Space Sunday: of Soyuz aborts and telescopes

Cosmonaut Alexey Ovchinin (l) and astronaut Nick Hague (r) prior to their flight aboard Soyuz MS-10 – a flight that was a lot shorter and a little more exciting than either man anticipated. Credit: Roscosmos

On Thursday, October 11th, 2018, the Soyuz MS-10 spacecraft carrying two crew – American astronaut Nick Hague and Russian cosmonaut Alexey Ovchinin to the International Space Station (ISS) suffered a core second stage failure, triggering an emergency launch abort. Both Hague and Ovchinin survived the ordeal – although the way some of the media were reporting things, one might have thought they were hoping otherwise.

Soyuz utilises a R7 booster family of launch vehicle. This comprises a single-engined core element (confusingly called the 2nd stage, surrounded by 4 liquid-fuelled strap-on boosters referred to as the first stage. Each of these also has a single motor with, like the core stage, four combustion chambers. At launch, all five elements are fired, with the four strap-on boosters running for around 2 minutes. Then, with their fuel expended, they are jettisoned.

The view from the ground as Soyuz MS-10 starts its flight, October 11th, 2018. Credit: NASA TV

It is at this point – 2 minutes into the vehicle’s ascent from the Baikonaur Cosmodrome, Kazakhstan, that things went awry,  and gave observers watching from the ground the first indication of trouble – telemetry being relaid to mission control in Star City, near Moscow give little indication of a problem, causing commentators there to keep to their prepared scripts even as the drama unfolded.

Due to the way they fall clear of the core stage, the four strap-on boosters perform a controlled tumble with their exhaust plumes still visible. Seen from the ground, this forms distinctive and almost symmetrical pattern around the core stage called the “Korolev Cross” in honour of the father of modern Soviet / Russian space flight, Sergei Korolev, who also designed the original R7 rockets.

On this occasion, however, following separation, a decidedly asymmetrical Korolev Cross briefly formed, before the sky around the rocket became spotted with debris as if something had broken up.  At the same time, video of the cabin in the Soyuz vehicle’s decent module, where the crew sit during both ascent to orbit and their return to earth, showed Ovchinin  and Hague suddenly experiencing a brief period of weightlessness, almost as if thrust from the vehicle’s second stage had ceased, before they were pushed back into their seats and the plush toy suspended in front of the camera (used as a very rough-and ready G-force indicator) suggested a rapid acceleration.

This sudden acceleration was the result of the launch escape system kicking-in, separating the payload shroud containing the upper two modules of the Soyuz from the failing rocket. The manoeuvre recorded a 6.7 G acceleration right when the crew would have been expecting a 1.5G climb up to orbit as a result of jettisoning the spent strap-on boosters.

Once clear of the rocket, the fairing deployed a set of aerodynamic breaking flaps, slowing it to allow the Soyuz descent module to detach. The normal parachute and retro rockets where then used to bring the capsule back to Earth and execute a safe landing.

The distinctive “Korolev Cross” of booster separation see with R7 launches (l), and how it looked with Soyuz MS-10 (r). The first visual indications from the ground that something had gone wrong. Credits: NASA TV

Precisely what caused the failure has yet to be determined. As well as recovering the two crew safely and returning them to Baikonour unharmed, teams have also been busy recovering parts of the failure rocket, and Roscosmos believe they’ll be in a position to use the parts so far recovered together with telemetry from the vehicle’s ascent to provide a preliminary report on the failure within a week.

In the meantime, space experts have been examining video footage of the launch, and it would appear some form of malfunction during the separation of one of the four strap-on boosters may have caused it to actually collide with the core rocket. In his analysis of the flight, Scott Manley points to both the asymmetrical pattern of debris from the booster separation and what appears to be a radical slewing in the exhaust plume of the core stage as evidence there was some form of collision.

