Risk Analysis

Potential risks have been identified and classified as follows.

Technology Development Risks

V/W-Band Transceiver Technology:

Space qualified equipment for Ka-band and below can be developed by and readily procured from numerous commercial vendors without risk.  There are extremely few commercial, government, and military applications in the V- and W-bands, however.  The V- and W-band front-end components will most likely need to be custom designed and space-qualified for this project, which will significantly complicate the beacon and receiver development.  During Phase 1, we will explore three main technology options for the beacon/transceiver chains:

• Discrete waveguided block based solutions (low risk, low integration, high weight/power, relatively quick development)
• Multi-chip MMIC-based solutions (medium risk, improved integration, greatly reduced weight/power, slower development)
• Integrated SiGe BiCMOS transceivers + higher performance LNA and PA (highest risk, maximum integration, least size/weight/power, slowest development)

InP LNAs: 

The InP LNAs proposed for use in the receivers are not commonly used outside of the remote sensing and radio astronomy communities and will need to be custom developed.  If the final trade studies indicate that these LNAs should be operated cryogenically in the Earth station transponder experiment receiver, the cryogenic performance of these LNAs will need to be thoroughly characterized.  If the gain and matching shift greatly, new cryogenically-optimized LNAs may need to be designed.  Space qualification should not be particularly difficult for these LNAs since InP technology is mature and is commonly used in sensitive receivers in space.

Earth Station W-band Transmitter Amplifier:

Due to the extreme path loss at W-band from Earth to a satellite in GEO, we propose using a klystron to achieve a high uplink EIRP and to maintain a high signal to noise ratio.  Klystrons are extremely expensive and are not commonly used (or required) in communications applications.  We will explore klystron purchasing/development options along with the possibility of using currently existing klystrons.  If necessary, we may move the Earth station locations if that will allow us to relatively cheaply utilize existing klystrons.

Experimental Risks

Degradation or loss of communication link:

Degradation or loss of communication link may occur on the transmission and/or receiver system. Hardware failure in the RF subsystem is a source of concern as it would cause the pre-mature termination of the project. However, the use of balanced amplifiers coupled with full reliability testing will largely mitigate this risk. This is a very low risk factor.

Power loss:

Partial failure of onboard power systems will result in termination of mission due to insufficient power for the communication subsystem. Power loss may reduce the available transmission power which will impair our ability to perform channel characterization in the V-band experiment and the onset of high error rates in the digital link for the W-band experiment. This is a very low risk factor.

Data loss and corruption:

The large amount of measurements and data from third party sources would require high frequency I/O access on the local storage solution. This usage pattern imposes heavy penalty on the lifespan of magnetic storage media and present potential risk on loss and/or corruption of data due to storage failure. This risk is easily mitigated through the implementation of a daily backup schedule to the offsite data processing centre. Furthermore, the central data processing centre is equipped with an highly intelligent storage solution which can sustain multiple storage node failures and supports data versioning and replication, making it extremely robust to data loss and corruption.

Radiation Risks

Damage Mechanisms:

The harsh radiation environment in space [1,2] imposes additional challenges on electronic circuit and system design [3].  There are two main types of radiation-induced effects on electronics – total ionizing dose (TID) damage and single event effects (SEE).  TID damage is caused by high-energy particles that pass through electronics and deposit charge.  This charge accumulates over a long period of time and degrades device and circuit performance.  This damage typically manifests itself at oxide-semiconductor boundaries.  In FETs, this results in increased threshold voltages and degraded performance.  In bipolars this damage primarily affects the emitter-base spacer oxide and manifests itself as leakage current at low bias.  This is a significant advantage for bipolar transistors in high-radiation environments – this leakage current typically only affects device performance far below the typical RF bias region, so RF performance of bipolars is typically barely affected up to multi-Mrad(Si) radiation doses.  SiGe HBTs in particular show excellent TID tolerance as fabricated [4], which would be a significant motivating factor for going with an integrated SiGe BiCMOS solution on the satellite.

SEE are short-term effects caused by individual high energy particles depositing large amounts of charge into electronics.  There are many types of SEE, some destructive and some non-destructive.  Some of the main SEE are as follows:

• Single Event Upsets (SEU): Change of state in a digital bit, leading to incorrect data.  This is a soft error.
• Single Event Transients (SET): Radiation-induced transient signals on sensitive analog circuitry which may change bias currents and disrupt the operation of subsequent analog circuits.  These are also soft errors.
• Single Event Latchup (SEL): Charge deposition causes parasitic bipolar transistors to be activated, which can result in shorting power to ground.  SEL can be destructive.
• Single Event Gate Rupture (SEGR): Breakdown in a FET’s gate oxide which destroys the device.

Radiation Hardening:

The critical hardware in our beacon and transponder will be contained in a shielded, thermally-stabilized enclosure to ensure stable operation.  This thickness of this enclosure will be adjusted based on a comprehensive radiation risk analysis to be conducted during Phase 1 so as to ensure reliable long-term performance.  Each of the potential technology scenarios outlined earlier on this page will be analyzed for TID and SEE susceptibility.  It may be cost-effective to select a higher-risk, lower size/weight technology solution which will allow for the use of more shielding for a given payload weight. A commercially-available radiation-hardened FPGA will be used to perform all on-board digital processing.  This low-risk solution will minimize the occurrence of SEE and ensure reliable digital operation (See Transponder Design for more information).

References:

[1] S. Bourdarie and M. Xapsos, “The Near-Earth Space Radiation Environment,” IEEE Transactions on Nuclear Science, vol.55, no.4, pp.1810-1832, Aug. 2008.

[2] B. R. Bhat, N. Upadhyaya, R. Kulkarni, “Total radiation dose at geostationary orbit,” IEEE Transactions on Nuclear Science, vol.52, no.2, pp. 530- 534, April 2005.

[3] E. G. Stassinopoulos, and J. P. Raymond, “The space radiation environment for electronics,” Proceedings of the IEEE , vol.76, no.11, pp.1423-1442, Nov 1988.

[4] J. D. Cressler, “On the Potential of SiGe HBTs for Extreme Environment Electronics,” Proceedings of the IEEE , vol.93, no.9, pp.1559-1582, Sept. 2005.