Power budget is the allocation, within a system, of the available electrical power among the various functions which need to be performed.

We need to know the power requirements of the system, that is to say, we need to know the average power that the system needs in order to work correctly during the whole orbit. We must bear in mind that, in the zone of eclipse, the power stored in the
batteries must be sufficient to totally satisfy the system needs.

The power subsystem of a spacecraft shall be able to generate, store, condition, distribute and monitor the electrical power used by the spacecraft throughout all mission phases in the presence of all environments actually encountered.

Power budget is designed to satisfy the following points:

• Simulation of the total power directly provided by the solar arrays.
• Power distribution among the different operation modes and satellite subsystems.
• Simulation of the total power CubeSat consumes during eclipse, which should be recharged during the daylight in order that CubeSat can be operated for long enough time.
• Simulations of the battery charging cycle.
• Ensure the minimum activity during the daylight in the event that all the batteries are lost.

Mission description

The 354km x 1447km with 71º of inclination orbit introduced above has been considered for this study. As RAAN and argument of perigee are not fixed parameters, four values for each of them has been considered: for covering the complete 360º spectrum of possibilities in an schematic way, 0º - 90º - 180º - 270º values have been studied for both parameters, therefore contemplating 16 orbits taking into account the 4 x 4 = 16 possible combinations: RAAN: 0º + arg. of perigee: 0º / RAAN: 0º + arg. of perigee: 90º / RAAN: 0º + arg. of perigee: 180º / … / RAAN: 270º + arg. of perigee: 270º.

Mission analysis

The mission analysis has been made regarding to the 354 km x 1774 km (altitudes of perigee / apogee), 71º orbit, provided by Vega as theXatcobeo deployment orbit. RAAN and argument of perigee are free parameters.

The spacecraft configuration adheres to the CubeSAT standards on a single layout: 10x10x10 cm and 1 kg.

P-POD interface

The Poly Picosat Orbital Deployer (P-POD) is a standard deployment system, which reduces the satellite development time for CubeSAT compliant devices. This standard deployer ensures that all CubeSAT developers may conform to some common physical requirements. The P-POD plays a critical role as the interface between the launch vehicle and CubeSATs.

The P-POD allows the satellite to separate from the launcher. Each P-POD is designed to carry three standard CubeSATs, which are stored in a rectangular aluminium box with an electrically activated spring-loaded door mechanism. After a signal is sent from the Launch Vehicle (LV), the door is opened and the CubeSATs are pushed out by a spring along guidance rails, ejecting them into orbit with a separation speed of a few m/s (approx. 1.6 m/s).

CubeSATs have to be compatible with the P-POD standard in order to ensure a correct deployment of every single satellite.

P-POD requirements (general requirements, dimensional and mass requirements, electrical requirements and operational requirements) will be described in the Technical Specification document.