Space Sunday: Hops, glows, plans and Perseids

SpaceX SN5 rises from its launch stand at the SpaceX Boca Chica, Texas, centre. Credit: SpaceX

SpaceX once again heads this week’s column after the Starship SN5 prototype became the first of the units to successfully make a “hop” into the air and back again, travelling some 150 metres up and several tens of metres sideways to navigate its way from launch platform to landing pad.

The flight of the “flying spray can” – the nickname derived from the vehicle’s cylindrical form topped by the nozzle-like 23 tonne ballast mass – only lasted around a minute once the Raptor engine fired, but the hop represented a huge leap forward for SpaceX in their development of the Starship vehicle.

As I noted in July, SN5’s unusual shape is due to it only comprising the section of the vehicle containing its fuel tanks, single raptor engine and landing legs. It lacks any upper sections (replacing by the ballast block) and the aerodynamic surfaces that will give Starship a lifting body capability during atmospheric operations. These will all be present in future prototypes, But for SN5, they are not currently required, as its initial flight(s) are purely about testing Starship’s ability to make a vertical descent and landing.

A starship cutaway showing the fuel tanks and engine bay (outlined in red) that form the prototype vehicle SN5, and the upper cargo / habitation space and aerodynamic surfaces that are not included on the current prototype. Credit: WAI (with additional annotation)

The successful test flight took place on Tuesday, August 4th – an attempt on Sunday, August 2nd was cancelled  due to unfavourable weather in the Boca Chica, Texas, area. Engine ignition came at 23:57 UTC (18:57 local time), the prototype rising vertically, but canted at a slight angle. This  was due to the initial prototypes being designed to operate with three Raptor motors, by SN5 is currently only fitting with one, offset from the vehicle’s vertical centreline, so the vehicle is canted (with the ad of the top ballast block) to compensate for the offset thrust from the motor, with small reaction control system (RCS) jets near the base and top of the vehicle occasionally firing to help maintain a stable flight angle.

As the craft rose, the Raptor motor was also gimballed (moved around like you move a joystick on a game controller, a common practice for rocket motors to allow them to use directed thrust to adjust a flight trajectory), vectoring its thrust so it could translate across to the landing pad for a successful landing.

Prototype nose cones being fabricated at Boca Chica. Credit: NASASpaceflight.com / BocaChicaGal

SpaceX released a video afterwards the flight showing the highlights. In it, SN5 can be seen lifting off, trailing a plume of vented cooling gas, the RCS jets visible as they fire to help maintain stability. The footage also clearly shows the Raptor’s offset exhaust plume moving as the motor in vectored, as well as the craft maintaining a brief hover at the apex of its flight before descending sideways and down towards the landing pad.

Cameras at the base of the vehicle show the landing legs being deployed, as well as a small, non-hazardous fire on the Raptor motor, likely the result of dust blown into the engine space at lift-off that subsequently ignited. This “inside” camera and one on the SN5 hull then captured the moment of landing and engine shut down.

Prototypes SN6, 7, and 8 are in development, and some of these will fly with the aforementioned forward / upper sections and flight surfaces in loftier (literally) and more complex flight tests. Currently, it not clear how many more flights SN5 will make. However, Musk has already indicated he would like to have Starship use a more “Falcon Like” set of landing legs to provide broader support when landing on uneven planetary surfaces, so SN5 might by used to test new landing leg configurations alongside testing of other prototypes.

Continue reading “Space Sunday: Hops, glows, plans and Perseids”

Space Sunday: SpaceX Starship update

A Starship / Super Heavy pairing lifts-off from a dedicated launch facility in this still from an animated video produced by SpaceX for the September 28th, 2019 update. Credit: SpaceX

On the occasion of the eleventh anniversary of SpaceX achieving orbit for the first time with their Falcon 1 rocket on September 28th, 2008, CEO Elon Musk presented an update on the company’s progress developing its massive Super Heavy booster and interplanetary class vehicle, Starship.

It has been some 12 months since the last update on the development of the two vehicles – the last update really being overshadowed by the announcement SpaceX planned to fly a Japanese billionaire and his entourage around the Moon and back (see Moon trips, Mr Spock’s “home” and roving an asteroid for more), and the programme has moved on significantly since then, as indicated by the fact that the 2019 update took place at the SpaceX facilities in Boca Chica and against the backdrop of the first of the Starship prototype vehicle.

