Sunday, October 22, 2017

Amateur manned multicopters. Flying cars are just around the corner.




Flying cars are just around the corner. Over the past several years there have been many examples of manned multicopter vehicles. Anyone that has several thousand dollars to spend on hobby aircraft parts and lots of free time can build a manned multicopter. Its not as complicated as one would expect. Someone can take hobby aircraft parts including electronic flight controllers and use them without much modification. Most of the manned multicopters use hobby parts meant for large scale model aircraft. Large high output brushless motors paired with large hobby propellers.




The biggest challenge with a manned multicopter is not lift, hobby motors and propellers are able to provide enough lift. Packing enough energy density into a power system to get a long flight is one of the biggest challenges. Building a manned multicopter becomes a balancing act, weight vs. lift vs. energy.
Increasing lift adds weight and uses more energy. Increasing energy adds weight and requires more lift. Increasing weight requires more lift. The props need enough power collectively to lift the vehicle and the passenger and power supply.




The power supply used for these type of experimental manned multicopters are usually an array of lithium based batteries. At the moment lithium based batteries provide the best energy density needed for a manned multicopter. The batteries are heavy and this means there is a limit to the amount of energy that can be carried onboard. Most of the experimental manned multicopters are only able to fly for 15-20 minutes max.

Some people have claimed that multicopters do not scale. One reason they cite is that larger props have too much momentum to be able to make the small changes in RPM needed for stable flight. Even the larger props are so light that this is not as much of a factor as some people think. There are a couple solutions to this anyway. One solution is to use many smaller propellers to gain enough cumulative lift. Other solutions people are working on are things like variable pitch props that change the amount of thrust instead of altering the RPMs of the rotor.



Battery technology is the limiting factor in this case. If there is a substantial breakthrough in consumer battery technology, then almost anyone could have a flying car. And they would not really cost too much looking at a minimalist build. Really light and strong modern materials like carbon fiber and ETFE can be used to further reduce the weight. For safety purposes someone could install a ballistic parachute commonly used on ultralight aircraft.

References:

https://en.wikipedia.org/wiki/ETFE
https://en.wikipedia.org/wiki/Carbon_fiber_reinforced_polymer
https://en.wikipedia.org/wiki/Ballistic_parachute










Monday, October 16, 2017

Is an amateur cube-sat launch possible?

Would it be possible for a volunteer based crowd-sourced project to launch a satellite into orbit? I think it is possible. Cube sats are micro sized satellites measuring only several inches in any dimension and very light. The CSXT(Civilian Space eXploration Team) launched their new “GoFast” rocket on July 14th to an confirmed altitude of 73.1 miles or 385,800 feet. (rocketry.wordpress.com). 73.1 miles is an impressive distance to achieve by hobbyists. The shortest distance between Earth and space is about 62 miles (100 kilometers) straight up, which by general accord is where the planet's boundary ends and suborbital space begins. Space for orbital things generally begins at 100 miles, and low earth orbit at 120 miles.


To be able to launch a payload into orbit a rocket would need to accelerate the payload to thousands of miles per hour horizontally and reach orbital altitude. The hobbyist rockets usually have several cameras and appear to have enough power to increase the payload. Most of the high altitude hobby rockets use a solid fuel that is cast into a mold. The fuel is the heaviest component to a high altitude rocket. Some amateur rockets use liquid gas fuels like liquid oxygen and a liquid fuel. The liquid fuels add additional levels of complexity (and cost) to a rocket project. Some liquid fuels require very cold temperatures etc. The benefit to liquid fuels is they may have more energy density, but are immensely more complex.


How much larger would the rocket need to be to be able to launch a cube-sat micro satellite into orbit?  This would account for the need of multiple stage rockets that separate from the main rocket. A cube-sat satellite is also much lighter in weight than payloads of larger rockets. A cube-sat might weigh a total of 0.5-20kg.


Most amateur high altitude rockets do not have stabilization including rotation prevention. Stabilization enables the rocket to make adjustments to ensure the rocket does not go off path. This also prevents high spin rates. In some of the amateur rocket videos the rocket spins so fast that the video is blurry. Stabilization could prevent this type of spin. A stable rocket is necessary to deliver the payload into orbit without any spin.



An example of smaller rockets that could achieve orbit are the S-Series fleet of sounding rockets funded by the Japan Aerospace Exploration Agency (JAXA) that have been in service since the late 1960s.

SS-520-4 is the fourth vehicle configuration of the SS-520, and this version includes a small third stage, which can put a 4 kg 3U CubeSat into a 180 km × 1500 km orbit with an inclination of 31°.


SS-520-4 Specifications

    Height – 31 feet (9.54 meters)
    Weight – 2.9 tons (2.6 metric tons)
    Diameter – 20 inches (52 centimeters)
    Payload to Low-Earth Orbit – ~9 lbs (4 kg)



An educated guess on cost for an amateur cube sat rocket would be around 6 figures in costs depending on the size of the rocket and fuel used.

UPDATE:

Space Enterprise at Berkeley is planning on sending a rocket to 135km(~84 miles) and they are doing it with a budget of only  $150,000 - $ 250,000 .

Japan successfully launches world’s smallest satellite-carrying rocket (SS-520)


References:

https://en.wikipedia.org/wiki/High-power_rocketry







Is an amateur cube-sat launch possible? from rocketry

Is an amateur cube-sat launch possible? • r/rocketry from aerospace