Greetings Fellow Rocketeers

Did I say that we were Building a RocketDream Chaser spacecraft Graphic on top of a Rocket for Launch?

by Robert Brand. No we haven’t, but here is the buzz – we are developing significant rocket technology.

It was ThunderStruck team member David Galea that headed his email with “Greetings Fellow Rocketeers” and it may stick because ThunderStruck is building rocket technology. We may be building more rockets later but right now we are specifically building a booster for a bigger rocket. A booster that could make it to space all by itself with a ThunderStruck suborbital winged craft as the payload (mounted right on top of the thruster). The rocket will be configured as a sounding rocket – not orbital. The picture (above right) is a similar craft, but a way bigger craft, on top of a bigger rocket. Non the less it will look similar.

Rocket Basics

This will take years to build and it may result in a static test fire in the Australian desert in the next year or two depending on financing. None the less, it will be an amazing opportunity for a small company to gain considerable traction in the rocket building field.

The info here is a basic format that hopefully high school students can understand.

Rocket design commencesRockets and Maths

Mathematics is essential in building space equipment, space craft and navigating in space to mention a tiny bit. Without maths, rockets would explode from over-pressure or fail to get to space because we over-engineered it and it was too heavy to be a work horse.

The image at right is a basic configuration. Solid fuel with an air core and a thrust and nozzle at the bottom. Looks simple, but the maths have to be done first to get an estimation of the pressure we can expect and the strength of the tank and the weight of the tank with different metals. note that as the fuel burns down from the inside towards the metal of the tank, the area burning is greater and the pressure thus increases in a big way. You can change the fuel configuration to burn slower or have less thrust, but that could change simplicity of equation below so we will assume that the fuel is the same for the entire burn. That has been done and we came up with two limits on the mass that we can now work with. The optimum design will be in the middle somewhere.

After putting a rough design on the table with a mass of 2,000Kg fully fueled, we managed to get to space with a big payload and a coasting altitude of 150Km or more. This was with a speed of 1.5Km (or more) per second at the 30 second burn when the fuel is exhausted.

A second design with 3,000Kg mass fully fueled only managed a bit less than 25km altitude. The optimum booster, configured as a sounding rocket lies somewhere in between. The next part of the work is to consider the options. That is:

  • Do we use more thrust and increase the tank and nozzle pressure?
  • We we increase the fuel load and mass?
  • Do we reduce the fuel load and mass?
  • Do we change the fuel and increase the pressure and even the burn time?
  • Do we reduce the mass of the payload (250Kg in this initial desktop design?
  • Do we reduce the mass of the rocket?

These are just a few of the options, but how do we calculate these things – Mathematics of course.

Below are the maths for the heavier second design that only got to under 25Km configures as a rocket. It would have made a poor booster.

NOTE: this is a simple bit of maths for model rockets, but it applies to the bigger ones too. It is not the whole deal, but will give a good estimate for the first pass.

David Galea’s maths for the second configuration performance:

ThunderStruck Rocket Flight Profile – Estimated Calculations

There are three basic equations to find the peak altitude for the rocket

  • Max velocity v, the velocity at burnout = q*[1-exp(-x*t)] / [1+exp(-x*t)] = 916
  • Altitude reached at the end of boost = [-M / (2*k)]*ln([T – M*g – k*v^2] / [T – M*g]) = 13,191.684 m
  • Additional height achieved during coast = [+M / (2*k)]*ln([M*g + k*v^2] / [M*g]) = 11,515.9877 m

Total Height Achieved = 24,707.67 m

All the terms in these equations are explained below on the method for using the equations.

