India has thus put more than 100 satellites into orbit in 2017 with a single rocket. Such rocket launches are multiplying to send small satellites into "low" orbits between 500 and 1000 km and an orbital period of about 90 minutes.
A public debate is imperative on the relevance and the real environmental cost of this or that data consumption : video streaming by satellite, streaming imagery for disaster management or Internet access for the whole planet. The direct cost is that of the launches themselves to install and renew the new constellations, but also that of the increase in space debris and now also that of visual pollution of the night sky. A constellation such as Starlink, which plans to send 12,000 satellites, and even announces up to 42,000, thus promises to generate light pollution in every square degree of the sky at any given time (1 square degree represents an area equivalent to 4 full moons).
On the other hand, for astrophysics, a less controversial and very promising use of nanosatellites is in the offing : they open up a new field that was previously inaccessible for observing the sky with minimal ecological impact, because they are shared between several missions.
Study the solar wind blowing across the Earth
A first example is the study of the solar wind : these particles (electrons, protons) are ejected with very high energy during eruptions on the surface of the Sun and reach us after a journey of a few hours to a few days. They are known to generate beautiful aurora borealis. The interaction of the solar wind with the Earth’s atmosphere, and in particular the ionosphere, is also a source of disturbance for artificial satellites : it jams telecommunications, blinds optical instruments or even destroys certain electronic components with the risk of total loss of control of the satellite, which then becomes space debris. Currently, small satellites are observing how signals from (large) GPS satellites are deflected by the ionosphere, studying its characteristics and impact on climate in real time.
Further away, between the Earth and the Moon or Mars, the violence of the solar wind and cosmic particles are no longer filtered by the Earth’s magnetic shield and become a risk for space exploration missions. Nanosatellites could probe the amount and direction of solar wind and cosmic radiation.
From the Earth’s atmosphere to probe the "dark ages" of the universe
Another example is the understanding of the Dark Ages of the Universe, an "image" of the sky shortly after the Big Bang at very low radio frequencies, alas filtered by the atmosphere and blurred by radio emissions from human activity. The detailed map of the sky in the radio spectrum below 30 MHz is simply unknown to this day ! With a swarm of nanosatellites orbiting the Moon, we could create a space interferometer that would send data to the Earth (visible side of the Moon) and would be protected from radio pollution (hidden side).
Getting very close to the asteroids
Finally, the news from space agencies shows a renewed interest in asteroids, those small bodies not yet spherical like planets, which revolve at their own pace around the sun, sometimes crossing the Earth’s orbit and sometimes entering our atmosphere. If the body is really small (most often), it burns up in the atmosphere and offers us the spectacle of a shooting star. But if it is bigger, and it is much rarer, it can create damage as in 2013 in Chelyabinsk or a global cataclysm like probably the Tunguska event in 1908 or even the extinction of the dinosaurs.
Space missions planned to study asteroids will be accompanied by auxiliary nanosatellites : one nanosatellite will take close-up images during the impact of NASA’s DART mission on the Didymos asteroid, the other two with ESA’s HERA mission will descend to the surface for close measurements that are too risky for the mother ship. The internal composition of an asteroid depends on its mass - to measure this, you need an object close by and slow enough to be deflected by the asteroid’s very weak gravitation. The two missions together will measure the effectiveness of hitting an asteroid as a possible deflection method if such a near-Earth asteroid threatens the Earth (which is not the case for the Didymos asteroid, which will only serve as a guinea pig). Such measures require flying nearby, slowly and for a long time. Autonomous and inexpensive nanosatellites brought to the site by the main mission will be perfect !
Designing and building nanosatellites
But there’s a snag ! Since the emergence of the CubeSat format in 2000, statistics have shown a 50% failure rate, unacceptable for scientific missions. The main cause would be a lack of ground tests, but where does this lack come from ?
In fact, the first cause is certainly the belief that a CubeSat is made in only 3 years. Thus, a team commits itself to an overly ambitious schedule, reserves its rocket launch in advance and then realizes that it has to make dead ends in the tests due to lack of time. But space does not forgive : what has not been tested will not work, it is said. From the technical definition to delivery, a minimum of 3 complete reviews are required, sometimes with significant challenges. The CubeSats that worked well took 5 to 7 years or were very preliminary and simplified demonstrators to the maximum. In any case, you must be prepared to postpone the rocket launch, even if it means paying a penalty to the launcher.
A second cause seems to be the youth of the New Space sector. On the one hand, suppliers are selling their products at questionable conditions (advance payments, flexible deadlines, non-guaranteed flight performance, etc.). On the other hand, scientists don’t have the experience yet. The procurement lead times are then underestimated and deliveries are too lax. PSL Université Paris Space Pole, C²ERES, at the Observatoire de Paris, has chosen to set up a development ecosystem : we acquire standard components of CubeSats in advance, with our own purchasing conditions, and test them outside of any particular project, then we train the scientific teams from the definition in model-based concurrent engineering (MBSE), to the integration and testing needs, through the calls for tenders to organize their choice of subcontracting with the new space actors.
Beyond the educational originality of CubeSats, the growing popularity of these nanosatellites is a major opportunity for scientists. They provide access to new space-based observations, including in support of traditional exploration missions.
The Île-de-France Region funds research projects in Areas of Major Interest and is committed through the Paris Region Phd scheme for the development of doctoral and training through research by co-financing 100 doctoral contracts by 2022. To find out more, visit iledefrance.fr/education-recherche..
source : https://theconversation.com/les-nanosatellites-permettent-aussi-de-faire-de-la-science-136274