Send a Teddy Bear to Space! (High-Altitude Balloon)

Learn how to make and launch your own payload to near-space! High-altitude balloons are an accessible way to get a small payload to the edge of space using helium to gently carry your equipment off the ground. There is loads you can do while you're off the ground: take some stunning photos, measure the atmosphere, track your flight using GPS, see how close to true space you can get - the sky is no longer the limit!

Suspended from the balloon is what is called a "payload chain". For our balloon, and for most balloons, this took the form (from top to bottom) of: Latex Balloon, Parachute, Radar Reflector, Main Payload. The Latex balloon and parachute are available to purchase online in various places - we got ours from randomengineering.co.uk. At the bottom of their page you will find a calculator to find the right balloon/parachute for you!

Building the Radar reflector and main payload box is a fun and easy task so here are the parts you'll need!

Radar Reflector:

• Cardboard
• Aluminium foil
• Glue (regular glue stick works well)

Main Payload:

• Polystyrene box (either a DIY one or a pre-bought polystyrene box) - this helps keep all our electronics toasty at -60*C!
• Pocket warmers - this help keep things warm because it can get very cold at altitude
• GPS tracker - we want to get all our equipment back so one of these is crucial! See 'GPS Tracker' below for more info on the variety of options!
• Cameras - when the balloon is high enough you can sometime catch the curvature of the Earth on the backdrop of space which makes for some amazing photos!
• Pilot - we wanted to send a teddy on this amazing voyage, but you can send whatever you like! People have been very inventive with their payloads before

General Parts and tools:

• Rope - see "Mission goals and Safety" for a bit more information on which rope you should use!
• Tape - always useful for holding things together!
• Zip ties - sealing the balloon after it has been filled with helium
• Some scales - we need to know the weight of our payload to choose the best balloon and parachute. We can also use the scales when filling up the balloon to see how much lift we are getting
• Box-cutter knife (please be careful with it)
• Filling tools - if you are filing you balloon from a helium canister you'll need a regulator and some tubing to connect it to your balloon

Other necessary items are dependent on you mission goals - see the below for more info!

Before launching your balloon, set your self/team a challenge to achieve with your launch! Whether this is to get as high as you possibly can, as far as you possibly can, or perhaps to perform an experiment at the edge of space; a clear goal will make planning for the mission a lot easier!

Some ideas for scientific experiments might include:

• Sending some seeds to space and comparing how they grown in comparison to seeds that remained on Earth
• Measuring temperature, pressure or humidity during your flight
• Investigating free-fall when the balloon bursts
• Measure radiation levels as you climb higher - is there any trend in the data?
• Film how marshmallows behave near space - does the lack of atmosphere have an affect?

There is loads on inspiration on the internet for more ideas. As this was our first launch, we wanted to send a teddy bear on the payload and see how well it fared!

Safety

Safety is an important one here so please do your research before you launch! Here in the UK, there are a few things you must do to comply with the law:

• Apply for a launch window with the Civil Aviation Authority (CAA) at least 28 days prior to launch - this grants you exemptions from certain laws and allows a Notice to Airmen (NOTAM) to be issued for your launch so aircraft know to avoid the area if possible. Top tip: you can apply for a launch window of a few days which is a great idea because the weather might not always be on your side! Applications can now be submitted online here
• Payload chain breaking force of no more than 230N - this specifies what rope we can use for the payload chain as it must take no more than 230N of force to break the rope. We, therefore, used this.
• Parachute - these are a must to ensure you payload descends at the right rate. We used the calculator at randomengineering.co.uk to pick a parachute that would keep our decent rate between 4-6m/s.
• Care when using helium. Helium, if improperly used, can leak and displace air causing people to become light-headed and lose focus. Quickest way to solve this is to fill you balloon either outdoors or in a large, well-ventilated space.

This is not an exhaustive list but these are key things to think about! Some information can be found here under "Unmanned free balloons". If you are not in the UK then please research the rules that apply to you.

