How small can a rocket get?

[JebKeb]

So. How small could one get? According to my calculations, a 1kg rocket could go to space, with a final weight of 50g. Is it possible, and how much smaller can you go ignoring controllability?

Edited May 29, 2016 by JebKeb

[Kryten]

How small can one get to do what, exactly? Do you mean an orbital rocket?

[RCgothic]

I doubt that 1kg rocket would get to space. Aerodynamic drag gets more significant as you get smaller thanks to increased surface area to volume ratio.

[cantab]

Drag mainly correlates with surface area, so a small rocket will suffer increase drag for its mass. That is likely to impose a lower limit. You also have factors like only being able to make fuel tanks so thin (again, surface area to volume considerations) and the relatively fixed mass of the guidance system.

One of the smaller space-capable sounding rockets I've been able to find is the Indian Rohini RH-300 Mk II. It can put a 70 kg payload to 150 km, and is 20 feet high, 1 foot wide, and weighs half a ton itself. Generally this sort of rocket is designed for cheapness and simplicity though, rather than minimum mass.

Orbit requires something rather bigger.

Edited May 29, 2016 by cantab

[Steel]

2 hours ago, JebKeb said:

So. How small could one get? According to my calculations, a 1kg rocket could go to space, with a final weight of 50g. Is it possible, and how much smaller can you go ignoring controllability?

You've also got to consider the challenges in making very efficient engines that are also small and light. I imagine the engine mass and the above mentioned drag issues would be the two main limiting factors.

Also do you mean just to space or into orbit? There is a huge difference in answer between the two.

Edited May 29, 2016 by Steel

[cubinator]

Here's a minimalistic rocket design that won't be able to go very far, but is very small:

• Conical fuselage made of something hard
• 2 Hydrogen atoms
• 1 Oxygen atom
• Feed the hydrogen and oxygen into the cone and use a spark to make them react
• Space! Not very far though.

You'd need something that could make a very, very tiny cone, and something to feed individual atoms into the cone, and a very tiny spark. But it's a really small rocket!

[PB666]

3 minutes ago, cubinator said:

Here's a minimalistic rocket design that won't be able to go very far, but is very small:

• Conical fuselage made of something hard
• 2 Hydrogen atoms
• 1 Oxygen atom
• Feed the hydrogen and oxygen into the cone and use a spark to make them react
• Space! Not very far though.

You'd need something that could make a very, very tiny cone, and something to feed individual atoms into the cone, and a very tiny spark. But it's a really small rocket!

in space, if you have a factory in space, the smallest is a couple of ounce ion drive motor couple to a cage and solar panel. Some small ion steering rockets. Put a zenon tank on that and the solar system is you war. 

[cubinator]

1 minute ago, PB666 said:

in space, if you have a factory in space, the smallest is a couple of ounce ion drive motor couple to a cage and solar panel. Some small ion steering rockets. Put a zenon tank on that and the solar system is you war. 

My cone concept might consist of less than 100 atoms, just large enough to fit the three fuel atoms. Sure, it's impractical and difficult to make, but it'd be the smallest rocket around! then you wouldn't be able to find where it went after you launched it...

[Astrojude]

Quote

My cone concept might consist of less than 100 atoms, just large enough to fit the three fuel atoms. Sure, it's impractical and difficult to make, but it'd be the smallest rocket around! then you wouldn't be able to find where it went after you launched it...

...I think that much fuel cannot propel anything... sorry for crushing your dreams

Lel

[magnemoe]

1 hour ago, cantab said:

Drag mainly correlates with surface area, so a small rocket will suffer increase drag for its mass. That is likely to impose a lower limit. You also have factors like only being able to make fuel tanks so thin (again, surface area to volume considerations) and the relatively fixed mass of the guidance system.

One of the smaller space-capable sounding rockets I've been able to find is the Indian Rohini RH-300 Mk II. It can put a 70 kg payload to 150 km, and is 20 feet high, 1 foot wide, and weighs half a ton itself. Generally this sort of rocket is designed for cheapness and simplicity though, rather than minimum mass.

