Where are we with Sat Nav?

By David Ord 

……………. So, where are we with SAT NAV?

A couple of years ago, it was reported that the divorce rate in the United States had fallen to its lowest rate for almost 40 years. The wide adoption of GPS technology has been accredited with removing one of the irreconcilable differences between couples. The dulcet tones of an automaton ensured that journeys to new destinations were no longer a source of contention. But, all is not well with the next generation of Global Navigation Satellite System (GNSS).

The Earth currently has two fully operational global systems, both of which were developed for the military. The American GPS and the Russian GLONASS are now both available for civilian applications. Coming on stream is the Chinese ‘BeiDou’, which is also within the control of the military. The first of the exclusively civilian driven GNSS is the European Union’s Galileo system, which is expected to be fully functional in 2018. The launch of the final 4 satellites this year will complete the constellation.

The problem with the military link to GNSS is that there is a danger it can be switched off or degraded for political reasons during times of extreme tensions or during military conflict. All of the original American satellites used for GPS had an option called Selective Availability. This was employed to downgrade the accuracy of the system to civilian users compared to the military. In 2000, President Clinton announced that the use of this option would be phased out completely by 2006, thereby proving a 10-fold increase in civilian GPS and reduced the time for the first accurate position reading from minutes to under 30 seconds. However, should a military need prove necessary, then Selective Availability could be re-invoked.

The GNSS on which the American GPS is based had some limitations in any case with regard to accuracy, which was typically within the 25-50 meter range.  GNSS receivers triangulate their position using their distance from at least four GNSS satellites. Because they measure this distance based on the time it takes a satellite signal to reach them, even the slightest errors – down to a few billionths of a second – can negatively impact accuracy. Errors in satellite orbit position can lead to around 2.5 meters’ loss of accuracy. Satellites clock errors can add another 1.5 meters. And perturbations in the troposphere and the ionosphere can add another one and five meters respectively – even more if the satellite is close to the horizon or during periods of intense solar activity.


The American GNSS for GPS

By far the largest error is caused by multipath effects, in which satellite signals reach the receiver on multiple or indirect trajectories, for example by bouncing off building walls in urban areas. In best conditions, standard accuracy GNSS receivers are accurate to within about two meters, typically though several meters more.

The accuracy of GNSS can be improved by adding a second transmitting signal from each satellite at a different frequency. Combining multiple signals from multiple satellites should mitigate any atmospheric perturbations and some signal bouncing. Tracking the satellites for drift can be improved by fitting laser retro-reflectors which will allow a laser beam to be bounced back to Earth for the most accurate satellite position.

One way to improve the data involves monitoring GNSS signals from base stations at known locations. Deviations from the base station’s position are observed and sent to a rover – a manned or unmanned vehicle equipped with a GNSS receiver – allowing it to obtain a more accurate position reading. In favorable conditions, this approach can be used to achieve centimeter-level accuracy. In effect, a calibration factor can be encoded into the transmitted signal of the satellite. This could also be charged for at a premium rate compared to the ‘standard accuracy’.

So, it was with much of the above in mind that the European Union embarked upon its Galileo GNSS project. The justification was that Galileo would not be subject to the needs of a foreign military and in addition, the satellites would carry transponder receivers which could be used to pick up distress signals from aircraft or shipping which could then be relayed to the monitoring base stations. On all new cars from April 2018, in the event of a major accident an eCall facility will dial the emergency services (112) and give the precise location of the vehicle.

Galileo would be a high precision GNSS with autonomous driving applications, drone flight control and potentially autonomous shipping in mind. At the outset, it was believed that the project would be predominantly funded by industry. However, the Americans announced that they would upgrade their GPS to improve accuracy, robustness of signal and remove the Selective Availability option which had allowed them to degrade the signal to civilian applications. European Industry could not be persuaded to stump up the funds in the face of the upgraded American GPS – which would remain free to use. And so, it was decided in early 2000s to fund Galileo through European tax payers.


A GNSS Satellite in the Galileo Constellation

The UK took on the lion’s share of Galileo funding at almost 20% of the bill, with major contributions from Germany and Holland.  A plan for public financing was put together by the unelected Brussels officials behind closed doors, without debate and in such a complex way (it also included the diversion of EU farm subsidies) that budget monitoring and control would be almost impossible. The plan was approved by the EU in November 2007.

In 2008, a British parliamentary committee were not convinced. They said the decision to proceed had been “pressed through in an unacceptable manner“, and “the Galileo program provides a textbook example of how not to run large-scale infrastructure projects“.

In a damning report, the UK MPs went on to say “The process for reaching a decision on the future of Galileo and its funding is impenetrably complex. We fear that this complexity… is creating an unstoppable momentum for a very expensive decision that is not supported by any robust evidence…”.

The committee accepted that it had no suggestions as to how the UK Government could in anyway stop or impose changes to the project. Only the EU at large could alter the program and the UK had demonstrated little influence over the larger body.

Contracts placed to implement the project are roughly in line with the proportion of the source of funding. So, UK companies should benefit to the tune of about 20% of project budget. In other words, all the UK can do is try to grab back as much of its own money as it can and try to make sure that the system is as good as it possibly can be.

Meanwhile, the EU also agreed to the combined use of both the American GPS and the Russian GLONASS with Galileo to create the most comprehensive and accurate system available. Base stations for calibrating the signals included the UK territories of the Falkland Islands and Ascension Island. Airbus in the UK won the bid to control the satellite constellation and Surrey Satellites Technology assembled the satellites.

Precise timing is at the core of all satellite-navigation systems. Atomic clocks generate the time code that is continuously transmitted to users on the ground to help them fix a position. Each Galileo satellite is equipped with 2 passive hydrogen maser clocks – a maser is a laser working in the microwave frequency of the electromagnetic spectrum. The clocks are determined to be accurate to one billionth of a second per day, or one second in three million years. In addition to the hydrogen masers, each satellite also carries 2 Rubidium atomic clocks as secondary standards.

