Smallest possible orbital rocket

[wumpus]

Er, like the untested (canceled before testing) Grom and the undeveloped [as of 2016] (and not for orbital use)  Meteor?  All to crank up the complexity to reduce fuel for 1000 m/s of delta-v?

Ok.  I like them.  They make the really big parts less big, and cut down on both fuel and oxidizer.  I'd love to see them in some sort of hybrid (rubberish fuel/N2O+intake air).  I suspect that it would be absolutely necessary to build "the smallest orbital rocket" (assuming you carry your energy supply), but can't see most "small rocket makers" building most air augmented rockets.

I'd have to assume that with a smaller payload (Pegasus can take 400+kg) and air augmentation (i.e. real delta-v from intake air) you would do better than 20% less weight than a Pegasus.

[magnemoe]

2 hours ago, Nothalogh said:

I mean an air augmented rocket, as in the Soviet Gnom missile or the MDBA Meteor.

Also known as a ramrocket, a ducted rocket, or a rocket ejector 

As Jf0 said https://en.wikipedia.org/wiki/Lambda_4S is less than 10 ton, can put an 26 kg satellite in orbit and is solid fueled it has 4 stages and boosters.
Solid fuel rockets tend to have many stages, no expensive engines and i think the empty weight of stage is higher making it smart to stage often.
An air augmented rocket has higher isp but is more complex, it has to be lighter than 10 ton to make any sense here. 
An scaled down gnome design would work here, it also give the pleasure of scaling down gnomes

Gnome managed to reduce the scale of an icbm to the half, probably not so easy with an orbital rocket who need higher speed but 6-7 ton sounds reasonable. 

[A Fuzzy Velociraptor]

4 minutes ago, magnemoe said:

As Jf0 said https://en.wikipedia.org/wiki/Lambda_4S is less than 10 ton, can put an 26 kg satellite in orbit and is solid fueled it has 4 stages and boosters.
Solid fuel rockets tend to have many stages, no expensive engines and i think the empty weight of stage is higher making it smart to stage often.
An air augmented rocket has higher isp but is more complex, it has to be lighter than 10 ton to make any sense here. 
An scaled down gnome design would work here, it also give the pleasure of scaling down gnomes

Gnome managed to reduce the scale of an icbm to the half, probably not so easy with an orbital rocket who need higher speed but 6-7 ton sounds reasonable. 

Empty weight of solid stages tend to be lower than empty weight of liquid engines. Solid enignes tend to have a lower ISP than liquid engines which is why they require more stages to get to orbit.

[DerekL1963]

5 hours ago, Nothalogh said:

I mean an air augmented rocket, as in the Soviet Gnom missile or the MDBA Meteor.

The MDBA Meteor is not air augmented, it's a ramjet.

[Nothalogh]

7 hours ago, DerekL1963 said:

The MDBA Meteor is not air augmented, it's a ramjet.

Bear in mind, though, that a solid fueled ramjet, such as the MDBA Meteor is just an air augmented rocket that is burning dirty and undergoing ram combustion in the air augmentor.

The line between ramjets and rocket ejectors is a rather fuzzy one 

[jf0]

11 hours ago, magnemoe said:

As Jf0 said https://en.wikipedia.org/wiki/Lambda_4S is less than 10 ton, can put an 26 kg satellite in orbit and is solid fueled it has 4 stages and boosters.
Solid fuel rockets tend to have many stages, no expensive engines and i think the empty weight of stage is higher making it smart to stage often.

This page

http://orbitalaspirations.blogspot.it/2011/10/japanese-lambda-4s-launcher.html

says:

"... is, to date, the smallest ground based launch vehicle to place a satellite into orbit..." If that is true, I feel like it would be very very difficult and unlikely that a "hobbyist" beat this, even tehough it is 1970s tech.

according to this also

http://www.isas.jaxa.jp/e/enterp/rockets/vehicles/l-4s/

you can see the mass at ignition and burn out for each stage, the mass ratio and specific impulse, for those interested. I would make a guess that solid rockets are used as they significantly simpler to build, cheaper and smaller. It's interesting at times on these forums people ask questions such as 'why would you use a solid rocket when x is 4 times as efficient!'. In reality, you can build 'anything' if money and time is no concern. But engineering is not about building 'the best', it is about finding a way to make something that meets the requirements, within the constraints. The most important constraints are: money, time, resources. The actual capability of current technology is rarely a real problem! Eg why did ww2 give so many leaps foward in technology? It is not because the war made people smarter, it is because it made governments pour money into the problem to make it go faster, so they could beat the enemy. There are always trade offs in engineering.

I would still say that it is far far far beyond a 'hobbyist' project, you would need at least a significant team of people and money to do such a thing.

