At 14.38 hrs on Tuesday, 3rd December, the Indian Space agency ISRO commenced the 25-hour countdown for the PSLV-C59/Proba-3 mission. The countdown is a process when the health checks of various systems and technical parameters of the rocket are conducted, liquid fuels are filled. At 16:08hrs on Wednesday, the 320-ton PSLV-XL rocket is to liftoff from the First launchpad at the Indian Spaceport, Satish Dhawan Space Centre in Sriharikota, Andhra Pradesh.
The 44-meter tall PSLV rocket will be carrying the twin(Occulter and Coronagraph) spacecraft of the European Space Agency(ESA), which weigh a total of 550kg. The mission is known as Proba-3. Proba is a series of missions where the ESA demonstrates new technologies in space.
The mission's name, 'Proba' is derived from the Latin word, which means "to try or try it"... Proba is an abbreviated version of ‘PRoject for OnBoard Autonomy’.
Around 18 minutes and 40 seconds after liftoff, the twin satellites will be injected into a 600kms x 60,000kms orbit. This is known as a highly-elliptical orbit, which means that the satellites' distance from Earth keeps varying drastically. A large number of satellites are injected into circular orbits, which puts them at a constant distance from the Earth. However, in elliptical orbits, satellites have an apogee(farthest point from Earth) and perigee(closest point from Earth), and their distance from the Earth keeps constantly changing.
What makes Proba-3 unique?
Proba-3 is the world’s first precision formation flying mission. It consists of two small satellites launched together that will separate apart to fly in tandem, to prepare for future multi-satellite missions flying as one virtual structure. Simply put, Proba-3 satellites will fly at a proximity(approximate distance of 150 meters) to one another. This is similar to how fighter pilots fly their planes in a close formation.
As a world first, its two satellites –the Coronagraph spacecraft and the Occulter spacecraft – will maintain formation to a few millimetres and arc second precision at distances of 144 m or more for six hours at a time. In effect, the pair will be forming a virtual giant satellite. This will be achieved autonomously, without relying on guidance from the ground.
What will Proba-3 study?
The solar corona (the outermost part of the sun's atmosphere) has many mysteries associated with it. The solar corona is a million degrees warmer than the surface of the sun, and it is the origin of coronal mass ejections(highly charged particles) which can affect the functioning of satellites, or communication and power networks back on earth. There is immense scientific interest in better understanding the solar corona and related phenomena.
A Coronagraph is a device that can artificially block out the bright light of the sun, thereby enhancing the visibility of the faint corona. A solar eclipse, when the moon blocks out the sun, is a great natural opportunity to study the solar corona. But eclipses are rare and occur only for a few minutes.
The two Proba-3 satellites will be precisely aligned so that the Occulter spacecraft casts a shadow across the Coronagraph spacecraft, thereby enabling the visibility of the faint solar corona. If the two are not perfectly aligned, then the bright disc of the Sun will not be hidden from the instrument and the corona will be obscured by its bright light.
Why is Proba-3 being launched from India?
India's PSLV-XL launcher was chosen to ferry Proba-3 satellites to space, as the European Space Agency(ESA) does not possess a medium-lift rocket that can launch the 550kg Proba-3 satellites into the desired orbit. The mass of the satellites is above the capability of ESA's Vega-C small rocket, while the large Ariane-6 rocket would be too costly for a mission of this kind. PSLV offers the perfect balance in terms of lift capability and cost. ESA will be paying around € 30 million (approx Rs.271cr) to avail the launch services from ISRO's commercial arm NewSpace India Limited(NSIL).
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