A remarkable shot of Soyuz MS-10 captured by ESA astronaut Alexander Gerst from the ISS. Credit: A. Gerst / ESA / NASA

Some confusion also exists over what actually happened during the abort sequence. Like Apollo crewed rockets, Soyuz has a tower-like escape system at its top. In an emergency, rockets mounted in the tower fire, pulling the crew module clear with a brief acceleration of about 14 G. As the reported acceleration with MS-10 was less than this, there was speculation the escape system hadn’t been used.

However, the Russian escape system, called the Sistema Avariynogo Spaseniya (SAS), unlike American systems, has two sets of motors: those in the tower, and a set of lower-thrust motors mounted directly on the payload fairing, and capable of around 7 G acceleration – the reported speed of the Soyuz on separation. It’s theorised it was these motors that pulled the Soyuz clear, the vehicle not having reached a velocity warranting the use of the tower rockets in order to pull the Soyuz clear.

Left: the Soyuz escape system (SAS) and how it works. The system uses two sets of motors which can be used together or independently of one another to pull the upper section of the payload fairing and the Soyuz clear of a malfunctioning rocket. The Soyuz descent module can then jettison, using its parachute and landing motors to return to Earth. Right: The SAS motor tower (boxed) with four rockets, and the second set of 4 RDG rockets mounted on the payload fairing (ringed). Credits: assorted.

Continue reading “Space Sunday: of Soyuz aborts and telescopes”

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Space Sunday: exomoons, dwarf planets and spaceflight plans

Artist’s impression of the exoplanet Kepler-1625b, transiting the star, with the candidate exomoon in tow. Credit: Dan Durda

A pair of Columbia University astronomers using NASA’s Hubble Space Telescope and Kepler Space Telescope have assembled compelling evidence for the existence of a Neptune-size moon orbiting a gas-giant planet 8,000 light-years away. If their findings are correct, it will be the first moon found orbiting a planet beyond our solar system.

The planet, Kepler 1625b, is between 5.9 and 11.67 times the size of Jupiter. It orbits a G-class main sequence star with around 8% more mass than our own in the constellation of Cygnus, every 287.4 days. The planet has been known about for some time, but whilst re-examining the data gathered by the Kepler space observatory that led to its discovery, Alex Teachey and David Kipping from the University of Columbia noticed anomalies in the way the planet dimmed the star’s light as it transited between the star and Kepler – anomalies that in ordinary circumstances should not have been there, but which were enough to get the astronomers 40 hours observing time using the Hubble Space Telescope.

Able to study the star with four times greater precision than Kepler, HST was used to observe Kepler 1625 both before and during one of the planet’s 19.5 hour transits across the star. In doing so, it recorded not only the anticipated dip in the star’s brightness, but also a second dimming along the same orbital path, starting some 3.5 hours after the first had started. The Hubble data also revealed that Kepler 1625b started its transit across the star 1.25 hours earlier than it should have.

When put together, the most likely explanation for both the “premature” transit and the extra dimming of light from Kepler 1625 is that a vary large, somewhat distance moon is orbiting the Jupiter-like Kepler 1625b. The presence of such a body in orbit would set a common barycentre (centre of gravity) between the planet and the moon that would cause the planet to “wobble” from its predicted location in its orbit, leading to variations in the start times for transits. Similarly, the presence of a large moon orbiting it would cause the additional dimming in the star’s brightness during a transit.

Diagram of the sequence of HST photometric observations. The purple object represents the planet Kepler 1625b, and the smaller green object is that exomoon, showing how the latter transits the star about 3.5 hours after the planet. Credit: NASA / ESA / D. Kipping (Columbia University), and A. Field (STScI)

Before the exomoon’s existence can be confirmed, further observations by Hubble are required. However, the preliminary data gathered suggests it could be around 1.5 percent the mass of its parent star – which is a very close mass-ratio between the Earth and its moon. However, given both the massive planet and its moon appear to both be gaseous in nature, should the moon’s existence be confirmed, it raises intriguing questions as to how it was formed.

In the case of solid satellites like the Moon, their creation is likely due to a collision between Earth and another planetary body that left debris that coalesced into the Moon. Such a path of formation for a gaseous body, however, is exceptionally unlikely: anything impacting with Kepler 1625b, for example, would likely be absorbed into it, rather than throwing off matter to form a separate orbiting body.

