The NOR Gate That Got Us To The Moon

Type G micrologic
The Fairchild Type ‘G’ Micrologic gate for the Apollo Guidance Computer – this is the flat pack verison

In a previous post I talked about how the going to the moon kick started the silicon age. If you haven’t read it, it is short but really interesting story about how NASA made Integrated circuits cheap, and partially funded what we now know as Silicon Valley. In this post I am going to take a slightly closer look at the circuit that ran the famous type “G” Micrologic gate that ran the Apollo Guidance Computer.

apollo 3 input NOR gate
The official NASA schematic of the Type G micrologic gate found in the Apollo Guidance Computer

As you can see in the above image, the circuit was not particularly complicated. You have to remember that this is very early logic, before CMOS or NMOS or any other fancy IC technologies. This is basically two 3 input NOR gates, they both run off the same power, with pin 10 at the top, and the negative which was likely ground being shared on pin 5. The output for the left NOR gate is pin 1, and the output for the right is pin 9. The three inputs for the left are pins 4, 2 and 3, with the right having pins 6, 7, and 8 as inputs. Simply put, the output is “pulled” high to power when all the inputs are OFF. The resistor between pin 10 and pin 1 (or 10 and 9) are a simple pull up resistor as you would find in most electronic circuits. As expected with a NOR gate, the output will be only be ON when all the inputs are OFF. When any of the inputs are ON the output of that gate will be pulled to ground. One two, or all the inputs can be on, but it just needs one to turn OFF the output. The resistors going into the base of the transistor are just to limit the current.

3 input NOR
My breadboarded version of the 3 input NOR gate, it is made with BC547 transistors and a DIP switch. the output has been inverted with the LED.

I made a simple recreation of this circuit using BC547 NPN transistors, but most NPN transistors would work, these were ones I found in my parts box. As you can see in the image above, I have made it on a breadboard, with the inputs being a DIP switch attached to the power (5V in this case). The base resistors for the transistors are 1K and the pull-up to 5V is a 10K. I recommend making up this circuit if you want to learn a bit more about logic, and is a cheaper method than going out to buy 74 series logic chips! As you can see in the images there are a number of states that I showed the circuit in, and notice that if any of the switches are on, the circuit turns on, this is slightly against what I mentioned earlier, but thats due to the output LED using the transistor as a current sink, not a source, so the output is inverted. Basically, when the output is 0 the LED turns on. The only time the LED is off (output high) is when no switches are on, meaning all the transistors are off.

apollo 3 input NOR gate
An image of the silicon die inside the Type G 3 input NOR gate. We will be going through how the layout works in a future post.

The final point for this post is why the circuit is actually quite inefficient. Modern logic is amazingly low power compared to this. One of the biggest issues is that it is always taking power in some way. When the inputs are off, there is still some leakage through the pull up resistor, when an input is on, then there is current going through the resistor to ground. Also, by the nature of the transistors there is always parasitic leakages, and inefficiencies in the process. They are only small numbers, but the AGC used over 3000 of these circuits, so the small leakages soon add up to draw some hefty power needs, especially for battery powered operations.

If you enjoyed this post, take a look at the rest of my blog, there is lots about space, electronics and random history. I am always open to ideas and feedback, and where is best to post links to my posts.

VA242: Ariane 5 Launch

VA242 launching
VA242 launching with two satellites aboard weighing almost 10 tonnes. Credit: Arianespace Twitter.

At 21:34 UTC on the 5th of april 2018, an Ariane 5 with ECA vehicle number L5102 launched two communications satellites into orbit. The successful flight launched from Kourou in French Guiana from Pad ELA-3. The mission named VA242 placed Japan’s DSN 1/Superbird 8 and Britain’s Hylas 4 into their planned orbit. VA242 was the 64th Ariane 5 ECA success in 66 flights. Both satellites were placed in a 250 x 35,786 km x 3 deg geosynchronous transfer orbits about 34 minutes after takeoff.

Ariane 5 liftoff
Ariane V L5102 lifts off from Kourou in French Guiana on April 5th. Credit: Arianespace twitter.

The Japanese DSN 1/Superbird 8 is designed to provide X-band communications for the Japanese Ministry of Defence. It will also provide Ku and Ka band commercial services for Sky Perfect JSAT Group from 162 degrees East. The satellite is a NEC Corporation DS2000 series, weighing 5,348kg.

Ariane V launch
VA242 lifts off from pad ELA-3 at 21:34 UTC placing a Japanese and British satellite into Geosynchronous Transfer Orbit. Credit: ArianeSpace Twitter.

