Tag: Spaceflight

Space Sunday: the last goodbye, super-Earths and spaceplanes

Posted on by Inara Pey
September 14th, 2017. One of the final images captured by Cassini as it approaches Saturn for the last time, with mysterious Enceladus visible beyond the limb of the planet. The thin blue haze seen in the picture is the atmosphere above Saturn’s cloud tops, where the spacecraft finally disintegrated. Credit: NASA/JPL / Space Science Institute

At 12:55 UT (13:55 BST, 08:55 EST, 05:55 PDT) the very last signal was received from the NASA / ESA Cassini spacecraft as it entered the upper reaches of Saturn’s atmosphere before disintegrating and burning-up. It was received 83 by NASA’s ground station near Canberra, Australia, 83 minutes after being transmitted – by which time the probe had already been destroyed.

At mission control, at the Jet Propulsion Laboratory, operated jointly by NASA and Caltech in Pasadena, California, it was an emotional moment. For many, the mission had been a part of their daily lives for nigh-on 20 years.

“The signal from the spacecraft is gone and, within the next 45 seconds, so will be the spacecraft,” Cassini programme manager Earl Maize announced, his voice catching, to the team gathered in mission control. “I’m going to call this the end of mission.” He then turned to Spacecraft Operations Team manager Julie Webster and hugged her, before giving Linda Spilker, the Cassini Project Scientist a hug as well. That loss of signal came within 30 seconds of the time predicted ahead of Cassini’s final dive.

Cassini Project Manager Earl Maize (centre left) and Spacecraft Operations Team Manager Julie Webster embrace after the Cassini spacecraft plunged into Saturn, Friday, September. 15, 2017. Credit: NASA / Joel Kowsky

As I reported last week, The Cassini-Huygens mission has been an incredible voyage of discovery, revealing so much about Saturn, its rings and retinue of moons, including hints on the evolution of life itself and revealing how moons Titan and Eceladus may have all the right conditions to support basic life while Tethys could – like Enceladus – have a liquid water ocean under its ice.

Cassini’s final approach commenced on September 11th, as it started back towards Saturn having made a final pass between the planet and its rings and looping away from both the week before. Passing by Titan, and once more using the moon’s gravity to push it into the correct trajectory, the probe headed back for its final encounter with Saturn. The Titan fly-by presented a last opportunity to image and study the moon before Cassini’s imaging system was focused on Saturn for the first part of the final approach. Imaging Saturn ended on Thursday, September 14th as the vehicle re-oriented itself to gather as much data on its brief passage into the upper reaches of Saturn’s atmosphere.

Time line of the final plunge. Credit: NASA

As I’ve previously noted in my Cassini mission updates, the primary reason for sending the probe into Saturn’s atmosphere was because it had exhausted almost all of its on-board fuel supplies used to orient itself and to adjust its flight through the Saturnian system, and the mission team didn’t want to leave the probe tumbling around Saturn’s moons where it might one day impact one of them and contaminate it with both Earthly microbes which may be dormant inside the vehicle, and which radioactive debris from its electrical power generators.

However, an alternative would have been to use the last of the vehicle’s fuel to boost it away from Saturn and out into space, but the scientific return promised by a final plunge into the planet was too good to refuse. “Saturn was so compelling, so exciting, and the mission we finally came up with was so rich scientifically that we just couldn’t — we had to finish up at Saturn, not some place else.” Earl Maize stated during a press conference after the probe’s fiery end.

There are currently no planned missions that will follow Cassini-Huygens to Saturn, although there are proposals to send missions to Titan. However, while the active part of the mission has come to an end, it’s not an end of the mission’s science.

“We have collected this treasure trove of data, so we have decades of additional work ahead of us,” Linda Spilker, the Cassini Mission Scientist said. “With this fire hose of data coming back basically every day, we have only been able to skim the cream off the top of the best images and data. But imagine how many new discoveries we haven’t made yet! The search for a more complete understanding of the Saturn system continues, and we leave that legacy to those who come after, as we dream of future missions to continue the exploration we began.”

As a closing note – for now – it’s not often that a space mission gains an official music video; but Cassini-Huygen has been a major inspiration for many over the past two decades, it has earned not one, but three official music videos which form a suite of music by three composes: Iniziare (Italian: “to start” by Sleeping At Last, aka Ryan O’Neal), Kanna (Icelandic: “Explore” by Sarah Schachner) and Amaiera (“end” or “stop” by Joseph Trapanese). I’ve embedded the first part below.

SpaceX Launch X-37B

On Thursday, September 7th, a SpaceX Falcon 9 booster launched the US Air Force X-37B secret mini-shuttle into orbit ahead of the Florida coast being hit by hurricane Irma. It marked the 13th Falcon 9 launch of 2017, and the fifth flight overall for the X-37B.

The USAF’s X-37B Orbital Test Vehicle (OTV) on the runway at Kennedy Space Centre, May 7th, 2017, at the end of the 717-day OTV-4 mission, being “safed” by a Boeing team in protective suits to guard against harmful fumes and gases given off by the vehicle. Credit: USAF

OTv-5 (Orbital Test Vehicle flight 5) saw the automated spaceplane placed into a higher inclination orbit than previous missions – thus expanding the vehicle’s flight envelope. However, in keeping with previous missions, the USAF has remained mostly silent on the mission’s objectives or its intended duration, revealing only that one experiment flying is the Advanced Structurally Embedded Thermal Spreader II (ASETS-II), which will measure the performance of an oscillating heat pipe.