To date, 22 satellites are in orbit about 24,000 Km above Earth. The final number will reach 30, which will include 6 spares. But, no one can claim that the Galileo project is anything but tortuous. Two of the satellites were launched into the wrong orbit by a failure of a Russian second stage rocket. Then, the clocks began to fail.

Currently, nine clocks in total – 6 hydrogen maser and 3 rubidium atomic clocks have stopped. One of the satellites has a lost both a maser and a rubidium clock. All the clocks naturally came from a Swiss supplier.

The cost of Galileo has escalated from 3 billion to 9 billion Euros, with the UK contribution to almost 1.5 billion euros. And we may not be able to use it!

Since Brexit, the European Commission has suggested that the UK may not be trusted with European Union’s most sensitive security information aspect of Galileo. The UK’s armed forces were planning to use Galileo to supplement their use of the US GPS system, but press reports suggest they will now be blocked from doing so. The US retains the more accurate and robust GPS signals for its own armed forces.

An EU discussion has taken place to exclude the UK from any further industrial participation in the program.

The UK has responded that they do not accept the European Commission’s position and have called for a 3 month freeze on procurement of the next batch of satellites. The UK Business Secretary stated that, if the European commission prevails, the UK will seek legal redress for the return of its funding to date. In addition, the use of the British base stations in the Ascension Islands and the Falklands would not be allowed.

Meanwhile, the seriousness of the tiff has escalated to the commissioning of a feasibility study by the UK Space Agency to launch the UK’s own GNSS. Most of the technology inherent in Galileo, its operation and satellite assembly are British. The Chief Executive of Airbus (UK) has stated that his company has all the skills and expertise to lead the development of a totally British GNSS and for substantially less than the cost of Galileo.

By 2022, it is estimated that the satellite navigation services market will be worth $290 billion. Well worth an argument or two.


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An obituary for Stephen Hawking

The group was saddened to hear today about the passing of Stephen Hawking. The following link is to an obituary written by Roger Penrose giving a summary of his life and contributions to science.



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Space law

By David A. Ord

……………. So, whose Space is it anyway?

The question is being asked with increasing frequency and in many different contexts.  The complexity of some of the answers has become the fuel of a rapidly expanding new legal business – Space Law. Several universities in the USA offer the subject as a specialist module to students of Law and just recently, the University of Sunderland was the first European university to offer the subject as a part of its graduate law course. Clearly, there’s money to be made from the interpretation of the confusion.

As early as the 1950s, it became obvious that some rules and regulations would be necessary to oversee the potential complexities of Space. Both the USA and Russia jointly approached the United Nations with outline legislation. The motivation for such a move was probably that each feared that the other may have the ability to take complete control of Space. Just in case, both wanted to agree some limitations.

The Americans drew an analogy for their proposals on the ‘Law of the High Seas’ whereby the vessels would be registered at a port of origin and subject to those laws, but Space, like the oceans, would be International and free.

The Russians on the other hand wanted the legislation to use airspace as the model. They put forward the argument that whatever was above your territory was a part of your sovereign state, right out to infinity. They were more sensitive than the West to spy missions flying over their territory and from very early on, they clearly saw this as potential misuse of Space.

Unfortunately, the launch of Sputnik-1, the world’s first Earth orbiter did not help the Russian argument. Sputnik crossed the USA 3 times as it orbited Earth and proved the futility of trying to control such activity by legislation. A satellite in Earth orbit will have a much greater capacity to view the territories beneath than any aircraft flying in a strictly controlled ‘air-space’ corridor.

So, in much of the early Space legislation discussions the American model prevailed. Eventually, this led to the 1967 ‘Outer Space Treaty’ which has been ratified by 107 signatories, including all of the major Space-faring nations such as Russia, the USA, China and the European countries. The treaty is overseen by the United Nations Office for Outer Space Affairs and sets out the important principles which include – ‘Space should be considered the province of all mankind; outer Space is free for exploration and use by all States; the Moon and other celestial bodies are to be used purely for peaceful purposes; and weapons will not be placed in orbit or in Space’.

The ‘Outer Space Treaty’ was augmented in 1968 by the addition of the ‘Space Rescue Agreement’ which requires the signatories to return home any astronauts who might land in their country, to help any astronaut in distress and to return any space objects to their owner. There are 97 ratified signatories to this treaty. Whereas most nations agree with the principles embodied in the Rescue Agreement some point out there is no reference in the Agreement as to who bears the cost of any ‘Rescue’.

In 1969, with the ink still drying on the intention that man’s endeavours in Space are for the benefit of all humanity, NASA could not resist planting an American flag on the Moon. Not that any claim to the real estate was intended, but they did have to make a point in the context of the space race.

In 1972, the third major plank of Space legislation came into being and this was on the subject of liability. This states that the launching party is “absolutely liable to pay compensation for damage caused by its space objects on the surface of the Earth or to aircraft”.  There are 89 ratified signatories to the ‘Space Liability Convention’.

In 1974, a fourth extension of the ‘Outer Space Treaty’ was brought into being which required the UN to be notified ‘as soon as is feasible’ when an object had been launched, the launcher, its planned orbit and its ‘general’ function. This treaty is referred to as the ‘Registration Convention’.  Note that the ‘specific’ function of the launched object is not required as this would certainly not be agreed to by several of the signatories. The military are still a major adopter of satellite technology. To date, there are 63 ratified signatories.

The fifth and final raft of Space legislation with the UN is the 1979 ‘Moon Treaty’, which gives jurisdiction of all celestial bodies (including the orbits around such bodies) over to the international community. To date, there 17 ratified signatories to the ‘Moon Treaty’; none of which are leading Space-farers.

