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Posts Tagged ‘NASA’

New images of the European Space Agency’s Beagle 2 have emerged recently, suggesting that it came closer to success than has long been thought. These new images have been analysed more thoroughly and carefully than previous images of Beagle 2, and with the help of a computer simulation it is being suggested that Beagle 2 did not crash land. Instead, this team led by Professor Mark Sims of Leicester University are arguing that Beagle 2 deployed, but not completely correctly. They suggest that, due to not deploying correctly, that it may well have done science for a period of about 100 days, before shutting down due to lack of power. They even suggest that there is a very slim possibility that it is still working.

I do have to take issue, however, with the way this story is worded on the BBC website. It implies that we now know, with certainty, that Beagle 2 operated for some period on the surface of Mars. This is not true. One study has argued that it did. One swallow does not make a summer. This particular team’s analysis and study will need to be looked at by others before we can say with any reasonable certainty that Beagle 2 survived its landing.

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New images of Beagle 2 taken by NASA’s Mars Reconnaissance Orbiter have been analysed by a computer model, suggesting it may have actually worked for a short period of time.

As with any suggestion which flies in the face of conventional wisdom, this claim will need to be checked and followed up by others. But, if the evidence is sufficiently strong that Beagle 2 did not crash, then it will come as a relief to those who worked on it and have long felt that it failed in a crash. Sadly, even if it did work, we have not received any data back from it; and that is not going to change.

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The Schiaparelli space probe has been in the news quite a lot this last week or so. It was due to land on the surface of Mars last Wednesday (19 October), but lost contact about one minute before this. On Friday (21 October) NASA released images taken by its Mars Reconnaissance Orbiter which have led ESA to conclude that Schiaparelli exploded on impact, probably due to a failure of the thruster rockets which were meant to guide it gently down over its last few kilometres of descent. For more on that story, see here. This separate story suggests that the failure of the thruster rockets to burn correctly was due to a computer glitch, and that they only burned for 3 seconds instead of the intended 29 seconds.

What has received far less attention than Schiaparelli is the larger spacecraft which transported it to Mars – the Trace Gas Orbiter (TGO). The TGO was successfully put into orbit about Mars after it and Schiaparelli separated. Whilst ESA scientists worried about the silence of Schiaparelli, they were nevertheless jubilant that the TGO had successfully manoeuvred into orbit about the red planet.

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ESA’s Trace Gas Explorer (TGO) transported the lander Schiaparelli to Mars, and is now successfully in orbit about the red planet.

The TGO’s primary scientific mission is to look for traces of methane emanating from Mars. This is of great scientific interest, because methane could be due to life on Mars. Many bacteria on Earth, in particular those that respire anaerobically, emit methane. The best known example are the bacteria which help digest food in the stomachs of many animals, including us. This is why cows are one of the primary sources of methane emission, the gas is coming from the bacteria in their stomachs.

Methane was first detected in the Martian atmosphere in 2003 by NASA scientists. The following year NASA’s Mars Express Orbiter and some ground-based observations detected methane at the level of about 10 parts per billion. Large temporal and positional variations in the methane concentration were measured between 2003 and 2006, which suggests that the methane is  both seasonal and local.

The other possible source of methane is geological activity. Any methane in the Martian atmosphere is quickly broken down by ultraviolet light from the Sun (there is no ozone layer to protect the molecules from UV light, as there is on Earth). This means that any methane present in the Martian atmosphere but have been recently produced. So, how can we tell the difference between methane due to bacteria and methane due to geological activity?

The key is to look for the presence of other gases along with the methane. If the methane is geological in origin it will be accompanied by sulphur dioxide. If, however, it is due to bacteria it will be accompanied by ethane and other similar molecules. The TGO will be able to measure both the methane and these other gases, and so hopefully will help us determine the origin of the methane. In addition, it will be able to measure and image other things, including sub-surface hydrogen down to a depth of a metre. This will help us better map out the amount and extent of subsurface water ice on Mars.

