Considerations When Making a Current Shunt Sensor

For battery powered projects, current consumption is a really important consideration when designing the circuitry. While designing my final year project I spent a huge amount of time researching how to put together a simple current sensor. Considering most applications for me are DC, fairly low current and low voltage, the most obvious design is to make a current shunt. The basic idea of a current shunt is that you put a very low value resistor between the circuit you want to measure and ground, and measure the voltage across it. When one side is of the shunt resitor is ground it is low side, there are also high side versions but are mlre complex. As the resistor has a small resistance, there will be a low voltage drop (usually mV) across it meaning it shouldn’t affect the load circuitry. The voltage will also be proportional to the current running through it, meaning if you measure it, and do the right maths you can get a consistent and reliable current reading. This post is about how to get that tiny voltage into 1’s and 0’s, while thinking about the considerations that have to be made about the design to make it accurate and reliable in the environments you want.

Final Year Project
My final year project needed current sensors on the motors as well as monitoring the drain on the battery.

The first thing that needs to be decided is the shunt resistor itself. A shunt resistor is basically a low value resistor, with very tight and known tolerance usually with a fairly high power rating. It can be used in AC and DC circuitry, with the concept behind it being that as a current flows  though it, a voltage is induced across it. The voltage can then be measured and using a simple calculation (based on ohms law) converted into a value for current. The value of the resistor depends on what it is measuring and what is measuring it. Start with what is measuring it. If you are like me, it is likely that it will be read by an ADC, probably on a 5V or 3V3 microcontroller. The voltage across the resistor is going to be amplified between 10 and 100 times (we will get to why in a moment) so pick a maximum voltage within that range. I tend to go with 100mV maximum voltage drop, which for a 5V ADC would require an amplification of 50. Then, take the maximum value of current you want to be able to measure. You can then use ohms law to figure the resistance you need. For example if I wanted to measure 1A, the resistor would be 100mV/1A = 100 mohm. Now we know the resistor value, use the power equation to work out the power eating we want. For this example we would need P = I V = 1 x 0.1 = 100mW. This is the minimum power rating you need, I personally would get a 250mW or even a 500mW just to keep the temperature of the circuit down.

The simple equation to work out what sizesunt resistor to use. Credit: Texas Instruments 

Now we have a voltage that will be somewhere between 0 and 100mV with reference to ground. We want this value to be scaled up to 0 to 5V. To do this we are going to use an operational amplifier. There are plenty out there, and most people have their favourites and I’m not here to convince you otherwise. I tend to use an op amp that I am using somewhere else in the circuit to make life easier. There are a few things you do need from an op amp in this circuit though, it needs to be rail to rail, and have a low input offset voltage. Offset voltage in an op amp is the voltage difference on the inputs, and even though they are tiny differences they can have a big effect because we are amplifying small voltages, and any noise or offset will be amplified too. The op amp needs to be in a simple non inverting configuration. The equations needed to design this are in most first year textbooks and there are plenty of calculators online. I have set a gain of 50 in my calculation, which is in the fairly common range. The output of the amplifier can then go straight straight into an ADC to be measured.

The basic layout of a current shunt sensor showing where the shunt resistors and gain resistors go in the circuit. Credit: Texas Instruments 
The first version of my current sense test circuit, using an OP170 made by TI.

Now let’s look at a few places where errors can come into a design like this. There are two types of errors that occur in a circuit like this, gain error and offset error. A gain error is one where the output error gets further away from the ideal output as the current gets higher. An offset error is one that has the same amount of error whatever the input, just like an offset. The only common source of offset error in a circuit like this is from the offset error in the op amp discussed previously, solved with an improved choice of amplifier. The gain errors are usually due to a difference in resistance from the ideal. Many things can cause this, one is the tolerance of the resistor used, we want to use a precision resistor of 1% or less tolerance. Another cause could be temperature changes in the resistor itself, it may be next to a large MOSFET or other hot component, or could have too low of a power rating making it heat up, wither way a change in temperature means change in resistance. Layout can also be an issue, if tracks are too thin or too long they can add extra unwanted resistance.

Great graphs showing the difference between gain an offset error. Credit: Texas Instruments.

If you want to add a bit of fancyness into the project, or really need to measure down to low currents, you need to tackle the zero-current error. The problem is that when using an op amp, even a rail to rail one, it never quite reaches the power rails. Even the best ones can only get within 100mV or so of the power rails, this is known as saturation. Solving this involves moving the power rails slightly so the saturation point is less than ground. If you have a negative voltage rail you can use that but home projects tend to be single supply, so we need another power source. This can be made using a voltage inverter (a type of charge pump). Usually only needing an external capacitor to work, they are cheap and easy to integrate into a project. I used a LTC1983, which creates a negative 5V rail, but there are plenty of others such as the LM7705. Research what fits your circuit and cost point, and just attach the negative output to the negative supply rail of the op amp.

 A great graph showing how the zero current error occurs, and what it would look like if you tested it. Credit: Texas Instruments.

Most issues with error can be fixed during the hardware design phase. You can pick better op amps, such as ones designed to combat offset voltage. Some amplifiers have internal calibration procedures, and some such as chopper stabilizers are specifically designed to correct these problems. You can also use a potentiometer instead of a power resistor, but they are more susceptible to temperature and can be knocked. Another way is to fix issues in software by creating a calibration procedure. Using a calibrated precision current source and a multimeter, measure the reading of the ADC and compare the value to the reading from the instruments. You should get an offset and gain value that can then be used to calibrate the sensor.

A simple set up that I used to calibrate an early sensor, with a big power resistor as the load and a variable power supply to change the current. Marked down to put into calibration.

I would suggest trying out a few of these sensors in future projects, they don’t cost too much, and can be a valuable addition to a design. Especially for power sensitive devices, or smart sensors, this could be a better solution than an off the shelf or breakout board solution. If you want to hear more about my current sensor designs, and how well the testing and calibration went then comment or tweet at me. I already have some documentation that I may release at some point.

