Why You Should Care About Quantum Key Distribution

We live in an ever changing world, and on the horizon is the era of quantum. We all hear about quantum computers, and how some may or may not have hit quantum supremacy, but one of the lesser known impacts of the advent of quantum computing is the impact it will have on encryption. In this day and age, encryption is used everywhere, and it is highly important. From protecting the messages to your friends on WhatsApp to keeping your credit car details safe when buying online, encryption keeps data safe by cleverly encoding it using secret keys that only the sender and receiver can decode… Or at lease that is the current working assumption.

For a moment think about how much data is out there. We are far away from the days where websites had a single static page and an email address. The internet of things is creating sensors that monitor our every moment, companies like Amazon are amassing our buying habits over generations, and almost all banking in the modern world is conducted online. Data is everywhere, and it is worth money, hence the need for solid encryption technologies. There are many working on what those technologies will one day look like, and to many, quantum key distribution (QKD) could be the answer to all of our problems.

Why is Current Encryption Tech Not Good Enough?

Encryption is split into two types, symmetric and asymmetric.

Starting with the simpler one, symmetric key encryption uses the same “secret” key for encryption and decryption. So you encrypt the data using your “secret” key, and give the encrypted data and the key to the person you want to read it. This is good if you are happy to literally take the data to person by hand on a memory stick, but how do you send the “secret” key secretly over the internet? It also has the problem that you are giving away your key, so your next message to a different person will need a different key. With a large user base, this becomes very difficult to manage. Asymmetric or “public” key encryption uses a different key for encryption and decryption. Every user in the network will have a “public” key and a “private” key associated with them. If you want to know more about the modern form of encryption, look into RSA.

This “public” key system is the bedrock to modern encryption algorithms. This is then added with the complexity of dealing with factors of very large prime numbers. When you multiply two large numbers together, you get a very large number that you can use for your key. The only reasons that computers struggle to beat the system is that modern computers cannot deal with these huge prime numbers effectively, and the process is too slow to be useful for malicious intent. The problem comes when we bring in quantum computing. There is a famous algorithm known as Shor’s algorithm that was developed in 1994, but would need a functioning quantum computer to be able to complete. If it ever works then it could in theory crack any encrypted data that uses these prime numbers as keys. So our banking data, all our messages and everything we currently use could be seen by anyone with a quantum computer. What all this means to us is that we need a fundamentally different way of encrypting data, or at least the way we generate and share keys.

Researchers at the National University of Singapore work on a QKD light source for a satellite (Source: NUS)

Why is QKD any better?

Quantum physics is basically the way we describe the way matter and energy interact at the sub-atomic level. This is a follow on to classical physics which describes things like why the apple hit Newton on the head, and we we don’t sink in a swimming pool.

I could go into detail at this point about all the different nuances about the differences between quantum and classical physics, but most of it doesn’t really impact on QKD, as all we really care about are photons, the carrier of light. All we need to know about photons are that the have a direction, and a polarisation. The direction bit is fairly self explanatory, but polarisation needs a quick explanation. Photons oscillate (go up and down like a wave) at a certain frequency depending on the energy, for this we don’t really care about the frequency, but imagine what that looks like if it was going slowly. It only oscillates in one plane, so if it was to go through a slit, it would have to be at the same angle as the direction the light was oscillating in to actually pass through it. This is actually how sun glasses work, it only lets through light of a certain polarisation, so only some of it is let through.

The creepy thing about this polarised light is what quantum physics tell us about the polarisation. You can only know what polarisation it is by measuring it, which might seem like a stupid thing to say, but its a key part of quantum physics. Until that photon is measured it has an unknown state, so it can be seen as having every state. This is the part of the QKD technology that makes it work. Imagine if you sent a series of photons with binary bits encoded in the polarisation of the photons, so each photon is at a different angle depending on the bit it represents. The person reading the photons would measure the polarisation, which means that they now have a known state, i.e it has been chosen. The key is that if somebody tried to intercept the photon, and then resend what they read, the photon that was resent cannot be exactly the same so there will be a mismatch between the data sent by the sender, and received by the receiver. If they compared a small portion of the data over insecure channels, they would realise that the data sent is corrupted and start again.

Now imagine if that was a “secret” key. It would mean that there is a way to guarantee that the key you have sent was not corrupted or intercepted by anyone, and it was safe between the people communicating. On top of that, you don’t have the problem with prime numbers and quantum computers defeating it. In fact it may be a way that quantum computers (especially the optical ones) communicate within themselves, and with others, as they utilise this phenomenon as well to function.

That is QKD in a nutshell, and why it could the thing that changes encryption, something we all rely on every day, for the better. For further reading, look up the first ever QKD protocol, named BB84, it explains how QKD started to be implemented in the real world.

Wartime RAF Harwell

As we found out about how RAF Harwell was created in a previous post, it was taken over by the RAF between the 2nd and 12th of February 1937. The first aircraft flown in that April were Hawker Audaxes of No. 226 Squadron, in from Upper Heyford. They were quickly followed by Hawker Hinds of No. 105 Squadron from Old Sarum in Wiltshire. These were all biplanes with open cockpits, the pilots wearing leather flying helmets with huge goggles, maybe even a trademark scarf and bomber jacket to go with it. Just imagine that scene in Blackadder when Baldrick is hanging out the back of the plane. That was until later that year when No. 105 (B) and No. 107 (B) Squadrons brought in the brand new monoplanes. The planes introduced were the Fairey Battle and the Bristol Blenheim. The first Fairey Battle arrived in august, with both the squadrons fully equipped by October 1937.

On the 9th of May 1938, His Majesty King George VI and Air Chief Marshal Sir Edgar Ludelow Hewitt visited Harwell as part of a tour of four airfields. They were visiting one airfield for each of the major commands, fighter, bomber, coastal, and training. At this point in time RAF Harwell was still a bomber station, so was visited as such. The tour itself was brief at only 50 minutes, with the king inspecting a line of bombers, most of which were flown in for the occasion. He also visited the aircraft hangars, stores, dining halls and armament sections. Finishing up in North drive to inspect the married officers quarters, allegedly some of the best in the country. He was then whisked off to RAF Upton. During the short time, the A34 which goes right by the site was lined with waving crowds. Just one week later, on the 16th of May the bomb stores began loading the eventual 240 tons of bombs, shells and bullets supplied from the depot at Altrincham. This is the same bomb stores that was at the end of the runway, meaning there were a few close run ins with pilots that didn’t gain enough speed to take off. When the site became an Operational Training Unit (OTU) in 1939 the king made a second visit to inspect the No. 15 OTU.

