Development of a Wireless Applicationfor Remote Control of Space Test Facilities

S. Scaranzin, E. Bonelli, F. Saito, F. ScortecciAEROSPAZIO Tecnologie s.r.l.Rapolano Terme, Siena, Italyaerospazio@aerospazio.com

Abstract-A wireless application based on a PDA and a mobilephone has been developed at AEROSPAZIO Tecnologie to allowremote control of space test facilities and increase the staffmobility. The application developed in house has been comparedwith available software over different networks. The testactivities and results are described.

Wireless; space test facilities, remote control; PDA; mobility.

1. INTRODUCTIONModem times are certainly the age of mobile

communication. Having access to the office or to the Internetfrom everywhere in the world (home, airport, hotel, etc.)facilitates mobile personnel allowing the companies to savetime and money.

In this regard, a wireless communication system has beendeveloped at AEROSPAZIO Tecnologie to allow remotecontrol of test facilities, including a Large Vacuum TestFacility (LVTF) used to perform tests on satellite ElectricPropulsion systems and space simulation.

Presently, the LVTF (Fig. 1) is used for the endurance testof the RIT-22 thruster [1, 2] developed by EADS SpaceTransportation GmbH and proposed for ESA scientificmissions (like BepiColombo to Mercury foreseen for the year2012) as well as for commercial satellites (like the newEuropean platform Alphabus).

Figure 1. The Large Vacuum Test Facility.

To date more than 2500 h of thruster endurance test havebeen performed in few months of continuous operations.

The flight qualification of Electric Propulsion systems oftenrequires several years of uninterrupted lifetime test. In thisregard, the test facilities must guarantee all the time reliablecontinuous operations in any environmental condition.

Therefore, for the value of the test activities and thecriticality of the processes involved in the experiments aspecific facility monitoring and control system is required. Forthese reasons, an advanced wireless remote control applicationwas developed at AEROSPAZIO so as to allow operators toperform a reliable monitoring of the state of the facilities and ofthe test article and to react readily from everywhere in case analarm is notified.

II. THE CONTROL SYSTEMThe LVTF consists of a 120 m3 stainless steel vacuum

chamber equipped with several stages of pumping system,vacuum gauges, test equipment and diagnostics [3].

A test article, for example an electric thruster, is placedinside the chamber and switched on for testing, when the rightpressure is achieved.

A Data Acquisition System (DAS) and a FacilityManagement System (FMS) have been developed to automateLVTF operations and control the test behaviour fromcomputer.

A. The Data Acquisition SystemAll the signals coming from sensors in the test are managed

by the DAS.

The DAS hardware is based on a PC architecture consistingof a 12 bit National InstrumentsS1 DAQ card multiplexed andconditioned by an extensible SCXITM system. To date a 32differential channels conditioning module is installed with 200kS/s max sampling rate, selectable gain and low-pass filter.

The DAS software, developed by AEROSPAZIO incollaboration with the Dept. of Information Eng. of theUniversity of Siena [4], allows the user to configure the DAShardware and stores the data converted in the appropriate unitsof measurement.

Product and company names listed are trademarks or trade names oftheir respective companies.

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B. The Facility Management SystemThe FMS has been developed by AEROSPAZIO [5] in

order to operate and control the test facility from computer.The FMS software, running on a PC located in the testlaboratory (Facility Control PC - FCPC), manages severaldigital I/O cards and control electronics in order to:

* monitor the state of the pumping system

* allow the operation of valves and pumps* execute predefined procedures to reach different

vacuum levels

* check and show data acquired by the DAS

* show the test article operations, managing webcams* detect major equipment failures and automatically

react starting safety operations and sending a specificvoice message to a list of phone numbers

* store all the events in a log file.In order to operate the facility continuously for long

duration tests (up to several years without interruption forlifetime tests) a number of automatic procedures have beenimplemented for normal and safety operations.

However, although the FMS sends a voice message tonotify an equipment failure, the wamed person can check theLVTF conditions and eventually restart the test only fromFCPC.