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Getting Ugly, Dead Bugs, and Manhattan Style

If you are anything like me, you love to build small circuits. I like to try and get my head around how things work by making it in front of me. This is usually in the form of breadboarding, but sometimes that doesn’t cut it, and soldering is needed. Veroboard tends to be my go to for building a simple circuit as something a bit more permanent, but it doesn’t always lend itself to certain designs. Take a design with lots of grounding points in the design, like an RF circuit, it can be difficult to have lots of ground strips everywhere, and the extra capacitance can mess with those high frequency signals. Also, designs with lots of different separate signal traces going round the board can make for a real pain. lots of slicing the traces, which tend to lead to mistakes. With my constant desire for order and straight lines, and pretty layouts this can get annoying quickly. Recently I have found a few new and simpler ways to throw together simple circuitry. For any budding electronic engineer, they are good skills to add to an arsenal.

A veroboard design of a hybrid microphone amplifier and level shifter I made for a recent project, prototyped on veroboard, many mistakes were made.

Ugly Circuits

As the name suggests, ugly circuits are not always the prettiest of designs. There are a few different definitions of what makes an ugly circuit, but my favourite is any circuit where the components are not completely mechanically connected to the substrate. The substrate usually being a copper clad board, but not always. This method can be a tricky one to master, as it is literally a balancing act. The prefered method that I see this being used is having a single copper clad board as a giant unobstructed ground plane. Two wire passives are usually the easiest to start with (standard resistors/capacitors), soldering one side to ground, then soldering the other side to another component in the air. This means any point that is not grounded is usually floating physically in the air (but depending on how good you are it could have floating voltage too). This can be a big benefit to RF circuitry or circuits that need good solid grounding. The unobstructed copper clad board means anything connected to it has a great connection to ground. It is fairly easy to build simple passive filters, but gets very fiddly and fragile if you aren’t careful.

A very “haywire” circuit constructed in the ugly style by Rick Anderson – KE3IJ in 2006. An experimental stage of his AGC-80 Regan receiver.
Not sure on the origin of this one, but it is more chaotic rather than ugly. It is definitely in the ugly style.

Technically ugly circuits don’t have to have a substrate at all, although it makes life easier. There are plenty of examples out there of ugly circuitry that just connects pins to pins via small wires. As said before, it can be very fiddly to make a circuit like this, but it is much cheaper to make singles as there is no need for expensive copper clad board. Plus after plenty of practice one can get very good at doing it. The wires connecting the parts together can be part of the structure of the unit, and if designed correctly could be very strong. The construction method can be useful in certain circumstances, and as long as you have the components, it can be build easily with just a soldering iron and solder. Although there are some amazing looking circuits made from this method, the majority do earn the name of an ugly circuit. If you can make a pretty one I would love to see.

Nathanxl at the Electro music forums creates some amazing almost artistic music project using the ugly style, but they look incredibly hard to make.
An Arduino Uno made without any substrate, just wires and components. Made by Kimo Kosaka, it is not an ugly, but it uses an ugly style of construction.

Dead Bugs

No, this method does not actually use dead insects as a manufacturing material, but it may look like it. The idea is to take an IC, traditionally in a DIP package, and place it upside down on the substrate. Usually glueing, but not always, with the pins facing upwards, so it has the look of a dead bug. The pins can be bent to attach to the substrate if required, but they tend to be facing up. Taking many methods from ugly, the pins are usually directly connected to passives or wires to other chips. This means the mechanical connections are usually in the air. The benefit to this method is that you don’t have to waste time drilling holes in in the substrate, and can integrate IC’s into an ugly design fairly easily. If trying to use this method, just be weary that all the pins on the chip will be the wrong way round as it gets flipped when placed upside down. I recommend making your own diagram to go from to make life easier.

As you can see in this use of dead bug mixed with ugly construction made by JCHaywire is the chip flipped over and the pins moved about with all the connections floating in the air

Although not really dead bugs, the concept can be seen in many modifications of PCB’s. It is easy to order the wrong package or get sections of pins wrong when designing and ordering PCB’s, especially if you have manually made the part. So it is not uncommon to find upside down IC’s on prototype PCBs or even sometimes on short runs. That being said, anything smaller than a DIP or SOIC package can get very fiddly, and is difficult to hand solder, and will need some extra magnification. Don’t be deterred though, there are many examples of even QFN and even BGA devices being hand soldered in the dead bug form, with very thin gauge jumper wires. With plenty of practice and spares, it can be a useful method of saving money without having a new run of PCB’s.

A bodge on a PCB before the real chip arrives, a 6650 is being used in dead bug style to get the circuit working by Dave Curran.

Manhattan Style

This one is my favourite styles of circuit design on the cheap and quick, and if done right can be very pretty and efficient. The big issue with the ugly method is that it is difficult to create, and often difficult to follow, and horrible to document. Manhattan is an upgrade, using cut out sections of copper board as small islands, much like manhattan. This method means there are no connections floating in the air, as all points on a component are mechanically connected to copper clad in some way, even if it is only a small bit. This leads to generally a much nicer laid out board, that can easily be followed and replicated. It also allows for use of SMD components, which is possible with ugly, but very difficult. The small pads don’t have to be separate, they can simply be cut outlines on the same backplane, making the process cheaper, but get it wrong and it can get messy. I much prefer manhattan as a quick construction method, due to its neat look and ease of use. Another reason for the name Manhattan is the fact the capacitors and resistors tend to line up and are perpendicular to the substrate, looking a bit like tower blocks and skyscrapers like Manhattan itself.

A great example of Manhattan style soldering by Dave Richards. Solid copper substrate with QRPme pads to attach components together. 
Another impressive circuit in the Manhattan style by Dave Richards, this one is a high performance regen receiver, with a full write up on his blog.
An example by VE7SL – Steve of making his own pads for his amateur radio transmitters and receivers, using an Ebay punch to make the pads.