King visiting Harwell
An image from when the his Majesty, Marshall of the RAF, King George VI on the 9th of May 1938. Credit: RAF, National Archives.

On the 10th of June 1938, four German officers visited the airfield by arrangement with the Air Ministry, with the German Air Attache (an Air Force officer who is part of a diplomatic mission) visiting a year later in June 39. They were likely looking for weaknesses in the airfields designs. On Empire Day 1939 (24th May) RAF Harwell held a public open day, inviting 11,000 visitors to come and see what the airfield looked like. There were reportedly many coaches of ‘charbancs’ from around the UK. There were also an unknown number of guests from Europe, of which there were likely a few German spies. They easily visited due to the reduced security for an open day. There were obviously many areas on the site fenced off the the public for safety and secrecy. There was one notable visit later on, by King Haakon of Norway. During the visit a display display was put on, three Avro Ansons flew in formation. Unfortunately two of them collided at low altitude, with one of the pilots parachutes failing to open in time. He died, with his plane crashing near Hendred Wood.

Hawker Hurricane, Likely at Harwell.
A Hawker Hurricane II held down, likely at Harwell. Taken in 1940. Credit: Paul Nash, the Tate.

This accident showed that flying was still a dangerous job, and the most dangerous flying (outside battles) was at nighttime. The landing strips were marked out at night by “goose necked flares” which looked a bit like a watering can or oil lamp. They burnt paraffin, with a big wick sticking out of the spout. The danger with them that was when the wind changed the flame could warm the chamber, potentially ending in an explosion. The ground of the airfield was well suited for its job as it had very deep ground water, meaning it was very unlikely to flood. That being said, anyone living in the area knows the ground is full of clay at the surface, and the famous chalk ridges to the south reach the site. This means when it all mixes together it gave everything a sticky white coating. Planes, cars and boots were all affected. In 1940 all this was over though, with the McAlpine company being contracted to build three concrete runways. It used stone from a quarry just up the road in Sutton Courtney, which afterwards became a water treatment plant, and is now a lake (bounded by Churchmere Rd and All Saints Ln). As well as this, the old paraffin lamps were replaced with electric runway lights, that would still be uncovered up to 50 years later. these lamps were built to last, with some still working half a century later after being buried!

goose necked flare
Goose-neck runway light from Tiree Airport. Similar flares would have been used at Harwell. Credit: an iodhlann

The winter of 1940 was known as a particularly cold one. Before planes could land, men with shovels would have to go out to move the snow out of the way. At the start of the war, the Fairey Battles left for France, with Wellington bombers taking their place. The first attack of the site was in February 1940 by Heinkel bomber, with their pale grey bodies,and black crosses on their side. Later that year on the evening of the 16th of August two bombers were refueled by the mound at the rear of hanger 7. A lone German plane came via Rowstock (NE of site), dropping 4 bombs and strafing first street. Both aircraft were destroyed, along with another nearby, with two men killed. One of the airmen died trying to pull a burning bowser (type of storage tank on wheels) away from the storage tanks. A bullet did get into the ventilation pipe but did not catch the main fuel tanks on fire. There was another raid that night at midnight, then another three days later. The 26th of August raid was the most serious, with four bombs being dropped on the bomb dump, with 6 civilian men dying while building a wall. In August 1942 a single aircraft managed to drop 7 large bombs on the airfield, with four failing to explode. It was at night, with some pilots thinking they saw a cat in a shower of sparks running between hangar 9 and 10. It was actually a 500 kg bomb! These bombs were made safe, emptied, painted white and mounted on the wall of the CO’s office in B77. After the war the scientists buried them in the bomb dump, and were found 50 years later in 2002.

storage tanks
The storage tanks at the rear of hangar 7. Credit: RAF, National Archives.

There was plenty of defense against attacks, with an important part being the air raid shelters littered around site. Land surveys in 2003 in SW corner of campus revealed four underground air-raid shelters. There are also lots of concrete tunnels connecting buildings around the site. Most of these tunnels are long forgotten, and most were not on any maps or plans even at the time for security reasons. Subterranean tunnels linked B150 with B151 and many air raid shelters came to light in surveying by UKAEA in the late 1990’s. The cellar underneath ‘B’ mess (B173) was also serviced by a tunnel that emerged via vertical steel steps into shrubbery 15 m away. This was apparently still accessible in 2005. Other similar structures and tunnels were constructed with half inch thick steel blast doors.

RAF Harwell Pill Box
A pill box just outside the Curie entrance of what is now Harwell Campus. Credit: Steve Carvel
pill box in the snow
The same pill box as above, but in the snow.

During an air raid in 1943 a German Junkers 88 bomber got into trouble and dropped its bombs over countryside between Upton and the A417 to Rowstock. They landed on the airfield and the two crew were captured as prisoners of war. Interestingly, when released a few years later they actually stayed in England and worked for the Thames water board. The last attack was in 1944 by a ‘doodlebug’ flying bomb, and it destroyed three aircraft. The war ended on the 2nd of September, and just a couple of months later there was a visit by JD Cockroft of DSIR, the Department of Scientific and Industrial Research. This was a very special reconnaissance mission, and was the start of the end of RAF’s occupancy of Harwell. Cockroft got a “somewhat frosty reception” by all accounts, but it made sense when you looked at the military secrets held at RAF Harwell, a heritage that was seen as useful to DSIR. This was the beginning of the age of Harwell being at the heart of Atomic research, but that is for another post.

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

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Red Star: The Soviets can Capture Enemy Planes Too


Read any book about the United States Air Force during the cold war and you will probably find a section about the secret fleet of soviet fighter jets that they kept, tested and stole technology from. The less known part is that the Soviets also captured US planes during conflicts, although it seems like less overall. This is the story of the F5 that ended up deep in Russia.


