ESA/NASA crew continue ISS spacewalk to install new solar arrays

Two astronauts have ventured outside the International Space Station (ISS) to attempt to continue installation… The post ESA/NASA crew continue ISS spacewalk to install new solar arrays appeared first on NASASpaceFlight.com.

ESA/NASA crew continue ISS spacewalk to install new solar arrays

Two astronauts have ventured outside the International Space Station (ISS) to attempt to continue installation of the first of six new Boeing-built solar arrays — part of a program to increase the station’s electrical power generation capacity as its science and research demands increase and future expansion plans continue.

The Extravehicular Activity (EVA) – officially known as US EVA-75 – began at 11:42 UTC / 07:42 EDT when Thomas Pesquet from the European Space Agency (ESA) and Shane Kimbrough from NASA took their spacesuits to battery power before exiting the Quest Airlock to begin their work.

IROSA background

The eight original Solar Array Wings (SAWs) on the ISS, which each produce around 30 kilowatts (kW) of power for a total of about 250kW are beginning to show signs of degradation, with the oldest array now having been in space since 2000 when the P6 truss and associated arrays was delivered to the station by Shuttle Endeavour’s STS-97 crew.

With over 20 years of use, and normal degradation of solar arrays, the eight SAWs now only produce around 160kW of power – against a backdrop of rising power demands from the station’s increasing users.

This led the Station program to develop the ISS Power Augmentation (IPA) plan, which called for adding six additional solar arrays to the station in order to restore the outpost’s power generation to its original levels.

Under the IPA program, six new ISS Roll Out Solar Arrays (IROSAs) will be added. Whilst the station’s original arrays were folded up and deployed in an accordion-like manner, the IROSAs are a new type of array technology which roll out in a mat-like manner from inside a cylindrical canister.

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  • The IROSAs will be installed on top of six of the station’s existing solar arrays, which will allow the IROSAs to utilize the same sun-tracking motors and be connected into the same electrical system as the current arrays.

    With the IROSAs being around 30% efficient, compared to the 14% efficiency of the original arrays, the IROSAs will generate roughly the same amount of power as the originals despite being only half their size.

    Each IROSA will produce 20kW of additional power, for a total of 120kW across all six arrays.

    However, because the IROSAs are smaller, they will not completely cover the half of the six SAWs they’ll be installed over. Instead, portions of the original arrays will still be power positive.

    The unshadowed portions of the original arrays will continue to produce 95kW as a result, making for a combined total of 215kW of power available to the ISS — an increase of nearly a third compared with the outpost’s current levels.

    This first IROSA was launched along with the second aboard the SpaceX CRS-22 cargo Dragon mission that launched from Florida back on 3 June. 

    The first EVA encounter numerous issues, primarily with Shane Kimbrough’s suit and a hardware interference with the solar array deployment that brought an end to the spacewalk well before the main objectives could be accomplished.

    EVA-74 issues

    US EVA-74 encountered numerous issues, primarily with Shane Kimbrough’s suit and a hardware interference with the solar array unfolding that brought an end to the spacewalk well before the main objectives could be accomplished

    After exiting the Quest Airlock, the first task for the pair was to translate out to the IROSA Flight Support Equipment (FSE). However, in a somewhat sign of things to come, the hatch covering would not close at first, and Shane had to spend more time than planned getting the airlock’s fabric hatch covering configured properly.

    The FSE, pallet on which the pair of IROSAs are attached, was removed from cargo Dragon’s trunk by Canadarm2, also known officially as the Space Station Remote Manipulator System (SSRMS) — part of the overall Mobile Base System on the station. Canadarm2 then installed the FSE onto the Mobile Base System (MBS) Payload ORU Accommodation (POA).

    For Pesquet and Kimbrough, after translating to the FSE, the duo began setup of the worksite and released launch restraint bolts on the IROSA.

    However, before the EVA could progress further, two issues were noted with Shane’s suit. First, a sensor in the suit’s sublimator — which provides pressure — registered a spike. Shortly thereafter, the Display and Control Module (DCM) in his suit malfunctioned, necessitating an immediate return to the Quest Airlock to connect back to Station umbilicals to attempt a restart of the unit.