Starship Mk1 under construction at the SpaceX facilities near Boca Chica, Texas. Credit: unknown

Since its first public unveiling in 2016, the Starship / Super Heavy combination has been through a number of iterations and name changes. However, it is fair to say that things have now settled down on the design front, and what was presented at Boca Chica is liable to remain largely unchanged, assuming everything proceeds as SpaceX hopes.

In this, the flight capable prototype Starship at Boca Chica is the first in a series of such vehicles. A second is  under construction at the SpaceX facilities in Cocoa, Florida, and three more are planned, one of which will be used to make the first orbital flight within the next 6 months, and Musk suggesting another could be used in a crewed orbital flight within the next 12 months – which sounds exceptionally ambitious. Construction of the two initial Starship prototypes has not exactly been secret: both have been literally assembled in the open. So even ahead of the September 28th event, some were already developing renderings of the new Starship design compared to the last known iteration.

A rendering by Kimi Talvitie comparing the 2018 design for Starship (l) with the prototype (r). The rendering of the 2019 prototype was based on direct feedback from Elon Musk

The new design sees some significant changes in Starship – notably with the fins, canards and landing legs. The 2018 variant was marked by three large fins, two of which would be actuated (hinged for up / down motion relative to the hull) for atmospheric flight, with all three fins containing the vehicle’s landing legs. At the time of that design, I commented that this approach appeared risky: a heavy landing on the Moon or Mars might conceivably damage one of the actuated fins, affecting the vehicle’s ability to undertake atmospheric flight on its return to Earth.

With the new design, the fins are reduced to two and reshaped, both of which are actuated to hinge “up” and “down”. In addition, the landing system is now independent of the fins, removing the greater part of the risk of damaging them on landing. The number of landing legs is also increased to six. At the forward end of the vehicle, the canards are enlarged and hinged in a similar manner to the fins.

Starship’s basic specification. Note the “dry” mass of 85 tonnes is incorrectly stated in the slide: it is expected the production version of Starship will mass around 120 tonnes (the prototype masses around 200 tonnes. Credit: SpaceX

The remaining aspects of the design are more-or-less unchanged as far as the body of the ship is concerned: it will be some 50 metres (162.5ft) in length and have a diameter of 9m (29ft). The forward end of the vehicle will be given over to crew and passengers or cargo (or a mix of the two), although Musk now estimates the vehicle will – with the aid of the Super Heavy booster – be lifting up to 150 tonnes to low Earth orbit – an increase of roughly a third – and return up to 50 tonnes to Earth.

To help achieve this, the motor system has been slight revised. While six engines will still be used, three will now be optimised for vacuum thrust, ideal for orbital flight and pushing the vehicle out to the Moon or Mars, and the remaining three optimised for sea level thrust and capable of being gimballed for use during a descent through an atmosphere and landing.

Starship’s motor arrangement: three central Raptor engines optimised for sea level thrust and capable of gimballing and three outer vacuum optimised motors with fixed, large diameter exhaust bells for maximum efficiency. The “boxes” visible in the rendering are potentially additional cargo bins. Credit: SpaceX

During the presentation, Musk explained the rationale behind the use of 301 cold rolled stainless steel in the design, noting a number of reasons. Firstly, the cold rolling process results in a stronger, light finished product, and this becomes even stronger when exposed to the very low temperatures of cryogenic fuels. Thus, Starship and Super Heavy in theory have a structural strength equitable to that of carbon composites – but at a much lower overall mass.

Secondly, the cold rolled steel has very high melt temperatures, reducing the amount of direct heat shielding required, again reducing the vehicle’s overall mass. It is also both highly corrosion-resistant and easy to work with. This means that basic repairs to a vehicle on the surface of the Moon or Mars could be effected, or even that a Starship could even be dismantled and the steel from the hull re-purposed. Finally, there’s the fact that all these advantages are gained in a product costing around 2% that of an equivalent mass of carbon composite.

Starship Mk 1 filmed during the September 28th livestream event. Credit: SpaceX

In terms of heat shielding, the “windward” side of Starship (the side facing the fictional heat of entry into an atmosphere) will be coated with lightweight ceramic tiles. Somewhat similar in nature to those used within the space shuttle, they will be of a hardier material and less prone to damage. The re-entry profile was also discussed, with Musk comparing Starship to a sky diver.

