Rocketry Planet

November 8th, 1998 began as a brisk Autumn day in Orangeburg, South Carolina for Jim Mitchell of Dynamic Propulsion Systems. It marked the second day of the Tripoli Experimental launch and the day Jim's massive Nike Smoke would take to the skies.

One of the most impressive large rockets ever flown at the Orangeburg site, the Smoke easily wowed the crowd at this year's event. Flying on 17,000 newton-seconds of DPS N-4750, the roar of the motor will be long remembered by the attendees.

Jim's project began life as a 12" diameter shipping tube. Outfitted with a 115mm motor mount tube, this is one rocket that can take a lot of abuse.

Weighing it at 160 pounds fully loaded, the Smoke is no lightweight. The airframe, which is roughtly .25" in thickness, was covered with layers of fiberglass cloth to strengthen the exterior.

The nose cone is a piece of art as well. It features a built-up construction using a core tube surrounded by a fiberboard outer form that was then filled with foam. It was then covered in layer after layer of fiberglass cloth to add the necessary rigidity to survive the landings for such a long nose.

You can see from the photograph at the left just how sturdy the construction of this rocket is. Everywhere you will find large fasterners and heavy duty mounting plates -- Jim skimped on nothing when building a rocket of this size. The nosecone alone weighs 26 pounds! Inside of the panel to the right, an Adept altimeter is housed to deploy the nosecone's main parachute. A separate altimeter in the booster section deploys the two drogue chutes at apogee, one of which is attached to the sturdy U-bolt visible to the left on the coupler.

The business end of the Smoke houses a 115mm motor mount tube, something Dynamic Propulsion Systems has been pioneering in the way of a motor standard. This flight was based on one of Jim's N-4750 motors, a behemoth of a beast that produces over 17,000 newton-seconds of thrust.

Noticable in this photograph is the fact that the airframe is removable, indicated by the slots leading to the rear of the airframe from the fins. This allows total access to the fins and motor mount area should the need arise to replace a structural component.

You can also see the rail guides that bolt securely to the aft centering ring. Hoisting a 160 pound rocket requires strong mounts, and the large aluminum bar stock provides just that while also allowing the weight to be kept to a minimum. The guides were machined from round aluminum bar stock and then welded to flat bar stock before being drilled with the corresponding mounting holes.

Jim's business is rocket propulsion, and he has created some very reliable motors of all sizes for the hobby rocketry industry. His motors feature reloadable design, reusable graphite nozzles and snap-ring assembly.

Jim is also one half of Thunder Flame Associates, the provider of the two day propulsion class that teaches you the basics of building rocket motors, including a chance to fly your own results. The class is given often at locations all around the country.

There were many DPS and Thunder Flame motors that were flown at this launch. I am not aware of any that failed. Jim's designs are solid and dependable, and the results speak for themselves.

After the motor was prepped, the recovery system was assembled for this particular flight. The recovery system uses t-w-e-n-t-y s-i-x grams of ffffG black powder to separate the sections at apogee. That's a LOT of black powder!

Other components consist of 2" wide seat belt-type nylon webbing to attach the sections together to the recovery system utilizing 5/16" thick quick links. A large drogue parachute is attached to the booster and another large drogue is attached to the nosecone.

At apogee, the primary altimeter fires the 26 gram charge, separating the nose from the body. Once separated, the two parts descend independently of each other to 750 feet where the primary recovery devices are deployed, the nose cone having it's own altimeter for primary deployment.

The main recovery parachute for the airframe is a 15 foot military surplus parachute factory-packed in it's own deployment bag. A pilot parachute attached to the deployment bag strips it away allowing the primary parachute to deploy at about 500 feet.

The airframe is loaded onto the rail first, then the nosecone is attached. The rail is a special heavy duty unit that Jim built especially for these large rockets that he loves to fly. It is built from 2" square tubing with angles welded to two sides, creating the rail slot. Earlier in the day, it was utilized to fly Jim's Banshee, a 7.5" diameter rocket stuffed with a large DPS M-class motor.

Once the airframe is secure, the nosecone is carefully placed in position and guided into the body tube. Special care is taken not to pressurize the altimeter compartment. After it is securely in place, the crew gathers around to raise it into position.

In an all-too-familiar Iwo Jima shot, the Smoke was lofted into the air and prepped for flight. Sonny Thompson snaked the ignitor into the cavernous tail of the N motor, and we all departed the scene to a safe distance to actually commence the countdown.

At ignition, the N motor powered to life and drove the Smoke straight up into the air. Even as big as this rocket is, at almost one mile, it was but a tiny speck in the sky. At apogee, the huge boom of the ejection charge signaled a successful separation, and the two drogue chutes took over, slowly lowering the two separate pieces back to earth.

At 750 feet, the primary ejection charges deployed the main parachute on the airframe, but the main parachute on the nosecone failed to eject. The airframe's main chute deployment bag was slowly peeled away and the 15 foot main chute billowed open, slowly lowering the airframe gently to the field of grass.

The nosecone continued on a faster than normal descent, but upon inspection there was only minor surface flaws visible in the finish. The nose cone's ejection charge had not gone off. The booster was in perfect condition, and the altimeter was beeping out 4,469 feet.

Curious as to why it didn't go higher, Jim inspected the motor and found a broken nozzle. It appeared the motor had fractured the graphite under thrust and broke away part of the divergence angle off the nozzle exit face.

Even so, it was one of the most exciting flights I have ever witnessed.

BONUS PICTURES: Slideshow from LDRS18 in Argonia, Kansas!