Absurd Design Exercise/Thought Experiment: Manned Amateur Rocket

[Clusterphiliac]

Hey all,

I've been bouncing this idea around for a while, and since finals are over crazy rocketry thought experiments seem like a good way of killing time.

The Copenhagen Suborbitals have the goal of launching a human being into space - a very ambitious project requiring things like pressurized capsules, liquid-fueled engines, an ocean launch platform, and very large rockets. But what about something less ambitious:

What would it take to build an amateur rocket capable of safely and legally launching a person into the air? (not space)

My thoughts so far are:

• Hybrid and liquid-fueled engines may have the ability to shut down mid-flight, but they have their own nasty failure modes, so a solid-fuel motor would be the best choice.
• If the flight remained below 15,000 ft ASL, a pressurized cabin and even oxygen masks would not be needed: 15k is the maximum altitude at which the FAA permits an aircraft with an unpressurized cabin to be operated without supplemental oxygen for all occupants. The limit for pilots is 14k, but the occupant of the rocket would essentially be a passenger.
• To minimize frontal area, the occupant would be in essentially a seated "fetal position" with feet and hips level and knees above them. This is not the optimal position for g tolerance, but it should be adequate: 5-6 gs should easily be sustainable for a few seconds without a risk of G-Loc. I'm not sure what the limit in shock loads is, but I've heard that you get shocks of something like 9 gs just sitting down on a couch, so I imagine it will be somewhere in the 10 g range.
• Let's selected the Black Rock Desert (3500 ft ASL) as a launch site because why the heck not?
• Assuming a constant thrust of 5 gs, an apogee at 12,000 ft AGL, and no air drag (IRL air drag should push the vehicle back under the 15,000 ft limit):
  During the burn the vehicle accelerates to a speed of A1*t = (5g-1g)*32.2 ft/s * burn time and travels 1/2*A1*t^2 = 1/2 * (5g-1g)*32.2 ft/s * burn time^2 feet. During the coast phase the vehicle travels an additional v_initial^2/(2*A2) = burnout velocity^2 / (2*32.2 ft/s).
  So, the total distance is: 1/2*A1*t^2 + 1/2(A1*t)^2/A2 = 1/2 (A1*t^2 + A1^2*t^2/A2). Since A1 = 4A2, this is 1/2(4A2+16A2)t^2,
  so the final altitude of the rocket is 322 * burn time^2 = 12000 ft. The burn time is therefore approximately 6.1 seconds.
• The total impulse required is approximately the rocket's mass times 300. Even with a 500 kg rocket this would still be a Q. Motors of this size are feasible.
• Who needs guidance besides fins? That's just another potential failure mode.
• What about shock loads on landing? Let's assume the recovery system nominally brings everything down at about 20 fps on a cluster of 3 parachutes. If one gets tangled, there's 2/3 the area so assuming a constant Cd, the touchdown velocity would be 24.5 fps. Just to be safe, let's make sure 30 fps doesn't result in serious injury. Momentarily assuming a constant deceleration and a maximum of 15 g, the capsule needs about a foot to stop safely. The playa obviously won't deform that much; we probably need some sort of deployable landing gear such as airbags.
• The parachutes should deploy from above the passenger - landing at 20 fps upside-down is a terrible idea. Let's do single-deployment for simplicity; Black Rock has plenty of space and the ability to use chase vehicles, so drifting a couple miles isn't a problem.
• Parachute deployment will be performed by two redundant altimeters. In addition, in an emergency both the passenger (via a button) and a spotter on the ground (via radio) will be able to command parachute deployment.
• The booster section will have its own parachutes, and use dual deployment. This also means that after separation it will fall faster than the cabin on its drogue, preventing a collision.

So... AFAIK by far the most common failure modes of amateur rockets are recovery system failure (can be avoided with redundant systems), shreds (can be avoided with good engineering, especially since the vehicle won't go anywhere near mach), and... motor problems. This seems to be the most dangerous one. How would a CATO be made survivable?

First of all, the failure itself. A forward closure failure must somehow be absorbed or deflected by the structure above it, while an aft closure failure can produce high momentary shock loads which must be absorbed.

But another problem is the loss of thrust and potential instability. A CATO which left the rocket going to something like 50 feet in the air where there isn't enough altitude for parachute deployment would be very, very bad. A cluster of really large motors could be nasty because of quality control with propellant. I think the best solution may be a Launch Escape System. We'll make this thing separate the booster section and be capable of tossing the capsule around a thousand feet from a dead stop. Accelerating at 10 gs, this requires a 1.2 second burn. Assuming our capsule, passenger, and LES weighs 400-500 lbs, we need 18-23 kN of thrust and 21-27 kN*s. That sounds like a job for eight Cesaroni K2000s, K1620s or L3200s.

And that's all I have for now. Feel free to discuss/contribute ideas of varying degrees of seriousness.

EDIT: Just saw there was a thread on this a couple months ago. Oh well, that was more "was it done?" and this is "(how) can it be done?"

 

[TopRamen]

Not this Thread again!

What gives?

 

[dixontj93060]

Come clean, you are really Billy Bob Thorton, right?

 

[RocketGeekInFL]

Didn't coyote try this once? I recall it didn't work out so well.

 

[BDB]

This was done (kind of) on an episode of Rocket City Rednecks. They launched a dummy to ~1 mile using a 2 motor cluster. They didn't say what the impulse was, but they appeared to be using commercial 98 mm motors. The parachute failed to deploy, so the whole thing crashed catastrophically.

 

[KenECoyote]

Been dreamed of since rockets were invented! :grin:

On a more serious note, it would take a lot of testing and money in order to determine the point where you can safely do it and then find someone willing to do it, so it is usually left to the gov't/NASA.

Also given the amount of investment required, it's probably simpler and funner to just make a jet pack or rocket pack IMHO.