1
Q
Six key components to collect for each vehicle and band?
A
- Time series of body rates or quaternion/Euler logs
- Typical tumble profiles
- TX/RX antenna specifications in the body frame
- Chamber gain pattern and cross-pol isolation
- Ground station polarization and dual-pol availability
- Waveform details such as symbol rate and interleaver depth
These components are critical for understanding antenna performance and communication reliability in varying conditions.
2
Q
Define polarization-mismatch loss for linear to linear polarization.
A
L_pol(dB) = -20 log10|cos(Δψ)|
Δψ represents the instantaneous polarization angle difference, which includes body rotation and Faraday rotation.
3
Q
What is the inherent loss when transitioning from linear to circular polarization?
A
Approximately 3 dB plus any axial-ratio penalty if the circular isn’t pure.
This loss occurs because one linear component couples during the transition.
4
Q
How does body rotation affect pattern-induced fades?
A
Body rotation causes the gain pattern to sweep through lobes and nulls, leading to periodic or quasi-periodic deep fades.
The rate of these fades is tied to the magnitude of body rates and the symmetry of the pattern.
5
Q
Fill in the blank: If the typical fade lasts T_fade seconds, then the burst length in _______ is N_burst ≈ R_s · T_fade.
A
symbols
This relationship helps in determining the necessary interleaver depth.
6
Q
What are the steps in the modeling workflow for antenna performance?
A
- Map antenna orientation to space
- Compute pattern and polarization loss vs time
- Get fade statistics
- Translate to symbols
- Size interleaver and pick code
- Validate with SDR I/Q
Each step is crucial for accurately modeling the communication link’s performance.
7
Q
What should you track during problem passes to understand SDR fades?
A
Body rates around problem passes and label SDR fades by attitude phase
This helps in identifying the periodicity of the fades related to body rotation.
8
Q
True or False: Using a circular polarization antenna on the spacecraft and a linear polarization on the ground will minimize polarization loss.
A
False
Using circular polarization on at least one side minimizes polarization loss and reduces the impact of body rotation.
9
Q
What are the benefits of using dual-pol diversity at the ground station?
A
- Shortens burst length
- Reduces outage duration
- Lowers required interleaver depth
This method can convert longer outages into smaller SNR dips, enhancing communication reliability.
10
Q
What is a rule-of-thumb for interleaver depth based on 95th percentile fade durations?
A
- ≤ 5 ms: mild interleaver
- 5–20 ms: moderate interleaver
- 20–100 ms: consider dual-pol diversity or reduce R_s
These guidelines help in selecting the appropriate interleaver configuration based on expected fade durations.
11
Q
What is the impact of interleaver latency on operations?
A
Interleaver latency is approximately depth/R_s.
Total one-way latency should be kept within operational limits to ensure effective communication.
12
Q
What are the quick defaults to consider if you must pick now for antenna and interleaver settings?
A
- Add dual-pol on GS
- Use circular polarization on space if AR ≤ 3 dB
- Start interleaver depth at 2000 symbols @ 100 ksym/s
- Use CCSDS LDPC (rate-1/2) as a baseline
These defaults can significantly improve communication performance in the absence of detailed measurements.
13
Q
List the items in the one-page checklist for operational readiness.
A
- Get ADCS body-rate/quaternion vs time
- Map antenna pattern & polarization into LOS direction
- Extract burst CDF from SDR
- Set interleaver depth ≥ N_{95}
- Verify post-FEC PER drop in flight
- For next-gen: circular on space, dual-pol GS, smoother pattern, ACM tied to elevation/body rate
This checklist ensures all critical aspects of the communication system are addressed before operations.
14
Q
Why does fine torque control matter for attitude control?
A
It allows for precise pointing and low jitter
Tiny changes in torque lead to tiny changes in angular acceleration.
15
Q
What does the motor drive need to behave like for effective attitude control?
A
A finely adjustable torque source
Not just a crude speed controller.
16
Q
What does FOC provide through its mechanisms?
A
- Direct current–torque mapping
- High-bandwidth current loop
These mechanisms enhance torque control for motors.
17
Q
In a surface-mounted PMSM, torque in d-q coordinates is approximately represented as?
A
𝑇𝑒 ≈ (3/2) * 𝑝 * 𝜓𝑓 * 𝑖𝑞
Where 𝑝 is pole pairs, 𝜓𝑓 is magnet flux linkage, and 𝑖𝑞 is q-axis current.
18
Q
What happens if FOC keeps 𝑖𝑑 ≈ 0?
A
The relationship between 𝑖𝑞 and 𝑇𝑒 becomes almost perfectly linear
Doubling 𝑖𝑞 results in doubling 𝑇𝑒.
19
Q
What does FOC measure to compute 𝑖𝑑 and 𝑖𝑞?
A
Phase currents 𝑖𝑎, 𝑖𝑏, 𝑖𝑐
It uses Clarke/Park transformation to compute these in the rotor-flux frame.
20
Q
What does the attitude controller choose?
A
A desired torque 𝑇∗
This torque is then used to compute the commanded q-axis current.
21
Q
What is the purpose of the high-bandwidth current loop in FOC?
A
To correct disturbances faster than outer loops can react
It runs at a control update rate of 10–40 kHz.
22
Q
What types of disturbances can the high-bandwidth current loop correct?
A
- DC bus ripple / supply noise
- Motor parameter drift with temperature
- Changes in friction, cogging, bearing drag
- Quantization noise in PWM / ADC
These disturbances can affect torque stability.
23
Q
What does the attitude controller expect from the reaction wheel?
A
To act like a pure torque source
High-bandwidth current control ensures this assumption is valid.
24
Q
What does FOC use for high-resolution PWM?
A
SVPWM
SVPWM uses the full space-vector hexagon for better DC-bus utilization.
25
What is the advantage of using **symmetrical, finely spaced duty cycles** in FOC?
It allows for small changes in commanded voltage, current, and torque
## Footnote
This helps avoid coarse granularity in torque commands.
26
What is the effect of **high timer resolution** (e.g., 12–16 bits) in PWM?