The British Hylas 4 was built for British-based Avanti Communications, is designed to provide Ka band communication services to Europe and Africa from 33.5 degrees West. Designed by Orbital ATK it is a GEOStar 3 series weighing 4,050 kg.

Birds flying
Birds flying away as VA242 launches from French Guiana. Credit: Arianespace twitter.

VSS Unity: Virgin Galactic Is Back

VSS unity Flight
VSS Unity during its first test flight. Credit: Virgin Galactic.

On Thursday 5th of April 2018, Virgin Galactic’s SpaceShipTwo conducted its first powered test flight of 2018. With very little in the media from Virgin Galactic recently, this has been a welcome development in the field of space tourism, and the development of space planes. Named the VSS Unity, this space plane is the newest development from the Spaceship Company.

USS Unity engine
USS Unity with an ignited engine rapidly accelerating into the sky. Credit: Virgin Galactic.

Virgin Galactic hasn’t performed a powered test flight since 31st of October 2014 when the VSS Enterprise experienced a catastrophic mid flight failure. The incident in the first of 5 planned SpaceShipTwo aircraft ended with a tragic accident which resulted in the death of one test pilot and serious injury to the other. With the program many years behind schedule, many critics thought this could have been the end for Virgin Galactic. Fortunately, Virgin Galactic have said the fault was not in the hardware, and was a change in safety procedure rather than a design overhaul. Over the last year, Virgin Galactic has made significant progress, leading to this powered test flight.

VSS Unity Gliding
VSS Unity, gliding back to earth after it has burnt all of the fuel, it can see the curvature of the earth. Credit: Virgin Galactic.

An NTSB investigation into the accident concluded that a pilot prematurely deployed the feathering system on the spacecraft. The system is used to increase drag during reentry. Many have criticised Scaled Composites (the manufacturer) and Virgin Galactic for not having fail-safe’s in place to prevent this problem. This is what lead into the review into the safety of the craft. After the loss of the USS Enterprise, and the safety reviews, the USS Unity was not ready until february 2016. This was the first plane to be built in house by The Spaceship Company.

WhiteKnightTwo carrying VSS Unity during the flight test, it will drop the craft at 50,000 ft. Credit: Virgin Galactic.

Up until this point the testing has been more gradual than planned, with captive carry tests, and a total of 6 successful glide tests. There was a dry run rocket test on 4th of August 2017, where water was mounted in place of rocket fuel to simulate the shift in gliding with various centres of gravity, as well as the change of weight as the rocket uses up the fuel. These tests ended positively, with the Chief pilot David Mackay stating “We are really pleased with what we saw today. We collected hundreds of gigabytes of data for us to review, and from the pilots’ point of view, it felt really wonderful.”

Pilots walking
The pilots walking toward the VSS Unity to conduct the first powered test flight. Credit: Virgin Galactic.

The FAA approved a revision to Virgin Galactic’s Commercial Space Transportation Licence in 2017. This allowed Virgin Galactic to launch out of Spaceport America in New Mexico as well as Mojave Air and Space Port in California. Virgin also announced that the Kingdom of Saudi Arabia would invest $1 billion across the Spaceship Company, Virgin Galactic and Virgin Orbit.Currently under review, if approved the deal would help finance SpaceShipTwo during 2018.

WhiteKnightTwo taking off
WhiteKnightTwo taking off to conduct the first powered test light of VSS Unity being held underneath it. Credit: Virgin Galactic.

VSS Unity is powered by a hybrid rocket engine called RocketMotorTwo. The engine originally used rubber based hydroxyl-terminated polybutadiene (HTPB) as the fuel, and nitrous oxide as the oxidiser. In 2014 Virgin Galactic switched to a plastic based thermoplastic polyamide for the fuel to improve performance. Although tested, and not the cause of the crash of VSS Enterprise, Virgin Galactic opted to use HTPB after extensive testing at Mojave.

spaceport America
VSS Unity attached to WhiteKnightTwo flying over Spaceport America. Credit: Virgin Galactic.

The test used WhiteKnightTwo to lift the VSS Unity to an height of 50,000 feet, then release it. Once clear, VSS Unity ignites and ascends rapidly. The burns during the real flights will last just over a minute, but this test used a much shorter burn. This is the incremental approach that Virgin Galactic have opted for. Unlike a normal rocket, the engine thrust will decrease over time, so that the G-forces stay reasonably comfortable, as this is meant to be a pleasure ride. Once the engine cuts off, the craft coasts to the apogee and glides back to the spaceport. The tests can only get the craft to 80 km, which is not officially recognised as space, due to the extra test equipment needed. Virgin Galactic claim to be confident that the craft will reach space in the final version.