One step on from Manhattan style, and the final step before fully fledged PCB’s is a little known style called Pittsburg, much like the steak. I have also seen it be called muppet style, and I am sure there are many other names for it. It is very similar to an actual PCB, usually etched, a layout is carved into the board, with traces and pads. The difference from a PCB is the fact there are no holes anywhere to be seen. Meaning you get the benefit of being able to etch a nice looking layout at home, and the benefit of not needing expensive routers/drills that quickly break. To allow for the pads to be soldered to as the main mechanical connection they are much bigger to allow for more solder on a bigger surface area. These pads would be overkill for a thru hole project, but also allows for easy use of SMD components. You can sometimes see specialist pads like Pittsburg to use SMD chips on a Manhattan style board. It is a matter of taste and confidence. These methods are obviously not suitable for all prototypes, but could come in useful for your next project. 

A Pittsburgh style PCB at one point sold by Joe Porter, unsure if they are still sold.

A good source of the small pads used in Manhattan can be found here. Reasonable price, and if you are doing lots of prototyping you can even buy the tools to make it yourself!

Thank you for reading, take a look at my other posts if you are interested in space, electronics, or military history. If you are interested, follow me on Twitter to get updates on projects I am currently working on.


Roundup: Parker Solar Probe Launch

Rocket flames
An awesome image of the Delta IV heavy launching from pad 37B. Credit: Aerojet Rocketdyne.

At 07:31 UTC on August the 12th 2018 the 10th ever Delta IV heavy vehicle launched the long awaited Parker Solar Probe from Cape Canaveral Space Launch Complex 37B. The Delta 4 Heavy launched PSP towards a heliocentric orbit. The mission aims to “touch the sun”, and to get as close to the sun as man has ever been. Getting as close as 3.9 million miles from the sun, that’s roughly 4% of the distance between the Earth and the Sun (roughly 93 million miles).

time lapse
A great timelapse of the Delta 4 heavy launching towards the sun. Credit: Marcus Cote.

The Parker Solar Probe was named after Dr Eugene Parker who discovered the solar winds in 1958. He was present at the launch at the Kennedy Space Centre, seeing the 685kg spacecraft lifted. The 7 year mission will make 24 elliptical orbits of the sun, and uses 7 flybys of Venus to drop the low point of the orbit. It will make the closest point of the orbit closer than any other man made object in heliocentric orbit. It will enter the sun’s “atmosphere”, a section known as the corona, the outermost part of the atmosphere. Protected by a 4.5 inch sunshield, it can withstand temperatures of 2500F (1377C). The aim is to understand how the sun can creates and evolves solar flares and solar winds. It is to understand how the highest energy particles that pass the Earth are formed. It is hoped that it will revolutionise our understanding of the sun, to help us develop and create technology here on Earth.

The rocket has three RS-68A boosters, with the outbound boosters cutting off at T+3 min 57 sec, the core then cut off a minute and a half later at T+5 min 36 sec. The Delta’s cryogenic first stage engine was RL10B-2, which began burning at T+5 min 55 sec, and stopped its first burn at T+10 min 37 sec. This burn entered the 3,044 kg load into a 168 km x 183 km x 28.38 deg parking orbit. The second burn started at T+22 min 25 sec, and ended at T+36 min 39 sec, accelerating it to C3 of 59 km2/sec2, roughly 5,300 m/s out of LEO. At this point the Probe was in solar orbit, the Star 4BV separated at T+37 min 9 sec, with it firing at T+37 min 29 sec. The burn ended a minute and a half later at T+38 min 58 sec, accelerating it to 8,750 m/s beyond LEO. The Parker Solar Probe separated four and a half minutes later. The orbits after this point become much more complicated to get to the prefered orbit touching the sun.

Engineers at the Johns Hopkins University Applied Physics Laboratory in Laurel, Maryland, work on NASA’s Parker Solar Probe spacecraft. Parker Solar Probe will be the first-ever mission to fly directly through the Sun’s atmosphere. Photo & Caption Credit: NASA / JHU-APL

The Delta 380 was the first Cape Canaveral Delta to use the upgraded “common avionics” system for its flight controller. The rocket was shipped to the Cape over a year ago, with it being assembled in the SLC 37 HIF. The rocket was then rolled out to the pad in April 2018, and there was a wet dress rehearsal on June 2 and 6th. The initial date for launch was the day before, august 11th but it was scrubbed at T-1 min 55 sec. Some of the best images of these launches are now taken by amateurs. I usually post a few of the images, but this launch was different as most of those who placed their cameras just a few hundred feet from the rocket got very damaged equipment.

Thank you for reading, take a look at my other posts if you are interested in space, electronics, or military history. If you are interested, follow me on Twitter to get updates on projects I am currently working on.

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The Items Apollo 11 Left behind on the Moon

Aldrin Looks Back at Tranquility Base
Buzz Aldrin Looks Back at Tranquility Base just after deploying the Early Apollo Scientific Experiments Package (EASEP). Credit: NASA.

July 21st 1969. The time is 2:56 UTC, Neil Armstrong is taking the first steps on the moon, 20 minutes later Buzz Aldrin is following. The landing site looks clean apart from the big lander that is their lift home. By the end of the two hour EVA on the lunar surface the site would be walked over, science experiments laid out, and a pile of rubbish left in a pit. A view you don’t get to see in the images from Apollo 11, the astronauts left over 100 items on the lunar surface. Some commemorative, but mostly items they didn’t need for the return journey.

The plaque
The plaque attached to the lunar lander, with a message from all mankind, just in case some other being finds it. It commemorates the first steps on the Moon. Credit: NASA.