Therefore, some remote control systems have beeninvestigated, in order to allow staff mobility in the companyduring working hours and everywhere outside the companyduring holidays.

The requirements of the systems dealt on are: safety,confidence of data exchanged, low cost and an appropriatetransfer rate.

III. THE REMOTE CONTROL SYSTEM FROM PERSONALCOMPUTERS

The first goal is to allow remote control from computers inthe AEROSPAZIO offices and from a PC equipped with aconnection to the telephone network through duplex cable as,for example, in the personnel houses.

A. Remote Control on LANThe facility remote control from AEROSPAZIO computers

was attained using RealVNCTm by RealVNC Ltd (VNC) overthe AEROSPAZIO Local Area Network (A-LAN).

VNC is an open-source software, which allows remotedesktop control of one computer (the server) using a simpleprogram (the viewer) running on another computer connectedto the server by TCP/IP protocol.

Running the VNC server component on the FCPC and theviewer component on computers in offices, A-LAN satisfiedall the requirements listed before, using the standard IEEE802.3 protocol with a speed of 100 Mbps.

B. Remote Controlfrom a PC Equipped with a Connectionto the Telephone Network through Duplex CableThe next purpose consisted in providing remote control of

the FCPC located inside AEROSPAZIO from anothercomputer equipped with a connection to the telephone networkthrough duplex cable.

As first step, a commercial software (Laplinkg Gold)allowing point to point modem connections was installed onboth computers. After the connection is established, Laplinkauthorizes FCPC desktop control by the host PC.

Unfortunately, desktop control of a remote PC requiresmany data to be exchanged, so the modem transfer rate (56Kbps) reduces the monitor refresh frequency. Moreover, thecall cost could increase too much depending on computersdistance and call duration.

Then, a Virtual Private Network (VPN) was developedbetween FCPC and other computers outside the company usedfor remote control. The advantages of using VPN are thefollowing:

* it is possible to access the A-LAN over the Internet atthe cost of the Internet Service Provider (ISP)

* data exchanged are encrypted and so hidden fromInternet users. However, the data can be accessedsecurely by authorized users through the VPN

* VPN supports the most common network protocols(TCP/IP, IPX and NetBEUI). Therefore, it is possibleto remotely run any application using these networkprotocols.

There is no need for the host PC to have direct access to theInternet in order to create a VPN connection.

In fact, there are two ways to establish a VPN connectionfrom a host PC: by dialing an ISP, or by connecting directly tothe Internet.

In the first case, considering the AEROSPAZIO situation,the VPN connection first dials to an ISP, then another call isrouted to the remote access server that establishes thecommunication protocol tunnel (PPTP).

In the second case, the user needs a computer where IPconnectivity is established during the operating systemstarting-up. For example, using a PC equipped with an ADSLservice or a PC member of a local area network linked to theInternet, the user creates a VPN tunnel dialing directly the IPaddress of the remote access server.

Anyway, after authentication, the user can access FCPC inthe A-LAN, and use VNC software to remote controlAEROSPAZIO facility.

IV. THE REMOTE CONTROL SYSTEM FROM PDAIn order to improve staff mobility outside the company

where a connection to the telephone network through duplexcable is not available, a notebook or, better, a less bulky PDA,equipped with a wireless Internet connection can be used toremote control the AEROSPAZIO facility.

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An Internet connection can be established by a Wi-Fi cardif the PC is near to an access point (for example in hotels,airports, ) or by a mobile phone via GSM/GPRS network. Inthe first case there are no expense, but access points are notavailable everywhere. On the other hand, in the second case theconnection costs can be very high especially using a remotedesktop control application (for example VNC for PDA) due tothe large amount of data exchanged. In fact, many telephonecompany tariffs depend on the amount of data exchanged andnot on the call duration.

Therefore, AEROSPAZIO decided to develop a WirelessRemote Control System (WRCS) to fully control LVTF facilityfrom everywhere using a PDA and a mobile phone minimizingconnection costs.

