Safe liquid-fuel rockets
 

Hello All,

That posting title might sound self-contradictory, but something that G. Harry Stine wrote in one of his professional rocketry-related books says otherwise. Here's what I found this week:

Along with many model rocketeers, I have long wished that liquid propellant model rockets were available. In addition to providing scale realism for flying scale models of liquid propellant vehicles (including rocket planes), such propulsion systems would enable the engine burn durations to be tailored to "fit" smaller flying fields, and adjustable non-pyrotechnic recovery system deployment timers would enable any desired delay time to be used. On page 50 of his 1957 book "Rocket Power and Space Flight" (Published by Henry Holt and Company, New York, Library of Congress Catalog Card Number 57-11690), G. Harry Stine wrote about a safe liquid monopropellant that he specifically suggested for hobbyist use:

"However, all monopropellants are not as dangerous as nitromethane. Take a recent newcomer, ethylene oxide. Some of the propellant chemists said it wouldn't burn at all. But the rocket engineers promptly put it into their cigarette lighters and proved them wrong!

"Ethylene oxide is so safe that it could readily be used in a small rocket engine for model airplanes. It boils at 52 degrees F. and has good performance. It costs about twenty cents a gallon, roughly. Someday, somebody is going to make a small fortune manufacturing ethylene oxide rocket motors for model rockets that really fly. A unit with about ten pounds thrust would be ample, and the chamber would be about the size of a lipstick case." ALSO:

These links (see: http://search.lycos.com/web/?q=ethy...451704d2b71c04a ) provide more information on ethylene oxide, including its use as a rocket monopropellant. Such liquid propellant model rockets might be rather like the Vashon Industries (later Estes Industries) Cold Propellant and Coldpower Convertible Freon 12-powered models (see: http://www.ninfinger.org/rockets/ca...74/74est42.html ), which had pressurized aluminum tankage. In this new century, what a wonderful thing it would be if "Stine the Younger" (or *anyone*) brought this 1957 vision of G. Harry Stine's to fruition!

I hope this information will be helpful.

a quick search reveals that Ethylene oxide and it's decomposition products are fairly nasty healthwise. I wouldn't want to try it in my lighter.
Rex

The products of combustion of ethylene oxide (C2H4O) don't appear to be any worse than those from black powder or composite solid propellant hobbyist rocket motors, and in any event, the exhaust is diluted by the ambient air. (*No* hobbyist rocket motor produces exhaust that one would want to breathe if the motors were fired in an enclosed space.) This JPL paper (see: http://authors.library.caltech.edu/18766/ ), "Ethylene Oxide as a Monopropellant," says that two sets of possible exhaust products are:

C2H4O --> CO + CH4 (carbon monoxide and methane)

C2H4O --> CO + 2H2 + C (two diatomic hydrogen molecules and a carbon atom) Also:

Ethylene oxide's specific impulse (ISP) is between 105.4 and 162.2 (depending on the reaction pressure and temperature), which would be fine for hobbyist use. In addition:

This EPA webpage on ethylene oxide (see: http://www3.epa.gov/airtoxics/hlthef/ethylene.html ) lists some negative effects of the unreacted chemical itself, but they refer to high-level exposure and long-term low-level exposure (which workers using it have), while hobbyist rocket uses of it would be low-level (probably very low-level) and brief. Ethylene oxide has a sweet smell, so detecting its presence would be easy. As well:

Having worked with RTV (Room Temperature-Vulcanizing) mold rubber, polyurethane and polyester casting resins (one of my sisters was into casting polyester resin items), epoxies, cyanoacrylate cements, methyl-ethyl-ketone (MEK) and toluene-based cements, sanding sealers, model airplane dope, and various lacquer and enamel paints (and having read and followed the guidelines of their MSDSs [Material Safety Data Sheets]), I see nothing about ethylene oxide that is any worse than these other commonly-used hobbyist materials. All of them must be used sensibly or they can cause harm, but if handled properly, they are safe and not harmful.