    The “warm restart” of the DCM meant that Shane’s suit momentarily lost its cooling and CO2 scrubbing capabilities; however, this is an acceptable condition, per EVA procedures, when attempting to “warm restart” a DCM. A failure to restart the unit would have meant a premature end to the EVA.

    The restart was successful, and ground teams sent Shane back out to Thomas while managers and engineers continued to discuss the sublimator issue — which itself could have also stop the EVA early. Fortunately, through a series of suit configuration tests, ground teams were able to determine that the sublimator was functioning properly and that a faulty sensor likely triggered an erroneous pressure increase reading.

    Angle showing how the new IROSAs will be deployed over the current arrays. (Credit: NASA)

    With his suit good to go, Kimbrough translated out to the P6 truss installation site — specifically the 2B Integrated Electronics Assembly (IEA) — to begin more setup while Pesquet – mounted to the end of Canadarm2 – held on to the IROSA while he was “flown” out toward the P6 truss.

    Inside the ISS in the Robotics Work Station in the Cupola viewing module, NASA astronaut Megan McArthur controlled Canadarm2; she was the one to physically drive Pesquet out toward the P6 truss.

    Due to the fact that P6 is at the very outboard end of the station, Canadarm2 cannot reach all the way to the worksite, meaning Pesquet had to hand-off the IROSA to Kimbrough, who then in turn held on to it whilst Pesquet dismounted the arm and repositioned.

    Once Pesquet was in position, Kimbrough handed the IROSA back to him. The duo then aligned the IROSA onto the mounting bracket of the “Mod Kit” — which was installed during a spacewalk earlier this year — at the base of the 2B Mast Canister Assembly (MCA).

    The IROSA was first soft-docked onto the mounting bracket before an attempt to unfolded it into its deployment configuration stalled due to interference/blockage from a nearby structure. At this point, already at the six hour mark into the spacewalk, ground teams decided to have the duo photograph the interference and firmly secure the IROSA as is and end the spacewalk.

    Teams will now evaluate a path forward to unfold the array, which must happen before it can be unfurled.

    Thomas and Shane also did not mount four electrical connections between the IROSA and the 2B MCA in order to connect the IROSA into the electrical system of the current 2B solar array as they ran out of time.

    The ISS once the new arrays are installed – via Mack Crawford for NSF L2.

    After returning to the Quest Airlock, the duo took their suits off battery power at 19:26 UTC / 15:26 EDT, concluding the 7 hour 15 minute spacewalk.

    EVA-75

    Sunday’s spacewalk will now attempt to complete the main objectives of US EVA-74, with Thomas and Shane moving out to the P6 truss worksite.

    After leaving the Quest airlock, Thomas will take the lead moving to the worksite. The pair will both work to unfold the new solar array on the 2B power channel, and Shane will drive in the two remaining bolts to secure the solar array in place.

    The two installed the new iROSA into its mounting bracket during th 16 June spacewalk, but an interference associated with the array’s hinge created an alignment issue and prevented a full roll-out.

    Ground teams have since identified the solution related to the sequence of deployment that will be employed on this spacewalk.

    The crew members will work together to deploy the solar array from its flight support structure. Once they complete unfolding and the new array and driving the final two bolts into place, the duo will install cables for connection to the station’s electronics.

    If successful, Thomas and Shane will then turn their attention to get-ahead work for the second iROSA installation, currently scheduled for US EVA-76 on 25 June.

    Overall, US EVA-75 is the 240th EVA in support of station construction and maintenance and the eighth spacewalk so far this year outside the outpost.

    (Lead image: Placement of the new IROSAs over the existing station solar arrays. Credit: Mack Crawford for NSF L2)

    The post ESA/NASA crew continue ISS spacewalk to install new solar arrays appeared first on NASASpaceFlight.com.

    Source : NASA More   

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    Europa volcanism & interior heating modeled in detail, offers research targets for upcoming missions 

    Europa, an icy Jovian moon that likely possesses an ocean beneath its icy crust, may… The post Europa volcanism & interior heating modeled in detail, offers research targets for upcoming missions  appeared first on NASASpaceFlight.com.