  1. Compute Some Useful Terms
    • Find the mass M of your rocket in kilograms (kg): 2950kg
    • Find the area A of your rocket cross-section in square meters (m^2): 0.342m^2
    • Note that the wind resistance force = 0.5 * rho*Cd*A * v^2, where
      rho is density of air = 1.2 kg/m^3
      Cd is the drag coefficient of your rocket which is around 0.75 for a model rocket shape.
      v is the velocity of the rocket. You don’t calculate this drag force, though, since you don’t know what “v” is yet. What you do need is to lump the wind resistance factors into one coefficient k:
      k = 0.5*rho*Cd*A = 0.5*1.2*0.75*A = 0.1539
    • Find the impulse I and thrust T of the engine for your rocket. I= 3907501 Ns , T= 118841.27 Ns
    • Compute the burn time t for the engine by dividing impulse I by thrust T:
      t = I / T = 3907501 / 118841.27 = 32.88 seconds
    • Note also – the gravitational force is equal to M*g, or the mass of the rocket times the acceleration of gravity (g). The value of g is a constant, equal to 9.8 meters/sec/sec. This force is the same as the weight of the rocket in newtons.
  2. Compute a couple of terms, I call them “q” and “x”
    • q = sqrt([T – M*g] / k) = sqrt([118841.27 – 2950 * 9.8] / 0.1539) = 764.427
    • x = 2*k*q / M = 2 * 0.1539 * 764.427 / 2950 = 0.079759536
  3. Calculate velocity at burnout (max velocity, v), boost phase distance yb, and coast phase distance yc (you will sum these last two for total altitude).
    • v = 764.427*[1-exp(-0.079759536*32.88)] / [1+exp(-0.079759536*32.88)] = 660.916
    • yb = [-2950 / (2*0.1539)]*ln([118841.27 – 2950 *9.8 – 0.1539*660.916^2] / [118841.27 – 2950 *9.8]) = 13191.684
    • yc = [+2950 / (2*0.1539)]*ln([2950 *9.8 + 0.1539*660.916^2] / [2950 *9.8]) = 11515.9877

Rocket SoftwareDavid says: I have double checked my calculations with wolfram alpha (https://www.wolframalpha.com) with the same results.

Well fellow Rocketeers, we will continue to let you know about our big adventure with things that could “go BANG” as we develop our technology.

The Screen shot at right is a basic program that you can get for free or you can buy a more professional version for model rocket hobbyists. None the less it is fine for early desktop modeling.

We will keep you in touch with the professional software that we will eventually choose and use for the serious design phase.

All you students, please get your head down and study maths. We will need to have capable people working in the space sector as Project ThunderStruck becomes an Australian Space staple.

Preparing for the Flight of ThunderStruck

Weather balloon burst

What a burst weather balloon should do! Disintegrate

ThunderStruck – Backup Preparations

Jason, our 12 year old pilot is no stranger to having to prepare for the worst and it is what we do every time we send up a payload. Our last flight of a balloon into the stratosphere was a case of just that. Two failures. One on launch and the second on decent. Each problem would be enough to cause most balloon payloads to be lost, but as part of our preparations, we carried two trackers for the one flight. This was a flight in preparation for our project and we are testing. We have had to cover our payload in the video. Our apologies.

Below: An artist’s view of the ThunderStruck aircraft under a zero pressure balloon (more on that another time) at 40km altitude. You may have guessed, I am the artist….. Note that on the ThunderStruck event, we will not be using weather balloons so there will be no unexpected explosions.

Balloon Flight with ThunderStruck

Failure One

The first failure was totally invisible to us. A massive downdraft. The first that we have ever encountered. Uplift-1, our first flight, started in an updraft and it rose at an incredible rate for the first kilometre. In the video below, you can hear me make the comment that there did not appear to be the lift that we knew we had because we had used scales to measure the lift. We could not feel the downdraft pushing the balloon down 15 metres above our heads. I mistakenly thought my lack of “feel” was because of the others also holding the payload. We released the payload and balloon and then our hopes sank as the payload only lifted slowly and then sank back to the ground. We ran to catch it, but it rose again and caught on the edge of the eve of the roof of a nearby wheat silo. It stayed there for only 2 minutes, but it felt like an eternity before it released. It rose quickly as calculated, but one tracker had had its GPS unit disconnected and the other had its antenna twisted 90 degrees effectively lowering the power considerably. None the less we could still track the flight – mostly.

One tracker disabled, but still sending its ID at full power, The other effectively made to look low power. Those GoPro cameras are great. hundred of metres above the ground you can hear (faintly) people talking and a dog barking! They make great gear.

Failure Two

The weather balloons are meant to explode and disintegrate. This one did not. The entire balloon, well over 1Kg fell into the parachute and tangled itself in the chute, effectively making the mass look like more like a tangled flag than a parachute. It slowed the payload in the thick air, but the fall from its maximum height was rapid and the entire fall from 30km only took 15 minutes. This was an average speed of 120kph. Given that the payload probably hit the ground at 30 to 40kph, the initial speed was probably close to 400kph in the thin upper air.

With the tracker only giving us effectively a poor signal, the last track that we received in one of the vehicles headed to the landing site was 2 km above the ground making the landing site potentially one square kilometre.  We also fond out later that the second tracker was never going to give us a signal, because the impact had caused a battery to eject from its holder. We only had one ID every 20 seconds and no GPS location! We used a directional antenna to lead us to the payload, but it was a slow and painful task.

