SpaceX has had a busy week. Following the loss of the Starship prototype SN4, the company has been pushing ahead with the construction of prototypes SN5 and SN6 – one of which is likely to complete the first flight tests for the vehicle.
These prototypes look a little odd to some, resembling little more than steel cylinders. This is because SpaceX is currently focused purely on the vertical ascent / decent capabilities of the vehicle, and for this they only need the section of the hull that contains the fuel tanks and the raptor motors. Experience in flying the smaller Starhopper vehicle demonstrated there is no need to include the vehicle’s upper sections or the dynamic flight surfaces – although these will be added as the test flights become more ambitious and broader in scope.
Also following the destruction of the SN4 prototype, the company started work on the SN7 vehicle. This caused some speculation as to where it might fit in the test vehicle series. Might it be the start of a prototype that does go on to include the said upper sections and flight surfaces? Was it being built in case SN5 or SN6 went the way of SN4 and SN3?
As it turned out, SN7 was constructed specifically for further tests on tank pressurisation. On June 15th, 2020 the tank, mounted on a test stand was filled with liquid nitrogen (used in testing because it mimics the super-cold temperatures of the propellants the tanks will eventually contain, and so exposes the tank to the same temperature stresses, but if the tank ruptures, it will not explode) to its maximum pressure. It resulted in a slight leak developing, which was repaired. Then, on June 23rd, the tank was once more filled with liquid nitrogen – but this time to a pressure well beyond it would have to face when in use during a launch.
The results were spectacular: an initial rupture occurs in the lower half of the tank, instantly expand into a tear along its base seam that released the liquid nitrogen in such bulk and pressure that it instantly vaporised en masse, venting with a force that lifted tank and test stand sideways off the ground. Immediately after the incident, SpaceX deployed their newest team member, Zeus.
A robot “dog” developed by Boston Dynamics (which they generically call “Spot”), Zeus is being used by SpaceX to assess potentially hazardous situations around the Boca Chica test site – in this case, the ground conditions following exposure to so much liquid nitrogen that took time to completely boil off. In typical SpaceX humour, the company has even erected a large Snoopy-style dog house on the grounds that’s allegedly the robot dog’s home.
One of the reasons for taking the test beyond limits was to check the steel used in SN7’s construction. Earlier versions of the Starship prototypes had been built with 301 stainless steel, but the company has opted to switch to the stronger 304L, and the degree to which the tank stood up to the test is being seen as indicative that the 304L is structurally a better choice.
Also during the week, NASA announced that the Crew Dragon currently docked with the International Space Station will likely return to Earth at the start of August 2020, with its crew of Robert Behnken and Douglas Hurley. Its return will pave the way for the first “operational” crew Dragon launch, which will carry astronauts Michael Hopkins, Victor Glover, Shannon Walker (commander) and Soichi Noguchi to the ISS at the end of August or early September.
In a separate announcement, the agency further indicated that in a change to their requirements, they will in future allow SpaceX to make use of re-used Falcon 9 first stages in Crew Dragon launches. Previously, the agency had specified that each crewed mission must take place using a new Crew Dragon and new Falcon 9 launcher. The change came after a second Falcon 9 first stage successfully completed its fifth launch and landing.
For parts of East Africa, the Middle East and Asia, the 2020 summer solstice of June 21st was marked by an annular eclipse of the Sun.
Solar eclipses – when the Moon passes between the Earth and the Sun – take a number of forms, of which the most spectacular is, of course, a total eclipse. These occur when the distance between the Earth and the Moon is such that entire disk of the Sun is covered by the Moon, and the Moon’s shadow – called the umbra – falls directly onto the Earth’s surface, reducing the landscape directly below it to a state of dusk-like darkness called Totality. And just before that period of Totality, that can last several minutes, the solar corona is displayed as a beautiful halo of pearly white light.
However, as the Moon’s orbit around the Earth is elliptical rather than circular, for a total eclipse to occur, the Moon needs to be around 379,100 km from Earth. At this distance, the conical shadow of the Moon (the umbra) is sufficient for us to witness Totality. When the Moon is further away from Earth – say at the 381,500 km of the June 21st, 2020 event – , we have an annular eclipse, in which the Moon’s umbra “falls short” of reaching the Earth’s surface. This means that only around 99-99.5% of the Sun’s disk is covered by the Moon when observed along the path of the umbra, leaving the Sun and Moon appearing as a “ring of fire” hanging in the sky. It is this “ring of fire” that makes an annular eclipse the second most spectacular type of solar eclipse.
