Bahnmechanik halt


Set of flashcards Details

Flashcards 29
Language Deutsch
Category Physics
Level University
Created / Updated 07.08.2016 / 15.01.2021
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Inertial Reference Frame

An inertial reference frame is a refrence frame with respect to which a particle remains in rest or uniform rectilinear motion if no resultant force acts upon that particle.

Inertialsystem --> Bezugssystem, in dem sich kräfterfreie Körper geradlinig und gleichförmig bewegen. 

Consequences Inertial reference frame

- Direct transformation between multiple reference frames is possible only if none of the frames have a relative rotation. 

- circular reasoning in the def. of Newton's laws.

- Pseudo IRF: e.g. for a short flight neglecting earth's rotation. 

 

Vernal Equinox (Äquinoktium)

Astronomical event in which the plane of earth's equator passes the center of the sun. Marks the beginning of spring in northern hemisphere. 

--> day as long as the night

Sidereal time (Sternzeit)

--> 23 h 56 min 4,091 sec

The duration of rotation of earth with respect to vernal equinox

- beruht auf scheinbarer Bewegung der Sterne

- Ein Sterntag ist die Dauer, die der Sternenhimmel (genauer: der Frühlingspunkt) für eine ganze scheinbare Umrundung der Erde benötig.

Laplace plane

Mean or reference plane about whose axis the instantanious orbit plane of a satellite precesses. Plane perpendicular to a systems mean angular momentum vector.

--> über lange Zeit gemittelte Bahnebene eines Körpers auf einer Umlaufbahn.

Consquences of n-body-problem

- no analytical solution 

- the center of mass of an n-body-problem does not experience an acceleration

- a non-rotating reference frame at the center of mass of all bodies in the universe is the primary IRF

- singularity at collisions

Three body Problem (a) Warum keine analytische Lösung? b) Tricks?)

a) Für den Fall n>=3 sind die Bewegunsintegrale nicht mehr algebraisch und somit nicht mit elementaren Funktionen lösbar.

 

b) - Masse eine der Körper als vernachlässigbar klein annehmen 

- Gleichgewichtsfall lösbar

- für den Fall identischer Massen exisitiert eine Lösung "unendlich"

Two-body-Problem (a) Assumptions, b) Spere of influence, c) Use)

a)

- the effect of bodies outside the sphere of influence can be neglected

- Force between bodies acts along the line between their positions

- the motion is planar

 

b) - the oblate-spheroid-shaped region around a celestial body where the primary gravitational influence on an orbiting object is that body

 

c)

- Satellite orbiting a planet

- planet orbiting a star

- motion of space probe 

Lagrange Points

Points in an orbital configuration of two large bodies where a smaller body affected only by gravity can maintain a stable position relative to the two large bodies. 

Ellipse (T, E, M, a, e, Flight path angle)

T --> Wahre Anomalie: Winkel zwischen der Verbindungslinie S/C-Fokuspunkt und Perigäum.

E--> Exzentrische Anomalie: Winkel zwischen Perigäum und S/C-Position projiziert auf einen Hilfskreis.

M--> Mitllere Anomalie: Winkel zwischen Perigäum und S/C-Position für konstante Winkelgeschwindigkeit

a--> große Halbachse

e--> Exzentrizität

Flight path angle: Angle between S/C-V-Vektor and local horizontal

Roche-limit

Distance where a celestial body, held together only by its own gravity, will disintegrate due to a second celestial body's tidal force exceeding the first body's gravitational self-attraction. 

Two line elements

Data format encoding a list of orbital elements of an earth-orbiting object for a given point in time, the epoch.

--> Elemente werden als Ziffernblöcke in zwei Zeilen dargestellt

--> Tracking-Programme, um Satelliten in Echtzeit zu verfolgen

Ellipse/Hyperbel/Parabel

Ellipse e<1

Parabel e=1

Hyperbel e>1

3D-Kepler-Orbit

- i --> Inklination: Neigung der Bahneben

- "GroßOmega" --> right ascension of the ascending note

- "KleinOmega" --> argument of the pericenter

- u=KleinOmega+Theta --> argument of latitude

Orbital perturbations Def. and Examples

- perturbations: complex motion of a massive body subject to forces other than the gravitational attraction of a single other massive body

- Bahnstörung: eine Abweichung der tatschächlichen Flugbahn eines Himmelskörpers von der anhand eines Modell berechneten Flugbahn

 

Ex.: 

- Sun (2nd)

- irragularities of gravitational force --> J2 (1st, earth flattened, oblate spheroid)

- atmosphere

- Solar radiation (2nd)

- relativity (3r)

 

Solar min/max --> when to start?

start at solar minimum --> atmopsheric density is lower

Influence of atmospheric drag on elliptical orbits?

Atmospheric drag causes a circularization of the orbit

Patched conics

Approximation of an interplanetary trajectory, splits the problem into a series of consecutive 2-body-problems

specialized orbits (and the main characteristics)

- geosynchronous (orbit period: 1 day)

- geostationary (fixed position with earth)

- repeat (groundtrack repeats after k orbits, j days)

- sun-synchronous (orbit plane fixed with sun)

- Molnija (stable pericenter)

- Lagrange point (fixed with two main bodies)

- frozen (stable pericenter and eccentricity)

- static (fixed with earth and sun)

- interplanetary escape (dealing with 2 spheres of influence)

Hyperbolic excess velocity

Under standard assumptions the body travelling along a hyperbolic trajectory will attain at infinity an orbital velocity called "Vinfinit"

Vinfinit=(mhu/(-a))^(1/2)

True horizon

The view of the horizon without any disturbances (true h=(13*h)^(1/2))

Unit sphere

Set of points of distance 1 from a fixed central point where a generalized concept of distance may be used 

Dual-axis-problem

The computation of a groundtrack is a dual-axis-spiral problem (for zero-eccentricity satellites)

- Rotation along primary axis must include earth's rotation

- Rotation along secondary axis is orbital motion around orbital pole

Astrodynamic basic principles

1. Newton's three laws of motion

2. Kepler's Law

Deltav-Budget (why necessary?)

- needed to enter into heliocentric orbit or into parking orbit around target planet

- Abschätzung des gesamten Deltav, welches für die Mission benötigt wird

- Summe aller Deltav benötigt für Antriebsmanöver während der Mission

- gibt an, wie viel Treibstoff für ein RFZ benötigt wird

- needed for plane changes

- needed to exit from and enter into orbit

radial component of perturbation

can have an effect on both semi-major axis, eccentricity and epoch of the pericenter passage  

basic requirement types

- functional requirements: how well it must perform

- operational requirement: how it is to be used

- constraints: what limitations are imposed on the system

Genetic Algorithm

- Initial population (random fill)

- Parent selection (random or weighted selection)

- Recombination (random intersection point)

-Mutation (probability)

 

--> GA is similar to Darwinian evolution in nature

--> Objectives: maximize number of red components in puppet

Crosstrack

"Querabweichung"  --> bezeichnet in der Navigation den Abstand zwischen der geplanten Route (gegeben durch zwei Wegpunkte) und der tatsächlichen Position