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ISU M2 > ENG - part 1 > Flashcards

ENG - part 1 Flashcards

for the January 2021 exam

1
Q

Outline spacecraft power requirements.

A
  • Functional Requirements
    • -28V, power margin, eqp switching, grounding
  • System-Level Considerations
    • solar cells, secondary battery, power bus, s/c stabilization
  • S/C Total Power Consumption
    • mission modes, s/c types
  • Subsystem Power Consumption
    • Pss= Psc - Ppl
  • Avg vs. peak power
    • varies w/ time
  • Mission Modes
    • margins and reserves
  • Power Margin
  • Eclipse Period
  • Solar-Panel Power Requirement
  • Battery Requirement
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2
Q

Describe space power system components.

A

Electrical Power Subsystem (EPS):

  • Produces electricity from a power source
  • Stores electricity for future use
  • Regulates the electricity as required
  • Distributes electricity around the spacecraft
  1. Power Sources:
  • Solar Photovoltaic Arrays (PV)
    • silicone replaced by gallium arsenide, within Jupiter orbit, sunlight necessary
  • Radioisotope Thermoelectric Generators
    • sun indep, low efficiency, nuclear decay generates heat that’s converted to elec. (Plutonium 238)
  • Nuclear Reactors
    • operate as a nuclear power plant (for > 100kWe power requirements)
  • Fuel Cells
    • electrochemical device - produce electricity from fuel and oxidant
    • heavy, short missions
  • Solar Dynamic
    • sun heats fluid-turbine
    • more efficient than PV

Energy Storage:

  • Batteries
    • NiCd/NiH2 replaced by Li-ion
    • voltage-current levels critical
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3
Q

Outline spacecraft thermal requirements.

A

Temperature control/ extremes =need to keep at operating temp

  • Temp Gradient - sun/shadow
  • Eclipse - move in and out
  • Propellents and batteries - sensitive to temp
  • Out-of-limit (OOL) temperature will affect both perf and lifetime

Heat Transfer:

  • Radiation
    • sun, earth albedo- reflected light, earthshine - IR emitted by the Earth
  • Conduction (inside s/c)
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4
Q

Describe space thermal control system components.

A

Temperature monitoring uses thermistors mounted throughout

the spacecraft.

Thermal control comes in two forms:

  • Passive control
    • paints and surface treatment
    • MLI - multi-layer insulation
      • = lower mass and power consumption and higher reliability.
  • Active control
    • moving parts and electric heating - louvres, heat/thermal switches
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5
Q

Explain the implications of absorptivity and emissivity in spacecraft thermal control.

A

Absorptivity: (defined by α)

= the proportion of S absorbed by the satellite depends on its surface properties (colour and treatment).

Emissivity: (defined by ε)

= the ability of a surface to radiate in the IR

Notes:

  1. The lower α/ε is, the lower will be the equilibrium temperature.
  2. α and ε also control thermal inertia.
  3. The lower the values of α and ε, the greater the thermal inertia because the surface will absorb and emit less easily.
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6
Q

Describe the first half of the space mission, analysis and design (SMAD) process in broad terms.

A

The SMAD Process:

  1. Mission Objectives
    • Define broad objectives & constraints
    • Most of the information should come from the mission statement.
    • As you go through the design, come back to the objectives “again and again and again” to make sure that they are being fulfilled.
    • Example on slide 15
  2. Preliminary Mission Requirements
    • Estimate quantitative mission needs & requirements
    • Quantify how well we wish to achieve objectives.
      • This means using numbers!
      • Do not set these too firmly first time – these may be
        iterated many times.
    • “Is this requirement NEEDED?”
  3. Mission Concepts
    • Define alternative mission concepts
    • A mission concept is a broad statement about
      how a mission will work.
    • It has four main parts:
      1. Data delivery
      2. Communications architecture
      3. Testing scheduling and control
      4. Mission timeline
  4. Mission Architecture
    • Define alternative mission architectures
    • A mission architecture includes:
      • Mission concept
      • Alternatives for each of the mission elements, most importantly:
        • Subject
        • Orbit
        • Communications
        • Ground segment
  5. Mission Drivers
    • Identify system drivers for each
    • A mission driver is a mission characteristic that has an effect on:
      • Performance
      • Cost
      • Risk
      • Schedule
  6. Characterize the Mission
    • Characterize mission concepts & architectures
    • A design budget is a numerical list of any
      parameters of a system.
      • Budgets are used to ensure that:
      • All of the elements are accounted for
      • Any of the elements is not accounted twice
      • The main design budgets for a spacecraft are:
        • Mass
        • Propellant
        • Power
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7
Q

Describe Mission requirements.