Previous OTV missions have been long-duration flights, with the maiden flight in 2010 lasting 224 days and 9 hours, which each mission lasting longer than the last, with the last mission completed, OTV-4,  totalling 717 days and 20 hours in orbit. The flights have, up until now, alternated between the two known X-37B vehicles, so although it has not been confirmed, it is believed this mission is being carried out by the first X-37B to fly in space.

The SpaceX Falcon 9 first stage descends to a safe landing at Cape Canaveral Air Force Station after sending the X-37B OTV on its way to orbit on September 7th, 2017. Credit: Ken Kremer

The launch took place from Kennedy Space Centre’s Launch pad 39A, which SpaceX has leased from the US space agency and refurbished to handle Falcon 9 and Falcon Heavy launches – and which is now liable to be the pad from which the company’s massive ITS super-heavy rocket will depart when it enters operations in the 2020s. After separating from the upper stage and its cargo, the Falcon 9 first stage performed a “burn-back” manoeuvre and flew back to SpaceX’s dedicated Landing Zone-1 (LZ-1) at Cape Canaveral Air Force Station alongside Kennedy Space Centre, offering spectators a superb view of the landing.

Continue reading “Space Sunday: the last goodbye, super-Earths and spaceplanes” →

Space Sunday: Cassini – a journey’s end

Posted on by Inara Pey
An artist’s impression of the Cassini spacecraft entering the upper reaches of Saturn’s atmosphere, high above the cloud tops, and breaking / burning up against the backdrop of the planet’s rings. Credit: NASA

On Friday, September 15th, 2017, just one month short of the 20th anniversary of its launch, the NASA/ Italian Space Agency (ASI) space probe Cassini will plunge into the upper reaches of Saturn’s atmosphere, bringing to a close the momentous NASA / ASI / European Space Agency Cassini-Huygens mission.

It will be a bitter-sweet moment for many the world over – most of all the vast international team who devoted up to fourteen years of their time on the mission – even before it launched. The Cassini vehicle has not only revealed so much about Saturn, its myriad moons, the rich complexities of the gas giant’s ring system- it has also helped inform us on the potential for life to exist elsewhere in the solar system and has even helped test Einstein’s work. It has also over the years returned some of the most stunning and evocative images of other worlds we have yet witnessed. Many of these images have been gathered together by National Geographic and have been put together in a superb interactive web presentation on the mission by Nadia Drake and Brian Jacobs.

A computer model of the hundreds of orbits Cassini has made around Saturn over the years (excluding the more recent orbits of the Grand Finale). Credit: Drake / Jacobs / National Geographic

In all seventeen countries have been directly involved in the conception, design, construction and operation of the Cassini-Huygens mission, both in terms of the Cassini orbiter and the Huygens Titan lander and the science instruments they carry. NASA carries primary responsibility for the orbiter’s design and construction, with the Italian Space Agency providing the all-important, dual-purpose high-gain radio antenna and its associated communications equipment, together with the low-gain communications suite which would provide continuous communications with Earth through the mission. ASI also incorporated a compact radar system in to the high-gain antenna systems, allowing it to function as a synthetic-aperture radar, a radar altimeter, a radiometer, and provide the visible channel portion of the VMS spectrometer package carried by the probe.

ESA was responsible for the Huygens lander, with France designing the vehicle itself, with the descent parachute system provided by Martin-Baker of America, while the science and communications packages were supplied by several European countries and the United States.

Cassini-Huygens stored within the payload fairing of an Atlas 4B rocket on the pad of Launch Complex 40, Canaveral Air Force Station, October 12th, 1997, 3 days ahead of its launch. Credit: NASA

The mission was named for the Italian-French astronomer Giovanni Domenico Cassini, who first observed the divisions within Saturn’s rings system (and after whom one of the divisions is also named) as well as for of the planet’s moons, and  Christiaan Huygens, the Dutch mathematician, physicist and astronomer, who first observed Titan, Saturn’s largest moon.

Work actually commenced on the mission in the 1980s, the goal being to develop a mission which could determine the three-dimensional structure and dynamic behaviour of Saturn’s ring system, investigate Saturn’s atmosphere and magnetosphere, determine the composition and likely structure of Saturn’s moons, including the nature and origin of the dark material on Iapetus‘s leading hemisphere, and, in conjunction with the Huygens lander, characterise Titan’s atmosphere, including the variability of the cloud haze, and characterise the moon’s surface at a regional level.

Initially, the mission was funded for a 10-year period from late 1997 through mid-2008, which included a journey of seven years to reach Saturn. The voyage took so long because at the time of launch, there was no launch vehicle combination capable of sending Cassini directly to Saturn. Instead, it completed a mini-tour of the inner solar system; six months after launch, Cassini flew by Venus, using the planet’s gravity to accelerate it into a wide elliptical orbit. A second encounter in June 2000 again accelerated the spacecraft, slinging it on to a further gravity-assist flyby of Earth in August 2000, which in turn accelerated it and bent it onto an trans-Jovian flight path.

In late 2000, Cassini reached the vicinity of Jupiter, making its closest approach to the planet on December 30th of that year. As well as using Jupiter’s gravity to sling it onwards to its final destination, Cassini used the encounter to study Jupiter and its faint system of rings. In all some 26,000 images of Jupiter, its moons and its rings were taken during the 6-month period of the flyby (October 2000 – March 2001). Cassini’s science suite was powered-up for the flyby, and resulted in some significant discoveries concerning Jupiter’s turbulent atmosphere, including breaking a long-held view. Jupiter’s banded atmosphere comprises a series of alternate bands of darker and lighter zones, in part caused by Jupiter’s rapid rotation. It had also been thought that the lighter bands were the result of the atmosphere rising upwards, giving rise to lighter cloud formations, before circulating downwards once more.

