Questions tagged [astrodynamics]

The study of satellite orbits and space flight dynamics.

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106
votes
13answers
52k views

What are the choices today for orbital mechanics simulation software?

I used to be familiar with the various choices out there for orbital mechanics simulation software. Alas, those days are gone. What are the choices today, preferably sorted by platform? This ...
30
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3answers
5k views

Orbiting Earth before heading to Moon

Each of the lunar Apollo missions (Apollo 8-17) entered Earth orbit immediately after launch. Each mission then left Earth after a few orbits by burning the S-IVB engine, and headed off to the Moon. (...
17
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1answer
2k views

What branches of mathematics are widely used in astrodynamics?

We knew that Voyager 1 and 2 exploited the gravitational slingshot from Saturn and Jupiter back in 70s, and the trajectories were predicted by Newton's laws of motion, and this law we used a lot in ...
16
votes
1answer
740 views

How important is plume impingement in rendezvous operations?

When performing space rendezvous operations close to the target vehicle (0-5 m relative distance), pursuer thruster escape nozzle gases can hit the target if firings are done in the direction of ...
13
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1answer
2k views

How to choose the best direction to leave Earth's sphere of influence?

What direction is optimal for spacecraft to leave Earth's sphere of influence (SOI) when it's going to an outer or inner planet? Let's presume that we have a spacecraft in a circular LEO (ecc=0.0). ...
11
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3answers
443 views

How is the trajectory of spacecraft transferring between planets monitored?

The doppler effect can give a pretty measure of radial speed relative to Earth, and radio transmissions can narrow down the radial position, but what about everything else? I can imagine several ways, ...
11
votes
1answer
487 views

Is it possible for moons to have their own moons?

I'm wondering, if it's possible for moons to have their own natural satellites, something big enough to be spherical? Stars have planets, planets have moons. Is it possible that moons have moons too?
10
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1answer
410 views

Why is FORTRAN recommended for astrodynamics rather than MATLAB?

I understand that FORTRAN might be faster in terms of computation time, but I don't understand why it is always recommended by people in the field. Everyone tends to avoid MATLAB for astrodynamics; is ...
10
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1answer
600 views

What are the practical uses of a state transition matrix?

I am studying different dynamical models of relative motion of satellites. In my work, I've always just used a numerical integrator like RK78 to integrate the cartesian system of equations: $\dot{r}=...
8
votes
2answers
816 views

How to find orbital elements of a binary system

I'm trying to find the rate of precession of a binary system consists of two similar mass stars A and B, so I need to find the value of the argument of periapsis $\omega$ first, with velocity and ...
8
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1answer
77 views

Increase in period and semi-major axis following near head-on collision between Cerise and Ariane debris (1996)

This report describes the collision of the French satellite Cerise with a piece of Ariane rocket debris (object no. 18208) in 1996: http://articles.adsabs.harvard.edu/cgi-bin/nph-iarticle_query?...
8
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0answers
113 views

Why haven't there been more space missions that use low-energy trajectories?

The Wikipedia article on low-energy transfers lists only 4 spacecraft over the past decades that at some point of the mission navigated low-energy trajectories, yet there has been extensive research ...
7
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4answers
3k views

What is the difference between Space Dynamics & Astrodynamics in the engineering perspective?

Within the context of Aeronautics, there are seemingly different meanings corresponding to Space Dynamics and Astrodynamics. What is the difference between them in an engineering perspective, such as ...
6
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1answer
132 views

Calculation of V1 (orbital speed) during ascent

I am studying instrumentation of NASA's Orion spacecraft, and there is a readout for V1 (I am assuming this is the "first orbital velocity", for circular orbit), and it seems to be in small decimals. ...
6
votes
1answer
470 views

How to numerically solve an optimal thrust-vectoring problem?

This question is a follow-up to this question and is linked to this question, where if needed more details can be found on the parameters used in the following. For an in-plane non-impulsive orbital ...
6
votes
1answer
360 views

Can we go anywhere in space with only THREE reaction wheels and ONE chemical thruster?

I had a discussion the other day with some of my peers and they were very keen on the fact the it is possible to change your orbit as desired using a single thruster and a three reaction wheels. The ...
5
votes
2answers
127 views

How does a Mars lander reach a chosen landing site?