Famously landing in the sea of tranquillity, the Eagle lander has a number of official commemorative items attached to it. The main one is a plaque proclaiming “Here men from planet Earth first set foot upon the Moon. July 1969, A.D. We came in peace for all mankind.” Under the “we come in peace” is a golden replica of an olive branch. Nearby is a small aluminium capsule with a tiny Silicon disc inside. It contained on it messages from four US presidents, and seventy three other heads of state. It was sketched onto it in microscopic lettering, with the wording found here. There are also a few non official items taken there by the astronauts. An Apollo 1 patch in memory of Roger Chaffee, Gus Grissom, and Ed White who died in January 1967 in a fire inside the first Apollo capsule. They also left behind two military medals that belonged to Yuri Gagarin and Vladimir Komarov, both famous USSR cosmonauts. It showed the respect these men had for Soviet cosmonauts who had achieved so many firsts, and went through the same trials and tests they did.

The Apollo 1 patch
The patch for the famous Apollo 1 where Roger Chaffee, Gus Grissom, and Ed White tragically died in a fire. The patch was left on the Moon. Credit: NASA

On top of this they left the science experiments that they had used, such as the passive seismic experiment. The experiment that used meteorite impacts on the surface to map the inside structure of the Moon. They also placed a master reflector so that scientists could measure the distance from Earth precisely. This retroreflector still works, and if you have access to a powerful enough laser you can measure it yourself. They also had to pick up lots of moon rocks and moon dust as part of the science mission. They used sample scoops, scales and even a small hammer. There are also many specific tools that were needed, but were discarded before the return journey.

Map of Tranquillity base
Map of Tranquillity base including the Toss Zone where all the rubbish was discarded. Credit: NASA

Overall they left roughly 106 random bits if rubbish at the launch site. Including lots of tools like the hammers, chisel and brushes needed for sampling; astronaut EVA gear such as the over boots and and life support systems; and actual rubbish like the empty food bags, some armrests they wanted to dispose of; a TV camera; insulation blanket; pins and plastic covers for items like the flag (and the flag itself) plus the urine, defecation and sickness bags, although there is no word on whether they were used. They threw all the items into an area behind the lander known as the “Toss Zone”, basically just a rubbish pit.

Buzz with science
Buzz carrying science experiments to the required place slightly away from tranquility base. Credit: NASA

The astronauts left a surprisingly large amount of stuff on the Moon, but it does make sense, as they needed that weight to be replaced with the 300 kg of Moon rocks that they wanted to bring back, so they just left it all there. There is a full list of the items on this webpage, and its worth a look. Archived by the Lunar Legacy Project, they count it as over 106 items. Depending on how you count it, there can be over 116 items left by the Apollo Astronauts.

Thank you for reading, take a look at my other posts if you are interested in space, electronics, or military history. If you are interested, follow me on Twitter to get updates on projects I am currently working on.


The Secret Side of Sleepy North Devon and Cornwall

Barrel Rock Bude
Barrel Rock at the end of the Breakwater on Bude beach, used to guide ships into the harbour.

North Devon and Cornwall, a sleepy area that is full of history of its fishing and farming past. Now with a bustling influx of tourists every summer to enjoy the museums, adventure parks and sunny beaches. Just getting back from a holiday there in Appledore It has all these things, but the one big thing I noticed was the large presence of military sites in the area. Just visible from Appledore is RMB Chivenor, a big marine base, as well as a Babcock site that has built military ships for over 160 years. Just down the road is a selection of old RAF radar stations and airfields, one of which is now a top secret GCHQ site that could be listening to a large portion of the world’s internet traffic.

View From Bude
A view of one of the satellite dishes at GCHQ Bude taken from Bude beach. Credit: me.

On a day trip to Bude in Cornwall, after the customary ice cream we took a walk down the beach and were drawn to the Breakwater. More specifically a big rocky section at the end of the breakwater called Barrell Rock. Named so because of the barrel on the end of a long pole used to guide ships around the dangerous rocky breakwater. It gave a great view of the beach and bude itself,  and the chapel said to be where Bude originated. One thing I did notice when looking north up the coastline was what looked like a satellite dish, and that got me wondering. Then I remembered we passed a single signpost on the way pointing to GCHQ. It turns out that just 6km up the coastline is GCHQ Bude.

A view of GCHQ Bude
A great View of GCHQ from the coastal path. Credit: Paul Phillips

Nestled between the small villages of Morwenstow and Coombe, during the second World War the Air Force built RAF Cleave. It was designed to house target and target support aircraft for the firing ranges along the north cornwall coast. After the war it then stayed in government hands, with little use. Then in the 1960’s it started changing. The main reason: in 1962 a satellite receiving station was established at Goonhilly Downs, mainly for linking with television satellites, it also carried large amounts of telecommunications data. A surprisingly important piece of satellite communications infrastructure it has played a key role in communications events such as the Muhammad Ali fights, the Olympic Games, the Apollo 11 Moon landing, and 1985’s Live Aid concert. Being only 100km south of RAF Cleave signals could be intercepted by placing receiver dishes on the grounds. Initially to intercept mainly signals from Intelsat, a commercial communications satellite, the construction of the station began in 1969, with two 27m dishes, with smaller dishes coming after. Initially signposted as CTOS Morwenstow (CTOS standing for Composite Signals Organisation Station), in 2001 when a third large dish was built the station was renamed GCHQ Bude.

RAF Cleave gun emplacement
Remains of an RAF Cleave gun emplacement, with the modern satellite dishes of GCHQ Bude behind

GCHQ Bude has come under fire many times because of the ethical implications of the work conducted there. Even as early as 1963 they could have been tapping the data classed as suspicious from the TAT-3 telephone undersea cable. There are cable landing points at Widemouth bay that connect the UK to the USA, just 10 km south of the Cleave camp. It was also featured in a BBC Horizons documentary where it is claimed that all the data that goes through that the internet landing cable at Skewjack farm in Cornwall (formerly RAF Sennen) is sent on to GCHQ Bude for processing. The Fiber-Optic Link Around the Globe cable that surfaces there is estimated to see around 25% of all internet traffic, just think about that for a second. In terms of satellite installations at GCHQ Bude there are twenty one satellite antennae of differing sizes, three of which having a diameter of 30m. In theory these dishes could cover all the main frequency bands. Based on the position, some have theorised that they are oriented towards satellites of the INTELSAT, Intersputnik, and INMARSAT communications networks over the Atlantic Ocean, Africa, and the Indian Ocean, as well as towards the Middle East and mainland Europe. As well as this in 2011 a torus antenna was installed which is able to receive signals from up to thirty five satellites at once.