What We Learnt From The Peter Beck AMA

Peter Beck is the CEO and founder of Rocket Lab, a US/New Zealand orbital launch provider who is trying to provide access to space for small satellites. On at 19:00 UTC on April 5th he participated in a Reddit AMA on /r/space, where he answered as many questions as he could about the Electron launch vehicle and the upcoming ‘it’s business time’ launch, as well as what the future of space access looks like. It was a good AMA, he answered lots of questions, and the full post can be found here. This post is to round up some of the most common and important questions he got asked for those interested.

Peter Beck by Electron
Peter Beck, president of Rocket Lab in front of the Electron launcher. Credit: Rocket Lab

The most questions came with reference to SpaceX, and the way their business model compares to Rocket Lab.

SpaceX didn’t see a market It’s known that the Falcon 1 was a similar size to the Electron and they quickly moved on from it. So people asked if SpaceX didn’t stay with it, why will it work for Rocket Lab?  Peter makes the point that SpaceX retired that rocket 10 years ago, and most of Rocket Labs customers didn’t even exist then. He mentioned that Electrons manifest is fully booked for the next 2 years for dedicated flights. He also doesn’t see a slowdown in demand anytime soon.

Reusability – On the SpaceX front, they have made big inroads to reusability and the Electron is not reusable, so many asked about plans to make a reusable version. The simple answer he gave was that reusability makes sense for medium lift vehicles like the falcon 9, but it doesn’t scale well to small vehicles. So it isn’t on the radar for them at the moment.

Electron Launch Vehicle
Rocket Lab’s first Electron rocket, seen here in a hangar at the company’s New Zealand launch site. Credit: Rocket Lab

Other Rocket Manufacturers – As there are many small rocket manufacturers popping up, and attempting to compete in this space, many wanted to know what the market is actually like for them. His comment was that not all of those manufacturers will make it, and they are currently the only dedicated small launcher that has actually made it to orbit. Others were quick to point out that other rockets of similar size do launch but nowhere near as frequently and do not have the same quality or launch frequency as the Electron.

Where else will they launch from – Currently they have a single launch site, but many wanted to know if they will branch out, to different pads of even different countries, maybe even pad-39A. He mentions that he wants to have many potential launch pads to serve many different inclinations, but Launch Complex 1 is a good start.

Going Bigger – There were lots of questions about making a bigger rocket, like an Electron Heavy. He made a point of saying they are currently only making one product really well. They have no plans to make bigger rockets, and they understand the market they are in. Rocket lab do not want to compete with SpaceX on these launches. He mentions that they can launch a huge amount of spacecraft to LEO, and going bigger only allows a 2% increase in market at the moment. That being said they will continue improving the rocket as they go along.

electron on the pad
The Electron launch vehicle waiting on the pad for takeoff, Credit: Rocket Lab

Using composites – As the LOX tank and other parts are made of carbon composites, there were questions about the difficulty surrounding the design and development of that. He talked about the several years developing and testing the composite tanks. The two main issues being microcracking and oxygen compatibility. They ended up with liner-less tanks with common bulkheads that have similar oxygen compatibility to aluminium but much lighter mass. All the composite manufacturing is in house. Some wanted to know how they manage to use such expensive processes, and he says that although carbon fibre is expensive, when done right you can use very little of it.

Why black – with most rockets out there being white, to help with the thermal efficiency, why did they go for black? Well the simple answer he gave was it looks better. Many engineers wanted to paint it, but the thermal experts made a special effort to make sure they could keep it black. Also, it does save some time/money/weight on paint.

It’s all about the money – The key question is, is it profitable, and when will they start making those profits? Well Peter states that they will see positive cash flow after their 5th flight. Each launch costs $4.9 million to each customer, and they get a dedicated launch, so no need to worry about rideshares where they have less control.

Electron Launch
Electron Rocket takes off from Rocket Lab Launch Complex 1 during the “Still Testing” mission. Credit: Rocket Lab

Adding to space junk – In the news recently, there has been lots of the junk that currently floats in space, so there were some questions on how the Electron tries to stop being just more rubbish. Peter talks about the Curie stage of the rocket that is designed to fix this issue. It puts it the second stage into an orbit that makes it deorbit quickly, and the kick stage can deorbit itself. Also most of the LEO payloads they will orbit will deorbit within 5-7 years.

Launch cadence – A few asked how often they are able to launch rockets, or at least the plans to do so. He mentioned that the current plan is to launch once a month for the next year, then once every two weeks, and then double down from there. The Launch complex 1 can support a launch every 72 hours, which is pretty impressive.