A. The Wireless Remote Control System ArchitectureThe WRCS architecture developed by AEROSPAZIO

includes the following devices:

* a desktop PC (FCPC) equipped with an AthlonTm 2600CPU and Microsoftg Windowsg 2000 Professionaloperating system, IEEE 802.1 Ig connection at 56Mbps, Ethernet card at 100 Mbps, digital and analogicI/O for AEROSPAZIO facility control

* ADSL Switch/Router NetGear® with static IP addressconnected to ADSL line at 1.6 Mbps for Internetconnection and equipped with IEEE 802.11g+connection at 108 Mbps

* Pocket PC ASUS® A730W equipped with MicrosoftgWindows® CE 2003 operating system, IEEE 802.1 lbconnection at 11 Mbps and Bluetoothg integrated

* GSM/GPRS mobile phone Motorola® A835 withBluetooth connection integrated.

A scheme of the system layout is shown in Fig. 2.

The PDA can connect directly to the AEROSPAZIO routerthrough the wireless LAN if it is near to the device. Otherwise,if the user is outside the company, the PDA can link theAEROSPAZIO router following the subsequent steps:

* the PDA links the mobile phone using Bluetooth

* the mobile phone works as a modem connecting thePDA to the Internet through GSM or GPRS network

* PDA creates a VPN tunnel up to the AEROSPAZIOrouter.

The router is wireless connected with the FCPC, whichcontrols the facility.

B. The Wireless Remote Control System SoftwareThe WRCS software is a Client-Server application

implemented to fully control LVTF equipment using a PDA.

The client component of the WRCS software, developedusing Microsoft® eMbedded Visual Basic 3.0®, runs on thePDA. It can create a VPN or wireless LAN connection withFCPC (Fig. 3). Then, the user can send commands, ask forinformation on the plant and see them on the control windows.Each window shows data (state and measurements) of relateddevices and sensors. For example, the control windowdescribing first two stages of the pumping system is shown inFig. 4.

The server component, implemented using Microsoft®Visual Basic 6.0, runs on FCPC embedded in the FMSsoftware. It formats and sends to the client the requiredinformation, evaluates commands forwarded by the user and ifpossible executes them sending back the updated state of theplant; otherwise an error message is generated.

After the connection is established, the two componentscommunicate using Ethernet packets.

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Figure 2. The WRCS architecture. Figure 3. Log-In window of WRCS software.

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Figure 4. Pumps & Valves window ofWRCS software.

Every packet contains a coded message consisting of fewASCII characters in the form shown in Fig. 5.

The software recognizes the part of the Ethernet packetuseful to control the LVTF, because the Start TransmissionDelimiter and the End Transmission Delimiter mark theboundaries of the message body. If one of the delimiters is notreceived or if the message body contains invalid data, an erroris caused.

The body of the message is different depending on thetransmission direction. If the message comes from the PDA,the body can contain a string to request readings from sensorsor to change the state of a device (a command). Examples ofcommands are: avl_on to open the angle valve 1, rot on toswitch on the rotary pump, tmp autostart to begin theautomatic procedure that waits the correct conditions to run upthe turbomolecolar pump, etc.

If the message comes from the FCPC, the body containstwo section: the first, consisting of two ASCII characters,identifies the type of message, the second contains a codedstring that can represent:

* the state of the facility (numeric string): each numeralcorresponds to a specific device of the facility andrepresents its state. For example, if the fifth numeral ofthe string is 1, the gate valve is open

* an error message (alphanumeric string): for example, ifthe user send an unknown command, the serveranswers command_error

Start Body ofmessage in EndTransmission Transmission. ASCII charactsiterDelimiterehl

* readings from sensors (alphanumeric string): eachreading is represented in scientific format with threenumerals for the mantissa and two for the exponentand is separated from the others by an underscore. Forexample, if the second number is 2. 03E-4, the pressuregauge I is measuring 2.03 x 10-4 mbar inside thevacuum chamber. If the sensor is not working, thestring Fault replaces the reading.

Every coded message is few bytes long (for example about30 bytes describe the state of the facility), so the connection'scost is minimized and refresh ofPDA screen is very fast over alow bandwidth line too.

