Water Powered Egg Lander

[christheman200]

For one of my courses next year I will have to construct a lander capable of returning an egg safely to the ground.
I don't find this particularly interesting, so I'm going to be one upping the criteria and constructing an automated water rocket lander, sky-crane style, that will place an egg gently on the ground with no packaging to protect it. The criteria I have set out is as follows:
The egg must be placed on the ground intact.
The egg may not have any materials protecting it. Only a harness may be used to attach it to the sky-crane.
The egg must be initially positioned 50 meters above ground.
The egg must be returned via retro-water rockets, and a parachute may be used as long as it is not active upon touchdown.

The idea comes about from the Curiosity lander's unprotected nature upon touchdown. If NASA can land an unshielded 1 ton rover on Mars, why can't I land a simple egg on the ground?
For the automated descent I am thinking of using software from a quadrocopter to land softly, utilizing gyroscopic and altimeter sensors.
Their will be one or two pressure vessels, and 4 nozzles spaced out around the frame. Individual quick-response valves will control the thrust of each nozzle, in order to keep the pitch of the craft under control.
I will have access to a 3d printer with dual-extruders to print water soluble plastics, metal and wood CNC machines, and a machine shop once school starts back up. I can currently use SolidWorks, AutoCAD, and Inventor to model the craft, although I have access to just about every modelling software on the market.

I am looking for knowledgeable partners in this venture, especially in the areas of calculations and pressure tank materials. If you find this interesting please consider "joining the team"!
Is this possible from the rocket-systems point of view? Can the jets be fired long enough to make contact with the ground?

[mazuzuri]

This sounds extremely interesting and very fun, but at the same time it will be a very tall order to make.
From the sounds of it you want to make something similar in nature to this am i right.
http://mars.jpl.nasa.gov/msl/multimedia ... ageID=3650

The biggest problem building something like this powered by water and pressurised air is that it does not contain a lot of power to weight compared to the usual rocket fuels used by nasa.
This means you will only have at most a few short seconds of thrust available without the craft exceeding the weight at wich you can no longer slow it's descent.
I will not say it is impossible as i have not trie something like this, but you will have to be spot on with everything you do and make the craft frame as light as possible.

As for pressure tank you will most definetly want to look at fiberglass or carbon fiber reinforcement to allow maximum pressure possible.
You will also have to figure out the best nozzle diameter that gives you enough force to slow the descent but small enough so you don't burn all your fuel in no time.
I will be able to help with calculations to a degree and would like to help you with ideas and such, mainly because i would love to see something like this actually built and working.

Mazuzuri

[christheman200]

Yes, I'm essentially looking to recreate the Curiosity rover landing.
I figure that if some of the rockets on here can reach 100Gs of acceleration and fire for a quarter of a second (if my memory serves me correctly), I should be able to provide thrust for long enough to land the egg.
Just from a very quick check on a water rocket simulator, a very basic rocket could provide an average acceleration of 100Gs, for 0.066 seconds. Now say I only need the retro-rockets to fire at 2Gs, the rocket could fire for 0.066x50 = 3.3 seconds if firing time and acceleration scale linearly. With much higher pressure and an extremely lightweight frame I imagine I could move the firing time up to around 12 seconds, although this does not factor in the weight of the egg.
I've been pouring over one of the Rocketdyne liquid propulsion system handbooks I have for it's data on constructing fuel tanks, although it's focused on much larger rockets.

[mazuzuri]

Sounds like you have given some thought on the matters i mentioned.
I can't remember if the thrust scales liniear but thats simple to find out.
What i would suggest doing as a start would be to try and calculate roughly the dry weight by designing the lander.
After that you can calculate needed thrust as well as pressure.

Where you thinking of making the frame via 3d printing?

[christheman200]

I am considering 3d printing the frame if it turns out to be strong enough.
I will make a model as soon as I know which valves I will use to control the thrust.
Also, how much might a 2 litre composite material pressure tank weigh? I'd like to know for some basic calculations.

[Blenderite]

I assume that since you have plans to 3D print the frame you have a 3D printer. If so, I was thinking you could get some RC gyros off hobbyking or something and then use a thrust vectoring system for your nozzle. Then you could use two servos to control the thrust direction.

Or you could 3d print a cap for the other end of one of these: http://www.grainger.com/product/SMC-PVC ... alve-3CGE3 The cap could have 3 ports printed into it to accept aquarium tubing which could be routed through 3 legs so that the thrust is evenly distributed and hopefully levels it out on the descent. If you wanted to get really fancy you could hook up three valves and some gyros. BTW, the valve is operated with a servo like in this thread here: http://www.wra2.org/forum/viewtopic.php ... lve#p13996

Just two ideas I came up with, not sure if either would work, but its worth a try I think.

