Nuts and Volts - May 2014

Sending payloads into near space is far less expensive than sending an identical payload to low earth orbit (LEO). That doesn’t mean, however, that near space is cheap. A near space launch costs about $120, putting the cost to around $10 per pound of payload. That compares favorably with launches to LEO where the cost is much closer to

$10,000 per pound.

Even at a low $120 per flight, you want to increase your chances of a successful mission. This is why testing payloads prior to a mission is critically important for anyone contemplating a near space launch. One of these tests should be a cold soak in near space like conditions.

Conditions in Near Space

If you’re a reader of this column, you’ll know that near space is a bitterly cold vacuum. Temperatures drop to - 60°F on a warm day and down to -90° during winter. There are a lot of things you might want to send into near space that don’t like these conditions. Here’s an example.

Batteries use a chemical reaction to create a current. Like all chemical reactions, a battery’s reaction rates increase when its temperature is higher. Operating a payload with the wrong type of battery is an invitation to disaster. That’s because once the battery’s temperature gets too cold, payload power ceases and the experiment fails. So, where can you test a battery prior to a near space launch? In a thermal vacuum chamber (TVC).

Thermal Vacuum Chambers

I wrote a series of articles on TVCs when the availability of affordable Chinese vacuum pumps made them a realistic bench-top test tool of near space research. Essentially, the near space TVC I’ve written about previously is a metal can connected to a vacuum pump. The exterior of the can is surrounded by dry ice and the interior is evacuated of air. Inside, the item under test experiences the cold and vacuum of near space.

The issue I’ve always faced with my TVC design is the determination

68 May 2014

I'm still in the process of upgrading my thermal vacuum chamber (TVC)

design. Part of the current upgrade is incorporating a thermometer. The problem is that I haven't located an affordable thermometer that reads below - 50°F.