One of the most intriguing theories for the moon’s possible existence is that it may have started life as a separate planet orbiting Kepler 1625, but over time it came under the gravitational influence of the massive Kepler 1625b, and over time was drawn into orbit around it. If this should prove to be the case, it could have interesting implications for future exoplanets and the moons that may be found orbiting them.

NASA Delays Commercial Crew Launches and Tensions with Russia Increase

NASA has confirmed that the first uncrewed test flights of the SpaceX Crew Dragon and Boeing CST 100 Starliner commercial crew transports intended to fly astronauts to the International Space Station (ISS) have been delayed.

SpaceX Crew Dragon (l) and the Boeing CST-100 Starliner: initial flights delayed. Credit: SpaceX / Boeing

Under the original schedule, the uncrewed flight test for Crew Dragon had been scheduled for November 2018 and would have been followed by a 2-week crewed flight with NASA astronauts Bob Behnken and Doug Hurley in April 2019.  Under the new schedule, these flights will now  occur in January and June 2019 respectively.

Similarly, the first uncrewed flight for the CST-100 Starliner is now planned for March 2019 with the crewed test previously scheduled for mid-2019 now set for August 2019.

If SpaceX and Boeing maintain the new schedule, NASA believe the first operational commercial crew mission could take place in August 2019 – which would suggest a Crew Dragon would be the vehicle used, given the CST-100 would just have completed its crewed test flight, requiring some post-mission analysis. The second operational will then follow in December 2019. Both of these dates straddle the end to the US government’s extended contract to use seats on Russia’s Soyuz vehicle to send US astronauts to and from the ISS.

While unrelated, the news of the delays came as US / Russia tensions concerning the hole found in a Soyuz capsule became strained once more.

As I’ve previously noted (see here and here), at the end of August a slow leak was detected in a Soyuz MS-08 docked at the ISS. Initially, it was thought the hole causing the leak was the result of debris puncturing the Soyuz hull. However, it emerged the hole appears to have been drilled. Core thinking around it was that a mistake had been made during the vehicle’s fabrication or in preparing it for flight at the Baikonur cosmodrome, and then hastily covered up. In either case, it is believed a substance unfit for purpose was used in the repair, which gradually degraded in space prior to failing completely, causing the pressure loss.

Continue reading “Space Sunday: exomoons, dwarf planets and spaceflight plans”

Space Sunday: taking an elevator into space

An artist’s concept of a “carrier” – the “elevator car” of a space elevator – climbing the elevator cable. Credit: unknown

The space elevator is perhaps one of the most intriguing ideas for reaching space. It was first conceived as a thought experiment in 1895 by the grandfather of astronautics, Konstantin Tsiolkovsky. In it, he considered the building of a massive tower reaching up to geostationary orbit at 35,756 km (23,000 mi) above the surface of the Earth, and which at the top would have sufficient horizontal velocity to launch vehicles into orbit. The vehicles themselves would be carried aloft by elevators like the ones climbing the Eiffel Tower.

Tsoilkovsky knew the construction of such a tower would be next to impossible, there simply were no materials capable of withstanding the compressional pressures exerted the mass of such a tower as it was built upwards – nor are there today. However, in 1960, another Russian,  Yuri N. Artsutanov suggested that rather than building the elevator up from the ground, it could be built both down and out from geostationary orbit, using tension along the cable from its lower end and through the “counterweight” of the outward extent of its length to maintain is tautness and balance. Referring to the design as a “heavenly funicular”, Artsutanov estimated it would be capable of delivering up to 12,000 tonnes of payload to geostationary orbit per day.

An artist’s impression of a solar-powered car ascending the “Sky Hook”. Credit: unknown

Six years later, working entirely independently of Artsutanov, four American oceanographers – John Isaacs, Hugh Bradner, George Bachus and Allyn Vine (after whom the deep-ocean research submersible Alvin was named) – published their idea for a “sky hook” that essentially used the same approach: build a cable both “down” and “out” from a geostationary starting point. Their idea became the inspiration for Arthur C. Clarke’s 1979 novel The Fountains of Paradise, which did much to promote the idea of space elevators in the public mind.