Job opportunities – As you would expect, many people asked how you get a job/internship at Rocket Lab. Peter gave a link to email a resume to, but mentioned that the bar is high, they are open to new people but they have to be passionate, and enjoy (and be good at) what they do. They are a small team trying to do big things! They care about what you do outside your formal education, what are you passionate about? what have you built, tested and broken?

Rocket testing
Rocket Lab testing its engines for the Electron launch vehicle. Credit: Rocket Lab

Some hardcore technical answers

  • Each propellant had a dedicated and independent pump system rather than a single electric motor.  That was due to wanting super accurate control over the oxygen fuel ratio and startup and shutdown transients.
  • Ignition is from an augmented spark igniter (a spark plug surrounded by a tube, what acts sort of like a blowtorch).
  • The engine is fully regeneratively cooled, 3D printed chamber.
  • The area ratios for the booster and vacuum nozzles are 14 and 100 respectively.
  • The steering and ullage on the upper stage is controlled by cold gas RCS and PMD.
  • The whole vehicle is non pyro, the decouplers are all pneumatic.

A New Years Trip to Stourhead

Although we are a few months into the year I thought I would make a short post about a trip we took just a couple of days into the new year of 2018. With the family and my girlfriend, we set out on a chilly day, with snow still in some shadowy areas, we visited the nearby Stourhead. A very picturesque place, and a nice place to spend an afternoon. Also, there is plenty of history surrounding the place to get stuck into. I took a few photos on my phone, and I thought I would share.

The Stourhead Sign
The national trust sign in the Stourhead cafe.

Stourhead is a 2,650-acre estate around the source of the river Stour. It is near Mere in Wiltshire, and contains the village Stourton, extensive gardens, farmland, woodland and a palladian mansion. The estate was owned by the Stourton family for 500 years, until they sold it to Sir Thomas Meres in 1714. The Stourton family has a Peerage associated with it, so there is a  Baron Stourton. In 1717 It was sold to Henry Hoare, the son of a wealthy banker, and he demolished the original manor house. Colen Campbell and Nathaniel Ireson designed and built the current house between 1721 and 1725. Over the next 200 years the family collected lots of heirlooms, including a large library and art collection. In 1902 there was a bad fire in the house, but most of the heirlooms were saved. The house was rebuilt almost exactly the same. The son of the final owner, Sir Henry Hugh Arthur Hoare, gave the house and gardens to the National Trust in 1946, a year before he died. His son died at the Battle of Mughar Ridge during World War 1.

The Stourhead Lake
The stourhead lake taken from next to the grotto.

Most people got to Stourhead the walk around the lake and gardens. Taking a walk around the lake is meant to evoke a journey based on Aeneas’s descent into the underworld. The buildings and monuments around the lake are in remembrance of family and local history. The style of the garden is meant to be inspired by a painting bought by Henry Hoare, Claude Lorrain’s Aeneas at Delo. The gardens were designed by Henry Hoare II  and laid out between 1741 and 1780. The lake was artificially created by damming the small stream. The concept of the small areas with a big monuments is that they invite you over, and then you can see the next one, and that invites you over to that, it is designed to make you want to walk round the garden.

The view from the grotto
The awesome view of the lake from inside the grotto.

Stourhead, as its name suggests is where the river Stour starts. It is a 61 mile (98km) river which flows through Wiltshire and Dorset, and drains into the English channel. It is sometimes known as the Dorset Stour to distinguish it from the rivers of the same name in Kent, Suffolk and the Midlands. According to Brewer’s Dictionary of Britain & Ireland, the name Stour rhymes with hour and derives from Old English meaning violentfierce or the fierce one. A large part of the river is followed by the now disused Somerset and Dorset Joint Railway. These trailways are now parts of the Stour Valley Way, a trail that follows the river from the mouth all the way to stourhead, running roughly 64 miles. A number of towns and villages in Dorset are named after the river, including East Stour, West Stour, Stourpaine, Stourton Caundle, Stour Row, Stour Provost, Sturminster Newton, and Sturminster Marshall. Sturminster Newton is famous for a water mill and town bridge which still has a notice warning vandals of penal transportation for those who wish to damage the bridge.

just a soppy photo
A soppy selfie of me and Katie walking up the big hill to the Temple of Apollo.

There are some great little facts that come from Stourhead,might be useful for a pub quiz, or just to annoy your friends.

