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- Calling from the Moon
History of Communication Satellites in a Nutshell These days we can call up someone in the remotest parts of Antartica and have a conversation as though they were right next to us. However, without the nifty technology that is the ‘Satellite’, none of this would be possible. They were first mentioned by Arthur C. Clarke (author of ‘2001: A Space Odyssey’) in his article ‘Wireless World’ written in 1945, where he described the transmission of TV programmes from manned satellites in 24-hour orbit around Earth; and then later looked at in detail by John R. Pierce in 1951-2, paving the way to the first communication satellite to be launched in 1957: Sputnik 1. Sputnik 1 Replica. Credit: NSSDC, NASA Following this, many more innovations came and with this, many more communication satellites. From Telstar 1 in 1962 which transmitted the first satellite TV (including images of the Eiffel Tower and Statue of Liberty, since it was sent from Brittany to Maine in north east USA); to e-BIRD: a broadband satellite which provided signal to parts of Europe with none. As well as their many innovations of everything from what they could transmit to where in Earth’s orbit they were (more on that later), communication satellites have also famously been getting smaller; a lot smaller. The small light (from 1 to 10kg) nanosats have become very popular in recent years: ever since the first six in June 2003, they’ve been providing an affordable way to collect data and send it back to Earth, needing little fuel to send them into Space and little material to make them. Another miniaturising innovation is the the smallsat: a satellite class slightly bigger than the nanosat at less than 180kg. They have been especially popular as communication satellites; most notably with Starlink and OneWeb. Aside from the disruption of Earth-based astronomy, their focus is on fast global broadband, reaching places that couldn’t get an internet connection before using much cheaper methods than older broadband satellites to provide more universal coverage . Model of OneWeb Satellite. Credit: NASA/Kim Shiflett Where are they? The simple answer is, of course, in orbit around Earth. However, Earth’s orbit is a very big place, so there are various common orbit types: Geostationary Orbit (GEO), Low Earth Orbit (LEO), Medium Earth Orbit (MEO), Polar Orbit and Sun-Synchronous Orbit (SSO), Transfer Orbits and Geostationary Transfer Orbits (GTO) and the Lagrange Points (L-points) . First, let’s look at GEO: 35,786km above Earth and travelling west to east to follow the rotation of the Earth along the equator, thereby staying above the same place on Earth at all times. They can serve large sections of Earth with constant coverage, and so ensure that area always gets coverage (for relaying signals, for instance) or is continually monitored (like with weather satellites) . LEO is, as the name suggests, low: less than 1000km high to be specific, following any plane (angle of orbit) they want, meaning there’s lots more space for satellites. This makes them fantastic for imagery satellites, but not so for satellite communications, since they’re travelling so fast, orbiting 16 times a day. However, mega-constellations like those of Starlink and OneWeb are in LEO, so how? It’s down to the fact they work together to cover the whole Earth at once, seamlessly changing the satellite in use after the previous one used is out of range. All this makes it extremely popular, whilst also creating a mine field of space debris . And where does our prized GPS fit into all this? Well, GPS satellites (along with other navigation satellites such as ESA’s Galileo system) orbit in MEO, found between LEO and GEO. They have the advantages of a lower time to send signals than in GEO, a larger footprint across Earth than LEO, and the option of going in any plane around Earth . Like LEO, SSO orbits at a similar altitude (600-800km) and does what it says on the tin: it orbits so, relative to the Sun, it’s fixed in the same position all the time, flying over certain locations at the same time each day and going over the North and South Poles within 20-30 degrees. This is helpful in seeing changes over time at certain places . Scale diagram of where the orbits around Earth are. Credit: Rrakanishu, CC BY-SA 4.0 Want to use little fuel but still want to go all the way to GEO? Simple; use GTO: putting a satellite into a GTO when offloaded will let them move, with little use of the satellite’s energy, into a higher orbit. This is because it’s an elliptical instead of circular orbit, with two foci instead of one (points where a curve is constructed) — in other words, a stretched circular orbit . However, what if you want to go much much further