The objection to the ‘Moon Treaty by the Space-faring nations is held to be the requirement that extracted resources (and the technology used to that end) must be shared with other nations. Perhaps following the ‘Law of the High Seas’ in creating Space Law has found its limit. The analogous law of the sea as enshrined in ‘ United Nations Convention on the Law of the Sea’ is believed to impede the development of extracting resources from the ocean bed.

At the end of 1976, a challenge to the Outer Space Treaty was made under the auspices of the Bogota Declaration. Eight Nations traversed by the equator felt that their ‘natural resources’ had been usurped by the Outer Space Treaty which established that ‘outer space’ and all celestial bodies were not subject to national control. All eight nations, Columbia, Ecuador, Congo, Indonesia, Kenya, Uganda and Zaire attempted to assert their rights of ownership to the geosynchronous orbit around the equator. With the signatories of the Outer Space Treaty vastly outnumbering those of the Bogota Declaration, nothing to date has arisen from the challenge. However, it remains a current topic of discussion in the burgeoning corridors of Space Law.

So, there is a basic framework of international legal agreements which can be applied to Space exploration and exploitation. One could argue that the UN is typically given many responsibilities on the international arena, but little in the way of authority. What can the UN actually do in the case of non-compliance?

The laws rarely get tested, but in 1978, the crash of the nuclear-powered Soviet satellite Kosmos 954 in Canadian territory led to the only claim filed under the Space Liability Convention. The satellite contained about 50 Kg of enriched Uranium and several of its fission products which had been generated during its operation, like plutonium, caesium and strontium. The debris field covered 15,000 Sq. miles and in many ways landing in a remote part of Canada was fortuitous. It was not a controlled landing and it could have been much worse. The Canadians claimed the $6 million cost of the clean-up under the ‘Space Liability Convention’. The Russians contested the claim but eventually settled for half the amount and a legal precedent had been set.

American assistance was keenly offered to the Canadians for the clean-up, although their motives may not have been purely philanthropic. There was interest in the Russian technology aboard Kosmos 954 and it is alleged that any surviving hardware was not duly ‘returned to its owner’, as specified under the ‘Space Rescue Agreement’. One piece in particular was a signal generator for the satellite’s radar which was driven by a Klystron unit – essentially, a vacuum tube based set. One for the Smithsonian.

In 2008, when a similar unscheduled de-orbiting fate was visited upon the American spy satellite USA193, the American military ensured that there was no chance of anyone getting a look at their technology. As the satellite re-entered Earth’s atmosphere over the Pacific, the US Navy engaged it with an SM-3 missile, reducing it to swarf. One assumes that legally, they were entitled so to do – or at least no one was about to argue.

The real problem with the current set-up is that the legal framework is geared toward nations. On behalf of its members, the United Nations can execute programs and even police them on a nation to nation basis. There is no obvious way in which their standard modus operandi deals with commercial organisations.

No one envisaged the commercialisation of Space to the extent that is now on the horizon. If a private American company, registered in Luxembourg launches a satellite for an Asian customer from a French island with the intention of recovering minerals from a celestial body, who gives approval for the mission? who owns the minerals? who covers any liability?  And, and, and many more questions. If anything goes wrong, then the UN has no interaction at a commercial level and can only hold a nation responsible – but which one?

At a superficial level, the current Space Laws would suggest that the launching nation gives mission approval, any minerals retrieved belong to everyone and if anything goes wrong, each of the nations involved has full responsibility with regard to any compensation. On such a basis, it is unlikely that there will be a sudden gold rush.

Space Law is mostly centred upon Space exploration and discovery – a sharing of knowledge and understanding for the benefit of mankind. The exploitation of Space by individual companies is not well served by current legislation.

For example, there is as yet no official definition of ‘Outer Space’ in any of the United Nations treaties. The Fédération Aéronautique Internationale (FAI), an international standards body for aeronautics has defined ‘Space’ based on the Kármán line at an altitude of 100 Km. This after the Hungaro-American engineer Kármán who calculated that at this height there was little atmosphere to contribute to lift for a vessel. This has been accepted by NASA, but curiously it is contested by the US Air Force, which advocates a more arbitrary 50 miles (80Km).

Why is this relatively small height difference important? Well, if you violate a nation’s defined airspace, then you stand a very good chance of being shot down – depending on the demeanour of the aggrieved. However, if you overfly the same territory in ‘Space’, then you are free to do so – provided of course that your purpose is for the ‘benefit of all mankind’.

The future of aviation will further blur the boundaries of Space. If Elon Musk1 is correct, then virtually all destinations on Earth will be reachable within a 1 hr flight. This will be achieved by launching a plane into low Earth orbit, accelerating to around 27,000Km/hr and re-entering Earth’s atmosphere in a matter of minutes before proceeding to the destination.  If each flight will be subject to the ‘Outer Space Treaty’ and its extensions, then there may be some frustration ahead for Mr. Musk.

The second major area which was not perceived in the concept of the ‘Outer Space Treaty’ is the commercial exploitation of Space through retrieval of minerals and other valuable elements of Space. The United States in particular is keen to encourage private enterprise to take on these ventures.

In 2015, the US government made an attempt to update the law on space mining, producing a bill that allows companies to “possess, own, transport, use, and sell” extra-terrestrial resources without violating US law. The problem is that putting this into practice violates the Outer Space Treaty, which states that no nation has sovereignty over these resources.

In Europe, the canny burghers of Luxembourg have decided to make a play for a piece of the pie. The government of Luxembourg has passed a bill giving companies the rights to space resources they extract from asteroids or other celestial bodies. They have made available 200 Million Euros in grants for companies who want to become asteroid miners. (Of course, they can also provide an attractive tax package for any of the companies who register in Luxembourg).

Can sovereign states make such claims over Space resources? Only time and legal challenges will tell. Some changes to the current Space Treaties are an absolute necessity to ensure that Space does not become a free for all – like the Gold rushes of the past carried out in a lawless vacuum.

