Reusable Open Stratospheric Explorer (R-OSE)

A Multi-Balloon Stratospheric Platform for Remote Sensing Experiments

Project summary

The R-OSE project aims to design an innovative observation platform with very high spatial resolution (less than a meter) based on the use of small multiple stratospheric balloons. The use of small stratospheric balloons comes with a limit on the payload that can be lifted into the stratosphere. The typical payload is around 1.5 kg per balloon (assuming a 600g balloon). By using a combination of more than one balloon, it is possible to significantly increase the mass of the payload and therefore increase the possibilities in terms of remote sensing projects. The R-OSE platform is not equipped with a separation system allowing the balloons to be released at the desired time or altitude. Instead, we count on the fact that at maximum altitude, a first balloon will burst so that the remaining thrust force will not allow the other balloon to remain buoyant. The payload will then begin its descent, slowed by the thrust of the remaining balloon and by the friction of the parachute. R-OSE consists of a triangular shaped platform on which the flight controller, an alarm and a GPS/Satellite beacon are placed to more easily find the payload at the end of the flight. The platform is partly made of floating material so that the recovery should be possible over water bodies. and a wind vane to limit its rotation. On the lower face of the platform, a universal joint is used to attach the camera system gondola to maintain nadir pointing even when the platform is tilted. The flight chain is made up, in order from bottom to top, the camera system, the platform, a swivel, a parachute and the balloon(s). An important part of the project consists of the creation of a simulator to determine the burst altitude of the first balloon as well as the ascent and descent speed. This information is typical input to trajectory simulators for stratospheric balloon flights.

The platform

The platform

The platform is basically made of triangular 25mm thick extruded polystyrene sheet. The triangle edge length is 2 feet (about 600mm( long.

We use a kevlar rope to attach the 3 vertices of the structure to the swivel. The center of the triangle is also tied to the swivel by using a taut-line hitch knot that allow us to tighten the rope in order to get a better support of the payload and reduce the risk of triangle breakout. To learn how to make the taut-line hitch knot, check that video https://youtu.be/_FfrIS8WQHc

Each of the 3 vertices are aimed to support different parts of the system (GPS/satellite device (a SPOT trace device), the flight controller PCB, a buzzer powered by 2 alkaline #23A 12 Volt batteries thermally isolated pack, and the 5V 5000 mAh powerbank. The powerbank is thermally protected by an isolated enclosure made with a piece of extruded polystyrene.

Flight controller

Components

PCB

The PCB contains many sensors and a raspberry pi zero W to read their values. It includes a GPS module that should be operating at least up to 30 km in altitude, a 3D accelerometer, an altimeter/barometer and a 3D magnetometer.

Battery packs

The flight controller is powered by a 5V 5000mAh powerbank. The camera system will be powered by a combination of 18650 lithium batteries. A DC-DC stepdown converter transforms the higher voltage of that battery pack into 5V supply.

GPS/Satellite beacon

We are using the VCC 3.3 pin, the GND and the RX and TX. RX and TX are respectively connected to GPIO 15 and GPIO 14 on the Raspberry pi zero W.

Buzzer

We use the buzzer to facilitate the retrieval of the platform after the flight. We selected the CLT1083 buzzer and power it with 12 Volt batteries. For convenience, we added a switch to activate the buzzer just before launch. The buzzer is available from Amazon https://a.co/d/ftuuRn9 but any other buzzer should be used without problem as long as it emits loud enough (~ 100 dB à 12 V CC / 30 cm).

Active stabilisation

We replicate the following project from https://charleslabs.fr/en/project-Reaction+Wheel+Attitude+Control The system aim to decrease the rotation of the platform. In our experimental flight without stabilisation, we observed a rotational oscillation of the platform completing a cycle typically every 15 seconds. Along with the use of the stabilisation system to reduce that oscillation, we think of scheduling the images acquisition when the rotational speed of the system will be close to zero.

Software

https://github.com/gal1leo31/r-ose

To download the code:

The multi balloon simulator

The launch procedure

The mass budget

Mass budget flight 1 (One 600g balloon)

Creative Commons Attribution-ShareAlike 4.0 International License

Useful links

• github repository