In all, the TGO has four scientific instruments on it, namely

  1. The Nadir and Occultation for Mars Discovery (NOMAD). This instrument has two infrared and one ultraviolet spectrometer channels.
  2. The Atmospheric Chemistry Suite (ACS) has three infrared spectrometer channels.
  3. The Colour and Stereo Surface Imaging System (CaSSIS) is a high-resolution colour stereo camera which will be able to resolve down to a resolution of 4.5 metres on the Martian surface. Being stereo, it will be able to create an accurate elevation map of the Martian surface.
  4. The Fine-Resolution Epithermal Neutron Detector (FREND), a neutron detector which can indicate the presence of hydrogen in the form of water or hydrated minerals. FREND can detect hydrogen down to a depth of 1 metre in the Martian surface.

NOMAD and ACS are the two instruments which will measure the methane and other trace molecules in the atmosphere. Twice each orbit, when the Sun is both rising and setting as seen from the TGO, it will use the passage of the Sun’s light through the Martian atmosphere to detect and measure the presence of trace molecules, down to a few parts per  billion (ppb).

The TGO will orbit Mars at an altitude of 400 km, in a circular orbit taking only 2 hours to orbit once. The orbit will be inclined at 74 degrees to the Martian equator.  It was launched on the 14 March, so took just over 6 months to get to Mars. In 2021 ESA plans to land a rover on the Martian surface, but whether this schedule is delayed due to the failure to successfully land Schiaparelli remains to be seen.

 

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Last week, two more Chinese astronauts (or “taikonauts” as they are sometimes known) blasted into space, to spend a month on-board China’s experimental space station Tiangong. They successfully docked with the space station just before 19:30 GMT last Tuesday (18 October). The 30-day stay on the space station will be the longest mission yet undertaken by Chinese astronauts.

This is the latest chapter in an ambitious space programme; China has plans to send manned missions to both the Moon and Mars, although it has not publicly stated a time-line for these two goals. In fact, nothing would boost China’s feeling of becoming the World’s premier superpower than if they were to get to Mars before the USA.

The pace of China’s space programme is impressive. They are spending some US$2.2 billion a year on it, and to-date have sent 11 people into space. They plan to build a permanent space station by 2020, and have already launched 181 satellites into space.

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A summary of some of the key numbers for China’s ambitious space programme.

In 2016 alone it will have launched 20 space missions. I have heard it argued that it is easier for a one-party state like China to achieve ambitious long-term programmes like exploring space than it is for democracies like the US. This is because any programmes suggested and funded in the US can be axed by Congress, or shelved by a new president. Such changes of government do not happen in China. Of course, it is looking increasingly likely that the first US manned mission to Mars will not be undertaken by NASA, but rather by one of the private companies like Space X.

The race is on to get to Mars first, who do you think will be first?

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Earlier this week it was announced that NASA’s Hubble Space Telescope had observed evidence for water geysers shooting from the surface of Europa, one of Jupiter’s larger moons. Here is a link to NASA’s press release. I was on BBC TV talking briefly about this on Tuesday (27 September), the day after NASA’s announcement.

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NASA has announced that the Hubble Space Telescope has observed water geysers emanating from the south pole of Jupiter’s moon Europa.

In fact, this announcement was additional evidence to add to a finding which had first been announced in 2013. In December 2012, astronomers used a spectroscope on Hubble to look in ultraviolet wavelengths at Europa. They found auroral activity near the moon’s south pole, and upon analysis of the spectrum of the UV emission from this auroral activity they found the spectral signatures of hydrogen and oxygen, the constituents of water.

Those 2012 observations have since been followed up using a different method. This time astronomers have observed how the Sun’s light, which is reflected from Jupiter, is affected as it passes Europa. As Europa transited in front of its parent planet, astronomers looked for signs of absorption of this light near the limb of the moon, which would be due to gases associated with Europa. Such a technique can, for example, be used to find and study the atmosphere of an extra-solar planet as it passes in front of its parent star.

Whilst not finding any evidence that Europa has an atmosphere, what the team found was that absorption features were seen near the moon’s south pole. When they calculated the amount and extent of material required to produce these absorption features they found that their results were consistent with the 2012 finding. They calculate that water jets are spewing out from the surface of Europa and erupting to a height of about 160 km from the moon’s surface.

We have had evidence since the Voyager mission in the 1980s that Europa has an ocean of water below its icy surface. This evidence was further enhanced during the Galileo mission in the 1990s. Where there is water there may be life, so it is possible that Europa’s ocean is teeming with microbial life. To find out, we need to directly study the water in this sub-surface ocean.