Extremely fine duty-cycle granularity
## Footnote
This translates to fine resolution in (i_q) and reaction torque.
27
The linear mapping (T_e propto i_q) indicates that torque command is almost the same as what?
q-axis current command
## Footnote
This relationship simplifies the control of torque in the system.
28
What does a **fast inner current loop** achieve in the drive system?
Quickly matches actual torque to commanded torque and rejects disturbances
## Footnote
This enhances system responsiveness and stability.
29
What is the net effect of **high-resolution PWM** on torque increments?
Very small, controllable increments in torque; no 'stair-step' behavior
## Footnote
This allows for smooth control of spacecraft angular acceleration.
30
What enables **precise pointing, low jitter, and clean disturbance rejection** in a high-performance ADCS?
High-resolution PWM and fast inner current loop
## Footnote
These features allow for tiny, predictable changes in spacecraft angular acceleration.
31
What is **bidirectional symmetry** in spacecraft attitude control?
The ability to control torques in both directions around each axis
## Footnote
This is essential for reaction wheels to store momentum in either direction.
32
Why does **bidirectionality matter** in spacecraft attitude control?
It allows for torques in both directions around each axis
## Footnote
This is crucial for effective momentum management.
33
What must a **single reaction wheel** do to manage momentum?
* Spin in the positive direction to store momentum one way
* Spin in the negative direction to store momentum the other way
* Pass smoothly through zero speed when reversing
## Footnote
These actions ensure effective control of spacecraft orientation.
34
How does **FOC handle direction** naturally?
By flipping the sign of (i_q) to flip the sign of torque
## Footnote
This allows for seamless control of torque direction.
35
What does the **same FOC structure** involve?
* Measures currents
* Transforms them to d-q with the estimated angle
* Runs the same PI loops
## Footnote
This structure remains consistent regardless of torque direction.
36
What is the effect of **reversing wheel direction**?
Commanding a torque opposite to current wheel momentum
## Footnote
This is essential for controlled momentum management.
37
What does FOC provide during the **controlled pass through zero speed**?
* Smooth deceleration
* Controlled pass through zero speed
* Smooth acceleration in the opposite direction
## Footnote
This behavior is crucial for reaction wheels.
38
What is the **net effect** of the discussed concepts?
* Good low-speed behavior
* Field weakening at high speed
* Bidirectional symmetry
## Footnote
These factors contribute to a wide speed range for reaction wheels.
39
What does good **low-speed behavior** provide?
Well-defined, low-ripple torque even when back-EMF is tiny
## Footnote
This is important when the wheel is almost stationary.
40
What does **field weakening at high speed** enable?
Ability to exceed the base EMF speed limit of the DC bus while maintaining control
## Footnote
This prevents inverter saturation and allows for very high RPM.
41
What does a single **FOC controller** provide for reaction wheels?
Stable, precise torque from 'barely moving' up to maximum design RPM, in both directions
## Footnote
This is essential for high-performance ADCS.
42
Why is a **wide speed range** important for reaction wheels?
* Tiny torques at low speed
* High wheel RPM for large torques
* Both positive and negative wheel speeds
## Footnote
A wide speed range allows for fine pointing and bias removal as well as the ability to store angular momentum.
43
What does FOC provide for controlling reaction wheels?
* Tools for low speed
* Tools for high speed
* Tools for reversing
## Footnote
FOC enables smooth operation across different speed regimes.
44
What is a problem with **simple 6-step / back-EMF commutation**?
Commutation becomes badly timed, leading to jerky torque or collapse
## Footnote
This is unacceptable for a reaction wheel that must produce controllable torque at low speeds.
45
How does FOC control torque differently than traditional methods?
* Controls torque through (i_q) in the d-q frame
* Does not rely on back-EMF zero crossings
## Footnote
FOC uses current control in the rotating frame for precise torque management.
46
What is the effect of **negative (i_d)** in FOC?
Weakens the effective field, allowing higher speeds
## Footnote
This helps maintain control and produce torque above base speed.
47
What happens at **base speed** without field weakening?
Inverter cannot supply enough voltage to keep up with rising back-EMF
## Footnote
Current control and torque production start to break down at this point.
48
What is the role of **field weakening** in FOC for reaction wheels?
* Allows higher RPM
* Maintains control of (i_q)
* Produces meaningful torque
## Footnote
Field weakening enables the use of reasonable bus voltage while achieving high top speeds.
49
Fill in the blank: FOC controls torque through _______ in the d-q frame.
i_q
## Footnote
This method does not depend on back-EMF zero crossings.
50
True or false: FOC allows for precise torque control even at very low mechanical speeds.
TRUE
## Footnote
This capability is crucial for reaction wheels starting from rest.
51
What is the effect of **6-step/block commutation** on phase voltages?
Phase voltages have big steps every 60°
## Footnote
This results in currents rich in low-order harmonics (5th, 7th, etc.)
52
What are the consequences of low-order harmonics in currents?
* Extra iron losses (hysteresis + eddy currents)
* Increased RMS current for the same average torque
## Footnote
High-frequency flux swings contribute to these losses.
53
How does **FOC + SVPWM** improve phase voltages and currents?
Phase voltages and currents are close to pure sinusoids
## Footnote
The main switching ripple is at the PWM frequency and its sidebands.
54
What does SVPWM minimize in line-to-line voltages?
Low-order harmonic content
## Footnote
This pushes most distortion into higher frequencies.
55
What is the consequence of minimizing low-order harmonic content?
* Less hysteresis and eddy current loss
* Lower RMS current for the same average torque
## Footnote
This results in less copper + iron loss for the same mechanical output power.
56
What is the net effect of aligning the current vector in a reaction wheel?
Maximum torque per amp
## Footnote
This leads to no wasted current components and minimum I²R loss.
57
What are the benefits of low harmonic content in a reaction wheel?
* Reduced iron loss
* Lower RMS current
## Footnote
This allows the inverter to draw less DC bus current.
58
What does high efficiency mean in the context of FOC for a reaction wheel?
