On 9 June 2015 the European Space Agency (ESA)’s 62nd parabolic flight campaign was performed, involving the participation of the GMV-led PATENDER (Net Parametric Characterization Parabolic Test) experiment to demonstrate the launch of nets and capture of satellites in zero-gravity conditions similar to outer space.
PATENDER is an ESA-funded activity within the Clean Space program, which aims to encourage the development of space-debris reduction projects, using custom-built technology to capture decommissioned satellites still orbiting the earth.
The Space-Debris Problem
A layer of orbiting space debris is now building up around the Earth: over 17,000 objects larger than a coffee cup have been recorded, all of which might hit operational satellites with catastrophic consequences. Even a 1-centimeter nut could hit a priceless satellite with the force of a hand grenade. These uncontrolled objects weighing several tons are veritable time bombs: sooner or later they are bound to crash into something or they might even explode beforehand due to the dregs of fuel in their tanks and the only partially discharged batteries heated up by the sun.
ENVISAT is an earth observation satellite of the European Space Agency (ESA) launched in March 2002. It was operative for ten years until April 2012 when all contact was lost. It can now therefore be considered to be a clear example of “space debris”, posing a huge hazard for NEO satellites due to its sheer size, over 25m long and 10m wide.
Possible solutions: satellite capture with nets
Within space-debris capture techniques, GMV has been studying the launching of nets as one of the most efficient methods. The aim of the project is to develop a software simulator that recreates the net deployment dynamic and contact with the target satellite. This simulator has been vetted by means of a real parabolic-flight experiment, and it has been filmed with high speed cameras that facilitate a 3D reconstruction of the trajectories of the net itself and each of its nodes.
The experiment: net behavior in zero gravity
From summer 2014 the team was busy for months designing the system and conducting initial simulator tests. For the real-life experiment the system was taken on 1 June to the site of Novespace, in Bordeaux-Mérignac airport (France). An initial, 2-day, in-depth inspection was made of all system elements (set up in 2 racks, one of 140 kg and another of 120 kg) to ensure integrity and safety of the operators, the aircraft and the experiment itself.
On 3 June the PATENDER experiment was installed on the deck of an Airbus A-310 aircraft. This aircraft has no seats or any other obstacles in its central part, thus providing an unobstructed space of over 20x5m for setting up the 12 different experiments carried out on GMV’s flight.
The final system check was carried out on 8 June, after which it was passed as fit for flying.
Flight day finally arrived on Tuesday 9 June. At 07.30 hours the experimental system was set in flight mode and at 8.30 the medical department ran a final check of the operators’ state of health.
After takeoff the aircraft climbed up to flying height. The four cameras were then positioned and orientated by taking pictures of a board of known dimensions and shape set in the central part of the experimental system. After this initial calibration phase the three A-310 pilots started on the scheduled sequence of parabolas, a net being launched in each one.
The net launching process began by positioning the 4 weights on the 4 launch cannons and placing the net in a specially prepared container. After initiation of the parabola and upon beginning to “float” in zero gravity, a further six-second grace period was given to ensure the best micro-gravity conditions (below 0.05g of nominal gravity). After this initial wait the operator turned on lamps in the experimentation area, curtained off to ensure a uniform black background against which to pick up the colored net nodes.
The nets used by the PATENDER experiment measure 0.6×0.6m with a square 13×13 node configuration and a 5cm mesh. They are made from Technora, an aramid fiber with high tensile strength, a high elastic modulus, low weight and excellent resistance to heat and chemicals. Although of plastic origin this material gives “steel cable” toughness. It is widely used for making the hawsers of merchant ships and is therefore a clear candidate too for making space nets.
Once the working area was suitably lit, the launch of the 4 weights was simultaneously triggered by releasing the compressed air from a closed 2-liter tank. The net flies at speeds of 1 to 1.5 meters a second; thanks to the initial angle of the launch cannons, the net is totally deployed in front of the satellite mockup. Upon hitting the satellite, the weights force the net to close round the target, capturing between them the Envisat satellite mockup and thus bringing this space-debris capture experiment to a successful conclusion.
Throughout the whole flight the nets were successively launched in each of the parabolas performed, obtaining over 15 deployments and successful captures within each one (in some cases the low ejection pressure meant that the weights did not reach deployment speed; in others, the capture was partial only).
After completion of the experiment ESA declared its satisfaction with the results, in the sure knowledge that they will help to mature net-based space-debris capture technology.
The next step now will be the construction of a net completely qualified for use in space and its launch in orbit aboard an atmospheric rocket.
Within the field of space-debris capture GMV is playing a leading role in various technologies related to the guidance, navigation and control of spacecraft, the capture of floating elements and orbit operations. GMV has also designed and consequently led the preliminary study of a possible orbit-demonstration space mission of various active space-debris capture techniques. ANDROID, the name of this possible mission, aims to perform a flight demo of three of the most critical aspects of this future process, the Guidance, Navigation and Control (GNC) system, rigid capture with a robotic arm and net-launch capture and deorbiting of a satellite, in ANDROID’s case the Belgian satellite PROBA-2.
The flight trial of 9 June represents one more stride towards the effective capture of space debris and cements GMV’s role in this challenging task.
Las opiniones vertidas por el autor son enteramente suyas y no siempre representan la opinión de GMV
The author’s views are entirely his own and may not reflect the views of GMV