Insertion of a CanSat in the CanSat launcher v6

A feature of Stratos II that is new for DARE, is that Stratos II will contain up to 12 external payloads. Payloads itself are not entirely new, as DARE has had some external payloads previously, in the form of the CanSats for the CanSat launchers. CanSats are small can-sized “satellites” designed and built by high school students, and then launched by DARE to 1 km altitude.

New is that the 12 external payloads in Stratos II will interface with the onboard computer. The power for the payload, as well as the data storage and wireless data link will be provided by the flight computer. Because such an system has never been designed or built by DARE before, after designing the electronics system on a very high, system level, the first subsystem that was paid attention to was the payload controller.

Interfaces

The primary function of the payload controller is interfacing. The rocket as a whole should interface both on an electrical and a mechanical level; in this post though only some rough details about the electrical interfacing will be stated. The following electrical interfaces exist:

• Power: payloads will be powered and will be limited to a maximum current. If they exceed this current, they will be powered off. This prevents a single payload that short circuits from blowing up the entire electrical system.
• Commands: Some very basic commands will be transmitted to the payload. Most of them will be simply to inform the payload of the current status of the rocket in flight.
• Data: To simplify payloads, payloads will be able to transmit a certain amount of data which will be communicated over a wireless link to the ground and also stored on a micro SD card. As seen before micro SD cards do not always survive rocket flight and therefore it is important that the data is also transmitted real time.

The payload controller is designed fail safe: everything is to be as isolated as possible, so that a failure in a single payload cannot cause failure in one of the adjacent systems or even the whole rocket.

The remnants of an SD card that encountered Earth with about M 0.8 (=1000 km/h)

Data multiplexer

Because the payload controller is already responsible for multiplexing the data from 12 external payloads, it was decided that the payload controller will also be interfacing with some of the Stratos II internal subsystems that generate data. As such it is not only the payload, but also the general data controller, that multiplexes (presumably 15 to 20) data streams and outputs a single one to the transmitter and data storage.

Status

Currently we are doing a block level design of the payload controller. We hope to finish this phase soon and get into schematic and PCB design soon, so that we can start building and testing it. The first version is planned to be ready for flight in April.

A mid-level schematic of the payload controller

So far the update from the electronics about the payload controller. In the next update we will probably look into a system that we have dubbed The Backbone, and how it will help preventing Stratos II from looking the same as the cable mess behind your desk.