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Cambridge N-Prize Team To Build Balloon-Assisted Rockets
Rob Goldsmith writes "Earlier this week we heard that Cambridge University Spaceflight would be entering the N-Prize competition. The N-Prize is a competition to stimulate innovation directed towards obtaining cheap access to space. Most importantly, the launch budget must be within £999.99. Cambridge University Spaceflight plan to win the prize using a balloon and a rocket. They have now opened up an official forum where the public can track their progress." The linked story has images from a test flight of July 23, and an interview with a member of the team, Ed Moore.
What if someone did it for just under £999.99 but then the price of say rocket fuel goes up?
I, for one, welcome our new balloon rocket overlords.
Otherwise known as BOC and Cambridge Precision .
I can see the usefulness of sponsorship by private enterprise, and it's reasonable to expect the sponsor to want their name on the craft, but this is ridiculous.
Loose lips lose spit.
I'm not really sure what the point of this is...what is anyone going to do with 10-20 grams in orbit? Can you even make a transmitter + power supply that small that would still be powerful enough to communicate with the ground? Or are you just supposed to send up 20 grams of foil or something that can be tracked with ground radar?
The X-prize was about getting people into space, which I think most people can see uses for (even if it was sub-orbital). I'm not really sure about this. Although I guess it's a great way to get a lot of free publicity, especially since the odds of anyone actually claiming the prize money are very low.
I'll admit, I don't know what the N-Prize is and I did not RTFA; I am assuming the goal is to reach some kind of sub-orbital or LEO flight. I've looked in to this for my own balloon projects. The energy savings from using a balloon are only a small percentage of the overall energy required to achieve orbit.
It takes about 20 times the amount of energy to reach LEO than it does to just reach the same altitude. When you compare this energy requirement to the savings of launching from the ceiling height of a weather balloon (40km) it is not much; especially considering you still have to get to the Karman Line (100km) plus the weight of fuel required, which must then be lifted by even larger balloons. Therefore, it's more economical and efficient to burn the fuel as close to ground as possible.
I'm only an armchair rocket scientist though, so I might have this all wrong. In any case, I certainly wish them good luck - Maybe I'll go read the article now.
I might have answered your question in another post.
One advantage I might imagine is that pulling a rocket up even a few kilometers and launching from there puts you above a large part of the atmosphere. Atmospheric density decreases exponentially height (http://en.wikipedia.org/wiki/Barometric_formula), so for example, at 5 km, the rocket only has to cross half the atmosphere, reducing drag a great deal. Naturally, the rocket must still accelerate above escape velocity (which is not significantly changed at 5 km above sea).
This wouldn't even make too much sense since
with that kind of money a kilogram in orbit would cost around 50000 pound. There are much cheaper means of getting to orbit:
http://www.futron.com/pdf/resource_center/white_papers/FutronLaunchCostWP.pdf
Interestingly small launchers seem to be less efficient than larger ones on average.
Maybe one should just try to hitch a ride.
On the other hand this seems to be a fun project.
I hope they are successful.
Je me souviens.
You are correct in your energy estimates, but a high altitude balloon launch has other significant advantages:
1. Your rocket engine can be an engine with vacuum geometry meant to work well in space. This differs from an engine meant to operate at low altitude.
2. Your rocket design does not need to include complicated supersonic flight in dense air, so your vehicle can be more optimized for the mission at hand rather than aerodynamic.
don't cut it off www.mgmbill.org
Achieving orbit is not about how far away you are away, it's all about your angular velocity. You could theoretically achieve orbit at sea level, but atmospheric drag keeps that from happening on earth.
As satellite orbits the Earth, it is constantly accelerating, not because its speed is increasing, rather because it is constantly changing direction (speed + direction = velocity, change in velocity = acceleration).
The acceleration of gravity is 9.8m/s, so if you can achieve an acceleration of 9.8m/s in the opposite direction, you will be in constant free fall and establish an orbit.
It takes a lot of energy (32MJ/kg) to sustain this acceleration on Earth and maintain an orbit. However, you are correct that it takes less energy to enter into a geo-synchronous orbit than other types of orbits from different latitudes. Sorry I can't find a reference for it at the moment though.
The "burn most your fuel close to the ground" only applies to big rockets that are having to use early fuel to get later fuel up to altitude.
In the present case both those assumptions are violated, making their approach more sensible than it sounds. First off, for a big rocket most of the energy required will be used to 1) get up to speed and 2) gain altitude, with 1) being the biggest concern. For a small rocket, both of these will initially be swamped by 3) friction. The higher you are when you start, the less of your fuel you will waste just overcoming drag.
Secondly, the rule only applies when you are gaining the altitude by burning fuel in the first place. When you aren't having to burn fuel to get up there, you'd always come out ahead launching from a balloon (or even a mountain top) provided you could figure out how to make it work. Heck, with a tall enough tower (hint: think GEO) based on the equator, you could launch a satellite by hand!
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How about rocket-assisted balloons? That would probably be a lot of fun, too.
But a cellphone cam might just work.
A cell phone CCD will be about 20 grams. But you also need the decoder, the DSP, and the transmitter, and the battery. If you still manage to do all that, then what's the use of a low-res image from 400 km? I understand that it might be cool once or twice, but that's what amateur satellites are for (this includes ham and non-ham ones.) These satellites don't weigh 20 grams - they are larger, but they actually work.
Usually amateur satellites hitch a ride on some other commercial launch, for a fraction of cost. There is no need to invent yer own rocket for $2,000 - use already developed hardware that works for real. Besides, rocketry is not a safe hobby when you deal with enough propellant to lift something to an LEO. When you try to do it on the cheap things only get scarier.
On subject of RC planes: a half a gram RC plane only needs to receive, so its power budget is not as tough as a satellite that has to have a large antenna and/or a powerful transmitter to send its status and data back to Earth. But half a gram RC plane is still an achievement, and it is useful because you can fly it and enjoy its flight. People are free to make a 20g satellite also, but it will be far less useful than a tiny RC plane.
E=mc^2 would only be relevant if the payload consisted of antimatter. And producing antimatter on that scale is far beyond our current capabilities.
I think the formula you're looking for is (1/2)mv^2, with a high value for v.