It wasn’t actually the Russians that captured the plane in the first place, it was the Vietnamese. At the end of the Vietnam war, there were many captured parts of american military equipment in different forms. Vietnam, a famously communist country gave several samples of captured US aviation equipment to the USSR, among it was a F-5E light fighter bomber. Overall 27 were captured during the war, along with 87 F-5A’s. Overall 877 aircraft were captured. The Vietnamese actually plan to bring some back into service. The particular F-5E had serial number 73-00807, and was an extremely valuable intelligence coup that had the ability to tell the communists about American design, and how this form of mass produced plane could function. Therefore how they could design planes to counter it.


The plane was sent to the VVS airbase in Chkalovsky before being transferred to the Akhtubinsk air base not long after. Engineers and research staff from the Aeronautical research institute were formed as a test team to investigate the American fighter jet and test its abilities. Overall they were impressed with the design of the jet, and admired the ease of maintenance on the F-5E while they operated it. They were also impressed with the wing design, as t gave the jet an impressive flying ability at high angles of attack and minimum speeds. The F-5E was known officially as the Tiger II. From the end of July 1976 to May 1977, a full scale test flight was conducted at the Air Force Research Institute. A.S.Byezhyevets and V.N. Kondaurov, both decorated Heroes of the Soviet Union, were the pilots in charge of the test flight.

test report of the USSR F-5E

They were surprised with the results, the F-5E was much more maneuverable than most Soviet aircraft, especially then the MiG-21, which was the highly capable soviet dog fighter of the time. It even showed some advantages over the MiG-23, the most advanced Russian fighter of the time. That being said, it was noted that the F-5E did have a disadvantage when it came to vertical maneuverability and energy when compared to the MiG-23. It also had a lacking arsenal, with nothing beyond visual range medium-range missiles, which the MiG-23 could hold. The Central Aerohydrodynamic Institute (TsAGI) in Moscow were in charge of static tests of the aircraft, with the results exhaustively recorded. It is interesting when you look at planes such as the T-8 and the T-10, as you can see some design features obviously lifted from the F-5E. Eventually it was moved in the 1990’s, or at least the nose was, to a display area known as Hangar 1, which is now virtually impossible for any outsiders to visit.

The USSR F-5E on display with descriptions around it

Thank you for reading, take a look at my other posts if you are interested in space, electronics, physics 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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What is an Atom Chip

Atom chip by RAL Space
Cold atom chip as a source for atom interferometer​. Credit: RAL Space, STFC, UKRI

If you follow physics or science news, you will know that a huge part of current physics research is in the field of particle physics. Scientists aim to understand and harness the power of atoms. In laboratories across the world, scientists have been using silicon circuitry to sense the effects of their experiments, with huge silicon detectors being commonplace. You will also find silicon circuitry in the driving circuits of things like magnets and lasers, but these instruments are usually large, as it only needs to fit in a lab. There is no need to minimise. There is also an upcoming exciting area of physics that uses all of these techniques to truly harness the power of the atom known as Cold Atoms. The world of cold atoms uses the concept of trapping small amounts of atoms in a very small area, and super cooling them very close to absolute zero. At this temperature the quantum effects of the atom take over, and can be observed and maybe even harnessed.

 Atom Chip
A close up of an atom chip by The Atom Chip Lab at Ben-Gurion University

This is where Atom chips come in. They are not the only way to practice cold atoms by any means, but it is becoming a popular method to practice the art. The popularity is down to how small the overall circuit is, and the lower amounts of instrumentation needed to drive it. That being said, they are also more temperamental, and much more sensitive to things like noise. The way to trap atoms in an area is to use electric, magnetic and optical fields, all these things have control of the location and activity of the atoms. Atom chips use these three fields to confine, control and manipulate the cold atoms. If you imagine a normal Integrated Circuit (IC), the electrons move through the surface, through things like transistors, capacitors and resistors. In Atom chips the atoms are trapped above the surface, and using forces that we can control, we manipulate their motion, and internal state. The electric, magnetic and optical fields come from small structures on the chip, sometimes protruding out.

Atom chip at Vienna University of Technology
Another example of an atom chip at TU Wien. Credit: Vienna University of Technology

The area that the atoms are held in is often around 1 micrometer squared, and the amount of atoms is around 10,000. This is a surprisingly small amount when you think about it, that’s the amount of students you would find at most universities. The atoms are held at a few hundred nano Kelvin, and due to their design are often well isolated from the warm solid state environment around it. This allows their quantum state to remain undisturbed for tens or even hundreds of seconds. This is partly the basis of modern Atomic clocks. In fact the atoms used are usually the same, strontium or cesium. When you see images of modern atomic clocks, there usually is some sort of atom chip controlling the cold atom cloud directly. This is down to the ease of both reducing the size and complexity of the clocks without impacting the resolution of the clock circuit itself.

Cold Atoms Lab ISS
An artists impression of the Cold Atoms Lab on the International Space Station. Using techniques similar to the ones mentioned here. Credit: NASA/JPL-Caltech

The basis of the trapping part of the circuit uses something known as a magnetic trap (sometimes known as a micro trap). Imagine a wire, for the moment we will imagine it it straight. When a current is induced through it a magnetic field is created around it, a bit like a tube moving round the wire at a certain distance. This is the red line on the diagram below. As you learnt in physics class, the intensity of that magnetic field is directly proportional to the current running through the wire. Control the current then we control the magnetic field. In a magnetic trap there is also another magnetic field induced across the entire experiment, that we can assume is constant and uniform. This is represented by the green line, and is called B. Although there is only one green line, The magnetic field ie everywhere, but the green line is the bit we really care about. Now it took me a while to visualise this, but these two magnetic fields interact, and add up. So if the wire magnetic field is travelling the same way as the field B at any point then the magnetic field gets stronger, if the magnetic field oppose then the field will get weaker at that point. This means there is a magnetic gradient across the entire experiment.

The point we care about is where the magnetic field is zero, meaning the wires magnetic field is equal to, and opposing the field B. As the magnetic field from the wire gets less as it gets further away from the wire, there is a point at a certain radius (R on the diagram) away from the wire where this is the case. The atoms used want to be in the lowest energy state, and are trying to get away from the magnetic field, so it will “seek out” the point with the minimum magnetic field. in this case, the point R distance away from the wire. The wire now has a single line of trapped atoms R distance away from it. Now imagine that wire is bent into a circle with a radius of R. All those atoms are no longer trapped in a line, but now at a single point in the center of the wire. In practice to get the required magnetic field strength it will be a coil rather than a single wire, but the concept is the same. You now have a collection of atoms trapped in a small area defined by you, to do an experiment. Most of the time the atoms are then super cooled with lasers, or trapped and compressed further. This allows experiments with Bose Einstein Condensates, and potential to make quantum “qbits” for quantum computers, but that is a post for another day.