The video below shows the impact and the wooden spars breaking. The camera continued to record! Nothing like a good wiring system to ensure that power kept flowing from the external battery. I did not mention that we use external batteries. The GoPro’s batteries, even with the additional power pack, just do not last for the entire flight if it goes over 2.5 hours and especially if it is taking both videos and stills – The new GoPros are amazing, but need more power for High Altitude Balloon (HAB) flights.

Initially the video above shows the incredible stability of our payload at 30km altitude. The Balloon explodes at the 30 second mark and then plummets and spins at a sickening rate of a  couple of times a second with the disabled chute causing the spin.  At 1 minute 45 seconds, we cut to an altitude of about 3km and it took 3 minutes to hit the ground at 60kph. At the 4:45 mark, the payload hits and spars shatter. The camera keeps recording. By the way, the big tree lined road is the Mid Western Highway. The payload was kind enough to land in a sheep paddock beside the main road. You can’t ask for better.

The Lesson

The lesson here is that if it can go wrong, it will go wrong. Yes, we have recovered every payload that we have sent up, but good preparations both in the payload design and build is important as are the preparations for recovery on the ground. We even carry poles to remove the payload from trees. We can manage 14 metre trees. After that we will have to look at other methods.

Our preparations will be backup, backup and more backup. Redundancy rules over weight considerations where possible. Systems will be over-engineered and more care will be taken than what appears necessary. Project ThunderStruck will fly while the world watches. Delays will be unacceptable. This was UpLift-20 and again we have 100% successful recovery rate. @0 flown and 20 recovered. As our flights become more aligned to the actual shape of the ThunderStruck aircraft, speeds will dramatically increase on decent and the videos will have way more interesting stuff to show, but these lessons were there to remind us not to get complacent.

Fund Raising – Launch Your Payload to the Stratosphere

The view from 30Km over central NSWFund Raising Payloads to the Stratosphere

Normally, prices start from $3,000, but for the next few weeks we will take your payload to the Stratosphere for $1,200 – almost 1/3 of the normal price. We can do this by sharing the payload and taking three or four small payloads up on our specially designed payload frame. One camera for each payload is included and you can either do video or still images. For $400 more, we will include a second camera if you needed it and the batteries to power it for the entire flight from launch to landing.

Your payload will get to 26Km or more or we fly it again. We are now achieving 30-33km altitude regularly. We will track and recover your payload and provide you with the images or video from the camera. We will give you 4 weeks to publish your photos or video, but we will reserve the rights to also place the pictures or video on our websites. Again, for a small fee, you can also have full rights to the media. Payloads need to be about 200 grams or less, but with some more dollars we can carry more – we need to buy bigger balloons and more helium to compensate. a 3Kg balloon will cost well over $500!

We cannot guarantee the payload safety as there are always lakes and other things, but that will affect our equipment too. Any loses for any reason are unfortunate, but the best we will do is re-fly your payload if you provide a second payload. To easy your minds on the matter of losing payload, after 20 flights, we have always recovered the payload and that includes flights with problems from unforeseen accidents like invisible downdrafts. Mind you we build our payload frames well and they provide extraordinary results.

Clinton Toyota Space Chicken

Clinton Toyota Space Chicken

This is Clintons Toyota “Space Chicken” was on all the covers of the local newspapers and many other papers and media. The outcome far exceeded the cost of the project and the papers did both a pre and post story with pictures.

The quality of our photography is exceptional and this is a still from a video we took of the flight. It was taken at 33,333km.

Occasionally the press get involved in our flights and this may give you more exposure. The video below was taken in Croatia early in 2014. We are well known all over the world. The two flights that took off from the centre of Zagreb were the first to be launched in the country and carrier student payloads for a competition organised by Team Stellar – one of our sponsors.

Contact me on 0448 881 101 if in Australia or +61 448 881 101 if calling from overseas and please leave a voice mail message if I do not answer the phone. You can also email me on contact@projectthunderstruck.org

Some things we can take up for you:

  • A sign with your name and/or logo
  • A photo
  • A mascot or small toy
  • A small science experiment

What we can’t take up:

  • Live animals
  • things that may injure people
  • things that would be of risk to planes if they, for any reason, impacted the craft
  • things taht may disintegrate in extreme cold or extreme low pressure.
  • Things that will interfere with the other payloads or the tracking systems.

There are plenty of other things that we can’t carry, but please talk to us and we will let you know. This is an extremely cost effective offer and requires complete payment up front. We can offer 50% refund if cancelled as we may have already allocated your slot on a flight and paid for materials. One week before the flight, cancellation will not be possible.

Remember these terms are not for our normal flights that are not at discount prices.

The final video is for Bulla Cloud9 Yogurt that we flew into the jet stream and “froze in the clouds”