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<big>'''N-Prize reflexion wiki'''</big>

This web site aims to gather to gather my researches in the field of astronautics, rocketry and other launch technologies that can be used for the N-Prize competition. It is not an official web site for the [[N-Prize]]. The official web site is here: http://www.n-prize.com/ . I'm not part of a team, nor did I register a team, because I don't really have the expertise to actually build it in time before the deadline of the project in september 2011.

==How to escape from Earth?==

Rockets have been used for 50 years to escape the gravity of earth. They are
good for two things: go fast and burn a lot of ergols. Indeed, the efficiency of
a propulsion engine is measured with a <i>specific impulse</i> (I_sp), and for
rocket engines, it is quite low. However, they are the only engines that provide
the sufficient thrust to climb up with large speeds.

Besides altitude, speed is the most important factor when orbiting an object.
Without it, satellites would fall down on Earth, even if you climb up at 200
miles. Once again, rocket engines, with their high thrust power can achieve
sufficient speed before falling back on Earth.

Rocket trajectories generally roughly form a square angle, while the final
direction of the flight is parallel to Earth's surface. The reason is that since
they achieve ultra-sonic speeds very quickly, the air pressure on their body
(mainly the fairing) is quite important. It is more efficient to first escape
the atmosphere and then change trajectory to gain the horizontal speed needed
for orbital injection.

That particular point of the cost of escaping the atmosphere made me thought
about using an aircraft to launch a rocket from the upper atmosphere, reducing
considerably the air pressure, the drag, and improving trajectory and
efficiency. Moreover, the specific impulse of a turbo-propeller is around <b>ten
times</b> greater than the Isp of a rocket engine, since it uses oxygen from the
atmosphere to burn its fuel, and not some embedded oxydizer. The fact that it
uses a turbo design is also part of the improvement. For the N-Prize, the cost
of the aircraft could be deducted from the overall price since it would be
reused.

I started searching, and I found out that Orbital already has developped an
air-to-orbit vehicle, called the [http://www.orbital.com/SpaceLaunch/Pegasus/ Pegasus].
It is able to push onto Low Earth Orbit a payload up to 1,000 lbs (450 kg), and it is
launched from a full-sized airplane. My goal is thus to study the feasability of
something similar, at low price, even for the aircraft. A rocket would
still be used for air-to-orbit link because nothing else is able to achieve
speeds around 9 km/s. Some specific technologies can be used to improve
efficiency, we'll see them below in the [[#The rocket|rocket]] section.

Several teams are working on using Helium balloons to get to the high
atmosphere, around 70km and then launch a rocket. It is a nice solution too, and
less expensive in the overall, but balloons are not reusable and suffer from
imprecise position localization due to winds.

==The aircraft==

Some aircrafts have been exploring the high atmosphere, around 30km high.
Contrary to what one would assume, high flight speeds are not needed. The [http://www.nasa.gov/centers/dryden/news/ResearchUpdate/Helios/index.html Helios] for example, flights at this altitude at 20km/h. Nevertheless, we
would benefit from high speeds of the aircraft, speed that wouldn't be needed by
the rocket to reach.

Fuel or electricity? Kerozene or alcohol?

How to build a £100 turbo-propeller?

===Staging===
Separation from the rocket is a big concern. If wings are directly mounted on
the rocket body and jettisoned, they would not need some guidance or attitude
control electronics, just a basic parachute system. If the wings are able to fly
without the rocket, two guidance systems are needed: one for the rocket and one
to get back the aircraft in one piece.

===Guidance===
GPS can probably be used in the plane for position tracking. Other sensors should be shared with the rocket's onboard computer.

==The rocket==

===Fuel===
Ergols represent the most important part of the weight of what we have
to launch. It should thus be chosen carefully regarding to its cost.

Alcohol has been used in the early ages of rocketry, in the german V-2 for
examples. It has the advantages to be cheap, and burns quite well. It is not
pure, generally used between 75 an 90 percent of volume ratio with water for the
rest. The loss of weight due to that water is often a good thing because it
burns producing so much heat that the water can keep the engine cool enough to
survive. Rocket-grade kerozene (RP-1) has been introduced later to replace
alcohol, providing a beter volume efficiency.

To my eyes, alcohol seems to be a very good low cost solution. RP-1 is still
used nowadays, and is only 20% more efficient than alcohol with a liquid oxygen
(LOX) oxydizer. The next question is thus: should we use some pure alcohol,
alcohol/water blend or alcohol/something else blend?

I believe that E85, a 85 percent alcohol and 15 percent gasoline fuel
recently used in automotive, is promising. I think that it's efficiency will be
slightly better than alcohol, still being very cheap, around £0.5 a liter.

===Oxydizer===
Using LOX has tons of drawbacks because of cryogenics. But are there any other oxydizers that can be used?

===Engine===
Aerospike engines should be seriously considered.

For the cooling, I only see [http://en.wikipedia.org/wiki/Regenerative_cooling_(rocket) regenerative cooling] as an option.

===Trajectory===
The trajectory has to be precise enough to get a launch authorization for
a specific orbit. I believe that simple cameras can be used on the rocket to
determine position of the sun and the Earth's horizon. Accelerometers, digital
gyroscopes and a compass are really cheap nowadays and can be used too.

Anyway, if sensors are available, actuators are different story. I see only
two possibilities, as fins won't have any impact in the vacuum of space: the
rocket engine has to be directionally controllable or control jets must be used
to control the attitude of the rocket. Both case imply lot of complications of
the rocket's hardware.


==The satellite==

Lots of strategies for the tracking of the satellite have been exposed:
flashing device, radioactive, narrowband EM emitting, mirrors...