Unfortunately, due to the thickness of the icy crust covering its ocean, studying this water directly poses a huge challenge. We currently don’t have the capability to drill through such a large thickness of ice, although it is certainly something we would hope to do in the future. This discovery of water jets provides a much easier way to sample the water directly, and so it is quite feasible that NASA and/or ESA could send a probe to fly through the jet, take a sample of the water, and analyse it to see whether there are any signs of microbial life. This is very exciting, and is why this discovery of water geysers erupting on Europa is so important.

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This interesting story about the Mars Curiosity Rover recently came to my attention – that its software has now been upgraded to allow the on-board computer to make decisions about choosing targets for its laser to zap. You can read the NASA press release by following this link.

It interested me for two reasons. Firstly, it is a reminder that we have two rovers actively studying Mars as I type (the Mars Curiosity Rover and the Opportunity Rover, which has been operating on the surface of Mars since January 2004!). Whereas Opportunity is about the size of a shopping trolley, the Curiosity Rover is about the size of a car, and has a whole suite of scientific instruments to learn more about the geology of Mars. This includes a chemical laboratory, which can analyse the composition of rocks. The laser is used to vaporise nearby rocks which are thought to be of interest. As the laser strikes the rock the gases emitted are analysed by a spectrometer, but Curiosity can also scoop up rock samples and place them in an on-board oven to heat them up and further analyse them.

But, the second interesting thing for me is that this marks a step forward in “artificial intelligence”. Now, I am very far from being an expert in “artificial intelligence”, so someone who knows more about it than I do may well correct much of what I am about to say. However, it is clear that the on-board computers on the Mars Curiosity Rover are now making decisions about potential targets for the rover’s laser, presumably based on analysing images of previous rocks which Mission Control (at the Jet Propulsion Laboratory in Pasadena) have chosen as targets. Thus, the computer has been learning which kind of rocks the geologists/experts on Earth have been choosing, and is now choosing its own based on some criteria of similarities. I find this very interesting (maybe I’m easily pleased!)

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NASA’s Mars Curiosity Rover can now fire its laser on its own, making decisions at to which rocks to fire it at, without mission control’s involvement.

Such computer-based learning and decision making are vital as we continue to explore the Solar System with robotic missions. The delay time between sending a command to a robot on a distant world and getting the response becomes longer and longer as we explore more distant planets and moons. With Mars the delay is not too bad, typically 20 minutes, but with Saturn it is more like 160 minutes between sending a command and getting the response. Nearly 3 hours is too long in some circumstances, so a rover on e.g. Titan in the future would need to be able to make some decisions on its own, after a period of being commanded and learning from those commands.

Having rovers which use artificial intelligence is, in my opinion, still no substitute for having a human being on Mars. The work which the various rovers on Mars have done in the last 12 years could have been accomplished by a skilled geologist in a few days. And, as the excitement over Tim Peake’s 6-month spell on the International Space Station has reminded us, nothing gets us more excited in the matter of space exploration than seeing a human being doing things in space; no matter how impressive are the things that robots can now do.Hopefully, I will see human beings on Mars in my lifetime.

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I have done a few interviews on the BBC in the last week about NASA’s Juno space probe; it is great to see the mission getting such press coverage. You can listen to my BBC Radio Cymru interview here, and my BBC Radio Wales interview here. With all the press coverage there have inevitably been a few misunderstandings, so I thought I would try and explain as clearly as I can what Juno hopes to accomplish and how it will do it.

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Artist’s impression of the Juno spacecraft. Juno is the first space probe sent to such a large distance in the Solar System (5 AUs) to be powered entirely by its solar panels.

Some background on Jupiter

Jupiter is by far the largest planet in the Solar System. All the other planets together would fit into it, and the Earth would fit into it over 1,300 times! Because it is the largest planet in  the Solar System, we believe that it would have dominated the formation of the planets. Once the gas in the central part of the solar nebula (the cloud of gas and dust from which the Sun and Solar System formed) had collapsed to form a nascent star, the disk of material around the still-forming Sun would have started clumping together under gravity and collisions to form the planets.