Since then, the idea has received many re-visits, and has also given birth to a number of experiments and ideas for the use of tensile cables  – referred to as “tethers” for doing things like “lowering” experiments into the upper atmosphere for research (such ideas being tested during the space shuttle era) and for creating “artificial gravity” in spinning space vehicles travelling to Mars. A space elevator even appeared in Kim Stanley Robinson’s Mars trilogy as the means to get from orbit down to the surface of the planet. Today, the space elevator is the subject of study by the International Space Elevator Consortium (ISEC), which holds annual conferences on the subject and supports research programmes into space elevator concepts.

The appeal of space elevators  – if they can be built – is that they could deliver huge amounts of payload and manpower to orbit around Earth for a relatively low-cost when compared to using traditional rocket launches. And deliver them not just to geostationary orbit, but to other points above the surface of Earth, referred to as “way stations”.

For example, a “way-station” at around 420-450 km (262-281 mi) altitude would impart a horizontal velocity for vehicles “launched” from it to keep them in a low Earth orbit. similarly, a way station placed above the geostationary orbit point, at say 57,000 km (36,625 mi) would impart enough horizontal velocity to a vehicle “launched” from it that it could escape Earth on a flight to Mars.

The space elevator concept, show an ocean anchor point, and the various “way stations” along its length, capable of supporting operations a low Earth orbit (LEO), geostationary orbit (GEO) and high earth orbit (HEO) altitudes, the latter of which could support missions to Mars and further out into the solar system. Credit: ISEC

But before this can happen, there are some significant issues to overcome. The “simplest” of these is that of finding a suitable anchor point on Earth.

To work at geostationary orbit, the primary station on an elevator would have to be positioned over the equator. The problem here is, an awful lot of the equator is ocean (78.7%), making the construction of such an anchor-point at best difficult. While the remainder of the equatorial region is over land, it brings with it the overheads of political haggling and leveraging to gain an anchor-point.

In The Fountains of Paradise, Arthur C. Clarke solved this problem by conveniently moving Sri Lanka (which he called by its ancient Greek name of Taprobane (Tap-ro-ban-EE) 1,000 km (625 mi) south of its current position to straddle the equator. Unfortunately, we can’t do that in the physical world.

The more significant issues, however, are exactly how to build the elevator tether and how to gradually and safely lower it through the denser part of Earth’s atmosphere, and without its “downward” mass simply ripping it apart before it can be anchored.

The most promising material for the tether construction is carbon nanotubes (CNTs). These are artificially “grown” structures with a number of unusual properties, one of which it their sheer strength: up to 10 times that of an equivalent steel cable, which comes at a fraction of a cable’s mass. CNTs have been known about for around 20 years and are seen as having a range of potential applications: construction, electronics, optics, nanotechnology, etc. However, there is one slight issue with their use in large-scale projects. So far, no-one has successfully “grown” a nanotube longer than 1.5 metres.

Even so, experimental cables have been lifted to altitudes of around 1 km (0.6 mi) using weather balloons and had scale “carriers” run up and down them to test how an elevator tether and its payload would react to the influence of wind and weather. Now, researchers at the Shizuoka University Faculty of Engineering are taking the practical research a step further, by deploying an experimental “space elevator” in space.

On Monday, September 7th, 2018, the  Kounotori-7 H-II Transfer Vehicle (HTV) resupply vehicle is due to be launched to the International Space Station (ISS). As a part of the six tonnes of supplies the vehicle will be carrying will be two small “cubesats” – satellites that are each just 10 cm (4 inches) on a side.

Computer model of the cubesats and their (not to scale) tether deployed in Earth orbit. Credit: Shizuoka University

These will be deployed in space, connected by a 10 metre (33 ft) tether. Once the tether is under stable tension, a little electrically powered “car” will traverse it, marking the first time a vehicle has travelled along a tether in space. The test is intended to see how a space elevator tether might react to payloads moving along it in whilst in the “vacuum” of space, together with the stresses placed on it and its “anchor points”, etc.