High-altitude balloons are very safe so just stick to the rules and everyone will be able to enjoy your launch!

To get all you equipment back you're going to need a GPS tracker! These come in many different forms such as:

• APRS
• RTTY Radio
• LoRa
• Satellite
• + a few more

Each one has it's pros and cons as well as different price points. Some popular off-the shelf options include:

• SPOT Satellite tracker (link) - Pros: Good coverage, easy to use; Cons: More expensive, will not work while balloon is above 18,000m
• Flextrak Pi board (link) - Pros: Not too expensive, open standard, works using a raspberry pi; Cons: Intermittent coverage (you might want to setup your own receiving station)
• Light APRS tracker (link) - Pros: Not too expensive, open standard, light weight; Cons: Intermittent coverage
• + plenty more

If you're feeling the DIY spirit, however, why not try and make your own!

Transmitter

We decided to make our own RTTY radio transmitter using an Arduino Uno. We used:

• NTX2 Radio transmitter (link) - this allowed us to send simple ASCII data using the Arduino
• uBlox MAX-M8C GPS board (link) - this collects our GPS data

We connected the transmitter to an Arduino Uno using the schematic and code here. And we did the same for the GPS module. We then integrated the two example scripts to make a program that outputs the GPS data over the radio signal! Once you have this working you can track your payload! You can opt to add some more sensors (temperature, humidity, SD card reader, etc) to get more data and log it. There are lots of online tutorials on how to get these sensors working with an Arduino Uno!

Once you have your final circuit schematic you can make your connections more robust my designing and printing a custom PCB. This is optional and relatively inexpensive but makes your end tracker compact and easy to use!

Receiver

To receive and decode the signal we used an SDR (Software Defined Radio) setup:

• Nooelec NESDR Smart (link) - this nifty little USB dongle can read off a range of radio signals
• Some receiving antennas tuned to 433MHz including a portable Yagi antenna (link) for directional pin-pointing in the event we cannot decode the signal but we are still receiving it

You will then need 3 pieces of software to interface it with a computer:

1. SDR# (or similar) to listen to the signal as audio (SDRSharp)
2. VB Virtual Audio cable to allow your computer to interpret the audio signal as data (VB-Audio)
3. DI-Fldigi to decode the audio data into ASCII plaintext (Fldigi)

Backup Tracker

We were lucky to get access to a satellite tracker as a backup to our own trackers. This tracker uses the Iridium satellite constellation to upload the GPS information. This is similar to how the SPOT satellite tracker mentioned above works.

We used two Apeman A79 action cameras to film the whole flight. These were placed inside a polystyrene box with the rest of the components. Here you get to choose where to place you cameras for the best shots! We went for one facing out the side and the other pointing downwards from above.

The payload box

The payload box plays a very important tole in keeping all you cool hardware protected from the elements. It can get as cold as -60 degrees Celsius at altitude! So some heat is required to keep your electronics operating smoothly.

Polystyrene, while not the only material option, is a good choice as it is lightweight, strong and helps to insulate the components from the cold. Pre-made boxes can be bought online or sheets of polystyrene can be made into a box using glue and tape.

Pocket warmers also help to keep the electronics warm. These are inexpensive and can be placed near electronics inside the payload box to keep them warm.

Top tip: Try and avoid air-activated pocket warmers as where we're going, there is little to no air!

This easy-to-make, simple piece of equipment is an important safety addition to our flight. Planes use Radar to detect other planes while flying. To do this, a large reflective area must be visible to the plane. We use cardboard and Aluminium foil to create this large reflective surface for Radar waves to bounce off of.

To make the reflector, first cut 3 squares of cardboard with a length of 20-30cm. Take two of the squares, and on both squares cut a slot from one of the corners to the centre. You can then slot these two pieces together.

Now, with the untouched square, cut it in half from one corner to another. On each of these half pieces cut from the centre of the longest side (hypotenuse) towards the 90 degree corner, but only cut half way towards this corner. Returning to the two squares we slotted together earlier, pick two opposite corners of the same square where we can cut another slit towards the centre. We can then slot the two half-pieces onto these slots.

