## Drones and satellite observations. Biodiversity and LiDAR.

There are satellites constantly observing every single part of planet Earth. Some of them with a resolution of about a meter, military ones even less. Sometimes they are single objects, other times they form constellations. ESA Copernicus Program is based on a constellation of satellites called Sentinels.

FA (TS Author)
Considering the price for same images you wonder if a drone cannot do the same or better for less money.

LO
This is a good question, but I imagine drones would have to fly higher than is currently permitted in order to do useful imaging, making them a serious hazard to passenger aviation. As far as I’m concerned, the fewer drones in the sky, the better.

No doubt drones could become dangerous if not used properly. Still following rigorous rules they could become a resource being complementary to satellite data.

FA (TS Author)
It depends on how vast is the observed area. Drones cannot compete with satellite when it comes to global observations. Still a city or a small agricultural region could be well covered. Since we have helicopters that fly over cities I think drones will be little hazard for civil aviation. Obviously we speak about a few drones per city not millions of them 🙂

ND
Probably. But you have to be physically near your AOI. The municipality where I live does a lot of its urban planning photography from a balloon. I don’t know about the economics of IR sensors, either. I can’t imagine they are cheap or easy to replace if you land your drone in the river.

Particularly drones based on LiDAR (Light Detection and Ranging) technology able to analyse the biodiversity of a region by mapping the distribution of plants in a forest. They are much more then simple IR sensors. Though IR could also provide great information on vegetation.

LiDAR combined with new 3D and autonomous cars diffusion could really become a fantastic combination for the future. You could find many videos on this technology and here I suggest one that may visually explain the concepts in this post.

Annunci

## Why are chemical rockets so useful when it comes to leaving the planet?

In order to reach a stable orbit it’s necessary to generate enough thrust to overcome the resistances, mainly gravitational and aerodynamic. We therefore consume energy, but what is important is how we consume that energy.

A thrust that is equal to the gravity force would not move the rocket at all. It requires an infinite quantity of energy just to maintain the condition of equilibrium.

Propellant is the main component when it comes to weight before take off. As the rocket becomes heavier, it will require more and more propellant. Technological limits indicate an optimal condition that allows to leave the planet, and the gravitational field, quickly consuming a reasonable quantity of propellant.

Usually to optimize the fuel consumption, rockets are divided into stages. This allows to get rid of components, and weight, that aren’t useful anymore.

$I_{sp}=\frac{I_{tot}}{m_{f}g_{0}}$
$I_{tot}=\int_{0}^{t}Tdx$

Chemical rockets have smaller specific impulse compared to electrical propulsion, which is usually choose for orbital maneuvers. That because in space we can build up necessary accelerations in weeks, months or perhaps years. In fact missions last for very long periods and slow accelerations build through electrical systems bring the advantages of having lighter space systems that can cover major distances.

Rockets are used because of the high power they can generate. This way it’s possible to leave the planet in the shortest time at maximum efficiency. Though they have a very short lifetime compared to the electric propulsion systems.