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Space Systems > TT & C, RF and OBDH > Flashcards

TT & C, RF and OBDH Flashcards

1
Q

What does TT&C stand for in spacecraft operations?

A

Tracking, Telemetry, and Command.

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2
Q

What is the purpose of a TT&C system?

A

To maintain communication between the spacecraft and the ground station for control and data exchange.

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3
Q

What are the two main segments in a TT&C system?

A

The space segment and the ground segment.

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4
Q

What type of antennas are used in the ground segment of TT&C?

A

High-gain antennas like dish and Yagi antennas.

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5
Q

What type of antennas are used on spacecraft for TT&C?

A

Low-gain omni-directional antennas.

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6
Q

Why is forward error correction (FEC) important in TT&C systems?

A

It ensures link reliability by correcting errors in data transmission.

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7
Q

Name the frequency bands commonly used for TT&C.

A

VHF, UHF, L-Band, S-Band, and X-Band.

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8
Q

What is the role of packetized TT&C?

A

To provide robust and secure communication links, and to interface with on-board data handling systems.

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9
Q

What organization sets standards for packetized TT&C systems?

A

The Consultative Committee for Space Data Systems (CCSDS).

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10
Q

What are the basic principles of spacecraft tracking and ranging?

A

Using techniques like Doppler tracking, tone ranging, and GPS to determine the spacecraft’s position and movement.

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11
Q

What is G/T, and why is it important?

A

G/T is the gain-to-noise-temperature ratio, which measures the performance of a receiving system.

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12
Q

What is the simple link budget formula?

A

C/N=EIRP − [LD​ + La + Le​] + (G/T) − K − 10log(B).

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13
Q

What is the “sinc(x)” function, and how is it related to antennas?

A

It represents the diffraction pattern of an antenna, showing main lobes and side lobes.

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14
Q

Define system noise temperature (Ts).

A

A measure of the noise generated by the receiver system and environment, expressed in Kelvin.

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15
Q

What is the role of a low-noise amplifier (LNA) in RF systems?

A

To amplify weak signals while minimizing additional noise.

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16
Q

What is

E<sub?b</sub> / N<sub?0</sub>

and why is it important?

A

It is the energy-per-bit-to-noise-density ratio, which measures the quality of a digital communication link.

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17
Q

How does ionospheric Faraday rotation affect RF links?

A

It rotates the polarization vector of signals, especially at VHF and UHF frequencies.

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18
Q

How can circular polarization mitigate Faraday rotation effects?

A

It minimizes polarization mismatch caused by ionospheric rotation.

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19
Q

Name two common OBDH network topologies.

A

Star topology and bus topology.

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20
Q

What are the advantages of a star topology in OBDH?

A

High reliability and centralized control.

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21
Q

What are the disadvantages of a bus topology in OBDH?

A

Vulnerability to single-point failures.

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22
Q

What is the role of CTUs and RTUs in the ESA OBDH bus?

A

CTUs (Central Terminal Units) manage data exchange, and RTUs (Remote Terminal Units) interface with subsystems.

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23
Q

What are Single Event Effects (SEEs), and why are they a concern in OBDH systems?

A

SEEs are disruptions caused by cosmic rays or radiation, which can lead to errors or damage in electronics.

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24
Q

What is EDAC coding, and how does it help mitigate SEEs?

A

Error Detection and Correction coding detects and corrects bit or byte errors in data storage and transmission.

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25
Q

What is memory washing in OBDH systems?

A

Periodically reading, correcting, and rewriting memory contents to prevent error accumulation.

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26
Q

How do Hamming codes and Reed-Solomon codes differ?

A

Hamming codes correct bit-level errors, while Reed-Solomon codes correct byte-level errors.

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27
Q

What is Triple Modular Redundancy (TMR), and how does it enhance reliability?

A

TMR uses three parallel systems and voting logic to detect and correct errors.

28
Q

Why is software engineering critical for OBDH systems?

A

To ensure reliability, predictability, and real-time performance.

29
Q

Name two programming languages commonly used for spacecraft software.

A

Ada and C/C++.

30
Q

Why is Ada preferred for critical spacecraft applications?

A

It offers strong typing, modularity, and built-in exception handling for reliability.

31
Q

What are the benefits of using FPGAs in OBDH systems?

A

High performance, reconfigurability, and integration of multiple functions.

32
Q

How does radiation affect COTS components in OBDH?

A

Radiation can cause errors or damage, requiring mitigation techniques like shielding and error correction.

33
Q

What is the difference between rad-hard and rad-tolerant components?

A

Rad-hard components are designed to withstand high radiation levels, while rad-tolerant components are less resistant but still functional in moderate radiation environments.

34
Q

Why is systematic software development important for OBDH systems?

A

To meet mission schedules, ensure quality, and provide fault detection and recovery.

35
Q

What is the role of intellectual property (IP) cores in FPGA-based OBDH systems?

A

IP cores provide reusable building blocks for implementing processors and other functionalities.

36
Q

How does shielding mitigate radiation effects in OBDH?

A

It reduces the radiation dose absorbed by sensitive components.

37
Q

What is the main trade-off of using Commercial Off-The-Shelf (COTS) components in space?

