X-Prize Competitor Rocket

NASA always spent billions of dollars every time they launched a Shuttle, so they offered an X-Prize for the first company that could launch a small satellite, during the late 1990s. The few companies that competed were all intimately involved with NASA, and their plans all involved many millions of dollars of costs.

I became intrigued and I designed an approach which should have cost less than $3000 total, to show Proof of Concept. But my approach would technically not have met one condition of the X-Prize, so I could not have won it. In addition, I was pretty sure that the FAA would not have approved of watching an object on radar which went up through their air-space, so I suspected I might have gotten arrested by showing that I could do it.

All rockets have to carry massive amounts of extra weight as fuel, which therefore requires far more rocket fuel to send even a small payload into orbit. The first Vanguard and Explorer I satellites only weighed a few pounds, but they required rockets which weighed many tons and which burned up many tons of fuel in those few minutes of flight. Multiple-stage rockets were developed during the 1960s which allowed much of the unneeded weight to be abandoned, to not have to be trying to accelerate all that extra weight. You probably watched a launch of a Saturn-V rocket to the Moon, where the greatest mass of the rocket body was abandoned after only about a minute, and then later, more of the empty shell was abandoned as the Third Stage was ignited.

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Even then, during the 1960s, and as a Physics student at the University of Chicago, the possibility of eventually working for NASA seemed realistic, so I thought about such things. I even Designed a very small rocket which I called a Segmented Rocket, but I never got around to actually building or launching any of them.

That basic idea required using a SOLID FUEL rocket, where individual segments which were basically large-diameter steel pipes, would be made. Each was to be quite simple, just sections of 6" steel tubing which were each 6" in length. Each segment also would have had a slightly smaller diameter pipe welded inside the top end, so that a male stub of 1/2" would have extended above the segment, which would therefore slide inside the (female) bottom end of the segment immediately above. By stacking 20 such segments, a ten-foot-tall rocket body could quickly be assembled. There were some additional small details, such as four minimal tail-fins attached to each segment, which would be slightly angled so that the entire rocket would spin like a rifle bullet spins (due to rifling there) which would ensure the vertical orientation of the entire rocket (without massive gyroscopic guidance systems and adjustable fin positioning).

Essentially, this would result in a 20-stage rocket! As the solid fuel was consumed in the bottommost segment, and the fuel in the next segment ignited, the bottommost (used) piece of pipe would simply fall away and the rocket would become lighter. The thrust of the downward vertical rocket blast would keep the bottommost segment pressed upward into the male-female coupling to the unused segments above, so no bolts or other actual connection would be necessary.

Instead of the constant vertical thrust having to accelerate the entire weight of the full rocket body, by the time the final segment ignited, only 1/20 of that weight would have to be accelerated upward. By Newton's F = m * a, the resulting vertical acceleration of that last segment would be close to 20 times as great as if the entire rocket had remained together. Burning the same total amount of fuel, the final vertical acceleration would be nearly twenty times as great, resulting in VERY fast final vertical velocity.

However, this tremendous increase in acceleration and velocity would cause a different problem, that of tremendous frictional heating from air friction. Some early US Rockets, such as the Nike Ajax, were limited by this issue, where the Ajax took off impressively rapidly and disappeared from view in just a few seconds. They were limited regarding the amount of fuel which could be used by how fast the Ajax body could fly through the atmosphere without burning up from air friction! My segmented rocket would have the same issue, if it used a decently powerful rocket fuel. It would likely have taken off (vertically) very impressively, but a few seconds later, it might be traveling at many thousand miles per hour while still in the thick atmosphere, where it would likely have burned up from that excessive heat, and or caused the solid fuel in some upper segments to ignite and the rocket disintegrate.

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Therefore, in 1998, for my idea regarding the X-Prize, I knew that I needed to get the rocket ABOVE the bulk of the atmosphere to avoid that air-friction drag and heating. Since the rocket which I proposed to build was rather small, just 10 feet tall and 6" in diameter, that only represented about 150 pounds of solid fuel and another 200 pounds of steel segments, along with a pointed nose-cone.