out? This is where the Lagrange Points come in. Totalling five, they are the points far away (1.5 million km) from Earth where a satellite can have a stable orbit, found using some cool maths curtesy of one Joseph-Louis Lagrange . Where the Lagrange Points are relative to the Earth and the Sun. Credit: NASA/WMAP Science Team How to Navigate and Phone from Space What do we do if we don’t have this massive network of satellites though, like when you’re a spacecraft flung off into the far reaches of Space? That’s where NASA’s Deep Space Network (DSN) and ESA’s Deep Space Antennae (DSA) come in. They are groups of enormous radio antennae (everywhere from Madrid in Spain, to just north of Perth in Australia) which transmit and receive data, used for telemetry (receiving the scientific data spacecraft collect) and command (controlling what the spacecraft does) . However, as well as this, they also help with the problem of navigation in Space. The antennae send signals to the spacecraft and time how long it takes to arrive at a receiving dish after a signal has been transmitted by the spacecraft, determining: how fast the craft is travelling, its distance from Earth, and where the spacecraft is in the sky. A signal can then be transmitted to instruct the spacecraft as to how it can change its course . A 70m antenna in Robledo de Chavela near Madrid, Spain, used in NASA's DSN Credit: Hector Blanco de Frutos, CC BY 2.5 That said, on longer missions, it may take many minutes, hours or days to do this (around 2.7 days for the Voyager 1 probe to receive, send and then receive a signal ). This is where pulsars come in: neutron stars (dying massive stars) which send regular pulses of light from their poles as they rotate. The spacecraft can use three sources of these pulses (the quicker the more precise) to measure changes in the timing between each pulse, thereby pinpointing its location in space . Navigation and Communication on the Moon Unlike the far reaches of Space, the Moon is much much closer. This means that some Earth based technology already in place can be used: notably our global navigation systems, such as GPS. Their signals may be directed towards Earth, but some signal spills over into Outer Space. And some engineers think we could use that ‘spill-over signal’ to navigate, though the signal would be pretty weak . This is where a new generation of satellites come into play: ones which take out the time issues; the weakness of signals and the trouble with a body like the Moon coming between you and the Earth. It’s called Lunar Pathfinder . With the help of Surrey Satellite Technology Ltd (SSTL - announced on 16th September), a satellite manufacturer based just outside Guildford in central Surrey, ESA will put a single satellite into orbit around the Moon in 2024 to provide continuous communication services for both robots and humans on the lunar poles and its far side (the side which never faces Earth) because there are thought to be sources of oxygen, rocket fuel and water in those locations . It will also hold three experiments: an ESA receiver to detect the signals from GPS and Galileo (ESA’s version of GPS) from Earth, demonstrating the possibility of Lunar navigation with the aid of Earth and Moon based satellites; a NASA mirror (or retro-reflector) to demonstrate the possibility of laser ranging (tracking the positions of the satellites by measuring the laser light reflect off them ); and an ESA radiation detector to measure levels of radiation in orbit . To do all this, the Lunar Pathfinder satellite will be put into a lunar orbit called an ‘Elliptical Lunar Frozen Orbit (ELFO). The ‘frozen orbits’ are where spacecraft can orbit the Moon at a low altitude (800-8,800km) indefinitely (though this satellite will end its mission after 8 years), and at a range of inclinations (angles of orbit): 27º, 50º, 76º and 86º (very close to those all important Lunar polar regions) . Image showing the various missions which are part of the future lunar initiatives including NASA's Artemis programme and ESA's Moonlight programme. Credit: ESA In years to come, we may have an array of satellites helping our astronauts and robots on the Moon find where they are and communicate with the same ease we enjoy on Earth. by George Abraham, ADAS member. #Moon #Satellite #ESA #SSTL #NASA #GPS Click here for the previous news article Click here for the next news article Click here to look at the current state of NASA's Deep Space Network (DSN) Click here to see where ESA's Deep Space Antennae are located Click here to look at how ESA's Ground Stations are doing (which include ESA's Deep Space Antennae) - found at the bottom of the page References "Communications Satellites: Making the Global Village Possible". NASA. Archived from the original on 18th