At present, the nation from where a launch is made basically has to underwrite the operation. Missions are currently insured in the commercial market at various stages through their progress. Most countries agree to cap the commercial insurance limit at around $60 million and the nation bears the difference. This encourages private enterprise and limits their liability – the cost to insure a $250 million communications satellite operating for 10 years is around $50 million. But if let’s say it failed and began to collide with other satellites then the cost could be several billions of dollars.

Clearly this is a huge risk that not many commercial operations are willing to undertake and therefore the liability cap and an underwriting by Governments will be key to how Space is developed. So, the role of a Nation in any future laws will still be important in the commercialisation of Space.

However, even when a legal framework is agreed, the next major issue will be how these laws will be policed. This will not be a trivial matter in Space.

1Elon Musk – vision of air travel   https://www.youtube.com/watch?v=xDEKjfnRhqQ



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Our experience of the Eclipse 2017

By Christine Ord

My husband David and I went to the US this August to experience our first total solar eclipse.

I am pleased to report that August 21st this year, the day of the total solar eclipse across the United States, dawned beautiful, hot and clear in Hendersonville, Tennessee. This is where David and I were booked into a hotel under the path of totality. In the days prior to the eclipse the weather reports were still reporting partially cloudy skies for the big day, so we were not certain as to whether we would be lucky and have a good view. The news reports were also advising that the roads were expected to be very busy as people got into their preferred locations for the eclipse. Based on these road forecasts, we decided to stay close to the hotel and not join one of the big events being advertised in nearby towns.

There was a lake and small park area just across the road from the hotel from where we decided to watch the eclipse, under a covered picnic area. Several people had set up telescopes and cameras with filters near the hotel. As the time approached for first contact (moon just beginning to cover the sun) a number of office workers came to the picnic area with lunch and drinks. They turned out to be the local council workers, plus the mayor who came out to watch the eclipse. They had such appropriate delicacies as ‘moon’pie, ’orbit’ gum, ‘milky way’ bars and ‘Sun’ gold drinks (as well as enormous sandwiches which didn’t have an event related name). We were invited to join them.

As the time drew near for the total eclipse, we had been watching the progress of the moon over the sun with the eclipse glasses over a period of about 1.5 hours. The weather held and we had a great clear view of the event for the 2 minutes 40 seconds of totality. Here are a few of our observations :-

  • It was surprising how much light the sun produced even when the majority of its surface was covered by the moon. If you didn’t have the eclipse glasses you wouldn’t know there was anything going on until the sun was completely covered.
  • As I was wearing glasses until the sun’s disc was covered, I didn’t see the first diamond ring effect. You really need to be watching naked eye at the last moment to catch it, as the glasses cut out too much light.
  • We didn’t see the Bailey’s beads effect, although one of the other observers who had seen several eclipses, said that they were not always in evidence as they can be affected by the relative positions of the sun, moon, and earth.
  • Totality lasted 2 minutes and 40 seconds and we could clearly see, naked eye, the white corona, which seemed to me to be wider round the equatorial plane of the sun and we could clearly see the red chromosphere.
  • The temperature dropped considerably during totality from the scorching heat of earlier and it was pleasant to stand out of the shade. Estimates given later on TV for the drop in temperature were between 8 and 10 degrees.
  • The sky didn’t go dark during totality. It was more a twilight effect, that time after sunset but before it really goes dark. It was however dark enough to see Venus and some of the bright stars, which was great.
  •  There weren’t many animals in the area so we couldn’t judge the effect on them very well. However, just as the sun was covered, the cicadas in the nearby trees started ‘singing’ and continued until totality was over and the sun was hot again. Some geese who were in the pond nearby got out of the water, but we don’t know whether they would have done that anyway.

The time of totality passed quickly and we clearly saw the diamond ring as the moon continued its journey and the sun gradually came back into view. It didn’t take long to get back to daylight and high temperatures, even though the sun was still partially covered for the next hour and a half.

We both thoroughly enjoyed the experience and were not disappointed. As with most observations of astronomical events, you are left wanting more. Perhaps next time a longer totality, a glimpse of bailey’s beads, a pair of binoculars to see some coronal detail ……

As we didn’t have a special filter for David’s camera he could only take pictures, of the Sun once it had been totally covered. He used a Canon EOS 80D camera.  We have included a few that he took of the event below.  Here are a few of the more unusual ones that other people took to take a look at.

This one was taken from a plane as the shadow of the moon fell on the ocean before making landfall.


The spaceweather website has a gallery of images taken around the world during the eclipse


Picture taken from a weather balloon showing the shadow of the moon across the earth.


This is NASA’s best collection, which includes some of the ISS passing in front of the Sun during the eclipse and some taken from the ISS itself.


David’s Photos


Diamond ring effect as moon begins to move            Fellow observers


Total eclipse

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An amateur detecting exoplanets

By Mark Trapnell


The detection of exoplanets – that is, planets orbiting stars other than our Sun – has rarely been out of the news since the first successful detection back in 1992.  A few months ago, headlines were full of items about the discovery of an exoplanet orbiting Proxima Centauri, possibly within that star’s “habitable zone” and so with consequences for life on a planet somewhere “near” to us.

I was fortunate to have studied a part-time course in Astronomy at University College London (UCL) over the last two years.  One of the course’s modules was on exoplanets and included detailed descriptions of the different methods by which exoplanets are actually detected by astronomers.  With one exception, those methods all require sophisticated systems which are way beyond the reach of even the most enthusiastic and well-heeled amateur.   The exception is detection through the transit method.

The transit method measures the apparent brightness (or flux) of a star over a period of time, looking out for changes in that brightness.  Regular small changes of a particular type and short duration may indicate the presence of a planet passing across the face of the star.  Periodic measurement of the star’s brightness should result in a light-curve which shows a pronounced dip during the time of the planet’s transit.


