Rocket design -300km range, 5-15kg payload, 200mg accuracy

[scapeish]

Rocket design --300km range, 5-15kg payload, 200mg accuracy

Hi, I'm working on a project for a mech engineering class where we have to design a remote control vehicle to carry a small payload 300km. It must be able to survive rain, crosswind speeds up to 70km/h, temperatures up to 50 degree Celsius and as low as 15*C, and still reach a target, within 200m, that is 200km from the launch point. I.e. Launched from point A (in the above conditions) and must be able to be remote controlled to within 200 meters of a Point B that is 200km from Point A.

A---300km--->(-200m-B-200m-)

The device can use any method of propulsion, but people have already taken the slots for the other choices so I'm stuck with a rocket. 3 designs must be made, and each of them must be the same essential design, but each must be designed to carry payloads of 5kg, 10kg, and 15kg, respectively. Bonus points if they are able to be reused at least twice (I don't really care about this, to be hones). Efficiency (cost-wise) and meeting the specifications required are the two primary items of importance.

Right now, my thought is that one of two choices would be best (efficient and would work) for the rocket's "steering" mechanism. The first idea is for the rocket two have two sets of four fins, one set at the base, and one just before the nose cone; and the second uses nozzles to provide directional thrust:

/\
/ \
/l ll l\
fins--> /_l ll l_\
l l
body/payloadl l
l l
fins-------> /l ll l\
------>/_l ll l_\
l__l<---- nozzles attached to bottom of this section

1. The top fins would consist of two immobile fins, and two fins with ailerons (I can't remember the name for an adjustable fin that directs air) that move independantly (or in concert, depending on the vector change desired) and can change the direction, as pictured, forwards and backwards (i.e. the fins with adjustible surfaces are on the x axis, and move the rocket's trajectory, as pictured, forwards and backwards).

The bottom fins would do the opposite; in the picture above (which obviously only shows two of four fins for both sets), the fins would be positioned on the z axis (not visible, as they would extend toward and away from the viewer) and would change the trajectory left or right (again, as it is pictured). In flight, depending on the rotation of the rocket, one set would change the trajectory up/down, and the other would change the trajectory left or right, as the desired flight direction would be horozontal (instead of vertical).

2. The second option I have considered is the use of two sets of fins for stability, but using directional thrust as the mechanism for steering. My thought would be that 5 holes would be preesent on the bottom, in a configuration similar to the "5" on a die; essentially, one large nozzle going straight down (i.e. 180 degrees from the direction of motion/the nosecone of the rocket) surrounded by four smaller nozzles, with 90 degrees between each secondary nozzle.
I have not come up with a method by which to control the thrust from each nozzle; they would not move, but instead, a plate or other material (I really have no idea) would be used to prevent thrust gases from escaping them when direction does not need to be adjusted.


My questions are the following:

Regarding #1: Do you see any obvious problems with this control mechanism? Would you suggest any changes? Regarding the mobile fins' control, see below.

Regarding #2: Any problems with this method? Do you think #1 or #2 would be more feasible? Most importantly, do you have any suggestions on how to control the flow of gases thru the (smaller) nozzles? I'm really just looking for a mechanism to move a steel plate or something similar to prevent the escape of gases, or another method to enable/prevent the flow of gases thru whichever smaller nozzle needs to be opened/closed, respectively.

Regarding the mechanical control of the movable fins/smaller nozzles: My thought is to use radio control via a receiver/controller in the nosecone of the rocket, which is connected (by wire, obviously) to solenoids/motor controllers; two solenoids would be needed for each set of fins -- for each set of fins, one solenoid would pull both movable fins in one direction (i.e. to turn left or up) and the other solenoid would pull both movable fins in the other direction (i.e. to turn right or down). Likewise, the motor controllers (reversible), one for each set of fins, would direct a step motor to pull the movable fins in one direction or another.
For the nozzles, a similar setup could be used to: a. open/close the opening connecting a combustion chamber to the smaller nozzles (an alternative setup would have one nozzle which could be adjusted (and therefore, its thrust directed) towards the up/down/left/right direction during horozontal flight) which would cause the rocket to turn.