GCHQ Bude facing East
A wide image of GCHQ Bude facing east with a sunset in the background.

This post is not about my opinion about what they do at GCHQ but I find it a very interesting place, with a serious amount of technology involved, but they have been in the news a lot. A report made public in 2001 showed concerns by some EU member states that CTOS Morwenstow was involved in industrial espionage. It is claimed that the Intelligence Services Act 1994 grants GCHQ access to anything that emitted an electromagnetic signal, so pretty much any electronic device. In 2011 the Guardian reported how GCHQ attempted to gain access to the Blackberry Messenger service for the use of police to trawl for riot organisers. In 2013 the Guardian reported a large amount of information about GCHQ Bude leaked by Edward Snowden. It talked about operation Tempora, where GCHQ tapped into undersea cables and kept the data for up to 30 days to assess and analyse it. A further article reported that it was eavesdropping on charities, German government buildings, the Israeli Prime Minister, and an EU commissioner. There are plenty of other similar articles out there with similar overtones, and about GCHQ in general. The thing I found crazy is that even though trespassing on the site is its own law, you can walk fairly close when going along the coastal path.

RAF Hartland Sign
A sign at one of the old radar stations at RAF Hartland Point, now used by the aviation authority. Credit: Exal66 on derelictplaces.co.uk

When researching this subject it can get into a deep pit of conspiracy, but the thing I enjoy the most is looking at old military installations. Just up the coast from Bude in the northwestern point of Devon is Hartland Point. We visited Hartland Quay (close by) and it is highly recommended for the views. Apart from the hundreds of shipwrecks along that coastline, a noticeable part of the view is the old radar station at the point. During World War 2 that was controlled by RAF Hartland Point. The foundations of the big type 11, 13 and 14 radars can still be seen around the radar station at the point. Great information about the radar systems and some more information about the base can be found here. There is also an old air raid shelter, and a former station building that has been commandeered by the coastguard. The radar that can be seen nearby (the spherical one) is used by the UK Civil Aviation Agency for air traffic control. A user on derelictplaces.co.uk shows some great images of his walk around the site.

RAF Hartland base
The base of a radar from WW2 at what was RAF Hartland point. The aviation authorities new radar is in the background. Credit Exal66 on derelictplaces.co.uk

The final place I want to mention is one that is very noticable to anyone who has called the Tarka Trail between Fremington and Bideford. It passes right across the river from the historical Appledore shipbuilders. With many owners and names in the 160 years it has been active, it is now owned and operated by Babcock international Ltd, the same company who run Devonport. The dockyard has built more than 350 vessels in its lifetime, including small and medium-sized military craft, as well as superyachts, bulk carriers, ferries and oil/LPG industry vessels. While we were there a Norwegian military ship was being worked on. Some of the most notable ships include HMS Echo, HMS Enterprise, HMS Scott, and RRS Charles Darwin. A trip down the Tarka Trail is highly recommended, especially by bike.

Appledore Babcock
The shipbuilders at Appledore, now owned and run by Babcock international, visible by the Tarka Trail.

Thank you for reading, take a look at my other posts if you are interested in space, electronics, or military history. If you are interested, follow me on Twitter to get updates on projects I am currently working on.


Record Breaking Falcon 9 Launch

Telstar 19V
The awesome flames of the Falcon 9 Block 5 carrying Telstar 19V. Credit: Marcus Cote.

On the 22nd of July 2018, at 05:50 UTC a record breaking Block 5 Falcon 9 launched Telstar 19V into subsynchronous transfer orbit. Launching from Cape Canaveral Space Launch Complex 40, F9-59 (launch designation) was the First Block 5 to launch from this pad. The 7,075 kg payload was more than the previous record holder, the 6,910 kg TerreStar 1 orbited by the Ariane 5 in July 2009. Although, the previous record holder launched the satellite to full geosynchronous transfer orbit. This launch was seen as a key test of the newly developed Block 5 launch system. The first stage was recovered on the autonomous drone ship “Of Course I Still Love You” off the Florida coast.

Telstar 19V medium
A great view of SLC-40 from across the water while Telstar 19V is being launched. Credit: SpaceX Flickr.

An SSL 1300 series satellite, Telstar 19V is part of the Telstar series. Owned by the Canadian Satellite Company Telsat, it was built by Space Systems Loral (MAXAR). Using Ka and Ku band transponders it is branded as a high throughput communications satellite, designed for high bandwidth applications that the communications industry is currently dealing with. It is collocated with Telesats Telstar 14R satellite at the same position. The companies first high throughput satellite was Telstar 12V, which sits 15 degrees west.

The upgraded engines of the Merlin 1D engines on the Falcon 9 block 5 can produce a total of 775.65 tonnes of thrust at sea level. The second stage produces roughly 100 tonnes of thrust when in space. The first stage with the designation B1047 burned for 2 minutes and 30 seconds before separating to perform reentry and landing burns. The second stage burned for 5 minutes and 38 seconds to reach a parking orbit, stopping T+8 minutes 12 seconds. The stage restated at T+26 minutes 49 seconds for a 50 second burn to put the satellite into a 243 x 17,863 km x 27 degree orbit. The satellite will then raise itself into a geostationary orbit at 63 degrees west to cover the Americas.

Telstar 19V long exposure
A great long exposure of F9-59 launching Telstar 19V from Florida’s Cape Canaveral. Credit: SpaceX.

