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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'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.
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!
--MarkusQ
Cost per kilo is somewhat missing the point.
Firstly, you can't buy a kilo to orbit. You simply can't.
You may be able to beg a ride-along if you have the right political connections, but otherwise it's impossible.
Secondly, it's unlikely that if 20g to orbit is $2000, 200g to orbit will be $20000.
Thirdly, and perhaps most importantly.
20g to orbit can't do much. You can put a bad camera, a radio, a solar panel, and a magnetometer on it, and maybe if you push the envelope really hard a 3-axis gyro. (to calculate your orbit)
200g however, even if it was $10000 per flight is in the realm where universities with modest physics, aerospace, or electronics facilities might consider it interesting to put up a small test sat.
Your cellphone weighs under 200g, even if it has GPS, GSM, accellerometers, wifi, camera, ...
With 200g in a small satellite, you've got a good shot at a reasonable camera, stabilisation using the earths magnetic field, GPS, a much better radio, solar panels, batteries to keep it alive during dark.
It's even reasonable that you could have a small part of it - say 50g - as a single-shot rocket able to optimise the trajectory.
I note that http://www.rcgroups.com/forums/showthread.php?t=814157 there are amateur build fully remote controlled planes at under half a gram.
How about rocket-assisted balloons? That would probably be a lot of fun, too.