I felt that I could buy thirty-two surplus 16-foot-diameter weather balloons, for about $10 each, and fill each of them with hydrogen gas (virtually for free from standard chemical reactions). That size of weather balloon, filled with hydrogen gas, would each have a total buoyancy / lift of about 160 pounds. I felt I could assemble a PVC structure of simple trusses where the 32 weather balloons would be firmly attached in a 170-foot diameter circle where a central PVC short cylinder would therefore be lifted by the symmetric 32 weather balloons. The assembly should therefore be capable of lifting around 32 * 160 or 5000 pounds, and the structure and position of the balloons should keep it all oriented vertically. The central PVC cylinder would be hung below the hexagon structure, so the weight of the rocket would ensure that the rocket was always aimed straight upward. Once the 32 balloons were all filled with hydrogen, the 5000-pound upward lift would cause the whole assembly to rise, probably drifting horizontally with ambient winds but still always pointing upward.

Such hydrogen-filled weather balloons have regularly risen to around 100,000 feet or 20 miles altitude, which is far above most of the dense part of the atmosphere, and even three times higher than passenger airliners fly at.

You probably now see how and why the rocket, if ignited at 20 miles altitude, could accelerate without any restriction of aerodynamic drag or frictional air heating, and the segmented rocket would accelerate upward impressively.

My first proposed demo rocket was to be very small, where the solid fuel would get used up rather quickly. Therefore I knew that such a minimal rocket would not be able to achieve the 17,500 mph velocity necessary for an actual orbit. But simple calculations based on the thrust of the specific solid fuel I was then considering, and the resulting thrust during each of the 20 segment's acceleration, and the simple Integral Calculus to determine the final vertical velocity, showed that I was confident of achieving a final vertical velocity of over 6,000 mph, which should have gotten my one-pound final payload up to about 600 miles altitude. That actually would have been far HIGHER than any of the X-Prize competitors dreamed about, and all for maybe $5,000 total cost!

When I looked into actually doing this in 1998, I expected to be able to obtain the solid rocket fuel from NASA or from the X-Prize organization, but neither seemed interested in helping see my demo occur. I suspect that each of those companies wanted to ensure that many millions of dollars would be given TO THEM in providing support for THEIR effort. If some home-made-rocket might have out-classed them for $5,000, I could see that I might not have been the most popular person around!

My Design had a few additional details. As the 32-hydrogen-balloon assembly lifted slowly through the atmosphere as a giant 'ring' 170 feet in diameter like all hydrogen-filled balloons do in the heavier oxygen and nitrogen atmosphere. Initially, the 16-foot-diameter balloons would have a total lift of 5000 pounds, easily lifting the weight of the entire truss-ring and the rocket. As the balloons lifted the hydrogen greatly expands and lift increases due to the larger balloon diameters. I would have had to provide for a way to release some hydrogen from each of the balloons, just to keep them all from expanding and bursting, but that is a simple feature to add.

The eventual rocket lift would be 5000 pounds. Also, INSIDE each segment, some small ribs were needed around the perimeter, to ensure that the rocket thrust always acted to push the bottommost segment upward, to keep the entire segmented rocket together, UNTIL each segment became empty of fuel and was THEN able to fall away. And a couple other minor details as well.

I had expected to get permission and the X-Prize Application in 1998, and do that first demo by the end of that year. My estimated initial calculations suggested that the nosecone of my tiny rocket might get to an altitude of around 600 miles before burning out and ballistically falling back to earth. Even though that would not qualify for the ORBIT requirement of the X-Prize but it would have gone ten times higher than any of the multi-million dollar corporate competitors.

This presentation was first placed on the Internet in April 2012.

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C Johnson, Theoretical Physicist, Physics Degree from Univ of Chicago