To explain: the vehicle will approach the atmosphere at a relatively high 60-degree incidence, using the heat generated by contact with the upper atmosphere to slow its velocity from Mach 25 to a point where, once within the denser atmosphere, the vehicle is literally falling more-or-less horizontally. The fins and canards can then be used to maintain the vehicles orientation in a similar manner to that of a sky diver using his arms and legs. in addition, the lift generated by fins and canards will further help slow its descent until, roughly 2 km above the ground, the vehicle will rotate to a vertical position and use the three gimballed Raptor motors to make a propulsive, tail-first landing.

SpaceX plan to offer Starship in support of lunar operations – but the company’s goal is to establish a permanent human presence on Mars. Credit: SpaceX

Starship Mk 1 is equipped with the same sea level optimised Raptor motors as intended for the production vehicles.  SpaceX hope to see it make at least one flight before the end of the year – although the company has yet to secure a permit from the US Federal Aviation Authority to commence flights. This first attempt will be to an altitude of around 20 km (12.5 mi) before a descent and landing. If successful, the test programme involving the various prototype vehicles will unfold from there.

Continue reading “Space Sunday: SpaceX Starship update”

Space Sunday: rocket power and space stations

Dude, why’s my car in orbit? Musk’s cherry-red Tesla photographed from its payload mounting on the Falcon Heavy upper stage. Credit: SpaceX

On Tuesday, February 6th, SpaceX launched one of the world’s most powerful launch vehicles – in fact, currently, the most powerful launcher in operation since NASA’s massive Saturn V rocket by a factor of 2 in terms of lift capability.

I’m of course talking about the Falcon Heavy, which after years of development and launch delays, finally took the to skies at 15:45 EST (20:45 UTC) on the 6th, after upper altitude wind shear delayed the launch from its planned 13:30 EST lift-off time – which would have been at the start of the four-hour launch window required to send its payload on a trans-Mars injection heliocentric orbit.

Three cores, 27 Merlin engines, 5 million pounds of thrust. A remarkable shot of the lower part of the Falcon Heavy at lift-off, captured by Ryan Chylinski. Credit: R. Chylinski / SpaceFlight Insider

The run-up to the launch was handled fairly conservatively by SpaceX: Falcon Heavy is a complex system – effectively three individual Falcon 9 rockets which have to operate in unison. So much might go wrong that even Elon Musk was stating he’d be happy if the vehicle was lost after it had cleared the launch pad. This was not a joke: in September 2016, a pre-flight test of a Falcon 9 lead to the loss of the vehicle, its payload and massive damage to its Cape Canaveral launch pad, putting a dent in SpaceX’s launch capabilities at the time. A similar event at Kennedy Space Centre’s pad 39-A, the only launch facility capable of handling the Falcon Heavy, would be a massive setback for the company’s 2018 aspirations.

However, and as we all know, the launch proved to be flawless. All 27 engines fired as required, generating the same thrust as 18 747 running all their engines at full throttle, and the vehicle took to the air. Two minutes later, the “stack” reached the point of “max-Q”, the point at which aerodynamic stress on a vehicle in atmospheric flight is maximised (symbolised in a formula as “q” – hence “max Q”). At this point, were the rocket’s engines to continue to run at full thrust, the combined stresses could literally shake the vehicle apart; so instead the motors are throttled back, easing the strain on the vehicle, prior to them returning to full thrust as “max-Q” has passed.

The Falcon Heavy flight path. Credit: SpaceX

After passing through “max-Q”, the vehicle completed perhaps the most spectacular part of its flight. Their job done, the two outer Falcon 9 stages shut down their engines and separated from the core rocket. Then then re-lit their engines to boost them vertically to where both could perform a back-flip and then return for a landing at Cape Canaveral Air Force Station, just south of Kennedy Space Centre. So perfect was this aerial ballet that the two boosters landed almost simultaneously.

The central first stage should have also made a return to Earth after separating from the upper stage, landing aboard one of the company’s two autonomous spaceport drone ship (ASDS) – necessary because the stage had flown too far and too high to make a return to dry land. This was the only point of failure for the flight. Unfortunately, it over-burnt its propellants, leaving it without enough fuel to land on the floating platform. Instead, it slammed into the sea at an estimated 480 km/h (300 mph), some 100 metres (300ft) from the ASDS – the only notable failure in the launch.

