Questions tagged [astrodynamics]
The study of satellite orbits and space flight dynamics.
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What ways can a University Student get involved in Trajectory Design?
As a physics student (not an engineer) in India, I can't seem to find a lot of opportunities to involve myself in what I find most appealing about what I'm studying in University i.e. astrodynamics. ...
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Differences between Semi Major Axes and ECF Magnitudes for Circular Orbits with J2 Perturbation
I have simulated (in STK) a satellite at near circular orbit, near-equator, with Brouwer Lyddane Mean Long SMA of 6935.31km, inclination 10 degrees, and eccentricity of 0.0001875 (these are solved-for ...
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2answers
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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 ...
5
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1answer
292 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 ...
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1answer
354 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 ...
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2answers
183 views
How big a nuke would be needed to break Phobos out of orbit?
Phobos
Radius: 11.267 km
Orbital period: 8 hours
Equatorial rotation velocity: 11.0 km/h (6.8 mph) (at longest axis)
With an 8 hour orbit around Mars it must be going at a fair clip already which ...
6
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0answers
106 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 ...
3
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1answer
140 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 ...
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77 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 ...
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1answer
114 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, ...
2
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1answer
245 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 ...
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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/...
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1answer
75 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 ...
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2answers
100 views
Properly calculating G-factor
This may sound rather simple, but I was told that technically, G-force readout should actually indicate zero-G on the earth's surface, as well as in a stable orbit. This is due to the fact that G-...
2
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2answers
184 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?
...
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1answer
122 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. ...
2
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2answers
220 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, ...
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1answer
73 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 ...
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0answers
221 views
Use of thrusters for Collision Avoidance Maneuver
I'm building an orbit propagator that gives the position of two satellites at time T. The position are expressed in ECI and after that are being transformed in LVLH frame (as mentioned ECI to LVLH ...
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0answers
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Help needed with obtaining position vector of Spacecraft in Heliocentric-Ecliptic frame
I have been now using the ephemeris table attached as an image. It gives the orbital elements of all planets on Jan 1 2000 calculated from Heliocentric-Ecliptic frame. The current planetary orbital ...
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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 ...
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1answer
436 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}=...
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1answer
151 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 ...
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2answers
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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 ...
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1answer
164 views
Angular momentum in non inertial frame [closed]
How to express the angular momentum in non inertial Earth frame like Earth Fixed frame so that angular momentum is conserved ?
Is H = R x mV still valid when R and V are taken in the rotating frame ?
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1answer
352 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 ...
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0answers
356 views
How to find Near Rectilinear Halo Orbits (NHROs)?
Looking all the good questions and answers in this site referent to CR3BP dynamics, periodic orbits, state transition matrices, etc. I wonder:
what algorithm or steps do I have to follow to find the ...
2
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1answer
752 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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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?
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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 ...
3
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2answers
199 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 ...
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0answers
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Attitude and orbit thrusters catalog
Typically, when trying to adjust simulation parameters (of orbit control, attitude control...) to real world values in order to validate algorithms with comparisons with past and current mission ...
2
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1answer
222 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 ...
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0answers
361 views
How to derive the differential equations of motion for a dumbbell system ,eg. dumbbell satellites around earth?
From Eq. 2.13 from Orbital Mechanics for Engineering Students (Curtis, 2005) the equation of relative motion between two bodies orbiting around a center of mass can be written as:
$$\ddot{\mathbf{r}}...
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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 ...
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1answer
673 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 ...
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1answer
453 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 ...
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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) ...
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2answers
457 views
Calculating hyperbolic orbit elements for interplanetary intercepts
As part of a final year project at university I'm currently trying to simulate an interplanetary transfer between Earth and Mars for a manned mission. The ultimate aim is to use NASA's GMAT to ...
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3answers
434 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, ...
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3answers
559 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 ...
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1answer
769 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 ...
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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. (...
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2answers
167 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 ...
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1answer
414 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 ...
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4answers
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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 ...
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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 ...
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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-...
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1answer
940 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 ...
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1answer
416 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?