A

COTS components are cost-effective and high-performance but require additional radiation-hardening measures.

38
Q

What are the three topology and three access protocols to consider for an OBDH network?

A

Topology:
- Single point failures
- Reconfigurability
- Complexity

Access protocols:
- Latency
- Flexibility
- Predicitability

39
Q

What are two disadvantages of a centralized topology such as the mesh or star?

A
  • Addition of new modules is not easy
  • Wiring harness becomes large
40
Q

what are the three common buses/networks mentioned?

A
  • MIL_STD-1553B
  • OBDH data bus (ESA standard)
  • I2C data and control bus (inter-integrated circuit)
41
Q

What are the three standards mentioned?

A
  • IEEE1394/Firewire
  • CAN (controlled area network)
  • Spacewire
42
Q

For the OBDH bus what are the 5 roles of the CTU and the three roles of the RTU?

A

CTU:
- Command handling
- Data gathering
- housekeeping
- clock reference generation
- Dedicated high speed interface

RTU:
- acquisition and multiplexing telemetry (A/D)
- remote distribution of commands
- event datation

43
Q

What are the 5 primary radiation effects?
What are their effects?

A

TID - accumulated radiation damage leading to leakage currents and eventual circuit failure
SEU - Particle hit causes ‘bit flip’ soft error
SEL - Can cause power to ground short and permanent damage
SET - transients resulting in overstressed components
SEFI - Unexpected malfunction usually requiring a power cycle

44
Q

Why is aluminium a good choice of material for radiation shields

A

Because it has a low Z (proton) number. It must be backed up with a high Z material such as Tantalum (Ta) or Tungsten (W)

45
Q

semiconductor processes are modified to make components rad-hardened. What are the three main trade offs?

A
  • Power
  • Density
  • Speed
46
Q

Name one example of a SOS proccessing unit?

A

MIL STD 1750 processor architecture

47
Q

What are three advantages of SOS

A

SEU immune
SEL immune
rad-tolerant

48
Q

What are three disadvantages of SOS

A
  • Specialist technology, small market and expensive
  • Power hungry versus COTS
  • Low level of integration versus COTS
49
Q

What effects do SEU have on memory

A

corruption of stored data or variable

50
Q

What two techniques are used to protect memory from SEUs?

A

Triple module redundancy (TMR)
Error detection and correction (EDAC)

51
Q

Describe how TMR works to protect memory from SEUs?

A
  • Sequential circuit elements are implemented three times in parallel
  • They are compared by a ‘voting’ circuit
  • If two outputs are the same, but one is different it will be outvoted
52
Q

What are three disadvantages to TMR?

A
  • Requires three times as much circuitry (mass, volume and cost)
  • 200 % memory overhead
  • If an SEU occurs to two of the parallel circuits then the voting circuit wont be able to deduce the correct output.
53
Q

How is a typical triple voted controller usually implemented?

A

Using an FPGA

54
Q

What does the FPGA do when an error is identified by the voting circuit?

A

It captures the address with the error and asserts an interrupt so that the correct data can then be rewritten to that memory address

55
Q

What are advantages of TMR?

A
  • Most comprehensive EDAC
  • Uses simple logic operations to determine where the error is
  • fast, low propagation delay
56
Q

With EDAC codes, what is the main principle that allows it to make corrections?

A

Adds additional bits to data words

57
Q

What are the 4 ECC schemes and which one decodes fastest and which one the slowest?

A

Hamming
Cyclic
Parity
Reed-Solomen

Hamming decode speed: 187.8 MBytes/s

RS decoding speed: 24.41 MBytes/s

58
Q

Which ECC has the largest bit overhead and which the smallest?

A
  • Hamming and Cyclic have a bit overhead of 12.5 %
  • RS has a bit overhead of 3.125 %
59
Q

What main benefit do the error correcting codes yield in terms of mission capabilities?

A

Spacecraft can travel further and withstand higher radiation environments.

60
Q

What is meant by the numbers in ‘Reed-Solomen (255, 252)?

A
  • 2nd number refers to the number of bytes being read/written
  • 1st number is the sum of bytes being read and additional code bytes used for correction
61
Q

What are the consequences of memory scrubbing?

A

Regular read, correct and rewrite of memory needs to happen to prevent accumulation of errors

  • This results in adequate CPU overhead
  • EDAC + scrubbing only protects memory external to the CPU, not data currently being processed at the CPU
  • Disabling the cache can reduce SEU errors since CPU must fetch from the EDAC protected memory
62
Q

For state of the art FPGAs, what is the maximum TID and how many logic gates do they possess?

A

<= 300 krad

<= 6 million

63
Q

What are the effects of adding software to OBC?

A
  • Increase in complexity and cost
  • increases flexibility of the OBC
  • both increases and decreases risk
64
Q

What are the four software requirements?

A
  • Phased predictable development to meet mission schedule
  • verifiable high quality
  • need fault detection isolation and recovery (FDIR)
  • hard real-time performance (HRT)
65
Q

What is the name of the MIL-STD programming language?

A

ADA

66
Q

What two philosophies are practiced when developing software

A
  • Top down development
  • Object oriented development

Space Systems (17 decks)

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