It’s a small step along the way to establishing a space elevator, but the test will be watched with interest by Japan’s massive construction firm, Obayashi Corporation. In 2012, they announced they would have the world’s first space elevator operating by 2050. They are actively sponsoring research into CNT development, and believe the issues of growing long strands of CNTs and “knitting” them together into a tether will have been resolved by 2030.

Obaysahi Corporation’s design for their GEO station on the space elevator, which the company says will use “inflatable” modules to reduce mass. Credit: Obayashi Corp.

Continue reading “Space Sunday: taking an elevator into space”

Space Sunday: moon water and space telescopes

A visualisation of subsurface water ice deposits within PSR – permanently shadowed regions – of the Moon’s south pole, including the craters Cabeus, Shoemaker and Faustini. Credit: NASA Goddard Space Centre

The Moon is a fascinating place; there is no two ways about it. Like many bodies within the solar system, it is proving to be a lot more surprising than we’d previously thought. Up until 2009, for example, it was accepted that the Moon was a dry, arid place with little or no subsurface bodies of water ice. This idea was turned on its head in 2009 after India’s first lunar mission, Chandrayaan I, and NASA’sLunar Reconnaissance Orbiter (LRO) confirmed the presence of water ice within the so-called permanently shadowed regions (PSRs) – deep craters around the lunar poles which never see direct sunlight in their basins.

However, one of the questions surrounding these discoveries is just how much water might actually exist as ice within these shadowed craters? A new study,  published in August 2018, has sought to address this question; it is the work of Shuai Li – a post-doctoral researcher at the University of Hawaii, and  produced with the assistance of researchers from Brown University, the University of Colorado Boulder, the University of California Los Angeles, John Hopkins University, and NASA’s Ames Research Centre.

Li’s study focuses on data returned by NASA’s Moon Minerology Mapper (M³), flown aboard the Chandrayaan I mission. M³ was designed to measure light being reflected from the illuminated regions on the Moon, making its use over the PSRs had been considered of minimal value. Nevertheless, Li believed that what data M³ had gathered on the south polar craters might hep in determining the potential volume of water ice within those craters, as indicated by the Lunar Orbiter Laser Altimeter (LOLA), Lyman-Alpha Mapping Project and Diviner Lunar Radiometer Experiment on the LRO mission. However, what he found came as a complete surprise.

While I was interested to see what I could find in the M3 data from PSRs, I did not have any hope to see ice features when I started this project. I was astounded when I looked closer and found such meaningful spectral features in the measurements … We found that the distribution of ice on the lunar surface is very patchy, which is very different from other planetary bodies such as Mercury and Ceres where the ice is relatively pure and abundant. The spectral features of our detected ice suggest that they were formed by slow condensation from a vapour phase either due to impact or water migration from space.

– Shuai Li, leader of the study team

 

Exposed water ice (green or blue dots) in lunar polar regions and temperature. Credit: Shuai Li

While likely the results of vapour capture following asteroid impacts, Li’s study again opens the door as to how much sub-surface water ice might also exist deeper within the polar regions of the Moon. As I recently noted, a separate study, evidence has been put forward for periods in the Moon’s early history when liquid water existed on the lunar surface at a time when the Moon had a volcanically-induced atmosphere. Much of this water was likely lost to space as that atmosphere dissipated at the end of the Moon’s active volcanic period; however, some of it may have gone underground again, notably in these polar regions.

Either way, the existence of water ice deposits strengthen the case for a return to the Moon and – as NASA Administrator Jim Bridenstine recently indicated – see the establishment of a permanent human presence on the Moon.  An available and plentiful supply of water would go a long way to easing many of the logistical requirements for such a human presence. Once melted, a local supply of water can be filtered and purified to provide drinking water; it can also be used in construction work and as “grey” water for use in growing local foodstuffs through hydroponic or other means; it can be electrolysed to produce oxygen in support of the atmosphere within a base and hydrogen than could be used to power fuel cells, and so on.

