the surrounding wetlands.

    Just one minute after it had left SLC-40 and the Falcon 9 and Dragon entered the region known as maximum dynamic pressure or “max-Q”—the point where aerodynamic stress on the Falcon 9 is at its maximum.

    Three minutes into the flight, the rocket’s first stage had completed its part in the mission and main engine cutoff took place. With its mission complete, staging occurred with the rocket’s first and second stages separating. At this point in the flight, the second stage’s lone Merlin 1D came alive and the nose cone that had shielded Dragon was jettisoned.

    SpaceX Ceo and Founder Elon Musk detailed his company’s latest successful test flight after the April 8 flight. Photo Credit: Pedro Vazquez / SpaceFlight Insider

    Nine minutes after it had left the pad, second engine cutoff or “SECO” took place with the spacecraft separating from the second stage approximately one minute later.

    Free of its launch vehicle, Dragon continued on its way, deploying its solar array three minutes after SECO took place. If everything continues apace, at about two hours and twenty minutes after launch, Dragon’s guidance and navigation control bay door will deploy. This will revealing the sensors that will be used on Saturday when the Expedition 47 crew will grapple Dragon and berth it to the ISS.

    Before today, SpaceX has only been able to retrieve a first stage once, the December 2015 flight of 11 Orbcomm OG2 satellites. That, however, was a ground landing at Cape Canaveral Air Force Station’s Landing Zone 1 (formerly known as Space Launch Complex 13). Today’s landing was a far more difficult sea landing.

    While some launch service providers might rest and review at this point, SpaceX is pressing ahead with a very busy 2016 launch manifest which currently shows as many as twelve more flights—including the inaugural flight of the new Falcon Heavy rocket.

    For SpaceX’s CEO and Founder, Elon Musk, practicality and testing new technology need not require separate programs.

    “It’s really hard to do these test flights without, actually, going to orbit. We could conceivably I suppose put a huge weight, a 120 ton weight on top of the boost stage, and then do these launches, drop the 120 ton weight and then try to land – but there’s no point in that. Why not just send a useful payload while you’re at it – instead of the dead weight,” Musk told SpaceFlight Insider.

    That regimen appears to have paid off big time for the NewSpace firm as it has successfully delivered payloads to orbit and demonstrated its ability to land the Falcon 9’s first stage not once, but twice.

    Today’s flight marked the successful return-to-flight for the Dragon spacecraft and the first successful sea landing for the Falcon 9’s first stage so far. Photo Credit: Mike Deep / SpaceFlight Insider

    来源机构: 航天飞行 | 点击量:19