Thank you for reading, take a look at my other posts if you are interested in space, electronics, physics 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 Difference Between Bolts vs. Screws

It is almost an age old question, and by many out there these two words are almost interchangeable. Ask one engineer and they will give you an answer, ask another you will likely get a slightly different answer. Over the last few hundred years engineers have developed fasteners, sometimes for very specific applications, so the line can sometimes become blurred. Some fasteners can only be defined when it has been put into an assembly, being dependent on the design. There are a few standards out there that make an effort to define this, with varying degrees of vagueness, but I am going to try and make sense of it in this post and give you a few examples to make it more obvious. So lets put a few definitions into the mix. The definition I think is the best I can find is from the Specification for Identification of Bolts and Screws, ANSI-ASME B18.2.1 1981. This document has been superseded a few times but the changes have been to add many more extra definitions rather than change this one. Their definition is:


A bolt is an externally threaded fastener designed for insertion through the holes in assembled parts, and is normally intended to be tightened or released by torquing a nut.


A screw is an externally threaded fastener capable of being inserted into holes in assembled parts, of mating with a preformed internal thread or forming its own thread, and of being tightened or released by torquing the head.

I like these definitions as they put it in super simple terms that you can get your head around. Think of how you can tighten the fastener, if you have to use the head then it much be a screw, if you have a nut on the other end it mush be a bolt. From there it gets a bit more complicated, as you can also often tighten a bolt by the head as well, but the point is that you can use either, whereas a screw can only be tightened or loosened by turning the head. The other key point is that a bolt should not be tapping its own thread in the part it fastens to. A screw doesn’t have to form its own thread in the material, but if it does it can only be a screw. Basically if it is pointy it is likely to be a screw, if it is flat ended it is more likely a bolt (but not always true as we will see. There is also one other way to loosely define a bolt and that is the way it drives. A screw drives from the center (like an Alan head or flat head screw) but a bolt tends to need to be fastened with a wrench, so away from the center. Some companies like Accu group use this as a definition but it is not defined in most standards I have read, but still a good rule of thumb. Now lets look at a few examples to get a better idea:

Bolts That Cannot be Unfastened by the Head

A definite subset of bolts, the round head, oval head and plow bolt have not way to be undone via the head. The round head and oval head both protrude above the surface, but are completely smooth and rounded on the edges, so there is no surface for a wrench to lever against, so they have to be fasted by a nut on the other end. These bolts usually have a non circular area near the head to stop it from turning when the nut is being attached.

Externally threaded fasteners with a head that cannot be used to fasten it in place is a bolt. Credit (1)

Screws That Cannot Use a Nut

The classic screw is something that we are all familiar with, with it tapering to a point, often with a straight thread with multiple pitch length, and cannot use a nut. The tapering prohibits the use of adding a nut, this describes a classic wood screw. Other screws such as tapping and grub screws with points or shanks are also definitely screws by the fact they often make their own thread and have a point in the end to make some sort of non screwed connection with another part.

An externally threaded fastener that which has a thread that cannot be used with a nut is a screw. Credit: (1)

Bolts That Need a Nut to Function

Some bolts such as a hex structural bolt that have a shaft the same diameter as the thread (no shoulder) and therefore go through a part and needs to be attached into a nut on the other side to be fastened. The bolt has a smooth shaft near the head which cannot be fastened on its own, therefore needing a nut. By the fact it needs a nut it has to be a bolt. Most classic bolts often need a nut to work in an assembly, and it is the best way to recognise a bolt over a screw.

A hex Structural bolt is a great example of a bolt that needs a nut to function as the lack of thread near the head cannot be used to fasten. Credit: (1)

Screws That Look Like Bolts

This is where things can get a bit iffy, fasteners that on the face of it look like bolts but act a bit more like screws. Set screws for instance are a screw as they never use a nut, and they are usually used to secure an object within or against another object. Things like attaching a gear or pulley to a shaft is a common example. The other is a shoulder screw which looks much like a normal bolt but is different by the fact that the non-threaded shaft is bigger than the threads, hence the shoulder. The threaded part does not tend to be screwed into a nut, leading to the definition of it being a screw rather than a bolt. They tend to be used as a shaft for rotating things like pulleys or gears.


  1. Distinguishing Bolts from Screws – U.S. Customs and Border Protection – July 2012
  2. I you can get access – Specification for Identification of Bolts and Screws, ANSI – ASME B18.2.1 1981
  3. If you can get access – Square, Hex, Heavy Hex, and Askew Head Bolts and Hex, Heavy Hex, Hex Flange, Lobed Head, and Lag Screws (Inch Series), ANSI – ASME B18.2.1 2012
  4. For interesting reading about a court case about this: Rocknel Fastener, Inc. v. United States, 24 C.I.T. 900, 118 F.Supp. 2d 1238 (Ct. Int’l. Trade 2000)

LM3909 – An IC Just to Flash an LED

So during my placement year I was getting really into old electronics, and old IC’s, especially those no longer in production. We were also on a project where we were trying to design a circuit that would flash an LED for a short period of time from the charge on a small super capacitor. The big issue we had was how to minimise current flow, and power an LED at really low voltages, less than 2V. This on the face of it seems like a simple problem, until you start to think about it.

Million Mile Light
Products like the Million Mile Light, a flashing low powered, high brightness LED indicator need to flash for long periods of time on very little charge, much like the problem I faced. Credit: Million Mile Light

There are two go to ways that most engineers would go with to make a flashing LED with a constant flash rate. First is to use a small microcontroller, such as an ATTiny, or a Pic12F series, and use software to flash the LED. This seems good on the surface (and it is what we used in the end product) but it has a big drawback, it can only output a voltage less than the power rail. some versions of the PIC12LF’s can function down to 1.8V, perfect for our power supply needs, but LED’s need upwards of 2.7V (usually) before they start to light, so although our micro will work the LED wont. The second go to way to make an LED flash would be to use the classic 555 timer, one of the most manufactured chips of all time. There is a good reason it is famous, it is extremely versatile. You can decide the frequency based purely on the capacitor and resistor choices. We still have a similar drawback though, a 555 timer needs at least 4.5v as a power supply. So with our potential sub 2V power supply, neither the IC or the LED will turn on. That is one way to conserve energy!