A total of 26 Falcon 9/Falcon Heavy core and booster stages have now been recovered in 32 attempts. Four of those successful landings have been on “Just Read The Instructions” off the California coast, 10 have been at Cape Canaveral Landing zone 1&2, and 11 on “Of Course I Still Love You off the Florida coast. Twenty unique first stages have been recovered, with fourteen of them flying twice, and eight being expended during their second flight. All of the successfully recovered first stages have been version 1.2.

Telstar 19V medium 2
A Falcon 9 launches from Space Launch Complex 40 with a record breaking satellite aboard. Credit: SpaceX Flickr.

To find similar photos, and to buy reasonably priced prints of some of the above visit www.marcuscotephotography.com

Delta II Launch Site Demolished

Delta II launch
The launch of the GRAIL mission from Launch Complex 17 by a Delta II. The final launch from SLC-17. Credit: NASA/Tom Farrar and Tony Gray

At 11:00 UTC on the 12th of July 2018 the two launch towers of Space Launch Complex 17 were demolished by controlled explosions. The crowd of onlookers cheered as the towers fell, and took some great images and videos of the demolition. The launch site had not been used since 2011 when Delta II 7920H-10C fired NASA’s GRAIL spacecraft towards the Moon. The launch complex had two pads named 17A and 17B. The site is now to be reused as a test bed for potential lunar landers made by Moon Express. Boasting some very prestigious missions well beyond Earth SLC-17 will be remembered as an important part of the history of American space.

Delta Echo 1
A delta Rocket carrying NASA’s Echo 1 satellite launching August 12th 1960. The Echo satellite inflated in orbit to reflect signals back to Earth. Credit: NASA.

It was built in 1956 for use as a launch site for the PGM-17 Thor missile. This was the first operational ballistic missile that the United States had in their arsenal. The first launch of a Thor missile from 17A was 3rd of August 1957, with the first launch from 17B being 25th of January 1957. In the early 1960s the site was upgraded to support a variety of Expendable Launch Vehicles, all of which were derived in some way from the Thor booster. We now know this family of rockets as the Delta rockets used by the United Launch Alliance. Thirty five early Delta rocket missions were launched from LC-17 between 1960 and 1965. At that point operated by the US Air Force. In 1965 the operation of the site was transferred to NASA.

View of LC-17
View of LC-17 viewing East. A fairly old photo taken by the U.S. Army Corps of Engineers. Credit: Martin Stupich

In 1988 the site was returned to the Air Force to support the Delta II program. The site had to be modified to facilitate the new more powerful rocket, with new platforms being installed and the D=Ground Service Tower was raised by 10 ft. The program entered service in 1989 after worries about the shuttle due to the Challenger disaster. Pad 17B was modified in 1997 to support a newer more powerful launch vehicle the Delta III which made its maiden flight on 26th of August 1998. Ending in failure, the next three attempts were failures in some sense and the programme was abandoned in late 2000. The Delta II continued to launch, with it’s fairly cheap price tag, and amazing track record it has been a favourite for NASA on a number of big projects. This post by NASA explains how the layout of the site and the small teams allowed LC-17 to be efficient and consistent over it’s 50 year lifespan. Some Delta II launches could be within days of each other because the launch crews were so effective.

Space Launch Complex 17
A view of Space Launch Complex 17, pads A and B taken in 2007. Delta II rocket with THEMIS aboard sits on Pad B. Credit: NASA/George Shelton

There have been some very famous spacecraft launched from SLC-17 in the years, mostly by Delta I and II rockets. Among them the Explorer and Pioneer space probes studying the physics of our solar system, and exploring some of it. All of the Orbiting Solar Observatories between 1962 and 1975 were launched from this site, as well as the Solar Maximum mission in 1980. Some of the first weather satellites like TIROS and later GOES were launched from SLC-17 allowing much better understanding of weather and improving (mainly military) weather reports. My personal favourite launches are those of the Mars Exploration Rovers in 2003. Both spirit and Opportunity (still going) were launched from this important launch site.

Spirit lifting off
A Delta II launching from pad SLC-17A with the MER-A or Spirit Rover towards Mars on June 10th 2003. Credit: NASA/KSC

Space Launch Complex 17 is also famous for being the last site where you had to press a button to launch the rocket. Most pads had a computerized auto-sequencer, much like the space shuttle, and in the modern world of rocketry it makes much more sense to do that. Even after 1995 when they got rid of the button (sadly) a human needed to press go on a computer to say launch. Bill Hodge, an electrical engineer at the launch complex said “If you didn’t push that button, it didn’t launch.” Tom Mahaney, project manager for the closeout of the complex described the site as “hectic, but not dysfunctional.” This is the best description I can find of this massively important historical site. In its time it has supported a total of 325 Thor and Delta rocket launches!

Thank you for reading, take a look at my other posts if you are interested in space or electronics, or follow me on Twitter to get updates on projects I am currently working on.


How the Moon’s Dust Could be Deadly

footprint on the moon
Very famous image of a footprint in the lunar soil, part of the 70mm Hasselblad image collection, you can see the dust and rocks that are classed as mature Regolith, Credit: NASA.

The space industry is changing, improving and looking at places to go. Although Mars is the big target for Elon Musk and SpaceX, revisiting the Moon is a big and real challenge that many are aiming for. Whether it is just getting people back there in a safer and cheaper way than Apollo or if it is companies wanting to design Moon bases, it is an active area of interest. Since the Moon landings over half a century ago, researchers have poured over the moon rocks, and images brought back from the mission. More recently though, researchers are looking at a slightly overlooked factor, lunar dust. They were a problem for the astronauts to landed there in the 60’s/70’s and they may pose a problem to future missions where they may spend weeks or months rather than just a few hours/days. The research below shows how the moon moon affects us when we are there, and how it could be very dangerous.