The European Space Agency (ESA) in particular is researching ways and means to build a lunar settlement using what is called “in-situ resource utilisation” (ISRU), or the use of locally available materials. In particular ESA has been using locally available “lunar simulants” available here on Earth – notably certain types of volcanic dusts that have been shown to have very similar properties to the dry dust of the surface-covering lunar regolith on the Moon – to test potential options for base construction.

One of these I’ve again previously written about, is the idea of using regolith to effectively “3D print” a protective “shield” of regolith over the facilities of a lunar base to protect it against solar radiation. Referred to as “additive manufacture”, such a technique might be aided with a readily available source of water which can help mix the regolith into a cement-like form that can be “printed” over the structure of a base in layers. In addition, ESA is using a regolith simulant to make “bricks” which can be used to physically construct the walls, floors and ceilings of a base – a process that might again  be easier with a supply of water for use in the process.

A “lunar brick” produced by ESA using “3D printing” techniques and lunar regolith simulants. Credit: ESA

But it is in production of oxygen and hydrogen, as well as offering a source for liquid water, that the ice deposits offer the greatest potential benefit. Up until now, ideas for oxygen production on the Moon have focused on “cracking” the regolith to release the oxygen within it (thought to be around 40% by volume). This requires a lot of energy to achieve –  more than is needed to melt and electrolyse ice to produce both oxygen and hydrogen.

However, it’s not all plain sailing for humans on the Moon. The dust comprising lunar regolith is extremely electro-statically charged, making it stick to just about anything – so keeping it out of a lunar habitat could prove difficult. Worse, it also presents a range of potential health hazards – up to and including major respiratory problems such as lung cancer. These risks have yet to be fully assessed, and countering them as far as possible must be a priority before there can be real talk of a long-term human presence on the Moon.

But in the meantime, Li’s study potentially adds important food for thought for those thinking about establishing research facilities on the Moon.

Continue reading “Space Sunday: moon water and space telescopes”

Space Sunday: exoplanets, flying crews to orbit and a movie

Could up to 35% of the Earth-sized exoplanets so far discovered be “water worlds”? Credit: NASA

Exoplanets between 2 and 4 times the size of Earth may feature water as a large component in their make-up, with many comprising perhaps up to 50% water by weight (by contrast, Earth has just 0.02% water content by weight).

This is the conclusion drawn by an international team of researchers who have being pouring (pun intended) over data from the Kepler Space Telescope and the Gaia mission gathered on the 4,000+ exoplanets discovered thus far, many of which tend to fall into two categories: those with the planetary radius averaging around 1.5 that of the Earth, and those averaging around 2.5 times the radius of the Earth.

It was a huge surprise to realise that there must be so many water-worlds. We have looked at how mass relates to radius, and developed a model which might explain the relationship. The model indicates that those exoplanets which have a radius of around x1.5 Earth radius tend to be rocky planets (of typically x5 the mass of the Earth), while those with a radius of x2.5 Earth radius (with a mass around x10 that of the Earth) are probably water worlds. Our data indicate that about 35% of all known exoplanets which are bigger than Earth should be water-rich.

– Dr. Li Zeng of Harvard University, lead researcher on the study

The teams findings could have major implications for our understanding of the composition of Earth-sized exoplanets. However, if the team’s conclusions are correct, it doesn’t necessarily mean these are especially balmy places. Many orbit so close their parent stars their surface temperatures are liable to be in the 200-500o Celsius range (392-932oF), so the water on them is liable to be very different to how we find it on Earth, existing as saturating vapour in the atmosphere, then a world-girdling warm ocean with ice under increasing pressure below it, wrapped around a sold core.

Data from the European Space Agency’s Gaia mission was used by the researchers. Launched in 2013, Gaia is on a mission to take a “census” of one billion of the stars visible from its orbit around the Sun-Earth L2 position. And if that sounds a lot, it is actually represents just 1% of the galaxy’s total population of stars. Credit: ESA

The beauty of the model is that it explains just how composition relates to the known facts about these planets, and offers insight into how they were formed – most likely in a similar manner to the cores of the giant planets in our own solar system.

