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Near Space Simulation


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These are the notes for the near space simulation given at GPSL 2009. In it, you learn how many aspects of a near space mission can be simulated on the ground and possibly save money.

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Near Space Simulation

  1. 1. Slide 1 Slide 2 I want to explain how I simulate aspects of near space missions. Slide 3 And by the end of this presentation, you should know the following. 1. What characteristics of a near space flight can be simulated 2. Why we may want to simulate near space missions 3. And how many of the characteristics of a near space mission can be simulated inexpensively Slide 4 So what are we going to simulate? Slide 5 It’s these six characteristics of near space. Clockwise from the upper right they are, 1. The near vacuum 2. The changes in acceleration 3. The altitude reports from the GPS receiver and mission elapsed time 4. The extreme cold 5. The ultraviolet levels 6. The background radiation Slide 6 Now why simulate them? Slide 7 One word, money. While a near space mission is cheap compared to launching a satellite into space, there’s still a cost involved. As this slide points out, there are several components in a near spacecraft with potentially significant costs. At minimum, you’re probably spending at least $200 for a near spacecraft and its launch. At the high end it can be over $1,000. Fortunately, much of that cost is recoverable. Unless that is, you lose the near spacecraft. Good simulation can reduce the risks associated with failed experiments and lost trackers. Slide 8 Now we get to the details and the toys Slide 9 Here’s a list of stuff you need to make simulators. That’s not too much, is it? Slide 10 The first is one of the simplest. Essentially, it’s a Styrofoam ice cooler filled with dry ice. You want to use dry ice in order to keep the interior dry. I recommend small fans be
  2. 2. installed inside the cooler to circulate the air. Doing so makes the interior more uniformly cold. Show my cooler Slide 11 Next is the vacuum pump. I recently found two variations. The most capable is a vacuum pump used for automobile air conditioners to evacuate the system of air and moisture. I found an affordable one at Harbor Freight that can evacuate a flour canister within one minute. The necessary plumbing supplies are available at your local Ace hardware. The pressure gauge however, I found at a Car Quest. With this system, I can achieve around 99% vacuum with a large container. That’s about 100,000 feet, which is plenty good enough for most any near space simulation. The major problem is sealing the lid properly. This semester I’ll get a better lid turned for the canister. Don’t demo the chamber just yet The second pump is a Handi-Vac. It’s a handheld bag sealer for freezing food. Now this sealer only reaches 50% vacuum, or the equivalent to 18,000 feet. This is ore appropriate for model rocketry tests. To prevent atmospheric pressure crushing the experiment, place it inside of a plastic Tupperware container with holes drilled in it. Then seal the closed container inside a bag and pump it down. I image this system may be useful for vacuum bagging composition structures while they harden. Demo the Handi-Vac Slide 12 Next is a simulator for the GPS reports a flight computer will receive. This PICAXE- 08M is programmed to replicate the GGA sentences a GPS receiver will output during a near space mission. The climb rate, maximum altitude, and descent rate are all adjustable by setting three constants in the code. It’s designed to plug right into the GPS port. So plug it in and watch your near spacecraft run through a mission over the next 2-1/2 hours from the comfort of your own kitchen. An upgrade will use a PICAXE with more memory so more GPS sentences can be simulated. Slide 13 The next simulator is Fiesta Ware, a popular chine from the 1950s. The orange plates have an interesting property; they’re radioactive. That’s because the orange uses a uranium-based chemical. Uranium is an alpha emitter with energies of around four million electron volts. Near space is filled with cosmic radiation. This radiation consists primarily of protons. But there are some alphas, betas, and gammas along with mesons. The alphas from uranium are not a perfect match, but they are better than letting an experiment sit here on the ground.
  3. 3. Next, I need to locate other radioactive sources. I already know that the beta emitter of a potassium isotope is too weak. Does anyone have some spare tritium? What about Cobalt-60? Slide 14 Near space missions reach the stratosphere. At maximum altitude, some near spacecraft are half way through the ozone layer and exposed to hazardous levels of ultraviolet radiation. There are three ultraviolet bands. UV-A makes it to the ground and is responsible for the vitamin D production of our skin and sunburns. UV-B is almost entirely blocked by the ozone layer and the one near spacecraft experience. UV-C is blocked at altitudes higher than almost any near spacecraft can reach. A cheap source of UV is the tooth brush sanitizer. I found one at Walmart for $10. The UV is generated with a mercury lamp and its battery operated. The lamp produces 254 nm UV which actually places it within the UV-C band. But for the price, it’s unbeatable. Slide 15 No one every said a near space mission was easy. There’s a whole lot of shaking going on at launch and when the balloon bursts. Then there’s a good bump when the near spacecraft lands on the ground. You can simulate this rapid changes in speed and acceleration with shake and drop tests. They are important when it’s important that experiments maintain their alignment or if delicate samples are packed inside the capsule. A 10 mph bump down is simulated with a drop of seven feet. So climb a ladder and drop away. The chaos at burst can be simulated by shaking the capsule on a cord tied to the end of a stick. Make the stick strong and long enough that you won’t bounce the capsule off your head. Slide 16 Now let me demo my environmental test chamber