(Source: AstronomyOnline.Org)

More details on all this can be found easily with a quick Google search.  NASA has a good website which includes a section on methods of exoplanet detection at https://exoplanets.nasa.gov.

My UCL course suggested to me that amateurs should be capable of detecting exoplanets using the transit method and I decided to have a go to see how easy or otherwise it might prove to do so.

Finding a previously undetected exoplanet is pretty much beyond an amateur.  Even if we assume (as now seems likely) that most stars have orbiting planets, the transit method relies on the planet’s orbit passing at some point between us and the star.  Because of all the possible orbits an exoplanet could have, the likelihood of that happening is about 1 in 100 for a large planet and about 1 in 200 for an Earth sized planet.  So I am quite happy to try to detect planets that are already known to orbit stars and to be detectable by the transit method!

My online research came up with a short book written by Dennis Conti which is aimed at amateurs and explains the mechanics of exoplanet detection.  It is free for download at http://astrodennis.com.  I would recommend it to anyone interested.  I think that anyone who is broadly competent at astrophotography should also have the ability to detect exoplanets.


The main question for me was what equipment was likely to be necessary for a successful detection.  Some research suggested that a few amateurs have successfully detected exoplanets, but had almost invariably used large Schmidt-Cassegrain telescopes of upwards of 12 inches diameter, with 16 inches being normal. I prefer to use refractors.  The largest refractor I own is a 6 inch f7 apochromat.  I found little to suggest that exoplanets could be detected with such a small telescope.  However, I decided to give it a go.

Here is what I think is needed:

  • A telescope. Of course.  My experiences suggest that a 6 inch refractor will do just fine, though I can see that a larger aperture scope might have some advantages, particularly in choice of target.  However, for the amateur, larger aperture normally means greater weight and longer focal length, both of which challenge other parts of the system.  Actually, I think a 5 inch refractor would probably have been fine too.
  • A mount. In my case it was a German equatorial mount – a Paramount ME.  I think it has to be (within reason) a good quality mount which is robustly set up and well calibrated with excellent polar alignment, tracking and pointing accuracy.  Shortcomings with any of these will make the process much more difficult.
  • A camera. I think pretty much any CCD (not video) astro camera will do.  I admit I have no idea whether a DSLR would work. I have my doubts.  I also don’t know whether a one shot colour camera would work.  Again, I have my doubts.  I used an elderly SBIG ST10XME which has a KAF3200 chip in it.   Certainly, a large chip isn’t needed and in many ways is a disadvantage as it increases file sizes unnecessarily.  The longer download times of older cameras is also a disadvantage as it restricts the amount of data that can be gathered over a finite exoplanet transit time.  I stuck with the ST10 because I think it has the most linear CCD chip of my cameras.  The key to the camera is that it has to be operated within its linear range (i.e. doubling the amount of photons hitting the detector doubles its output signal rather increasing it by some other random amount).  More on this below.

I am very lucky to have a permanent small observatory near Benidoleig.  Based on my experiences, I don’t think this is necessary, but it certainly helps.


Finding the target star, controlling the mount and acquiring images all needs software.  For this I used Software Bisque’s The SkyX Professional.  Other programmes will work equally well, I am sure.

What I found so helpful as to be close to essential (for me at least) was the additional use of a plate-solving programme.   For example, if an image I have taken of a star field is loaded into The SkyX, the programme will compare the picture to its star database and when it finds a good match, will place and show that image at the right location in its planetarium programme.  Other programmes do the same thing using online data resources.

Plate-solving of this kind is useful for several reasons: (i) finding the right star in the first place.  The target stars are not the stars we all know and love and can point to in the sky.  They are often unnamed or feature in an obscure catalogue and so can be quite hard to find in practice; (ii) pointing the telescope, once identified and shown in a planetarium programme, at the right star; and (iii) subsequently checking that data has indeed been acquired from the right star.

There are several databases of exoplanet hosting stars and the one I used (http://var2.astro.cz/ETD/) provides a 15 arc-minute square Deep Sky Survey (DSS) image of the target star and its immediate surrounds.  I used The SkyX to plate-solve the DSS image so as to show me where in the sky the star is located.  In fact The SkyX also then allows accurate movement of the telescope to the exact location of the DSS image.  I was then also able to take a test exposure, plate-solve the resulting image and check that it coincided with the DSS image.  These kinds of advances in relatively mainstream software now enable amateur astronomers to achieve far more than would have been possible only a few years ago.

Once the data has been acquired, the resulting images need to be calibrated and aligned.  There are a number of programmes that will do this.  I used CCDStack.  See further later.

Finally, the target star’s brightness needs to be measured and the results plotted in a graph.  Again, I am sure there are any number of available and suitable programmes.  I had already used AstroImageJ during my studies at UCL.  It is a popular and powerful photometry programme and is available as freeware at http://www.astro.louisville.edu/software/astroimagej/.  It isn’t a particularly easy programme to use.  I think it is designed primarily for professional scientists.   However, following step by step instructions, after trial and plenty of errors over quite a few hours as I learned how the programme works, resulted in the output of a recognisable light curve.

Gathering Data

My first attempt wasn’t too successful.  I was in a hurry having arrived at my observatory only a couple of hours before the predicted exoplanet transit.  As a result I made a mistake and set an exposure time for the camera that was too long and resulted in some of the camera’s pixels containing the target star image being saturated, something I didn’t discover until I examined the image data the next morning.  The moment they are saturated, pixels are no longer linear and so do not react proportionately to an increase or decrease in signal.  Indeed, I suspect they stop being linear some time before they saturate.

The following day I tried again on a different (and dimmer) target star.  This time I was much more careful with exposure times and worried instead whether I had gathered sufficient signal to overcome background noise.  As it turned out I had, though I suspect if I had increased exposure time slightly I might have had a cleaner light curve.