A
  • Quantify how well we wish to achieve objectives.
  • Defines characteristics that can
    • give a deliverable product
    • be quantified
    • be verified
  • We need broad, top-level requirements here.
    • Functional – how well must mission perform?
    • Operational – how must users operate the system
    • Constraints – cost, schedule, policy/law, technology, etc.
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8
Q

Describe Mission constraints.

A

Types of constraints

  • cost
  • schedule
  • policy/law
  • technology
  • sponsor
  • performance
  • etc.
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9
Q

Discuss design drivers.

A

A mission driver is a mission characteristic that has an effect on:

  • Performance
  • Cost
  • Risk
  • Schedule

The drivers can be controlled by mission designers

  • These usually include the number of spacecraft, operational altitude, power, payload size and mass, etc.
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10
Q

Discuss the process of configuration and the
dependence on drivers, requirements and constraints.

A

Spacecraft configuration:

  • the overall arrangement of payloads and subsystems inside the s/c
  • the external architecture of the s/c

Key Trades:

  • Whether or not S/C is delivered directly to operational orbit
  • Propulsion (chemical vs electric vs. none)
  • Attitude control (none, gravity, dual spin, 3-axis)
  • Power (chemical, solar, radio-isotope
  • Payload main driver
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11
Q

Discuss Mission Operations.

A

Set of activities performed by all teams during the active phases of a mission.

  • Should be prepared at earlier phases of mission planning and development (including dev of hardware, software & training of operators).
  • Integrated system of operators, procedures, hardware, software to accomplish mission operations.
  • The strategy of operations to achieve mission objectives and goals within allocated resources and constraints.

Functions:

  • Procurement
  • Training
  • Facility Maintenance
  • R&D
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12
Q

Explain what a spaceport is.

A

A spaceport (or cosmodrome) is a site for launching or receiving a spacecraft or reusable launch vehicles.

It includes the following sites:

  • Launch site for spacecraft for orbits around Earth or interplanetary missions
  • Launch sites for sub-orbital flights for testing or human flights
  • Space stations or bases on the moon for further journeys
  • A site for receiving reusable launchers
  • Aircraft runways for takeoff or landing to support spaceport operations.
  • Infrastructure
  • Technical zone
  • Launchpad
  • Tracking station
  • Rescue & recovery service
  • Additional services
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13
Q

Outline current development in spaceports.

A

8 new spaceports projected according to slide 29. Furthermore, old spaceports are transiting and lease their pads or facilities to other companies. In addition to this, private and commercial spaceports are built. Here the list of spaceports discussed during the lecture:

  1. KSC (Kennedy Space Center) - used by SpaceX, Blue Origin, Boeing, and Lockheed Martin
  2. VAFB (Vandenberg Air Force Base) - used by SpaceX, Lockheed Martin, and United Launch Alliance (ULA)
  3. MARS (Mid-Atlantic Regional Spaceport) - used by Orbital ATK
  4. Spaceport America - used by Virgin Galactic
  5. SpaceX South Texas Launch Site - first private facility of SpaceX
  6. Corn ranch - private spaceport of Blue Origin
  7. Baikonur Cosmodrome - available for many programs
  8. Vostochny Cosmodrome - reduce dependency on Baikonur
  9. Wenchang Launch Center - for Chinese space missions
  10. SDSC (Satish Dhawan Space Center) - for Indian space missions
  11. Rocket Lab Launch Complex 1 - commercial spaceport
  12. Air Launch to Orbit -
  13. Sea Launch to Orbit - commercial launch site
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14
Q

List the main operational tasks in the launching site.

A
  • Launch vehicle integration;
  • Spacecraft checkout and processing;
  • SC and LV combined operations;
  • Launch of launch vehicle.
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15
Q

Understand the spacecraft launching operation.