Thoughts on improving this setup for control? In particular, do you have suggestions for alternatives to radio control and/or methods of controlling the directional control fins/nozzles (or the one larger, directional nozzle I suggested as an alternative)? Would you suggest the '5' die setup or the larger directional nozzle setup? Would both of these be less efficient in terms of cost/performance than the fin design? Would a combination of the two be worthwhile?

Finally, in order to properly 'guide' the rocket, the control receiver in the nose cone would also have a GPS, speedometer, gyroscope (not for any control purpose; rather, to detect any wobble/imbalance) and altimeter (sp?; the device used to measure altitude). This data would be relayed in real-time (say, every 5 seconds) to the controlling device, likely a computer attached to a radio transmitter/receiver. I need suggestions on a few things here:

1. Are those devices adequate (at least for a prototype)? Should I add/remove something? To save money, perhaps a method to measure distance from the controller would suffice; the rocket's distance (and rate of change thereof) from the controller, coupled with altitude and speed (from onboard, albeit lightweight & cheap, instruments) could allow a calculation of its position, albeit the controller would be unable to determine whether, when facing it's launch point & assuming the rocket was not on a line directly connecting the launch/target zone, it was on the left or right side of the aforesaid line. Thoughts & suggestions?

2. In order to power those instruments (altimeter, speedometer, GPS/distance measuring device, solenoids/motor controller/motor, etc.), I have essentially two practical, and one not-so-practical, options (in order):
a. batteries (fairly self-explanatory), the advantages of which are simplicity & reliability, and the freedom to use solenoids/motor controllers that do not have shading rings (constant power output means that the position of the mobile fins won't be affected by the 'low' power sections of the power cycle from a generator); the disadvantages of which are weight, a low power-to-weight ratio, and power output (wattage) limitations.
b. a small fan based AC/DC generator. Using either a permanent magnet or a small battery (magnet is preferable for such a small application, but if you have suggestions as two which I should choose, I would appreciate them) as the source of the electrical field a copper wire winding would be used as the electrical current "receiver." I'm leaning towards the rotation of a permanent magnet (the armature) within a wire winding. Suggestions for other setups (i.e. a copper wire/winding [I'm trying to find a design with this setup], connected to the load circuit using brushes, that rotates between two opposite poles of permanent(or temporary) magnets) are more than welcome. A small "fan" will be position in front of the rocket, and will be rotated by air; this will be connected to the armature (either magnet (permanent or temporary) or winding, depending on design) which will rotate within the stator (winding or magnet, respectively) and generate the electricity needed to activate the solenoids/motor controllers & motors.
still b. I'm leaning towards a combination of the two (battery & generator), using a small rechargeable battery to power a temporary magnet so the power generated can be adjusted (or turned off, if necessary) and using that same battery (with regulator, obviously) to power the solenoids/motors[controllers], so the wattage is consistent and keeps the force applied to those fins (and therefore, the steering of the rocket during turns) consistent. Suggestions?
c (not practical). use heat from the combustion chamber to boil steam to turn a fan (and then use the system above) or keep a reservoir of superheated (and pressurized) water, and allow that water to come in contact with thermal ceramics, that expand/contract depending on temperature. A worthless idea, and an exercise in futility as the control of that water would depend on a battery already.


3. Do you have any suggestions for vendors for these supplies?

 

[enigma]

Do you have to actually build it, or only come up with a feasible design?

Do you have mass limits?

Does the payload have to survive the landing? Typically, rockets are used as weapons. They're not so good at slowing down. This will feed into the control system.

If you have a GPS and a MEMS accelerometer, then you have an altimeter and a speedometer. The GPS in your car assumes you're on the ground, but the data from the satellites doesn't only apply to surface locations.