This particular event began at 03:45 UTC on June 21st, 2020, with the Moon “cutting in” to the disk of the Sun, and ended at 10:34 UTC as the Moon moved clear of the Sun. However, the period of maximum eclipse – the time at which the “ring of fire” might be seen – occurred at 06:54 UTC and was visible along a narrow track of the eclipse path just 21 km wide for around 35-60 seconds. Even so, it was still spectacular for those who witnessed it.
For people north and south of this narrow band of passage, the eclipse varied in nature from a partial ring of fire (where the disk of the Moon is jut off-centre enough relative to the Sun for the ring not to be completed) to a partial eclipse (where the disk of the Moon partially sits between the Earth and the Sun, but leaves a fair amount of the latter visible.
As direct viewing of the Sun is dangerous, ahead of the event, Astronomers Without Borders – a global group based out of the United States – worked with regional governments and astronomical groups and societies in Africa to get 16,000 pairs of solar glasses distributed to help people view the eclipse safely. For those well outside the path of the event who wished to witness it, the eclipse was streamed through You Tube and other platforms by a number of organisations such as SLOOH.
Eclipses are seasonal in nature, and generally occur in pairs: one lunar – when the Earth is between the Sun and the Moon, so that the later moves within the Earth’s shadow. This annular solar eclipse was preceded by a penumbral lunar eclipse on June 5th. However, and somewhat unusually, it will be followed by a further penumbral lunar eclipse on July 4th / 5th. A penumbral eclipse is one where the Moon is only within the outermost extent of the cone of Earth’s shadow, dimming it as it reflects the Sun’s light, rather than blocking sunlight falling on it entirely.
The next pair of eclipses will take place in November / December 2020, with a penumbral lunar eclipse on November 30th and a total solar eclipse visible from Chile and Argentina occurring on December 14th. For now, here’s a video of the June 21st event.
Six Billion Earths?
A new study from the University of British Columbia estimates that there could be as many as six billion Earth-type planets in the Milky Way galaxy orbiting within the habitable zone of stars with the same G_Type spectral class as our own Sun.
This may seem a surprisingly high number, but it requires context. In this case, it is estimated our galaxy has 400 billion stars of which some seven percent are G-Type. This means that if the study’s findings are correct, Earth-type planets orbiting in the habitable zone of G-Type stars averages out as just 0.18 per star.
The study findings are based on extrapolations from the data on 200,000 stars in the Kepler Space Telescope catalogue, with some adjustments to calculations.
The adjustments were required because Kepler used the transit method of exoplanet detection: watching for regular dips in a star’s brightness. However, given that a large planet will cause a correspondingly greater dip in a star’s brightness than one the size of Earth, the Kepler data is naturally biased towards finding larger planets. Further, it is possible that the dips caused by Earth-sized worlds could be mistaken for transient data rather than actual planets. So to handle things, Michelle Kunimoto, one of the researchers in the study used a technique called forward modelling.
I started by simulating the full population of exoplanets around the stars Kepler searched. I marked each planet as ‘detected’ or ‘missed’ depending on how likely it was my planet search algorithm would have found them. Then, I compared the detected planets to my actual catalogue of planets. If the simulation produced a close match, then the initial population was likely a good representation of the actual population of planets orbiting those stars.
– Michelle Kunimoto, University of British Columbia
Images of Proxima Centauri (l) and Wolf 359 (r) captured by NASA’s New Horizons spacecraft 7 billion km from Earth, are overlaid against images taken of the two stars from Earth-based telescopes, showing how the stars appear to “move” depending on the viewpoint. Credit: NASA
For the first time in history, a spacecraft has been used to demonstrate parallax as it applies to the stars – and in the process, underlining the fact that the constellations beloved of astrology are little more than a matter of line-of-sight as seen from Earth.
The spacecraft in question is New Horizons, the mission that performed a fly-by of Pluto in 2016, and which is now some 7 billion kilometres from Earth – far enough to give it a unique view of the heavens around our solar system. On April 2nd/23rd, 2020 the spacecraft was commanded to turn its telescope on two of our nearest stellar neighbours, Proxima Centauri and Wolf 359 (a star doubtless familiar to Star Trek: The Next Generation), some 7.9 light years from Earth, to take pictures of both.
