Skip to main content

GAGA-1: Redundancy and Independence

When I first thought about building GAGA-1 I imagined building a single flight computer that would control everything: it would read GPS, transmit telemetry, send SMS messages and operate the camera. But that would have created an enormous risk of complete failure.

If the main computer failed (and there are so many ways to fail: bad software, a hardware fault, loss of electrical power, loss due to low temperature/pressure) the entire flight would have been a failure: no pictures, no telemetry to aid recovery. In fact, the only thing that would have worked is the dumb latex balloon happily exploding at altitude.

So I've opted for a design with three independent systems with no electrical connections between them and independent power.

1. Flight computer

This main computer will receive data from the primary GPS, read internal and external temperatures, and transmit telemetry over the RTTY link. This is the Arduino-based system for which I am building a custom shield. The flight computer will transmit telemetry via an antenna on the bottom of GAGA-1 (since its primary use will be in flight we'll have a clear view of the capsule's underside). The GPS antenna will be on the top so that it 'points' towards the GPS satellites.

2. Recovery computer

This secondary computer will have an independent GPS and a GSM modem for low altitude telemetry. While the balloon is below 3km it will transmit its position and altitude using SMS messaging via an external antenna mounted on the top of GAGA-1 (since its intended to be used on and near the ground). This separate board will use it's own 3.7v battery from an old cell phone.

3. Camera

I've previously described the camera which will operate automatically throughout the flight.

The flight goals are as follows:

1. Safe recovery: hence the two independent computers for telemetry and GPS using independent GPS modules and different transmission methods.

2. Photography: the camera could fail, but I can't afford the weight budget of two cameras for this flight so I've done extensive testing on the camera itself.

3. Constant tracking: the flight computer will transmit RTTY as has been used by many others to track their flights. I hope to have constant RTTY data available so that the flight can be tracked continuously (since that's part of the fun).

The flight can survive a loss of either computer, and if both computers failed I'd still have balloon flight prediction and a mobile number stencilled on the box to aid recovery.

Comments

Popular posts from this blog

Your last name contains invalid characters

My last name is "Graham-Cumming". But here's a typical form response when I enter it:


Does the web site have any idea how rude it is to claim that my last name contains invalid characters? Clearly not. What they actually meant is: our web site will not accept that hyphen in your last name. But do they say that? No, of course not. They decide to shove in my face the claim that there's something wrong with my name.

There's nothing wrong with my name, just as there's nothing wrong with someone whose first name is Jean-Marie, or someone whose last name is O'Reilly.

What is wrong is that way this is being handled. If the system can't cope with non-letters and spaces it needs to say that. How about the following error message:

Our system is unable to process last names that contain non-letters, please replace them with spaces.

Don't blame me for having a last name that your system doesn't like, whose fault is that? Saying "Your last name …

All the symmetrical watch faces (and code to generate them)

If you ever look at pictures of clocks and watches in advertising they are set to roughly 10:10 which is meant to be the most attractive (smiling!) position for the hands. They are actually set to 10:09.14 if the hands are truly symmetrical. CC BY 2.0image by Shinji
I wanted to know what all the possible symmetrical watch faces are and so I wrote some code using Processing. Here's the output (there's one watch face missing, 00:00 or 12:00, because it's very boring):



The key to writing this is to figure out the relationship between the hour and minute hands when the watch face is symmetrical. In an hour the minute hand moves through 360° and the hour hand moves through 30° (12 hours are shown on the watch face and 360/12 = 30).
The core loop inside the program is this:   for (int h = 0; h <= 12; h++) {
    float m = (360-30*float(h))*2/13;
    int s = round(60*(m-floor(m)));
    int col = h%6;
    int row = floor(h/6);
    draw_clock((r+f)*(2*col+1), (r+f)*(row*2+1), r, h, floor(m…

Importing an existing SSL key/certificate pair into a Java keystore

I'm writing this blog post in case anyone else has to Google that. In Java 6 keytool has been improved so that it now becomes possible to import an existing key and certificate (say one you generated outside of the Java world) into a keystore.

You need: Java 6 and openssl.

1. Suppose you have a certificate and key in PEM format. The key is named host.key and the certificate host.crt.

2. The first step is to convert them into a single PKCS12 file using the command: openssl pkcs12 -export -in host.crt -inkey host.key > host.p12. You will be asked for various passwords (the password to access the key (if set) and then the password for the PKCS12 file being created).

3. Then import the PKCS12 file into a keystore using the command: keytool -importkeystore -srckeystore host.p12 -destkeystore host.jks -srcstoretype pkcs12. You now have a keystore named host.jks containing the certificate/key you need.

For the sake of completeness here's the output of a full session I performe…