  • The Temple of Apollo and Palladian Bridge can be seen in the 2005 film Pride & Prejudice, the one starring Keira Knightley.
  • In the Thunderbird TV series (the original one with the puppets), the model for Lady Penelope Creighton-Ward’s mansion was based off of Stourhead house.
  • The corporate font for the National Trust font is based on an inscription in the grotto. It was created in 1748 but was accidentally destroyed by mistake in the 1960’s, so the one there now is a replica.
  • King Alfred’s tower, a folly on the Stourhead estate, was built near Egbert’s stone, where it was said that Alfred the Great, King of Wessex rallied the Saxons in May 878 before the Battle of Edington.
  • King Alfred’s tower is the start of a 28 mile footpath called the Leland Trail that runs to Ham Hill country park.
The View From Apollo
The view of the lake from the Temple of Apollo

link to information about the Stour Valley Way (Long Distance Walkers Association):



Falcon 9 Re-Supplies the ISS on CRS-14

Launch of CRS-14
Threatnigh thunderstorms, an image taken by a sound triggered camera at Space Launch Complex 40. Image from @marcuscotephoto on twitter.

On April 2nd, 2018 at 20:30 UTC a Falcon 9 took off from Launch complex 40 at Cape Canaveral AFB. Aboard was a refurbished Dragon capsule with CRS-14, a resupply for the ISS. This was the 14th of up to 20 CRS missions contracted with NASA, with new Crew Dragon variants soon to be used. The capsule safely reached the ISS and was docked 20 minutes earlier than planned. The cost of the mission was reported to be around $2 billion, and comes under a contract between NASA and SpaceX.

Reused Dragon Capsule on CRS-14
The CRS-14 just before launch, carrying a reused Dragon Capsule for CRS-14. Image from @marcuscotephoto on Twitter.

The Dragon capsule carried 2,630kg  of cargo to the International Space Station, including supplies and research equipment. it has 1070 kg of science equipment, 344 kg of supplies for the crew, 148 kg of vehicle hardware, 49 kg of advanced computer equipment and 99 kg of spacewalking gear. Aboard there are a number of experiments, such as a new satellite designed to test methods of removing space debris. There are also frozen sperm cell samples, a selection of polymers and other materials, all experiments to test what happens to different items when exposed to space and microgravity.

CRS-14 launch
Launch of F9-53 on April 2nd 2018, carrying CRS-14 using a reused rocket and capsule. Image from SpaceX Flickr.

Designated F9-53, the Falcon 9 used booster B1039.2, which previously boosted the CRS-12 mission in August 2017, where it returned to landing zone 1. As is customary, the first stage was left “sooty” from it’s first flight. It powered for 2 minutes and 41 seconds before falling back to earth. For the sixth time in the last 7 Falcon 9 launches, the first stage was purposefully expended, even though it carried landing legs and steering grid fins. As with other expenatures, the rocket went through the re-entry landing sequence, but just didn’t have anything to land on and ended up in the sea. It was the 11th flight of a previously flown Falcon 9 first stage, five of which have been purposefully expended during the second flight, only 3 first stages remain that can be reflown.

A Sooty Falcon 9
The Falcon 9 was left sooty after its first flight which has now become the norm. Image from @marcuscotephoto on twitter.

The second stage completed its burn at 9 minutes and 11 seconds after takeoff, to insert Dragon into a Low Earth Orbit inclined 51.6 degrees to the equator. The Dragon 10.2 is a refurbished spacecraft capsule that first flew during the CRS-8 mission in April 2016. CRS-14 was the third launch of a previously flown Dragon capsule. This was also the first time that both the Dragon capsule and the Falcon 9 were refurbished versions on the same rocket. The docking process was carried out for around 20 minutes, and at 10:40 UTC Kanai detached the lab’s robotic arm to hook the free-flying Dragon capsule. At around 12:00 UTC Houston and Canada took control of the robotic arm and maneuvered it to the Harmony capsule of the ISS. It will be unpacked in a very slow process over a number of months.

Falcon 9 CRS-14
A falcon 9 lifting off from Cape Canaveral AFB Launch Complex 40. Image from SpaceX Flickr.
CRS-14 vapour streams
You can see the vapour streams coming off the falcon 9 as it sends its cargo towards the ISS. Image from SpaceX Flickr.

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

SpaceX Launches NEXT 10 Iridium Satellites For a Fifth Time

Iridium-5 Launch 4
The Falcon 9 F9-52 launching with the Iridium NEXT-5 satellites aboard. Image from SpaceX Flickr.

At 14:13 UTC on March 30th 2018, SpaceX launched a Falcon 9 from foggy Vandenberg Air Force Base. Although designated F9-52 this was the 51st Falcon 9 launch. Using a v1.2 variant booster, the rocket delivered 10 Iridium NEXT satellites into orbit. This was the fifth of eight planned Iridium NEXT missions.

Iridium-5 Launch 2
The Falcon 9 lifting off from Vandenberg AFB california. After the fog had lifted. Image from SpaceX Flickr.


