Technology Taking Shape – Radio Links

Control SystemFinalising ThunderStruck’s Radio Links

Aside from the airframe and servos, one of the hardest planning jobs is designing and building the various radio links.

It is pretty simple. Radio links are essential and not just nice. They will be mission critical to the success of the project, but we will have backups to complete the flight without crashing, etc. The links must be solid and with no breakup and must operate over long distances.

It is very important to realise the differences with the ground based systems and the aircraft systems. With the ground based systems we can have high power, large antennas, antenna tracking, mains/generator power and much more. on the aircraft we have both power and space issues. We also have temperature issues and the equipment must be tested in chambers that have had the air pumped out – I don’t like to use the term “vacuum”, but it is descriptive for most people.

How many links will we need?

At the moment we will need 4 radio links – 2 for the balloon and 2 for the aircraft.

  • The balloon telemetry system
  • The balloon camera system
  • The aircraft telemetry system
  • The aircraft camera system

We want to keep the video links separate from the telemetry as delays in the telemetry information can cause major issues. If you have ever had a large file download interrupt a Skype call?  you will know exactly what I mean. Imagine flying a supersonic aircraft and having dropouts on the links to the flight system! We can’t have that so we separate the systems. We also need to separate the balloon and aircraft systems as we will need to maintain video from the balloon well after the aircraft has separated from the balloon. We will also need to command the balloon to terminate its flight after separation. The most critical link of the 4 is the aircraft telemetry system and we have chosen a 900MHz 1 watt system. It is pretty amazing and handles 56Kb per second both ways at a distance of 80Km with diversity. Diversity is super important. I have posted the specifications on and earlier post, but I will repost them below. It can link directly to our control system and also to a navigation system such as the Pixhawk that we have chosen. The simple set up can be seen in the following diagram. More on this and the other links in a later post.

Control System

Note that in the above radio link system, the yagi antennas may have auto-tracking and will probably be vertical and horizontal diversity. We are toying with the idea of circular polarisation. More on patch antennas later.

From the RFDesign Website:

RFDesign is an electronics design and manufacturing company specialising in Embedded systems, Radios, Antennas and high frequency electronics. We are located in Brisbane, Australia with our office located in Acacia Ridge, QLD. 

Features:

  • Long range >40km depending on antennas and GCS setup
  • 2 x RP-SMA RF connectors, diversity switched.
  • 1 Watt (+30dBm) transmit power.
  • Transmit low pass filter.
  • > 20dB Low noise amplifier.
  • RX SAW filter.
  • Passive front end band pass filter.
  • Open source firmware SiK (V1.x) / tools, field upgradeable, easy to configure.
  • Multipoint software capability with MP SiK (V2.x)
  • Small, light weight.
  • Compatible with 3DR / Hope-RF radio modules.
  • License free use in Australia, Canada, USA, NZ

 Interfaces:

  • RF : 2 x RP-SMA connectors
  • Serial: Logic level TTL (+3.3v nominal, +5v tolerant)
  • Power: +5v, ~800mA max peak (at maximum transmit power)
  • GPIO: 6 General purpose IO (Digital, ADC, PWM capable).

Specifications:

  • Frequency Range:  902 – 928 MHz (USA) / 915 – 928 MHz (Australia)
  • Output Power: 1W (+30dBm), controllable in 1dB steps ( +/- 1dB @=20dBm typical )
  • Air Data transfer rates: 4, 8, 16, 19, 24, 32, 48, 64, 96, 128, 192 and 250 kbit/sec ( User selectable, 64k default )
  • UART data transfer rates: 2400, 4800, 9600, 19200, 38400, 57600, 115200 baud  ( User selectable, 57600 default )
  • Output Power: 1W (+30dBm)
  • Receive Sensitivity: >121 dBm at low data rates, high data rates (TBA)
  • Size: 30 mm (wide) x 57 mm (long) x 12.8 mm (thick) – Including RF Shield, Heatsink and connector extremeties
  • Weight: 14.5g
  • Mounting: 3 x M2.5 screws, 3 x header pin solder points
  • Power Supply: +5 V nominal, (+3.5 V min, +5.5 V max), ~800 mA peak at maximum power
  • Temp. Range: -40 to +85 deg C

Software / GCS Support:

The software solution is an open source development called “SiK” originally by Mike Smith and improved upon by Andrew Tridgell and RFDesign. A boot loader and interface is available for further development and field upgrade of the modem firmware via the serial port.