The cratered moon Tethys slips behind Saturn’s largest moon, Titan, as seen by Cassini on November 26th, 2009. Credit: NASA/JPL / Space Science Institute

However, Cassini revealed the dark bands were peppered with individual storm cells of upwelling bright-white clouds too small to see from Earth, suggesting the vertical circulation of Jupiter’s atmosphere to be far more uniform than thought. The probe’s findings also showed that Jupiter’s thin and dusty rings to be made up from small, irregularly shaped particles, most likely created by ejacta from micrometeorites impacting the Jovian moons.

Cassini reached Saturn in 2004, officially entering orbit around the planet on July 1st of the year. Prior to doing so, the vehicle was part of a test of Einstein’s theory of general relativity. This states that any massive object like the Sun causes space-time to curve, causing a beam of light or any other form of electromagnetic radiation that passes close to it to travel farther (the Shapiro time delay). In 2003, with the Sun coming between Earth and Cassini, scientists on Earth measured the frequency shift in radio signals being received from the spacecraft. Similar experiments had been carried out with the Voyager and Viking missions, but Cassini provided for much more refined measurements to be taken, and firmly validated Einstein’s theory.

A geyser sprays water ice and vapour from the south polar region of Saturn’s moon Enceladus. Cassini’s first hint of this plume came during the spacecraft’s first close flyby of the icy moon on February 17, 2005. Credit: NASA/JPL / Space Science Institute

Cassini‘s primary mission at Saturn commenced as it approached the planet for orbital insertion. Although the orbiter was capable of functioning – all things being equal – through until around 2017, this primary mission was scheduled to last just 3 years and 261 days, ending in mid-2008. This was sufficient time for the primary goals of the mission to be achieved, but Cassini was always designed to achieve so much more. With this in mind, the programme was granted two funding extensions. The first, called the Equinox Mission, funded the project through until the end of 2010, and gave a particular focus on Titan (15 flybys) Saturn’s ice-covered moon Enceladus, thought two of the locations in the Saturnian system where life might have taken hold.

The second extension, granted funding in 2010 to the tune of around US $60 million a year, is referred to as the Solstice mission (as it would end a few months past Saturn’s summer solstice). It guaranteed that, avoiding any spacecraft failures, the mission would continue through to the point where Cassini’s manoeuvring propellants would be practically depleted. This phase of the mission allowed for a more extended study of Saturn, its rings and moons. It meant Cassini could witness never before seen seasonal changes in the planet’s atmosphere and study. It also meant Cassini could study Saturn’s atmosphere and magnetosphere at exactly the same time as NASA Juno mission studied Jupiter’s atmosphere and magnetosphere, allowing a direct comparison of the two. Finally, the extension would carry the mission through its 5-month “grand finale”, probing the region between Saturn and its complex ring system.

Continue reading “Space Sunday: Cassini – a journey’s end” →

Space Sunday: water, spaceplanes and clockwork rovers

Posted on by Inara Pey
TRAPPIST-1 compared in size to our own Sun. Credit: NASA.

Since the February 2017 announcement on the discovery of seven rocky planets orbiting the nearby red dwarf star TRAPPIST-1, multiple studies have been conducted to ascertain whether any of the planets might harbour conditions suitable for life. The nature of their parent star would suggest this to be unlikely. However, an international team utilising the Hubble Space Telescope (HST) to study the TRAPPIST-1 system believe they’ve found evidence that some of the planets have the right conditions to allow liquid water to exist.

Vincent Bourrier, from the Observatoire de l’Université de Genève in Switzerland, and his team used the  Space Telescope Imaging Spectrograph (STIS) to study the amount of ultraviolet radiation each of the TRAPPIST-1 planets receives. If there were too much UV light, no water could survive on the surface because the water molecules would break up and escape through the top of the atmosphere as hydrogen and oxygen gas.

The team found that the inner planets in the system – TRAPPIST-1b and 1c – receive so much UV radiation from their sun, they may have lost more than 20 Earth-oceans worth of water in the course of their history, estimated to be between 5.4 and 9.8 billion years old. Thus, they are almost certainly devoid of water, and their surfaces are likely sterile. However, the findings also suggest the outer planets in the system – including the three within TRAPPIST-1’s habitable zone, may have lost less than three Earth-oceans’ worth of water throughout their history, and could possibly still possess liquid water, making them more amenable for life to rise.

As well as suggesting some of the TRAPPIST-1 planets may have liquid water present, the study has broader implications for the potential of other exoplanets harbouring life. Up to 70% of the stars in the Milky Way are believed to by M-class red dwarfs – and the majority of rocky exoplanets thus far found are orbiting such stars. So this study might indicate that many more of the exoplanets orbiting such stars could support liquid water and, perhaps, conditions suitable for life. However Bourrier and his colleagues emphasise that the study is not conclusive, and further research is needed to determine if any of the TRAPPIST-1 planets are actually watery.

SNC Prepares Dream Chaser for Glide Flight Testing and UN Mission

Sierra Nevada Corporation (SNC) carried out a “captive / carry” test of a Dreamer Chaser Cargo vehicle test article on August 31st, 2017. The flight, with the vehicle slung beneath a helicopter forms the first step towards the Dream Chaser Cargo carrying out glide flights and landings.

