Questions tagged [terminology]

Questions regarding words and abbreviations used in the fields of spaceflight and space exploration, and their meaning when used in those contexts.

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4
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3answers
606 views

Are there terms for Earth orbits with rational number multiples of 1 sidereal day?

An Earth orbit with a period of 1 sidereal day (and zero inclination) is a geosynchronous orbit, orbits slightly above and below that are supersynchronous and subsynchronous orbits, and a Molniya ...
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How far do you have to be from Earth to be "in space"?

According to a recent news article a group of USC students are attempting to launch a rocket "in to space" with a planned height of 62 miles. Making them "the first group of students to successfully ...
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What is a "suicide burn"?

The term suicide burn occasionally comes up in answers and comments, usually without any real explanation or definition. What is meant by the term "suicide burn"?
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Nuances of the terms (mean / osculating / Keplerian / orbital) elements

I've been assuming that osculating, Keplerian, and orbital elements are all synonyms, with mean orbital elements just being these averaged over some time. However occasional comments make me suspect ...
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How do apsides of celestial bodies get their names?

If you look at this site, it shows some of our common bodies' apsidal names, as shown below: Objects Periapsis Apoapsis Galaxy Perigalacticon Apogalacticon Black hole Perimélasma ...
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What is the difference between Cape Canaveral and Kennedy Space Center?

Cape Canaveral and Kennedy Space Center are both at pretty much the same location in Florida. I do not understand why they are referenced separately in media. How much are they separate entities? Is ...
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What precisely is downrange distance - how is it defined mathematically?

Wikipedia: Downrange is the horizontal distance traveled by a spacecraft, or the spacecraft's horizontal distance from the launch site. Spacecraft don't travel horizontally. I don't even know how ...
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What's the planetary exploration word for "impact parameter" (distance of closest approach if gravity were "turned off")?

In particle scattering there's a term called "impact parameter", which is the minimum distance a particle would pass a second particle at rest, if the attractive or repulsive force were ignored or "...
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Opportunity's last tau was 10.8; what does that mean and how is tau defined and measured?

@ahiijny added a direct link to the Sol 5110-5114 MER B Downlink Report. These are the final days that signals were received from Opportunity. The message "Tau Value is NOT a Typographical Error" ...
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1answer
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What is BECO? (Gemini) Same as MECO?

This answer links to this answer which shows the acceleration g-force envelopes experienced by early astronauts, reaching as high as almost 7.5g! Both show BECO, which is what I might call MECO or ...
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What are these orientations called in orbit?

Let's say a spacecraft is in an orbit like this one: If the red arrows point to prograde and retrograde, and the blue arrows point to normal and antinormal, what do the green arrows point to? In ...
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Is Dawn's upcoming low periapsis orbit for XMO7 "resonant"?

The Spaceflight Insider article Dawn will enter lowest ever orbit around Ceres says: In his Dawn Journal blog, mission director and chief engineer Marc Rayman discussed the challenges of bringing the ...
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1answer
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What does "in the bucket" mean?

I've heard this expression a couple of times before. It seems related to the engines, but I can't find any information on it, except in the context of testing them. Here's two videos where it occurs: ...
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What does “supersonic large amplitude ID maneuver PTI” mean, and what does a tumble motor do?

In this question I linked to a YouTube video of the Ares X-1 launch. You can start listening at 02:00 for the point where these are mentioned: "Supersonic large ...
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1answer
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What (actually) is a 1:1 resonance, and is 2016 HO3 in one with the Earth?

In my question How was Earth's "quasi-satellite" 2016 HO3 "first spotted" and it's orbit determined? I link to two videos of simulations of views of 2016 HO3's orbit seen in two ...
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1answer
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What is the equivalent of Curiosity's "MSL" in the context of Perseverance? What's the official name of the mission? Are the distinctions similar?