Most parameters are configurable via AT commands, Eg. baud rate (air/uart), frequency band, power levels, etc., please see the 3DR wiki for commands below for now.

V2.x firmware has been updated to support multipoint networking on the RFD900.

V1.x (non multipoint) is suitable for point to point links – the sourcecode is located at:   https://github.com/RFDesign/SiK

The user manual / datasheet can be found here : RFD900 Datasheet

A software manual for SiK firmware is here : RFD900 Software manual

RFD900 configuration tool: http://rfdesign.com.au/downloads/

RFD900 binary firmware repository: http://rfdesign.com.au/firmware/

3DR/RFD900 compatible configuration tool : http://vps.oborne.me/3drradioconfig.zip

Wiki for the 3DR radios (RFD900 has same commands): http://code.google.com/p/ardupilot-mega/wiki/3DRadio

Integrated support for configuring the RFD900 radios is supported by APM Planner, with other GCS solutions in development.

The default settings are at 57600 baud, N, 8, 1, and 64k air data rate.

Software features include:

  • Frequency hopping spread spectrum (FHSS)
  • Transparent serial link
  • Point to Point, or Multipoint networking
  • Configuration by simple AT commands for local radio, RT commands for remote radio
  • User configurable serial data rates and air datarates
  • Error correction routines, Mavlink protocol framing (user selectable)
  • Mavlink radio status reporting (Local RSSI, Remote RSSI, Local Noise, Remote Noise)
  • Automatic antenna diversity switching on a packet basis in realtime
  • Automatic duty cycle throttling based on radio temperature to avoid overheating

website, http://rfdesign.com.au for more information.

What is Project ThunderStruck?

ThunderStruck verticalProject ThunderStruck set to Break Barriers

by Robert Brand

This project is two projects in one. The total aim of ThunderStruck is to build as small a space craft as possible that will handle reentry, remain stable and land softly. The “softly” is important as commercially there are payloads that may need to be conducted in a “weightless” environment and then be brought down without too much jarring. A parachute landing will not be suitable. My son who is very aerospace savvy was keen to be involved in some way and Project ThunderStruck was born. We will help do the low altitude testing – when I say low, i mean from 40Km altitude (25 miles)

Imagine a time when a 12 year student could design and build a supersonic glider 2.5m / 8ft long, attach it to a huge helium or hydrogen balloon and take it to the edge of space, release it, fly it into a dive back to earth that will reach Mach 1.5 / 1,800kph / 1,120mph and land it. Well that time is now and the student is Jason Brand from Sydney Secondary College / Balmain Campus. He is in year 7 and has already broken plenty of records with his hobbies. Breaking the sound barrier will be another cool record.

New Science, New Data, New Opportunities

Apart from the glitz of the big event in 6 months (a 12-year-old breaking the sound barrier) there is a lot of science being done. In fact the event side of this project will be funded by sponsors and the crowd funding will be for the additional science outlined below.

There is a commercial opportunity to design and create a winged re-entry vehicle specifically for delicate payloads and experiments that last for more than 4 minutes in a weightless environment (tourist sounding flights to space). These are experiments and payloads that would find a parachute landing too harsh. There is a final output of the work and that is a spacecraft for experiments or even a payload taxi service back to earth. The most important aspect of this work is determining the smallest size of a winged spacecraft that can remain stable during re-entry. There are three stages of the physical testing:

  • Transonic – Project ThunderStruck in 6 months time
  • Reentry from space (delivered on a sounding rocket – no orbit); 2-3 years away.
  • Re-entry from orbit; 6 years away

There are two science components to the upcoming testing over the next 6 months:

  • Stability of a small aircraft at mach 1.5 / 1,800kph / 1,120mph and lower speeds for landing
  • testing a new type of surface for high-speed flight. (not a heat shield)

Since Jason has experience and a fantastic track record in High Altitude Balloon flights and flying remote control aircraft, he wanted to look after that first phase of the project. The transonic Phase. Transonic flight is the flight around the area of breaking the sound barrier. All sorts of problems occur near the sound barrier. When we drop the aircraft from 40Km altitude, first we have to get through the sound barrier as the drag increases significantly, but once through the barrier, the drag essentially reduces until your speed increases further. The real testing then commences as our tests will be about slowing, not increasing speed. We will be measuring the behaviour of the craft and airflow over the surfaces.