Harrison Schmitt collects samples
NASA astronaut Harrison Schmitt retrieving lunar samples using a scoop during the Apollo 17 mission in 1972. Credit: NASA.

At time of writing, twelve people have been known to walk on the Moon, all between 1968 and 1972. The longest any group spent on the Moon was the crew of Apollo 17 who spent just over three days there. Sleeping in the Lunar Exploration Module, the astronauts tended to collect lots of dust during the EVA’s (Extravehicular Activity). As the moon has a much lower magnetic field it gets blasted with much more radiation from the sun on the surface.  This electrostatically charges the dust particles making it much more likely to stick to the astronauts spacesuits. This linked with the lower gravity of the Moon means that the particles do not drift to the ground as fast like on Earth. Plus when the dust got into the Spacecraft it had no gravity on the trip home. All these factors meant that the astronauts inhaled lots of lunar dust during the mission.

Lunar dust particle
Fine like powder, but sharp like glass. An image of a lunar dust particle. Credit: NASA/JSC.

On earth, dust tends to be fairly round, eroded over time by wind and water. It is also not only rocks, but biological as well,  On the moon, the dust is just rocky and hasn’t been eroded over time as there is no wind or water. The particles are spikey, abrasive and nasty. All twelve of the people who landed on the moon suffered with what NASA astronaut Harrison Schmitt described as “lunar hay fever”. They had symptoms like sneezing, nasal congestion and often they took time to fade. Most people know that the astronauts describe the dust as smelling like burnt gunpowder, but don’t know that it made them quite ill. Even the astronauts themselves might not have known the true reasoning behind the illness. Part of the reason is that the lunar dust has silicate in it, often found on planetary bodies with volcanic activity. As well as making the astronauts ill, it was so abrasive that it ate away at layers in the spacesuit boots, and destroyed vacuum seals on sample containers.

Eugene Cernan Hay fever
NASA astronaut Eugene Cernan inside the lunar module, still on the moon after his second moonwalk of Apollo 17. With spacesuit covered in lunar dust he complained of hay fever like symptoms. Credit: NASA.

One study by Stony Brook University School of Medicine, NY looked into the toxicity and DNA damage as a result of exposure to Lunar dust. They attempted to mimic the effect of lunar regolith (the dust) on mammalian cells. They took lung and neuronal cells and then exposed them to materials processed to mimic lunar dust so they could assess survival and genotoxicity. They showed that the soil can cause death to some cells and DNA damage in both neuronal and lung cell lines. Certain forms of the dust had more effect than others, but it was shown that depending on conditions, lunar soil can be cytotoxic (toxic to living cells) and genotoxic (damages genetic information) to both neuronal cells and lung cells. Testing was done by cultures and not tested on real people or animals. Kim Prisk, a pulmonary physiologist from the University of California with over 20 years of experience in human spaceflight is taking part in similar research as Part of an ESA research program. She mentions that “Particles 50 times smaller than a human hair can hang around for months inside your lungs. The longer the particle stays, the greater the chance for toxic effects”. ESA make simulated moon dust from a volcanic region in Germany. See their post on Lunar dust here.

Thank You for reading, take a look at my other posts if you are interested in space or electronics, or follow me on Twitter to get updates on projects I am currently working on.


The Final Block 4 Changes the Florida Sky

Smoke left over by CRS-15
The smoke stream left over by CRS-15 after the launch from Cape Canaveral, FL. Credit: Marcus Cote.

On the 29th of June 2018, at 09:42 UTC the last Block 4 type Falcon 9 rocket launched a cargo mission to the International space station. Launching from Space Launch Complex 40 at Cape Canaveral Air Force Base, the Falcon 9 was carrying CRS-15, a resupply for the International Space Station (ISS). This is the 15th mission of up to 20 CRS missions that have been contracted with NASA to resupply the ISS. Initially planned for April 2018, it was eventually pushed to the 29th of June. Previous resupply missions have been conducted by SpaceX and Orbital ATK.

Long Exposure CRS-15
A great long exposure image of the CRS-15 launch. Plenty of other versions of these out there, but this one has the great smoke shapes at the end. Credit: Marcus Cote.

B1045 (the first stage booster) was the seventh and final “Block 4” Falcon 9 v1.2 first stage manufactured by SpaceX. For this reason it is very likely that this was the final Block 4 first stage orbital vehicle. SpaceX has since developed the Block 5 the debuted in May. Together the seven Block 4 Falcon 9’s boosted twelve missions, with most being expended on the second flight. This stage was purposely expended at the end of the mission, the ninth purposeful expenditure in the last twelve launches. This stage was not equipped with landing legs or titanium steering grid fins. It was the 14th flight of a previously flown Falcon 9 first stage, and the eighth to be expended on the second flight.

CRS-15 by Spacex
The night launch of the CRS-15 mission to resupply the ISS with a Dragon capsule. Credit: SpaceX

B1045.2 had previously boosted NASA’s TESS towards orbit on April 18th 2018, I wrote about that launch here. With it returning to the autonomous drone ship “Of Course I Still Love You” downrange. For this mission it launched the two stage rocket and powered it for 2 minutes and 51 seconds. With a Dragon 11.2 refurbished spacecraft that was previously used on CRS-9 in July 2016 the main payload for the rocket. The first put the capsule and the second stage into a 227 x 387 km x 51.64 degree orbit. The block 5 second stage burned for about 8 minutes and 31 seconds after liftoff, inserting Dragon into the required orbit. The burn was 36 seconds shorter than previous Block 4 launches as this rocket had higher thrust. Dragon rendezvoused with the ISS on the 2nd of July after an extended coast.

CRS-15 smoke
The great view of the remanence of the CRS-15 launch, taken from the Vehicle Assembly Building at Cape Canaveral. Credit: Marcus Cote.

This launch left a particularly cool looking smoke cloud afterwards. With many Twitter users posting images of the smoke remnants hundreds of miles away. The night launch also allowed for some great photos by many of the keen photographers that are at every launch, capturing many of the images in this post. To see more of the awesome rocket launches, I have posted about many, and will continue to do so.