From Vandenberg AFB Space Launch Complex 4 East, the first stage of the rocket lasted 2 minutes 34 seconds, separating a few seconds after. The second engine fired for 6 minutes 23 seconds. This part of the webcast was purposefully cut short due to a NOAA remote sensing licensing requirements. This is an issue with SpaceX not having the right licence to broadcast images from certain parts of space. This burn placed the rocket in a roughly 180 x 625 km parking orbit. The Thales Alenia Space satellite then deployed an hour after launch, after a second brief 11 second burn. This put the satellites into a 625km x 86.6 deg orbit.

Iridium-5 Long Exposure
A 53 second long exposure of Falcon 9 F9-52 launching from Vandenberg AFB. Image from SpaceX Flickr.

The rocket used another “Fairing 2.0”, which is slightly larger than usual, but equipped with recovery systems. These systems include thrusters, a guidance system, and a parafoil. The ship, named Mr Steven has a large net to capture the halves of the fairing. Again, the ship failed to catch one of the fairings, due to a parachute system issue. In a tweet by Elon Musk, it was reported that the GPS guided parafoil twisted so the fairing impacted the water at high speed. He also said that SpaceX are doing helicopter drop tests to fix the issue.

Iridium-5 launch 3
The Falcon 9 launching, with a view of the surrounding buildings and fuel tanks. Image from SpaceX Flickr.

Five of the six previously used Falcon 9 vehicles have been fully expended, this was the tenth flight of a previously-flown Falcon 9 first stage. Four of these ten have been purposely expended during their second flight. The first stage (B1041.2) was previously flown during the Iridium NEXT 3 launch on October 9th, 2017. It performed the 2 minute 34 second boost, and performed what SpaceX call a “simulated landing” into the ocean. SpaceX appear to be only launching a reused stages for one reflight, with the soon to launch “block 5” likely to be reused multiple times. Currently the company only have 4 first stages that might be flown, with one allocated for the upcoming CRS-14 dragon resupply mission.

Iridium-5 mission 1
The Falcon 9 F9-52 launching with the Iridium NEXT-5 satellites aboard. Image from SpaceX Flickr.

Explorer 1 and the Van Allen Story

On February 1st, 1958 at 03:48 UTC (January 31st at 22:48 EST), the first Juno booster launched Explorer 1 into Low Earth Orbit. It was the first satellite to be successfully launched by the United States, and the third ever, after Sputnik 1 and 2 in 1957. Launched from the Army Ballistic Missile Agency’s (ABMA) Cape Canaveral Missile Annex in Florida, now known as Launch Complex 26. The launch played a pivotal part in the discovery of the Van Allen Belt, Explorer 1 was the start of the Explorer series, a set of over 80 scientific satellites. Although sometimes looked over in the history of space, it guided the US space program to what it eventually became.

William Hayward Pickering, James Van Allen, and Wernher von Braun display a full-scale model of Explorer 1 at a crowded news conference in Washington, DC after confirmation the satellite was in orbit.

In 1954 The US Navy and US Army had a joint project known as Project Orbiter, aiming to get a satellite into orbit during 1957. It was going to be launched on a Redstone missile, but the Eisenhower administration rejected the idea in 1955 in favour of the Navy’s project Vanguard. Vanguard was an attempt to use a more civilian styled booster, rather than repurposed missiles. It failed fairly spectacularly in 1957 when the Vanguard TV3 exploded on the launchpad on live TV, less than a month after the launch of Sputnik 2. This deepened American public dismay at the space race. This lead to the army getting a shot at being the first american object in space.

The launch
Launch of Jupiter-C/Explorer 1 at Cape Canaveral, Florida on January 31, 1958.

In somewhat of a mad dash to get Explorer 1 ready, the Army Ballistic Missile Agency had been creating reentry vehicles for ballistic missiles, but kept up hope of getting something into orbit. At the same time Physicist James Van Allen of Iowa State University, was making the primary scientific instrument payload for the mission. As well this, JPL director William H. Pickering was providing the satellite itself. Along with Wernher Von Braun, who had the skills to create the launch system. After the Vanguard failure, the JPL-ABMA group was given permission to use a Jupiter-C reentry test vehicle (renamed Juno) and adapt it to launch the satellite. The Jupiter IRBM reentry nose cone had already been flight tested, speeding up the process. It took the team a total of 84 days to modify the rocket and build Explorer 1.

