Pw-sat

The project was launched in 2005 by members of the student space association, with the intention of becoming the first team to develop the first Polish spacecraft. Later, they were joined by students of engineering . The number of developers has increased to 70-80 people. In 2011, the group was reorganized, and the number of people employed in the project was reduced to 22, with a core of 9 members. Before they began to build a satellite, the team decided to develop a satellites scheme as simple as possible to minimize the probability of failure. Their preliminary work includes the “ CubeSat ” wooden models that were used to test antenna deployment.

The most important criterion for the success of a project is proof of the satellite’s ability to operate in space . The main secondary goal of the development was to mitigate the problem of space debris , which is one of the most important problems facing the exploration of outer space. The first ideas about using a balloon and a sail for the braking system were eventually dropped, in part because of low reliability. After some organizational problems were solved, the team began to cooperate with the Space Research Center of the Polish Academy of Sciences. This led to the creation of a new payload, which consists of a weighting device that increases atmospheric resistance (shield), the surface of which serves as a framework for a new type of solar cells. The main goal of this experiment is to test the concept of using atmospheric braking on a satellite.

The developers expect to be able to bring the satellite out of orbit at the predicted time, about a year after launch. The second goal is to test solar cells that have never been used in space before. During the flight, the satellite will transmit telemetry with information on the status of each subsystem and the shield deployment parameters that amateur radio operators can receive. ^[one]

Corps

The body is an aluminum frame that provides support for all elements. This ensures the correct positioning of the elements during the launch of the rocket and protects the subsystems from mechanical damage. At the same time, it plays an important role in the thermal stabilization of a satellite. If one of the subsystems generates a large amount of heat, then it is absorbed by the structure (it has a very high heat capacity). Excess heat radiates from the hull directly into space. Form Factor - “CubeSat”.

Power System

The PW-Sat power supply system works solely due to the energy coming from the sun . It is converted into electric current in eight solar batteries, which are located on the sides of the satellite. Panels mounted on one side provide a minimum power supply of 2 watts. This power is partially used to charge the lithium-ion battery , which provides energy when the satellite is in the shadow of the Earth. The efficiency of solar cells is about 27%. PW-Sat will also be equipped with additional experimental panels. They will not be connected to the main power system and are part of the experiment. Only they will be used on the shield for de-orbiting.

Communication System

A communication system is needed to send data to Earth and to receive commands from a ground station. It consists of two modules: a communication module and an antenna module. Four 55 cm long cassette antennas are the basis of the antenna module. During takeoff, they were deployed half an hour after separation from the upper stage. The sweep process took only 3 seconds. Communication is supported on two frequencies: 435.032 MHz (transmission - to the satellite) and 145.902 MHz (reception - from the satellite).

Payload

A few weeks after PW-Sat is separated from the upper stage, the ground station sends a command to deploy the brake flap. It is a meter spiral with a rectangular cross section. On all four sides, it is covered with elastic solar panels. During the launch, it will be hidden inside the satellite.

Satellite Stabilization

PW-Sat is not equipped with a stabilization system. Its orientation can be estimated on the basis of data on the deployment of solar cells.

On-board computer

The on - board computer controls the operation of the entire satellite. Using the communication system, he receives commands from the Earth and controls the execution of tasks by the subsystems. It also collects information about the temperature and operation of the subsystems in a buffer and prepares it for transmission to the ground station. The central processing unit of the computer is an 8-bit microcontroller . The program is written in C language.

In addition to the main subsystems, there is also an additional one that monitors satellite subsystems before it is put into orbit. ^[five]

Deorbitation

Deorbitation ( eng. Deorbitation ) is a descent from the orbit of a spacecraft with its subsequent combustion in dense layers of the atmosphere. The earth observer will see a small meteor at this time. In a similar way, the Hayabusa spacecraft was destroyed. Destruction of a satellite by de-orbiting the Earth increases the safety of space launches. Many satellites, after the end of their mission, can continue to orbit around the Earth for decades. Inactive objects that are not controlled become space debris . They are becoming a serious threat to new spacecraft (including manned flights and orbital stations). We could observe the reality of this threat on February 10, 2009 , when the collision of the satellites Cosmos-2251 and Iridium 33 occurred. ^[6] The wreckage resulting from the collision poses a threat to other satellites. To avoid such situations in the future, developers should use deorbitation systems.

In the case of a satellite in low orbits, the influence of the upper layers of the atmosphere (up to 900 km) can be a factor accelerating deorbitation. Just as the opening of the parachute will increase the aerodynamic resistance by increasing the satellite area in low near-earth orbit, it will cause a gradual but noticeable slowdown. The consequence of this will be a decrease in orbit, a further increase in resistance and a rapid descent. Up to the entrance into the dense layers of the atmosphere.

The main payload of PW-Sat will be a system that causes an increase in the aerodynamic drag of a satellite. Although it may seem a little strange, PW-Sat is sent into space to be destroyed as quickly as possible. The PW-Sat de-orbit system is a shield. It has the shape of a square section and a length of about 1 meter. The flap is covered on the sides with flexible solar panels. At launch time, the entire structure is folded into specially prepared places inside the satellite. A few weeks after the launch, the earth-breaking mechanism's pyrotechnics are burned by a command from Earth and the flap goes out in a split second. With antennas and a panel the satellite will be approximately 150x100x13 cm in length.

PW-Sat without a de-orbit system (like 10x10x13 cm ³ ) will remain in its elliptical (300 × 1450 km) orbit for almost four years. The expected increase in aerodynamic drag should shorten the life of the satellite by one year. Such systems can be installed on new satellites and used when their mission comes to an end. This will clear the orbit of unwanted space debris.

Solar Panels

The main way to provide electricity for the vast majority of satellites and space probes is to use solar panels. Solar radiation is converted to electricity in solar panels, which are part of satellite equipment. The greater the power available to the subsystems, the greater the capabilities of the satellite. In this regard, there is a need to create more efficient photovoltaic cells that cover a larger area. However, increasing the size creates problems with launching the satellite into orbit by a launch vehicle. The designers of the Hubble Space Telescope encountered a similar problem many years ago, trying to place an observatory and photovoltaic cells in the cargo hold of the space shuttle . This happened because it was decided to roll up the solar panels - by installing them on flexible material at such a distance from each other that the whole group could be folded and delivered into orbit in a compact form.

Flexible flexible photocells will be tested for the first time in space during the PW-sat mission. They are attached to the four sides of the shield and will begin to work in a few weeks after the launch of the satellite. The cell efficiency is about 5%, which means that only 5% of the solar energy that reaches them will be converted into electricity. This is very small compared with even the main PW-Sat solar panels, which are about 25% more efficient (the best existing photocells designed for space flight reach 45-50% of efficiency). In the case of PW-Sat, the amount of electricity generated is not a big problem (electricity from experimental panels will not be used to power satellite subsystems), but the main focus is on testing the concept of flexible photovoltaic cells. ^[7]

The launch was carried out by the Vega launch vehicle from the Kourou cosmodrome on February 13, 2012 as a secondary load. These orbits: Polar orbit with an altitude of 354 km x 1,450 km, inclination = 71 °, orbital period = 103 minutes (14 revolutions / day). About 75% of the orbit in sunlight ^{[8] [9]} .