Here, broadly, are the steps I took:

  • Identify a suitable target star. The exoplanet database I mentioned above is great.  It allows the input of the user’s longitude and latitude and will then show a list of stars with predicted exoplanet transits for any given night together with data about sky coordinates, the predicted beginning and end of the transit and the likely fluctuation in measured brightness of the star during the transit.  The key is to select a target star that shows a significant change in brightness.  The star I chose (Wasp-52, named after the Wasp programme that first detected the exoplanet orbiting around it) would apparently show in excess of a 2% change when its exoplanet (Wasp-52b) transits.  For some reason, the naming convention is that the first detected exoplanet associated with a particular star is given a “b” identifier, not an “a”!
  • Check the position of the target star in the sky before and after the transit. Ideally it should be as close to the zenith as possible so as to mitigate atmospheric disturbance to the images.  One disadvantage of a GEM is that the telescope and imaging equipment rotate around the telescope’s axis which is aimed at the pole star.  It is inclined at the angle of the astronomer’s latitude.  They rotate continuously while tracking a star and so soon after passing the meridian, the telescope may hit the ground or the pier that the mount sits on.  To avoid this, GEMs have to reverse themselves around the meridian and perform a so-called “meridian flip”.  For a GEM user, I assumed that ideally the target star should not cross the meridian during the transit measurement period so as to avoid the need for a meridian flip, which would involve reacquiring and centering the target star after the flip as well as causing other practical complications which at best would result in an interruption of at least several minutes in data gathering run.  Wasp-52 crossed the meridian about 45 minutes before the exoplanet transit was due to start.  The data run should ideally start an hour before transit and end an hour after transit so as to give a proper light curve.  Meridian crossing meant that I would not be able to start until about 45 minutes before the predicted transit, which turned out not to be a problem.
  • Focus the camera. Focus isn’t highly critical.  Indeed, some techniques utilise deliberate defocusing to assist in smoothing out scintillation effects in the star image.  This seems to be particularly useful if the target star only covers a few pixels on the detector.  In my case, the star covered at least 10 pixels, so I didn’t bother defocusing and focused normally.  It is worth noting that the data gathering run lasts several hours – nearly four hours in my case.  I can see that a substantial temperature swing might cause focus problems, but I was lucky and the temperature dropped by only one degree during my data run.
  • Plate-solve the DSS Wasp-52 image and move the telescope to the indicated position on the planetarium programme (in my case, The SkyX).
  • Start auto-guiding. Auto-guiding takes images of a guide star every few seconds.  The software detects any movement of the guide star on the CCD detector and communicates correction instructions to the mount.  It is important to keep the star in pretty much the same position on the camera’s CCD chip during the entire transit run.  This is because otherwise variations in the brightness of the image field could produce false results.  This can be addressed to an extent by dark and flat-field subtraction, but research sources were all clear that it is better to start by eliminating movement on the chip as much as possible.  I guided at 5 second intervals and achieved accuracy of  about +/- 0.2 pixels through the data run.
  • Start taking images. I set my exposure time at 25 seconds for each frame.  The data run would last about 3 hours 15 minutes.  So allowing for download times, that resulted in  about 330 images!  Here is one of my images, indicating the position of Wasp-52.  Note how the star in the top right has saturated pixels, which give rise to “blooming” in this camera.  This is the problem I had the night before with my target star, but in this case it had no effect on Wasp-52 which was not saturated.


  • The next morning (the data run finished at about 3 am), calibrate all the images with darks and flats taken the previous evening. A dark is an image taken at the same temperature (CCDs are typically cooled to reduce noise, mine was running at -10 degrees C) and same exposure length as the main image, but with no light falling on the detector.  It results in an image of the detector’s inherent noise which can then be subtracted from the actual image.  Flats are images taken of an even (flat) light source (for example an illuminated white screen or early evening sky) which model the light variations inside the telescope and imaging equipment.  The flat is then divided into the actual images to compensate for those variations.  The sources are adamant that dark and flat calibrations need to be done very carefully, so I combined 30 separate darks and 30 separate flats to make respective masters and then used those masters for calibration of the 330 images in CCDStack.  My laptop couldn’t cope with calibrating all 330 images at once – I had to batch process 50 images at a time.  Even so, its not a huge task with modern programmes and the whole process probably took me no more than about three or four hours.  If the camera moved between exposures, it would also be necessary to register (align) all the images so that the next stage, photometry, would work properly.  Given my guiding results, I decided not to bother with registration as the 330 images were close to perfectly aligned already.
  • Load the calibrated images into AstroImageJ and press “Go”! Well it isn’t quite that simple, but once the programme is properly configured with the coordinates of the target star, it is pretty much like that.  The main other input is first to load one of the images into the programme and identify the target star as well as several other comparator stars in the same image by placing a pre-defined measurement “annulus” over each star.  The annulus measures the star’s brightness as well as that of the sky background to determine the true brightness of the star itself.


The programme automatically assumes that the first star chosen (T1) is the target star and that the others (C2-6) are comparator stars.  The idea is that the brightness of the target star (Wasp-52) is measured for each frame, as is that of each comparator star, which hopefully doesn’t have an orbiting planet affecting its brightness and isn’t a variable star, an orbiting binary or anything else that might cause signal fluctuations.  That way, if the target and the comparator both vary at the same time in brightness by proportionate amounts, that variation can be ignored as resulting from external variations such as clouds passing across the target.  If in any given image the target varies but the comparator does not, the programme registers the variation as it must have a source inherent to the target star.  The literature does discuss the choice of comparator stars and checking beforehand that they aren’t variables or binaries.  I just used a pin and assumed that if one of my five comparators wasn’t good, that would show in its data compared to the others and I could eliminate it.  Not very scientific, but it seemed to work.