The reaction wheel operates with the least possible electrical and thermal overhead
## Footnote
This results in cooler running motors and electronics, less thermal stress on components, and longer component lifetime.
59
Why is **efficiency** important for **reaction wheels**?
* Continuous operation for months/years
* Heat rejection requirements
* Power limitations for payload
* Reduced lifetime due to stress on components
## Footnote
Extra wattage leads to heat that must be managed and reduces available power for other uses.
60
What does **FOC** help achieve in reaction wheels?
* Aligning current with rotor flux
* Continuous estimation of rotor angle
* Minimizing copper loss
## Footnote
FOC optimizes the performance of the motor by ensuring efficient current usage.
61
In the rotor-flux (d-q) frame for a surface PMSM, what is the equation for **torque**?
𝑇𝑒 ≈ (3/2) * 𝑝 * 𝜓𝑓 * 𝑖𝑞
## Footnote
Where 𝑝 is pole pairs, 𝜓𝑓 is permanent-magnet flux linkage, and 𝑖𝑞 is q-axis (torque) current.
62
What is the ideal value for **𝑖𝑑** in a surface PMSM?
𝑖𝑑 ≈ 0
## Footnote
This means that the d-axis current does not contribute to torque.
63
What does the **Park transform** do?
Rotates stator currents into the d-q frame
## Footnote
This allows the controller to optimize the current vector for maximum effectiveness.
64
What is the consequence of poor alignment in current for torque production?
* Increased RMS current needed
* Higher copper loss (𝐼²𝑅 loss)
## Footnote
Poor alignment leads to inefficiencies in torque production.
65
How does FOC minimize **copper loss**?
By ensuring current is oriented where it’s most effective
## Footnote
This results in minimum current for a given torque, thus reducing heating.
66
What happens in a **6-step / trapezoidal drive**?
* Blocky phase currents
* Non-torque-producing current components
## Footnote
The controller only knows which two phases are active, leading to inefficiencies.
67
What does FOC explicitly control in terms of current?
* 𝑖𝑞: set to desired torque
* 𝑖𝑑: minimized or optimized for specific conditions
## Footnote
This ensures that non-torque current is either minimized for efficiency or used effectively.
68
What is the formula for **copper loss**?
𝑃𝐶𝑢 = 3 * 𝐼𝑝ℎ𝑎𝑠𝑒,𝑟𝑚𝑠² * 𝑅𝑠
## Footnote
This shows how current that does not contribute to torque results in wasted power as heat.
69
What is the benefit of FOC's axis control for a reaction wheel?
Minimized necessary current for torque and speed
## Footnote
This leads to significant gains in thermal margin and power budget for long-duration operations.
70
What are the **PMSM voltage equations** in the rotor-flux (d-q) frame?
* v_d = R_s i_d - ω_e L_q i_q + L_d (di_d/dt)
* v_q = R_s i_q + ω_e (L_d i_d + ψ_f) + L_q (di_q/dt)
## Footnote
These equations describe the voltage relationships in a Permanent Magnet Synchronous Motor (PMSM) using the d-q transformation.
71
What do the **cross-terms** in the PMSM voltage equations indicate?
* −ω_e L_q i_q appears in the d-axis equation
* ω_e L_d i_d appears in the q-axis equation
## Footnote
These terms indicate that the d and q axes are naturally coupled, meaning changes in one affect the other.
72
What is the purpose of the **FOC 'decoupling' strategy**?
To cancel the natural coupling between d-axis and q-axis controls
## Footnote
This strategy allows the d-axis loop to mainly control i_d and the q-axis loop to mainly control i_q.
73
Why is **decoupling** important for smooth torque?
* Prevents transient torque spikes
* Ensures speed changes or small flux-control actions don’t affect torque
## Footnote
Without decoupling, changes in speed or i_d could create unwanted torque ripple.
74
What is the **net result** for a reaction wheel with decoupling?
* Sinusoidal currents lead to minimal commutation torque ripple
* i_q acts as a direct torque handle
* Decoupled dynamics prevent torque modulation from speed changes
## Footnote
This results in a high-bandwidth, low-ripple torque actuator for spacecraft.
75
What are the benefits of a reaction wheel behaving like a **high-bandwidth, low-ripple torque actuator**?
* Ultra-smooth pointing
* Low jitter in precision instruments
* Predictable attitude dynamics across the entire operating range
## Footnote
These characteristics are essential for maintaining stability and precision in spacecraft operations.
76
What produces a **reaction torque** on the spacecraft?
𝑇_rw = 𝐽_wheel ⋅ 𝑑𝜔_wheel/𝑑𝑡
## Footnote
This equation shows the relationship between the wheel's inertia and its angular acceleration.
77
What happens if **motor torque ripples**?
Micro-vibrations and jitter in attitude
## Footnote
This occurs due to the wheel's angular acceleration rippling.
78
What is the role of **FOC** in reaction wheels?
Make electrical variables behave such that mechanical torque is steady and linear with the command
## Footnote
FOC stands for Field Oriented Control.
79
Without **FOC**, what type of current do each phase see?
Flat 'blocks' of current with abrupt commutations
## Footnote
This occurs every 60 electrical degrees.
80
What is the effect of using **FOC** on current waveforms?
Current waveform matches the sinusoidal back-EMF → electromagnetic torque becomes almost constant
## Footnote
This reduces torque pulsations.
81
What does the **q-axis** represent in a surface-mounted PMSM?
The 'pure torque' axis
## Footnote
It is crucial for torque control in reaction wheels.
82
In the equation for electromagnetic torque, what does **𝑇_e** represent?
𝑇_e = (3/2)𝑝(𝜓_f𝑖_q + (𝐿_d - 𝐿_q)𝑖_d𝑖_q)
## Footnote
This equation relates torque to the currents in the d and q axes.
83
What is the implication of keeping **𝑖_d** approximately equal to zero?
Torque is essentially proportional to **𝑖_q** only
## Footnote
This simplifies torque control in reaction wheels.
84
How does the **inner current controller** regulate torque?
Regulates **𝑖_q** tightly to the commanded value
## Footnote
This allows for direct, linear torque control.
