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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
Why are carbon-fiber-reinforced plastics used in spacecraft structures?
High strength, low thermal expansion, and excellent dimensional stability.
26
What is the importance of low CTE materials in optical systems?
To minimize thermal expansion and maintain optical alignment in space.
27
Why are optical baffles critical in spacecraft?
To block stray light and improve imaging quality.
28
How is contamination controlled in optical systems?
Using clean rooms, laminar flow benches, and sealing optics with dust caps.
29
What type of polymer is unsuitable for space applications and why?
PVC; it outgasses and becomes brittle in vacuum conditions.
30
Why are fused silica tiles used in spacecraft?
They serve as optical solar reflectors due to their low thermal expansion and high reflectivity.
31
What are the wavelength ranges for UV, visible, and NIR radiation?
UV: 0.28–0.38 µm; Visible: 0.38–0.78 µm; NIR: 0.78–1.0 µm.
32
How do lenses and mirrors bring light to focus?
Lenses refract light, while mirrors reflect it to converge rays at a focal point.
33
What is the f-number of an optical system?
The ratio of focal length to aperture diameter.
34
What is the Rayleigh diffraction limit?
It defines the smallest angular resolution that a system can achieve due to diffraction.
35
How is a diffraction-limited system determined?
By comparing the diffraction limit to the detector's pixel size and resolution.
36
What is the main advantage of a whiskbroom scanner?
High resolution over a small area with few detectors.
37
What is the main disadvantage of a push-broom scanner?
Requires precise detector alignment and calibration over a wide field.
38
Why are doublets and triplets used in lenses?
To correct chromatic aberration by compensating for wavelength-dependent refractive indices.
39
What materials are suitable for infrared lenses?
Germanium, silicon, and gallium arsenide.
40
How does an interference filter work in a radiometer?
It selectively transmits wavelengths by constructive interference in a multi-layer dielectric coating.
41
What are the two categories of spacecraft mechanisms based on usage?
Continuous-use mechanisms (e.g., antenna pointing systems, reaction wheels) and one-shot mechanisms (e.g., separation systems, solar array deployment).
42
What are the main design challenges for spacecraft mechanisms?
Ensuring high precision, reliability, and longevity in the harsh environment of space, including temperature extremes and vacuum.
43
Why is inertia an important consideration in space mechanisms?
In microgravity, mechanisms must overcome an object's inertia to initiate or stop motion, as mass (not weight) governs the forces required.
44
What is the significance of the moment of inertia in rotating bodies?
It quantifies a body's resistance to rotational acceleration about an axis, determined by mass distribution relative to the axis.
45
What is Newton’s second law for rotational motion?
T=Iα, where T is torque, I is the moment of inertia, α is angular acceleration.
46
How is angular momentum (H) of a rigid body expressed?
H=Iω, where ω is angular velocity, I is the moment of inertia tensor.
47
What are principal axes of inertia?
Axes where products of inertia are zero, simplifying calculations for symmetric bodies or systems.
48
How do internal and external torques affect angular momentum?
Internal torques conserve total angular momentum; external torques can change its magnitude or direction.
49
What causes the gyroscopic effect in spacecraft?
A spinning mass resists changes in its orientation due to the conservation of angular momentum.
50
How is the gyroscopic effect used in attitude control?
Reaction and momentum wheels exploit this effect to stabilize and adjust a spacecraft's orientation.
51
What is precession in a gyroscopic system?
The slow change in orientation of the spin axis due to a torque applied perpendicular to the axis of rotation.
52
What is the principle of kinematic constraint?
A rigid body requires six independent constraints to fix its position and eliminate all degrees of freedom.
53
What is overconstraint in kinematic systems?
When redundant constraints introduce uncertainty or distortions, leading to reduced precision.
54
How does the Kelvin clamp ensure kinematic precision?
It uses three spheres contacting three V-grooves at 120° intervals to achieve six independent constraints.
55
Why are ball bearings preloaded in spacecraft applications?
To prevent rattling during launch and ensure smooth operation under dynamic loads.
56
What are the advantages of dry lubricants like MoS₂ in space?
They perform well in vacuum, resist outgassing, and reduce contamination risks.
57
Why are wet lubricants sometimes preferred for high-speed systems?
They reduce wear and provide better heat dissipation, though they require careful containment to avoid migration.
58
What distinguishes brushless DC motors from brushed motors?
Brushless motors have higher reliability and longevity as they lack brushes that wear out, but they require more complex electronics.
59
Why are stepper motors ideal for precision applications in space?
They move in discrete steps, enabling precise angular positioning without feedback control.
60
What is a hybrid stepper motor, and why is it common in space?
It combines features of permanent magnet and variable reluctance motors, offering high torque and precision.
61
How do pyrotechnic devices function in space mechanisms?
They use controlled explosions to actuate mechanisms like pin pullers or cable cutters quickly and reliably.
62
What precautions are taken with pyrotechnic devices in space?
Dual redundant firing circuits and safe-arm mechanisms prevent accidental detonation.
63
What are tape booms, and how do they deploy?
Curved metal strips unroll and stiffen to form booms, relying on their stored strain energy for deployment.
64
What are Solar Array Drives (SADs), and what is their purpose?
SADs rotate solar arrays to maintain optimal orientation to the Sun, using slip rings for continuous power transfer.
65
Why are momentum wheels sealed in low-pressure helium?
To reduce oil evaporation, minimize frictional losses, and ensure consistent operation over long durations.
66
Why must mechanisms withstand vibration and stress during launch?
The launch environment subjects components to extreme forces, risking damage or misalignment.
67
How does thermal expansion affect spacecraft mechanisms?
Differential expansion can cause distortions or misalignments; careful material selection minimizes these effects.
68
What is cold welding, and how is it prevented in space mechanisms?
Cold welding occurs when clean metal surfaces bond in vacuum; it is mitigated using coatings or surface treatments.
69
Why is a large stall torque margin necessary in motors?
To overcome initial static friction and provide reliable operation under varying loads.
70
How is torque related to angular velocity and power in motors?
P=T⋅ω, where P is power, T is torque, ω is angular velocity.

Space Systems (40 decks)

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