Once “Go” has been pressed, the programme analyses each image identifying variations and starts creating the light curve, dot by dot. It is a great experience to see the dots start appearing, and even better when they begin to head downwards in a curve indicating a successful exoplanet detection and then later head back upwards as the transit ends.  Here is the curve I generated from my 330 images:


The top (horizontal) row of blue dots clearly shows the Wasp-52b exoplanet light curve.  The two horizontal rows of magenta and orange dots underneath are the plots of two of the comparator stars.   I actually used five comparators, but removed the other three from the measurement plot so it isn’t too cluttered.  It can be seen from the vertical axis that there was an almost 3% dip in brightness of the target star (from 1.01 down to 0.98 on the relative flux scale) during the transit and that the transit lasted nearly two hours.  All exactly as predicted!  The radius of the host star is known from its spectral type and so the amount of the dip in the light curve allows calculation of the radius of the planet, which turns out to be about 1.3 x the radius of Jupiter.  The period of the orbit is only a few days, so the orbit of Wasp-52b is clearly close to its star, making it a “hot Jupiter”, the easiest type of exoplanet to detect.

The quality of the curve isn’t bad, considering this was a first effort.   The right hand side deteriorates in quality compared to the left hand side, but its trend is still very clear.  The change in quality affects the target star and the comparators and I guess is due to the stars dropping in altitude during the imaging run and so becoming increasingly affected by atmosphere instability.


I proved to myself that a keen amateur with reasonably normal equipment and some CCD imaging experience can successfully detect an exoplanet from a back yard with a small telescope.   It also turned out not to be that difficult, though admittedly I chose as easy a target as I could.

The sense of achievement as the planet’s light curve gradually appeared on my computer screen was immense.  This felt like proper science!

The success is of course primarily attributable to the quality of equipment and software now available to amateurs at a reasonable cost and the immediate availability of help and information on the internet.

I am not sure what if anything I will do with that new found ability.  In a  few months time, I suppose I may have another go and pick a more difficult target.  It seems that amateurs do have a role in exoplanet detection by providing further data in respect of planets already discovered where the professional community has moved on to other targets.  But for the moment, I am happy to leave the fun to astronomers and their telescopes in Mauna Kea, La Silla or up in space.

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Experimenting with a star analyser

Experimenting with a Star Analyser (200 lines/mm)

By Peter Gudegon

The Star Analyser looks like an ordinary 1.25″ glass filter, but is a diffraction grating that splits-up the light coming from a star into its various colours. Many stars show absorption lines in their spectra where they have certain colours missing, while some others may have bright spots on their spectra where they emit most of their light at particular wavelengths. Suddenly each of those otherwise bland normal stars start to reveal their own individual identity…. some people refer to it as looking at a star’s fingerprint.

The analyser can be used in a variety of ways:-

  • You don’t need a telescope. If you have a camera (preferable a DSLR) you can mount the star analyser in-front of the camera lens, either by mounting it on a piece of black card, or by buying a special filter holder. This limits the lens aperture size, but is fine for bright stars.
  • Those with a telescope that uses standard 1.25″ dia eyepieces can simply screw it into the eyepiece as you would a normal filter, then observe the star and it’s spectra through the eyepiece as normal. Additional spacers between the analyser and eyepiece can be used to increase the spread of the spectra, making it easier to see any detail.
  • But the most versatile way of using it simply, is with a telescope and camera (with no lens) and mounting the analyser just in front of the camera (most telescope/camera adapters already have the thread there for mounting filters).

The cost of these analysers is around €130-155 (August 2016) and they come in two versions:- 1. A 100 lines/mm (this is the standard type usually recommended), B. A 200 lines/mm, intended more for work with CCD cameras, and has a lower profile to allow it to fit inside filter-wheels.

What makes these so good is that they use a “blazed” grating. A normal diffraction grating has most of the light passing straight through it, with a relative low percentage of light being directed into 1 of several orders of diffraction, creating a rather dim image. A “blazed” grating uses a method that increases the amount of light being directed to one particular order of diffraction, in some designs up to 70% of the incident light may appear in the preferred diffraction.

For my own use, I used a (large) normal camera lens in place of a telescope (Sigma 150-500mm zoom), then a slim EOS lens to T2 adapter, followed by a Filter-Drawer (in which sits the star analyser), in front of a QHY9 (monochrome) CCD camera.

Unlike a normal (and very expensive) spectroscope that passes the light through a very narrow slit, this relies on the star image being as small and stable as possible (ideally a stationary point source). Too high a magnification (with a telescope) amplifies any movement of the star due to the atmosphere, which greatly reduces the resolution of the end result.
Although a zoom lens might be frowned upon by most astronomers, on a mount that has to be erected/dismantled every night it provides a very neat, portable solution, and makes initial alignment of the mount very easy before zooming in to use the full diameter of the objective. The relative low magnification means the motorised drive easily allows exposures of 30 seconds without the need to set up an auto-guide, and to my surprise has already allowed me to record spectra from stars down to magnitude 10.
After a quick test on some of the stars in Lyra, what I really wanted to try this on are some Wolf-Rayet stars. These stars have very strong emission lines, but unfortunately they are quite rare, and in the Northern hemisphere the best known/easiest to observe are a group in Cygnus. However they are all quite faint, the brightest being magnitude 6.7 (ie. below naked-eye visibility).

Below is a highly enlarged part of a picture showing the star WR136 on the left and on the right its resulting spectra, in which you can clearly see some bright spots.

Spectra WR136

But to analyse the results you really need to turn the spectra image into a graph and calibrate it (which turns out to be much easier than it sounds). Using RSpec to do this created the following graph. Although determining the significance of each line is where it becomes interesting…..and involves a lot of “Googling”.

Spectra Graph of spectra for WR136

Next another couple Wolf-Rayet stars, this time WR135 and WR137 which are known as Carbon rich stars….The difference in their spectra from the above is immediately obvious. These type of WR stars are known for their strong C [III] & C[IV] lines at 5690-5820 Angstroms. But I was surprised that with this relatively simple set-up I could look at these two stars, about magnitude 8.5, and even record the differing amplitude of the C [III] line and that they are noticeably narrower for WR135, which distinguishes it as a spectral type WC8, compared to the spectral type WC7 of WR137.

