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A look inside

Among the thermal control techniques for space applications the passive systems are for sure the most attractive ones. Passive systems show several advantages as no additional pumping systems, a simpler and lower maintenance, small size and a generally low cost.

One of these is the PHP (standing for Pulsating Heat Pipe), the principle “subject” of our experiment.
The PHP is a simple aluminum tube, folded in many turns and filled with a refrigerant fluid. The device is then closed end to end in a loop. The PHP needs to be strictly in contact with a heat sink, a paraffin wax.

A small critical diameter is required in order to obtain the desired pulsating flow regime. At ground conditions we have a critical diameter after which our device will not work. Instead In milli-gravity environment the critical diameter is bigger than that calculated on ground, so the performance of PHPs in that condition may increase. UPHOS intends to prove the increasing in performance of a PHP under milli-g condition and validate a device that could be widely used in the space field.

This experiment is made by a consistent number of parts, so we are working to join the hardware and the software, in order to have all the information we need to prove the efficiency of this system.

Foto U-Phos-003


The experiment will be successful if significant data are collected.
Although this task is mostly performed by the electronic subsystem, mechanics has the important role of protecting all the experiment components (the PHP, batteries and electronics) against damages due to launch vibrations or environmental conditions.


Following this requirements, the PHP system is fitted into an airtight box to prevent any leakage and the electronic board for data handling is contained in a metallic box, named “data handling box”, fixed on the bulkhead, as close as possible to the experiment box.

Mechanics has also to project the disposition of every single component inside the rocket module, considering the critical point of each part (electronics overheating, connectors and cables arrangement, …)

Both the PHP and the paraffin are contained in an aluminum box, which we call “experiment box”. The box is airtight to avoid any leakage of paraffin, which could be dangerous for other experiments in the rocket.

Moreover the PHP needs to be heated. This can be achieved via ceramic heaters in contact with the turns of the PHP. The heaters are powered using batteries, which are collected in a pack bolted on the bulkhead.

The bulkhead is the only interface between the experiment and the rocket module. It is a metallic disk fixed on the module using some brackets.

Like the electronics subsystem, the power control unit must be protected by fixing it inside a box, named “power management box”. The box is similar to the data handling box, but this time it is set near the battery pack, in order to better interface these two elements.



Electronics is necessary to control all the experiment, to provide power to heat up the PHP, to acquire data and sending them to Ground during the flight.

The hardware platform is the TS-7200, a board that offer an ARM A9 processor and several Input/output interfaces.

In fact, obviously, all the electronic components of the experiment are connected to the interfaces of this board exchanging information with it.


The collecting main unit is a set of optical fibers that works as temperature sensor (temperature data are essential for a good characterization of the PHP).

In addition, it collects data on the pressure, the power delivered to the PHP and the accelerations (3-axis) to which the PHP will be subject.

How electronics is structured?

First of all, a commercial board (TS-7200), called  MCU (Main Control Unit), is present to manage the experiment timeline (so, switching on and off the experiment in appropriate instants), to control all the other boards and to send data to Ground.

To do that, it interacts with Rexus module by a dedicated interface board.

The Rexus Module is embedded on the rocket and shared by all the experiment, and it is useful to send the signals of start and stop of the experiment; it also provides a RF interface for communication with Ground.

Moreover, the MCU perform the data acquisition, measuring itself the pressure of the PHP fluid and interacting with an innovative board (the SBI, Single Board FBG Interrogator), to measure the temperature in various points of the PHP.

To perform this measurements, SBI stimulates some FBG (Fiber Bragg Grating) sensors which are embedded in two optical fibers, properly twisted around the PHP, assuring high immunity to all the disturbs, an easy integration and good performances as regard as the measurement of thermal transient.

Finally, we use a dedicated board, the PDU (Power Distribution Unit), to provide power to all the boards and to the experiment heaters.

Electronics is entirely supplied by the power provided by the Rexus Module; instead, the power for heating and preheating is provided by an appropriate battery pack.



The software must overcome some constraints: first, it must be reliable! In fact, we have only one chance to hit the target! Secondly the software must run on board (and not on a “computer”) so it must be designed in order to operate in a limited resource environment.

The software is split in two main modules: the Ground Software and the On-Board Software.


Ground software

It will run on a computer in the control room made available by ESA. The purpose of this software module is to receive the data sent on earth from our experiment. This software implements functions to check the consistency of the data and discards corrupted ones, stores the correct data packets and provides a graphical environment for the real time monitoring of the experiment.

On-board software

It is managed by the TS-7200 board, that offer an ARM A9 processor and several Input/output interfaces in order to control all the electronic components of the experiment.
This board receive signals from the collecting main unit about temperature, pressure, power delivered to the PHP and acceleration (3-axis) to which the PHP is subjected.
These signals, once collected, are sent on Ground via the Rexus RF communication module.