{"id":2257,"date":"2018-02-08T15:28:04","date_gmt":"2018-02-08T15:28:04","guid":{"rendered":"http:\/\/www.daveakerman.com\/?p=2257"},"modified":"2018-02-09T11:48:05","modified_gmt":"2018-02-09T11:48:05","slug":"2257","status":"publish","type":"post","link":"http:\/\/www.daveakerman.com\/?p=2257","title":{"rendered":"I’ve Got No Strings"},"content":{"rendered":"

NASA have given us many iconic photographs, such as “EarthRise<\/a>” and “Man On The Moon<\/a>“, but there’s one which is more easily replicated if you’re not NASA or Elon Musk, and that is the image of Bruce McCandless<\/a> floating freely in space during the first untethered spacewalk:<\/p>\n

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So several months ago I set about replicating this as best I could, under a high altitude balloon.<\/p>\n

Revell Model<\/h2>\n

Revell USA made an astronat\/MMU kit back in 1984; samples now are rare and expensive, but eventually I found an unused kit in the UK on ebay.\u00a0 It was a good price, complete and original:<\/p>\n

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The kit arrived late last year, and I assembled it over the Xmas break, in preparation for a launch on (hopefully) February 7th, 34 years to the day after the original flight.<\/p>\n

Cameras<\/h2>\n

I wanted to include several cameras for the flight, both video cameras and still cameras for downloading live to the ground during the flight.\u00a0 Having tried several different action cameras in the past, my current favourite is the Gitup Git2 camera – reliable, inexpensive and plenty of options in the firmware.\u00a0 I combined\u00a02 of these (one Git2 with wide-angle lens, and one Git2P with a normal lens) with some AA-powered powerbanks to extend the run time from about 90 minutes to several hours using 64GB SD cards.<\/p>\n

I also wanted live images, ideally from different viewpoints.\u00a0 The only reliable live image cameras I’ve used are the Pi models, and these are one-per-Pi.\u00a0 So I built a small network with 3 Pi boards using the built-in wireless modules to pass image files between them; a Pi3 as an access point, and Pi Zero Ws as clients.\u00a0 All live images were then downlinked in squence by one Pi using LoRa.<\/p>\n

In the end it wasn’t really feasible to set up vastly different viewpoints as the astronaut model is quite large and the payload would have then been huge (and cumbersome, and delicate), so I had the cameras all quite close to each other.<\/p>\n

Payload Build<\/h2>\n

I decided to place each Pi in its own Hobbycraft box.\u00a0 The Zeroes are very small of course and even with an AA powerbank there was space to fit a video camera with its own powerbank inside the box:<\/p>\n

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Next came the main Pi, with its own camera, 3G (later removed due to insufficient power from the powerbank) and UBlox USB GPS, all inside 2 of the same boxes glued together:<\/p>\n

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Finally, I added a backup tracker in case the main one failed for any reason, and to provide a programmed cutdown to prevent the flight drifting too far:<\/p>\n

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There was one last thing to do – my Revell model isn’t identical to the version that NASA flew, and most prominently was missing a camera.\u00a0 Easily fixed with some foam polystyrene and a plastic cap!<\/p>\n

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Bruce Junior was now ready for flight!<\/p>\n

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The Flight<\/h2>\n

The flight predictions for my chosen date were not ideal, but quite good for the time of year.\u00a0 Initially I was going to have help from another HABber but he couldn’t make it that day, so I launched alone.\u00a0 To make that task easier I removed some items from the flight, allowing for a smaller balloon and less gas.\u00a0 I also chose to launch later in the day than planned, which meant I didn’t need to overfill the balloon so much to keep it away from the sea.\u00a0 Here’s the predicted flight path:<\/p>\n

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Less gas means less lift which makes it easier to tie the balloon and handle it afterwards. Aside from the cold, it was a very nice day to launch – fairly clear skies and not too much ground wind.\u00a0 Here’s the partially-inflated balloon:<\/p>\n

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Meanwhile the payload cameras were recording and transmitting to the other HAB enthusiasts online:<\/p>\n

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With the balloon fully inflated, tied off and tied to the parachute and payloads, it was time to launch:<\/p>\n