During the test, SNC collected data on the vehicle’s performance in flight, including operation of radar altimeters, air data probes and other systems that cannot be fully tested on the ground. The captive /  carry test followed a series of ground tests where the vehicle was towed behind a truck down a runway at speeds of up to 100 kph to ascertain its ground handling on landing.

The Dream Chaser Cargo test article is lifted aloft by helicopter in a captive/carry test. Credit: Sierra Nevada Corporation

SNC developed Dream Chaser to transport astronauts to and from the ISS. However, NASA selected capsule designs by SpaceX and Boeing. After a protest over the decision, filed with the U.S. Government Accountability Office, failed, SNC turned their attention to other potential uses for Dream Chaser.

One of these has been the development of a cargo variant to service the International Space Station (ISS) alongside existing resupply contractors,  Orbital ATK and SpaceX, and in 2016, NASA confirmed Dream Chaser Cargo has been selected to fly resupply missions to the ISS between 2019 and 2024.

On July 19th, 2017, it was announced that SNC had signed a contract with United Launch Alliance for the first two launches of these resupply missions, using the Atlas 5 552 launch vehicle. The first launch is scheduled for 2020 and the second in 2021, although NASA has yet to formally order any Dream Chaser flights.

A Dream Chaser Cargo vehicle will also be used in 2021 to launch the first United Nations mission into space. The United Nations Office of Outer Space Affairs (UNOOSA) said an agreement between them and SNC to fly the dedicated Dream Chaser mission is part of a broader effort by the office to increase access to space to emerging nations.

The mission will be open to all nations, but with a particular emphasis on those that don’t have the capabilities to fly their own experiments in space. UNOOSA are in the process of soliciting payload proposals with a goal of selecting payloads by early 2018 so that the winning countries have time to build them for a 2021 launch.

Unlike the majority of Dream Chaser Cargo missions, which will focused on ISS resupply work, the UNOOSA flight will see the vehicle placed in orbit around the Earth, and SNC have indicated the vehicle will be capable of operating freely in orbit for extended periods of time, should the UN desire a longer mission.

While billed as the UN’s first space mission, the Dream Chaser flight is part of UNOOSA’s Human Space Technology Initiative, launched in 2010 with the goal of providing developing countries the possibility to access space in microgravity conditions. Currently, the initiative includes two other major projects. The first is a cooperative project with the Japan Aerospace Exploration Agency (JAXA), designed to give developing nations the opportunity to launch cubesats from the ISS. Another programme, to be operated in cooperation with China’s space programme, will allow UN-backed missions to be flown aboard China’s space station, when it becomes operational in 2020.

Continue reading “Space Sunday: water, spaceplanes and clockwork rovers” →

Space Sunday: Voyager at 40

Posted on by Inara Pey
Voyager: 40 years on. Credit: NASA

August 20th 2017 marks the 40th anniversary of the launch of Voyager 2, which with its sister craft Voyager 1 (launched on September 5th, 1977) are humanity’s furthest-flown operational space vehicles, with Voyager 1 being the most distant human made object from Earth, at some 140 AU (AU= astronomical unit, the average distance between the Earth and the Sun; 140 AU equates to about 20.9 billion kilometres / 13 billion miles).

Despite being so far away from Earth, both craft are still sending data back to Earth as they fly through the interstellar medium in the far reaches of the solar system (the Pioneer 10 and Pioneer 11 craft which pre-date the Voyager programme by some 5 years, ceased transmissions to Earth in January 2003 and September 1995 respectively, although Pioneer 10 is the second most distant human made object from Earth after Voyager 1).

The Voyager programme stands as one of the most remarkable missions of early space exploration. Originally, the two vehicles were to be part of NASA’s Mariner programme, and were at first designated Mariner 11 and Mariner 12 respectively. The initial Mariner missions – 1 through 10 – were focused on studying the interplanetary medium and  Mars, Venus and Mercury (Mariner 10 being the first space vehicle to fly by two planets beyond Earth – Venus and Mercury – in 1974). Mariner 11 and Mariner 12 would have been an expansion of the programme, intended to perform flybys of Jupiter and Saturn.

A drawing of the Voyager vehicles. Credit: NASA/JPL (click for full size)

However, in the late 1960s Gary Flandro, an aerospace engineer at the Jet Propulsion Laboratory (JPL) in California noted that in the late 1970s, the outer planets would be entering a period of orbital alignment which occurs once every 175 years and which could be used to throw a series of probes out from Earth, which could then use the gravities of the worlds they encountered to “slingshot” them on to other targets. This led to the idea of a “Grand Tour” mission: sending pairs of probes which could use these gravity assists to fly by Jupiter, Saturn, Uranus, Neptune and Pluto in various combinations.

Funding limitations eventually brought an end to the “Grand Tour” idea, but the planetary alignment was too good an opportunity to miss, and so elements of the idea were folded into the Voyager Programme, which would utilise Mariner 11 and Mariner 12. However, as the mission scope required some significant changes to the vehicles from the basic Mariner design, they were re-designated as Voyager class craft.

