New(ish) Team:Delta V Factory

[Delta_V]

Hello,

I'm the official spokesman (and solitary member) of the Delta V Factory team.

Just a quick introduction to where this team/I stand.

I registered for the prize last November, and I've finally come up with some sort of near final design I'll probably test soon.

It's along the lines of most of the other teams, a rockon/ballocket, the balloon being a hydrogen filled weather ballon (about 2 kilo lifting ability), followed by two rocket stages. First rocket stage will give the satellite the altitude (aiming for 110-150 km), second will give it the velocity. Both are spin stabilized. After ascending to around 80 000 feet, the rocket is released from the balloon, and a "rocket belt" fires on the outside producing tangential thrust and spin. After the spin stabilized first stage takes the contraption to 110-150 km, the thing is de-spinned by a yo-yo type device like those used on early (real) satellites. The now slowly spinning contraption is tilted by the firing of a small tip rocket so while spinning it changes its inclination. Once a magnetic field detector determines it's pointing in the right direction and an accelerometer determines it's at the right inclination the last stage separates, fires another spin inducing rocket belt, and then ignites.

The final stage is a metal can shaved down to reduce weight, covered with wrapped carbon fibre, a pvc base and a nozzle, and a tiny transmitter. It's in a similar vein to the Wikisat team in that respect. The entire thing, empty, will weigh in at around 12 grams, and it'll have 600 grams of propellant, giving us a mass propellant ratio of 50. The propellant for everything is solid magnesium ammonium nitrate composite propellant, and with a (theoretical, anyways) isp of 230-240 s, in theory it'll give us orbital velocities.

The transmitter will be powered by a button cell, that'll load up a supercap which will discharge into a LCR circuit, modulated by a varicap, producing a beep on a VHF marine frequency every 20 seconds or so. The idea is that any receiver with access to vhf marine frequencies should be able to pick up the signal for tracking, or at least with something like a Yagi antenna to boost the signal. Also with an elongated polar orbit, it should be in the line of sight over much of Europe and parts of NA atleast for part of the orbit, making verification of a near impossible feat that much less difficult. I may throw in a thermistor to modulate the power output, if natural radiative heat dissipation doesn't prevent the temp from varying too much.

Anyways, I hope to do some static tests soon to characterize the propellants, as well as to see if the rocket can actually fire without blowing up instantly. Then it's testing the transmitter, and finally I'll fire the thing entire thing from the ground. If all goes well, I was hoping to try directly for the prize without any further intermediate testing. I figure the chances of anyone succeeding are so remote that extensive testing will only help marginally anyhow.

[SANEAlex]

You might want to have a look at some of the ideas on the registers Lohan project they are not as far as I am aware planning to enter the n-prize but they have done some tests that suggests that there can be problems due to cold/vaccum etc at height that make it hard to ignite solid propellent at weather balloon heights. They also have some possible solutions and have done some testing that might help you before you commit one way or another. Anyway welcome to the forum its been a bit quiet here for a while.

http://www.theregister.co.uk/Wrap/lohan/

[Jay]

I have been working on an idea to remedy the cold vacuum ignition problem. I have not tested it yet, but you are welcome to give it a try. If it works, all I ask is to be credited with the invention. If it doesn’t work, then the credit is all yours! As always, you are responsible for your own safety.

• Apply a layer or two of flash paper (nitrocellulose) over the entire length of the core mandrel before casting the fuel grain. Make sure you use a mold release that will not harm the paper. A light wax should work.

• After the grain is removed from the mold apply electrical resistance ignitors directly to the exposed surface of the flash lining within the void of the grain.

• Then fill the void with a low-density open-cell latex spray foam (or something similar). You might want to use a smaller secondary mandrel to create a void in the center of the foam. Open-cell foam is critical because closed-cell foam will try to expand when exposed to a vacuum.

Ignitor.pdf

Grain core lined with flash paper and foam plug for ignition in cold vacuum

(10.72 KiB) Downloaded 1355 times

Before disintegrating, the foam plug should briefly insulate and maintain enough gas pressure as the flash paper burns to heat the propellant to ignition. The large surface area of the flash paper increases the chances of ignition occurring somewhere on the inner surface of the grain. If the void in the foam is necessary, large enough and possibly star-shaped, the foam plug should vaporize before overpressurization becomes a problem.

You will have to test it in a vacuum chamber, preferably cryogenic.

Small batches of nitrocellulose paper can be prepared at home from ordinary paper using ice-cold sulfuric acid and nitric acid. You can find a recipe online.

Jay

P.S. I erred when I wrote "open-cell urethane spray foam." Open-cell spray foams are usually latex. The error has been corrected above. Soft urethane foam padding is open-cell, but urethane spray foams tend to be rigid and closed-cell. DAPtex Plus is an open-cell latex spray foam commonly available for about five dollars a can.

