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Spaceflight > I2S - Lecture 4-5 > Flashcards

I2S - Lecture 4-5 Flashcards

1
Q

State Kepler’s laws of Planetary Motion

A
  1. Law = each planet’s orbit about the Sun is an ellipse. The Sun’s center is always located at one focus of the orbital ellipse.
  2. Law = the imaginary line joining a planet and the Sun sweeps equal areas of space during equal time intervals as the planet orbits.
  3. Law = the squares of the orbital periods of the planets are directly proportional to the cubes of the semi-major axes of their orbits. Kepler’s Third Law implies that the period for a planet to orbit the Sun increases rapidly with the radius of its orbit.

https://science.nasa.gov/resource/orbits-and-keplers-laws/

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2
Q

How changes the total energy of an object in an orbit?

A

The total energy is always constant, sum of potential energy (gravitation, bigger the further away) and kintetic energy (velocity)

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3
Q

What are the six orbital elements?

A
  1. Semi-major axis (a), orbit size
  2. Eccentricity (e), orbit shape
  3. Inclination (i), between orbit plane and plane of reference
  4. Right Ascension of Ascending Node (RAAN), angle between reference direction and ascending node
  5. Argument of periapsis (w), angle between plane of reference and orbit plane
  6. True anomaly (v), angle between periapsis and location of body
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4
Q

What reference point is mostly used for Earth?

A

First Point of Aries (Vernal point), was orignally in the constellation Aries, till it moved due precession of Earth’s axis. It is shared by the equatorial and elliptical coordinate system and is used to specify the direction of the x-axis

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5
Q

When and what are the nodes called, when sun and earth are in line towards the first point of aries?

A

Vernal equinox: March 21
Autumnal equinox: September 23 (Ascending Pov Earth)

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6
Q

State the reference frames, depending on the origin point of the coordinate system

A
  • Heliocentric (Origin in the center of the sun)
  • Geocentric (Origin in the center of the Earth)
  • Topocentric (Origin in the observation point)
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7
Q

What is the Ground Track?

A

A ground track or ground trace is the path on the surface of a planet directly below a satellite’s trajectory

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8
Q

What are GSO and GEO?

A
  • GSO = Geosynchronous orbits = circular orbits with a period of 24 hours
  • GEO = Geostationary orbit = a GSO with i=0, therefore it hang motionsless above one position and are ideal for some types of communications and meteorological satelllites
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9
Q

What is the approximate orbital period for objects in LEO?

A

Approx. 90min (260km) up to 105min (1000km)

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10
Q

What are the Footprint and Access Area?

(Satellite)

A
  • Access Area = Area that a given instrument could potentially see at a given moment
  • Footprint Area = Area that the instrument sees at a given moment
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11
Q

What is HEO, which orbits of it are common for satellites and why should one use them?

A
  • HEO = highly elliptcal orbit
  • Molniya / Tundra Orbit
  • Due its elliptical form, it stays for long time of its orbital period over specific areas of earth
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12
Q

What does the Tsiolkovsky equation do?

A

(Rocket equation)
It relates the delta v (max change of velocity) with the effictive exhaust velocity c_e, initial mass m_0, and final mass m_f of a rocket

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13
Q

What is a fuel efficient way to transfer between orbits?

A

Hohmann transfer, elliptical transfer orbit tangent to the initial and final orbits

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14
Q

Where does the s/c velocity change for plane change ( a = const)?

A

If we want to change only the orbits’s inclination or RAAN, we must change the velocity at either the ascending node or the descending node

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15
Q

Where in an elliptical orbit, should a orbit-change maneuver happen?

A

In an elliptical orbit, the maneuver should take place at the apoapsis where velocity is at his minimum

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16
Q

What is a rendevous?

A

This maneuver is used to let s/c meet with another one (same orbit and same place/time)

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17
Q

What is the bi-elliptical transfer?

A

It consists of two half-elliptic orbits. First burn expends delta-v into a transfer orbit with expanded semi-major axis, second burn at the apoapsis sends the s/c at the desired radius. 3rd burn injects the s/c into the desired orbit

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18
Q

What are the advantages/disadvantages of the bi-elliptic transfer?

A
  • (+)lower delta-v than HT if ratio of final to initial semi-major axis is >= 11.94
  • (-) in general more travel is required
  • one more burn is needed
19
Q

What is a gravity assist manoeuvre?

A

Is the use of the relative movement and gravity of a planet to alter the path and speed of a s/c, typically to save propellant and reduce expense.
Orbit pumping = changes magnitude of velocity
Orbit cranking = change direction of travel

20
Q

With what planets did Voyager 1 and 2 swing-by’s?

A
  • Voyager 1: Jupiter, Saturn
  • Voyager 2: Jupiter, Saturn, Uranus and Neptune
21
Q

What types of interplanetary trajectories are there?