I see lots of questions how landing sites are chosen, but none so far how these landing sites are reached. It already looks like magic how the target planet can be reached at all, but when are ...
5
votes
3answers
569 views

notation to describe an elliptical orbit? (3000km x 40000km)

For a project a professor assigned, he described an elliptical orbit by using the notation: (3000km x 40000km). Ive never seen this notation before and couldn't find much help online. I just assumed ...
5
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1answer
198 views

Why is there a singularity in Lambert solutions for transfers of pi-multiple degrees?

Lambert provides a solution as long as the transfer angle is not 0, 180 or 180-multiple degrees. Why is that?
5
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1answer
2k views

How to derive the polar form of the equations of motion?

As part of an optimal control problem (see linked problem), I need the polar form of the equations of motion (EOM) defining the orbit of a spacecraft. In e.g. Bryson and Ho (1969) and Vallado (2007) ...
5
votes
1answer
149 views

Launch vehicle trajectory tool for ascent phase to orbit using PYTHON

Currently, I am developing a trajectory optimization tool for launch vehicle from lift-off to orbit using python for my project. Since I'm new to optimization problem, I am finding it hard to ...
5
votes
1answer
83 views

Trouble deriving rectangular components of acceleration of satellite in orbit around Earth with J2 consideration

I am trying to derive the rectangular components of acceleration for a satellite in orbit, with Earth oblateness in consideration, in order to use the RK4 method to find the updated position and ...
5
votes
1answer
970 views

How to model a continous burn and recalculate orbit properties post burn

I've been working on this for a while with little success. I'm trying to model a continuous burn orbit maneuver for say 5 minutes. I've tried to split the burn into multiple sub-burns that are ...
5
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1answer
88 views

How to implement a relative motion STM without any numerical integration

I am trying to program the Gim-Alfriend state transition matrix. You can read all about it here. The GA STM is a complex analytical model that maps relative motion of a deputy satellite in a ...
5
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0answers
81 views

Russian Soyuz MS-09 Launch - back and forth rotation of the second stage (along the length axis). Precession?

In the ISS Expedition 56-57 Launch of Russian Soyuz MS-09, in the first view from the external camera at around 3:30, an obvious back and forth rotation (along the length axis) of the rocket can be ...
5
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0answers
154 views

Small-bodies landing strategies

Looking at past landing missions on small bodies such as Eros, Itokawa and 67P I found different landing strategies Eros: NEAR Shoemaker probe performed 4 impulsive pre-planned open-loop maneuvers to ...
5
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0answers
232 views

Trajectory optimization [closed]

I'm confronted to a problem of trajectory optimization. The problem consists in going from point A to point B in the Hill frame (relative navigation) subject to a dynamics described by Clohessy-...
4
votes
3answers
110 views

Speed at aphelion is decreasing for Parker Solar Probe with each new orbit despite being closer to the Sun

Sorry for the really bad picture I am looking at some data from the Parker Solar Probe mission and I was looking at the speeds of PSP at perihelion and aphelion at each new, different, orbit (the ...
4
votes
1answer
124 views

Could you track small particles in space and could you control their position with lasers or reflected light?

If you released a large amount of small but precise particles (the size of glitter or confetti) is space, between a group of cube sats. Could you track the particles with cameras and/or lasers? And ...
4
votes
1answer
185 views

Is the amount of accurate information in a TLE equal to that of a single state vector?

My question is basically regarding whether there is orbital information "lost" when converting from a Two Line Element set (TLE) to a state vector. Given that the following are true: I have a TLE, ...
4
votes
1answer
96 views

Does Kepler's Method for Determining Time of flight between two True Anomalies break down with eccentricities approaching 1?

Pretty simple question here. I'm calculating time of flight between two true anomalies by converting those true anomalies to mean anomalies and using the following equation: $\Delta t = t_2-t_1 = \...
4
votes
1answer
40 views

How can I generate Chebyshev cofficients from SPICE for J2000 Inertial to Moon ME Frame?

I want to extract the Chebyshev coefficients in order to be able to calculate the time-varying transformation from the ICRF / J2000 Inertial frame to the Moon ME (moon mean earth) frame. I know I can ...
4
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0answers
41 views

Does the short-angle solution of Lambert's Method break down for very Delta-V intensive maneuvers?

