Colorado Space Grant1 DINO Safety Review DINO Communications Team: Hosam Ghaith Mike Li Zach Allen

Colorado Space Grant 2 Bonding and Grounding Satellite Structure must be bonded to the ICU chassis ground to prevent charge accumulation Resistance between any payload point and the Orbiter must be less than 1 Ohm. Bonding can be achieved by metal-to-metal contact, or by conductive coating and surface treatments.

Colorado Space Grant 3 Example Calculate the total resistance between points A and B. Worst case scenario: the two Ohm resistors are not grounded, and total resistance is Ohms (less than 1).

Colorado Space Grant 4 Different Bonding Methods Alodine or chemical conversion: helps to prevent corrosion and, thus, strengthens bonds. Bare metal to metal contact guarantees conductivity Bonding strap: conductive and also secure bonding Anodizing both parts is NOT a good bonding method: results in insulation, not conductivity.

Colorado Space Grant 5 Grounding Core ICD document and states that “the Orbiter D.C. power return from a Cargo element shall be … D.C. isolated from structure ground in the Cargo element by a minimum of 1 Mega Ohm.”

Colorado Space Grant 6 Example The following scheme does not satisfy the requirement: need an extra 1 MΩ resistor between ground and negative side of battery

Colorado Space Grant 7 SIP The resistance between any point on the Nanosat and the satellite interface panel (SIP) must always be less than 2.5 milli Ohms. Why? To prevent excessive heating or thermal dissipation To prevent static build-up (which may damage some parts).

Colorado Space Grant 8 Fault-Tolerance (Fixed Antenna) Electrical inhibits (interruption feature) are not necessary  No mechanical/pyrotechnic functions  Fuses?

Colorado Space Grant 9 Fault-Tolerance (Deployable Antenna) Accidental deployment prevention  Premature deployment could affect Orbiter operation (Catastrophic Hazard) 1  Minimum of 3 independent inhibits (2 fault tolerant) 2  Need one independently controlled inhibit in the ground return path – “SPECIFIC CATASTROPHIC HAZARDOUS FUNCTIONS: Planned Deployment/Extension Functions ” – “must be controlled by a minimum of three independent inhibits” – “the ground return for the function circuit must be interrupted by one of the independent inhibits” Section numbers refer to NSTS B

Colorado Space Grant 10 Power Concerns COMM system meets Unpowered Bus Exception 1  COMM might have catastrophic hazards  System is de-energized prior to payload deployment c(3): Unpowered Bus Exception Section numbers refer to NSTS B Satellite System Catastrophic Hazard Battery Satellite Subsystem Critical Hazard Relay 1 Relay 2 Relay 3

Colorado Space Grant 11 Question 14: Nanosat Power System Solar array Inhibit 1Inhibit 2Inhibit 3 Inhibit 4 RF System Deployable Antenna

Colorado Space Grant 12 Safety Exam, Question 14 Two extra independent inhibits needed:  1 inhibit between the solar panel positive output and battery.  1 inhibit in solar array ground return path, between solar array and battery. Inhibits do not need to be monitored for RF system because it is not more that 6 dB over ICD limits. Inhibits need to be monitored since only 3 between battery and antenna mechanism

Colorado Space Grant 13 Transmissions Two types of transmissions  Cargo Bay Doors Closed Max. intentional radiated field of 0.5 V/m 1  Cargo Bay Doors Open Payload to orbiter limit of 4 V/m 2 1. ICD section ICD diagram

Colorado Space Grant 14 Diagram : Payload to Orbiter Field Limit

Colorado Space Grant 15 RF Power Levels NSTS B section 202.5d:  “For payload transmitters in the payload bay or crew cabin, three independent inhibits are required whenever the intentional radiation would exceed the ICD limits and is assessed as hazardous.” NSTS B section 202.5e:  “RF transmitter inhibits do not require monitoring unless the radiation levels would exceed the ICD allowable levels by more than 6 dB in which case two of three inhibits must be monitored. “

Colorado Space Grant 16 Potential Interference with STS Communications 919 Communication Channels  Channel 1 through 801 (STDN) Receive Frequencies 2200 MHz to 2300 MHz  Channel 850 through 882 (NASA DSN Deep Space Network) Receive Frequencies MHz to MHz

Colorado Space Grant 17 Potential Interference with STS Communications Channel 900 through 919 (DOD/SGLS)  MHz to MHz Closest Potential frequency: Tip Mass Wireless Ethernet Transmitter  2412 MHz to 2462 MHz DSSS (Direct Sequence Spread Spectrum) Close to 6 th harmonic of 400 MHz Ham Band

Colorado Space Grant 18 Conclusion Communication Subsystem will probably have at least one catastrophic hazard  Deployable Antenna  Transmit Power? Will not know if hazard is critical or catastrophic until Communication System is designed further