Pegasus Details

General Description

The DPR is stowed in the space between the solar arrays and the communication panels. Once the satellite in orbit, first the solar arrays will be deployed and then once the satellite reached the target orbit the DPR will be deployed.

The thermal transfer from the spacecraft to the deployable radiator panel is performed via Loop Heat Pipe(s) (LHP). The evaporators collect the heat from the communicatino payload units and transfer it via LHP to the condenser which is embedded in the DPR. The LHP lines comes from the S/C and then connect to flexible hoses located in the deployable mechanism and finally goes to the condenser.
The system consist in two LHP, one nominal and one redundant. The DPR is sized to allow a functioning with one LHP failed.

The size of the LHP evaporator saddle is specified in such a way to obtain a high level of thermal conductance at system level (thermal resistance in the evaporator I/F with heat pipes is one of the most importance in the thermal chain between units and radiative surface).


The DPR Subsystem is composed by a sandwich panel (DPR itself) with aluminum skins and honeycomb which has embedded the LHP condenser.

The DPR remains stowed during the launch phase by means of Hold Down and Release Mechanisms (HDRMs) similar units used for solar arrays and reflector antennas. Then, the HDRMs release the panel and the Deployment Mechanism does its job through clock springs deploying the DPR 180º. The final deployed position is guaranteed through an end-stop.

The DPR subsystem is totally passive. LHP type fluid loops are used to transfer the heat power from the heat source to the deployable radiators. Heaters are used for starting-up (boost heating), to LHP shutdown (inhibition heaters) and to avoid the LHP freezing (on condensers and flex lines).

Pegasus Deployable Radiator for satellite

2. Subsystems Description

2.1 Thermal Subsystem

The DPR Heat rejection capability from the evaporator I/F is > 1000 W with the evaporator I/F temperature at 50ºC.
The radiator is covered with Optical Sun Reflectors (OSRs) in both faces having a total radiative area of 4.8m2.
The thermal performance is guaranteed for a temperature range [10°C, 80°C] between evaporator saddle and radiator on the temperature range .
The DPR performance considers all the thermal cases for a typical telecom satellites (WS, EQX, AE, SS) for both BOL and EOL.

The heat transport is through ammonia.

The evaporators are inside of the S/C, in the communication module collecting the heat dissipated by the comm. units. The lines goes inside of the S/C having brackets which thermally isolate from the S/C environment and connecting to the flexible hoses.

Heatres are distributed along the condenser to avoid freezing the ammonia, and on evaporators and compensation chamber for start-up and shot-down possibilities.

MLI will cover those areas in the radiator without OSRs.

2.2 Structure Subsystem

The radiator is a sandwich panel with aluminum skins and honeycomb. Two different honeycomb density is used for mass saving reasons, using the most dense one in local areas to get higher strength.
The panel is connected by means of a boom or arm to the deployment mechanism. The boom is made of aluminum and with a U-shape cross section allowing the LHP lines being routed inside it.
Typical bobbin inserts are used to connect the boom to the panel.
The structure subsystem is sized to support the launch environment. In order to decouple dynamically the DPR for the S/C modes, the DPR is sized to meet the natural frequencies requirement and the rest of mechanical environments:Quasi-Static loads, sine, random and acoustic environment.

The DPR subsystem interfaces with the S/C side wall through 4 HRMs and the deployment mechanism. 4 HRMs are needed to meet the natural frequency requirement.

2.3 Mechanism Subsystem

Deployment Mechanism

Deployment Mechanism (DM) consist in two hinges with clock springs and damper. The DM is designed and qualified under the ECSS-E-ST-33-01C.


Hold-Down and Release Mechanism are non pyrotechnic units and consists of a bracket or pod, release mechanism (from NEA supplier), HRM insert (embedded in the panel) and Tie rod.

The pod is fixed to the satellite side wall and the insert (or bushing) in fixed to the DPR panel.

The tie-rod is preloaded in order to avoid any gapping and slippage caused by the launch environment.