(As an aside, the Mariner class is the longest-lived of NASA’s space probe designs; as well as the ten missions of the 1960s and 1970s which carried the design’s name,  the Mariner baseline vehicle – somewhat enlarged – was used for the Viking 1 and Viking 2 orbiter missions to Mars, and formed the basis of the Magellan probe (1989-1994)  to Venus and the Galileo vehicle (1989-2003) which explored Jupiter. And uprated and updated baseline Mariner vehicle, designated “Mariner Mark II”, formed the basis of the Cassini vehicle, now in the terminal phase of its 13-year study of Saturn and its moons.)

Each of the Voyager mission vehicles is powered by  three plutonium-238 MHW-RTG radioisotope thermoelectric generators (RTGs), which provided approximately 470 W at 30 volts DC when the spacecraft was launched. By 2011, both the decay of the plutonium and associated degradation of the thermocouples that convert heat into electricity has reduced this power output by some 57%, and is continuing at a rate of about 4 watts per year.

To compensate for the loss, various instruments on each of the vehicles have had to be turned off over the years. Voyager 2’s scan platform and the six instruments it supports, including the vehicle’s two camera systems, was powered-down in 1998. While the platform on Voyager 1 remains operational, all but one of the instruments it supports – the ultraviolet spectrometer (UVS) – have also been powered down. In addition, gyro operations ended in 2016 for Voyager 2 and will end in 2017 for Voyager 1. These allow(ed) the craft to rotate through 360 degrees six times per year to measure their own magnetic field, which could then be subtracted from the magnetometer science data to gain  accurate data on the magnetic fields of the space each vehicle is passing through.

However, despite the loss of capabilities, both Voyager 1 and Voyager 2 retain enough power to operate the instruments required for the current phase of their mission – measuring the interstellar medium and reporting findings back to Earth. This phase of the mission, officially called the Voyager Interstellar Mission, essentially commenced in 1989 as Voyager 2 completed its flyby of Neptune, when the missions as a whole was already into their 12th year.

A plume rises 160 km (100 mi) above Loki Patera, the largest volcanic depression on Io, captured in March 1979 by Voyager 1. Credit: NASA/JPL

Voyager 2 was launched on August 20th, 1977. Of the two vehicles, it was tasked with the longer of the planned interplanetary missions, with the aim of flying by Jupiter, Saturn, Uranus and Neptune. However, the latter two were seen as “optional”, and dependent upon the success of Voyager 1.

This was because scientists wanted the opportunity to look at Saturn’s moon Titan. But doing so would mean the Voyager craft doing so would have to fly a trajectory which would leave it unable to use Saturn’s gravity to swing it on towards an encounter with Uranus. Instead, it would head directly towards interstellar space.

So it was decided that Voyager 1, which although launched after Voyager 2 would be able to travel faster, would attempt the Titan flyby. If it failed for any reason, Voyager 2 could be re-tasked to perform the fly-past, although that would also mean no encounters with Uranus or Neptune. In the end, Voyager 1 was successful, and Voyager 2 was free to complete its surveys of all four gas giants.

Along the way, both missions revolutionised our understanding of the gas giant planets and revealed much that hadn’t been expected, such as discovering the first active volcanoes beyond Earth, with nine eruptions imaged on Io as the vehicles swept past Jupiter. The Voyager missions were also the first to find evidence that Jupiter’s moon Europa might harbour a subsurface liquid water ocean and to return the first images of Jupiter’s tenuous and almost invisible ring system. Voyager 1 was responsible for the first detailed examination of Titan’s dense, nitrogen-rich atmosphere, and Voyager 2 for the discovery of giant ice geysers erupting on Neptune’s largest moon, Triton. In addition, both of the Voyager vehicles added to our catalogues of moons in orbit around Jupiter and Saturn, and probed the mysteries of both planet’s atmospheres, whilst Voyager 2 presented us with our first images of mysterious Uranus and Neptune – and thus far remains the only vehicle from Earth to have visited these two worlds.

This is the last full planet image captured of Neptune. Taken by Voyager 2 on August 21st, 1989, from a distance of 7 million km (4.4. million mi). A true colour image white balanced to reveal the planet under typical Earth lighting conditions, it shows Neptune’s “Great Dark Spot” and surrounding streaks of lighter coloured clouds, all of which persisted through the period of Voyager 2’s flyby. More recent Hubble Space Telescope images suggest the “Great Dark Spot”, initially thought to be a possible cloud / storm formation, similar to Jupiter’s Great Red Spot, has vanished, leading to speculation that it may have actually been a “hole” in a  layer of Neptune’s layered clouds. Credit: NASA/JPL

The flyby of Neptune also sealed Voyager 2’s future. Scientists were keen to use the flyby of the planet to take a look at Triton, Neptune’s largest moon. However, because Triton’s orbit around Neptune is tilted significantly with respect to the plane of the ecliptic, Voyager 2’s course to Neptune  had to be adjusted by way of a gravitational assist from Uranus and a number of mid-course corrections both before and after that encounter, so that on Reaching Neptune, it would pass over the north pole, allowing it to bent “bent” down onto an intercept with Triton while the Moon was at  apoapsis – the point furthest from Neptune in its orbit – and well below the plane of the ecliptic. As a result, Voyager 2 passed over Triton’s north pole 24 hours after its closest approach to Neptune, its course now pointing it towards “southern” edge of the solar system.

Continue reading “Space Sunday: Voyager at 40” →

Space Sunday: of life elsewhere and launches

Posted on by Inara Pey
Titan’s structure (via wikipedia)

Saturn’s giant moon, Titan, has been a source of speculation of decades. Shrouded in a dense, methane-nitrogen rich atmosphere, potentially harbouring a liquid water ocean beneath its crust, the moon has long be thought to have the conditions in which basic life might arise.