85
What does the attitude controller output as a desired torque?
**𝑇***
## Footnote
This desired torque is converted to a desired **𝑖_q*** for control.
86
Holding **𝑖_q** constant results in what type of motor torque?
Very steady motor torque
## Footnote
This leads to very steady reaction torque on the spacecraft.
87
What is the core physical difference between **reaction wheels** and **magnetorquers**?
* Reaction wheels: Internal actuator generating torque via internal exchange of angular momentum
* Magnetorquers: External actuator creating torque through interaction with Earth's magnetic field
## Footnote
Reaction wheels use motors and spinning wheels, while magnetorquers rely on magnetic dipoles.
88
In a **reaction wheel**, torque is directly proportional to what?
**Electrical current** you command
## Footnote
No external environment is needed for torque generation in reaction wheels.
89
In a **magnetorquer**, torque depends on which two factors?
* Current you command
* Local magnetic field vector
## Footnote
No magnetic field means no torque can be generated.
90
What is the transfer function from torque to body rate for a **reaction wheel**?
G_{\Omega}(s) = -\frac{1}{J_s s}
## Footnote
This indicates a clean, linear plant behavior.
91
What is the effective torque constant for a **magnetorquer**?
K_m(t) = N A |\mathbf{B}| \sin\gamma
## Footnote
This constant is time-varying and direction-dependent.
92
True or false: The **reaction wheel** has high authority and bandwidth.
TRUE
## Footnote
Reaction wheels can generate large torques and have fast electrical dynamics.
93
What are the primary uses of **reaction wheels**?
* Fine pointing
* Jitter-sensitive payloads
* High-precision ADCS
## Footnote
Reaction wheels are ideal for applications requiring precise control.
94
What are the limitations of **magnetorquers** regarding torque generation?
* Limited by Earth's magnetic field strength
* Can only generate torque perpendicular to the magnetic field
## Footnote
This restricts their effectiveness in certain maneuvers.
95
What type of control strategies are often used for **magnetorquers**?
* Bang-bang control
* Simple B-dot control
* Time-varying or orbit-averaged models
## Footnote
These strategies account for the time-varying nature of the magnetic field.
96
What is the modeling approach for **reaction wheels** in control design?
* Clean, mostly time-invariant plant
* Input: torque from FOC-controlled current
* Output: body rate / attitude
## Footnote
This allows for the use of standard LTI tools in design.
97
What is the modeling approach for **magnetorquers** in control design?
* Explicitly time-varying plant
* Gain depends on orbit position & attitude
## Footnote
This complexity makes standard transfer functions less central in design.
98
What is the practical role of **reaction wheels** on a spacecraft?
* Fine control
* High precision
* High bandwidth
## Footnote
They are modeled as FOC-driven torque sources with clean dynamics.
99
What is the practical role of **magnetorquers** on a spacecraft?
* Coarse control
* Limited and time-varying control axes
* Momentum dumping
## Footnote
They are used for initial detumble and low-precision control.
100
In a combined system, what do **reaction wheels** and **magnetorquers** primarily handle?
* Reaction wheels: fine, fast, linear control
* Magnetorquers: long-term momentum management and gross maneuvers
## Footnote
This division of labor optimizes spacecraft control.
101
What do the **actuators** in a spacecraft control system consist of?
* Reaction wheels
* Magnetorquers
## Footnote
Actuators are responsible for producing torques based on commands.
102
What is the role of the **star tracker** in spacecraft attitude control?
* Provides absolute attitude w.r.t. an inertial frame
* High accuracy, relatively slow (1–10 Hz)
## Footnote
Outputs are often in the form of quaternions.
103
What does the **magnetometer** measure in a spacecraft?
* Local magnetic field in the body frame
* Faster (tens of Hz), noisier, environment-dependent
## Footnote
It plays a role in attitude estimation and magnetorquer control.
104
What is the function of the **estimator** in the spacecraft control system?
* Fuses data from sensors to produce best estimates of:
* Spacecraft attitude
* Body rates
* Wheel speed
* Magnetic field in body frame
## Footnote
Typically involves Kalman or complementary filters.
105
True or false: The **controller** directly uses raw sensor data to command actuators.
FALSE
## Footnote
The controller uses processed estimates from the estimator, not raw sensor data.
106
How does the **star tracker** influence wheel behavior in spacecraft?
* Provides precise attitude error
* Leads to precise torque commands
## Footnote
This results in better pointing and less wheel momentum buildup.
107
What is the purpose of **momentum management** in spacecraft control?
* Tracks stored momentum in wheels
* Plans magnetorquer-based unloading maneuvers
## Footnote
Helps maintain optimal pointing and prevents wheel saturation.
108
What is the relationship between **magnetorquer torque** and the magnetic field?
* Torque is given by:
[mathbf{T}_ ext{mtq} = mathbf{m} imes mathbf{B}]
## Footnote
The direction of torque generated depends on the magnetic field.
109
What is **B-dot control** used for in spacecraft?
* Creates a damping torque against rotational motion
* Reduces initial large angular rates after deployment
## Footnote
It sets up the spacecraft for precise control by reaction wheels.
110
Fill in the blank: The **actuator allocation** process splits the desired torque (mathbf{T}_ ext{cmd}) into components from __________ and __________.
* Reaction wheels
* Magnetorquers
## Footnote
This allocation is based on the characteristics of each actuator.
111
What does the **control flow** in a spacecraft system involve?
* Sensors → Estimator → Attitude Controller → Actuator Allocation → Actuators
## Footnote
This pipeline ensures that sensor data is effectively used to control the spacecraft.
112
What does the **estimator** produce as best estimates?
* (hat{q}_{BI}): spacecraft attitude
* (hat{Omega}_s): body rates
* (hat{omega}_w): wheel speed
* (hat{mathbf{B}}_B): magnetic field in body frame
## Footnote
These estimates are crucial for the control laws.
113
What is the primary assumption of **FOC** regarding command inputs?
**FOC assumes you can command any (i_q) you want** within some bounds
## Footnote
In reality, there are limits such as current, voltage, and wheel RPM limits that affect performance.