Two from one: the moment at which two Falcon 9 cores are about to touch-down at Cape Canaveral Air Force Station following the February 6th, 2018 launch of Falcon Heavy. Credit: SpaceX

The second stage, however, performed perfectly, the payload fairings jettisoned, and the world got its first look at a car in space: Musk’s own Tesla Roadster, complete with a spacesuited mannequin (“Starman”) at the wheel, Don’t Panic – a reference to The Hitch Hiker’s Guide to the Galaxy – displayed on the dashboard. During the ascent, he was apparently listening to David Bowie’s Space Oddity played on the car’s stereo.

Right now, “Starman” and the car are en-route to a point out just beyond the orbit of Mars. It is is on a heliocentric (Sun-centred)  orbit, travelling between 147 million and 260 million km (91.3 million and 161.5 million mi) from the Sun, and passing across both the orbits of Mars and Earth in the process – but without actually coming close to either. It will continue in this orbit for millions of years. Continue reading “Space Sunday: rocket power and space stations”

Space Sunday: reusability, habitability, survivability

SpX-13 lifts-off from Space Launch Complex 40 at Cape Canaveral Air Force Station, Florida, marking the first time SpaceX has launched a previously-flown Dragon 1 resupply capsule atop a previously flown Falcon 9 first stage, in SpaceX’s 17th launch for 2017. Credit: NASA

SpaceX Has completed its first mission to the International Space Station with a Falcon 9 first stage and a Dragon 1 resupply vehicle which have both previously flown.

The launch took place at 15:36 GMT (10:36 EST) on Friday, from Space Launch Complex 40 at Cape Canaveral Air Force Station. As well as being the first time a previously used Falcon 9 first stage and Dragon capsule have flown together, the launch also marked the first from SLC-40 since a pre-launch explosion of a Falcon 9 rocket in September 2016, which completely destroyed the rocket and its Israeli payload, and severely damaged the launch facilities.

Three minutes after the launch, the first and second stages of the Falcon 9 separated, the latter continuing towards orbit while the former performed its “boost-back” manoeuvre, and completed a safe return to Earth and a vertical landing at SpaceX’s Landing Complex 1 at Canaveral Air Force Station. The landing marked the 20th successful recovery of the Falcon 9 first stage – with 14 of those recoveries occurring in 2017.

The Dragon capsule, carrying some 2.2 tonnes of supplies for the ISS, was first used in a resupply mission in April 2015. In its current mission, it reached the station on Sunday, December 17th, where it was captured by the station’s robotic arm and moved to a safe docking at one of the ISS’s adaptors where unloading of supplies will take place. The capsule will remain at the station through January, allowing science experiments, waste and equipment to be loaded aboard, ready for a return to Earth and splashdown in the Pacific ocean, where a joint NASA / SpaceX operation will recover it.

The SpX-13 Dragon sits alongside the International Space Station on Sunday, December 17th, waiting to be grappled by one of the station’s robot arms and moved to its docking port. Credit: NASA/JSC

The mission is a significant milestone for SpaceX, bringing the company a step closer to it goal of developing a fully reusable booster launch system. Thus far the company has successfully demonstrated the routine launch, recovery and reuse of the Dragon 1 capsule and the Falcon 9 first stage. On March 30th, 2017, as part of the SES-10 mission, SpaceX performed the first controlled landing of the payload fairing, using thrusters to properly orient the fairing during atmospheric re-entry and a steerable parachute to achieve an intact splashdown. This fairing might be re-flown in 2018. That “just” leaves the Falcon 9 upper stage, the recovery of which would make the system 80% reusable.

However, recovering the second stage is a harder proposition for SpaceX – at one point the company had all but abandoned plans to develop a reusable stage, but in March 2017, CEO Elon Musk indicated they are once again working towards that goal – although primary focus is on getting the crew-carrying Dragon 2 ready to start operations ferrying crews to and from the ISS.

The major issues in recovering the system’s second stage are speed and re-entry. The second stage will be travelling much faster than the first stage, and will have to endure a harsher period of re-entry into the Earth’s denser atmosphere. This means the stage will require heat shielding and a means to protect the exposed rocket motor, as well as the propulsion, guidance and landing capabilities required for a full recovery.