CRS-15 launch
The launch of the CRS-15 mission. You can see the flames from the 9 Merlin-1D engines. Credit: SpaceX

To find similar photos, and to buy reasonably priced prints of some of the above visit www.marcuscotephotography.com

Charon: The Man Who Gave His Wife a Moon

Charon Enhanced
An enhanced colour version of Charon taken by New horizons space probe. It is enhanced to show the differences in surface composition. Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute.

On June 22nd, 1978 James Christy was trying to refine the orbit of Pluto when he noticed something odd about the images. Going straight to Robert Harrington, his supervisor at the U.S. Naval Observatory in Flagstaff, Arizona, together they concluded that they had found what we now know as Pluto’s largest moon Charon. Discovered just 6 miles away from where pluto itself was found (Lowell Observatory), discovering Charon began a journey from Pluto being a dot on a telescope to its own planetary system. With some amazing images coming from a probe NASA sent there, we have a glimpse of the edge of our solar system. The best part of the story, Charon is named after Christy’s wife.

40 years after christy
40 years on, Christy shows the images he used to discover Charon, and now one of the New Horizons images is his PC wallpaper. Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute/Art Howard/GHSPi

In 1930, Clyde Tombaugh discovered Pluto, and although famous in itself, there was limited study on this dot in the far reaches of the solar system. So on the fateful day James Christy asked his supervisor Bob Harrington for something to do, Harrington pulled some telescope plates of Pluto from the Naval Observatory at Flagstaff to look over. Christy looked over them for some time under a microscope and noticed some inconsistencies with the images, with the asymmetry being different between them. In simple terms he noticed a bump on the side of Pluto that seemed to move over time. Although at first he thought he might be seeing things, when he took it to Harrington he agreed with the findings.

Jim Christy points
Jim Christy pointing to the photographic plate that he used to discover that Pluto has a moon. Credit: U.S. Naval Observatory

When  looking at other images of Pluto, the bump was constantly moving from one side to the other. Further examination showed the bump moved around Pluto at the same own rotational period, 6.39 days. There were two potential theories as to what it was, either Pluto had a mountain thousands of miles high (meaning Pluto was not very spherical) or it has a satellite in synchronous orbit. In the 48 years since Pluto’s discovery at Lovell Observatory in 1930, there had never been any evidence spotted that Pluto had a moon. The next steps included scouring the archives for more cases of an elongated looking Pluto.

The Charon images
The discovery at the US Naval Observatory, Flagstaff was seen as a time varying bulge on the image of Pluto. This is a negative version of the one Christy looked at. Credit: US Naval Observatory.

Christy measured the angle from the north where the strange elongation was. At the same time Robert Harrington calculated what the answer would be if the elongation was from a satellite. They then compared their results, and they were the same. To be sure they waited for the Observatories 61 inch telescope to make a final confirmation on the matter. On the 2nd of July 1978 new images showed an elongation exactly where they expected it to be. Five days later they announced the discovery to the world. Pluto’s first satellite had been discovered.

40 years difference
The difference of 40 years, top left is one of the images Christy used to discover Cahron, the big image is from New Horizons flyby. Credit: U.S. Naval Observatory; NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute

By astronomical tradition, the discoverer of an object gets the first chance to suggest a name for the object. The name does not have to be recognised by the International Astronomers Union. Christy wanted to name the moon after his wife, Charlene. To make it sound more scientific he took his nickname for her “Char” and added an “on”. The “on” was from his interest in atoms, and words like proton and neutron. He suggested the name on the June 24th, 1978. Colleagues at the observatory prefered the name Persephone, but Christy noticed that Charon was actually a real Greek mythological figure. Charon is the ferryman of the dead, associated with the god Hades. Creepily the Romans identified Hades with their god Pluto. The name was eventually adopted on January the 3rd 1986.

The greek Charon
The name Charon was partially adopted because it is the name of the ferrymen of the dead in greek mythology. this is a nineteenth century painting by Alexander Litovchenko

Charon is the largest moon of Pluto, and is about the size of Texas. It also makes Charon the largest moon relative to its parent planet at about 12% of the size. So big in fact that Charon and Pluto are seen as a double planet or binary planets. They have a common centre of gravity that is outside of either of them. It is believed that it was formed by some sort of giant impact, much like the Earth and the Moon. The sheer size and proximity to Pluto meant it was a good choice for a scientific mission to take a closer look at the system. The mission, New Horizons was launched in 2006, with a  primary mission to performa flyby study of the Pluto system.

New Horizons Artist
An artistic impression of what New Horizons looked like when it passed Pluto and Charon. Credit: NASA Goddard Media Studios.

Passing about 18,000 miles (29,000 km) away from Charon on the 24th of July 2015, New Horizons gave the world a brand new stunning view of the moon from up close. At its closest point it was 7,800 miles (12,500 km) from Pluto, mapping both the planet and the moon using its long range imaging cameras. It mapped them to a resolution of 25 mi (40 km). The way they entered the system and the speed they were going allowed them to map all sides of both bodies. They took multiple images with the close range camera to find any surface changes. They also characterised the atmosphere, using the on board ALICE experiment.

Best Charon Images
A mosaic of the best images taken by New Horizons of Charon, from a few different angles. Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute

The science gained by New Horizons has given astronomers a new look into the outer reaches of the solar system, and it is still planning to take more images of comets and asteroids it comes into contact with in 2019. The first close up images of Charon were revealed  to the world at the John Hopkins Applied Physics Lab in Maryland to a packet auditorium. Jim Christy, the discoverer of Charon and his wife who it was named after were there at the unveiling, were recognized by the crowd. He said “When you go from this little blur in which you don’t actually see anything, to the enormous detail New Horizons sent back,” Christy said, “it’s incredible.” That amount of change in just 40 years.