114
What happens to **wheel momenta** near saturation?
* Slowly walk up due to constant external disturbances
* Controller asks for torque it physically can’t get
## Footnote
This behavior is significant in the context of **ADCS**.
115
What is the purpose of **magnetorquers** in the context of saturation?
**Desaturation**
## Footnote
Magnetorquers are used to bleed wheel momentum to keep the FOC system in its comfortable linear region.
116
What factors are not included in clean transfer functions that affect **reaction wheel torque**?
* Flex in the solar panels
* Wheel imbalance
* Mount stiffness
* Bearing micro-vibrations
## Footnote
These factors can excite structural modes and affect performance.
117
What should the **attitude loop bandwidth** be in relation to structural modes?
Comfortably below any significant structural modes
## Footnote
This helps prevent amplification of jitter and other issues.
118
What are some **parameter drifts** that can affect model accuracy?
* Resistances drift with temperature
* Inductances and magnet flux change with temperature and aging
* Moments of inertia can change
## Footnote
These variations can lead to estimation errors and imperfect decoupling.
119
What is a critical aspect of **mode-based control** in spacecraft?
* Detumble mode
* Coarse pointing
* Fine pointing
* Momentum dumping
* Safe mode
## Footnote
Each mode affects the behavior of the same hardware differently.
120
True or false: **Magnetorquers** are suitable for instantaneous precision control.
FALSE
## Footnote
Magnetorquers are better for long-timescale momentum management and detumble.
121
What are the characteristics of **reaction wheels + FOC**?
* Internal
* High-bandwidth
* Nearly-linear torque source with constraints
## Footnote
This model is well handled by differential equations and state-space representations.
122
What is the role of a **star tracker** in spacecraft attitude control?
High-accuracy absolute attitude anchor
## Footnote
It helps convert spacecraft-level error into precise torque commands.
123
Fill in the blank: **Quantization & numerical stuff** actually matter for _______.
PWM resolution, ADC resolution, and numeric precision
## Footnote
These factors directly impact small-signal torque resolution and noise floors.
124
What is the **first step** in defining mission-level requirements for an ADCS?
Establish a specification
## Footnote
This includes defining key parameters such as attitude requirements and environmental constraints.
125
List the **attitude requirements** that must be defined for an ADCS.
* Pointing accuracy
* Pointing stability/jitter
* Slew rates
* Settling time after a slew
* Allowed momentum build-up before desaturation
* Power and thermal constraints
## Footnote
These requirements are crucial for the performance of the ADCS.
126
What are the **environmental/platform constraints** that affect an ADCS?
* Orbit (LEO, MEO, GEO; inclination, altitude)
* Disturbances (aero drag, solar pressure, gravity-gradient, magnetic torques)
* Spacecraft structure (inertia tensor, flexy appendages)
* Power budget, mass budget, volume for ADCS components
## Footnote
These factors influence the design and functionality of the ADCS.
127
What is the purpose of creating a **short ADCS requirements document**?
To outline specific system requirements with measurable parameters
## Footnote
The document should state: 'The system shall …' with defined numbers.
128
What does **slew rate** refer to in the context of ADCS?
The speed at which the system can repoint
## Footnote
This is a critical factor for maneuvering the spacecraft.
129
True or false: **Pointing stability/jitter** is irrelevant to the performance of an ADCS.
FALSE
## Footnote
Pointing stability is essential for maintaining accurate orientation over time.
130
What factors can affect the **disturbances** experienced by a spacecraft?
* Aero drag
* Solar pressure
* Gravity-gradient
* Magnetic torques
## Footnote
These disturbances can impact the spacecraft's attitude control.
131
What is meant by **allowed momentum build-up before desaturation** in an ADCS?
The maximum momentum that can accumulate before corrective action is needed
## Footnote
This is important for maintaining control and preventing system overload.
132
What are the components of the **inertia tensor** relevant to spacecraft structure?
* Jxx
* Jyy
* Jzz
* Off-diagonals
## Footnote
The inertia tensor is crucial for understanding the spacecraft's rotational dynamics.
133
What types of **flexy appendages** might be considered in spacecraft design?
* Solar arrays
* Booms
* Antennas
## Footnote
These components can affect the spacecraft's inertia and attitude control.
134
135
What are the **actuators** chosen for the ADCS?
* Reaction wheels (probably 3 or 4)
* Magnetorquers
## Footnote
Reaction wheels are used for momentum control, while magnetorquers assist in desaturation and detumbling.
136
What are the key specifications for **reaction wheels** in the ADCS?
* Wheel sizing (max momentum, max torque, max RPM)
* Motor type (PMSM/BLDC for FOC)
* ESC/FOC controller (custom)
## Footnote
These specifications ensure optimal performance of the reaction wheels.
137
What is the minimum realistic sensor stack for a **custom ADCS**?
* Star tracker (or camera-based equivalent)
* Magnetometer (3-axis)
* Gyros / IMU
* Sun sensor(s) (optional)
* Possibly wheel speed sensors
## Footnote
This stack provides high-accuracy attitude determination and control.
138
What is the role of a **magnetometer** in the ADCS?
* Attitude/heading support
* Magnetorquer control
* B-dot detumble
## Footnote
Magnetometers help in determining the spacecraft's orientation relative to Earth's magnetic field.
139
What are the functions of the **ADCS brain MCU/SoC**?
* FOC for N wheels
* Estimator (EKF/complementary)
* Attitude control laws
* Mode management & safing
## Footnote
The MCU/SoC is crucial for processing and controlling the ADCS operations.
140
What types of **internal buses** are used in the ADCS?
* SPI
* I²C
* CAN
## Footnote
These buses facilitate communication between sensors and wheel controllers.
141
List the **ADCS modes** that should be defined.
* Detumble (B-dot with MTQs)
* Coarse pointing (gyros + MTQs + maybe wheels)
* Fine pointing (wheels + star tracker)
* Momentum dumping (MTQs + wheels)
* Safe mode (minimal power)
## Footnote
Each mode serves a specific purpose in the operation and safety of the ADCS.
