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Space Systems > Mechanisms and Optical Systems > Flashcards

Mechanisms and Optical Systems Flashcards

1
Q

What is the inertia tensor, and why is it important?

A

The inertia tensor describes a body’s mass distribution and relates torque to angular momentum in rotational dynamics.

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2
Q

How does the gyroscope effect assist in spacecraft attitude control?

A

The gyroscope effect stabilizes spacecraft orientation by maintaining angular momentum.

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3
Q

Why do motors in spacecraft require a 100% stall torque margin?

A

To ensure they can overcome unexpected loads or friction during operation.

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4
Q

What are the six degrees of freedom of a free body?

A

Translation along X, Y, Z axes and rotation about X, Y, Z axes.

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5
Q

Why is kinematic constraint important in mechanisms?

A

It ensures precise positioning and minimizes unwanted motion.

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6
Q

What are the advantages of dry lubricants in space mechanisms?

A

No outgassing, reduced contamination, and suitable for vacuum environments.

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7
Q

What are the disadvantages of dry lubricants in space mechanisms?

A

Limited lifetime and lower load-bearing capacity compared to wet lubricants.

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8
Q

Why are momentum wheels hermetically sealed in low-pressure helium atmospheres?

A

To prevent oil drying out and minimize windage losses.

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9
Q

What are the advantages of pyrotechnics in space mechanisms?

A

High energy efficiency, rapid action, and reliability.

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10
Q

Name an alternative to pyrotechnics for one-shot mechanisms.

A

Shape-memory alloys, such as TiNi, which change shape when heated.

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11
Q

What are the three main classes of radiation effects in space electronics?

A

Total Ionizing Dose (TID), Displacement Damage (DD), and Single Event Effects (SEE).

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12
Q

What causes radiation effects in spacecraft electronics?

A

Galactic Cosmic Rays (GCRs), Van Allen Belt particles, and solar particle events.

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13
Q

How does TID affect MOS devices?

A

Causes threshold voltage shifts, leakage currents, and speed degradation.

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14
Q

What is Enhanced Low-Dose-Rate Sensitivity (ELDRS)?

A

Increased damage in some bipolar devices when exposed to low radiation doses.

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15
Q

How can TID effects be mitigated?

A

By using shielding, redundant systems, and turning devices off during solar events.

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16
Q

What is Single Event Burnout (SEB)?

A

A catastrophic failure in power transistors caused by ion-induced avalanche breakdown.

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17
Q

How can SEB be mitigated?

A

By operating power devices well below their rated breakdown voltage.

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18
Q

Why is shielding less effective against high-energy protons?

A

High-energy protons penetrate typical spacecraft materials and cause dose damage.

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19
Q

What is cold redundancy in radiation mitigation?

A

Keeping spare devices unpowered to reduce exposure to radiation damage.

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20
Q

Why are low-Z materials like aluminum used for outer spacecraft shields?

A

To reduce Bremsstrahlung radiation while still providing effective shielding.

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21
Q

Why are aluminum alloys commonly used in spacecraft?

A

Lightweight, machinable, corrosion-resistant, and thermally conductive.

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22
Q

What is the main drawback of magnesium alloys in space?

A

Susceptibility to corrosion.

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23
Q

Why do spacecraft metals require surface treatment?

A

To prevent corrosion and enhance conductivity or thermal control.

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24
Q

Name a disadvantage of using optical glass in space.

A

Its brittleness makes it vulnerable to launch vibrations and microcracks.

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25
Q

Why are carbon-fiber-reinforced plastics used in spacecraft structures?

A

High strength, low thermal expansion, and excellent dimensional stability.

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26
Q

What is the importance of low CTE materials in optical systems?

A

To minimize thermal expansion and maintain optical alignment in space.

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27
Q

Why are optical baffles critical in spacecraft?

A

To block stray light and improve imaging quality.

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28
Q

How is contamination controlled in optical systems?

A

Using clean rooms, laminar flow benches, and sealing optics with dust caps.

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29
Q

What type of polymer is unsuitable for space applications and why?

A

PVC; it outgasses and becomes brittle in vacuum conditions.

30
Q

Why are fused silica tiles used in spacecraft?

A

They serve as optical solar reflectors due to their low thermal expansion and high reflectivity.

31
Q

What are the wavelength ranges for UV, visible, and NIR radiation?

A

UV: 0.28–0.38 µm; Visible: 0.38–0.78 µm; NIR: 0.78–1.0 µm.

32
Q

How do lenses and mirrors bring light to focus?

A

Lenses refract light, while mirrors reflect it to converge rays at a focal point.

33
Q

What is the f-number of an optical system?

A

The ratio of focal length to aperture diameter.

34
Q

What is the Rayleigh diffraction limit?

A

It defines the smallest angular resolution that a system can achieve due to diffraction.

35
Q

How is a diffraction-limited system determined?

A

By comparing the diffraction limit to the detector’s pixel size and resolution.

36
Q

What is the main advantage of a whiskbroom scanner?

A

High resolution over a small area with few detectors.

37
Q

What is the main disadvantage of a push-broom scanner?

