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Are there any rocket engines that are small and light enough to be held in one or both hands? Gas, liquid and hybrid designs are fine but solid motors are excluded (with the exception of solids that are some way exceptional from the rest). Along with engines, small thrusters are also good.

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    $\begingroup$ I think one could hold this in one hand if the tanks weren't full space.stackexchange.com/a/32969/12102 but I guess it would be called a thruster rather than a rocket engine. Which makes me wonder if you'd like to exclude thrusters and only include "rocket engines" proper? $\endgroup$ – uhoh Jan 22 at 6:15
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    $\begingroup$ How about the compression-based , water-expulsion rockets you can buy in any toy store? $\endgroup$ – Carl Witthoft Jan 22 at 12:26
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    $\begingroup$ Are you specifically excluding model rocket motors from this question? Asking because you can get those in very small sizes. A typical A10-0T is around 10x45mm in size for example. $\endgroup$ – Austin Hemmelgarn Jan 22 at 13:05
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    $\begingroup$ Would an RPG(Rocket Propelled Grenade) count? Various troops around the world use small propelled devices with similar small concept. I don't really know what the mechanics are of it, but if it truly is a rocket, that could be an example, unless you specifically mean ones that could be used in space? $\endgroup$ – dave k Jan 22 at 14:36
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    $\begingroup$ What about just fireworks? Okay, most of these use solid fuel, but then there are some space-faring rockets that use solid fuel as well, and nobody argues that they aren't rockets because of that. $\endgroup$ – Darrel Hoffman Jan 22 at 14:48
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Colloid microthrusters are probably the smallest.

enter image description here

If you want liquid, I'd say RD-4D RCS thruster used on Apollo spacecraft, at 8lb weight would be a reasonable example. enter image description here

Chamber Pressure: 6.93 bar.
Area Ratio: 164.
Thrust to Weight Ratio: 13.7.
Oxidizer to Fuel Ratio: 1.65.
Coefficient of Thrust vacuum: 1.89.
Unfuelled mass: 3.63 kg (8.00 lb).
Height: 0.55 m (1.82 ft).
Diameter: 0.28 m (0.92 ft).
Thrust: 490 N (110 lbf).
Specific impulse: 312 s.

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    $\begingroup$ How large is the second engine? I can't quite figure out the scale from the picture. $\endgroup$ – BillThePlatypus Jan 22 at 20:03
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    $\begingroup$ @BillThePlatypus You can grab it with your hand around the combustion chamber. :) $\endgroup$ – SF. Jan 22 at 20:33
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    $\begingroup$ @BillThePlatypus, based on the size of the plug, I'd guess it stands about a foot and a half high. $\endgroup$ – Mark Jan 23 at 1:49
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The MR-106E rocket engine is most likely the smallest liquid rocket engine. It uses hydrazine monopropellant. It could easily be held with one hand. It has a length of 18 cm, and weighs about 1 pound (about 500 grams). It was used on NASA's Mars Atmosphere and Volatile EvolutioN (MAVEN) satellite.

enter image description here

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    $\begingroup$ Didn't anybody learn anything? I've been caught out by manufactures' being unable to correctly convert to units other than SI. $\endgroup$ – D Duck Jan 22 at 17:45
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Sure. Take a look at a 1960s Mercury-Atlas vernier thruster:

Thruster image

Probably not something you can hold comfortably with one hand, but going by the scale of the stepper motors, definitely carryable with two hands.

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Rocketlab's sea level Rutherford engine is probably near the upper limit. It masses 35kg, and estimating from the 25cm nozzle diameter is about 75cm high. Despite it's awkward shape, that would still be single hand lift-able by a person of average/somewhat above average strength.

https://upload.wikimedia.org/wikipedia/en/8/8d/Rocket_Lab_Rutherford_rocket_engine-NonFree.png

(Originally from Rocketlab)

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Of course there are the RCS (Reaction Control System) engines used in every manned space ship as well as in larger satellites and space probes like Voyager, Cassini-Huygens and New Horizon. Small cubesats don't use them.

See the red markings in the drawing of the Apollo CM and the LM image of Apollo 11.

enter image description here

enter image description here

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We can't mention the Hypercurie and ignore the Curie (on the right):Curie vacuum-optimized rocket engine by Rocket Lab[A sneak peek at a hypercurie nozzle (left) vs. std Curie. Hypercurie is our latest spacecraft engine, it’s Electric pumped, on orbit storable, non toxic and It’s perfect to get payloads to the moon and..........Venus!
Peter Beck on Twitter]

You see the Hypercurie nozzle for scale. The Curie is tiny.

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  • $\begingroup$ Wow, tiny indeed. $\endgroup$ – Organic Marble Jan 24 at 20:59
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Since Dan Is Fiddling By Firelight already mentioned Rocket Lab's Rutherford engine, we should also add the Hypercurie:Hypercurie vacuum-optimized rocket engine by Rocket Lab, with banana for scale![The new HyperCurie engine for deep space and planetary missions on Photon. Banana for scale, apparently bananas are now recognized units of measure?
Peter Beck on Twitter]

I don't know the mass of this engine, but unless it is made from depleted uranium, it can't be that heavy. Also, it's made for spaceflight …

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  • $\begingroup$ I almost made a joke about the rocket looking like a banana before I read the caption. $\endgroup$ – HenryM Jan 24 at 22:33

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