Because Jupiter is the largest planet, it sucked up most of the material in the disk of the solar nebula. It is mainly hydrogen and helium, as that is what the Sun and most of the Universe is made up of; about 75% hydrogen and 24% helium. But, the details of Jupiter’s composition are mainly based on theory rather than any hard observations.

What are Juno’s (main) scientific goals?

According to NASA’s Juno webpage (click here to go to it), the main objectives of Juno are

  • Determine how much water is in Jupiter’s atmosphere
  • Look deep into Jupiter’s atmosphere to measure composition, temperature, cloud motions and other properties
  • Map Jupiter’s magnetic and gravity fields, which will reveal the deep structure of the planet
  • Explore and study Jupiter’s magnetosphere near the planet’s poles, especially the aurorae, and provide new insights into how the planet’s enormous magnetic field is generated and how it affects the planet’s atmosphere

I will blog about each of these four points over the next few weeks, so let me start with the determination of how much water is in Jupiter’s atmosphere.

How much water is there in Jupiter’s atmosphere?

The reason this is an important question is that the two most popular theories for how Jupiter formed predict different amounts of water. Jupiter is thought to have either formed (i) from the collapse of a massive fragment of the Solar nebula, or (ii) from the build-up of planetesimals. In the first theory, the amount of water would be less than in the second theory, as the rocky planetesimals in the second theory would have been been coated in water-ice and ammonia-ice.

If you look at an astronomy textbook the interior model of Jupiter shows a solid core, but we have never actually observed this core.

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A model of the interior of Jupiter. We believe that it has a rocky core, with a region of hydrogen under such extreme pressure that it takes on metallic properties and can conduct electricity. But, we have no direct observations of the interior.

Therefore, measuring the amount of both water and ammonia should help us decide which theory is closer to the truth. Water, ammonia, carbon dioxide and methane are examples of what we call ‘ices’ in astronomy, as in the environment of the Solar System all of these compounds can exist as gases but also as solids.

The water and ammonia will be measured by a microwave radiometer. This instrument consists of six antennae measuring the radiation at 600 MHz, 1.2, 2.4, 4.8, 9.6 and 22 GHz. These are the only microwave frequencies which are able to pass through the thick Jovian atmosphere. These radiometers will measure the abundance of water and ammonia down to a pressure of 200 bar, which corresponds to a depth below the cloud tops of 500 to 600 km. This is a small fraction of the radius of Jupiter, which is about 70,000 km, but it is still further below the cloud-tops than we have so far been able to study.

In the next blogpost on Juno, I will talk about how it will measure the gravitational and magnetic fields of Jupiter.

 

 

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Later this morning (Monday 4 July) I will be on BBC radio talking about NASA’s Juno mission to the planet Jupiter. This is the latest space probe to be sent to study the largest planet in the Solar System, and follows on the highly successful Galileo spacecraft which studied Jupiter in the 1990s.

Juno left Earth in August 2011 and is due to arrive at Jupiter today. But, in order to go into orbit about the planet a rocket needs to be fired to slow the spacecraft down and put it into orbit. This is due to happen tomorrow (Tuesday 5 July). The rocket engine which will do this was built in England. If the ‘burn’ fails, the mission will fail, as the space probe will just hurtle past Jupiter and continue on into the outer Solar System.

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NASA’s Juno satellite was launched in August 2011 and arrives at Jupiter this week. It will be put into a polar orbit about the planet, but with a highly elliptical orbit which will take it out beyond Callisto’s orbit. Each orbit will take 14 days.

What are Juno’s scientific objectives?

In addition to studying Jupiter, the Galileo spacecraft spent a great deal of time studying her four large moons; Io, Europa, Ganymede and Callisto. Galileo was in an equatorial orbit. Juno, on the other hand, will be put into a polar orbit. Its main objective is to study Jupiter, rather than its moons.

Jupiter is what is known as a gas giant. It is mainly hydrogen, and contains more mass than all the other planets in the Solar System put together. In fact, it is a failed star; if it were some 10 times more massive it would have had enough mass to ignite hydrogen fusion in its core. Even though it is not burning hydrogen, it is still leaking heat left over form its collapse into a planet 4.5 billion years ago.

