# Tag Info

23

Since the term "grain" is already in use in the solid rocket context, I'm favoring the term "cereal". Cereals contain about 66–76% carbohydrates -- mostly starch (55–70%) plus some sugars and cellulose. Cellulose combusted with gaseous oxygen yields surprisingly good specific impulse, up in the 240 sec range; sugars with potassium nitrate ...

14

What a fantastic question! Absolutely it's possible! $N_2O$ is $N_2O$, whether you get it from an 8g whipped cream charger or a massive industrial tank, it oxidises just the same. The valve you'll need to buy/make for 8g canisters is called a pin valve. Here's an example; basically it is just a hollow needle that breaks the seal when the canister is ...

10

According to this recent article by one of the Space Propulsion Group partners, paraffin-based fuels give hybrid rockets more oomph, because the fuel that is exposed to combustion melts, atomizes, and becomes entrained in the flowing oxidizer [inset]. This enlarges the surface area over which the fuel can vaporize and react. More fuel in the mix, faster ...

10

Wood burns just fine with LOX or gaseous oxygen; it would "work" in the sense that it would produce hot exhaust gas which could be accelerated through a convergent-divergent nozzle to produce thrust. Wood is primarily made up of cellulose and other carbohydrates; cellulose has been fired with GOX for a respectable 247s of specific impulse. There are at ...

8

Its still in active development. Two options for the sample return ascent vehicle are being worked, either a single-stage paraffin-MON hybrid vehicle or a two-stage solid fueled vehicle. No decision has been made yet on which will be selected (if the program continues at all, given Starship etc). Both options have similar mass, payload capacity, system ...

6

No. AS far as I know no hybrid propulsion rocket has ever been used for orbital launch. Back in the 1990s AMROC tried but failed. At least 7 companies that I'm aware of are dabbling with hybrid propulsion for orbital launch vehicles in various stages of development. They include: Nammo Onera Rocketcrafters Whittinghill Aerospace Gilmour Space Leaf Space ...

5

The book Burt Rutan's Race to Space by Dan Linehan describes why the predecessor of Spaceship Two chose a hybrid engine. Rutan ruled out solid motors because they cannot easily be shut off (a safety concern). He ruled out liquid motors because of cost and complexity. Rutan settled on a hybrid engine as the best compromise between safety and cost. Also ...

5

Helium is a noble gas, meaning it does not react with other atoms. In fact, it is the least reactive of them all. No compounds containing helium has ever been found, although some of the heavier noble gasses have formed unstable compounds. As helium can not be part of any molecule, it can not release chemical energy in any way thus failing to be an oxidizer. ...

5

You just found the primary shortcoming of hybrid engines: fuel flow cannot be controlled on the fly. The engine can be shut down and restarted unlike common SRB, but throttlability is lousy and lossy. And lots and lots of promising fuels were abandoned due to bad melting or evaporation temperatures. You can prepare the optimal fuel a'priori by choosing the ...

5

Yes it is possible to construct a hypergolic solid-liquid rocket propellants. Case in point a metal organic framework of imidazole derivatives with Zinc, Cadmium or Cobalt metals as the solid phase and concentrated nitric acid as the liquid oxidizer. Paper https://chemrxiv.org/articles/Hypergolic_Zeolitic_Imidazolate_Frameworks_ZIFs_as_Next-...

5

Virgin Galactic (VG) is about as forthcoming with technical details/rationale as SpaceX, i.e., not very. The closest observer of VG I know of is the blog parabolicarc.com. They have covered the engine switcheroo extensively over the years, but it's largely based on rumors. Here's a decent summary from an August 2015 post: When they switched to the ...

4

Keep in mind that for bipropellant chemical rockets, fuel-rich combustion is generally preferred: it keeps temperatures more manageable than stoichiometric combustion, and tends to produce simpler molecules in the exhaust, which leads to less kinetic energy held in vibrating intra-molecular bonds and more kinetic energy going straight down the nozzle. ...

4

Wax/Paraffin has gained interest for the last ~5 years as a fuel of choice for Mars Sample Return because the unique requirements of this mission mean being able to withstand more thermal cycle extremes than most most missions, making it really tough for solids to be a solution. The small vehicle size and layout restrictions (carried by a rover) also make ...

4

I'd point out that moisture, and in low enough quantities even minerals, may not add combustion energy but do serve as reaction mass. Unfortunately I suppose minerals would tend to produce abrasive ash which would be bad for the throat and nozzle. The low density of wood also makes it a good insulator so one might have low-temperature tolerant material ...

4

The typical hybrid rocket arrangement consists of a hollow cylinder of solid fuel, with liquid or gaseous oxidizer in a separate pressurized tank, introduced at the top end of the cylinder. The oxidizer flows down the hollow, combusting with the fuel all along the inner surface of the cylinder. Rocket engines used for ascent often don't need to be ...

4

Here's some information from Delft University with a table showing 275-300s specific impulses for various HTPB and PE hybrids. Here's a nice hybrid overview paper with a broader table, giving LOX-carbon Isp 249s, LOX-HTPB/Al 40% Isp 274s, LOX-paraffin 281s. These figures are all for chamber pressure of 3.5MPa (~35 atmospheres), exhausting at sea level ...

3

Yes, the chamber pressure in a pressure-fed engine must be lower than the propellant supply pressure. For example, the space shuttle Orbital Maneuvering System engine operated at a chamber pressure of ~130 psi and was fed from tanks pressurized to ~250 psi. Another issue that is going to limit the thrust from that demonstration engine is that it doesn't ...

3

Just a quick response here, but from doing some hybrid engine research as part of a student organization I think there is also the issue of layers beneath the actual boundary layer of wax melting and causing some instabilities with the grain. I believe additives such as carbon black help this issue by lowering radiation being transmitted through to lower ...

2

Specific impulse of an engine is directly proportional to exhaust velocity - and hydrogen, being the lightest of elements (a H2 particle being just two protons + 2 electrons), using the same amount of energy can be accelerated to much higher velocities than any other elements. A single Carbon is about six times heavier as a H2 particle - and only in ...

2

Asking an expert at my work, the answer is that it's not a strong risk for hybrids. The reasoning is that pogo is typically due to an interaction between a pump and a long vertical run of tubing on a rocket (like where a propellant line goes from the top tank around or through the bottom tank to get to the engine). Since hybrids only have a single liquid ...

1

Cereals are largely composed of complex sugars: starch and cellulose. Simpler sugars combined with an oxidizer are sometimes used in rockets, and there seems no fundamental reason that more complex sugars wouldn't work. A solid fuel rocket is, however, a serious pressure vessel, unlike a silo.

1

Here is another future possibility to add to @CarlosN's thorough answer, though I don't have recent information. Below is a BBC News report that covers both Taiwan's National Space Organization and a separate effort, the Advanced Rocket Research Center which at the time had done significant research on hybrid rocket engines. ARRC's web page: https://www....

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