A cut out from the datasheet, with a basic view of the circuit inside the IC, which I will go through in another post, and a pinout diagram, very useful for prototyping. Credit: National Semiconductor.

This is where the LM3909 came in to play. You have to remember that this chip was developed prior to 1995 (so it is older than me) when the electronics market was very different. Battery technology was not the same, and nowhere near as cheap. It was much more common for people to want to use off the shelf single use batteries such as AA, C and D batteries, or even coin cells in most projects. If you wanted something with a little flashing light on it there were plenty of applications for it. There are buoys in the ocean, store signs and displays, and Christmas lights, all of which would benefit from minimising weight of batteries, but lasting for serious amounts of time. Just as a reference, you could get to 4.5V (to power a 555) by using 3 AA batteries, but the voltage across them would soon dip below this, so you would need at least 4 in most applications. 4 AA batteries take up a lot of space, and weight, not great for many of these applications. Plus most of the chips we have discussed use a fair amount of power, the 555 uses at least 3mA while running, not including the dissipation in the resistors, and all of the power charging the capacitor wasted.

1.5v schematic
A snippet of the datasheet, showing the simplest connection diagram, and a graph of typical current consumption with relation to the battery voltage. It also has a great table describing how long standard batteries tend to last in this configuration, up to 2 years! Credit: National Semiconductor.

So how does the LM3909 solve these issues? well it makes use of a clever concept similar to the 555 of charging up a capacitor. The difference is that the 3909 uses that charge in the capacitor to flash the LED. Although it is slightly more complex than the below schematic, you can think of it as there being a switch inside that oscillates between two states. We will go through how it actually works in a future post. To start with the capacitor is in series with the battery, and in parallel with the LED. The LED wont light, but the capacitor charges up to near the power supply voltage. Once charged, the switch inside flips, and now the power supply, charged capacitor, and LED are in series with each other. To the LED it now sees the capacitor (charged to 1.5V) plus the 1.5V power supply, equivilent to 3V, more than the forward voltage it needs to turn on. As there is a very small resistance, the LED will be on as long as the capacitor has some charge, which isn’t very long as it will discharge fairly quickly. This is the “flash”, as once the cap is discharged the LED will turn off, and the switch will flip back. The capacitor starts charging again, and the whole process restarts. This goes on for as long as the battery has power to give.

Rob Paisley
A great description of the basic principle of how the LM3909 works, charging the capacitor up, and then releasing all that energy through the LED, with increased voltage. Credit: Rob Paisley.

A couple of points to note, the timing and the brightness of the flashing is based upon the capacitor you use, which is quite clever. There are two settings, depending in the pin you put the capacitor in will also double (or halve) the time the cap will take to charge. This means slower flashing, but longer lifetime. Having a smaller capacitor will mean faster, but less bright flashing, and a bigger cap will therefore be slower and much brighter flashing. The design of the chip also means that only two external components are needed for it to work, a capacitor and the LED, compared to the many resistors and extra cap needed on things like a 555 timer. The fact it can use less than 1.5V power source means we can use a single AA battery to power this device, and according to the data sheet it can last up to 6 months on one battery! I have one on my desk that has lasted longer than this.

my LM3909 circuit
My version of this circuit fit into a AA battery box, with it being powered by a single AA battery. It has a switch meaning I can turn it on and off. Poundland LED lights are a good source of these!

All in all I can see why National Semiconductor decided to make this chip, it filled a gap, and was used widely for a long time. Developments in battery technology, and more complex designs needed for the applications this was for has meant that they no longer make the LM3909, but they are still available on Ebay and some Chinese manufactures make them. There is also a design out there to make a discrete version of the LM3909, and I may try that for a future post, as it looks interesting.

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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Delta 4 Medium Makes Penultimate Launch

John Kraus photos
A great image taken by John Kraus of the Delta 4’s main booster and four smaller boosters, and the awesome power they produce. Visit his patreon to find more! Credit: John Kraus

Just after midnight, 00:23 UTC on March 16th 2019, a Delta 4 medium rocket placed a US military network relay satellite into orbit. Launching from Space Launch Complex 37B at Cape Canaveral AFB in Florida, the 66 meter tall Delta 4 is nearing retirement, with this being its second to last launch. After several technical issues, the ground teams eventually got the rocket and the satellite tracking network functioning correctly. The hydrogen fueled RS-68A main engine ignited moments before liftoff for 5 seconds before the hold down bolts released at T-0, firing away with 1.8 million pounds of thrust. This mission has extended ULA’s streak of successful missions to 133 since its inception in 2006.

Marcus Cote
Maybe the photo of the night by Marcus Cote, showing the huge exhaust plume created by the Delta 4 in 5, 4 configuration. Credit: Marcus Cote
marcus cote
A great time lapse of the Delta 4 launching WGS10 satellite into a geostationary orbit. Credit: Marcus Cote.

The rocket veered towards an easterly direction over the Atlantic Ocean, aiming to place the communications satellite to its final operating position 36,000 km (22,000 miles) above the equator in geostationary orbit. The solid rocket boosters burned out and were jettisoned in pairs roughly 1 minute and 40 seconds into flight. The main engine continued to fly on until 4 minutes in when the first stage was cut off, and then released shortly after. The first stage then fell back to Earth into the Atlantic Ocean. The upper stage was powered by a RL10B-2 engine, made by Aerojet Rocketdyne, the same manufacturers of the main engine. The upper stage engine ignited twice to push the satellite into an elliptical transfer orbit. The satellite separated from the second stage at T+36 minutes 50 seconds.

An image showing the scary power of the rocket boosters at liftoff, the rocket firing 1.8 million pounds of thrust into the ground trying to escape the Earth. Credit: ULA.