September 2021. "A Brief History of Satellite Communications". Ground Control. Archived from the original on 18th September 2021. "Cubesats: Tiny Payloads, Huge Benefits for Space Research". Space.com. Archived from the original on 18th September 2021. "Starlink". Starlink. Archived from the original on 18th September 2021. "July 12, 1962: The Day Information Went Global". NASA. Archived from the original on 18th September 2021. "Telestar 1 Legacy: 1st Live TV Broadcast by Satellite Turns 50". Space.com. Archived from the original on 18th September 2021. "What are SmallSats and CubeSats?" NASA. Archived from the original on 18th September 2021. "Types of Orbits". ESA. Archived from the original on 18th September 2021. "What is Low Earth Orbit?" Universe Today. Archived from the original on 18th September 2021. "Popular Orbits 101". Aerospace Security. Archived from the original on 18th September 2021. "What are Lagrange Points?" ESA. Archived from the original on 18th September 2021. "What is the Deep Space Network?" NASA. Archived from the original on 18th September 2021. "DSN Function". NASA. Archived from the original on 18th September 2021. "Navigation in Deep Space". Time and Navigation. Archived from the original on 18th September 2021. "Deep Space Communication and Navigation". ESA. Archived from the original on 18th September 2021. "Mission Status". Voyager. Archived from the original on 18th September 2021. "Path set for commercial communications around the Moon". ESA. Archived from the original on 18th September 2021. "Lunar Mission Services". SSTL Lunar. Archived from the original on 18th September 2021. "Welcome to ILRS". ILRS, NASA. Archived from the original on 18th September 2021. "Bizarre Lunar Orbits". NASA. Archived from the original on 18th September 2021. "Options for Staging Orbits in Cislunar Space". NASA. Archived from the original on 18th September 2021.
- Timperley Country Fair 2021
Photo of the Chair with Audrey Binch, Alma Singers Chair and Andrew Jeffries, Sale Male Voice secretary Credit: Christine Lavender I am extremely pleased to report that the Timperley Country Fair on Saturday was a success well beyond reasonable expectation and, particularly, for the joint ADAS and Trafford Arts Association stall. The attendance at the stall by all age groups was outstanding. The children’s quiz, galactic star search and alien drawing were enthusiastically tackled by many very young to youthful participants. Copies of the quiz and star search were taken to be completed at home, scanned and emailed back to the chairman. The outdated leaflets handed out to the public were verbally amended re: the website address and email contact and recipients were referred to the internet to access 'astroadas.space' for current info. Several local people were potential recruits for membership to ADAS. Also the TAA display was well-received. The chair arrived at 8.00 and was assisted by Parkinson’s Trafford branch in erection of the TAA gazebo. The stall was set up before members of the TAA arrived at 10.00 am and others, later on. Chris Lavender, ADAS, was in attendance for the majority of the day. Interviews were arranged by ALTY local radio at which both the Chair for ADAS and Andrew Jeffries for the TAA promoted the organisations in some detail. Heartfelt and grateful go to Christine L (ADAS), Andrew Jeffries, Bob Davies (both of Sale Male Voice), Audrey Binch, Terry Oddy (both of Alma Singers) for their enthusiastic attendance. The fair closed after 4.00 pm and the chair was assisted by TAA members, Andrew and Terry, in deinstallation of the displays and gazebo. A report will verbally presented at the next ADAS meeting. Apologies were noted from Ged and several TAA members. Take care and stay safe. by Peter Baugh, ADAS Chairman. #TimperleyFair Click here for the Timperley Country Fair website
- How to Find a Bone… from over 200 Million Kilometres Away
The Bone The bone in question is one “216 Kleopatra (A880 GB)” named colloquially as the “Dog Bone” because of its bone-like appearance. It is an asteroid (otherwise known as a minor planet) lying over 200 million kilometres from Earth in the Asteroid Belt, and measures only 270 kilometres in diameter . However, how did such an asteroid come to be? It all comes down to the formation of our Solar System some 4.6 billion years ago (for comparison, the Universe is only 3 times older than that!). This asteroid, along with others (1,113,527 in all currently) ranging from just 10 meters to 530 kilometres across (Vesta), started their lives in the proto-planetary disk of gas and dust orbiting the young Sun. The planets coalesced themselves from this soup, along with many smaller objects such as dwarf planets (like Pluto — sorry!), during the first 5 million years of the Solar System . They