Orbit requires something rather bigger.

This, for very small payloads its an nice idea to use an plane as first stage, fighter jets are perfect as they can go ballistic and are designed to drop stuff.
The plane don't add much speed or even attitude however you get rid of most of the air resistance, as an bonus you can go right for vacuum optimized engines saving an atmospherics optimized stage

[cubinator]

1 hour ago, Astrojude said:

...I think that much fuel cannot propel anything... sorry for crushing your dreams

Lel

I think it can propel the cone a short (like maybe 100 picometers if it's small enough) distance, which technically qualifies it as a rocket.

[cantab]

I think OP implied, even if they didn't outright state, that the rocket should reach space from the surface of Earth.

[Scotius]

This one is pretty small

It's a 13 milimeter rocket round for a Gyrojet rifle. It won't go to space, but it can easily kill a man.

[PB666]

Get a 1 centimeter square of dry ice, fill a 50 ml conical centrifuge tube with about 15 ml of water, and a graduate cylinder that will fit the tube. place the water in the tube, put the dry ice in the tube. Quickly place the cap on it, invert it quickly and drop it into the graduated cylinder. Don't stick your head over the cylinder, small goes up for  a few seconds, then falls. Total cost of tube and dry ice all but nothing. 

 

[kerbiloid]

Guys, you're so wise here... Let me too.

When a free-neutron-at-rest decays, it gives proton, electron and neutrino.
Due to the conservation of energy and momentum, we can treat the neutrino as a rocket (and payload itself) while proton and electron as an exhaust.

So, this neutrino is the least possible, ultra-relativistic, space rocket.

Not even a nano-rocket, but a sub-yocto-rocket (as electron mass 0.000911 yg, nucleon 1.6726 yg);
It doesn't require any fuel from human, even more: it creates hydrogen fuel (p+e).

This rocket is not afraid of violent space conditions and sticks at nothing.

It's lightweight in the most direct sense of this word: only the light itself can be more lighter!

Edited May 30, 2016 by kerbiloid

[magnemoe]

13 hours ago, cantab said:

I think OP implied, even if they didn't outright state, that the rocket should reach space from the surface of Earth.

I assumed so, of you want to reach orbit from other places you can manage with an far smaller rocket. 
NASA Mars sample return had one who looked more like an anti tank missile. it would dock with an craft in mars orbit who would put it in an capsule and take this to earth. Red dragon think about an rocket going from surface of mars to Earth, it would be far larger say 2 meter long and 50 cm diameter. 
An Moon sample return rocket would also be small even if it went directly to earth surface, Soviet did this. 

[1of6Billion]

Ok, for the sake of argument, let's assume we want to launch a postage stamp sized probe of 1gram into low earth orbit just to Sputnik around a bit. What would it take?

Edited May 31, 2016 by 1of6Billion

[RCgothic]

I that case the payload is essentially negligible. Plucking numbers essentially out of the air:

Spacecraft:

Let's say guidance and telemetry can be handled by a smartphone. ~100g. 

There's a minimum volume of monopropellants that would be effective for control. Call it a half-litre plus tankage, maybe 400g. 

So minimum 0.5kg for the spacecraft.

2nd stage:

Payload is 0.5kg, plus engine, plus tank. Assume it does most of the work, 6.8km/s orbital insertion. Atmosphere negligible.

Smallest H2/LOX engine I could find is India's CE-20, but it weighs 590kg and has 45kN thrust. ISPvac of 443. A bit overpowered... Stage would weigh about 4.6mt with 3.6mt of fuel and 370kg of tanks at a 10:1 tankage ratio (cryogenic).

An Airbus Aestus based second stage (N2O4/MMH, 111kg, 30kN, 325 ISPvac) would weigh about 1.6mt, with 1.4mt of fuel and 70kg tanks (20:1 non-cryogenic). TWR a bit ridiculous at 2 to 17, but I assume our postage stamp doesn't care much about that. 