SpaceX has proven the reusability of the Falcon 9 first stage (left) and the Dragon capsule system (right). All that remains is developing a reusable second stage, most likely for use with the Falcon Heavy – or as a part of the ITS / BFR. This image shows the discontinued proposal for a reusable Falcon 9 second stage. Credit: SpaceX

The problem here is that of mass. The nature of rocket staging means that – very approximately, every two kilos of rocket mass on the first stage reduces the payload capability by around half a kilogramme.  With a second stage unit, this can drop to a 1:1 ratio. So, all the extra mass of the re-entry / recovery systems can reduce the total payload mass, making the entire recovery aspect of a Falcon 9 second stage both complex and of questionable value, given the possible reduction in payload capability. However, with the Falcon Heavy due to enter service in 2018, a reusable second stage system does potentially have merit, as the combined first stages of the system can do more of the raw shunt work needed to get the upper stage and its payload up to orbit.

The Habitability of Rocky Worlds Around a Red Dwarf Star

Red Dwarf stars are currently the most common class (M-type) of star to be found to have one or more planets orbiting them. Many of these worlds appear to lie within their parent’s habitable zone, and while that doesn’t guarantee they will support life, it does obviously raise a lot of questions around the potential habitability of such worlds.

There tend to be a couple of things which often run against such planets when it comes to their ability to support life. The first is that often, they are tidally locked with their parent star, always keeping the same face towards it. This creates extremes of temperature between the two side of the planet, which might as a result drive extreme atmospheric storm conditions. The second is – as I’ve noted in past Space Sunday articles – red dwarf stars tend to be extremely violent in nature. Their internal action is entirely convective, making them unstable and subject to powerful solar flares, generating high levels of radiation in the ultraviolet and infra-red wavelengths. Not only can these outbursts leave planets close to them subject to high levels of radiation, they can cause the star to have a violent solar wind which could, over time, literally rip any atmosphere which might otherwise form away from a planet. This latter point means that one of the most vexing questions for those studying exoplanets is how long might such worlds retain their atmospheres?

In an attempt to answer to that question, planetary astronomers have turned to a planet far closer to us than any exoplanet: Mars.

Continue reading “Space Sunday: reusability, habitability, survivability”

Space Sunday: looking back on Earth and landing rockets and probes

The Earth and Moon, as seen from orbit over Mars, November 20th 2016
The Earth and Moon, as seen from orbit over Mars, November 20th 2016

Two marbles sit on a midnight background, one a swirl of blue, white, brown and green, the other tinted in shades of grey. Together they are the Earth and her Moon as seen by the most powerful imagining system currently orbiting the planet Mars.

It is, in fact a composite image, although Earth and the Moon are the correct sizes and the correct position / distance relative to one another. The images were captured by the High Resolution Imaging Science Experiment (HiRISE) camera on NASA’s Mars Reconnaissance Orbiter (MRO) on November 26th, 2016.

The images were taken to calibrate HiRISE data, since the reflectance of the moon’s Earth-facing side is well-known. As such, this is not the first image of our home planet and its natural satellite captured from Martian orbit, but it is one of the most striking. Whilst a composite image, only the Moon’s brightness has been altered to enhance its visibility; were it to be shown at the same brightness scale as Earth, it would barely be visible. That it appears to be unnaturally close to Earth is in fact an illusion of perspective: at the time the pictures were taken, the Moon was on the far side of Earth relative to Mars, and about to pass behind it.

The image of Earth shows Australia prominent in the central area of the image, its shape just discernible in this high-resolution image, taken when Mars and the MRO were 205 million kilometres (147 million miles) from Earth.

For me, this is another picture demonstrating just how small, fragile and unique our home world actually is.

 Falcon 9 Makes Triumphant Return to Flight

With Federal Aviation Authority (FAA) approval given, SpaceX, the private space company founded by Elon Musk, made a triumphant return to flight status with its Falcon 9 launch system on Saturday, January 14th.

January 14th, 2017: the SpaceX Falcon 9, carry 10 advanced Iridium Next communications satellites in its bulbous paylod fairing, lifts-off from Space Launch Complex 4E, Vandenberg Air Force Base, California Credit: SpaceX
January 14th, 2017: the SpaceX Falcon 9, carry 10 advanced Iridium NEXT communications satellites in its bulbous payload fairing, lifts-off from Space Launch Complex 4E, Vandenberg Air Force Base, California Credit: SpaceX

SpaceX launches had been suspended in September 2016, after a Falcon 9 and its US $200 million payload were loss in an explosion during what should have been a routine test just two days ahead of the planned launch (see here for more). Towards the end of 2016, and following extensive joint investigations involving NASA and the US Air Force (The Falcon 9 was located at Launch Complex 40 at the Canaveral Air Force Station when the explosion occurred), SpaceX were confident they had traced the root cause for the loss to a failure of process, rather than a structural or other failure within the vehicle itself. However, they had to wait until the FAA had reviewed the investigation findings and approved the Falcon 9’s return to flight readiness before they could resume operations.

