# Questions tagged [orbital-mechanics]

Orbital mechanics or astrodynamics is the application of ballistics and celestial mechanics to the practical problems concerning the motion of rockets and other spacecraft. For the movements of celestial bodies, see [celestial-mechanics].

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### Nickname and citation for famous, historic three-body spacecraft trajectory design “manual”; something like “DoKaRoMo”?

There is a heavily-cited work about the use of three-body orbits with four authors, I think some at NASA at the time. I know that I've cited this abbreviation in my own posts a few times, but I can't ...
94 views

### Why does it cost more to get to L4/5 than C3=0?

I was looking at Delta-V budgets and noticed that it costs 4.1 km/s to get from LEO to L4/5, but just 3.2 km/s for LEO to geocentric C3 = 0 (escape velocity). I find that counter-intuitive. Why does ...
245 views

### Drag-only and gravity-only satellite orbit propagation, need help understanding the results

I'm trying to propagate the orbit of an Earth satellite. I've tried my calculation with gravity only (no drag), and also with drag only (no gravity). The gravity-only calculations work fine and ...
174 views

### How to calculate the radii of high orbits above the parallels of 45 and 80 degrees?

The new theories in the field demonstrate the possibility of non-Keplerian orbits. https://www.pourlascience.fr/sd/spatial/de-nouvelles-orbites-geostationnaires-10636.php I am interested in ...
150 views

### How fast are trips to the Moon for unmanned spacecraft typically?

The period of an orbit around the Earth is given by: $$T = 2 \pi \sqrt{a^3/GM}$$ For Earth GM is about 3.986E+14 m^3/s^2. Put in $a$ = ((6378+400)*1000) for the ISS in LEO (as a test) and you get ...
182 views

### Speed needed for the ship to escape Mars, on The Martian movie

Based on the two speeds and altitudes that are presented in the movie: "The Martian" which are respectively 741 m / s and 1350m, 850 m / s and 1843 m I would like to prove with calculations whether or ...
79 views

### Is a 2:1 “figure-eight” Lissajous orbit possible in the Circular Restricted Three Body Problem?

Was Queqiao in a halo or Lissajous orbit? Why do sources disagree? says Proper halo orbits have the same period for their in-plane oscillations and out of plane oscillations, so they are closed ...
434 views

### What's considered the boundary for “earth orbit?” [closed]

According to this CNET article, The last time a human broke free from Earth's orbit was the Apollo 17 mission in 1972. I thought that the moon orbited the Earth, and that visits to it were still ...
58 views

### When B is directly below A, as shown, what's B’s velocity (in vector notation) relative to A?

Spacecraft A and B are in coplanar circular orbits around the Earth. The orbital radii are as shown in the figure. (Not looking to use C-W equation. Just the equation describing relative velocity ...
137 views

### Which point in an orbiting body most closely follows its Keplerian trajectory?

Keplerian orbits can describe the motion of a negligible mass around a massive fixed central body, but they can also describe the motion of two bodies around their center of motion... with some ...
170 views

### “NASA's Europa Clipper has been liberated from the Space Launch System” How would the “physics” of a Starship-based mission differ from SLS?

The Hill's NASA's Europa Clipper has been liberated from the Space Launch System is quite an illuminating read about the politics of space launch. However, I noticed that it also says: Both the ...
134 views

### Does the arrow in this STEREO trajectory animation point heliocentric prograde, or towards the Sun?

This answer links to this NASA page. The first video shows the two STEREO spacecraft use two and three passes by the Moon to leave Earth orbit and enter into an orbit around the sun. Below is a GIF ...
114 views

### Could the $C_L$ of the X-15 be calculated from the flight data near the Kármán line altitude?

The "lift coefficient" $C_L$ can be very different for one specific aircraft at different speeds. According to this article from NASA about the lift coefficient: So it is completely incorrect to ...
426 views

### Could Phobos be easily saved from falling apart?

Edit: Since i've learned a lot from the excellent answer below, i've changed the content of my question totally to make it more realistic. The orbital radius of Phobos is gradually decreasing by 2 ...
170 views

### Could a framework of mirrors static in space above the Lunar south pole illuminate a moonbase there continuously?

When near the south pole of our Moon a permanent human community is established to search for and produce water in the permanently shadowed regions there, it would be nice to have some light from ...
192 views

### How would molten or liquid metal be transported in open space? [closed]

How to transport a ball of liquid, molten metal nearest to the Sun possible? It must be close to the Sun for the metal to stay molten. However, to stay safely cool enough, the spacecraft must always ...
121 views

### Is it correct to apply the vis-viva equation to an airplane that flies in a straight line at the Kármán line?

The vis-viva equation models the motion of an orbiting body and it applies when the only force acting on the body is it's own weight. So is it correct to apply this equation to an airplane that ...