A

Requires precise detector alignment and calibration over a wide field.

38
Q

Why are doublets and triplets used in lenses?

A

To correct chromatic aberration by compensating for wavelength-dependent refractive indices.

39
Q

What materials are suitable for infrared lenses?

A

Germanium, silicon, and gallium arsenide.

40
Q

How does an interference filter work in a radiometer?

A

It selectively transmits wavelengths by constructive interference in a multi-layer dielectric coating.

41
Q

What are the two categories of spacecraft mechanisms based on usage?

A

Continuous-use mechanisms (e.g., antenna pointing systems, reaction wheels) and one-shot mechanisms (e.g., separation systems, solar array deployment).

42
Q

What are the main design challenges for spacecraft mechanisms?

A

Ensuring high precision, reliability, and longevity in the harsh environment of space, including temperature extremes and vacuum.

43
Q

Why is inertia an important consideration in space mechanisms?

A

In microgravity, mechanisms must overcome an object’s inertia to initiate or stop motion, as mass (not weight) governs the forces required.

44
Q

What is the significance of the moment of inertia in rotating bodies?

A

It quantifies a body’s resistance to rotational acceleration about an axis, determined by mass distribution relative to the axis.

45
Q

What is Newton’s second law for rotational motion?

A

T=Iα,

where T is torque,

I is the moment of inertia,

α is angular acceleration.

46
Q

How is angular momentum (H) of a rigid body expressed?

A

H=Iω,

where
ω is angular velocity,

I is the moment of inertia tensor.

47
Q

What are principal axes of inertia?

A

Axes where products of inertia are zero, simplifying calculations for symmetric bodies or systems.

48
Q

How do internal and external torques affect angular momentum?

A

Internal torques conserve total angular momentum; external torques can change its magnitude or direction.

49
Q

What causes the gyroscopic effect in spacecraft?

A

A spinning mass resists changes in its orientation due to the conservation of angular momentum.

50
Q

How is the gyroscopic effect used in attitude control?

A

Reaction and momentum wheels exploit this effect to stabilize and adjust a spacecraft’s orientation.

51
Q

What is precession in a gyroscopic system?

A

The slow change in orientation of the spin axis due to a torque applied perpendicular to the axis of rotation.

52
Q

What is the principle of kinematic constraint?

A

A rigid body requires six independent constraints to fix its position and eliminate all degrees of freedom.

53
Q

What is overconstraint in kinematic systems?

A

When redundant constraints introduce uncertainty or distortions, leading to reduced precision.

54
Q

How does the Kelvin clamp ensure kinematic precision?

A

It uses three spheres contacting three V-grooves at 120° intervals to achieve six independent constraints.

55
Q

Why are ball bearings preloaded in spacecraft applications?

A

To prevent rattling during launch and ensure smooth operation under dynamic loads.

56
Q

What are the advantages of dry lubricants like MoS₂ in space?

A

They perform well in vacuum, resist outgassing, and reduce contamination risks.

57
Q

Why are wet lubricants sometimes preferred for high-speed systems?

A

They reduce wear and provide better heat dissipation, though they require careful containment to avoid migration.

58
Q

What distinguishes brushless DC motors from brushed motors?

A

Brushless motors have higher reliability and longevity as they lack brushes that wear out, but they require more complex electronics.

59
Q

Why are stepper motors ideal for precision applications in space?

A

They move in discrete steps, enabling precise angular positioning without feedback control.

60
Q

What is a hybrid stepper motor, and why is it common in space?

A

It combines features of permanent magnet and variable reluctance motors, offering high torque and precision.

61
Q

How do pyrotechnic devices function in space mechanisms?

A

They use controlled explosions to actuate mechanisms like pin pullers or cable cutters quickly and reliably.

62
Q

What precautions are taken with pyrotechnic devices in space?

A

Dual redundant firing circuits and safe-arm mechanisms prevent accidental detonation.

63
Q

What are tape booms, and how do they deploy?

A

Curved metal strips unroll and stiffen to form booms, relying on their stored strain energy for deployment.

64
Q

What are Solar Array Drives (SADs), and what is their purpose?

A

SADs rotate solar arrays to maintain optimal orientation to the Sun, using slip rings for continuous power transfer.

65
Q

Why are momentum wheels sealed in low-pressure helium?

A

To reduce oil evaporation, minimize frictional losses, and ensure consistent operation over long durations.

66
Q

Why must mechanisms withstand vibration and stress during launch?

A

The launch environment subjects components to extreme forces, risking damage or misalignment.

67
Q

How does thermal expansion affect spacecraft mechanisms?

A

Differential expansion can cause distortions or misalignments; careful material selection minimizes these effects.

68
Q

What is cold welding, and how is it prevented in space mechanisms?

A

Cold welding occurs when clean metal surfaces bond in vacuum; it is mitigated using coatings or surface treatments.

69
Q

Why is a large stall torque margin necessary in motors?

A

To overcome initial static friction and provide reliable operation under varying loads.

70
Q

How is torque related to angular velocity and power in motors?

A

P=T⋅ω,

where

P is power,

T is torque,

ω is angular velocity.

Space Systems (18 decks)

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