So let's go with the Aestus. Burn time is 144s, which sounds not ridiculous. The first stage needs to boost this to 100km and 1km/s.

Diameter (engine) is 1.31m. Nitrogen Tetroxide is mixed at a 1:9 ratio with hydrazine. The average density is 0.93g/cm3 and required volume 1.46m3. That would fit in a slightly elongated spherical tank (~15 cm cylindrical section) with internal bulkhead, which would be hilariously stubby, but then we already know this is massively over-engined. Engine is 2.2m long, stage approx 1.3m dia and 4m long including spacecraft as a cone.

1st Stage:

Payload is second stage (1.55mt) to 100km altitude and 1000m/s at that point. Needs to fight atmosphere. Gravity approximated as 9.8 all the way to orbit. If atmosphere is negligible above 10km, then you'd need to be travelling 1660m/s as you passed 10km assuming a coast from there to orbit.

Climb to 10km is a bit of a guess. You need at least 442m/s, plus extra to fight gravity, plus extra to fight air resistance. Assuming 2G acceleration, let's call gravity losses 220m/s and probably the same again for air losses. 

Earth's rotation at the equator gets us 465m/s. 

That's 2.1km/s. Let's call it 2.5km/s for margin.

The smallest 1st stage engine I can find is our friend Space X's Merlin 1D FT. RP/LOX, 756kN, 470kg, ISPsl 282, can deep throttle. It needs approx 3.2t of fuel to get the job done. 160kg tankage. TWR a truly ridiculous 4.5 to 14 even at 40% throttle. Burn time 30s.

The Merlin 1D is actually smaller diameter than the Aestus, so we keep our diameter at 1.3m. Density of RP/LOX is approx 1g/cm3. 3.2m3 required. That's a hemi-ended cylinder approx 2.8m long for tanks. Engine is 2.9m. First stage approx 5.7m tall.

1st stage mass: 5.4t.

Total craft mass: 6.9t.

Total craft size: 1.3m diameter by 10m tall.

These are just my crude back of the envelope scopings dependent on what's available engine-wise according to Wikipedia. I'm sure someone else could come up with something better.

 

Edited May 31, 2016 by RCgothic

[cantab]

Those figures don't seem that far off some of the smallest orbital launchers flown actually. For example the Russian Volna is an orbital launcher conversion of the R29R submarine-launched ballistic missile, which is 14.4m tall and 1.8 m wide weighing 35 tons. The Volna can put 100 kilos to LEO, or a bit more if the submarine sailed to the equator to launch instead of doing it from the near-polar Barents Sea.

[PB666]

On May 30, 2016 at 0:54 AM, kerbiloid said:

Guys, you're so wise here... Let me too.

When a free-neutron-at-rest decays, it gives proton, electron and neutrino.
Due to the conservation of energy and momentum, we can treat the neutrino as a rocket (and payload itself) while proton and electron as an exhaust.

So, this neutrino is the least possible, ultra-relativistic, space rocket.

Not even a nano-rocket, but a sub-yocto-rocket (as electron mass 0.000911 yg, nucleon 1.6726 yg);
It doesn't require any fuel from human, even more: it creates hydrogen fuel (p+e).

This rocket is not afraid of violent space conditions and sticks at nothing.

It's lightweight in the most direct sense of this word: only the light itself can be more lighter!

Neutrinos are not stearable, you therefore they give you no net thrust, and because there rest mass is so tiny they only give you n = 300MW

[kerbiloid]

Spoiler

Not steerable. No net thrust. All its energy is fully released before it leaves the place of reaction (i.e. inside the barrel). A rocket.

Neutrino is more or less the same.

[fredinno]

3 hours ago, RCgothic said:

I that case the payload is essentially negligible. Plucking numbers essentially out of the air:

Spacecraft:

Let's say guidance and telemetry can be handled by a smartphone. ~100g. 