On board was the WGS 10 military communications satellite. It is a 6000kg (13,200 lb) broadband satellite, that is joining nine others that have been slowly placed in orbit since 2007. The idea is to form a globe spanning network that can relay video, data and other useful information between the battlefield and the headquarters, wherever they may be. The WGS fleet transmits both classified and unclassified information, and supports the US and its allies. On board is a digital channelizer that allows the satellite to relay signals using high data-rate X-band and Ka-band frequencies during its 14 year expected life. All of the WGS satellites were launched on ULA rockets, with the first two on Atlas V’s and all the rest on Delta 4’s. This mission had an estimated price tag of $400 million.

Glen Davis
An almost artistic image of the Delta 4 medium launching. Heavily edited, but still capturing that raw power. Credit: Glen Davis

Marking the second to last flight of the Delta 4 Medium variant rocket, it is noticeable as only having a single first stage core, whereas the Delta 4 Heavy has three. ULA are retiring certain areas of their launch family as they plan to debut the new Vulcan booster soon which will apparently be cheaper than their current offering. The decision to halt selling of the Delta 4 medium flight was made in 2014, but this and the next launch were already on the books at that time. The Delta 4 medium is apparently more expensive than the Atlas V launcher, but with a similar launch capability, leading to the reason for retirement. ULA described it as it being cheaper to run a few launchers more frequently than many launchers sporadically. The bigger Delta 4 heavy will continue to launch heavier payloads well into the mid 2020’s. Another reason for keeping the Delta 4 Medium was to allow the US military to have two choices to launch their payloads, that and the Atlas V. Now that the Falcon 9 is cleared to fly military satellites there is less need for the Delta variant.

marcus cote
The Delta 4 sitting on the pad, ready to launch the WGS10 satellite. Taken close up by Marcus cote the day before when setting up the remote cameras for the launch. Credit: Marcus Cote.
mike seely
A behind the scenes photo of setting up cameras before the launch. Credit: Mike Seeley.

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 Crew Dragon Flies

Crew Demo landing

This weekend a very important event happened, something many rocket enthusiasts have been waiting for. The first capsule designed to hold commercial crew was launched by SpaceX. A successful launch, the Falcon 9 carrying the first crew Dragon lifted off from pad 39A at the Kennedy Space Centre, Cape Canaveral, FL on the 2nd of March 2019 at 07:49 UTC. This was the first orbital test of the Dragon capsule, and although it was unmanned, it did hold a dummy test astronaut nicknamed Ripley, after the heroine from Alien.

loading the rocket
The modified Falcon 9 being rolled out towards the launch pad on the specially designed trailer. Credit: SpaceX
Crew Dragon
A close up side on view of the Crew Dragon while it it waiting to be loaded. Credit: SpaceX

The capsule was launched on top of the 70m tall Falcon 9 that had minor changes to work with NASA’s strict requirements for commercial crew. Trailing off in a north easterly direction, the Dragon capsule sailed on a 27 hour autonomous route towards the International Space Station. The capsule itself is 16ft tall, and 13ft in diameter, and is designed to be able to hold 7 people in relative comfort (compared to the previous equivalents). This capsule sits on top of a trunk that could contain some cargo on future trips. The capsule is 12ft tall, 12ft in diameter, and coated in solar arrays. The cargo section is not designed to survive a journey back to Earth, with the heat shield and thermal protection system being on the capsule itself.

John Kraus Photos
A great long exposure shot of the Crew Demo launching, taken from Merritt Island. FL. Credit: John Kraus Photography. Click on the photo and buy one of his rocket prints!

The first stage of the Falcon 9 powered through the thick lower atmosphere for about 2 and a half minutes before shutting down and separating. The booster B1051.1 was brand new, performing landing burns on its way back through the atmosphere to come back and land successfully on the autonomous drone ship “Of Course I Still Love You”. The landing was particularly rough with choppy seas out in the Atlantic that day. The booster did not manage to hit right on the X on the pad, but was still stood up when it returned to port Canaveral. This was a big moment as it is now the 35th successful booster recovery. Just a minute after the first stage landed the second stage engine cut-off. A few moments later the Crew Dragon was released from the second stage to begin the 27 hour journey to the ISS.

A landscape view of the launchpad 39A at Cape Canaveral, with the first commercial crew mission on board the Falcon 9. Credit: Marcus Cote Photography. Click the image and go buy one of his prints!

The 400lb capsule glided to an automated docking early on Sunday morning, completing one of the major milestones of the mission. Aided by a laser rangefinder and a thermal camera the Dragon capsule approached the space station and linked with the docking port on the forward end of the complex at 10:51 UTC. This is now the first privately owned human rated spaceship to reach the ISS. The link up happened at over 400km over the northern end of New Zealand during what is known as orbital night time. The capsule first held back at around 60 m from the station, testing radio links. When given the go ahead it then moved towards the ISS at 10cm per second or 0.2mph. The capsule actually arrived 9 minutes ahead of schedule when the latches engaged to create a connection with the International docking adapter.

Crew Dragon
The Crew Dragon moving slowly towards the ISS. Credit: NASA

The station docking adaptor was installed over the old space shuttle docking port, at the forward end of the Harmony module. The arrival marks the first time a visiting spaceship has docked there since the last flight of the shuttle Atlantis in 2011. Once docked 12 hooks closed to forma firm mechanical connection, and then two umbilical lines were attached by robotic arms to allow the stations electrical system to power the Dragon module during the stay. After a number of checks, Saint-Jacques opened the crew Dragons hatch, becoming the first person to board the ship. The crew wore face masks when entering the Dragon, as they would with any other visiting spacecraft, for precaution. Once the capsule was given the all clear the crew removed their masks and unloaded the 100 lb of cargo stowed under the seats. On board the Dragon was a small stuffed toy in the shape of Earth, made by Celestial Buddies. NASA astronaut Anne McClain quickly picked it up and made a video with it. Celestial buddies were unaware that they would have one of their toys would be going on a mission, and they are therefore sold out for now, but they have some great other toys on offer instead.

Crew Dragon
A closer view of the Crew Dragon, just moments bore docking. Credit: NASA
long exposure of the Falcon 9
A 277 second exposure of the Falcon 9 launching from LC-39A, so long that it shows the separation of the first stage. Credit: Mike Seeley.