formed into larger and larger clumps due to the effects of gravity, whilst other material wasn’t so lucky, forming into small clumps and scattering into the Asteroid Belt and Kuiper Belt (due to the positioning and orbits of the planets) . Kleopatra seen at different angles on different dates Credit: ESO/Vernazza, Marchis et al./MISTRAL algorithm (ONERA/CNRS), CC BY 4.0 Asteroid Composition To differentiate them from comets (bodies with two bright tails), asteroids are defined as rocky bodies, as opposed to the comet’s icy composition. There are three classes: C-types, S-types, and M-types. C-types (or Carbon-types), also known as chondrites, are the darkest colour, most common and oldest types of asteroid. Named because of their high carbon content (making them look charcoal-like), they’re made of clay and silicate rocks. Their age is testament to their distance from the Sun (in the outer reaches of the asteroid belt mainly), leading to them only heating up to below 50ºC . You may have heard about the famous Winchcombe meteorite being called a carboniferous chondrite (or CM2-type). It’s similar to the pure chondrites I’m talking about, though these are also similar in composition to the Sun (without the volatiles like hydrogen and helium), providing an unprecedented view into the Solar System’s history (considered to be the best preserved bodies from the very beginnings of the Solar System) . The display of the Winchcombe Meteorite in the Natural History Museum Credit: Amanda Slater, CC BY-SA 2.0 Then there are the the S-types (or Siliceous-types), which are the 2nd most common in the Solar System. They make up some of the largest known asteroids (some big enough to be seen through 10x50 binoculars) and are found a bit further in than C-types, in the inner asteroid belt. They’re made of mostly nickel-iron and magnesium silicate materials, leading to a brighter appearance than their C-type counterparts . 253 Mathilde. Credit: NASA And finally there are the the M-types (or Metallic-types), which are some of the least studied asteroids, with only part of their composition known to us, though what we do know is many are made of nickel-iron sometimes mixed with stone. They’re found in the middle of the asteroid belt and can get up to 200km in diameter. This is in fact the type our Dog Bone is, metallic in composition (though predicted to be 50% empty space to make its density the low 3.6 grams per cubic metre it is) . The Widmanstätten pattern seen within many M-type meteorites. Credit: Daniel Baise, CC BY-SA 3.0 You may wonder how they can classify asteroids into such ambiguous categories, but there is in fact an easy way, through spectroscopy. More specifically, it’s through looking at the spectra of light reflected off the asteroid, as well as light produced by the asteroid (heat being given off as low-energy light). The shape of a spectrum (usually on a graph of the strength of light, or the amount reflected, against the wavelength or energy of that light) then dictates what elements are present in the asteroid, and therefore what category it fits into . Graph showing the spectrum of an asteroid which orbits a different star: white dwarf GD 40. This shows that this particular asteroid is high in silicates. Credit: NASA/JPL-Caltech/UCLA The Dog To find our bone scientists employed something which is used a lot on anything from ships to military bases to some cars: radar. Standing for “RAdio Detection And Ranging”, a radar instrument sends a pulse of microwaves (low energy light, like what you find in your microwave, but much stronger - though they won’t cook anything in their way!) to the object in question, before an instrument measures the signal which is reflected (otherwise known as an echo). The Arecibo Observatory (was used partly to observe planets using radar technology). Credit: JidoBG, CC BY-SA 4.0 Because scientists know the properties of the signal which was sent, they can deduce what the properties of the object are by using the idea of doppler shift (when the wavelength of the light is either stretched or squashed, making the light redder or bluer) by comparing the received signal to the transmitted signal. Unlike other astronomical observing methods, radar actively creates a signal, meaning measurements can be more precise. In fact, it’s so useful it has been used to accurately map Mercury, the Moon, Mars and Venus, as well as many asteroids including our Dog Bone. In fact, on 14th August 2021, the 1,000th asteroid (2021 PJ1) was observed using radar, just over 50 years after it was first employed for this use to observe the first target: 1566 Icarus. The North Pole of Venus as seen by the Magellan probe which used a radar to penetrate Venus' clouds and observe Venus. Credit: SSV, MIPL, Magellan Team, NASA However, it