A
  • Type I: If the interplanetary trajectory carries the s/c LESS than 180 deg around the sun
  • Type II: If the trajectory carries it 180+ deg around the sun
22
Q

Realism vs Model
What’s the difference wrt to in-space manoeuvres?

A

An impulsive manoeuvre is the mathematical model of an instantaneous change in velocity, however in the physical world this is not possible as a “infinite force” during an “infintite short time” is required. Anyway the approximation as impulse describe the effect of a manoeuvre on the orbit well enough (for us atleast)

23
Q

What are the two main types of atmospheric entries?

A
  1. uncontrolled entry, space debris, metroids etc
  2. controlled entry (re-entry), s/c capable of following a predetermined course. Technologies allowing the controlled atmospheric entry, descent, landing (EDL)
24
Q

At which altitude occours atmospheric entry for earth?

A

Entry occours by convention at the Karman line at an altitude of 100km

25
Q

Describe the two shock wave forms that results from re-entry

A
  1. Attached shock wave (streamlined) - shock wave may attach to the tip and transfer a lot of heat
  2. Detached shock wave (blunt) - shock wave will detach and curve in front of the vehicle, leaving a boundary of air between the shock wave and the vehicle’s surface
26
Q

Describe the re-entry corridor

A

A three dimensional corridor through which a re-entry vehicle must pass to avoid skipping out ( =overshoot, too little drag) or burning up (=undershoot, too much deceleration)

27
Q

What parameter do you need to consider for re-entry?

A
  • Re-entry velocity and flight-path angle
  • Vehicle size and shape
  • Thermal-protection systems
28
Q

What is aerobraking?

A

A spaceflight technique wherein a s/c brushes against the top of planetary atmosphere. The friction against the surface of the s/c slows down
-> saves cost and mass

29
Q

What are the building blocks of self-sustaining space mobility?

A

Propulsion, Power, Radiation, Communication, Navigaton, and Ressource extraction, refining, storage,…

30
Q

What are the criterions to pick a space transportation system?

A
  • Performance - is it capable to perform the manoeuvre
  • Price
  • Availabilitiy (time) (+Launch site)
  • Reliability
  • Service level
31
Q

What are two common staging methods?

A
  • Tandem/Sequential = launcher consist of more than one stage that are operational sequentially (more stages = higher delta-v, higher complexity/cost)
  • Parrallel = stages burn simultaneously (high accelerations and aerodynamic resistance)
32
Q

What are the satellite classes?

A
  • Large = > 1000kg
  • Mini Smallsats = 100-1000kg
  • Micro = 10 - 100kg
  • Nano = 1 - 10kg
  • Pico = 0.1 - 1kg
  • Femto satellite (on a chip) = 0.01 - 0.1kg
33
Q

Rank the launch distribution?

A
  1. North America
  2. Asia (China)
  3. Europe
34
Q

How much cost access to space?

approx 2020

A

1.8k up to 25k$

35
Q

State some main components of a launch system

A
  • Structure incl. mechanisms and payload adapters
  • Propulsion subsystems
  • Electrical subsystem/ software
  • Thrust-Vector control
  • Altitude control
  • Seperation subsystem
  • Pyrotechnical chain
  • Re-entry thermal protection
  • Recovery / Landing
36
Q

State two launch system configurations

A
  • Horizontal take-off
  • Vertical take-off
37
Q

What is a optimal trajectory to launch from earth?

A

There are two major losses (drag and g-t), when minimize one of them, the other increases. The optimum lies somewhere between them.
(To limit drag, fly straight up, to limit g-t loss, fly perpendicular to earth)

38
Q

Name some launch sites and their respective launch velocities

A
  1. Sea launch (equator, 0°) - 464 m/s
  2. Kourou (5.2°) - 463m/s
  3. Canaveral (28.5°) - 408m/s
  4. Baikonour (51.6°) - 288 m/s
  5. Plesetsk (62.7°) - 213m/s
39
Q

What impact does launch sites have on the launcher?

A

Earth’s rotation provides a dv, which has advantages for GTO, but disadvantages for SSO or polar orbits. Additionally the “inclination” ( = further away from equatorial plane) dictates the inclination of the initial orbit.

40
Q

Where is the Ariane 5 launch pad?

A

Kourou, French Guiana

41
Q

From where started the Space Shuttle or Falcon 9?

A

Florida, USA

42
Q

What is the ESTRACK?

A

ESA Tracking Network designed to support ESA’s s/c missions by providing tracking, telemetry, command, and data reception services.
Some key ground stations are in Australia, Spain, Argentina, French Guiana, and Portugal.
Furthermore collaborates ESTRACK with other space agencies through cross-support agreements

43
Q

Regarding reliability of the engines, what is the difference between launchers and aviation?

A

Engines in launchers are by far the most unreliable subsystem, while engines in aviation are by far the most reliable subsystem

44
Q

What is a average time for launchers to reach LEO?

A

LEO = it takes usually around 10min (Falcon 9)

Spaceflight (8 decks)

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