With a new generation of Earth-based telescopes capable of peering at distant planets currently gaining remarkable optical updates (such as ESO’s Very Large Telescope)  or under construction (the Giant Magellan Telescope or GMT), not to mention the James Webb Space Telescope and the Transiting Exoplanet Survey Satellite (see below for more in this), the hope is that the findings presented by the team will soon be backed-up with hard data as atmospheres around these distant worlds are properly characterised.

TESS Starts Work

TESS, the Transiting Exoplanet Survey Satellite launched on April 16th, 2018, has started its primary mission – taking over from the ailing Kepler mission in locating exoplanets. This initial primary mission will last for 2 years, in which it is anticipated TESS will pay particular attention to the 200,000 brightest stars around us in the hope of detecting planetary bodies in orbiting them. It will do this using the transit method of observation – looking for dips in the brightness of stars which might indicate the passage of an orbiting planet between the star and the telescope.

How TESS will survey the stars around it. Left: The combined field of view of the four TESS cameras. Middle: Division of the celestial sphere into 26 observation sectors (13 per hemisphere). Right: Duration of observations on the celestial sphere. The dashed black circle enclosing the ecliptic pole shows the region which JWST will be able to observe at any time. Credit: NASA Goddard Spaceflight Centre

The first data gathering element of the mission commenced on July 25th, and will continue through most of August before the data is transmitted by to Earth from TESS’s unique orbit, a “2:1 lunar resonant orbit“, which allows the craft to remain balanced within the gravitational effects of the Moon and Earth, providing a stable orbital regime which should last for decades.

As a part of the mission, the TESS science team aims to measure the masses of at least 50 small planets whose radii are less than four times that of Earth, offering the opportunity to characterise their likely structure and composition. Many of TESS’s planets should be close enough to our own that, once they are identified by TESS, scientists can zoom in on them using other telescopes, to detect atmospheres, characterise atmospheric conditions, and even look for signs of habitability.

In this latter regard, TESS will pave the way for detailed studies of candidate exoplanets by the James Webb Space Telescope (JWST), now scheduled for launch in 2021. While TESS cannot look for atmospheric or other signs of life on the distant worlds it locates, JWST will be able to do just that, which could see the 2020s a decade of remarkable extra-solar planetary discoveries.

Continue reading “Space Sunday: exoplanets, flying crews to orbit and a movie”

Space Sunday: to touch the face of the Sun

Ignition! The three main stages of the Delta 4 Heavy fire, starting the Parker Solar Probe on its mission to examine the Sun up close and personal. Credit: NASA

On the morning of Sunday, August 12th, 2018, NASA launched the Parker Solar mission, which it describes as being “to touch the face of the Sun”. It will be the first mission to fly through the Sun’s corona – the hazardous region of intense heat and solar radiation in the Sun’s atmosphere that is visible during an eclipse, and it will gather data that could help answer questions about solar physics that have puzzled scientists for decades. Over the course of its initial 7-years the Parker Solar Probe mission will allow us to better understand the fundamental processes going on in, on, and around the Sun, improving our understanding how our solar system’s star influences, affects and changes the space environment, through which we travel as the Earth orbits the Sun.

The probe and mission are named for Dr Eugene Parker, an American solar astrophysicist, who in 1958 first posited  the theory of the supersonic solar wind, and who also predicted the Parker spiral shape of the solar magnetic field in the outer solar system. Now 91, he was present at NASA’s Kennedy Space Centre as a distinguished guest of the agency, to witness the probe’s launch, the mission (and vehicle) being the first in NASA’s history to be named after a still-living person.