Just a (hopefully) quick qualitative question that I'm having a bit of trouble extracting from the literature: I've implemented a universal-variables Lambert's method in python, and it has been ...
3
votes
2answers
218 views

Spacecraft Horizon Sensors for Lunar orbit

Recall that "traditional" horizon sensors for Earth missions utilize the IR wavelength regime since this can reveal a good contrast between the cold space and the warm Earth-limb edge. If we were to ...
3
votes
1answer
427 views

Calculate time to impact on elipisoid Earth

As a simple project to introduce myself to orbital mechanics I'm attempting to calculate impact times of an object close to Earth. Right now I am using only Keplerian mechanics (no air resistance or ...
3
votes
1answer
148 views

What forces a spacecraft, returning from Earth orbit, to synchronize with Earth spin?

This seems like a banal question, but the more I think about it, the less I understand the mechanics of it. Does the progressively denser atmosphere pick up the spacecraft and carries it along the ...
3
votes
1answer
363 views

Converting UT1/UTC to Julian Date

I am reading about the algorithms to convert from date and time format to Julian Date from the Fundamentals of Astrodynamics and Applications by Vallado (4th Edition) p183. My question is ...
3
votes
1answer
559 views

Transformation between ICRF and Fixed in STK

I am building a satellite orbit propagator in MATLAB and I am using STK as a reference. Comparing TwoBody propagator using RKN78 (MATLAB) with HPOP (degree 1, order 1), I am getting quite good ...
3
votes
0answers
89 views

Can we calculate elliptical properties in a spherical coordinate system?

Can we calculate the elliptical properties like the semi-major axis and eccentricity using the state vectors (position and velocity) in the spherical coordinate system? http://www.braeunig.us/space/...
2
votes
2answers
7k views

Does the speed of ISS slow down at the time of a spacewalk or does it become stationary?

The International Space Station (ISS) is orbiting at nearly 7.66 km/s. At such high speeds, how do astronauts perform tasks outside the ISS? Or is it all relative like astronauts are having same speed ...
2
votes
2answers
111 views

Is it more efficient to burn all needed fuel in an Oberth manoeuvre at once or burn a fraction of the fuel for each orbit?

I was looking into Parker Solar Probes trajectory and was wondering what would be the most optimal way to utilize a retrograde thrust at perihelion to reduce the number of needed gravity assists. I ...
2
votes
2answers
196 views

Is a solar free-return trajectory possible?

I'm coining a new phrase: "Dyson circuit". Is it possible, with current solar orbital capabilities (see Parker Solar Probe), to drive artificial satellites in a free-return trajectory around the Sun? ...
2
votes
1answer
900 views

What is the amount of Delta-V required to enter lunar orbit following Trans-Lunar Injection?

How much do you need to decelerate in order to be captured into a stable lunar orbit from a Trans-Lunar Ejection or TLI-type trajectory?
2
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2answers
168 views

Libration points - Science prospects

There have been quite a few missions to libration points. As far as the dynamical possibilities are concerned, libration point vicinity offers a spectrum of orbit profiles. What science data is not ...
2
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2answers
258 views

Orbit, circularizing, apogee/perigee

First - my question: After the orbit insertion, in the coast stage, and assuming perigee is out of the atmosphere, and neglecting any external forces and influences - is the orbit now "fixed"? As in, ...
2
votes
1answer
793 views

Determine the eccentricity of the orbit

A satellite is in orbit at an altitude of 62.5km, with a speed along the earth-relative position vector of 3.98km/s, and a speed perpendicular to the earth-relative position vector of 7.763km/s. What ...
2
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1answer
106 views

If a spacecraft is orbiting around the Moon, what direction would the nadir axis be?

Nadir for a craft orbiting the Earth would be radially in, is nadir always pointed towards the Earth or is it pointed towards the celestial body that the craft is orbiting?
2
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1answer
232 views

Reference frames - why do I need to convert to Geocentric Equatorial State Vector to solve equation of motion?

I am asking this question in relation to an example shown in the 'Orbital Mechanics for Engineering Students' book by Howard Curtis (third edition) pp659 example 12.1. The example is demonstrating how ...
2
votes
1answer
45 views

Determining orbital elements from r and v vectors - Fundamentals of Astrodynamics Example Problem

I am fighting my way through Fundamentals of Astrodynamics 1st edition for the fun of it. I have made it up to section 2.4 and have successfully completed all the example problems and chapter ...
2
votes
1answer
166 views

What liquids last the longest in space?

I am trying to find something that is somewhat stable as a liquid in space. What happens to various liquid elements and compounds in a vacuum? Is there a list or table of the effects of local space ...