Spectra Graph of spectra for WR135


Spectra Graph of spectra for WR137



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Cubesats and new bright night-time object

By David A. Ord

…………….the debate on the subject of Cubesats is warming up

Three student-built CubeSats were launched into space On April 25th on Soyuz flight VS14 from Europe’s spaceport in Kourou, French Guiana. The CubeSats hitched a lift with the launch of the European Earth monitoring satellite Sentinel -1B. The launch is a part of ESA’s outreach program ‘Fly your Satellite’, set up to encourage education in space technology. They all successfully called home and are currently in low Earth orbit.

CubeSat is a term measuring a satellite’s approximate size and mass. A 1-unit cubeSat is a 10-centimeter cube weighing about 1 kilogram. Most launched so far are in the 1- to 3-unit size, but the industry is expanding so rapidly that these early trends may not endure.


Artist’s impression of a CubeSat in orbit

In the last decade, CubeSats have gone from curious toys to capable tools. Advances in technology have expanded their capabilities in areas as diverse as imaging the Earth, studying space weather and even military interest. They are attracting great interest from scientists and venture capitalists alike.

All CubeSats are in low Earth orbit, but NASA announced that it will send a pair of CubeSats on their first interplanetary mission with InSight, its next mission to Mars. The pair of tiny satellites will enter a 3,500 Km orbit of the red planet and provide a communication relay for the Insight orbiter. NASA sees this project as a test for CubeSat technology and with the traffic currently orbiting Mars, there will be no shortage of alternative communication paths, should the worst happen to the CubeSat.

cubsat communication relay

CubeSats will provide a communication relay for the Mars Insight mission

To date, in excess of 450 CubeSats are known to have been launched, with many more waiting to hitch a ride on a host launcher. There are also probably quite a few which have never been fully documented.

Most CubeSats have no on-board propulsion. They are generally obliged to take such launch opportunities as are available to them. They are typically a ‘secondary’ payload and must accept whatever orbit is required for the rocket’s main customer.

Having to hitch a ride can mean accepting a launch to an orbit in which their spacecraft will remain for many decades, long after their operational lives of two years or so. Many do not include a de-orbiting strategy. And therein begins the problem.

Satellites and debris are monitored by the US Air Force Joint Space Operations Center (JSpOC) and CubeSats in their atomic form—10 centimeters on a side—are near the lower limit of what can easily be tracked. Even larger CubeSats still pose difficulties in obtaining precise positions, resulting in greater uncertainties.

JSpOC is the body which provides information to satellite operators to avoid collisions with debris and provides the data to ensure the safety of astronauts aboard the ISS. Several times, the ISS has had to be moved out of the path of debris and on two or three occasions, the astronauts have been ordered to take refuge in the Soyuz spacecraft ‘lifeboat’ for additional protection.

No wonder then that there are those in the industry who derisively refer to CubeSats as ‘debris Sats’. The more hardware there is in space, the greater the chance of collisions. To mitigate these risks, CubeSats are supposed to come down within 25 years. However, there is no enforcement of this rule. NASA claimed that by the end of 2014, 1 in 5 of US originating and over a third of all non-US CubeSats are in direct contravention of the 25 year ‘guideline’.

Even if everyone complies, operational issues arise to increase the risk of collision. The space station, for instance, will release a lot of CubeSats at the same time. These CubeSats will come off in this cloud, and the JSpOC is trying to track them and add them to their catalog of objects, so that other satellites can avoid them.

The problem with this “cloud” of satellites is that it can take up to a week for JSpOC to figure out which satellite is which and add them to their catalogue. Other spacecraft cannot take action against them because their position is not known. There is always this time lag after launch of a CubeSat, or deployment of a CubeSat, when other objects can’t be protected.”

Based on a prediction that CubeSat launches will exceed 200 per annum and at that volume, some argue that the risk is too great. Because of the much greater uncertainties in the positions of the CubeSats, a simulation found that the collision risk posed by the CubeSats was 30 times greater than for a single satellite.

Worryingly, that simulation has already proved accurate in one instance. It predicted CubeSat collisions should have started in the 2013 to 2014 period and, sure enough, the first one happened in May 2013. It resulted in the loss of Ecuador’s first CubeSat, NEE-01 Pegaso.

The follow on to accidental collision opens a huge can of worms labelled Space Law. There are few precedents, no laws, multi billions of dollars at stake – perfect, fertile ground for the legal profession.

Who can launch want and into what orbit? Should there be enforceable laws?

So, it is against this backdrop that a Russian project comes to the fore. As stated in an earlier story; as of January of this year, Roscosmos, the Russian equivalent of NASA became a ‘private’ commercial entity. This was to better enable it to sell more RD-180 rocket engines to the Americans without them seeming to come from the ‘state’ – with which the Americans still have an embargo.

If there was any doubt about the switch from communism to commercialism, Roscosmos confirmed a project to be paid for by the Russian ‘crowd funding’ organisation ‘Boomstarter’. The project is called Mayak, meaning Beacon and some 1.7 million roubles has been raised by this novel funding method. What does the crowd want for its money – an orbiting mirror to reflect the Sun as a memorial to the history and tradition of Russian achievements in space!

boomstarter beacon

Reflecting the Sun and new bright object in the sky

The 16 metre tetrahedron shaped reflector is a possible launch later this year on a Soyuz-2 rocket and will take its place in a low Earth orbit. It will bounce back the sun’s rays to Earth as it orbits, making it brighter than any star in the night sky.

So later this year when you look up at the brightest star you can see in the sky, you can say (to paraphrase John McEnroe) ‘You cannot be Sirius’ – Seriously?.

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