In the last 20 years we have discovered many Jupiter-like planets orbiting other stars. Most of these are much closer to their parent star than Jupiter is to the Sun, and this has raised questions about how gas giants can be so close to their parent star, and how is Jupiter where it is in our Solar System? Jupiter is about five times further away from the Sun than the Earth is, and much further away than the Jupiter-like planets we have found around other stars. Did Jupiter start off closer to the Sun and get kicked further out, or did it migrate inwards from further away? We don’t know.

Some of the things Jupiter hopes to determine are

  • the ratio of oxygen to hydrogen in Jupiter’s atmosphere. By determining this ratio it will effectively be measuring the amount of water, which will help distinguish between competing theories of how Jupiter formed.
  • the mass of the solid core believed to lie at the planet’s centre, deep below the very thick and extensive atmosphere. This also has implications for its origin.
  • the internal structure of Jupiter – it will do this by precisely mapping the distribution of Jupiter’s gravitational field.
  • its magnetic field to better understand its origin and how deep inside Jupiter the magnetic field is created.
  • the variation of atmospheric composition and temperature at all latitudes to pressures greater than 100 bars (100 times the atmospheric pressure at sea level on the Earth).

Juno has a funded operational lifetime of about 18 months. In order to better study the interior of Jupiter, the spacecraft will plunge into the planet’s atmosphere in February of 2018, making measurements as it does so.

++UPDATE++

Juno’ rocket successfully fired at about 3:20 UT today (Tuesday 5 May) and is now in orbit about Jupiter. It will complete two large 53-day orbits before being inserted into its 14-day orbit for science operations. This 14-day orbit is highly elliptical, and at its closest the probe will come to within 4,300 km of the cloud tops. 

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On May 10, NASA announced that the Kepler mission had discovered and confirmed 1,284 new extra-solar planets (exoplanets). This is the largest trawl of exoplanets ever announced at one time, and takes the total of known exoplanets to over 3,000. It is sometimes hard to remember that the first exoplanets were only being discovered in the mid-1990s; we have come a long way since then.

 

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On 10 May, NASA announced that the Kepler mission had discovered and verified 1,284 new planets, taking the total of confirmed exoplanets to well over 3,000

 

Kepler discovers planets using the ‘transit technique’. This involves staring at a particular patch of the sky and looking for a dimming of particular stars. If the dimming of a particular star happens on a regular basis, it is almost certainly due to our seeing that star’s planetary system edge-one. It is a safe bet that repeated and regular dimming is caused by a planet passing across the disk of the star. This is similar to the effect Mercury would have had on the Sun during the recent Transit of Mercury (see my blogpost here about that event).

Kepler was launched in March 2009 and put into an Earth-trailing orbit. In July 2012 one of the four reaction wheels used for pointing the telescope stopped working. In May 2013 a second one failed, and in August 2013 NASA announced that they had given up trying to fix the two failed reaction wheels and Kepler ceased operation. It used the reaction wheels to keep it pointing at the same patch of the sky, a nearly square patch which covered parts of the constellations Cygnus, Lyra and Draco. This field is shown in the diagram below.

 

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The patch of sky observed by Kepler, covering parts of the constellations Draco, Cygnus and Lyra. The field of view covered 115 square degrees; the Full Moon would fit into this area over 400 times. Within this area there are over half a million stars, with about 150,000 being selected for observation.

 

Although the first exoplanets were discovered using the parallax technique (see my blog here for details of that method), Kepler has led to a huge increase in the number of known exoplanets. In fact, since its launch in 2009, Kepler has slowly become the dominant instrument for detecting new exoplanets. It took a few years for it to do this, as so much data were acquired during its mission that it has taken several years for the results to start coming out.

 

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The growth in the number of exoplanets discovered between 1995 and 2016. Since Kepler’s launch in 2009 the numbers have boomed, with Kepler being responsible for the majority of new discoveries since 2013.

 

Incredibly, in addition to this announcement of 1,284 more confirmed exoplanets, Kepler has found a further 1,327 which are more than likely to be exoplanets but require more study to be confirmed. Of the nearly 5,000 planet exoplanets found to date, more than 3,200 have been verified and 2,325 of these have been discovered by Kepler. Based on their size, nearly 550 of the newly announced 1,284 exoplanets could be rocky planets like the Earth. Nine of these 500 orbit their star in the habitable zone, the zone around a star where we believe it is possible for liquid water to exist. This means that we have discovered a total of 21 exoplanets in the habitable zone.