Edited February 18, 2016 by jf0

[magnemoe]

15 minutes ago, jf0 said:

This page

http://orbitalaspirations.blogspot.it/2011/10/japanese-lambda-4s-launcher.html

says:

"... is, to date, the smallest ground based launch vehicle to place a satellite into orbit..." If that is true, I feel like it would be very very difficult and unlikely that a "hobbyist" beat this, even tehough it is 1970s tech.

according to this also

http://www.isas.jaxa.jp/e/enterp/rockets/vehicles/l-4s/

you can see the mass at ignition and burn out for each stage, the mass ratio and specific impulse, for those interested. I would make a guess that solid rockets are used as they significantly simpler to build, cheaper and smaller. It's interesting at times on these forums people ask questions such as 'why would you use a solid rocket when x is 4 times as efficient!'. In reality, you can build 'anything' if money and time is no concern. But engineering is not about building 'the best', it is about finding a way to make something that meets the requirements, within the constraints. The most important constraints are: money, time, resources. The actual capability of current technology is rarely a real problem! 

I would still say that it is far far far beyond a 'hobbyist' project, you would need at least a significant team of people and money to do such a thing.

Yes an hobbyist is unlikely to beat this, also the success ratio on the rocket was one of five on a budget far higher than an hobby group would have. 
air augmented rockets would be far outside the hobby area, its something who is hard to do even for experts. 
 

[Matuchkin]

Idk, the SPARK super-strypi, maybe?

[wumpus]

12 hours ago, A Fuzzy Velociraptor said:

Empty weight of solid stages tend to be lower than empty weight of liquid engines. Solid enignes tend to have a lower ISP than liquid engines which is why they require more stages to get to orbit.

While this is true in general, I suspect it is far easier to make a last, lightest stage a solid for a "lightest possible load".  Assuming a single cubesat, it would be hard to build a liquid engine lighter than a solid casing.  You can also buy ammonium perchlorate engines off-the-shelf, I'd assume that the market is sufficiently small that the same company would fill a carbon-fiber or titanium casing without too much of a fuss.

If you are more concerned about cost then absolute minimal weight, don't ignore solids in the stages before/after air augmentation.  In kerbal designs (i.e. g forces have no effect on engines, nor rocket weight), solids can easily be more efficient by having less gravity losses to make up for Isp.  Don't be too surprised if you run into a similar effect even accounting for requiring a more robust rocket (you really want at least 3 gs here).

[sevenperforce]

What's the absolute smallest final stage that it would make sense to build?

[Rakaydos]

17 minutes ago, sevenperforce said:

What's the absolute smallest final stage that it would make sense to build?

Probably twice the mass of your payload.

[sevenperforce]

8 minutes ago, Rakaydos said:

Probably twice the mass of your payload.

And if your payload is zero?

[Rakaydos]

Just now, sevenperforce said:

And if your payload is zero?

Fractal stages.

[sevenperforce]

15 minutes ago, Rakaydos said:

Fractal stages.

At some point, scaling is going to start hurting your efficiency, right?

[A Fuzzy Velociraptor]

33 minutes ago, wumpus said:

If you are more concerned about cost then absolute minimal weight, don't ignore solids in the stages before/after air augmentation.  In kerbal designs (i.e. g forces have no effect on engines, nor rocket weight), solids can easily be more efficient by having less gravity losses to make up for Isp.  Don't be too surprised if you run into a similar effect even accounting for requiring a more robust rocket (you really want at least 3 gs here).

A lot of Kerbal physics while fine for a game don't translate well into real-life. Also while you may be able to decrease gravity losses through a faster burning engine you will in-turn increase your drag as well as structural requirements.

 

On the topic of very small rockets, there is a small company called Aster Choronautics, that claims their launch vehicle would be able to carry a 5kg payload to orbit on a vehicle with a mass of 1000kg in a single stage version or 50kg with 1250kg in two stages.

[Kerbart]

According to wikipedia, you will need about 9400 m/s DV to make it into orbit. Plugging that into the rocket equation with an I_sp of 300 gets you a dry mass/wet ratio of around 24 if I did the math right; so for every kg of construction material your rocket will need 24 kg of propellant.

We can argue over the I_sp of 300 but if anything this is probably too high for an amateur rocket so real numbers might be worse.

[GreenWolf]

Note that staging massively impacts your mass ratios, because the final mass ratio of your rocket is the product of the mass ratios of the individual stages.

Also note that at mass ratios above (or below) Euler's number (e, approximately 2.27) you're not getting the full benefit of your exhaust impulse. This is, of course, unavoidable when launching from Earth, because you need a mass ratio of about 25 to get to orbit.

[sevenperforce]

Solid fueled rockets will be cheaper and more attainable, but will suffer from lower impulse. But staging isn't a bad thing. 

As you scale down, one of the few things that doesn't scale is chamber pressure and temperature. But since the size of the chamber does scale, the wall thickness required to contain the nominal chamber pressure will become a larger and larger percentage of the rocket diameter, increasing the dry mass fraction. That's the point where you want to stop scaling down.

[DerekL1963]

4 hours ago, Nothalogh said:

12 hours ago, DerekL1963 said:

The MDBA Meteor is not air augmented, it's a ramjet.

Bear in mind, though, that a solid fueled ramjet, such as the MDBA Meteor is just an air augmented rocket that is burning dirty and undergoing ram combustion in the air augmentor.

From the description of the gas generator, that doesn't seem to be the case, as there's nothing indicating it contributes significantly to thrust.

Edited February 18, 2016 by DerekL1963