The joint NASA-ESA Cassini-Huygens mission has, over the span of thirteen years, added immeasurably to our understanding of Titan – and to the mysteries of its potential. In doing so, it has also provided us with evidence of processes taking place which are the precursors to the development of life. For example, we know that within Titan’s ionosphere, nitrogen, carbon and hydrogen are exposed to sunlight and energetic particles from Saturn’s magnetosphere. This exposure drives a process wherein these elements are transformed into more complex prebiotic compounds, which then drift down towards the lower atmosphere and form a thick haze of organic aerosols that are thought to eventually reach the surface.

However, while the drivers of the process are known, the nature of the process itself has been something of a mystery – one which an international team of scientists led by the University College London (UCL) think they now understand.  In Carbon Chain Anions and the Growth of Complex Organic Molecules in Titan’s Ionosphere the team identify Titan’s upper atmosphere contains a negatively charged species of linear molecule in Titan’s atmosphere called “carbon chain anions” – which, it has in the past been theorised, may have acted as the basis for the earliest forms of life on Earth.

The molecules were detected by CAPS, the Cassini Plasma Spectrometer, as the vehicle passed through the upper reaches of Titan’s atmosphere on a final flyby before commencing its “Grand Finale” of flights between Saturn and its rings. The discovery came as a surprise, as carbon chain anions are highly reactive, and should not survive long in Titan’s atmosphere. However, what particularly caught the attention of the science team was that the data show that the carbon chains become depleted closer to the moon, while precursors to larger aerosol molecules undergo rapid growth. This suggests a close relationship between the two, with the carbon chains ‘seeding’ the larger molecules – those prebiotics mentioned above – which then fall to the surface.

How complex molecules are thought to form in Titan’s atmosphere. Credit: UCL

“We have made the first unambiguous identification of carbon chain anions in a planet-like atmosphere, which we believe are a vital stepping-stone in the production line of growing bigger, and more complex organic molecules, such as the moon’s large haze particles,” said Ravi Desai, the lead author for the study in a press release from UCL.

He continued, “This is a known process in the interstellar medium – the large molecular clouds from which stars themselves form – but now we’ve seen it in a completely different environment, meaning it could represent a universal process for producing complex organic molecules. The question is, could it also be happening at other nitrogen-methane atmospheres like at Pluto or Triton, or at exoplanets with similar properties?”

With its rich mix of complex chemistry coupled with its basic composition, Titan is something of a planetary laboratory; one which probably mirrors the very early atmosphere surrounding Earth before the emergence of oxygen-producing micro-organisms which started the transformation of our atmosphere into something far more amenable for the advance of life. As such, the discovery of carbon chain anions in Titan’s atmosphere potentially confirms that long-held theory that they help kick-start the life creating processes here on Earth, and suggest conditions on Titan might allow the same to happen there. It also offers insight into how life might start elsewhere in the galaxy.

“These inspiring results from Cassini show the importance of tracing the journey from small to large chemical species in order to understand how complex organic molecules are produced in an early Earth-like atmosphere,” Dr Nicolas Altobelli, ESA’s Cassini project scientist, said in the same press release. “While we haven’t detected life itself, finding complex organics not just at Titan, but also in comets and throughout the interstellar medium, we are certainly coming close to finding its precursors.”

Dream Chaser ISS Flights target 2020 Commencement

Sierra Nevada Corporation (SNC) has confirmed than United Launch Alliance (ULA) will provide the veritable Atlas V booster as the launch vehicle for the Dream Chaser Cargo mini-shuttle, which will be joining fleet of uncrewed vehicles from America, Russia and Japan keeping the International Space Station (ISS) supplied with consumables, equipment and science experiments. The company also indicate that launches of the vehicle could start in 2020.

The Altas V – Cream Chaser Cargo launch configuration. Credit: United Launch Alliance

Dream Chaser was originally conceived to fly crews to and from the ISS as part of NASA’s commercial crew transportation joint venture with the private sector. Four companies vied for contracts to supply NASA with vehicles capable of shuttling up to six personnel to and from the space station. Despite being one of the most advanced of the designs in terms of feasibility and development, the Dream Chaser was not selected for that work, with NASA opting for the SpaceX Dragon 2 vehicle and Boeing’s CST-100 Starliner capsule.

However, support within the US space agency for the Dream Chaser continued, allowing SNC to propose the development of Dream Chaser Cargo, a revised version of the original concept, capable of supplying up to 5.5 tonnes of cargo to the ISS. In January 2016, in renewing its contract with SpaceX (Dragon) and Orbital ATK (Cygnus) for such resupply missions, NASA extended it to include SNC. This was followed a year ago by formal approval being given for Dream Chaser missions to the ISS, which allowed SNC to push ahead with testing of the revised vehicle.

Dream Chaser will launch atop the commercial Atlas V in its most powerful configuration, dubbed Atlas V 552, with five strap on solid rocket motors and a dual engine Centaur upper stage. The cargo vehicle will be held inside a five metre diameter payload fairing with its wings folded. Cargo will be carried both within the vehicle itself and in a support module mounted on the rear of the spacecraft, which will also house a docking adaptor for connecting with the space station. The latter will be supplied to SNC by the European Space Agency, which is also supplying NASA with the Service Module for the Orion multi-Purpose Crew Vehicle.

