Imagine solar-powered ion-propelled aircraft. Ion propulsion allows flight at high altitudes like 40-50 km. The air is rarefied at high altitudes, that means the aircraft should have high velocity like 1-2 km/s to maintain the altitude. Solar energy allows unlimited range. So, such an aircraft can be long-range and high-speed.
For high velocity such an aircraft should have enough power like 0.2-0.4 watts per gramm of mass.
If it has some 5 watts per gramm, it might be able to reach the space.
Imagine a fixed-wing airplane with ion engine and solar panels. Currently it cannot take off from Earth surface due to very low thrust. It is caused mostly due to insufficient power of energy input.
But what if the size of the apparatus decreases. According to Square–cube law, decreasing dimensions n times will lead the surface area decreases n*n times while the volume and mass decreases n*n*n times. This means power-to-mass ratio increases n times. Small enough apparatus might have enough power to take off from the surface, fly in the atmosphere and become a satellite.
Travelling in lower and upper atmosphere seems to be possible. See Ion-propelled aircraft and Atmosphere-breathing electric propulsion.
Photovoltaic is good as an energy source:
1. Virtually unlimited amount of on-board energy.
2. High electric power density - thin-film solar cells might generate some 10 Watts per gram. For comparison Plutonium-238 generates 0.57 Watts of power per gram, that power yet needs to be converted to electricity.
3. Photovoltaic can produce high voltage output just by connecting solar cells in series. High voltage is necessary to power ion engines.
4. Lasers can provide additional power. The lasers can be designed to be safe for eyes.
So, there is a chance, Non-rocket spacelaunch will appear in the near future for small-sized payloads, e.g. several grams.