A

The launch operation is based on
one of the three main portfolios of LV processing at a spaceport:

  1. Horizontal integration and transportation to pad
  • Horizontal integration & processing of a launch vehicle, its mating with a spacecraft and testing of LV-S/C composite at the technical zone;
  • Transportation of the LV-S/C composite to the launch pad in the horizontal position;
  • Erecting the LV-S/C composite and fixing in the launch pad
  • Advantages
  1. No need for tall integration building;
  2. Excellent conditions for LV integration and testing;
  3. No need for complicated transportation /launch platform
  • Disadvantages
    1. Additional testing after erecting LV;
    2. Connection of fuel, gas and electric interfaces with launch pad twice;
    3. Additional requirements of LV and S/C design.
  1. Vertical integration and transportation to pad
  • Vertical integration and processing of launch vehicle, mating with a spacecraft and testing of LV-S/C composite in the technical zone;
  • Transportation of the LV-S/C composite to the launch pad in the position;
  • Advantages
    1. Excellent conditions for propellant, gas, power interfaces connections in the processing building conditions;
    2. Good conditions for LV integration and processing;
  • Disadvantages
    1. Tall integration and processing building needed;
    2. Complicated design of the mobile launch platform;
    3. Additional requirements LV and S/C design.
  1. Vertical integration at the pad
  • Horizontal or vertical integration and processing of separate stages of a launch vehicle at the technical zone;
  • Transport stages separately to launch pad in the horizontal position;
  • Erect each stage at pad and integrate launch vehicle at the launch pad,
    mating with a spacecraft and testing of LV-S/C composite at the launch
    pad
  • Advantages
    1. Simplified launch vehicle integration and processing building;
    2. Simplified transporting facility;
    3. Used experience of military applications.
  • Disadvantages
    1. Difficult testing conditions at the launch pad;
    2. Low launch rate due to an occupation of the launch pad for launch
      vehicle integration and testing;
    3. Additional launch vehicle and spacecraft design requirements.
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16
Q

Name the most important condition to be able to successfully operate a spacecraft, and describe why this is so important.

A

Spacecraft Operations is all about Communication. The spacecraft needs to communicate with the Operations Center via the Ground Station. The Operations Center needs to communicate with the Science Community and with the spacecraft to run the mission. The communication is present during the whole spacecraft operation.

If you cannot communicate with the spacecraft, you cannot control it.

17
Q

Identify the conditions for establishing a good communication link with a spacecraft.

A

Conditions for establishing a communication link:

  • Visibility – you have to be able to ‘see’ it
  • Attitude Control – it has to be pointing at the Earth
  • Power – it needs to be powered
18
Q

Explain how operations steps are organized.

A

Follow the Timeline** and follow the **Procedures

Timelines come from the Operation Concept and the Procedures from the S/C Manual & TM/TC Database. Procedures in a mission are always standardized so you have a checklist and start doing each step.

19
Q

Explain how operations procedures are validated.

A

Validated by keeping track of the procedures you’ve completed and the telemetry received after each step.

What Systems do you Need to Operate a Spacecraft?

  • Development
  • Test & Validation
  • Training/ Simulations

If something goes wrong, you also have a checklist for emergency procedures.

What do you do When Things Go Wrong?

  • Trust your Training
  • Trust the Tested Procedures
  • Use the Simulator
  • Communicate
20
Q

List the typical elements of a ground segment.

A
21
Q

Describe at a high level the test and validation of the ground segment.

A

see slides

22
Q

Describe at a high level which types of spacecraft activities are carried out in routine operations and how these are prioritized.

A

see slides

23
Q

Identify the main characteristics of a mission that determine the operations concept.

A

Operations Concept Largely Determined by:

  1. Spacecraft Orbit
  2. Duration of Ground Station Passes
  3. Level of On-Board Autonomy
24
Q

Give an example of training scenarios and goals needed in preparation for
spacecraft operations.

A

Scenarios & Anomalies

  • Nominal Scenario
  • Easily detectable failures
  • Subtle failures
  • Multiple minor failures
  • One major failure
  • Distraction during critical activity
  • Replacing key players

Goals

  • Familiarisation
  • Efficiency
  • Monitoring skills & support
  • Coordination & concentration
  • Multiple input & accuracy
  • Focus & prioritization
  • Flexibility & cross-training
25
Q

Give some thought to the evolution of operations considering the current trends.

A
  • Autonomy & Automation
  • Increased Data Volumes
  • CubeSats / SmallSats
  • Constellations
  • Distributed Operations
26
Q

Explain orbital rendezvous.

A

The first spacecraft must arrive at the same place and at the same time as the second spacecraft.