Power it with batteries. I'm not entirely sure how you would even feasibly get power from your (b) option. You need to turn the magnet to generate power, and even if you did, magnets are heavy... especially so if you want to get any meaningful wattage from it.

For vendors of control systems, electronics, etc., I suggest you do some research into cubesats or microsats. They have tons of information and small, light satellite components which could easily do double duty as rocket parts.

For the motor of the thing, find a local hobby shop and ask if there are any local rocketry clubs near you. Pick their brains for ideas.

 

[DaveC426913]

Thus?

   /\
  /  \
 /llll\
/_llll_\ fins
  l  l
  l  l   body/payload
  l  l
 /llll\
/_llll_\ fins
  l__l   nozzles attached to bottom of this section

 

[Filip Larsen]

If you want your design to use a realistically possible propulsion mechanism, I think you need to spend a bit of time considering your options in that department. The choice of propulsion mechanism in rocket flight is usually one of the primary design drivers, meaning you shouldn't expect to get a workable design if you wait and "tack on" the propulsion later.

For one, rockets with vertical launch capability needs a high thrust engine, but a simple such engine is usually not throttable, or even restartable, meaning it will spend its fuel fast and the only way you can get range from that is to let it fly high and then coast down, only with the small fins needed for low drag missiles do not glide well. If you instead go with a low thrust design that uses a bigger wing for lift so you can get range (like a cruise missile) you need another method for the actual launch (like booster staging, catapulting from a ramp, or drop from a carrier airplane) which quickly can become an equally complex design task.

Secondly there is also the issue with controllability. You should not expect to be able to manually fly a high-speed rocket around with a remote control like its "just another" RC-plane. To control attitude your rocket must use either aerodynamic controls (the fins) or thrust vectoring of some kind. Since the later is fairly complex, a simple design must manage using aerodynamic control, but that again gives a trade-off between drag and maneuverability. Long range gives less maneuverability which again usually requires some on-board controller that gives the rocket a fairly fixed and pre-planned trajectory during the boost phase in order to stay within constraints and in order to reach the target.

I am aware that for this project you are probably going to focus on other design challenges than the propulsion, so I say these thing mostly so you can be aware that in real life rocketry there often are some serious and over-arching design constraints involved.

 

[scapeish]

the payload would be very study, think a sturdy metal cylinder filled with with a solid substance. The metal cylinder must have a volume of 12000cm^3. Right now, a length of 45cm and a base radius of 10cm sounds about right. I think fins rather than thrust vectoring would be optimal.

My essential question would be how much (a range estimate, obviously) propellant would be required to have that rocket travel 300km, with a payload weighing 10kg, and land within 2km of a target location (i've expanded the accuracy required; i give this information so anybody who can help includes this in the range of propellant needed)?

It sounds like fins would be far easier to control the rocket with, rather than using thrust vectoring. Therefore, what setup would you suggest for controlling the movement of the fins? Obviously solenoids would be the easiest, and would simply be energized when a change in direction is necessary; probably just 2-5 seconds of fin movement would be necessary for each adjustment, and no more than 150 [at absolute most] adjustments per set of fins [the nose cone set & on the outside/just in front of the combustion chamber] would be needed, total, during the flight.

I need suggestions for either:
a. keeping the rocket oriented so one set controls vertical adjustment and the other controls horozontal adjustment
b. putting some mechanism that would allow the rocket's steering mechanism to calculate what combination solenoids (the solenoid that, when activated, pulls the fins in the correct direction appropriate combination [i.e. to turn change in a direction exactly 45 degrees in between the two sets, both should be activated sets should be activated in the direction opposite of the desired vector] to enact a specific vector change) would result in the appropriate vector change. To clarify, a mechanism that calculates the appropriate combination of fins that would change the vector in the desired direction.

