Poorman's Space Program
Paul Verhage
Paul.Verhage@boiseschools.org
An Introduction
As Captain Kirk says, space is the final frontier. And what amateur scientist wouldn't want to explore this final frontier? Just seeing earth from space would be pretty neat by itself. But it's not just a pretty view up there. There's atmospheric science, astronomy, resource monitoring, and physics to explore (and that's just for starters).
But there's a major problem, for space flight is very expensive. While it's possible to launch a payload into space for less than $10,000 per pound, that cost is still way beyond the means of the average amateur scientist. And now in the post-Columbia NASA, Get Away Specials (GAS) on the Space Shuttle are no longer available. So for those who want to explore the final frontier, what options are available for us amateurs that are close enough to the real thing?
I have one. Near space is close to real space in most aspects. And it's far more accessible to the amateur scientist.
What is Near Space
There's no standard definition for near space, but the United States Air Force has one that's as good as anyone else's. They define near space as those altitudes above 18.3 km (60,000 feet) but below the International Aeronautical Federation's boundary of space of 100 kilometers (328,000 feet). Airplanes are good for altitudes below near space and sounding rockets are good for altitudes above near space.
Only a few aircraft have flown to 3 km (100,000 feet), including the U-2 (or TR-1), SR-71 and F-104. This leaves only one vehicle for regular trips into near space, and it's much cheaper than an airplane or a sounding rocket.
Getting to Near Space
Over 200 helium-filled weather balloons make the trip into near space every day. The National Weather Service launches weather balloons (their payloads are radiosondes) to measure the temperature, pressure, and relative humidity profiles of the atmosphere. By radio tracking the flight of the balloon they can also measure the wind speed and direction at various altitudes. Readers can use the same sounding balloons to carry their payloads to extraordinary heights in the name of amateur science.
Benefits of Balloons over Rockets
Some amateurs launch experiments on amateur rockets. But these amateur rockets have limitations that weather balloons don't (I'll discuss four of them). Weather balloons (also called sounding balloons) can lift 5 .4 kg (12 pounds) of payload with minimum trouble according to Federal Aviation Administration (FAA) regulations. Because you'll want your experiment back, some of those 5.4 kg will be tracking equipment. But if it's done right, most of those 5.4 kg will still be experiments. There aren't many amateur rockets that can carry 5.4 kg of experiments.
Launching experiments on a sounding balloon exposes them to a lot less acceleration stress than a rocket launch. This means more of your payload weight will go into the actual experiment and not into survival structure.
Balloons take on the order of 90 minutes to climb to their peak altitude (mine average 26 km or 85,000 feet). So more data-collecting time is available on a balloon flight than on an amateur rocket flight.
Finally weather balloons and helium are cheap compared to an amateur's high power rocket and rocket motor. Dollar for dollar, you're experiment will go higher on a balloon than an amateur rocket. Balloons really are the poorman's space program.
Conditions in Near Space
Just how close is near space to real space? Let's look at a several environmental conditions and find out.
Standing 1.8 m (6 feet) tall, you'll typically see 5 km (3 miles) to the horizon (assuming the ground is flat). Space Shuttle astronauts in orbit see around 1,600 km (1,000 miles) to the horizon. From an altitude of 3 km (100,000) feet a weather balloon sees nearly 640 km (400 miles) to the horizon. On the surface we see a flat horizon. But photographs taken from near space shows that the earth is curved.
Figure 1. The horizon as photographed from a high-altitude balloon.
As a rule of thumb, the air pressure decreases by 50% for every 5.5 km (18,000 feet) increase in elevation. So at an altitude of 3 km (100,000 feet) the air pressure is just 1% of the air pressure at mean sea level. Atmospheric refraction, specifically Rayleigh scattering, makes the sky blue. But above an altitude of around 2.3 km (75,000 feet) there is too little air to scatter enough light for the sky to appear blue. Therefore the sky becomes black, just like in space.
Figure 2. Atmospheric pressure during the flight of a high altitude balloon.
On the earth's surface we're protected from cosmic radiation by the atmosphere. This means that aircraft pilots and passengers can sometimes fly high and long enough to be exposed to more cosmic radiation than we are at the earth's surface. A Geiger counter flown into near space detects a cosmic ray flux over 100 times greater at 18.9 km (62,000 feet) than at launch.
Figure 3. Cosmic ray intensity increases with altitude as shown by this data from the flight of a high altitude balloon.
Near space has a near vacuum, black sky, high cosmic ray fluxes, distant horizons, and a curved earth. So in many ways the conditions in near space are closer to those in space than to those near the earth's surface.
One thing that near space doesn't have that space does is zero gravity. Since the balloon isn't in free fall like an orbiting satellite, the 1% reduction a balloon sees in the acceleration of gravity at about 31 km (100,000 feet) is brought about by its increased distance from the earth's center. For safety reasons I don't recommend trying to replicate zero gravity conditions through free fall. Leave that to the professionals.
One final note: At an altitude around 31 km the atmospheric pressure closely matches that of the surface of Mars. While there is still shielding from cosmic radiation by earth's magnetic field, the conditions at 31 km are a good analogy for the surface of Mars. So you may want to think about testing that Martian experiment in near space before you try to fly it to Mars.
Some References
The Poorman's Space Program column will explain in detail how to design and fly experiments into near space. It will also discuss some results from experiments performed in near space. I want to share not just my experiments but also the experiments of my readers. Ultimately I'd like to develop a procedure that will manifest amateur experiments on balloon flights. Perhaps amateurs can recreate the old Shuttle GAS (Get Away Special) experiments.
Meanwhile you can look over these web sites for additional information. My near space book is available as a free download from Parallax. Parallax makes the BASIC Stamp, an easy to use and capable microcontroller. This microcontroller is the best toy I've every played with and I encourage readers to give them a try. They make possible a lot of experiments, including near space flights. You can download a copy of my book at http://www.parallax.com/html_pages/resources/custapps/app_nearspace.asp
Ralph Wallio is Amateur Radio High Altitude Ballooning's (ARHAB) greatest advocate and supporter. You'll find lots of links and background information at his web site, http://showcase.netins.net/web/wallio/
I maintain a web site of my near space activities at http://nearsys.org
Background Information
Some information on the cost of space flights can be found at these two web sites.
http://www.spaceref.com/news/viewnews.html?id=301
http://www.futron.com/pdf/resource_center/white_papers/FutronLaunchCostWP.pdf
Onwards and Upwards, Paul.
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