Project ThunderStruck has Commenced Flying Tests

Just in case you are concerned that this is all talk and no action, we started test flights in Sept 2014. The results are simply amazing and we will use them to refine our project.

The event will take 6 to 9 months to complete and the testing is the most important aspect of this project. It is new territory for us and almost the entire world. There is still fresh science to be done and innovative ways to use new materials and designs. Recently we learned a lot when a non-aerodynamic payload (space chicken from Clintons Toyota) reached speeds of 400kph / 250mph with its parachute deployed. This is because the air is pretty thin up at 33.33Km or 1/3 the way to space. Our payload took several measurements during the fall.

Rankins Springs Free Fall UpLift-19The space chicken was a simple test and we are now happy that we can easily fly at speeds of Mach 1.5 in the very thin air high up in the stratosphere. Left is a picture of the chicken falling back to earth at 400kph. Even the parachute could not slow the payload in the thin air. It slowed down as it reached 28Kms altitude and the air got a bit thicker.

We have started fund raising as we need help to cover the costs of the science parts of the project. Once we know what we have, we can decide on the extent of the program. We need $20,000 or more just for science and we have turned to crowd funding for that.

We have some “Perks” as part of crowd funding that I hope you will love. Some of our payloads will go supersonic before the big event, but they will not be aircraft. We might even donate one of our supersonic payloads to a generous contributor.

STEM – Project ThunderStruck set to Inspire Kids Worldwide.

Fighter jets break the sound barrier every day, but this radio controlled aircraft has no engine, weighs 9Kg (20lbs), is 2.5m (8 ft) long. So the pilot must be a really experience Top Gun to fly this plane at 1,800kph (1,120mph)? Well, no. His name is Jason Brand and he is 12 years old.

This is probably one of the most important demonstrations of STEM education that you can support. This is beyond the ability of almost every adult on the planet, yet a 12 year old student is set to inspire kids around the world with a daring project that is pure STEM – Science Technology Engineering Mathematics. It will make the seemingly impossible the domain of the young if they choose to break down the barriers imposed by themselves or others. Not only that, there is real science going on here.

Your Assistance is Essential

Your crowd funding help now is essential. It gets us started immediately. Flying balloons to the edge of space for testing is an expensive exercise and we have a 7 hour drive each way to get into areas of low air traffic away from the major aircraft trunk routes. We also have to buy a lot of radio systems to allow remote control from the ground when the glider is up to 100kms distance.

You can click on one of the 2 crowd funding links at the top right of the page. Even $1 will help unlock new discoveries and bed down older science.

Who is Jason Brand?

He is a 12 y/o student from Sydney Secondary College, Balmain Campus in Sydney, Australia.

He carried out his first High Altitude Balloon (HAB) project at age 9 and was so inspired that he sat for his amateur radio license at 9 years old. Since then he has launched a total of 19 HAB flights and recovered all 19. Some flights were in Croatia where mountains, swamps and landmines are risks not seen in Australia. He is also the Student Representative for Team Stellar – A Google Lunar X-Prize team attempting to get a rover onto the moon.

J20130414 Jason Brand on the Fuzzy Logic Science Showason appears on Radio and TV regularly and the picture right shows him talking about HAB flights on Canberra’s Fuzzy Logic Science Show in 2013. He is also a member of the Australian Air League, Riverwood Squadron. He plans to solo on his 15th birthday.

His father Robert Brand is an innovator in creating low cost solutions for spaceflight. He speaks regularly at international conferences, is a regular guest lecturer on aerospace at Sydney University, writes about aerospace and takes a very “hands on” approach to space. He supports Jason’s project fully.

How will ThunderStruck work?

The same way that the first pilots broke the sound barrier: in a steep dive. The problem is that since there is no engine and the biggest issue is air resistance, Jason will launch the aircraft from over 40km altitude or nearly half way to space! He will get it there on a high altitude balloon. The air is very thin at that altitude and the craft should accelerate past the speed of sound before it is thick enough to slow it down. A tiny fraction of one percent of the air at sea level. During the dive, the craft will accelerate to well over Mach 1 and way less than Mach 2 and will need to be controllable by its normal control surfaces to pass as an aircraft. As the air thickens at low altitudes, the craft will slow and with the application of air brakes will slow and then be levelel off for normal flight to the ground.

