# Tag Info

## Hot answers tagged terminology

82

As explained in the answer that Organic Marble dug up, aerospatial "nominal" is really a shorthand for something like within the allowed tolerances around the nominal (i.e. specified) value. We can speculate about how that shorthand evolved. Example: Assume the thrust of an engine according to its design and specification -- its nominal thrust -- is 45 kN, ...

50

For a powered descent to the surface of a massive body like the Moon, it turns out to be most fuel efficient to do all your deceleration at the very end of the trajectory, right before impact. (This is because if you decelerate sooner than that, you will be in flight longer; the longer you're up, the more fuel you need to spend counteracting gravity ...

45

Jupiter being a gas giant is not about its appearance, as another answer stated. It's only about the mass distribution of a planet. Jupiter's mass is 320 Earth masses, while we know from the Juno mission that the rock/ice in the core account for 5–25 of these Earth masses. So the rest of about 300 Earth masses is gas. Thus Jupiter is a gas giant. It is ...

44

So far as I can tell, it was first a saying used by military personnel as the phrase "Rapid Unintentional Disassembly", for a phrase when a gun broke apart if you misused it. This was used by a book for Navy Personel in 1970, so I suspect it was in use for a while before then. This seems to have evolved from that phrase somewhat over the years. The earliest ...

41

It has many names, depends on who you ask. In English, one name for our moon is simply the Moon. Notice the article the and the capitalization making it a proper noun. This is similar in convention as the Galaxy for our own galaxy that is otherwise also known as the Milky Way. But the word galaxy actually already implies something related to milk in Greek ...

28

The basic difference between docking and berthing methods is as described by @OrganicMarble and the linked article, that berthing involves the robot arm and docking does not. The reasons why one is used rather than the other was discussed by the NASA PRO in a recent webcast. Obviously, if the vehicle is not capable of docking it must be berthed; however it ...

23

The Soyuz line all the way back to the R-7 has straps or cables connecting the boosters to the core. The straps, plus a "socket" on the core catching the front tip of the booster, are apparently how they're held on. One of the straps, near the base of the booster, is shown highlighted in blue here: This RussianSpaceWeb page has a rendering of the boosters ...

22

These boosters are called “strap-on” because there is little structure besides the separation mechanism holding them on, and the rocket is still a viable launch vehicle without them. In a few designs, like the Atlas V, the number of boosters can be customized per-mission. Also, in some cases the booster design is shared between launchers like the Shuttle and ...

21

We are "in space", in fact everything that exists and has a physical presence is. But what we usually mean by it is to describe "outer space" conditions of near (or hard) vacuum, where atmospheric pressure is already low enough to affect matter differently than under true atmospheric conditions, for example at atmospheric pressure below triple point of water....

19

The “Sailboat Island” gets its name from a Poincaré Surface-of-Section (SOS) plot of potentially stable S-type family of orbits in the Pluto-Charon system. From NASA Ames' blog post titled Playing Marbles at Pluto. Looking at the Dynamic Dust Environment. Generators, Sweepers, and Sweet-Spots by Kimberly Ennico: Othon Winter (UNESP Brazil) spoke about “On ...

19

The terms docking and berthing have a nautical origin. Smaller ships come into port under their own authority and dock. Large ships instead are berthed. They come to a stop outside of the port, relinquish control to the port authority, and are towed into port by tug boats. Docking with the International Space Station is essentially a controlled collision ...

18

Here's a reference from 1967 in "The MAC Flyer", Volume 14, Issue 5. This appears to be a periodical of the US Military Airlift Command. I have not been able to locate full text (but would certainly appreciate updates).

17

I can't say that the terminology is consistent across all users, but where I work (at JPL) we use aerobraking to refer to many light dips to lower an orbit, aerocapture to refer to a single deep dip to bring a hyperbolic approach to an elliptical orbit, aeroentry or simply entry to refer to an entry into an atmosphere with no exit, and aeroassist as a ...

16

The space shuttle throttled down its main engines from the normal setting of approximately 104% to around 67% as it was passing through the region of max dynamic pressure ("max q"), to make sure that the certified dynamic pressure limit was not exceeded. Once the threat had passed, the engines throttled back up. If you plotted throttle level vs time on a ...

15

This latest (second powered) test flight of the SpaceShipTwo was really interesting to watch (YouTube video, the "feathering" aerobraking starts at 2:14 into it), but this currently unique to The Spaceship Company designs (owned by its sister company Virgin Galactic that's itself within the Richard Branson's Virgin Group) approach to aerobraking was actually ...

