Thursday, March 31, 2011

Tentative launch date for GAGA-1: April 10, 2011

In my original post on GAGA-1 I said that I'd like to launch in time for the 50th anniversary of Yuri Gagarin's 1961 flight. It looks like I might manage.

The most recent predictions show the wind dropping next week making a weekend flight possible. The kind folks at CUSF have agreed to help out on the day. Thanks, guys!

So, tentative launch date is April 10, 2011. Hoping for a morning UTC launch. I'll be following along in a car (which will be trackable on the tracker using the comic callsign CarCar-1, GAGA-1 will be transmitting RTTY with call sign GAGA-1 on 434.650 Mhz SSB).

Of course, between now and then the wind could change, but here's hoping...

Even if I don't launch it's going to be a busy weekend, two launches are planned for April 9.

Thursday, March 24, 2011

GAGA-1: Parachute Test

As a small test of the opening of the GAGA-1 parachute I attached it to a bag containing 1kg of sugar using the same cord as will be used for the flight and with the assistance of a colleague threw it out of the window of our office.

We are 8 stories up, so we get a bit of flight time. Here's the video:

The parachute opened nicely and the bag of sugar survived the fall.

Tuesday, March 22, 2011

The Piral

Do you ever think to yourself, "If I took the first 400 digits of pi and drew lines proportional to each of the digits with a fixed angle between each line what it would look like? And then if I change the angle what an animation of that would look like?" Probably not, but I did on the bus home tonight and so with a bit of Processing here's a little animation that I'm dubbing "The Piral".

It starts with the angle between segments as 90 degrees and works its way up to a straight line. The length of each little segment is proportional to the digit of pi (i.e. 3x, 1x, 4x, 1x, 5x, etc.). As pi swirls around it sometimes stretches itself out, and sometimes bunches together, ultimately it spirals ever larger until it becomes a line.

Strangely pleasing to watch.

PS Before you ask. Here's the code
int w = 1024;
int h = 768;

float ad = 90;

void setup()
  size( w, h );

String pi = "314159265358979323846264338327950288419716939937510
void draw()
  float cx = w / 2;
  float cy = h / 2;
  float angle = 0;
  for ( int i = 0; i < pi.length(); ++i ) {
     float d = float(pi.substring(i,i+1))+1;
     float ex = cx + d * cos(radians(angle)) * 3;
     float ey = cy + d * sin(radians(angle)) * 3;
     line( cx, cy, ex, ey );
     stroke(255/d, 25*d, 64/d);
     angle += ad;
     if ( angle >= 360 ) {
       angle -= 360;
     cx = ex;
     cy = ey;
  ad -= 0.06;
  if ( ad < 0 ) {

Sunday, March 13, 2011

Geek Weekends

Here's a quick summary of all the "Geek Weekend" posts I've made.
  1. Bletchley Park, Bletchley
  2. The Brunel Museum, London
  3. The Curie Museum, Paris
  4. Foucault's Pendulum, Paris
  5. The Arago Medallions, Paris
  6. Institut Pasteur, Paris
  7. Kew Bridge Steam Museum, Kew
  8. London Transport Museum, Acton Depot
  9. Charles Darwin's Home

GAGA-1: The Stack

I'm calling the combination of balloon, parachute and capsule "the stack". Here's a diagram of how GAGA-1 will fly:

The balloon is attached to 2mm climbing cord which has a strength of 120 daN (decanewtons). That corresponds to roughly 120x the force of gravity on a 1kg mass. As the capsule has a mass of roughly 1kg there's plenty of safety margin (unless things get really hairy in the jet stream).

4m of cord attach the top of the parachute (where is has an X for that purpose) to the balloon. The balloon is 4m above the parachute so that when the balloon bursts the remnants fall well clear of the parachute and don't get tangled. Note that the parachute is open at all times, when ascending it's pulled taut by the lift from the balloon; once the balloon is gone the parachute simply opens slowing the descent.

To keep the remnants hanging down on 4m of cord away from the capsule there are 8m of cord between the bottom of the parachute and the capsule attachment. You can see the cord bundles in the photograph above. They are attached to the parachute using double bowline with a stopper.

On the capsule there are cords that pass through the polystyrene itself (I pierced it with a long metal skewer and threaded the cord through). Here's a shot of the capsule hanging by its four cords. On the top are the two GPS antennas, the GSM backup antenna for the recovery computer, and the small black tube is the external temperature sensor sticking through.

On the bottom you can make out the UHF antenna that will transmit telemetry to the ground (there's a cardboard cover protecting it which will be removed before flight).

Here's the underside showing the cord threaded through.

And here's the top where the cords come through both the capsule and its cover.

Saturday, March 12, 2011

Geek Weekend: Charles Darwin's Home

A few weekends ago I went to visit Down House where Charles Darwin and his family lived from 1842. It's very close to London and an easy drive. The house is managed by English Heritage and contains a combination of restored rooms and an exhibition covering Darwin, his family life and his work. It was completely restored in 1996.

The museum explains how Darwin ended up thinking about natural selection and contains a large selection from Darwin's own collection. There are his original notebooks on display as well as items he collected, such as these Galapagos finches:

His family life is covered, including the death of his daughter Annie aged 10. This log book details Darwin's observations of his daughter's health and treatments tried.

It's clear that Darwin had a lot of affection for his children. This is a slide he had built that attached to the staircase inside the house to his children could slide down on pillows.

The museum has many parts that are suitable for children. Here's a game that explains how traits are passed down in birds and there's another that shows the link between the number of cats at Down House and the amount of clover growing on the lawn (cats kill mice, mice attack bee hives, bees pollinate; increase the cats and you get more clover).

Darwin himself wasn't averse to a good game. There's a room in the house dedicated to billiards where Darwin would go to relax from the strain of the public reaction to his theory of natural selection.

In his study, there's his armchair which he modified so that it had wheels attached. This allowed him to scoot around the room to get books or specimens without having to get up. Since he would be sitting with a board across his lap for writing it was more efficient to glide around.

Lest you think Darwin was physically lazy any trip should end at the bottom of the large garden with a walk around Darwin's sandy thinking path inside a copse. Darwin had it constructed so he could take a daily constitutional walk while thinking. He would walk around the path using a pile of stones to count the number of circuits he'd done while thinking.

Making an old USB printer support Apple AirPrint using a Raspberry Pi

There are longer tutorials on how to connect a USB printer to a Raspberry Pi and make it accessible via AirPrint but here's the minimal ...