[christheman200]

Upon first consideration, thrust vectoring makes a good deal of sense. But upon further inspection it reveals too many faults to consider as a contender. It would be nice to use a single nozzle and a thrust vectoring system, but the egg can not be dropped to the ground in this manner. Most importantly, as the rocket loses fuel mass the thrust would increase to many magnitudes more than is required. If the thrusters are angled inwards towards the craft in order to compensate for the high thrust, the structure may crumple from excessive force and the efficiency of the rocket would plummet.

I'm afraid that the valves you mentioned would not have high enough response times to get the job done. As well, I will likely be dealing with around 400 psi (ballpark estimate) which I'm afraid is too high for those valves. I am looking into similar setups however.

Thanks for the suggestions. Every one helps.

[mazuzuri]

I am considering 3d printing the frame if it turns out to be strong enough.
I will make a model as soon as I know which valves I will use to control the thrust.
Also, how much might a 2 litre composite material pressure tank weigh? I'd like to know for some basic calculations.

When it comes to weight of a 2 liter composite tank you would first want to know what material you are using, then decide how much you need, lastly check the weight of the fabric, usually given in g/m2. take the total weight of the material and doubble it, this should give you roughly the weight whith resin added.
I have however no idea how many layers of what material is needed to achieve the required strength for 400psi, but more than likely you will be adding a few hundred grams total weight.

If you are lucky you may be able to get someone who has done more extensive work with composites to tell you some of their test results to give you an idea of how to do it.
The strongest and most leightweight method for making high pressure composite tanks would be to use filament winding, however this is usually only possible to do with a at least 2 axis filament winder.

[christheman200]

Is there anyone who could give a hand on what it would take to construct a 400 psi carbon fibre composite tank? I am currently looking into the properties of carbon fibre structures in solidworks but I am afraid that they may not be very accurate.

[mazuzuri]

I have been attempting to find that information myself for my own carbonfiber rocket, unfortuneatly the very nature of carbonfiber and fiberglass makes it extremely difficult to make any calculations. Since every fiber has its own breaking point and the fibers are not perfectly uniform you would have to take each fiber and calculate them individually to get exact numbers.
http://en.wikipedia.org/wiki/Ultimate_tensile_strength

A little down on this wikipedia page there is a chart showing some tensile strength of different materials, among them is carbonfiber in a laminate.
I don't know if it is usable, but one should be able to calculate roughly how strong a pressure vessel will be based on the numbers given.
If you really want to dictate the strength then unidirectional carbonfiber gives you more control over orientation, but it will also require more work and knowledge of laminating as you would have to make sure to reinforce in such a way you don't end up with all the strenght in 1 direction to the axis of the pressure vessel.

[christheman200]

I haven't gone much into the composite materials yet.
Putting pencil to the paper reveals that at a pressure of 120psi at a mass fraction of 11.78 is needed to fire the thrusters at 1G for 3.2 seconds, which is the maximum attainable velocity from a fall of 50 meters with no air resistance. At 400 psi a mass fraction of 3.84 is needed.

I pose the question to all members of this forum: What are the mass fractions of your rockets? This is simply the mass of the rocket with fuel divided by the mass of the rocket without fuel.
As well, please feel free to post an informative guide to constructing materials from carbon fiber.

[bugwubber]

I haven't gone much into the composite materials yet.
Putting pencil to the paper reveals that at a pressure of 120psi at a mass fraction of 11.78 is needed to fire the thrusters at 1G for 3.2 seconds, which is the maximum attainable velocity from a fall of 50 meters with no air resistance. At 400 psi a mass fraction of 3.84 is needed.

I pose the question to all members of this forum: What are the mass fractions of your rockets? This is simply the mass of the rocket with fuel divided by the mass of the rocket without fuel.
As well, please feel free to post an informative guide to constructing materials from carbon fiber.

My fractions are TLAR or 144"WC. ;-)

[christheman200]

Anyone with actual measurements?

[Blenderite]

Upon first consideration, thrust vectoring makes a good deal of sense. But upon further inspection it reveals too many faults to consider as a contender. It would be nice to use a single nozzle and a thrust vectoring system, but the egg can not be dropped to the ground in this manner. Most importantly, as the rocket loses fuel mass the thrust would increase to many magnitudes more than is required. If the thrusters are angled inwards towards the craft in order to compensate for the high thrust, the structure may crumple from excessive force and the efficiency of the rocket would plummet.

I'm afraid that the valves you mentioned would not have high enough response times to get the job done. As well, I will likely be dealing with around 400 psi (ballpark estimate) which I'm afraid is too high for those valves. I am looking into similar setups however.

Thanks for the suggestions. Every one helps.

400PSI?!?!?! Are you launching an Ostrich egg?!

[christheman200]

I'll need 31m/s of delta-v to land the egg. At 400 psi I only need a mass fraction of 3.8 to achieve this.