# Could a model rocket be launched into space by balloon?

1. Aug 23, 2011

### tackyattack

Say you had a small platform lifted by a high altitude balloon capable of reaching 30 miles above the earth. And on the platfrom you had a small model rocket. If you launched this small rocket from 30 miles above the earth, could it reach the Kármán line? How powerful would the rocket have to be?

2. Aug 23, 2011

### LostConjugate

The escape velocity is

$$\sqrt{\frac{2GM}{r}}$$

The total kinetic energy required would be $$\frac{GMm}{r}$$

r is the distance from the center of the earth to your platform
M is the mass of the earth
m is the mass of your rocket
G is the gravitational constant

The amount of power you need depends on how quickly you want to get it to space. I do not know the limitations of a model rocket.

3. Aug 23, 2011

### phinds

30 miles is a VERY slight addition to the radius of the earth, so unless the model rocket is right on the edge of being able to reach escape velocity from the surface, it won't be able to from 30 miles up, and I don't think there are any model rockets that can come close to escape velocity.

4. Aug 23, 2011

### K^2

The advantage of launching from 30 miles is the reduced drag, which is a big deal for a small rocket. It will definitely make a difference, but you still need a heck of a rocket. Nothing amateur built has ever come close.

5. Aug 23, 2011

### xts

Balloons reaching 30 miles are also not of those amateur built, if they are suspected to carry any load...

6. Aug 23, 2011

### K^2

Good point.

7. Aug 23, 2011

### LostConjugate

Well if it is any help the r is measured in meters. So 30 miles becomes like 48,000 more r's

8. Aug 23, 2011

### K^2

Earth radius is about 6,300km. You are adding to it 48km, or about 0.75% r. You should look at ratios of relevant quantities. Not absolute numbers.

9. Aug 23, 2011

### Delta Kilo

Well, as I understood, the OP only wants to reach 100Km mark, not to attain orbital velocity. Still, assuming you start at 50Km (30 miles) altitude, ignoring the question how you get there and ignoring air resistance for a moment, the delta-V required to cover the remaining 50km would still be sqrt(2gh) = approx 1km/s or about 3M. I have serious doubts model rocket can get to 3M. I guess a dedicated individual can build such a rocket but it would not be a model rocket anymore.

10. Aug 23, 2011

### JeffKoch

11. Aug 24, 2011

### Lsos

Rifle bullets can exceed 1km/s, so perhaps this speed wouldn't be so difficult to get attain...

12. Aug 25, 2011

### Sodoshi

Yes, model rockets can reach space from a high-altitude balloon. (The first was in 1997 - http://www.rocketryplanet.com/content/view/16/95/ )

The cost has dropped massively since then, and the parts can be bought cheaply from amateur stockists (eg. http://www.randomsolutions.co.uk/Random_Aerospace/Balloons.html )

The current frontier (holy grail) is having a payload reach space and return to a launch site, and many groups (eg. http://ukhas.org.uk/ ) are working with systems such as ArduPilot and running tests with powered parachutes or stable balloon altitude systems for more stable gantries (One was tested today - see the post about PicoAtlas at http://groups.google.com/group/ukhas )

Anyway, to answer the question as to how powerful the rocket needs to be:

http://www.rocketryplanet.com/images/stories/features/16/2.gif

So-chan

13. Aug 26, 2011

### cjameshuff

...irrelevant, because the given goal was to reach the Karman line, not to escape Earth, or even to go into orbit.

Balloon launch was commonly used in early sounding rockets, because it can directly add tens of km to the altitude achieved (simple altitude being the goal of such rockets), and the reduction in drag adds even more, particularly on a small balloon-loftable rocket. Van Allen did a lot of work with such "rockoons".

Reaching 100 km this way with amateur equipment would not certainly be cheap or easy, but is certainly possible. Amateurs have broken 100 km from the ground, after all:

14. Aug 30, 2011

### mheslep

That would be the KE obtained upon reaching escape velocity, right? Then the total energy required to achieve escape would have to include atmospheric drag. I assume that (energy lost to drag) is a significant fraction of the total energy required?

15. Aug 30, 2011

### mheslep

I think the point was to demonstrate the order of magnitude of energy that must be produced by a group intent on getting anywhere close to orbit.

16. Aug 30, 2011

### cjameshuff

And again, that's irrelevant. The question was not about reaching orbit.

17. Aug 30, 2011

### mheslep

The Go-Fast rocket reached 6M according the Wiki reference Jeff K found. I suppose those "amateurs" were amateur only in the sense they weren't being paid for that shot.