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As anyone who hasn’t been living under a rock knows, the International Space Station (ISS) orbits the Earth with (typically? always?) six astronauts on board. It has been doing this for something like the last fifteen years. One of the astronauts currently on board is the Disunited Kingdom’s first Government-funded astronaut, Tim Peake.

The first British person to go into space was Helen Sharman, but she went into space in a privately funded arrangement with the Russian Space Programme in 1991. Other British-born astronauts have gone into space through having become naturalised Americans, and going into space with NASA. But, Tim Peake has gone to the ISS as part of ESA’s space programme, and his place is due to Britain’s contribution to ESA’s astronaut programme. So, he is the first UK Government-funded astronaut, which is why there has been so much fuss about it in these lands.

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Official NASA portrait of British astronaut Timothy Peake. Photo Date: August 28, 2013.

Anyway, I digress. This blog is not about Tim Peake per se, or about the ISS really. I wanted this blog to be about whether Tim Peake is getting older or younger whilst in orbit. Of course everyone is getting older, including Tim Peake, as ‘time waits for no man’ as the saying goes. What I really mean is whether time is passing more or less quickly for Tim Peake (and the other astronauts) in the ISS compared to those of us on Earth.

As some of you might now, when an astronaut is in orbit he is in a weaker gravitational field, as the Earth’s gravitational field drops off with distance (actually as the square of the distance) from the centre of the Earth. Time will therefore pass more quickly for Tim Peake than for someone on the Earth’s surface due to this effect. This is time dilation due to gravity, a general relativity (GR) effect.

But, there is also another time dilation, the time dilation due to one’s motion relative to another observer, the time dilation in special relativity (SR). Because Tim Peake is in orbit, and hence moving relative to someone on the surface of the Earth, this means that time will appear to move more slowly for him as observed by someone on Earth. Interestingly (at least for me!), the SR effect works in the opposite sense to the GR effect.

Which effect is greater? And, how big is the effect?

Time dilation due to SR – slowing it down for Tim Peake

As I showed in this blog, the time dilation due to SR can be calculated using the equation

t^{\prime} = \gamma t \text{ where } \gamma = \frac{ 1 }{ \sqrt{ ( 1 -v^{2}/c^{2} )} }

If he is in orbit at an altitude of 500km (I guessed at this amount, according to Wikipedia it is 400km, but it does not alter the argument which ensues) then his distance from the centre of the Earth (assuming a spherical Earth) is 6.371 \times 10^{6} + 500 = 6.3715 \times 10^{6} metres. The centripetal force keeping him in orbit is provided by the force of gravity, and in this blog I showed that the centripetal force F_{c} is given by

F_{c} = \frac{mv^{2} }{r}

where m is the mass of the object in orbit, v is its velocity and r is the radius of its orbit.This centripetal force is being provided by gravity, which we know is

F_{g} = \frac{ GMm }{ r^{2} }

where G is the universal gravitational constant, and M is the mass of the Earth. Putting these two equal to each other

\frac{ mv^{2} }{ r } = \frac{ GMm }{ r^{2} } \rightarrow v^{2} = \frac{GM}{r}

Putting in the values we have for the ISS, where r=6.3715 \times 10^{6}, G=6.67 \times 10^{-11} and M= 5.97237 \times 10^{24}, we find that

v^{2} = 6.2522 \times 10^{7} \rightarrow v = 7.907(067129) \times 10^{3} \text { m/s} = \boxed{ 7.907(067129) \text{ km/s} }

But, this is the motion relative to the centre of the Earth. People on the surface of the Earth are also moving about the centre, as the Earth is spinning on its axis. But, we cannot calculate this speed as we have done above; people on the surface are not in orbit, but on the Earth’s surface. For something to stay e.g. 1 metre above the Earth’s surface in orbit it would have to move considerably quicker than the rotation rate of the Earth.

The Earth turns once every 24 hours, so for someone on the equator they are moving at

v_{se} = \frac{ 2 \pi \times 6.3715 \times 10^{6} }{ 24 \times 3600 } = 463.348(5554) \text { m/s}

where v_{se} refers to the speed of someone on the surface of the Earth. Someone at other latitudes is moving less quickly, at the poles they are not moving at all relative to the centre of the Earth. The speed of someone on the surface will go as v_{se} \cos (\theta) where \theta is the latitude. This is why we launch satellites as close to the Earth’s equator as is feasible; we maximise v_{se} and thus get the benefit of the speed of rotation of the Earth at the launch site to boost the rocket’s speed in an easterly direction.