When compared to images of the two stars as seen from Earth, those from New Horizons clearly show how differently the two appear against the background of other stars when seen from different points of observation that are sufficiently far apart.
Use of parallax is a common astronomical exercise, used to measure the distance of stars from Earth. However, up until the New Horizons experiment, the average separation between points of observation have been opposite sides in Earth’s orbit around the Sun – or a mere 297,600,000 km apart when averaged out. That’s far enough to allow for an accurate measurements of other stars, but not far enough to show how differently a star might appear from different points in the sky.
It’s fair to say that New Horizons is looking at an alien sky, unlike what we see from Earth.nd that has allowed us to do something that had never been accomplished before—to see the nearest stars visibly displaced on the sky from the positions we see them on Earth.
– Alan Stern, Principal Investigator, New Horizons
For the experiment, the images from New Horizons were compared with images captured by the Las Cumbres Observatory, Panama, operating a remote telescope at Siding Spring Observatory in Australia, and from the Mt. Lemmon Observatory in Arizona, both of which imaged the stars on the same night as New Horizons captured its images, so as to provide a direct comparison.
Witnessing the Birth of Stars
The Rho Ophiuchi cloud complex is a dark nebula of gas and dust that is located 1° south of the star ρ Ophiuchi in the constellation Ophiuchus. Some 460 light-years from Earth, it is one of the closest and active start-forming regions to the Sun.
It’s called a “dark nebula” because the dust cloud is so dense, visible light from stars within it is almost completely obscured. However, astronomers using the Atacama Large Millimetre/submillimetre Array (ALMA) have found something of interest within the cloud.
The item in question is IRAS 16293-2422, a system that has a long history of being observed in the infra-red. However, it had been thought the system comprised a binary pairing of protostars, simply referred to as A and B some 700 AU apart. However, the new study has revealed that the star known as A is actually itself a pair of stars, now called A1 and A2. They are both of similar in mass to the Sun – A1 being slightly smaller, and A2 around 1.4 times larger, and each is surrounded by its own accretion disk from which it is drawing material.
These stars and their disks have certain fascinating aspects. The first is that they are only separated by a distance slightly greater to that of Pluto when at aphelion relative to Earth. They also complete an orbit around one another one every 360 terrestrial years. In addition, the accretion disks around A1 and A2 are also unique.
Both disks are extremely active, filaments of matter streaming into the stars at the heart of each, and further filaments of dust flowing into the disks from the nebula. In addition, the disk around A2 disk appears to be oddly inclined compared to the disks around A and the more distant B, suggesting complex interactions may be at play around it. The disk also appears to have parts rotating in opposite directions relative to one another, the first time such a phenomenon has been seen in a protostar accretion disk. It suggests that should planets eventually form around the star, those nearer to it may orbit the opposite direction to those further out.
Organic scans of the disk also detected glycolaldehyde — a simple form of sugar – and Chloromethane, also called methyl chloride, an important biomarker, together with Carbon Sulphide, Isocyanic Acid, Formamide, and Formic Acid. The presence of the organics is important as it shown that the basic building blocks of life can exist within the accretion disks around stars, and so may be available when the remnants of that disk forms planets.
It’s not clear if / when the formation of either star may reach a point of nuclear ignition, or how such an event might affect the other. However, their confirmation provides astronomers with a first-hand opportunity to witness the earliest stage in the process of stellar evolution.
NASA and its partner, the German Aerospace Centre (DLR) finally have some good news about the Heat Flow and Physical Properties Package, or HP³, carried to Mars by the InSight Lander: they’ve made some progress towards perhaps getting moving again.
As I’ve noted in past Space Sunday articles, the experiment has been a source of consternation for scientists and engineers since InSight arrived on Mars in November 2018. Following the landing, HP³ was one of two experiment packages deployed directly onto the surface of Mars by the lander’s robot arm. One of the key elements of the experiment is the “mole”, a self-propelled device designed to drive its way some 5m into the Martian crust, pulling a tether of sensors behind it to measure the heat coming from the interior of Mars.