Preparing the explorer 1
Explorer 1 is mated to its booster at LC-26

The satellite itself, designed and built by graduate students at California Institute of Technology’s JPL under the direction of William H. Pickering was the second satellite to carry a mission payload (Sputnik 2 being the first). Shaped much like a rocket itself, it only weighed 13.37kg (30.8lb) of which 8.3kg (18.3lb) was the instrumentation. The instrumentation sat at the front of the satellite, with the rear being a small rocket motor acting as the fourth stage, this section didn’t detach. The data was transmitted to the ground by two antennas of differing types. A 60 milliwatt transmitter fed dipole antenna with two fiberglass slot antennas in the body of the satellite, operating at 108.3MHz, and four flexible whips acting as a turnstile antenna, fed by a 10 milliwatt transmitter operating at 108.00MHz.

Explorer 1 parts
A diagram showing some of the main parts of the Explorer 1 satellite

As there was a limited timeframe, with limited space available, and a requirement for low weight, the instrumentation was designed to be simple, and highly reliable. An Iowa Cosmic Ray instrument was used. It used germanium and silicon transistors in the electronics. 29 transistors were used in the Explorer 1 payload instrumentation, with others being used in the Army’s micrometeorite amplifier.  The power was provided by mercury chemical batteries, what weighed roughly 40% of the total payload weight. The outside of the instrumentation section was sandblasted stainless steel  with white and black stripes. There were many potential colour schemes, which is why there are articles models and photographs showing different configurations. The final scheme was decided by studies of shadow-sunlight intervals based on firing time, trajectory, orbit and inclination. The stripes are often also seen on many of the early Wernher Von Braun Rockets.

NASM flight spare
The flight ready spare of the Explorer 1, now shown at the National Air and Space Museum.

The instrument was meant to have a tape recorder on board, but was not modeled in time to be put onto the spacecraft. This meant that all the data received was real-time and from the on board antennas. Plus as there were no downrange tracking stations, they could only pick up signals while the satellite was over them. This meant that they could not get a recording from the entire earth. It also meant that when the rocket went up, and dipped over the horizon, they had no idea whether it got into orbit. Half an hour after the launch Albert Hibbs, Explorers System designer from JPL, who was responsible for orbit calculations walked into the room and declared there was a 95% chance the satellite was in orbit. In response, the Major snapped: “Don’t give me any of this probability crap, Hibbs. Is the thing up there or not?”.

Explorer 1 Mission Badge
The official JPL mission pac=tch for the Explorer 1 mission.

The instrument was the baby of one of Van Allens graduate students, George Ludwig. When he heard the payload was going into the Explorer 1 (and not the Vanguard) he packed up his family and set off for JPL to work with the engineers there. He has a good oral history section on this link, talking about designing some of the first electronics in space. He was there watching the rocket launch and waiting for results. From the Navy’s Vanguard Microlock receiving station they watched the telemetry that reported the health of the cosmic-ray package. The first 300 seconds were very hopeful, with a quick rise in counting rates followed by a drop to a constant 10-20  counts per second, as expected. The calculations told them when they should hear from the satellite again, but 12 minutes after the expected time, nothing showed up but eventually, after pure silence, Explorer 1 finally reported home.

The Van Allen Belt
This diagram showcases the Van Allen belts, which were first detected by instruments aboard Explorer 1 and Explorer 3. The Van Allen belts were the first major scientific discovery of the space age.

Once in orbit, Explorer 1 transmitted data for 105 days. The satellite was reported to be successful in its first month of operation. From the scientist point of view, the lack of data meant the results were difficult to conclude. The data was also different to the expectations, it was recording less meteoric dust than expected and varying amounts of cosmic radiation, and sometimes silent above 600 miles. This was figured out on Explorer 3 when they realised the counters were being saturated by too much radiation. Leading to the discovery of the Van Allen Radiation Belt. Although they described the belt as “death lurking 70 miles up” it actually deflects high energy particles away from earth, meaning life can be sustained on earth. The satellite batteries powered the high-powered transmitter for 31 days, and after 105 days it sent it’s last transmission on May 23rd 1958. It still remained in orbit for 12 years, reentering the atmosphere over the pacific ocean on March 31st after 58,000 orbits.

When Planes Need an Eye Test

Naval Outlying Field Webster
The photo resolution marker at Naval Outlying Field Webster, From Google Maps

A few years ago, The Center for Land Use Interpretation (CLUI) reported on the dozens of Photo calibration targets found in the USA. They are odd looking two dimensional targets with lots of lines on the of various sizes, used as part of the development of aerial photography. Mostly built in the 1950’s and 60’s as part of the US effort of the cold war.

Shaw Air Force Base
The photo resolution marker at Shaw Air Force Base. From Google Maps

At this point, just after the second world war, there was a huge push to get better information about the enemy. The military needed better aerial recconasance. This very problem lead to the development of the U-2 and the SR-71. As part of this, there needed to be methods of testing these planes with the big camera systems attached to them. This was before the development of digital photography, so resolution is much more difficult to test.