  1. Coplanar rendezvous
    • Timing is critical
    • Transfer and wait time depending on angular velocities
  2. Co-orbital rendezvous
    • To perform a coplanar rendezvous, the interceptor needs to enter a phasing orbit which will return to the same spot after one orbit at the time the target arrives there. Because the orbit will be changed when the interception happens. The phasing orbit helps the interceptor to come back to its original orbit.
    • This is achieved by slowing down, which causes the interceptor to enter a smaller orbit which has a shorter period.
    • ΔV1 slows the interceptor down and puts it into the phasing orbit.
    • ΔV2 returns the interceptor to the original orbit to rendezvous with the target.

Note that ΔV1= ΔV2

27
Q

Describe the basic steps involved in getting from one planet in the solar system to another.

A

Co-ordinate system:

  • Heliocentric (Sun-centered)
  • Ecliptic (in the plane of the Earth’s orbit)

The vernal equinox is however required for direction.

Transfer time and phasing of planets key!

synodic period - angular arrangement of planets needs to align to reduce time and assure planet position upon arrival

  1. Patched conic approximation
  • Earth, sun, target gravity sources
  • Consider one gravitational field at a time (3 smaller two-body problems)
  • SOI - depends on mass & proximity to the Sun
  1. Sun-centered transfer from earth to the target planet
    • Sun’s gravity dominates
  2. Earth Departure
    • Starts in a circular parking orbit and fires engines to enter a hyperbolic escape trajectory.
    • Coasts to the SOI boundary.
    • Enters the heliocentric elliptical transfer orbit.
  3. Target Arrival
    • here the target’s planet gravity predominates

After coasting along the interplanetary trajectory, the spacecraft:

  • Arrives at the boundary of the SOI.
  • Coasts on a hyperbolic arrival trajectory.
  • Fires its engines to enter a circular parking orbit.
28
Q

Explain how we can use the gravitational pull of planets to get “free” velocity changes, making interplanetary transfer faster and cheaper.

A
  • Earth’s Sphere of Influence (SOI) defines an imaginary boundary in which the Earth’s gravitational pull dominates.
  • If a spacecraft in the planet’s SOI passes behind the planet, it is pulled in the direction of the planet’s motion.
  • As a result, it gains velocity with respect to the Sun and leaves the SOI on a different heliocentric trajectory.
  • If a spacecraft passes in front of a planet, it is pulled in the opposite direction.
  • As a result, it loses velocity with respect to the Sun and again leaves on a different heliocentric trajectory.
  • These techniques are known as the gravity-assist technique.
29
Q

Appreciate pico/nanosatellite ‘CubeSat’ technologies & how their operations differ from (typically larger) commercial missions from FUNcube&Surrey.

(not sure this question is relevant)

A
  • History: Bob Twiggis invents the concept of CubeSat: 1kg, 10x10x10cm. The US Government stimulates the concept and promotes the idea with USD 1 million in US Universities. In 10 years from 2000, 150 CubeSats missions are flown.
  • Reliability: after 15 years in orbit, the average Sat has reliability between 90% and 95%, mini- and microsats 30% - 40%, nano- and picoSat nearly zero.
  • General Recommendations:
    • redundant systems increase reliability;
    • COTS subsystems do NOT guarantee reliability;
    • keep each system as simple as possible;
    • single master-bus architecture to be avoided (single point of failure);
    • longer development time does not guarantee higher reliability.
  • What CubeSats are good for?
    • Education (Surrey STRAND program), Technology demonstration.
  • What frequency do CubeSats transmit?
    • 437 MHz (more than 100 CubeSats)
30
Q

Understand the advantages and disadvantages of CubeSats/SmallSats. Discuss new distributed satellite missions.

A
  • Advantages:
    • cheaper satellites mean more satellites in orbit and quicker/more data points;
    • could be used to remove (or create) debris;
    • Faster return of science and application data
    • Shorter development time
    • Lager variety of missions
    • Risk / Cost Reduction
    • Greater involvement of regional industry
    • Shorter Revisit times → Constellations, Body Pointing
  • Missions
    • ESA and NASA are looking for using CubeSats for exploring Moon and Mars.
    • 57% of demand for 10-150kg SmallSat
    • 32% Technology
    • 28% EO
    • 21% Science
    • 14% Telco
    • 14% other

ISU M2 (16 decks)

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