can’t be used for further away objects because of Inverse-Square Law: energy dissipates, spreading to 4 times the area when it’s twice as far from the source, leading to the intensity of light dropping to a quarter of the previous intensity. This means that the echos of signals can’t be observed if looking at far-off targets without pumping lots of energy into the signal . Diagram to show inverse square law. Credit: NASA/JPL-Caltech Kleopatra’s Friends The asteroid observed isn’t your normal target by any stretch, not only because of its ‘bone-like’ appearance, but because of the two moons that orbit it. Named AlexHelios and CleoSelene (after Cleopatra’s twins: Alexander Helios and Cleopatra Selene II), the moons (or more correctly, the satellites - moons are only classed as bodies in orbit around the planets ) are explained by Kleopatra’s formation as a rubble pile held together by gravity: the collision of two asteroids to form one. Any time after the start of the Solar System the asteroid came to be after a collision with another asteroid. Then, 100 millions years ago, the asteroid was impacted by another asteroid, causing it to spin much faster than it was previously. This caused it to elongate and eject what came to be the most distant of the two moons: AlexHelios. Then, around 10 million years ago, the inner CleoSelene was shed. These moons aren’t just there for show though: they’ve helped scientists determine Kleopatra’s density by looking at their orbits . Image taken by the Spectro-Polarimetric High-contrast Exoplanet REsearch (SPHERE) instrument on the VLT, showing the two moons and Kleopatra. Credit: ESO/Vernazza, Marchis et al./MISTRAL algorithm (ONERA/CNRS), CC BY 4.0 Observing The Dog Bone Recently, the European Southern Observatory’s (ESO) Very Large Telescope (VLT) observed the Dog Bone, obtaining the best images yet of it, creating a 3D model of its unusual shape. Not only does it show the Dog Bone itself, but also the two moons that orbit it, helping them calculate new and more precise estimates for Kleopatra’s mass and volume. It was 35% lower than previously thought, showing Kleopatra must be extremely porous and backs up the rubble theory. It was also found to be 270km in length, similar to that of the English Channel! Also, they found its rotation was almost at critical speed: the speed at which the asteroid would fall apart. This then backs up the other theory that the asteroid shed the two moons it has today. SPHERE Optical Bench (an instrument on the VLT to improve the detail and accuracy of images taken by the VLT, such as the one of Kleopatra). Credit: ESO, CC BY 4.0 However, with the new telescope being built by ESO (the Extremely Large Telescope, or ELT) it’s hoped that even better measurements can be taken of 216 Kleopatra, along with the possible discovery of smaller satellites that orbit this strangest of asteroids . by George Abraham, ADAS member. #Asteroid #Kleopatra #ESO #radar #VLT Click here for the previous news article Click here for the next news article Click here to see the list of asteroids observed by using radar Click here to look at where a visible C-type asteroid is in the sky (10 Hygiea, from an apparent magnitude of around 9 to 11) Click here to look at where a visible S-type asteroid is in the sky (3 Juno, from an apparent magnitude of around 7 to 11) Click here to look at where a visible M-type asteroid is in the sky (16 Psyche, from an apparent magnitude of around 9 to 12) Click here to look at the news article about the Winchcombe meteorite by the Natural History Museum, who now has the meteorite on display. 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- Upcoming Events | Altrincham and District Astronomical Society | Timperley
UPCOM ING EVENTS Date Subject Presenter 01/10/2021 TBC TBC NEXT EVENT TBC TBC 1 Oct 2021 TBC TBC 579th Meeting Subscribe Google Calendar Subscribe Apple Calendar Timperley Village Club, 268, Stockport Road, Timperley, Greater Manchester, WA15 7UT 15 parking spaces available behind the Timperley Village Club Local tram stop 22min walk (1.1 miles) 6 bus stops from 177ft to 0.1 miles First Friday of every month, except in July and August. Arrive at 8pm £3 for non-members to attend a meeting £1 for children to become members for a year - Click for more information £20 for adults to become members for a year - Click for more information Meeting from now on will be in person , starting at 8pm. Please click here to find out how to get there. If you aren't comfortable coming back, please join via Zoom. The link will be shared via email (to get emails, join , or if you are a member, email email@example.com ).
- Contact Us | Altrincham and District Astronomical Society | Timperley
- Terms of Service | Altrincham and District Astronomical Society | Timperley