[Xan]

A mass propellant ratio of 50 is unreal.
See "Space_Products_Catalog_B"
Best ratio is about 10. Without load.

Second.
Altitude should be about 250 km or higher.
viewtopic.php?f=8&t=396

Good luck!

[Delta_V]

Thanks for the replies and interest everyone.

I had heard about the Lohan effort before, but I didn't see the wealth of information they posted online, that could be useful.

I was actually contemplating using a detachable outer cover that would warm the whole thing on the ballon ascent, mainly because the ammonium nitrate oxidizer isn't phase stabilized so cracks in the grain could arise from the changes in temperature, and as a bonus this will prevent any problems with cold ignition. On the other hand it's good that you alerted me to the possibility of ignition failure from inadequate pressure. It got me thinking along the lines of using some type of gas generator, like a half gram of gun powder, along with a partial plug in the nozzle (a plug in the throat with a needle leak, to let the pressure inside fall to vacuum but at the same time helping the pressure build up at ignition) made out of something like clay. It's a balance between making the plug resistant enough so pressure builds up to ignition, but at the same time it has to be ejected fast enough so the pressure doesn't build to the point of bursting. Thanks for the ideas Jay, those seem far more refined than what I have.

I took a look at that catalogue. It's reasonable that they would have much smaller ratios, since their main concern is safety, while for our purposes a ten percent chance of the casing bursting is no big deal. Also they didn't use any composites or carbon/glass fiber, while my rocket structure is a thin layer of aluminum to provide a container, and then the bulk of the hoop tensile strength is coming from loose carbon fiber tow. I calculated that I need less than 2 grams of fiber to provide sufficient strength (also the rocket will operate at fiarly low pressure, ~100 atm or less). While I'm certainly optimistic with my mass propellant ratio of 50, it certainly seems reasonable to expect something around 20, in which case the whole thing changes only minimally (might have to add another stage, and beef up the balloon lifting capacity).

Thanks for the heads up about the altitude. I hadn't yet done drag/mass calculations and was using the number roughly (and I'm planning on having a very elliptical orbit, so the satellite will spend only a fraction of total orbital period near the perigee), but that information you provide is certainly useful.

[rick m]

[rick m]

[rick m]

[Delta_V]

I always like hearing about very simple and elegant solutions to potentially complex problems. The video shows just how effective this type of thing is. May I ask about specifics of your design? I'm specifically interested in the mechanism used to release the mass. One embodiment of the release mechanism I was considering is a wire with a low melting point holding the mass secure to the rocket, and then at the right time a current heats and melts the wire to release the weight. Should be as low in complexity and mass as I can realistically get.

I was considering using a solar cell too, but likewise had issues with mass and especially power/mass. Another possibility is using some sort of thermocouple/seeback effect generator. It might be feasible to have two surfaces, both as nearly black as possible, insulated from one another, with a thermocouple joining the two. One absorbs the sun's radiation, the other radiates it into free space. Since the sun's radiance is around 1000 W/m^2, it might be workable as a respectable power source. At any rate, since I'ld still need a battery, and weight is an absolute premium, I decided the smallest button cell is all that is required. Unlike (I think) every other team so far, my entire transmitter package is limited to less than about 5 grams, since I'm planning to have the entire empty second stage as the orbiting satellite.

For temperature control, a lot of the regulation comes from the fourth power dependance of spectral radiance. For example, using this battery: http://www.panasonic.com/industrial/inc ... CR2025.pdf
and restricting the temperature variation to -20 to 50 degrees C, the radiance varies by a factor of three. Also lavalamp did an excellent analysis that showed that passive temperature control is feasible if the transmitter falls within certain parameters:
viewtopic.php?f=8&t=354


At any rate, along with passive temp control I plan on using a positive coefficient thermistor to regulate power input to the transmitter. Temp increase will reduce the power input, helping to self regulate. This will reduce the efficiency of the transmitter significantly, but it's absolute simplicity that I'm after.

Besides the thermal sensitivity of the battery (which turns out to be quite rugged if I allow for reduced power capacity), a big issue is the thermal sensitivity of the capacitor in the transmitter circuit. I was hoping to match the tempco of a couple of capacitors so the sum would be nearly zero, but it looks like that won't be feasible. Fortunately crystals have a reasonable stability over a high temperature range, so I'll probably use a crystal-transistor or crystal-pll transmitter of some sort.

I shouldn't have nearly the same difficulty with grain brittleness since the binder is specific for composite rocket grains, but I will keep your learned wisdom in mind.

[Jay]

Rick, your brittleness problem got me thinking. Have you considered adding collagen? Then you could do the first Jello Shot to Space!