The Delta 4 Heavy carrying the Parker Solar Probe sits on the pad of Space Launch Complex (SLC) 37 at Canaveral Air Force Station, Florida, following the aborted launch attempt of Saturday, August 11th, 2018. Credit: Vikash Mahadeo / SpaceFlight Insider

Lift-off came at 03:31 EDT (6:31 GMT / 7:31 BST) on Sunday, August 12th, after the initial launch attempt was scrubbed on Saturday, August 11th, when a troubled countdown was halted just one-minute, 55 seconds before the engines on the United Launch Alliance (ULA) Delta 4 Heavy rocket were to ignite. The halt was called following a gaseous helium red pressure alarm, and investigations into its cause extended beyond the 65-minute launch window, resulting in the launch scrub.

The Sunday morning launch countdown proceeded without any significant hitches, and the Delta 4 Heavy – the most powerful rocket in ULA’s fleet of launch vehicles, comprising 3 Delta 4 first stages strapped side-by-side, the outer two functioning as “strap-on boosters” – lit up the Florida coastline as it took to the early morning skies.

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Although a flight to the Sun might sound an easier proposition than reaching the outer solar system, it actually isn’t; it actually requires 55 times more launch energy than a launch to Mars. Hence why the relative small and light Parker Solar Probe, weighing just 685 kg (1,510 lb) at launch, required the massive Delta 4 and a rarely-used Star 48BV variant of the Payload Assist Module (PAM).

Originally developed as the upper stage for Delta 2 launch vehicles in the 1965, the Star family of solid-fuel PAM units were commonly used with the space shuttle for satellite launches from orbit: the shuttle would carry them aloft, release the PAM / Satellite combination, then move to a safe distance before the PAM motor was ignited to push the satellite on to its require Earth orbit. For the Parker Solar Probe, the Star 48BV was used to impart as much velocity as possible into the vehicle at is starts on it journey.

Dr. Eugene Parker, now 91, watches the launch of the probe named in his honour as it lifts-off from SLC-37, Sunday, August 12th, 2018. Credit: NASA / Glenn Benson

What makes a flight to the Sun so hard is that the Earth is moving “sideways” relative to the Sun at about 107,000 km/h (67,000 mph), and the probe has to cancel out a whopping 84,800 km/h (53,000 mph) of that “sideways” motion as it makes its way to the Sun in order to achieve orbit. At the same time, the probe needs to gain velocity as it moves in towards the centre of the solar system in order for it to balance the Sun’s enormous gravitational influence and achieve the required elliptical orbit.

The use of the Delta 4 / Star 48BV combination got both of these requirements started, by pushing the probe towards Venus in an arc that will both start to shed the “sideways” velocity, whilst also accelerating the craft in towards the Sun. But it will be Venus that does the real grunt work for the mission.

On October 1st, 2018, the probe will make the first of a series of flybys of Venus, where it will use the Venusian gravity to shed still more of the angular velocity imparted by Earth’s orbit and increase its velocity towards the Sun.

In all, seven such fly-bys of Venus will occur  over the 7 year primary mission for the probe, and while only the first is required to shunt the vehicle into its core heliocentric orbit, the remaining six play an important role in both maintaining the vehicle’s average velocity across the span of the mission and in gradually shrinking its elliptical orbit around the Sun as the mission progresses.

The first pass around the Sun  – and the start of the science mission – will occur in November / December 2018. At perihelion, the vehicle will be just 6.2 million km (3.85 million mi) from the Sun’s photosphere (what we might call its “surface”). During this time, the vehicle will be well within the corona, and will also temporarily become the fastest human-made vehicle ever made, achieving a velocity of around 700,000 km/h (430,000 mph) – that’s 200 km per second (120 mi/s), or the equivalent of travelling between London and Tokyo in around 50 seconds! At aphelion – the point furthest from the Sun, and brushing Earth’s orbit, the craft will be travelling a lot slower.

The corona is a very hot place – hotter than the “surface” of the Sun, however, it is also comparatively thin as far as an “atmosphere” goes. The distance at which Parker Solar Probe will be travelling from the Sun at perihelion, combined with its speed, mean that the ambient heat of the corona isn’t a significant issue. Direct sunlight radiating out from the Sun, however, is a significant problem.

Continue reading “Space Sunday: to touch the face of the Sun”