After a good start, the probe came to a halt with around 50% of its length embedded in the soil. At first it was thought it had hit solid bedrock preventing further motion; then it was thought that the mole was gaining insufficient traction from the hole walls, on account of the fine grain nature of the material it was trying to move through. That was in February 2019.
Since then, scientists and engineers have been trying to figure out what happened, and how to get the mole moving again – because of the delicate nature of the sensor tether, the HP³ experiment couldn’t simply be picked up and moved to another location and the process started over. instead, various attempts were made to try to giving the mole material so it might gain traction.
Most of these revolved around using the scoop at the end of the lander’s robot arm to part-fill / part compress the hole created by the mole, the theory being that loose regolith would gather around the head of the mole and help it regain the necessary fiction to drive itself forward once more. Initially, some small success was had – until the mole abruptly “bounced” almost completely back out of the hole.
Further attempts were made to compress the ground around the hole, but all forward motion remained stalled, leading scientists to believe the mole had struck a layer of “duricrust” – a hard layer formed as a near the surface of soil as result of an accumulation of soluable materials deposited by mineral-bearing waters that later leech / evaporate away. These layers can vary between just a few millimetres to several metres in thickness, and are particularly common to sedimentary rock, which itself has been shown to be common on Mars.
The rub for the InSight mission is that if it is a layer of duricrust beneath the lander, it is impossible to tell just how thick it might be.
Earlier this year it was decided to use the scoop on the robot arm more directly, positioning it over the exposed end of the mole and applying pressure in the hope it could push the mole gently down into the ground in a series of moves that would allow the mole to get to a point were it could resume driving itself into the ground.
However, this approach has not been not without risk. The end of the mole has a “harness” – a connector for the tether, so the scoop has to be precisely positioned and any sort of pressure applied very gently and carefully to avoid any risk of slippage that might result in damage to the tether and / or harness and render its ability to gather data and information from the probe useless.
However, on June 3rd, NASA announced that a series of gentle pushes had resulted in the mole being completely below the surface, and with no apparent damage to the tether or harness. However, whether or not this means the mole is able to proceed under is own self-proplusion is unclear, as NASA noted in their tweet.
In all, the tip of the mole is now some 3m below the Martian surface. That’s deep enough for it to start registering heat flow, but to be effective, the mole still needs to drive itself down the full 5 metres. It is only at this depth that the mole and sensors can correctly start to measure the sub-surface geothermal gradient, and thermal conductivity, the two pieces of information required by scientists to obtain the heat flow from deeper in the planet. By studying the thermal processes in the interior of the planet, scientists can learn a lot about the history of Mars, and how it formed. They may also gain insights into how other rocky bodies formed.
Attempts have yet to be made to see if the mole can move under its own spring-driven propulsion, but for now NASA and DLR are rightly treating the current status of the probe as a victory. The tether harness at the end of the mole is undamaged, so if the mole can resume progress under its own power, there’s not reason why it shouldn’t start recording information.
On April 24th, 1990, the Space Shuttle Discovery thundered into a spring Florida sky on one of the most important missions of the entire space shuttle programme: the launch of the Hubble Space Telescope (HST), one of the four great orbital observatories placed in orbit in the closing years of the 20th century.
At the time of its launch, the telescope probably didn’t surface to any great degree in the broader public consciousness, although in the 30 years it has been in operation it has become if not a household name, then certainly one most people will recognise, even when abbreviated down to just “Hubble”.
As I noted when marking 25 years of HST operations, Hubble’s roots go well back in history – to 1946, in fact; while the whole idea of putting a telescope above the distorting effects of the Earth’s atmosphere can be traced back as far as the early 1920s. A joint NASA / European Space Agency operation, HST faced many challenges along the road to commencing operations: it’s low Earth orbit – vital for it to be within reach of servicing astronauts – meant it had to face bot extremes of temperature as it orbited the Earth, passing in and out of sunlight, and it would also have to contend with a slow but inexorable atmospheric draft, so would have to be periodically boosted in its altitude.
However, these issues paled into insignificance after HST was launched, when the commissioning process revealed something was badly wrong with the telescope’s optics, resulting in badly blurred images being returned to Earth. The problem was traced back to an error in the production of the 2.4m primary mirror – one side of which has been ground an etra 2.2 nanometres (a nanometre being one billionth of a metre) compared to the other, leaving it “out of shape”. Small as the error was, it was enough to prevent Hubble focusing correctly, leading to the blurred images – and the entire programme being seen as a huge white elephant around the world, despite HST completing some excellent science between 1990 and 1993.