The Dream Chaser Cargo, built by SNC, and the International Berth and Docking Mechanism, to be supplied to SNC for Dream Chaser flights by the European Space Agency. Credit: SNC

In addition to flying up to 5.5 tonnes to the ISS, Dream Chaser Cargo will be able to return some 2 tonnes of equipment, experiments and other items from the space station to Earth, where it will make a conventional runway landing using the former space shuttle runway at Kennedy Space Centre – or any other suitable landing facility in the United States.

It is expected that Dream Chaser cargo will fly a total of six missions to the ISS between 2020 and 2024, when it is currently anticipated the space station will be decommissioned.

Continue reading “Space Sunday: of life elsewhere and launches” →

Space Sunday: ninja space stations, Falcons, Dragons and ET

Posted on by Inara Pey
The cislunar Deep Space Gateway with an Orion Multi-Purpose Crew Module approaching it. Credit: NASA

Lockheed Martin has announced it will build a full-scale prototype of NASA’s proposed Deep Space Gateway (DSG), a space habitat occupying cislunar space. The facility, which if built, will be both autonomous and crew-tended, and is intended to be used as a staging point for the proposed Deep Space Transport NASA is considering for missions to Mars, as well as for robotic and crewed lunar surface missions.

DSG is part of a public-private partnership involving NASA in developing technologies for carrying humans beyond low Earth orbit called Next Space Technologies for Exploration Partnerships (NextSTEP). A Phase I study for the facility has already been completed, and the full-scale prototype will be constructed as a part of the Phase II NextSTEP habitat programme, which will examine the practical issues of living and working on a facility removed from the relative proximity of low Earth orbit, outside of the relative protection of the Earth’s magnetic field and subject to delays of up to 3 seconds in two-way communications.

“It is easy to take things for granted when you are living at home, but the recently selected astronauts will face unique challenges,” said Bill Pratt, Lockheed Martin NextSTEP program manager.

“Something as simple as calling your family is completely different when you are outside of low Earth orbit. While building this habitat, we have to operate in a different mindset that’s more akin to long trips to Mars to ensure we keep them safe, healthy and productive.”

The proposed Gateway, which if built would likely enter service in 2027/2028, will be designed to make full use of the Orion Multi-Purpose Crew Module as its command and control centre, and will also use avionics and control systems designed for the likes of NASA’s MAVEN mission in order around Mars and the Juno mission at Jupiter, which will allow the facility to operate in an uncrewed automated flight mode around the Moon for up to seven months at a time.

NASA’s MPLM mission logo. Credit: NASA / Marshall Space Flight Centre

The core of the prototype will be the Donatello Multi-Purpose Logistics Module (MPLM), originally designed and built for flights aboard the space shuttle and capable of delivering up to nine metric tonnes of supplies to the International Space Station (ISS). Two of these units, Leonardo and Raffaello flew a total of 12 missions to the ISS between 2001 and 2011, with Leonardo becoming a permanent addition to the space station in early 2011. And if film and comic fans are wondering, yes, the modules were all named after a certain band of mutant ninja turtles – hence the MPLM mission logo (right).

Donatello was a more capable module than its two siblings, as it was designed to carry payloads that required continuous power from construction through to installation on the ISS. However, it was never actually flown in space, and some of its parts were cannibalised to convert Leonardo into a permanent extension to the space station. In its new role, Donatello will form the core habitat space for the DSG prototype, and will be used as a testbed for developing the living and working space in the station, which will also have its own power module and multi-purpose docking adapter / airlock unit.

The Phase II development of the DSG is expected to occur over 18 months. Mixed Reality (augmented reality and virtual reality) will be used throughout the prototyping process to reduced wastage, shorten the development time frame and allow for rapid prototyping of actual interior designs and systems. The results of the work and its associated studies will be provided to NASA to help further the understanding of the systems, standards and common interfaces needed to make living in deep space possible.

The DSG is one of two concepts NASA is considering in it attempts to send humans to Mars. The second is the so-called Deep Space Transport (DSH). This is intended to be a large vehicle using a combination of electric and chemical propulsion to carry a crew of six to Mars. It would be assembled at the Deep Space Gateway.

While having a facility in lunar orbit does make sense for supporting operations on the Moon’s surface, when it comes to human missions to Mars, the use of the DSG as an assembly  / staging post for the DST actually makes very little practical sense. Exactly the same results could be achieved from low Earth orbit and without all the added complications of lunar orbit rendezvous. The latter simply adds an unnecessary layer of complexity to Mars missions whilst providing almost no practical (or cost) benefits, and perhaps again demonstrates NASA’s inability to separate the Moon and Mars as separate destinations – something which has hindered their plans in the past.

Musk Walks Back SpaceX Aspirations

SpaceX CEO and chief designer, Elon Musk has walked back on expectations for the initial lunch of the Falcon Heavy booster and on longer-terms aspirations for the Dragon 2 crew capsule.

Musk: a successful maiden flight of the Falcon Heavy “unlikely”. Credit: Associated Press

Speaking at the International Space Station Research and Development Conference held in Washington DC in mid-July 2017, Musk indicated that a successful maiden flight of the Falcon Heavy rocket is extremely unlikely. He also indicated that the company is abandoning plans to develop propulsive landing techniques for the Dragon 2 when returning crews to Earth from the ISS – and to achieve a soft landing on Mars.

Falcon Heavy is slated to be the world’s most powerful rocket currently in operation when it enters service in 2018, capable of lifting a massive 54 tonnes to low Earth orbit – or boosting around 14 tonnes on its way to Mars. Designed to be reusable, the rocket uses three core stages of the veritable Falcon 9 rocket – one as the centre stage, two as “strap on boosters” either side of it.

