Rocket candy to orbit

[Jarvitä]

"Rocket candy" is a solid propellant, a 60:40 mixture of KNO3 and sugar. Depending on manufacturing specifics, it usually has a specific impulse of around 130s, which is pretty low compared to other propellants commonly used in launch vehicles.

However, it has the advantage of being legal to cook in your garage, and being basically as cheap as effective rocket fuel can get.

Solid fuel rockets have a maximal mass ratio of around 10, due to limitations imposed by structural integrity requirements, given that the entire rocket is in effect a giant combustion chamber.

Given those limitations, is a rocket candy powered orbital launcher possible? There doesn't have to be any payload, the last stage reaching LEO would be sufficient. The closest I've been able to get in my calculations is around 5.5 km/s delta-V with a 3 stage configuration and a total mass of 160 tonnes.

 

[SiberianTiger]

If there's a limit on how big a booster can be made, maybe it's ok to use a honeycomb pack of thin and small boosters at 1st stage with outward boosters burning out first and separating? Thus making a sort of "fuzzy" staging.

I have no clue how a separation system for such thing can be made and possibly thermal interchange between the neighbouring "matches" may be a nuisance.

 

[Jarvitä]

In theory, there is no limit. However, in practice, with a 3-stage configuration the added delta-V is negligible beyond 200-300 tonnes.

Also, did you just propose an OTRAG with bathtub fuel? With solid fuel, that kind of system generally requires 100% reliability, a single node "malfunctioning" means blowing up all of the nodes around it and possibly causing a chain reaction.

 

[T.Neo]

First of all: why 160 tons? A GEM 40 A is already only 1360 kg empty, 11 700 kg full. It doesn't need to be an orbital monstrosity, just get the upper stage to LEO.

A sort of OTRAG setup might work, but in this case I fear it'd run into complexity issues... either way, just having identical stages that stage parallel would be a good idea, providing you could ignite it properly.

I propose a four-stage system, with composite motor cases. Stages one and two share a diameter, with stage two being around half length. Both stages have attitude control through liquid injection into the exhaust stream (similar to on Titan), with an indeterminate liquid, with a cold gas roll control system housed on top of the second stage.

Stages three and four would mimic the arrangement of stages one and two, but with a reduced shared diameter, and no LITVC- instead, a cold gas RCS for both roll control, and pitch/yaw control, would be placed on top of the fourth stage, along with flight avionics and communications beacons.

Of course, all of this is easier said than done...

 

[SiberianTiger]

Also, did you just propose an OTRAG with bathtub fuel? With solid fuel, that kind of system generally requires 100% reliability, a single node "malfunctioning" means blowing up all of the nodes around it and possibly causing a chain reaction.

The hope is that a smaller booster would have better reliability than a bigger one.

 

[Jarvitä]

Do you have any specific numbers? Even with a 4-stage configuration, there's no getting it past 7 km/s.

Keep in mind the maximal exhaust velocity is in the 1000-1500 m/s range.

 

[T.Neo]

At least to my knowledge, dV has nothing to do with overall mass- rather, it has to do with ratio.

130 seconds is around 1275 in m/s terms, btw.

If a 9400 m/s dV is split up equally into four stages, each stage only needs a mass ratio of around 6.5 to do its share.

If the empty mass of the fourth stage is 500 kilograms, that correlates to an overall mass of just under 50 tons.

 

[Jarvitä]

I think you may be forgetting to take the mass of the higher stages into account when calculating the dV. The first stage can't possibly achieve a mass ratio above 3 once you account for all of the stages on top of it.

 

[Ghostrider]

You will need a kind of payload anyway, the guidance system...

 

[Jarvitä]

You will need a kind of payload anyway, the guidance system...

Since we're talking about overall mass in tens of tonnes here, I think it's safe to assume that mass to be negligible.

 

[T.Neo]

I think you may be forgetting to take the mass of the higher stages into account when calculating the dV. The first stage can't possibly achieve a mass ratio above 3 once you account for all of the stages on top of it.

In that case, adjust the ratios. That's why the early stages are larger than the later ones.

That, or increase the number of stages... strap-on boosters might be an option, but increase complexity.

Bottom line is making 170 tons of rocket candy is never going to happen, and is certainly not going to happen in a garage... if you have the budget to make 170 tons of rocket candy, you have the budget to make use of more efficient, more sensible propellants- amateur rocketeers already do.

I bet you'd already get a good performance increase if aluminium powder or something like it was added to the fuel mix, but in that case it'd stop being strictly rocket candy.

 

[Tommy]

Adding Iron Oxide can improve the ISP some, not sure how much. FeO2 can be made by burning steel wool, then rubbing the "ash" through a screen. You'ld have to search around the web to find out how much to add, one possible search term would be "red powder", a gunpowder substitute similar to rocket candy.

 

[tori]

It's Iron(III) Oxide, Fe2O3. It increases the burn rate in the motor by preheating the propellant, thus increasing the pressure and ISP, but the overall impulse is slightly lower than a vanilla rcandy.

Tommy, regarding red powder - people are actually using this? I thought I was the only one :lol:. Could you give me a link? I couldn't find anything good.

 

[Tommy]

I've only heard of "red powder" when I was in the military, it's described in a training manual (improvised munitions handbook). If I still have my copy I'll send you a recipe. The basic recipe is a bit cruder than the ones here on the forum (in the backyard rocketry section) but the relative measures may prove handy.

 

[tori]

Thanks, the context was all I needed. I found this patent application.

 

[Tommy]

This appears to be something different than the "red powder" I was referring to. The stuff I was referring to is sugar/KNOx mixture (called "white powder") with Iron Oxide added. Haven't had a chance to dig out that old manual, but it dates back to the 1960's, where this appears to be more modern, and not based on sugar.

 

[tori]

I know what you mean. We've been using it since we were kids - by sweeping up the dust from the bottom of the propellant grain box. There were always a couple grains that cracked and fell apart during the winter, so we had plenty of powder to play with in the spring. Did the RP look something like the one I'm using in this video at 0:18?

 

[Tommy]

Unfortunately, the computer at work (no internet at home) is too slow/old to play Flash video - but the "Red Powder" I'm talking about looks just like rocket candy - except it has a red color (of course). There would be some variation in the shade and texture, depending on how it was made - just like regular rocket candy.

White or Red Powder for munitions is usually cooked a bit less, leaving it softer so it can be grated through a window screen to get the small gunpowder type grains - rather than the big "rolled" grains typical for a rocket propellant. This is because firearms munition propellant needs a very fast burn - all the propellant needs to burn before the bullet leaves the barrel, where in a rocket a slower sustained burn is better.

 

[tori]

Here's a frame from the video for your convenience.

I'm pretty sure we're talking about the same thing. The grains we're using are about Ø 0.5 mm, sifted to remove the fine meal powder in between that would slow it down.

 

[Tommy]

Yep, that's about what it looks like. I'll try to have the ratios for you on Wednesday, but there's a recipe in the "Backyard Rocketry" sub-form that is better that the "White/Red Powder" formula (which just uses sugar, KNOx, and water), and uses fructose as well as sucrose.

For rockets, I tend to "roll" the grain around a spindle until it matches the casing diameter. Then I "inhibit" the kernel, using a few short lengths rather than one long piece. This helps even out the thrust by helping keep the surface area more uniform during the burn. Otherwise only the inner diameter is exposed, a fairly small surface area, when the rocket first fires (reducing the initial thrust), and thrust increases as the inner diameter increases. I use pieces that are about 3 times the diameter in length, this has worked well for me.