    Europa volcanism & interior heating modeled in detail, offers research targets for upcoming missions 

    Europa, an icy Jovian moon that likely possesses an ocean beneath its icy crust, may have an interior that is hot enough to produce volcanic activity on its seafloor. New research provides evidence that this seafloor volcanism likely occurred in the moon’s past and maybe ongoing at present as well.

    The team of researchers, led by Dr. Marie Běhounková of Charles University in the Czech Republic, developed their own 3D models of Europa’s interior and heating transfer properties to investigate the possibility of volcanism on Europa’s ocean floor given other volcanism seen in the Jovian system.

    Scientists have proposed the idea of a subsurface ocean under Europa’s crust for years, and have strong evidence from multiple missions to support the theory. Běhounková et al.’s new research provides evidence to the idea that that seafloor could be volcanically active.

    These volcanoes would form due to the melting of Europa’s interior and heat transfer from the rocky interior of Europa to the seafloor. Models developed by Běhounková et al. show that many different factors — including radiogenic power and tidal forces — contribute to the melting of the icy moon’s interior.

    But why this type of research regarding Europa?

    “In the Jovian system, it is known that there is huge activity on the moon Io, so we wanted to explore if it’s a possibility that there is something similar, although, to a lesser extent, going on on Europa,” said Dr. Běhounková in an interview with NASASpaceflight.

    the can be found here.

    However, the extent of volcanism depends on how much melting is occurring and how heat is transferred to the seafloor.

    Běhounková et al. modeled Europa’s internal heating to understand exactly where and how this melting and volcanic activity is occurring. Their model is the most detailed of Europa’s interior ever developed and represents the internal heat production and transfer throughout the moon’s history.

    A prime candidate for the mechanism behind Europa’s heating is tidal forces imparted to it via gravitational interactions with Jupiter, Io, and Ganymede. And those forces can be difficult to model.

    “From a point of view of numerical modeling for moons and planets, tidal heating is more difficult to model because of the interaction with other bodies. This is something many people are working on now, not only in the Jovian system, but also for extrasolar planets.”

    In the case of creating the model for Europa, the team had to consider the moon’s changing orbital parameters over the course of its 4.5+ billion year existence. “The evolution of orbital parameters is, in our case, only parameterized. But in this case, the main influence on this evolution is Io, which we didn’t model in our case. So that’s why we studied several parametric models for the eccentricity evolution.”

    This is in part due to the Laplace resonance of Europa with Io and Ganymede. A Laplace resonance is a phenomenon that occurs when three planetary bodies with an orbital period ratio of 1:2:4 exert regular and periodic gravitational effects on each other. These nudges create tidal forces that translate to the heating of the body’s interior.

    It’s that interaction that led Běhounková et al.’s research toward the conclusion that this resonance and the associate tidal forces can cause increased periods of volcanic activity — called magmatic pulses — on Europa.

    “These magmatic pulses are basically periods of increased volcanic activity which can be induced by changes in orbital parameters — in this case, [the moon’s changing] eccentricity [and its] Laplace resonance with Io and Ganymede.”

    These magmatic pulses on Europa would result in the release of volatiles from silicate melt locations on the seafloor. “That silicate melting can produce this volcanism on the top of the mantle or the bottom of the ocean,” said Dr. Běhounková.

    Additionally, the model developed by Dr. Běhounková and her team shows that Europa’s eccentricity evolution is periodic, which suggests increased periods of magmatic pulses on the moon.

    “There are models that the eccentricity evolution can be periodic, with increased periods of eccentricity which would induce a higher volcanic activity. The volcanic activity can be important as a source of energy for the chemical environment on the floor of Europa’s ocean.”

    However, tidal forces created by the Laplace resonance and Europa’s changing eccentricity has not always been the leading cause of internal melting. For the first few billion years of the moon’s formation, radiogenic power would have been the main cause of mantle melting and volcanism on the Jovian moon.

    However, due to radiogenic decay, this source of heating ends up having less control over Europa’s internal melting rate over the course of the moon’s evolution, allowing orbital eccentricity and the Laplace resonance effects to take over as the more dominate mechanisms.

    “On the other hand, the tidal evolution can be slightly different, and tidal flexing can also evolve with time. And based on eccentricity and interaction with other bodies, it can even increase with time. This is the principal difference between the radiogenic sources of energy and tidal sources of energy.”

