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.

Comments

Inflation

[circlingthesun]

What if someone did it for just under £999.99 but then the price of say rocket fuel goes up?

Re:Inflation

[Anonymous Coward]

To mod as Insightful the person who mentions "What if fuel prices increase?" while modding down as "Offtopic" the person who discusses why they have and might increase is contradictory, at best. They are either both offtopic or both insightful. I think sometimes moderators forget that "Offtopic" and "Troll" are not synonymous with "I disagree" and "I don't like what that guy said but I won't try to refute it".

Re:Inflation

[causality]

To mod as Insightful the person who mentions "What if fuel prices increase?" while modding down as "Offtopic" the person who discusses why they have and might increase is contradictory, at best. They are either both offtopic or both insightful. I think sometimes moderators forget that "Offtopic" and "Troll" are not synonymous with "I disagree" and "I don't like what that guy said but I won't try to refute it".

This was a politely worded post. You worded this in a non-inflammatory manner and explained why you feel the way that you do, did not use invectives or name-calling and did not even take a very controversial position, and yet you were still modded as Troll. This is one of the better statements on the recent quality of Slashdot moderation that I've seen in a while. You point out that they were not applying the moderating guidelines and they respond by failing to apply them some more, without ever explaining why they disagree with you because they probably realize they would not have a leg to stand on. I'm fully expecting to get modded to -1 myself for pointing this out, but that's okay. I have karma to burn and I'll feel better for having done it since I believe this sort of bullshit needs to be called out wherever it occurs.

Re:How much does the balloon help?

[TimeTraveler1884]

I always thought that the way orbit worked was that you got far enough away that you could equalize the reduced pull of the earths gravity with your forward momentum to achieve a stable relationship.

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.

Close to the ground for BIG rockets

[MarkusQ]

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