The Crew Dragon will depart the space station early on Friday at 07:31 UTC, followed by a de-orbit burn at 12:50 UTC. The spacecraft jettisons the unpressurised trunk section, with the solar panels and radiator, what will burn up in the atmosphere. The heat shield on the Crew dragon will then protect it as it comes into the atmosphere from a northwest to southeast direction. Aiming for a splashdown under the four parachutes somewhere in the Atlantic Ocean, east of Cape Canaveral at 13:45 UTC. The next big test for the Crew Dragon will be a launch where the launch escape system is tested. Designed to push the capsule away from the rocket if there is a major failure, that launch will be in late June of 2019 if all goes well. The first crewed mission is planned for July this year.

A great image turned into a poster from the rocket launch, with an emotive quote by Elon Musk. Credit: Erik Kuna.

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 First Launch of a Commercial Lunar Lander

Marcus Cote Photo
A Falcon 9 lights up the sky above the Space Coast for the first time in 2019. Here’s a long exposure from 321 Boat Club in Melbourne, Florida. Credit: @marcuscotephoto

At 01:45 UTC on February the 22nd 2019 an already flown Falcon 9 was the first SpaceX rocket flown from the Cape in 2019. Launching from SLC-40 in Cape Canaveral, FL, the 70 metre high rocket flew three satellites into space. On board was an Indonesian communications satellite, a privately funded Israeli moon lander and an experimental space surveillance satellite for the US Air Force. The Falcon 9 first stage booster successfully landed back on Earth for a third time, landing on the autonomous drone ship “Of Course I Still Love You”.

SpaceX launch
A shot of the Falcon 9 launching from SLC-40 at Cape Canaveral with 3 satellites on board. Credit: SpaceX.

The Israeli moon lander is the first of its kind, attempting to be the first privately funded mission to the Moon. It was also the first to separate from the rocket at 33 minutes after liftoff. Within minutes of separation the spacecraft opened its four landing legs and radioed ground control with a status report. At 585 kg at launch it is not especially heavy for a spacecraft, and not the heaviest on board, but without fuel it would only be 150 kg. It is roughly 2m in diameter and 1.5 m tall with the landing legs extended. It is named Beresheet after the Hebrew title of the biblical book of Genesis. After several orbits of the Earth the spacecraft will begin to slowly raise its orbit with the on board thrusters. The process will take roughly 7 weeks to reach the Moon’s area of gravitational influence. At that point the spacecraft will perform manoeuvres to be captured into a lunar orbit, staying there for between two weeks and a month. When in the correct orbit, it will attempt a soft landing on the surface, aiming at the northern end of Mare Serenitatis. The landing zone is a circle of about 15 km.

SpaceIL co-founders Kfir Damari, Yonatan Winetraub and Yariv Bash insert a time capsule on the Beresheet spacecraft. Credit: SpaceIL
spacex launch
Great view of the 9 engined, 70m rocket launching from the Cape in late February. Credit: SpaceX

The aim of the Moon lander, beyond being the first commercial lander, is to measure the Moon’s local magnetic field to help understand how it formed in the early solar system. To do this it has an on board magnetometer, made by the Weizmann Institute of Science. It also has a laser retroreflector array payload provided by NASA Goddard Space Flight Center. This is a device that will reflect a laser back the direction that it came from. The Apollo astronauts installed a similar device that is still used today to measure the distance the Moon is from Earth at any one time. You do need a very powerful laser to achieve this though. With minimal science instruments the spacecraft is not designed to last long on the surface. It has no thermal control so is expected to quickly overheat when functioning. It therefore has an expected life of just two days after landing on the surface. The craft also has a digital time capsule that contains over 30 million pages of data, including a full copy of the Bible, English-language Wikipedia, many children’s drawings, memories of a Holocaust survivor, Israel’s national anthem, the Israeli flag and a copy of the Israeli Declaration of Independence.

rocket landing
The Falcon 9 rocket’s first stage lands on SpaceX’s drone ship “Of Course I Still Love You.” Credit: SpaceX

Made as a competitor for the Google Lunar X prize, Beresheet is made by SpaceIL. They are a non-profit, and have reportedly produced the mission for less than $100 million, which is extraordinarily cheap for this kind of mission. This is going to be the first private interplanetary mission that’s going to go to the moon,” said Yonatan Winetraub, a co-founder of SpaceIL, which had its origin in a brainstorming meeting in a Tel Aviv bar. “This is a big milestone. This is going to be the first time that it’s not going to be a superpower that’s going to go to the moon. This is a huge step for Israel.

“Until today, three superpowers have soft landed on the moon — the United States, the Soviet Union and recently, China,” . “And (we) thought it’s about time for a change. We want to get little Israel all the way to the moon. This is the purpose of SpaceIL.”

Winetraub, in a news conference
long exposure launch
Long exposure of the launch from across the water. Credit: SpaceX

The Indonesian Nusantara Satu communications satellite was by far the heaviest payload on board at 4,100 kg, deployed 44 minutes into flight. Formerly known as PSN-6, Nusantara Satu is a high throughput satellite that will provide voice and data communications as well as broadband internet throughout the Indonesian archipelago and South East Asia. Built by SSL for PT Pasifik Satelit Nusantara, it was the first private telecommunications company in Indonesia. The cost of the project is estimated at $230 million. The mission uses solar electric ion thrusters to get to the correct orbit, but will employ conventional chemical thrusters to stay in that orbit. It is expected to last at least 15 years.

Nusantara Satu
The Nusantara Satu spacecraft, topped with the Beresheet lunar lander and the U.S. Air Force’s S5 space situational awareness satellite, is pictured before encapsulation inside the Falcon 9 rocket’s payload fairing at Cape Canaveral. Credit: SSL

The other secondary payload on the Falcon 9 was an experimental Air Force satellite intended to test space situational awareness technologies. The flight was brokered by Spaceflight, a Seattle based company that finds rideshare launch services. The S5 satellite was made for the Air Force Research Laboratory (AFRL). Although the mission has had very little information released about it there has been some. Blue Canyon Technologies announced in September 2017 that it won a contract from AFRL to build two small satellites to operate in GEO. One was identified as S5, a 60 kg satellite using a payload provided by Applied Defence Solutions. The illustrations released show an optics system attached to a satellite bus, and a solar array. “The objective of the S5 mission is to measure the feasibility and affordability of developing low cost constellations for routine and frequent updates to the GEO space catalog,” Blue Canyon Technologies said in its statement. The S5 satellite is attached to the Nusantara Satu satellite and will be until it reaches GEO, where it will separate, turn on, and start its mission. This is not dissimilar to Hispasat 30W-6 that also deployed a smallsat after launch last year.

blue canyon S5 smallsat
Blue Canyon Technologies announced in September 2017 it won an AFRL contract to provide the bus for an experimental smallsat called S5 for space surveillance applications. Credit: Blue Canyon Technologies

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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Mars InSight Has Been Busy

insight selfie
This is NASA InSight’s first full selfie on Mars. It displays the lander’s solar panels and deck. On top of the deck are its science instruments, weather sensor booms and UHF antenna. Credit: Nasa/JPL-Caltech.