142
What is the purpose of the **sun sensor(s)** in the ADCS?
Backup/coarse attitude reference
## Footnote
Sun sensors provide additional data for attitude determination, especially in the absence of other sensors.
143
What is the function of **gyros / IMU** in the ADCS?
Bridge between star-tracker updates & high-rate attitude dynamics
## Footnote
Gyros and IMUs are essential for maintaining accurate attitude information during dynamic conditions.
144
What is the role of **momentum dumping** in the ADCS?
MTQs + wheels, relaxed pointing
## Footnote
Momentum dumping helps manage the angular momentum of the spacecraft to maintain stability.
145
What are the components of the **reaction wheel hardware**?
* Mechanical wheel assembly
* Motor
* FOC ESC PCB
## Footnote
The mechanical wheel assembly includes rotor, bearings, and housing; the motor is typically PMSM/BLDC; the FOC ESC PCB involves a 3-phase inverter and microcontroller.
146
What does the **mechanical wheel assembly** consist of?
* Rotor (mass, inertia, balance)
* Bearings (space-rated or high-rel hybrids)
* Housing, alignment features
## Footnote
These components are crucial for the functionality and stability of the reaction wheel.
147
What type of motor is used in the **reaction wheel hardware**?
PMSM/BLDC
## Footnote
The motor should have known pole pairs, Rs, Ld/Lq, and flux linkage.
148
What is the purpose of the **FOC ESC PCB**?
* 3-phase inverter per wheel
* FOC microcontroller or smart gate driver
* Shunts + amplifiers for current sense
## Footnote
The FOC ESC PCB is essential for controlling the reaction wheel's motor effectively.
149
What are the options for **ESC configuration** in reaction wheels?
* One ESC per wheel
* Central multi-channel ESC driving a wheel stack
## Footnote
This configuration affects the design and control of the reaction wheels.
150
What components are included in the **magnetorquer hardware**?
* Coils or rods
* Driver electronics
* Current sensing
* Protection
## Footnote
The coils or rods need to be designed with specific turn counts, wire gauge, and resistance.
151
What is the function of the **driver electronics** in magnetorquer hardware?
* H-bridge or simple current drivers
## Footnote
These drivers are essential for controlling the current through the magnetorquer coils.
152
What does the **sensor suite** include?
* Star tracker interface
* Magnetometer board
* IMU
* Optional sensors (sun sensors, coarse sensors)
## Footnote
Each sensor plays a role in the attitude determination and control system.
153
What is the purpose of the **star tracker interface**?
* Digital link (LVDS, CAN, SpaceWire, custom)
* Power conditioning, EMI filtering
## Footnote
This interface is crucial for accurate navigation and positioning.
154
What are the requirements for the **ADCS controller board**?
* MCU/SoC with floating-point capability
* Sufficient RAM/flash for FOC + estimation + ADCS logic
* Power regulation
## Footnote
The controller board must manage various interfaces and ensure clean power for sensors and actuators.
155
What types of interfaces are needed for the **ADCS controller board**?
* To OBC (main computer)
* To EPS (power system)
* To telemetry/radio
## Footnote
These interfaces are critical for communication and control within the spacecraft.
156
What are the **key components** of **FOC implementation**?
* Clarke/Park transforms
* d-q current controllers (PI)
* SVPWM
* Sensorless or sensored angle estimation
* Over-current / over-voltage protection
## Footnote
These components are essential for low-level control in motor systems.
157
What is estimated during **motor identification routines**?
* Rs
* Ld
* Lq
* Flux linkage
## Footnote
These parameters are crucial for understanding motor characteristics.
158
What is the **attitude representation** used in estimation?
Quaternions
## Footnote
Quaternions are preferred for representing orientations in three-dimensional space.
159
Name the types of **filters** used in estimation.
* Extended Kalman Filter (EKF)
* Multiplicative quaternion EKF
* Robust complementary filter
## Footnote
These filters help in processing sensor data for accurate attitude estimation.
160
What are the **inputs** for the estimation process?
* Gyro rates (high rate)
* Star tracker quaternions (low rate, high precision)
* Magnetometer (with Earth field model)
* Optional sun vector
## Footnote
These inputs are used to derive the attitude and rates of the system.
161
What are the **outputs** of the estimation process?
* 𝑞^𝐵𝐼
* Ω^𝑠
* Maybe biases & wheel momentum estimates
## Footnote
These outputs provide essential information for control and navigation.
162
What are the two types of **controllers** mentioned for the outer attitude controller?
* PD/PID on attitude + rate
* LQR / LQG
## Footnote
These controllers are used to manage the attitude and rate of the system.
163
What does **torque allocation** map desired body torque into?
* Reaction wheel torques (fast component)
* Magnetorquer torques (slow / desat component)
## Footnote
This mapping is crucial for effective control of the spacecraft's orientation.
164
What is used to compute **coil dipole** in magnetorquer mapping?
B-field estimate
## Footnote
The B-field estimate is essential for determining the required magnetic torque.
165
What does the **supervisory logic** in mode management handle?
* Switching between detumble / coarse / fine / desat / safe
* Handling sensor dropouts
* Backing off when actuators saturate or overheat
## Footnote
This logic ensures the system operates safely and effectively under varying conditions.
166
What are the **real-time loops** tasking frequencies mentioned?
* FOC at kHz
* Estimator at 10–100 Hz
* ADCS at ~1–10 Hz
## Footnote
These frequencies are critical for maintaining system performance and responsiveness.
167
What type of **scheduler** is mentioned for flight software infrastructure?
RTOS or cooperative scheduler
## Footnote
These scheduling methods are used to manage tasks in real-time systems.
168
What telemetry hooks are mentioned for **dumping state estimates**?
* Torque commands
* Wheel speeds
* B-field
## Footnote
These telemetry hooks are essential for monitoring system performance and conducting on-orbit tuning/debug.
169
What are the **simulation tools** mentioned for spacecraft dynamics?
* Dynamics simulation
* Closed-loop ADCS sim
* Monte Carlo for parameter variations & sensor noise
## Footnote
These tools are essential for analyzing spacecraft behavior under various conditions.