Obviously, b. would be much more complicated, so if you all have suggestions for number a., that would be great. at the moment, my thought would be to add a lead (the heavy metal, not electric) wire the length of the rockets body on the inside the its weight keeps the rocket in an orientation such that the lead wire is always on the bottom. The "cutouts" below show the cross-section at a few different points the length of the body.

Just behind the nose cone: (.) middle: (.) behind the combustion chamber: (.)

the parentheses represent the body of the rocket (and if I could, they would be a perfect circle with the wire on the bottom, running in a straight line along the length of the rocket's body at the same angular position.

Are there any problems with using this idea?

Finally, I would like any links you all have on buidling home-made rockets designed to carry a small (10kg) payload, and any data on appropriate propellants to be used.

 

[scapeish]

Thus?

   /\
  /  \
 /llll\
/_llll_\ fins
  l  l
  l  l   body/payload
  l  l
 /llll\
/_llll_\ fins
  l__l   nozzles attached to bottom of this section

perfect, but with a longer body, more tapered nosecone, and four fins at both the nosecone (well, just behind the nosecone) and just above the bottom/combustion chamber. Thank you (and I know that you couldn't add the details I said, I just added them for clarification) for redoing my "picture."

 

[AlephZero]

I think your posts are starting at step 2 or 3 of the design process rather than at "the beginning" - but there's nothing wrong with brainstorming some ideas before you start evaluting them.

"Step 0" is probably thinking about what similar devices already exist, like the WWII V1 rocket, or modern cruise missiles (though both have much larger payloads than your spec).

I would start by thinking about what flight profile (altitude and speed) you can fly. The way I read your spec, you need a 300km range in still air and a 200km range with a 70kph head wind, so the minimum horizontal speed is 210kph for 300km in still air or 140 kph fpr 200km against the wind, which gives a flight time of about 1.5 hours.

At the other extreme, if you want to stay away from supersonic aerodynamics the fastes speed is about 340 x 0.8 m/s = 1000 kph, which for a low level flight would give a time of 0.2h for 200km (the effect of wind speed is small enough to ignore). For a "high level" flight profile the time would be longer since the horizontal component of velocity would be less.

For each flight profile you could iterate to get a suitable sized vehicle, with plausible lift and drag coefficients, which could contain the fuel to fly the mission. Then, you will have some idea what control forces are needed to fly it, and how fast the control response needs to be, so you can make some rational decisions about how to generate those forces, and draw something based on that quantitative information rather than just a "concept". (Of course at this stage, or before it, you may find you need to start again with some different ideas - but that's how the design process usually goes in practice).

It could be that for a rocket powered design, a 10kg payload is almost negligible compared with the rocket itself.

 

[russ_watters]

Finally, I would like any links you all have on buidling home-made rockets designed to carry a small (10kg) payload, and any data on appropriate propellants to be used.

Is this just an academic exercise or are you actually intending to build this? What you are suggesting requires quite a bit of expertise and money.

 

[enigma]

I'll echo Russ's question. I'll go further and point out that 10 kg and 300km isn't a small payload or a 'home-made' type project. What you're proposing building is a short range ballistic missile. If this is going to be an academic exercise, fine, but you're not going to find much online. Weapons systems aren't published to the web. For an undergraduate course, unless you're working in a big team, you're going to need to do a bunch of handwaving. The questions you're asking are much too specific for this phase of the design. You're going to need to start by defining your requirements and then running some numbers to find out roughly how big you need to be before you get into specifics about solenoids for fin control, etc.

First step is assume the rocket is a brick launched from a cannon. Go back to physics 101 and find out how fast it has to be going at the start to hit the target. Next, plug that into the ideal rocket equation to find out how big the rocket needs to be. I'd ballpark 10% rocket mass to fuel mass ratio, not including the payload. That is your first size estimate. From there, you can start designing and refining specifics.

Another question I asked before: does the payload need to survive the landing? It makes a big difference for design if the rocket needs to touch down at less than 10kph instead of impacting at 700kph.