Hard Light Productions Forums
General FreeSpace => FreeSpace Discussion => Topic started by: Flaser on March 03, 2005, 09:54:29 am
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Spaceflight 101
I made this thread (-mostly cut&paste job on Wiki articles-) to clear up the terms and methodology spaceflight and space travel.
I also intend this thread to serve as a guide for mission designers for orbital, reentry, lauch or scientifically accurate missions.
Planetary orbit
In physics, an orbit is the path that an object makes, around another object, whilst under the influence of a source of centripetal force, such as gravity.
History and basic theory
Orbits were first analysed mathematically by Kepler who formulated his results in his laws of planetary motion:
- Kepler's first law (1609): The orbit of a planet about a star is an ellipse with the star at one focus.
(http://upload.wikimedia.org/wikipedia/en/8/87/Kepler-first-law.png)
- Kepler's second law (1609): A line joining a planet and its star sweeps out equal areas during equal intervals of time.
(http://upload.wikimedia.org/wikipedia/en/2/25/Kepler-second-law.png)
- Kepler's third law (1618): The square of the sidereal period (the time that it takes the object to make one full orbit around the Sun)(T) of an orbiting planet is directly proportional to the cube of the orbit's semimajor axis (one half the major axis)(a).
a^3/T^2 = constant
Isaac Newton demonstrated that Kepler's laws were derivable from his theory of gravitation.
(http://en.wikipedia.org/math/b65000f8f887a68545ce63eb1cada232.png)
- F is the magnitude of the gravitational force between two objects
- m1 is the mass of first object
- m2 is the mass of second object
- r is the distance between the objects
- G is the gravitational constant, that is approximately : G = 6.67 × 10^−11 N m^2 kg^-2
Understanding orbits
- As the object moves, it falls toward the orbited object. However it moves so quickly that the curvature of the orbited object will fall away beneath it.
- A force, such as gravity, pulls the object into a curved path as it attempts to fly off in a straight line.
- As the object falls, it moves sideways fast enough (has enough tangential velocity) to miss the orbited object. This understanding is particularly useful for mathematical analysis, because the object's motion can be described as the sum of three one-dimensional orbits around a gravitational center.
(http://upload.wikimedia.org/wikipedia/en/c/cc/OrbitingCannonBalls.png)
Orbiting and reaching space
From a spaceflight perspective, the definition of space usually used is that space begins 100 km (62 miles) above Earth's surface. The United States sometimes uses a 50 mile definition. (See boundary to space.) (http://en.wikipedia.org/wiki/Boundary_to_space)
*This is a legal definition, there is no solid boundary where the atmosphere begins.
Achieving orbit is a prerequisite for going anywhere else, such as to the Moon or Mars.
The first successful orbital launch was of the Soviet unmanned Sputnik I mission on October 4, 1957.
The first orbital flight made by a human being was Vostok 1, carrying Yuri Gagarin on April 12, 1961.
One can distinguish the sub-orbital spaceflight and the orbital spaceflight (cf. Difference between sub-orbital and orbital spaceflights). (http://en.wikipedia.org/wiki/Difference_between_sub-orbital_and_orbital_spaceflights)
Sub-orbital spaceflight
A sub-orbital spaceflight (or sub-orbital flight) is a spaceflight that does not involve putting a vehicle into orbit.
The sub-orbital spaceflight should not be confused with a partial orbital spaceflight: a low Earth orbit, with deorbiting after less than one full orbit.
If the objective is just to reach space, sub-orbital flights are appealing because this is very much easier (it simply means going higher than the edge of space) than to achieve orbit (which requires a velocity of about 8 km/s (18,000 mph)). A dedicated sub-orbital spacecraft can therefore be built and operated much more cheaply than an orbital spacecraft. Less powerful sub-orbital craft may not reach speeds much higher than around 1.1 km/s to 1.3 km/s (2,500-3,000 mph).
Orbital spaceflight
An orbital spaceflight (or orbital flight) in the general sense is a spaceflight where the trajectory of a spacecraft reaches the height of, and through having an appropriate velocity enters into, orbit around an astronomical body
Note too that the edge of space (100 km) is much lower than the altitude where a vehicle can circle the earth even once without reentering due to atmospheric drag. Also note that the required speed to "go orbital" (to achieve orbit with known methods) requires atleast 9 km/s (18,000 mph) delta-v.
(EDIT - this is the begining I while write more to this, and feel free to add your opinion and knowledge on the issue)
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I can't add much to it, it's pure physics, which I never liked. :p
Good work collecting all this data, but keep in mind that FS isn't known about following science.
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Very true. (Deceleration of craft once engines are turned off, sound in space, etc) but still this clears up a lot of confusion about orbital physics.
Also note that the required speed to "go orbital" (to achieve orbit with known methods) requires atleast 9 km/s (18,000 mph) delta-v.
Crap! I'm gonna have to redo a whole mission! I guess I should have done my homework first!
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Meh. Just invent 'unknown' methods to go orbital; this is science fiction, after all.
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Poop. Already deleted. :(
But fear not! I shall re-create better than ever!
Orbital speed: 15 m/s! :D
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since when has FS ever stuck to physics anyway????
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Relative speed is relative compared to the planets surface!
In game it doesn't matter since never anyone ever said what are speed measured to.
I write all this crap so we will have some guide on what things can and can't be done in spaceflight, so we won't have Spacebattleship Yamato - esque nonsense with ships going head on to a planet and ect. ect...
@aldo_14 - this is just the begining, the important stuff will come later.
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Meh.
For those who have a vague need for realism...
http://www.projectrho.com/rocket/index.html
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what What WHAT!!!
Flasher - "so we won't have Spacebattleship Yamato - esque nonsense with ships going head on to a planet and ect. ect..."
Newtonian Physics are NOT your friend, plus it's NOT nonsence, it's classic anime (Cooks Flasher with the Wave Motion Gun, change name to Flash Fried!)...
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sorry, Getter Robo G, but it is quite nonsence. it doesn't matter how much you like the show.
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I like it too, but its concepts are so outdated and IMHO the youth are already fed enough BS as it is.