# Tag Info

55

Imagine you have a very heavy book and a bookcase, and your goal is to put the book on the top shelf of the bookcase. How much time would you spend doing that? Maybe five seconds, maybe fifteen. Would going much slower help you? No, it would not, because simply carrying the book is exhausting to you. You would never be able to hold the book up for an entire ...

43

A very good question! The reason is essentially to do with tides. And a slightly over-simplified summary is: If the moon orbits more slowly than the rotation of the parent body (as our Moon does, 12 degrees per day while the Earth rotates about 360 degrees per day) then the moon will gradually orbit further and further away. If the moon orbits faster than ...

15

Circular orbits at different altitudes require different speeds, so if you start with a radial separation, the spacecraft and station will tend to drift further apart unless they accelerate themselves radially to close the distance. The effect is small at small distances, larger at long distances. To a first approximation, the separation is the difference ...

12

The orbital mechanics of satellites are independent from the mass of the satellite. As long as the sats mass is tiny compared to the mass of Earth. The total mass of the ISS is much larger than the mass of the dragon capsule itself, the same is true for the volume and surface of both. So the atmospheric drag of both changes only very little after docking.

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Orbits beneath synchronous orbits have a higher angular velocity than their planets rotation, orbits above have a slower angular velocity. Drag (atmospheric or tidal) would try to match the angular velocity to the planets rotation. So below a synchronous orbit objects get slower, above it they would speed up (and slow down the rotation of the body they are ...

9

From the diagram given in this answer We see that radial "in" burns shift the perigee towards the burn point, and radial "out" burns shift the apogee towards the burn point. Thrusting radially outwards (that is, away from the center of the Earth, or "up") creates an initial vertical motion in the desired direction, but the chaser then begins falling ...

7

The general concept of doing things slowly generally allowing better efficiency in a design is certainly correct. The difficulty with applying this to rocket launches is the concept of gravity loses that in general mean getting to orbit as quickly as possible is better. Slow/efficient space access via space elevator and related designs is the logical ...

6

For Python and TLE propagation using SGP4 one very handy option is https://rhodesmill.org/skyfield/ As you probably already know a TLE is a strange animal. It does not really contain proper orbital elements, but instead is engineered with one purpose; to be fed into SGP4 so that that will generate reasonable position information for at least a few days ...

5

Skimming CCSDS RECOMMENDED STANDARD FOR ORBIT DATA MESSAGES, it looks to me like three different message types are defined: Orbit Parameter Message (OPM), Orbit Mean Elements Message (OMM), and Orbit Ephemeris Message (OEM). OPM gives position and velocity and optionally "osculating Keplerian elements". It is "suited to exchanges that "do ...

3

There are some concepts for slow access to space being developed. The most fameous one is probably the space elevator. However there is a concept more like the one you are asking for called airship to orbit (more details in this question Is the "airship to orbit" mission profile feasible?) this is currently beyond our engenering skills to construct ...

3

Units are always a challenge, and when you think you've got it right it's also important to check them with dimensional analysis. Sometimes people calculate orbits in dimensionless units, so for example with $\mu=1$ and $a=1$ the period is just $2 \pi$. If you have two massive bodies then $\mu_1 + \mu_2 = 1$. But when we're doing thins with real world ...

3

You would not save fuel by going "Large & Slow but Steady into Outer Orbit over months rather than in a Day", you would need a lot more. The longer it takes to reach orbit, the longer you have to fight gravity with a lot of fuel. Keeping the same height below orbit needs fuel.

3

The basic idea is that if you can get there within a small fraction of the orbit, the orbital dynamics do not matter at all. You are close enough that the two spacecraft will essentially be in the same orbit. As a low orbit is 90 minutes or so, if you can get there in 5 minutes you don't have to worry about what the gravity does. If you can get much ...

2

As you have written, an object (infinitesimal near) near an unstable point will drift to a stable point, but it will not stop there but drift further. So an object (starting infinitesimal near) an unstable point will also oscillate around a stable point. But while the "amplitude" near a stable point is very small, an object at an unstable point has an ...

2

Not for a landing. Moon, 1730 m/s. Mars requires twice as much, 3800 m/s.

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It is one of the Lagrange Planetary Equations. A very similar form is given by Archie E. Roy (The Foundations of Astrodynamics, 1965 at page 175 and Orbital Motion, 1978 at page 184). Be careful in the integration, the $f_{tdrag}$ needs to be negative. Also, since drag is opposite the velocity direction you need to calculate the components of drag. As ChrisR ...

2

There are two parts to an answer to this question. I am going to assume that you want to get into space with some kind of flying machine, so in particular I'm not talking about a space elevator: space elevators are a hugely cool idea but we're not very close to being able to build one. The first thing, as other people have said, is that the main bit of ...

2

Units I aways use kilograms, meters and seconds (MKS) to avoid getting tripped up by mixed units. Horizons offers both AU & AU/day and km & km/sec options and the first thing I do when importing ephemeris data is convert the km & km/sec to m & m/sec! This is from this JPL Horizons tutorial Central force ("monopole term") The main ...

1

Universe Sandbox is probably what you want. Great tool, drag and drop, add in objects where you desire, etc. Orbits all figured in. There's a ton of stuff you can do with it, I've used it in a few videos to explain supernovas and stuff like that, but it works well for orbital mechanics too.

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I would like to add on to the other answers. You can't get to space slowly because that would be horrendously ineffective. But once you get to space and reach an orbit, what about getting to further places? Spacex is planning to do something that somewhat comes close to your suggestion: Throw many spaceships to space (quickly every time, but one at a time) ...

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As for any research, the first question you need to answer for yourself is: "how much time do I realistically have and what happens if I don't finish this research in time?" Organization It seems like your scope is quite wide. From my experience, I would recommend organizing your research ideas into incremental steps. Each step feeds into the next step of ...

1

Altitude is usually via a burn at the apogee/ perigee, as you mentioned. RAAN changes are usually done over time. If you are slightly over or under your target orbit, your RAAN will drift over time. This may take weeks to months, but you will eventually get there, without the expenditure of a lot of fuel. Of some note is that there are some orbits that don'...

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Eric Stoneking / NASA Goddard Space Flight Center share '42' as the (mostly harmless) spacecraft dynamics simulation It's cross platform, has various capabilities, and is a neat tool overall. https://github.com/ericstoneking/42

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