170
Name the components of **dynamics simulation** for spacecraft.
* Spacecraft rigid-body dynamics (3D Euler / quaternion dynamics)
* Reaction wheel dynamics
* Disturbance torques
* Orbit & environment factors (Earth B-field model, Gravity gradient, Simplified drag & SRP)
## Footnote
These components help in understanding the motion and forces acting on the spacecraft.
171
What does **HIL** stand for in the context of spacecraft testing?
Hardware-in-the-Loop
## Footnote
This method allows for testing the interaction between hardware and simulated environments.
172
What are the two types of **processor-in-the-loop** tests mentioned?
* Run ADCS firmware on real MCU while simulating spacecraft
* Spin a real reaction wheel against a dynamometer or a fake inertia
## Footnote
These tests validate the performance of the ADCS firmware in real-time scenarios.
173
What is the purpose of **magnetorquer testbed**?
* Create known B-fields using Helmholtz coils
* Measure generated torque
* Verify control law
## Footnote
This setup is crucial for testing the effectiveness of magnetorquers in attitude control.
174
What is the function of an **air-bearing table** in ADCS testbeds?
* Mount spacecraft mockup or real bus
* Allow nearly frictionless rotation
* Use wheels & MTQs to command maneuvers
## Footnote
This setup simulates the spacecraft's environment for testing maneuvering capabilities.
175
What are the considerations for **vibration & thermal** testing?
* Ensure wheel assemblies survive launch conditions
* Ensure ESCs and sensors survive on-orbit conditions
## Footnote
These tests are critical for verifying the durability and functionality of spacecraft components.
176
What are the key concepts in **Controls & estimation**?
* Linear systems (state-space, TFs, eigenvalues)
* PID / PI loop tuning in cascade
* Basic LQR/LQG concepts (optional but nice)
## Footnote
Comfort with these concepts is essential for effective control systems design.
177
What are the basics of **Estimation** that one should be familiar with?
* Kalman filter basics
* Quaternion kinematics
* Sensor fusion (gyro + star tracker + mag)
## Footnote
These concepts are crucial for accurate state estimation in dynamic systems.
178
What skills are necessary for **Power electronics & FOC**?
* Designing 3-phase inverter PCBs
* Implementing Clarke/Park transformations
* PI current control
* SVPWM
* Over-current/over-voltage protection
* (Optionally) sensorless observers
## Footnote
Understanding these skills is vital for developing efficient motor control systems.
179
What are the layout rules for **designing 3-phase inverter PCBs**?
Low-noise, high-current FOC ESCs
## Footnote
Proper layout is critical for minimizing electromagnetic interference and ensuring reliable operation.
180
What are the key concepts in **Spacecraft dynamics & ADCS**?
* Rigid-body attitude dynamics (Euler’s equations, quaternion form)
* Disturbance torque budgeting
* Magnetorquer physics and B-dot control
* Reaction wheel sizing & momentum management
## Footnote
Mastery of these concepts is essential for effective attitude determination and control in spacecraft.
181
What are the **ADCS requirements** for a hypothetical CubeSat?
Write ADCS requirements (numbers!)
## Footnote
This is the first step in creating a minimum viable ADCS roadmap.
182
Define the **architecture** for the ADCS.
* 3 wheels
* 3 MTQs
* gyro
* mag
* star tracker
## Footnote
This architecture outlines the essential components needed for the ADCS.
183
What is the purpose of building a **full simulation** in Python/MATLAB?
* Spacecraft
* wheels
* MTQs
* environment
* Estimator
* controller in the loop
## Footnote
The simulation helps in testing the ADCS design before hardware implementation.
184
What is the first step in designing a **reaction wheel**?
Design one reaction wheel + ESC
## Footnote
This includes implementing FOC on your favorite MCU.
185
What should be tested when designing a **reaction wheel**?
Bench test torque vs command
## Footnote
This ensures the reaction wheel responds correctly to commands.
186
What is the next step after designing a reaction wheel?
Design one MTQ + driver, test torque in a Helmholtz setup
## Footnote
Alternatively, use a simple B-field emulator if DIY.
187
What is the goal of integrating **ESC + MTQ + sensors**?
Integrate ESC + MTQ + sensors on a single ADCS controller board
## Footnote
This integration is crucial for the functionality of the ADCS.
188
What does **HIL + air-bearing tests** involve?
Run your flight-like code against real hardware and simulated environment
## Footnote
This step is essential for validating the ADCS performance.
189
What should be done after conducting HIL + air-bearing tests?
Iterate on gains and mode logic
## Footnote
This helps refine the control algorithms for better performance.
190
What are the typical **motor loads** for a satellite?
* Reaction wheels / CMGs (attitude control)
* Solar array drive mechanisms (SADM)
* Antenna/gimbal pointing mechanisms
* Filter wheels, shutters, focusing stages for payloads
* Pump / compressor / valve actuators
* Robotic arms / mechanisms on big platforms
## Footnote
These components are essential for various functions such as attitude control and payload operation.
191
What types of motors can drive satellite mechanisms?
* Brushed DC motors
* Steppers
* BLDC / PMSM motors
* Harmonic drives / gear trains
## Footnote
Each type of motor has its own advantages and applications in satellite systems.
192
Fill in the blank: **FOC** is only relevant when using _______ and caring about smooth torque, efficiency, and/or noise.
BLDC/PMSM (or synchronous reluc./induction)
## Footnote
FOC stands for Field Oriented Control, which is important for optimizing motor performance.
193
What is most likely used in **satellites** for high-performance reaction wheels?
A. High-performance reaction wheels / CMGs
## Footnote
Reaction wheels are crucial for attitude control in satellites.
194
Why do **reaction wheels** need very smooth torque?
* Jitter corrupts pointing stability
* High efficiency (they spin continuously)
* Wide speed range (very slow torque to thousands of RPM)
* Fine torque control down to tiny levels
## Footnote
Smooth torque is essential for maintaining stability in satellite pointing.
195
What does **FOC** stand for in the context of satellite technology?
