## Constellations of satellites for Optical Earth Observations

Being able to access maps of any part of the globe updated on daily basis whenever necessary could have important benefits for scientific reason as well as for better emergencies evaluations.

Constellations can avoid one of the most common problems with Earth Optical Observations from satellite. Clouds covering a region and blocking the view. If there’s one single satellite that passes over a region every 30 days and there’s a cloudy day it may be necessary to wait till next time the satellite will be above the same region, 30 days later. Doubling the observation time for many applications is not acceptable.

Most of the time different satellite operators, from different countries, may share data solving the problem, perhaps with only some days of delay.

Why is the update frequency of the maps important?

Agricultural improvements. Instead of receiving data once each month, being able to access information everyday on crops and soil condition that may allow farmers to deal with droughts more efficiently increasing the overall productivity.

Emergencies like earthquakes, floods, forest fires, humanitarian crisis etc. All these need rapid information in order to coordinate the emergency teams more efficiently. For example in case of earthquakes or floods it could be possible to identify places with major damage or obstacles that could slow emergency teams.

Planet Labs is a company that works with a constellation of optical satellites (Doves) many about 10x10x30 cm in size. They manage to create maps of the whole globe updated on daily basis. Gallery of some of their photos from space.

## Trappist-1 and the 7 Earth-Size planets

The discovery of 7 Earth-Size planets by Nasa has been very popular. Let’s see some key aspects of this star and its planets.

Trappist-1: red dwarf with a mass equal to 8% of the solar mass. Just above the limit for nuclear fusion to be possible.

7 planets: Orbital period from 1.51 to maximum 20 days. Distance from star is about 3% Earth distance from Sun. Planet radius between 0.76 and 1.13 Earth’s radius.

As we can see the 7 planets are Earth-Size planets but besides that the system itself is very different from our own. This could mean it had a completely different evolutionary process.

Planets the size of Earth do not guarantee the necessary conditions for life to develop even if situated in the habitable zone of the solar system. A planetary magnetic field is required in order to have an atmosphere. Latest discoveries have proved how Mars lost its atmosphere because of the solar wind that slowly ripped away the molecules.

Even if the Trappist-1 is smaller then the Sun the planets are much closer then Earth. Star radiation could be a problem and other negative aspects due to this proximity could also be present.

Life needs challenges that force it to evolve, an unstable environment. Systems that are too stable don’t create the necessary conditions for life to evolve. Too unstable ones destroy the elementary life forms.

So why should someone do these researches? Models built to describe how the Solar System has formed need to be verified. Similar stellar system at different evolutionary stages could help understand what happened and what will happen to our system.

Trappist-1 is about 39.5 light year away. The simplest conversation would take about 80 years just for the initial presentations. Finding extraterrestrial life sure is interesting but it’s just the last of the goals.

## 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.

## Moon, necessary step towards the future of space exploration

After the Apollo landings of the past century the Moon has been “abandoned” as Mars became much more attractive, at least for human landings and long permanence. The idea of establishing a permanent base on the red planet is yes ambitious but incredibly hard and dangerous at the same time.

As recent discoveries proved Moon may have resources necessary for the full development of a permanent base. But the main objective could consist in the construction of base models including orbit assistance. The technology would then be used for other missions by just adding little changes depending on the particular environment we need to deal with.

Let’s see some of the main problems we need to deal with in the case of a permanent Moon base:

• lack of atmosphere

There is a need of structures easy to build to satisfy the need of expanding in short time and recreate life conditions for humans and plants. Lack of atmosphere or weak external pressure need structures capable of containing the internal pressure. In this particular case the technology of inflatable elements is the one that better meets the requirement of the project.

Some radiation is harmful to life. We therefore need to create a shield able to filtrate harmful radiation from the one essential for terrestrial life development. In some cases water could be used as a filter. Technology capable of extracting water from local resources is fundamental.
Underground structures may be considered, if ground radiation itself is absent. The thickness of the layer made by rocks and dust may prove an excellent shield against harmful radiation. External inflatable structures need to be integrated with the underground solution.

• raw materials exploitation

A permanent base needs to rely on local resources for most of it’s needs. External radiation or fission from nuclear material could be used to power the station. Local soil has to be exploited in order to get water and other necessary minerals.

• transport

Short range transportation could be guaranteed efficiently by land, possible by autonomous driving cars. In the case of multiple far apart bases long range transportation may prove cheaper by small rockets, since there is no drag due to atmosphere like in the case of Earth.

## 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.