High-Tech Blimps Earning Their Wings

coondoggie writes "The US Army this week showed off its latest high-tech blimp laden with powerful radar systems capable of detecting incoming threats 340 miles away. The helium-filled blimps, or aerostats, are designed to hover over war zones or high-security areas and be on guard for incoming missiles or other threats. The Army wants them to reduce some of the need for manned and unmanned reconnaissance flights. The aerostat demonstrated this week is known as the Joint Land Attack Cruise Missile Defense Elevated Sensor System (JLENS), which is designed to fly up to an altitude of 10,000 feet. According to GlobalSecurity.org., the $1.4 billion JLENS is a large, unpowered elevated sensor moored to the ground by a long cable. From its position above the battlefield, the elevated sensors will allow incoming cruise missiles to be detected, tracked, and engaged by surface-based air defense systems even before the targets can be seen by the systems."

Comments

Re:Shoot down at 10,000 feet is easy

[c6gunner]

In World War 2 the Germans had anti-aircraft guns that could easily get to much over 20,000 feet

Well, yes, artillery is referred to as "guns", but that's a bit misleading, don't you think? If the bad guys have managed to move artillery pieces that close to your base of operations, you've got bigger problems than whether or not your blimp gets shot down.

Many cheap modern shoulder held anti-aircraft missiles can easily shoot this high and a blimp would be easy to hit

Yeah, most modern shoulder-launched ground-to-air missiles could get a lock at that range, but most of these missiles also use infrared guidance. Would a blimp give off enough of a heat signature for a lock?

Re:Why Helium and not Hydrogen?

[RobVB]

This page, despite the horrible colors, does a pretty good job of explaining why helium is used instead of hydrogen.

The main reason to use helium is that hydrogen is indeed flammable, even though it may not have caused the fire on the Hindenburg, it's still highly reactive to oxygen.

From the link:

Hydrogen (atomic weight 1, but exists as pairs of atoms (diatomic), molecular weight 2), should weigh 2g per 24 litres at room temperature, whereas Helium (exists as lone atoms (monatomic), atomic weight 4), should weigh 4g per 24 litres at room temperature. But the mistake is to think that this would automatically make it float twice as buoyantly. The fact that's important is not the weight of the gas in the balloon, but the weight of the air which it displaces.

[...]

Both Hydrogen and Helium weigh almost nothing for the purposes of buoyancy in air. In contrast, air is mainly nitrogen, as pairs of atoms, which has a weight of about 28g per 24 litres at room temperature. To put some figures on it, a 24 litre helium balloon would seem to weigh 4g minus 28g = minus 24g in air. In comparison a 24 litre hydrogen balloon would seem to weigh 2g minus 28g = minus 26g in air. -24g or -26g, take your pick? The difference is about 8%.

So basically, you're either flying a safe blimp, or a giant bomb with 8% better buoyancy.