The USAF test target
The 1951 USAF test target from wikipedia, they can still be bought.
Fort Huachuca
The photo resolution marker at Fort Huachuca. From Google Maps

This is where the photo resolution markers came in. Much like an optometrist uses an eye chart, military aerial cameras used these giant markers. Defined in milspec MIL-STD-150A, they are generally 78ft x 53ft concrete or asphalt rectangles, with heavy black and white paint. The bars on it are sometimes called a tri-bar array, but they can come in all forms, such as white circles, squares, and checkered patterns.

Beaufort Marine Corps Base
The photo resolution marker at Beaufort Marine Corps Base. From Google Maps

The largest concentration of resolution targets is in the Mojave desert, around Edwards Air Force Base. This is the place most new planes were tested during this time, with the U-S, SR-71 and X-15 being just some of the planes tested there. There are a set of 15 targets over 20 miles, known as photo resolution road. There are also plenty of other resolution targets at aerial reconnaissance bases across the US, such as Travis AFB, Beaufort Marine Corps Base and Shaw Air Force Base.

Elgin Air Force Base
The photo resolution marker at Elgin Air Force Base. From Google Maps

Semi Autonomous Robotic Platform

As part of my degree I had to complete a project as part of the third year in the field of robotics and electronics. I chose to make a robotic platform, a simple idea that could be completed to a high quality with the right amount of effort. What is a robotic platform I hear you ask? well it essentially is a small buggy/rover that that moves around an assigned area completing simple jobs such as transporting goods, picking up parcels or any job that needs a moving vehicle. Usually autonomous, and very expensive, the majority of systems are very application specific. Some simple systems without any sort of control system can cost tens of thousands of pounds, and are not easy for the average employee to operate. Tackling the problem of expensive, application specific robotic platforms was the basis of my project.

4WD robotic platform
The Nexus 4 wheeled drive mecanum robot has an arduino based control system, and mecanum wheels, but will set you back $1500

Named the Semi Autonomous Robotic Platform, the idea was very simple, make a modular system, with building blocks that could be easily interchanged, and didn’t cost the world. These modules were things like motor controllers, sensors and power systems. If a user had a working platform built from this system, it would take minimal effort to swap out any of these modules to bigger motors or better sensors. This means a user can make a robot and only buy the bits they need, and even make their own modules, as long as they fit to the standard written as part of the project.

system block diagram
The initial block diagram of the system, showing how the modules can be controlled in hierarchy structure.

In most robotic systems, mainly to keep costs cheap, there is one controller that controls everything. This idea makes sense for small integrated systems that don’t need to change, but doesn’t really work when systems need to be dynamic. For instance, say you decide that your DC motors driving your robot aren’t giving you the control you want. You source some stepper motors, but this means completely changing the motor controller and therefore the software that controls it. Because one controller is in charge of everything, the software for the whole system needs to be re-written, and re-tested. That small change could have affected any of the other systems that that controller is in charge of. Make a change that breaks something important, you could set back a project weeks. This shows how painful a setup like this can be, especially when it starts to become a complex robot. Add on top of that the potential for computer intensive algorithms being used on the robot, like route planning or SLAM, and that controller suddenly has a lot to do. My system design separates these jobs out to a selection of individual controllers, such as a system specifically for motor control, or power systems. These controllers can deal with the nitty gritty hardware, and leave the master controller to orchestrate a higher level version of control.

Final Year Project
My design, near the end of the project, with the mecanum wheels, ultrasonic sensors and multiple controllers.

The added benefit of separating out all these jobs means that multiple engineers can work on the same robot, at the same time on different areas and not be worried about breaking the other person’s design. The system specification defines how the modules interact in terms of communication speeds/type, the way to alert other modules and how those communications are scheduled. The master controller (shown in the system block diagram in green) schedules all these communications and decides which modules need specific information. Warnings, control signals and user inputs are all calculated and scheduled, then communicated to and from the required modules. A power system doesn’t care that a user has pressed a button to scroll through an LCD screen, and the master controller means it doesn’t see it.

The above video shows how the robot moves with its mecanum wheels, and how it can easy move around environments. I will explain the more technical parts of the project in a later post, but this simple idea became a very heavy hardware based project, rather than the software project it started as. I learnt about mechanical design, PCB design and good techniques associated with electronic design. For these reasons, the robot won the “Best Project” award for 2017. Thank you to: Cubik Innovation for help with electronic design, and providing PCBs, VEX Robotics for donating the wheels, and Altium Designer for providing their electronic design software. I would not have been able to produce the robot I did without them.