    Tidal heating is the reason why Io is so volcanically active, and as Dr. Běhounková said, Io’s tidally heated volcanism is one of the reasons why her team wanted to research Europa for the same phenomena.

    Europa may consist of an iron core, surrounded by a rocky mantle in direct contact with an ocean under the icy crust. New research models how internal heat may fuel volcanoes on the seafloor. (Credit: NASA/JPL-Caltech/Michael Carroll)

    Based on the model created by Běhounková et al., Europa’s heating from tidal forces is not uniformly distributed around its oceanic surface. High latitude regions near the poles are much more prone to tidal heating melting of rock and associated volcanism than at the equatorial regions, where cold downwellings typically prohibit enhanced amounts of melting to occur.

    Despite the difficulties with modeling, Běhounková et al.’s research shows that Europa was likely very active — from a volcanism standpoint — during its years of development and is likely still an active world today. 

    So what does this all mean, and why is this model of Europa’s heating environment and volcanic history (and present) so important?

    It comes down to the moon’s ocean. Where there is water and heat energy on Earth, there is life — even in the deepest recesses of the planet’s oceans, where hydrothermal vents support thriving colonies of various lifeforms.

    As Běhounková et al. state in their paper, “The occurrence of magmatic activity on the seafloor is essential to determine if it constitutes an environment hospitable to life.”  

    They continue, stating, “Jupiter’s icy moon Europa harbors underneath tectonically modified ice shell (Figueredo & Greeley, 2004; Kattenhorn & Prockter, 2014) a salty ocean (Kivelson et al., 2000) in direct contact with a rocky interior that may still be active (Moore & Hussmann, 2009). Such an oceanic environment makes Europa a primary target in the search for a habitable world beyond Earth (Hand et al. 2009).”

    “The chemical evolution of Europa’s ocean and its habitability is conditioned by the interaction with the rocky seafloor (Vance et al., 2016). It depends on the heat released from the deep interior to the seafloor (Altair et al., 2018), and hence by the intensity of magmatic activity.”

    But one sticking point remains: how to prove the model is correct and how to prove that volcanism did occur and is still occurring today?

    For decades, Europa has been one of the select few locations in our solar system where life is proposed to have possibly existed or exist currently. Because of this, dozens of missions have been proposed to visit the moon.

    Two upcoming flights, NASA’s Europa Clipper and ESA’s JUpiter ICy moons Explorer (JUICE), will specifically study Europa.

    While these spacecraft do not feature the proper instruments needed to perform a detailed study of seafloor volcanism on the Jovian moons, they can still be incredibly helpful in unlocking Europa’s heating and volcanism history.

    “There will still be many things we can work with,” said Dr. Běhounková. “There will be better constraints on the evolution of orbital parameters which can help to determine the condition inside the bodies. There will be gravimeters, and the gravity field will be known with better accuracy than we know right now.”

    “This can also help, and this can possibly detect some large anomalies on the seafloor. If we are lucky, we can detect some chemical and water species. It will be interesting for us to have this data and, basically, narrow the possibilities, of what’s going on in Europa and Jovian system.”

    JUICE is currently targeting launch on a Ariane 5 rocket no earlier than 9 June 2022. After five gravity assist maneuvers with Earth, Venus, and Mars, the craft will enter Jupiter’s orbit in October 2029 before dispatching a dedicated orbiter to Ganymede for a September 2032 orbital arrival around that moon.

    Europa Clipper meanwhile is currently scheduled to launch no earlier than 10 October 2024 on a U.S. commercial launch vehicle — which almost certainly will be SpaceX’s Falcon Heavy due to numerous NASA studies on which commercial vehicles were viable alternatives to the US Congress’s original law that shackled the craft to the SLS rocket.

    If launched in 2024 on a Falcon Heavy, Europa Clipper will perform two gravity assists with Mars and Earth in February 2025 and December 2026, respectively, before entering orbit of Jupiter on 11 April 2030.

    (Lead image: Europa Credit: NASA/JPL-Caltech/SETI Institute)

    The post Europa volcanism & interior heating modeled in detail, offers research targets for upcoming missions  appeared first on NASASpaceFlight.com.

    Source : NASA More   

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