The difference in speeds between the ISS and someone at the equator on the surface of Earth is therefore

7.907(067129) \times 10^{3} - 463.348(5554) = \boxed { 7.443(718574) \times 10^{3} \text { m/s} }

Referring back to my blog on time dilation in special relativity that I mentioned at the start of this section, this means that the time dilation factor \gamma, using this value of v, is

\gamma = \frac{ 1 }{ \sqrt{(1 - (v/c)^{2})} } = \frac{ 1 }{ 0.9999999997 }
(where c is, of course, the speed of light).
This value of \gamma is equal to unity to 3 parts in 10^{10}, so it would require Tim Peake to orbit for about 3 \times 10^{9} seconds for the time dilation factor to amount to 1 second. 3 \times 10^{9} seconds is just over 96 years, let us say 100 years.

The time dilation due to GR – speeding it up for Tim Peake

For GR, the time dilation works in the other sense, it will run more slowly for those of us on the Earth’s surface; we experience gravitational time dilation which is greater than that experienced by Tim Peake. In this blog here, I derived from the principle of equivalence the time dilation due to GR, and found

\Delta T_{B} = \Delta T_{A} \left( 1 - \frac{ gh }{ c^{2} } \right)

where, in this case, \Delta T_{B} would be the rate of time passing on the Earth’s surface, \Delta T_{A} the rate of time passing on the ISS,  g = 9.81 (the acceleration due to gravity at the Earth’s surface) and h is the height of the orbit, which we have assumed (see above) to be 500 km = 500 \times 10^{3}.

Plugging in these values we get that

\frac{ \Delta T_{B} }{ \Delta T_{A} } = 1 - 5.45 \times 10^{-11}

So, the GR effect is about one part in 10^{11} (100 billion). In six months, the number of seconds that Tim Peake will be in orbit is about 1.6 \times 10^{7} seconds, so a factor of about 10,000 less than for the GR effect to amount to 1 second. Tim Peake would need to be in orbit for about 5,000 years for the GR effect to amount to 1 second of difference!

Conclusions

In conclusion, the SR effect on how quickly time is passing for Tim Peake is about 3 parts in 10 billion, in the sense that it passes more slowly for Tim Peake. The GR effect is even smaller, about one part in 100 billion, but in the sense that time is passing more quickly for him. The SR ‘time slowing down’ effect is greater than the GR time ‘passing more quickly effect’, by roughly a factor of 300.

Tim Peake is therefore actually ageing more slowly by being in orbit than if he were on Earth. But, he would need to orbit for nearly 100 years for this difference to amount to just 1 second! And, none of this of course takes into account the detrimental biological effects of being in orbit, which are probably not good to anyone’s longevity!

 

 

 

 

 

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The European Space Agency’s JUICE mission to Jupiter moved a step closer recently with the signing of an important contract between ESA and Airbus. JUICE stands for JUpiter ICy moon Explorer, and is an ESA mission to send a probe to explore Jupiter and her moons, with a launch date of 2022 and an arrival at Jupiter in 2029. The contract signed with Airbus will see them lead the development and construction of this satellite. There will also be some involvement from NASA and the Japanese space agency JAXA.

Upon arrival at Jupiter, JUICE will manoeuvre to achieve close passes of its moons Callisto and Europa, before settling into orbit about its largest moon Ganymede. Ganymede, together with Europa and possibly Callisto, is believed to have a liquid ocean beneath an icy crust.

 

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Airbus have recently signed a contract with the European Space Agency (ESA) to lead the construction of JUICE, a probe which will be sent in 2022 to study Jupiter’s moons.

The main focus of the JUICE mission will be to see how habitable Ganymede is for microbial life. With liquid water, and heating from the tides caused by Jupiter’s tides, Ganymede, Europa and Callisto are believed to be amongst the most likely places in our solar system for life to have developed. Longer term plans are to build a probe which will be able to burrow through the icy crust of one of these moons and actually look directly for life in their oceans.

 

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