15

Project Mercury used imperial units of measure. For example, the Mercury spacecraft main instrument panel indicated altitude in FT (feet):        The Mercury spacecraft main instrument panel from Project Mercury Indoctrination, May 1959 (Source: NASA. Click for full size) They used statute miles as a measure of distance in ...

15

Usually the term 'closest approach' is used. It applies to any two bodies in motion. Perigee is a term occasionally used, but the dictionaries say it only applies to things orbiting Earth. Use your discretion. In the case of the planets that orbit farther from the sun than us their closest approaches occurs when they are on the opposite side of Earth that ...

15

One reason they are called gas giants is because they are mostly composed of elements that are gaseous at Earth like temperatures and pressures. Jupiter is primarily composed of hydrogen with a quarter of its mass being helium, though helium comprises only about a tenth of the number of molecules. Jupiter's upper atmosphere is about 88–92% hydrogen ...

15

There's no conflict here. Because delta-v is a scalar figure, the result of applying velocity changes in different directions to a single object in 3 dimensional space over a period of time doesn't necessarily add up linearly. If a spacecraft applies a delta v of 100 m/s in one direction, then another maneuver of 100 m/s in a perpendicular direction, it ...

14

It's more a question of semantics, rather than a physical reality. An ocean would probably be thought to have a clearly defined surface. On the other hand, terminal velocity is only about 5m/s, which is a moderate running speed (Usain Bolt does 10 m/s). This gives you an idea about how thick the gas really is. In fact, one of the Pioneer Venus probes kept ...

13

Milton is not, in fact, the first English author to use 'space' in this sense. He is antedated by Lucy Hutchinson and John Evelyn, both of whom use 'space' to translate 'spatium' in their English versions of Lucretius's De Rerum Natura. Milton probably did help the English sense to catch on, and he too was alluding to Lucretius. By the way, Paradise Lost, ...

13

In the case of a Keplerian orbit, an orbit is a 360 degree change in true anomaly. Suppose a spacecraft in low Earth orbit (LEO) passes directly over some point on the Earth. Where is that point relative to the spacecraft one orbit later? I'll use 90 minutes, or 1/16 days, as the orbital period for our spacecraft. The Earth rotates to the east by 22.5 ...

13

Edit: Thinking about this some more, the answer is a result of physics: gases exert pressure (due to molecules bumping into each other). This is what causes a gas to expand to occupy all available volume. The only force at work is a repellent one, so the answer must be "blown out". In everyday language, there are some exceptions. We say a vacuum cleaner ...

13

It is entirely correct to replace "artificial" with "simulated" or even "emulated" or "imitated". Simulated can be defined as "imitating the conditions of something". In that vain, simulated gravity would in no way imply that we are somehow creating actual gravity. It simply means that we are creating conditions similar to gravity. Replacing "gravity" with ...

13

Berthing is when the vehicle is grappled by the robot arm and moved to a port. Docking is when it flies in on its own.

13

Your assumption is a good starting place and its good to be cautious about it. Many of us are guilty of abbreviation or outright misuse of the terms for convenience. Here's my rough guide, not meant to be precise but rather to address the overlapping usage. I've spent a bit more time on the basic definitions as this is probably where variations in usage ...

12

I'm not sure there's any generally agreed on convention, but spaceships are often regarded as, well, ships, so similar terms will be often used. E.g. for the red arrows that you describe as prograde and retrograde orientation vectors, from a spaceship's point of view and relative to its movement, also ram-facing and wake-facing is often used to describe ...

12

The English word space originates from Latin word for expanse - spatium (also written spacium in Medieval Latin), and later French word espace, through the use of which English variant space was formed. The earliest mention of space in relation to the 'outer space' is attributed to the 17th-century English poet John Milton, that used it in his epic poem ...

12

They have absolutely used these, in various mission badges: This was the logo for the Mercury project: Here's a patch from the Viking program: (source: colostate.edu) And one from Mariner 2, to Venus: None of these are for any sort of technical reason; I'm sure the symbols aren't used for anything important, but as a little bit of astronomical history,...

12

I am not aware of anyone using a Kármán line on another planet, but it's not hard to calculate. I get about 88 km for Mars. The equation is $r\,\rho(r)={2m\over A\,C_L}$, where $r$ is the radius of the Kármán line from the center of the body, $\rho$ is the density as a function of the radius, $m$ is the mass of the aircraft, $A$ is the planform area, and \$...

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