But computer modelling has revealed that firing all 27 motors on the stages (nine engines apiece) at launch has dramatically increased vibrations throughout the vehicle stack, making it impossible to gauge by simulation whether or not the rocket will shake itself apart without actually flying it. Hence Musk’s statement that the maiden flight of the Falcon Heavy  – slated for later in 2017 – is unlikely to achieve a successful orbit. However, telemetry gathered during the flight – should the worse happen – will help the company more readily identify stresses and issues created by any excessive vibration, allowing them to be properly countered in future launches.

Once Falcon Heavy is fully operational, all three of the core stages are intended to return to Earth and achieve a soft landing just as they do when used as the first stage of a Falcon 9 launch vehicle, and SpaceX is also working to make the upper stage of the Falcon 9 / Falcon Heavy  recoverable as well.

Also at the conference, Musk announced SpaceX will no longer be using propulsive landings for the crewed version of their Dragon 2 space capsule, due to enter operations in 2019 ferrying crews two and from the ISS, operating alongside Boeing’s CST-100 Starliner capsule. Initial flights of the Dragon 2 were intended to see the vehicle make a “traditional” parachute descent through Earth’s atmosphere followed by an ocean splashdown – the technique currently used by the uncrewed Dragon I ISS resupply vehicle.

However, SpaceX had planned to shift Dragon 2 landings from the sea to land – using parachutes for the majority of the descent back through the atmosphere, before cutting the vehicle free and using the built-in Super Draco engines (otherwise used as the crew escape system to blast the capsule free of a Falcon launch vehicle if the latter suffers any form of pre- or post-launch failure). The engines would fire during the last few metres of decent, placing the capsule into a hover before setting it down on four landing legs.

Extensively tested in tethered “hover” flights, propulsive landings would in theory made the recovery and refurbishment of Dragon capsules for future launches a lot easier, lowering the overall operating costs for the capsule. In announcing the decision to scrap the propulsive landing approach, Musk indicated it would have unnecessarily further drawn out the vehicle’s development as SpaceX sought to satisfy NASA’s requirements for crewed vehicle operations.

The decision also affects Musk’s hope of placing a robotic mission on the surface of Mars in 2020. Under that mission, a special cargo version of Dragon 2 – called Red Dragon- would fly a NASA science payload to Mars and use supersonic propulsive landing to slow itself through the tenuous Martian atmosphere and achieve a successful soft landing. This approach was seen as ideal, because using parachutes on Mars is extremely difficult with heavy payloads – NASAs studies suggest parachute on Mars have an upper limit of payloads around 1.5-2 tonnes. A Red Dragon capsule is liable to mass around 8-10 tonnes.

SpaceX have dropped plans to use propulsive landings on both their crewed Dragon 2 vehicles returning from the ISS and on their Red Dragon automated Mars lander (above). Credit: SpaceX

However, Musk no longer believes the use of a propulsive landing mechanism is “optimal” for Red Dragon, and the company has a better way of realising their goal – although he declined to indicate what this might be. Instead, propulsive landing systems would seem to be something the company will return to in the future – particularly given their hopes of placing vehicles massing as much as 100 tonnes on the surface of Mars.

No, ET Isn’t Calling Us

The Internet was agog recently after it was announced some very “peculiar signals” had been noticed coming from Ross 128, a red dwarf star just 11 light-years away. While not known to have any planets in orbit around it, and despite the best attempts of astronomers – including the team picking up the signals at the Arecibo radio telescope, Puerto Rico – news of the signals led to widespread speculation that “alien signals” had been picked up.

The usual signals – officially dubbed the “Weird!” signal, due to the comment made in highlighting the signals in an image – were first picked up on May 12th/13th, 2017. However, it was not until two weeks later that the signals were identified and analysed, the PHL team concluding that they were not “local” radio frequency interference, but were in fact odd signals coming from the direction of Ross 128 – sparking the claims of alien signals, even though the director at PHL and the survey team leader -Abel Mendez – was one of the first to pour water on the heat of the speculation. “In case you are wondering, he stated in response to the rumours, “the recurrent aliens hypothesis is at the bottom of many other better explanations.”

The Weird! signal. Credit: UPR Aricebo

Without drawing any conclusions on what might be behind the signals, PHL liaised with  astronomers from the Search for Extra-Terrestrial Intelligence (SETI) Institute to conduct a follow-up study of the star. This was performed on Sunday, July 16th, using SETI’s Allen Telescope Array and the National Radio Astronomy Observatory‘s (NRAO) Green Bank Telescope. The fact that SETI was involved probably also helped fan the flames of “alien signal” theories. However, initial analysis of the signal and the portion of the sky where it was observed have suggested a far more mundane explanation:  geostationary satellites.

“The best explanation is that the signals are transmissions from one or more geostationary satellites,”  Mendez stated in an announcement issued on July 21st. “This explains why the signals were within the satellite’s frequencies and only appeared and persisted in Ross 128; the star is close to the celestial equator, where many geostationary satellites are placed.”

While certain this explanation is correct, Mendez does note it doesn’t account for the strong dispersion-like features of the signals (diagonal lines in the figure). His theory for this is that it is possible multiple reflections caused the distortions, but the astronomers will need more time to evaluate this idea and other possibilities.

So sorry, no ETs calling out into the night – yet.