846 TS - The Need for Speed


In the beginning there was the Snark. That is how the Holloman High Speed Test Track (HHSTT) got its start. The Snark, a name taken from the Lewis Carroll poem, was a ground-launched, jet-powered cruise missile with a range of nearly 1500 miles, weighing nearly 14 tons and was the size of a large jet fighter. It was designed to be launched by a pair of on-board rockets but they were not ready when the missile was. So, the Air Force decided to launch Snarks from a rocket-powered sled. And so in 1950 from a 3500-foot long track, a Snark missile was launched from a moving sled. That became sled run number one. More than 11,000 more sled runs of all types were to follow.

On that same track in 1954, Dr. (Major) John Paul Stapp made his "fastest man on earth" ride aboard the Sonic Wind rocket sled. Eventually retiring at the rank of Colonel, Dr. Stapp was testing the effects of high speed acceleration and deceleration on humans to increase the chances of pilot survival in case of an airplane crash. Colonel Stapp sustained more than 40 times the pull of gravity in both positive and negative directions (or, eyeballs-in or eyeballs-out if you prefer). Not only did these tests pave the way for further crew survival testing, but they also served as the genesis of the lap and shoulder safety belts in automobiles. So, whenever you "buckle-up" in your car, you are actually fastening something similar to a "Stapp Strap." 

The track been extended several times over the past few decades and is now an astounding 10 miles long. This increase in track length improved test mission capability and expanded HHSTT mission areas. One of these missions is testing aircrew ejection systems from various supersonic aircraft. Well over 1,000 such ejection tests have been performed over the years at HHSTT. Similarly, if you need to test a missile payload, warhead or artillery shell, then the HHSTT is where you come.

As the HHSTT and its missions have evolved, it has become the most precisely surveyed, most accurately aligned and best instrumented test track in the world. Indeed, the HHSTT has long been a key national defense asset and is regarded as the "gold standard" in the ground-based testing arena. Much of the high regard accorded the HHSTT is due to the quality of the electronic and photographic data collected for each test.

The electronic data collected at the HHSTT provides customers with very detailed information about their test - each second of data is divided into 10,000 individual slices. That is equivalent to having your car odometer measure your mileage every 6 inches!

Of equal value to HHSTT customers is the extraordinary photographic data collected during each test. The HHSTT photo team provides the finest quality, ultra-high speed images in the business. Using a combination of traditional and high-tech methods, images of striking clarity and diagnostic utility are provided to each customer.

In the mid 1960s, test speeds of Mach 6 (six times the speed of sound) were achieved; then on the 18 December 1969 a new world land speed record exceeding Mach 7.3 was set. A novel sign as you approach the HHSTT headquarters states the speed limit in Great State of New Mexico is Mach 10! The HHSTT, nearly always referred to as simply "the Track," continues to set world land speed records.

Although the physical constraint of controlling aerothermal heating has slowed the progress of achieving Mach 10, the HHSTT keeps edging closer. In the early morning of 30 April 2003 the HHSTT set the current world land speed record. A test projectile weighing nearly 200 pounds was propelled down the track at Mach 8.6, more than three times the muzzle velocity of a high-powered hunting rifle. The elusive Mach 10 speed may yet be reached as HHSTT works to satisfy its customers' demands for greater velocity. However, there are limits on how fast a test object can be propelled through the atmosphere, even in the thin air of the high Chihuahuan desert of southern New Mexico.

Just as meteors are burned up by friction in the upper atmosphere, air friction can cause a high-speed sled to burn up, even if made of the toughest steel alloys. An engineering sleight-of-hand is used to increase those "burn-up" limits by reducing the density of the atmosphere around the track. To do this, one needs a safe, non-toxic, low-density gas such as helium. Helium is only one seventh the density of air, significantly reducing friction between the high speed sled and the atmosphere. Enter the "helium bag" concept.

No one person takes ownership of the idea, so it was probably a combination of brainstorming and inspiration. But like any elegant engineering solution, simplicity is at its heart. It involves enclosing a portion the track with a plastic sheet, not unlike the plastic drop cloth found at the hardware store. This tube is sealed off and pumped full of helium to force out the air. A helium-filled tube that can stretch for more than a mile then covers the track.

Although initially used in early 1972, the first completely successful test mission was in support of a warhead fuse impact test when 5,000 feet of helium bag was used on 5 October 1982. During this test, the sled reached a peak velocity of over Mach 8.1, which at that time was another world land-speed record.

Getting the plastic bag to stick to the concrete base of the track in order to prevent helium leaks was quite a challenge. The engineers tried using weights, tie-downs and double-sided tape, but these methods proved to be only partially successful. Just recently, that nagging problem was solved using another elegant engineering solution. The bag is now fixed in place with a rubber tube spline that secures the plastic in a groove along the track's edge - just like you'd use to fix a window screen. It is zip-lock tight and can withstand the elements for extended periods, holding the bag in place with few leaks.

The helium bag is proven technology, but the question now is how to further reduce the effects of the atmosphere. Ideally one would like to have the track run through a near-vacuum chamber to simulate high altitude or near-space conditions. Although there have been various concepts proposed for creating such a structure at the HHSTT, the construction costs for now are too expensive. But if past performance is any indicator, the engineers, technicians and artisans at the HHSTT will use their innovative approach to meet this challenge.

Their desire is to go fast, save money and get data like no other place on earth. Compared to an actual flight test, the track can provide a 90% solution at 10% of the cost. That's why customers from all over the world continue to line up at the Holloman High Speed Test Track - to make sure their test missions stay on track toward the future.