Again, as I reported five years ago, the optical error lead to a “Hubble rescue mission” in 1993, when the crew of the space shuttle Endeavour arrived to give HST corrective optics called COSTAR and an updated imaging system, the Wide Field and Planetary Camera (WF/PC). Together these effectively gave HST a corrective set of glasses that overcame the flaw in the primary mirror. In doing so, they assured Hubble’s place in history, as they allowed the telescope to exceed all expectations in its imaging capabilities, turning into into perhaps the most successful astronomical / science instrument of modern times.
When launched, HST could see both in the visible light and in the ultraviolet (the region in which it saw outstanding results even before the operation to correct its “eyesight”). In 1997, during another servicing mission which saw the Discovery return to the telescope it had launched and deployed, HST was given a set of infra-red eyes as well. These allowed it to see farther into space (and thus further back in time) than we’d been able to do previously, and they allowed Hubble to peer into the the dusty regions of the galaxy where stars are born, opening their secrets.
Together, Hubble’s various eyes and its science instruments – and the men and women supporting HST operations here on Earth – have given us the ability to look back towards the very faintest – and earliest – light in the cosmos, study star clusters, look for planetary systems around other stars, increase our understanding of our own galaxy, look upon and study our galactic neighbours, help to verify Einstein’s theories of the universe, and do so much more.
Before Hubble, we knew essentially nothing about galaxies in the first half of the life of the universe. That’s the first 7 billion years of the universe’s 13.8-billion-year life. Now Hubble, through remarkable surveys like HXDF [Hubble Extreme Deep Field] capability, has probed into the era of the first galaxies. Through this type of work, Hubble has discovered galaxies like GN-z11, the most distant discovered by Hubble. Just 400 million years after the Big Bang, Hubble is looking back through 97% of all time to see it, far outstripping what can be done with the biggest telescopes on the ground.
– Garth Illingworth, HST project scientist
Hubble is a truly unique platform in this regard. Despite issues over the years such as with its various flywheels (the gyroscopes designed to hold it in place whilst it is capturing images), it can remain rock-steady for extended periods with no more than 0.007 arcseconds of deviation. To put this into context, that’s the equivalent to someone standing at the top of The Shard in London and keeping the beam of a laser pointer focused on a penny taped to the side of the Eiffel Tower in Paris, for 24 hours without wavering.
HST’s science mission is so broad, it occupies the working days of literally thousands of people around the globe. Dedicated teams manage the programme for both NASA and ESA, with the Space Telescope Science Institute (STScI) located at the Johns Hopkins University Homewood Campus in Baltimore being the primary operations centre, supported by the European Space Astronomy Centre (ESAC), Spain, both of which will manage operations with the James Web Space Telescope when it is launched. Beyond these teams, scientists and astronomers around the globe can request time using HST and its instruments for their projects and observations, all of which makes the telescope one of the most used globally.
Many of those currently working with Hubble share a unique link to it: they have either grown up with it as a part of their lives, learning about it at school and through astronomy and science lessons, or they been with Hubble since its launch, and have lived their entire careers with it.
Hubble has changed the landscape of astronomy and astrophysics,. It has far exceeded its early goals — no other science facility has ever made such a range of fundamental discoveries. It’s been a privilege to be associated with this effort that has become embedded in the culture of our time.
– Colin Norman, HST manger and senior manager, STScI (1990-2020)
The Kepler Space Telescope might be shut down, but the work of analysing the data it gathered on possible exoplanets continues, and an international team of scientists reviewing some of the earliest data from the mission have confiemd what had been thought of as a “false positive” is in fact an Earth-size exoplanet orbiting within its star’s habitable zone, the area around a star where a rocky planet could support liquid water.
The planet, Kepler-1649c orbits its small red dwarf star some 300 light years from Earth. It is so close to its parent, that its year is the equivalent to 19.5 Earth days. It is actually the second planet to have been found orbiting the star, hence the “c” designation in its name, and the system as a whole contains a series of points of interest for astronomers that make it particularly intriguing.
