A.

TDP8 for Alphasat In-Orbit Validation

First flight opportunity raised under the frame of the TDP8 project, framed in the Alphasat mission, where DAS delivered a flight optical board with four optical transceivers for digital communications. The experiment allowed the demonstration of the performance of 4 optical links working @1Mbps and 4 optical links working @100Mbps.

Fig. 2.

Optical experiment boarded on TDP8 for Alphasat

As part of the in-orbit validation activities, the non space qualified components were submitted to a complete space assessment campaign with good results.

Fig. 3.

Constructional analysis of photonic component

Although the satellite suffered some delays, finally was launched in 2013. At this moment DAS is receiving telemetry from the experiment with some error burst detected. Since each channel has a different optical power margin DAS is investigating the cause for these errors and if they are produced by events in the FPGA or because disturbances in the transceivers.

Table 1.

Optical experiment on TDP8 @SAT, detected errors

The table shows the events when errors were detected and the number of them. SIOS_BER1:4 are 1Mbps channels and SIOS_BER5:8 are 100Mbps channels. Each channel has different optical power margin from 3.87dB up to 7.38dB. Since each number of detected errors is always a burst of ‘1’ (ex: 127=‘1111111’) followed by another set of ‘1’ for all remaining channels the most probably cause for this is a SEE in the FPGA that causes a set of bit upsets storage word before to be sent to the platform. Therefore no error bit occurred in the optical links.

B.

HERMOD for Proba-V In-Orbit Validation

The second flight opportunity, HERMOD, was in Proba-V satellite, where DAS and T&G Elektro developed a test bed to validate MTP connectors and multi-fibre cables. Thanks to the good results during TDP8 activity, T&G trusted DAS to design and manufacture an experiment that allowed both companies to demonstrate the feasibility of the technology for future space applications.

This flight opportunity consisted in single equipment with 4 optical channels SpW compatible working at 100Mbps and interconnected through four MTP connectors. Each optical channel was configured with different power margin between transmitter and receiver in order to check the complete losses (including MTP connector) in the channel.

Fig. 4.

Optical experiment boarded on Proba V

This experiment was executed within a very stringent schedule of 6 months. The Proba-V satellite was launched in April 2013. Collected data from the experiment telemetry allows to have more than one year of results producing representative BER information of the optical channels.

TABLE 2.

1 YEAR PROBA-V EXPERIMENT BER

No errors have been detected in any channel except for the channel_2, but since the error distribution is centered in each equipment switch on, it seems that the error is produced due to a bad start of the equipment. The start procedure was changed on flight, and no errors were detected beyond this change.

A.

AOC Design Development

The design of AOCs has been relied on the information and knowledge acquired in previous activities by DAS and Airbus DS. The selection of components followed a conservative approach using EEE qualified, if possible. Components that are not qualified were submitted to a verification test campaign to assess their behaviour under space environment.

MIL-STD-1553, CAN and SpW are protocols well known and used in intra-satellite communications [4]. The key points of the AOC design were to improve such points where optic fibre has strong advantages against copper, minimizing the impact on the equipment in terms of power consumption and signal integrity.

Necessary optical and electronics components to implement the electro-optical conversion are integrated inside the connector backshell. So, another key point was the reduced electrical connector used in SpW and CAN Bus. The uD-9 has very low profile and this fact constrained the mechanical design of the AOC in order to have the same size than the uD9 connector plus the backshell. AOC can be assembled almost in every kind of connector.

The AOC transceiver will perform the electro-optical and the opto-electronic conversion in order to be able to transmit optical signal through a fiber optical cable.

Fig. 5.

AOC transceiver block diagram

Current AOCs design considers that modules are externally power supply at 3.3V, but power supply could also be provided through a connector spare pin since current load of each transceiver is quite low, less than 100mA.

The figure below shows the block diagram for the SpaceWire DATA link, the STROBE link is identical. The internal architecture of bus transceivers is similar just adapting the drivers to be compliant with target protocol.

B.

Component assessment

Since photonic and some EEE parts used in the optical transceivers are non space qualified because of the lack of available parts for these technologies [5][6], a components assessment was needed to be performed. The obtained results along with the previous information from other activities, the viability of the use of the parts will be determined for future missions.

Previous data results from other activities were used to complement the GSTP components assessment:

The life test of 1000 hours @85°C was performed on 20 samples of each component type used in the AOC. No major degradation was observed during the life test and all components survived to the test.

Fig. 6.

Life test, output optical power of first set of 10 lasers

Also, a verification programme of the soldering process for the assembly of micro-D connector to the board inside the transceiver of the AOC was performed. Since in order to optimize the size of the optical transceiver an approach not supported by ECSS[7][8] was needed to be used. This verification programme produced successful results and the process was validated for this application.

Fig. 7.

uD9 soldering assement

C.

AOC bus issues

Both buses, CAN and MIL-STD-1553, presented similar technological barrier from an architecture point of view. Copper buses are easy to implement since each terminal connected to the bus can transmit the information bidirectional to all terminal but optic fiber has directionality and the protocol architecture from bus to ring but with lower mass cost than the copper architectures. The total mass of the bus will be decreased from a classical bus with copper wire. This change in the topology does not affect the communication among interfaces; each one will maintain perfectly the communication with BC and all RTs.

Fig. 8.

Bus AOC transceiver block diagram

During the test phase, some issues were detected in both buses. Mainly, these issues were produced during IDLE time of the bus, since the low frequency of the line affected the photodiode and TIA response, causing glitches and loss of information.

Fig. 9.

Bus AOC issues, sent data and received with loss of information

The investigations showed that to remove these issues the transceiver shall be redesigned increasing the complexity since a special treatment of IDLE and low frequencies shall be implemented in order to be compliant with the optronic devices.

Whereas system integrators have not shown a commercial interest for 1553 optical solution, optical CAN Bus is very attractive for them. Therefore, further investigations are being performed to overcome IDLE and management issues in optical CAN buses.

D.

SpaceWire AOC test campaign

Due to the issues found in optical buses, only SpW AOCs were manufactured and submitted to the test campaign. This test campaign was performed using representative values and profiles on all test in order to cover as much as typical application cases as possible for future flight missions.

Fig. 10.

SpW AOC

Test campaign at AOC level included the following tests [9][10]:

None of the tests comprised in the test campaign produced destructive or detectable degradation on the performances of the AOC.

Fig. 11.

Errors distribution at 200MeV, flux 1E8 p/cm2/s, fluence 1E11 p/cm2

For protons irradiation some errors were detected due to single events. This experimental data allowed inferring future behavior in flight mission extracting the expected BER figure. For a GEO mission (15 years) the expected BER will be from 3.6E-18 to 1.7E-16 and for a LEO mission (8 years) the expected BER will be from 5E-18 to 1E-15. Both values are much lower than the requirement for a SpW communication, 1E-12.

Radiation tests such as gamma and proton were performed upon the transceivers with and without the mechanical package in order to measure the different behavior of the AOC. No important effects were measured in both tests.

Fig. 12.

TID test, transceivers with and without mechanical package