The January 14th launch came via the SpaceX West Coast facilities, again leased from the US Air Force, and saw a Falcon 9 booster lift-off from Space Launch Complex 4E at Vandenberg Air Force Base in California. The rocket was carrying the first ten out of at least 70 advanced Iridium NEXT mobile voice and data relay satellites SpaceX will launch over the coming months, as Iridium Communications place a “constellation” of 81 of the satellites in orbit around the Earth in a US $3 billion project.

All ten satellites were successfully lifted to orbit and deployed following a pitch-perfect launch, which had to take place at precisely 9:54:34 local time (17:54:34 UT) in order for all ten satellites to be correctly deployed to reach their assigned orbits. However, all eyes were on the Falcon 9’s first stage, which was set to make a return to Earth for an at-sea landing aboard one of the company’s two autonomous drone landing barges, Just Follow The Instructions.

Down and safe: the Falcon 9 first stage, seen via a camera aboard the autonomous drone barge Just Follow The Instructions, shortly after touch-down on January 14th, 2017. Credit: SpaceX
Down and safe: the Falcon 9 first stage, seen via a camera aboard the autonomous drone barge Just Follow The Instructions, shortly after touch-down on January 14th, 2017. Credit: SpaceX

Operating the Falcon 9 on a basis of reusability is core to SpaceX’s future plans to reduce the overall cost of space launches. While the company has previously made six successful returns and landings with the Falcon 9 first stage, this being the first attempt since September 2016’s loss added further pressure on the attempt. but in the event, it went flawlessly.

After separation from the upper stage carrying the payload to orbit, the first stage of the Falcon 9 completed what are called “burn back” manoeuvres designed to drop it back into the denser atmosphere. Vanes on the rocket’s side were deployed to provide it with stability so that it dropped vertically back down to Earth, using its engines as a braking system and deploying landing legs shortly before touchdown – and the entire journey was captured on video, courtesy of camera built-into the rocket’s fuselage.

Continue reading “Space Sunday: looking back on Earth and landing rockets and probes”

Space Sunday: water on Europa, Rosetta on a comet and Musk on Mars

Euorpa's icy, mineral-stained surface as imaged by NASA's Galileo mission - see bwlow (credit: NASA / JPL)
Euorpa’s icy, mineral-stained surface as imaged by NASA’s Galileo mission – see below (credit: NASA / JPL)

On Monday, September 26th, after some teasing beforehand, NASA provided an update on the venting of water by Jupiter’s icy moon, Europa.

As I noted in my last Space Sunday report, Europa is covered by shell of water ice, much of it discoloured by mineral deposits and by deep cracks, beneath which it is believed to have a liquid water ocean about 100 km (62.5 miles) deep. The ocean is believed to be made possible by tidal flexing enacted by the massive gravity of Jupiter as well as from the other large Galilean moons. This generates heat within Europa, and this heat stops the water from freezing solid.

In 2012, The Hubble Space Telescope (HST) captured what appeared to be a huge plume of water erupting some 200 kilometres (125 mi) above the surface of Europa, using its Space Telescope Imaging Spectrograph (STIS) instrument. The update offered on September 26th provided information on further plumes, strengthening the case of water existing under the ice crust of Europa in the process – a crust which may be far thinner than thought.

Europa transit illustration. Europa orbits Jupiter every 3 and a half days, and on every orbit it passes in front of Jupiter, raising the possibility of plumes being seen as silhouettes absorbing the background light of Jupiter. Credit: A. Field (Space Telescope Science Institute)
Europa transit illustration. Europa orbits Jupiter every 3 and a half days, and on every orbit it passes in front of Jupiter, raising the possibility of plumes being seen as silhouettes absorbing the background light of Jupiter. Credit: A. Field (Space Telescope Science Institute)

Over a 15-month period, astronomers used Hubble’s STIS to observe Jupiter and Europa in the ultra-violet spectrum. During that time, Europa occulted (passed in front) of Jupiter on 10 separate occasions. The observations were an attempt to examine a possible extended atmosphere around the moon, which is slightly smaller than our own. However, on three of the passes, astronomers witnessed what appeared to be plumes of water erupting from the surface – and in pretty much the same location as seen in 2012. Analysis of the plumes revealed they were made up of hydrogen and oxygen consistent with water vapour being broken apart by Jupiter’s radiation in a process known as radiolysis.