Moreover, the WRCS software exchanges data only ondemand to reduce further the traffic over the network.However, the LVTF safety is not compromised, because FMSupdates sensor readings and devices state at regular intervals(typically every second) and, in case of equipment failure,executes safety procedures.

V. COMPARISON BETWEEN REMOTE CONTROL SYSTEMSConsidering that the main aim of this work is to allow

AEROSPAZIO staff to remote control the facilities with theminimum mobility constraints, using a PDA and a mobilephone becomes necessary. Therefore, it is interesting tocompare the performance (cost and speed) of differentnetworks and software.

In particular, some tests have been performed using VNCand WRCS software to control FCPC through GSM and GPRSnetworks.

Costs of the tests have been calculated using tariffs of theItalian society Tre Mobile Video Company. Note that whileGPRS costs depend on the amount of data exchanged, GSMexpense increases with the call duration.

The control session, considered as benchmark forcomparison, comprehends the following operations:

* connection to FCPC

* check of measurements and devices state

* sending of a command

* check of measurements and devices state.

Unfortunately, remote control with VNC on GSM does notsatisfied the AEROSPAZIO speed requirements due to thelarge amount of data exchanged on the low bandwidth network(9.6 Kbps).

On the contrary, a VNC/GPRS control is satisfying,because the transfer rate (115 Kbps) is more than ten timesfaster than GSM. Therefore, the desktop refresh is fluid and thecall duration is about 6 min. However, the GPRS coverage isless widespread than GSM.

Using WRCS software, the amount of data exchanged toachieve operations described before is much smaller, so it canbe used both over GSM and GPRS networks. In both cases, theconsidered control session takes about 5 min. In fact, even if

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Figure 5. Scheme of the coded message used by WRCS software.

GPRS is faster than GSM, most time elapses withoutexchanging data while the user checks the facility state.

Tab. 1 summarizes results from benchmark tests. Inparticular, the cost ratio between VNC/GPRS andWRCS/GPRS in the considered example is about 2:1.However, if the user need to perform many operations andchecks, the ratio between data exchanged increases rapidly, andso does the cost relation.

TABLE I. COMPARiSON BEETWEEN REMOTE CONTROL SYSTEMSUSING PDA AND MOBILE PHONE

Control T Speeda Duration Data cost"Sw Network (Kbps) (mm:ss) (KB) (OVNC GPRS 115 5:23 335 0.6 + 1.34

WRCS GSM 9.6 5:35 - 0.15 + 0.9

WRCS GPRS 115 5:02 15 0.6 + 0.12a. It is referred to nominal value.

b. Calling unit + calling rate

VI. FUTURE IMPROVEMENTSVoice and video data from the LVTF and the test article

will be included in the WRCS software in order to improve thesense of presence in the laboratory. Further tests will beperformed to check the system performance on the UMTSnetwork whose deployment is presently ongoing in our area.

REFERENCES[1] H. J. Leiter, R. Killinger, H. Bassner, J. Mueller, and R. Kukies,

"Development of the radio frequency ion thruster RIT XT," IEPC-01-104, Proc. of the 27' International Electric Propulsion Conference,Pasadena, CA, October 2001.

[2] H. Leiter et al., "A survey of the 'New grid systems for ion engines'technology project," Proc. of the 4th International Spacecraft PropulsionConference, Chia Laguna, Italy, June 2004.

[3] F. Scortecci, E. Bonelli, B. Michelozzi, F. Saito, S. Scaranzin, and A.Turco, "Performance of a large vacuum test facility for spacecraftpropulsion testing," Proc. of the 4th International Spacecraft PropulsionConference, Chia Laguna, Italy, June 2004.

[4] E. Bonelli, Sistema di acquisizione dati per prove in camera a vuoto dipropulsori elettrici satellitari. Master Thesis, University of Siena, June2003.

[5] F. A. Saito, Gestione e controllo remoto di una camera a vuoto. DegreeThesis, University of Siena, June 2004.

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