So I have talked previously about the launch of the latest lander on Mars, named Mars Insight. Launched on the 5th of May 2018 by an Atlas V 401 from Vandenberg AFB, it began its 6 month journey to the red planet. Travelling across 484 million km it landed on 26th of November 2018. It landed much like the Curiosity and Phoenix missions with a parachute decent and then using rockets to lower the lander onto the surface gently. The mass of the lander is about 358 kg, but due to the gravity on Mars being two thirds less it only weighs 134.6 kg on the surface. Just a few hours after touchdown the Mars Odyssey orbiter relayed signals indicating that the solar panels had successfully opened, generating power. The relayed signal also contained a pair of images of the landing site. For the next few weeks InSight checked the health of the on board systems and monitor the weather and temperature of the landing site.

InSights workspace
This mosaic, made of 52 individual images from NASA’s InSight lander, shows the workspace where the spacecraft will eventually set its science instruments. The lavender annotation shows where InSight’s seismometer and heat flow probe can be placed. Credit: NASA/JPL-Caltech

The images relayed were used to find the best area to place the Seismometer instrument. There was then some time for scientists to evaluate the information and pick the best spot to place the sensitive instrument. On the 19th of December Insight used its 8ft robotic arm to pick up the Seismometer from the deck of the lander, and place it on the ground nearby. The position picked was one fairly free of rocks, making the leveling process easier. There was then another set of a few weeks to adjust the cable and ensure the SEIS instrument was perfectly placed. Then the arm picked up a protective cover from the lander to place over the instrument. This is designed to minimise noise from the surrounding atmosphere, being introduced from huge temperature changes and wind vibrations. This will allow the seismometer to pick up the tiny tremors that the planet may have. This is the first time another planet has been studied this way, the only other planetary body being the Moon. Viking 1 and 2 had seismometers on board but design flaws meant the results were inconclusive.

Temperature is one of the biggest issues with a mission like this. On Mars the temperature can range over 90 degrees Celsius in just a single sol (Martian day). The protective cover is ringed with a thermal barrier and a section of chain mail around the bottom. The wind and thermal shield has been specifically designed for the environment to moderate the temperatures. JPL has a history dealing with Mars temperatures from the many missions it has sent there including the Phoenix lander, and the Curiosity rover. The SEIS instrument was provided by the French Space Agency CNES, and developed by the Institut de Physique du Globe de Paris, with JPL building the wind and thermal shield. There is also a great British part of the instrument with some of the silicon sensors designed and fabricated by Imperial College London. The microseismometers were designed to pick up the faintest seismic activity from the surface. Scientists from Oxford’s Department of Physics also supported the development, and the Rutherford Appleton Laboratory’s RAL Space worked closely with the team to develop the front electronics of the instrument as well as the space qualification.

SEIS instrument cutaway
Cutaway illustration showing interior components of SEIS. Credit: NASA/JPL-Caltech/CNES/IPGP
One of the microseismometer sensors, carved from a single piece of silicon 25mm square. Credit: Imperial College/T.Pike.

On the 12th of February the lander deployed the HP3 package onto the surface. Known as the Heat Flow and Physical Properties Package, it was placed about a meter away from the seismometer. The Idea of HP3 is to measure the heat flow through Mars’s subsurface, hopefully helping scientists to figure out how much energy it takes to build a rocky planet like Mars. An interesting instrument, it has a self-hammering spike, or mole, allowing it to burrow up to 5m below the surface. This is much deeper than any previous mission. Viking 1 only scooped down 8.6 inches, and the predecessor of Insight, Phoenix dug to 7 inches. The probe was provided by the German Aerospace Centre (DLR). A tether attached to the top of the mole features heat sensors to measure the temperature of the Martian subsurface. Heat sensors in the mole itself will measure the soils thermal conductivity (how easily the heat moves through the surface). The mole plans to stop every 50 centimetres to take the measurements, as the hammering creates friction, releasing heat that would likely impact the instruments readings. It is then heated up by 28 degrees Celsius over 24 hours, with the temperature sensors measuring how rapidly this happens.

A GIF of the Insight lander placing the instruments on the ground. Credit: NASA/JPL-Caltech

Along with the Insight lander, the launch also contained a new first, a pair of cubesats known as MarCO-1 and MarCO-2. The size of small suitcases the pair were the first cubesats to enter and work in deep space. The team nicknamed the WALL-E and EVE, and they functioned as communications relays during the insight landing, beaming back data from the decent, along with the first image. WALL-E also managed to capture its own great images of Mars as it soared past it. The mission cost was about $18.5 million, much less than most missions, and was designed by JPL as a technology demonstrator mission. Neither is still in contact with Earth, with WALL-E losing contact on the 29th of December 18, and EVA losing contact on the 4th of January 19. JPL says they will attempt to contact the pair again in the future, but it is unlikely. The MarCO satellites will still live on though, with some of the spare parts going towards other cubesat missions, including experimental radios, antennas and propulsion systems. They also pushed the idea of using commercial parts to develop the system.

Engineer Joel Steinkraus uses sunlight to test the solar arrays on one of the Mars Cube One (MarCO) spacecraft at NASA’s Jet Propulsion Laboratory. Credit: NASA/JPL-Caltech
MarCO-B, one of the experimental Mars Cube One (MarCO) CubeSats, took these images as it approached Mars. Credit: NASA/JPL-Caltech

Just as an addition, there is a great comic that can be found here about Mars Insight, by the oatmeal. It is worth a quick read.

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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