The plumes are not constant, but rather flare up intermittently, possibly as a result of the surface ice on Europa flexing in response to the same gravitational influences that are keeping the ocean beneath the ice from freezing out. This suggests that the icy crust is, at least around the region where the plumes are occurring, thinner than had been thought. This is important, because it could mean that any automated mission sent to Europa could have a fair chance of cutting its way through the ice to deploy a submersible vehicle which could then search for any evidence of life in Europa’s salty ocean – which contains between two and three times as much water as all of Earth’s oceans combined.

The Gentle Crunch: Rosetta Mission Ends

The European Space Agency’s Rosetta spacecraft said farewell on Friday, September 30th, bringing the 12-year mission that bears its name to a close.

Launched in 2004, Rosetta was a daring attempt to rendezvous with a short-period comet, 67P/Churyumov-Gerasimenko, then orbit it and study it as it swept through the inner solar system and around the sun on its (roughly) 6-year obit. The aim was to give us unique insight into cometary behaviour and – more directly – to study one of these tiny lumps of mineral and chemical rich rock “left over” from the solar system’s formation, and thus gain greater understanding as to how things came to be, and perhaps how life itself might have begun.

Rosetta, Europe's mission to unlock the secrets of the early solar system through the study of comet 67p-C/G, and the Philae comet lander (image: European Space Agency)
Rosetta, Europe’s mission to unlock the secrets of the early solar system through the study of comet 67P-C/G, and the Philae comet lander (image: European Space Agency)

Rosetta travelled almost 8 billion km (5 billion miles), including three flybys of Earth and one of Mars, and two asteroid encounters, before finally arriving at 67P/C-G in August 2014. In November of that year, The Philae lander was deployed in the hope of studying the comet from the surface and gathering samples of its material for analysis. Unfortunately, Philae’s anchoring mechanism failed, sending the little lander bouncing across the comet, until it came to rest in a location where it was receiving insufficient sunlight to recharge its batteries. Nevertheless, in the time it did have before its batteries were almost depleted, the washing machine sized lander some 80%+ of its science goals.

Meanwhile, Rosetta studied the comet in the long fall towards the Sun, and carried out an extensive mission of study, analysis and image capture, much of which has completely altered thinking around comets like 67P/C-G. For example, the mission discovered that water within the comet has a different ‘flavour’ to that of Earth’s oceans, suggesting that the impact of such comets with primordial Earth played far less of a role in helping start Earth’s oceans than had been thought.

The final descent: Rosetta’s OSIRIS narrow-angle camera captured this image of Comet 67P/Churyumov-Gerasimenko from an altitude of about 16 km above the surface during the spacecraft’s final descent on September 30, 2016. Credit: ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA.
The final descent: Rosetta’s OSIRIS narrow-angle camera captured this image of Comet 67P/C-G from an altitude of about 16 km above the surface, as the spacecraft commenced its final descent on September 29th, 2016. Craggy hills about 614 metres wide rise from a surface smothered in dust redeposited on the comet’s surface after being outgassed during its active phase. Credit: ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA.

As the comet became more active during its approach to the Sun, Rosetta found complex organic molecules – amino acid glycine, which is commonly found in proteins, and phosphorus, a key component of DNA and cell membranes – were present in the dust vented by 67P/C-G, reinforcing the idea that the basic building blocks for life may have been delivered to Earth from an early bombardment of such rocks. The mission also confirmed that the comet’s odd shape – two potato-like lobes of different sizes joined at a narrow waist – was the result of a very slow-speed collision very early in the comet’s 4.5 billion-year age.

In all the spacecraft  operated in the harsh environment of the comet for 786 days, made a number of dramatic flybys close to its surface, survived several unexpected outgassings, and made two full recoveries for potentially serious “safe mode” situations. However, all things must inevitably come to an end, and with its manoeuvring propellants almost exhausted, on September 29th, Rosetta set course for a gentle crash landing on 67P/C-G.

Continue reading “Space Sunday: water on Europa, Rosetta on a comet and Musk on Mars”