Field-Oriented Control
## Footnote
FOC provides clean, sinusoidal currents, reducing torque ripple.
196
What are the benefits of using **FOC** in high-performance designs?
* Reduces torque ripple
* Better control of Iq (torque) and Id (flux)
* Minimizes copper loss
* Achieves smooth torque at low speed and during reversals
## Footnote
These benefits enhance the performance of satellite systems.
197
When is **FOC** typically used in precision attitude control systems?
* Star tracker + gyro + wheel torque quality drive pointing requirements into the arcsecond or micro-rad range
* Where EMI and vibration from commutation have to be minimized
## Footnote
FOC is crucial for maintaining precision in satellite orientation.
198
What are **Solar Array Drive Mechanisms (SADM)** used for?
* Rotate array 360° over an orbit to track the sun
* Steer large high-gain antennas or reflector dishes
## Footnote
SADMs are essential for solar energy collection and communication in satellites.
199
Historically, what types of motors have been used in **SADMs**?
* Steppers with microstepping
* Brushed DC with simple feedback
## Footnote
These motors have limitations in terms of smoothness and efficiency.
200
What advantages does **FOC** provide when using a BLDC/PMSM in SADMs?
* Low-speed smoothness (no cogging / step impulses)
* Precise torque control → smoother structural loads
* Better efficiency → lower thermal load in the drive
## Footnote
These advantages enhance the performance and reliability of satellite mechanisms.
201
What are some examples of **payload mechanisms** in satellites?
* Filter wheels in multispectral instruments
* Focus/zoom stages in telescopes
* Scan mirrors in imaging payloads
## Footnote
These mechanisms are critical for capturing high-quality images and data.
202
Why is **FOC** a natural fit for payload mechanisms using BLDCs?
* Very quiet, smooth motion (avoid jitter in images)
* Exact positioning with feedback encoders
## Footnote
FOC allows for high precision and stability in imaging applications.
203
What do high-resolution encoders combined with **FOC** provide?
* Smooth motion profiles
* Precise position/velocity control
## Footnote
This combination is essential for high-performance satellite imaging systems.
204
What is a common actuator type used in **cubesats/smallsat mechanisms**?
* Tiny cubesats using steppers
## Footnote
Simplicity is favored in many low-budget missions.
205
In low-budget missions, why is **FOC** considered overkill?
It requires precise control not needed for many applications
## Footnote
Simplicity wins with steppers and basic control mechanisms.
206
What type of control do steppers in cubesats often use?
* Open-loop control
* Quasi-open-loop control
## Footnote
These control types simplify the design and implementation.
207
List some characteristics of actuators used in low-budget missions.
* More torque ripple
* Coarser motion
* Higher margin designs
## Footnote
This includes oversized actuators and slower slews.
208
What are examples of **on/off type actuators**?
* Simple latch valves
* Deployment actuators
* Limited-duty pump motors
## Footnote
These actuators are used for straightforward control tasks.
209
What is the control problem for on/off type actuators?
Turn on for N seconds
## Footnote
This differs from regulating torque precisely over a wide range.
210
What types of drives are typically used for on/off actuators?
* Brushed DC drives
* Simple BLDC drives
## Footnote
These drives often include basic current limiting.
211
What are the primary concerns for **FOC** in space applications compared to drone/EV systems?
* Radiation & reliability
* Torque ripple and jitter constraints
* Efficiency and thermal constraints
## Footnote
Space applications prioritize reliability and performance under extreme conditions.
212
How is the **MCU/FOC controller** designed for space applications?
* Often rad-tolerant / rad-hard
* Simpler, heavily-reviewed firmware
## Footnote
These design choices ensure reliability in harsh environments.
213
What characteristics define the **FOC algorithm** used in space applications?
* More conservative
* No fancy AI/auto-tuning
* Deterministic fixed-point math
* Thoroughly verified corner cases
## Footnote
The algorithm prioritizes reliability and predictability over complexity.
214
What are the **tuning goals** for FOC in reaction wheels and gimbals?
* Minimize harmonic content in torque
* Avoid structural resonances
* Maintain extremely constant torque even at low speeds
## Footnote
These goals are crucial for the stability of the attitude control loop.
215
What does **FOC** aim to achieve regarding **current ripple**?
* Very low current ripple
* Carefully shaped current references
## Footnote
This helps in maintaining smooth operation and minimizing vibrations.
216
Why are **efficiency and thermal constraints** critical in space applications?
* No convection
* Limited radiator area
* Every watt of loss must be radiated
## Footnote
Efficient operation is essential to manage thermal concerns in space.
217
How does FOC improve **motor efficiency** in space applications?
* Better control of currents
* Reduces copper and switching losses
* Runs motors closer to optimal efficiency
## Footnote
This efficiency is particularly important for high-power platforms.
218
What is a significant thermal concern for **reaction wheels/gimbals** in space?
* Continuous operation can lead to thermal issues
## Footnote
FOC's efficiency gains help mitigate these concerns.
219
FOC is used in satellites when the motor is **BLDC/PMSM** and the application needs what?
* Very smooth, low-ripple torque
* High efficiency over long duty cycles
* Fine control across a wide speed range
## Footnote
These requirements are critical for applications like reaction wheels and precise gimbals.
220
FOC is usually implemented with what type of rotor position sensing?
Sensored rotor position (encoder/resolver)
## Footnote
This is preferred over sensorless HFI for better reliability.
221
What type of firmware is typically used in FOC implementations?
Conservative, thoroughly tested firmware
## Footnote
This is important for operation on a rad-tolerant controller.
222
What components are expected in a high-reliability FOC design?
* Discrete gate driver
* FETs
* Kelvin shunts
## Footnote
These components contribute to the overall reliability and performance of the system.
223
True or false: FOC is always used when actuators are simple on/off.
FALSE
## Footnote
FOC is not necessary for simple actuators or when stepper open-loop is sufficient.
224
FOC is NOT always used when the mission doesn’t justify what?
The complexity/heritage cost
## Footnote
This indicates that simpler solutions may be preferred in less demanding applications.
ELARA/ODIN
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