There's a minimum volume of monopropellants that would be effective for control. Call it a half-litre plus tankage, maybe 400g. 

So minimum 0.5kg for the spacecraft.

2nd stage:

Payload is 0.5kg, plus engine, plus tank. Assume it does most of the work, 6.8km/s orbital insertion. Atmosphere negligible.

Smallest H2/LOX engine I could find is India's CE-20, but it weighs 590kg and has 45kN thrust. ISPvac of 443. A bit overpowered... Stage would weigh about 4.6mt with 3.6mt of fuel and 370kg of tanks at a 10:1 tankage ratio (cryogenic).

An Airbus Aestus based second stage (N2O4/MMH, 111kg, 30kN, 325 ISPvac) would weigh about 1.6mt, with 1.4mt of fuel and 70kg tanks (20:1 non-cryogenic). TWR a bit ridiculous at 2 to 17, but I assume our postage stamp doesn't care much about that. 

So let's go with the Aestus. Burn time is 144s, which sounds not ridiculous. The first stage needs to boost this to 100km and 1km/s.

Diameter (engine) is 1.31m. Nitrogen Tetroxide is mixed at a 1:9 ratio with hydrazine. The average density is 0.93g/cm3 and required volume 1.46m3. That would fit in a slightly elongated spherical tank (~15 cm cylindrical section) with internal bulkhead, which would be hilariously stubby, but then we already know this is massively over-engined. Engine is 2.2m long, stage approx 1.3m dia and 4m long including spacecraft as a cone.

1st Stage:

Payload is second stage (1.55mt) to 100km altitude and 1000m/s at that point. Needs to fight atmosphere. Gravity approximated as 9.8 all the way to orbit. If atmosphere is negligible above 10km, then you'd need to be travelling 1660m/s as you passed 10km assuming a coast from there to orbit.

Climb to 10km is a bit of a guess. You need at least 442m/s, plus extra to fight gravity, plus extra to fight air resistance. Assuming 2G acceleration, let's call gravity losses 220m/s and probably the same again for air losses. 

Earth's rotation at the equator gets us 465m/s. 

That's 2.1km/s. Let's call it 2.5km/s for margin.

The smallest 1st stage engine I can find is our friend Space X's Merlin 1D FT. RP/LOX, 756kN, 470kg, ISPsl 282, can deep throttle. It needs approx 3.2t of fuel to get the job done. 160kg tankage. TWR a truly ridiculous 4.5 to 14 even at 40% throttle. Burn time 30s.

The Merlin 1D is actually smaller diameter than the Aestus, so we keep our diameter at 1.3m. Density of RP/LOX is approx 1g/cm3. 3.2m3 required. That's a hemi-ended cylinder approx 2.8m long for tanks. Engine is 2.9m. First stage approx 5.7m tall.

1st stage mass: 5.4t.

Total craft mass: 6.9t.

Total craft size: 1.3m diameter by 10m tall.

These are just my crude back of the envelope scopings dependent on what's available engine-wise according to Wikipedia. I'm sure someone else could come up with something better.

 

Try using an advanced SRB motor- say, a GEM motor, since those can be built a lot smaller, plus maybe a 3-stage config, and air-launch from the equator, to maximize payload capacity.

But the net weight probably isn't going below 4T...

 

Another way is by just launching the rocket from a balloon. NASA did it with the Mars Inflatable Heat Shield tests, and it only took a single STAR37.

Using that method, we might only need a STAR20 or smaller to make a SSTO to space. 3-stage is even better.

[Kryten]

The closest thing to a minimal orbital launcher which has actually flown is the NOTS EV-1 Pilot from the late 50's, with a ~1kg payload to LEO. The rocket itself was under a metric ton, and even if you include the launcher aircraft total system mass is only 11 tons. Smallest ground-launched LV was the Japanese Lambda-4s, with was under 10 tons for a ~40kg payload. Both of these are all-solid vehicles with relatively primitive fuel forumations, we could do better now.