The Technology

We will have a camera in the nose of the aircraft and it will transmit TV images to the pilot on the ground. Jason will be either in a darkened room with a monitor or wearing goggles allowing him to see the view from the on-board camera. This provides what is known as First-person Point of View (FPV). The aircrafts instruments will be overlaid on the video signal. This is known as “On Screen Display” or OSD. Below is a view typical of what will be seen by Jason as he lands the craft.

osdThe video signal must travel over 100kms to be assured of the craft being in the radius of the equipments limits. Similarly we must send commands to the control surfaces of the radio controlled aircraft. Again this must work at a distance of over 100kms. The craft has ailerons, elevators and rudder as well as air-breaks and other systems that need controlling. We will use a 10 channel system to ensure that we have full control of every aspect of the craft and a “binding” system will ensure that only we can fly the aircraft.

We will have to buy 2 x $5,000 GPS unit capable of sampling at what is essentially the speed of a missile. These are highly restricted items, but essential. The unit will record to an SD card and send back telemetry every second. It is essential to know the speed during the flight rather than waiting until after the event. After all Jason needs to knowthe speed to be able to fly the aircraft. We will also need 2 x radar responders to allow other aircraft and air traffic controllers to know where our craft is and our balloon is at any time.

The Big Event

We can expect global TV News coverage of the event and many records to be broken. The day will start by filling a large Zero Pressure Balloon like the one pictured below.

OLYMPUS DIGITAL CAMERAThe balloon will carry the aircraft to over 40km where it will be released and go into a steep dive and break the sound barrier. As the air thickens, the speed will slow and the craft will be pulled out of the dive and leveled off to drop speed. The aircraft will eventually land and data and video records will be recovered. We will already know the top speed, but there is nothing like solid data rather than radio telemetry that may miss the odd data packet. Both the balloon and the aircraft will be transmitting live video.

There will be opportunities to attend, but it is likely to be in a rather remote part of the state (NSW, Australia) or a nearby state. The flight will be broadcast over the Internet and the opportunity to track and follow the flight will be available to all. The chance to be involved is high and the science and inspiration will be out of this world. Project ThunderStruck is set to thrill.

Visit our sister site wotzup.com for more space and balloon stories

Project ThunderStruck Update 1

More News on Project ThunderStruck

Thanks for the support in both contributions of dollars and more importantly at this stage, getting the word out and helping with services. Tim Gagnon is a fine graphic artist from Florida and he has pledge support by offering to design the mission patch. If you have any thoughts about his skills, have a look at his website. I believe that he has done one or two before!

KSCartist.comKSCartist.com Fine Art & Graphic Design from America’s Space Coast

Spending Your Contributions

Now a little detail on how we will spend your contributions. I did say it would cost $80,000 and that was no exaggeration. For a start there is about $10,000 worth of electronics to buy and test for the final flight and that is just the TV link, the telemetry, the control system for flight, cameras, video from the balloon to see the aircraft and the release, the tracking systems for the balloon and the tracking for the aircraft, the balloon flight termination system. The balloon for the final flight will cost over US$10,000 and the helium will cost $3,000. We will have to buy 2 radar transponders to warn aircraft of our position and they cost $2,000 to $5,000 each (and are heavy too).

Every two weeks we will do a weather balloon flight to test the latest systems for Project ThunderStruck and these will cost between $1,000 and $2,000 dollars each and take up our whole weekend traveling and staying in hotels. Petrol alone costs us $300 for the trip and launching and recovering our systems. Below is a video of a launch we did in Croatia. You will see that it is very difficult and requires a lot of materials and you don’t always recover them. So far we have recovered 100% of our payloads, but one day….

phased circula polarised antenna - double mushroomThe GPS tracking system will be special as ordinary systems will not work at supersonic speeds. You need a special clearance to buy these and we need 2 and they cost $6,000 each.

The airframes will be expensive and we will need two. Jason has said that since most of our antennas are internal, the airframe cannot be made from carbon fibre alone or the signals will be severely attenuated. He will also need to have sections of the fuselage and possibly parts of the wing fabricated from a material such as Kevlar.

The picture, right, is an antenna that may be on the aircraft and shows why we must locate it inside of the airframe. It is a little fragile to leave out in a 1,800kph airstream!

 

CASA – Australia’s Civil Aviation Safety Authority

Our Civil Aviation Safety Authority will also likely want us to travel to a remote part of the country for the big event. That will probably be one of our biggest costs – transporting all that gear and setting it up in the middle of nowhere and that is not a two person activity. We will need transport and accommodation for a huge crowd of people.

I look forward to telling you more about the technical parts of the mission in the next update for Project ThunderStruck.