They might not have known all the aspects of it in 1955-1957.

Tech Jerry

That could be--in "Rocket Power and Space Flight," G. Harry Stine referred to ethylene oxide as a 'newcomer' monopropellant. On the Jet-Ex-Press Yahoo! e-mail discussion group (in response to my ethylene oxide posting there), Jim Fackert suggested an alternative monopropellant: MTP (Medium Test Peroxide). It's a lower-concentration hydrogen peroxide (HTP--High Test Peroxide--is, at least in British rocketry parlance, the term for highly-concentrated hydrogen peroxide). Also:

He wrote that [when] "Stabilized, it is safe but then kicking it off is challenging." Might a hot-wire nichrome igniter, perhaps a thicker, possibly reusable one (more like a filament), coated with silver catalyst, serve to fire MTP in a rocket engine? The simplest system would be a "cold" one (utilizing only the MTP's decomposition into steam, rather than using the freed-up oxygen to react with a fuel, as in "hot" peroxide rockets), in which the MTP tank could be pressurized with gaseous nitrogen, or maybe carbon dioxide. In addition:

A more advanced system (for larger rockets, such as HPR ones) could be pump-fed, using a tapped-off and (upstream of the turbopump) catalyzed-decomposition flow of MTP to power the turbopump's turbine. The MTP could be used for regenerative cooling in small and large hobbyist rocket engines (HTP, which is much more volatile, successfully provided regenerative cooling in many British "cold" hydrogen peroxide rocket engines for missiles and RATO aircraft takeoff boost units). Smaller, short-burning duration MTP hobbyist rocket engines could probably use simple radiative cooling, as many hydrogen peroxide thrusters do.

MTP is practical on a variety of levels. It could be pressurized passively with a recirculating hose to the fuel tank with a regulator to limit the system pressure to say 800 psi. MTP is commercially available and is the feedstock to make HTP. MTP can be catalyzed with either a sintered silver catalyst, which would have to be replaced every 20 hours or so, or one of the new composite catalysts once they become declassified.

It is scalable up and even down to the limit of regulator size. The components could be either passivated aluminum or stainless steel. The steel would be about 1/2-5/8 the thickness of a reloadable casing.

86% HTP ISP is about 113. 30% MTP is about 39. Pretty sad. If you make it into a hybrid it might increase 50-75%.

Black powder is looking pretty good now, eh?

When you put a black powder grain into a fiberglass SU case at 500 psi the ISP increases to about 145 vs 70-80 for Estes. That sounds like the low hanging fruit to me.

Jerry

All of those attributes of MTP sound good. Even its low ISP doesn't seem to be a negative for a hobbyist rocket engine. The Freon-12 Vashon/Estes Coldpower rockets' ISP couldn't have been spectacular compared with black powder's ISP, considering the mass of Freon-12 that they had to expend to equal black powder "A" and "B" motors in total impulse; a hobbyist MTP rocket's main attractions and advantages would be scale realism and the ability to tailor the burn duration to "fit" any flying field. They could even be used in combination with black powder or composite motors (scale Aerobee models with solid boosters [which could use streamer or parachute recovery] and liquid sustainers are just one possible example).

MTP doesn't burn. It decomposes.

If the manufacturer of the product made 60% MTP custom for the product the ISP would be reasonable and it would catylize far more easily.

I am well aware of that--Jetex fuel didn't burn either (it too decomposed exothermally), but the term "burn time" (thrusting time) is still used when referring to such rockets (just as we still refer to "dialing a telephone number" even though today's phones have no rotary dials).That's good news. How long (and how safely) can 60% MTP be stored? I'm hoping that if kept in a light-proof, non-pressurized (but vented, if needed [it is for HTP]) container, it might store for as long (or nearly so) as the low-concentration drug store hydrogen peroxide. Are there (hopefully not toxic) stabilizing additives that could slow down its natural tendency to decompose gradually over time?