The first is that the data Kepler gathered on the planet suggest it is one of the closest in terms of size to Earth so far discovered, being just 1.06 times larger. The second is that its parent, Kepler-1649, is a class-M red dwarf with relatively low luminosity, so that despite it’s close proximity, that planet receives around 75% of the sunlight Earth receives from Sol. so it is entirely possible that if it has an atmosphere, conditions on it surface might be somewhat similar to our own in terms of average temperatures and with regards to surface water.
However, whether the planet does have an atmosphere has yet to be determined. As I’ve previously noted in this column, red dwarf stars are so small they rely on convection as the main form of energy transport to the surface, and this can give rise to violent solar outbursts which over time can rip away a nearby planet’s atmosphere. There’s also the question of how stable any atmosphere might be. Again, its close proximity to its parent means it is liable to be tidally locked, always keeping the same face towards its star. This is liable to make any atmosphere the planet does have could be exceptionally turbulent and prone to storms along the terminator dividing the light and dark halves.
However, Kepler-1649 has thus far shown itself to be one of the more stable M-class stars that has been observed over the years from Earth – which means it may well still possess a temperate atmosphere. If this is so, the combination of size and atmosphere then of all the red dwarf orbiting exoplanets thus far discovered, Kepler-1649c could be closer to Earth than most so far discovered.
An additional intrigue with the Kepler-1649 system is that the two planets share an unusual orbit resonance: for every nine times Kepler-1649c orbits its parent, the inner planet, Kepler-16949b, orbits almost exactly four times, giving a 9:4 ratio. This indicates the system is extremely stable, likely to survive for a long time.
9:4 is also something of a unique ratio; usually resonances take the form of ratios like 2:1 or 3:2. As such, it is thought that the Kepler’s system’s resonance might be indicative of a third planet between Keplert-1649b and Kelper-1649c, which would give the system a more regular pairing of 3:2 resonances between the middle and inner planets and the middle and outer planets. However, the existence of any third planet has yet to be confirmed.
In the meantime, the discovery of Kepler-1649c adds significantly to our understanding on exoplanets around M-class stars.
The more data we get, the more signs we see pointing to the notion that potentially habitable and Earth-size exoplanets are common around these kinds of stars. With red dwarfs almost everywhere around our galaxy, and these small, potentially habitable and rocky planets around them, the chance one of them isn’t too different than our Earth looks a bit brighter.
– Andrew Vanderburg, co-author of a paper on Kepler-1649c exoplanet
Curiosity: A New Level of Remote Working
As the SARS-CoV-2 virus continues to prevent us from working normally, members of NASA’s Mars Science Laboratory Curiosity team have revealed how they’ve been continuing with normal operations since the Jet Propulsion Laboratory (JPL) shut down operations in February 2020.
Of course, in some respects the rover team has always been working remotely from their “office”, the rover never being at least 56 million km from Earth. However, the shut-down of NASA facilities ordered by Administrator Jim Bridenstine brought additional challenges to operating a rover so far away – and I’m not talking about distractions caused by the need to feed the cats or take the dog for a walk, being reliant on e-mail and video conferencing, etc.
Take driving the rover, for example. This requires a complex process of scanning the rover’s surroundings to build up a complete view of the rover’s environment, having the means to view this in 3D and to compare it to high-resolution images of the rover’s surroundings captured from orbit, then mapping a potential route that avoids any aspects of the landscape that present a risk to the rover whilst also encompassing points of interest, converting the commands into software code, testing it, and finally transmitting it to the rover for execution. Similarly, manoeuvring and using the rover’s robot arm requires precision and care, rehearsal and coding.
Much of this work requires high-powered computers. Analysing potential route from images, for example, requires not only high-resolution image processing, but also high-end gaming PCs and 3D headsets to give a greater depth of field and better visualisation of contours of the landscape and rocks. A similar approach is used to manoeuvring and manipulating the robot arm. The problem is, not all of the systems required to achieve all of this could easily be transitioned from JPL’s facilities to home use. Teams are, for example, restricted to using laptops, rather than gaming PCs; they’ve therefore had to swap from using specialised 3D headsets that rapidly shift between left- and right-eye views to better reveal the contours of the landscape, and instead rely ordinary anaglyph glasses to achieve the same ends.