This may sound confusing so refer to the diagram on where to cut the slots. Cut along all lines, and then slot together the matching colours. The result should be a cool cube-ish shape

Now, take the glue stick and coat the disassembled cardboard sections in glue. Stick a sheet of foil to each face and cut/wrap it where appropriate. Once all sides are coated in foil, slot the pieces back together again. You now have a Radar reflector!

You may wish to add tape for security, a hole for the rope to go through, and some smaller holes on the upwards facing piece to allow more airflow during ascent/descent (optional).

If you have followed all the above steps (including applying for a launch window) you should now be ready for launch!

Launch day can be exciting and scary so take your time and use a checklist to organise your team

1. Before the launch, make sure all of your equipment is ready to go
2. Make sure the weather is good for a launch - use weather forecasts and sites such as habhub to predict the flightpath of your balloon. Only launch if winds are low, there is no rain, and the predicted flightpath has your payload returning somewhere safe and away from urban areas
3. Check your flight permissions are in effect - some authorities might ask for extra notice of your balloon launch to implement things like Notices to Airmen (NOTAM)
4. Start filling the balloon - using some scales and a weight tied to the balloon, start filling the balloon with helium. You will be able to use the scales to see how much lift your helium is producing. Using the calculator at randomengineering, you can calculate how much lift you need for your balloon given the weight of your payload and your desired ascent velocity (between 4-6m/s is typical)
5. When you balloon is filed and tied (see below tips), attach your payload and move to your launch site. Make sure your balloon is well anchored and someone is holding onto it to stop it accidentally floating away!
6. Do any final checks - make sure those cameras and trackers are switched on!
7. Launch!

Success! You got your first balloon off the ground! Well done! Now for the tricky bit... trying to get it back!

Tips for filling the balloon:

Insert the filling tube in the uninflated balloon and use electrical tape to secure it to the balloon. make sure you tape the tube to the balloon and don't wrap just the balloon in tape! Now attach the balloon neck to your weight/scales. Slowly fill the balloon with helium - stopping every now and then to allow the helium to reach thermal equilibrium with the environment (helium is an expanding gas so will change temperature when released into the balloon. This can change your measured lift). Once you have your desired amount of lift, turn off the helium. Have two people hold onto the neck of the balloon and slowly disconnect the fill tube. Now, use tape to seal two points on the neck of the balloon, and zip ties to ensure an air-tight closure (be careful of sharp corners on cut zip ties!). Now, bend the bottom of the neck of the balloon upwards so the two taped areas meet. We now tape these areas together to form a loop to attach the rope to. Again, zip ties are a good idea to ensure a strong connection.

Top tip: turns out some older iPhones don't like helium so can stop working when near the balloon! They should only stop working temporarily but this can be avoided entirely by keeping them away from the balloon

The chase is on! Now, using all you tracking equipment, follow the balloon! The flight predictor should give a rough idea of where the balloon is going to land. One popular technique is to aim to be underneath the balloon when it bursts as this will give you a good idea of where it is going to come down.

Once it has landed, if you are using a radio tracker you can analyse the signal strength in different directions to pin-point it's location if the data becomes difficult to decode.

Don't venture anywhere unsafe when retrieving the balloon and also seek land-owners permissions where necessary.

Now have a good look at all the data you've collected!

It's important, even if you don't manage to get your payload back, to analyse what went well in the project, and what you will do better next time. That way, your projects will become better and easier to do.

The lessons our team learnt from this were:

• Air-activated heat packs don't work when there is no air
• A longer length of rope to the balloon will improve stability
• Don't leave things to the last minute to test - give yourself loads of time!
• It is very cold at altitude - this cause our trackers to stop working for a while until they returned to a lower altitude (hence the gaps in the data)

Our balloon made it to approx. 20km altitude and we managed to successfully recover the teddy who we are now preparing for future flights!

I wish you all the best in your project and hope you manage to get to space!