Answers to Where does MSL end and Curiosity begin? explain the difference. There was much fanfare for the naming contest for the Perseverance rover, but I don't know what the mission is called. ...
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Karman line analog on other celestial bodies

Is there a common definition of where the space begins on other planets (and other celestial bodies)? An equivalent of the Karman line. How far one should go from the martian surface to get to the ...
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1answer
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Orbital vocabulary confusion! How can the tangential velocity of an elliptical Kepler orbit not be tangent to the orbit?

I'm now officially confused about the usage of "tangential" when breaking down orbital velocity components. It started with edits and comments on this answer to Orbital speed is (vector) sum of ...
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1answer
208 views

Gravitational keyhole for spacecraft flyby?

Is there a term for the area near a planet a spacecraft must pass through for a gravitational-assist flyby, or does 'gravitational keyhole' apply to gravitational assists as well as for asteroids?
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1answer
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What is a "Sailboat Island of Stability"?

The New Horizon's team, in response to an announcement of a press conference from the Hubble team, posted some speculations as to what the press conference might be about. On the list includes "Small ...
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What is feathering?

I heard that Virgin Galactic's SpaceShipTwo just tested something called “feathering”. What is it? How come I didn't hear about the shuttle doing this, it is unique to Virgin Galactic's ship?
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1answer
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What is and what isn't ullage in rocket science?

This comment and others below this answer address ullage. "Ullage" basically just means "the portion of the tank that isn't filled with liquid". The extended rocket-science implications of ullage ...
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Are any "strap-on" boosters held in place by actual straps?

Have there been any strap-on boosters that are attached to the main body of a rocket with actual straps (like bands of metal or something similar), as the name implies? If not, what's the origin of ...
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Origin of term "Block I", "Block II", etc

In NASA spacecraft development, subsequent versions of a design are referred to as "Block 1", "Block 2", etc. What is the origin of this naming convention? Why not just call them "Version 1", "...
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1answer
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How were the Space Shuttle missions named?

For example, why was the 19th Shuttle mission named STS-51F instead of something more obvious like STS-19? Side note: One reason I'm asking is because in the DVD commentary of Apollo 13, Tom Hanks or ...
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When was the first strap-on booster used in spaceflight?

The first use of the term "strap-on" in Google Ngram viewer is in 1930 and presumably that wasn't about a booster being attached to a rocket for additional thrust at lift-off. When was a ...
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Who coined the phrase 'Rapid Unscheduled Disassembly'?

Usually simply abbreviated as a RUD, and also sometimes expanded as Rapid Unplanned Disassembly, and being a way of understating that a rocket exploded. I saw it attributed recently to Elon Musk, ...
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Does the moon have a name?

Is there any scientific name for "The Moon", Earth's satellite, when talking about it apart from, but in context of, other moons? Google simply states that Earth's only natural satellite is simply ...
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Are there any “Third Order” acronyms used in space exploration?

On a recent episode of the Planetary Radio podcast, the topic of Third-Order Acronyms was brought up. At NASA, there are many Second-order acronyms like SAFER - Simplified Aid For EVA Rescue, where ...
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1answer
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Why did the S-IV-B refer to "jettison"ing its ullage?

This is based on a recent question about S-IV-B ullage motor shutoff timing, specifically something found in the Technical Information Summary AS-501, page 15: Ullage Jettison ~ 532. But why "...
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1answer
664 views

Are ion thruster trajectories classified as brachistochrones?

Usually, when performing trajectory optimizations for chemical rockets, the limiting factor is the $\Delta v$ budget. That means velocity change is the optimization factor, with things like transfer ...
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What (the heck) are "space-fixed coordinates" as described in Apollo mission trajectory analyses?

@Ludo's answer to If I wanted to reconstruct an entire Apollo mission's crewed spacecraft trajectories, what are the key sources of historical data I'd look for? shows the table and its source shown ...
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Where can the term "Sol" used?

Alright, I know that "Sol" is used on Mars to count days. But is the sun called: "Sol"? And can you use that term on Earth as well? The reason for the question is that the term "sol" is used in two ...
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1answer
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Pitch and yaw axes of rocket systems such as Apollo

Broadly speaking, most rocket systems appear to have at least 3 or 4 fold radial symmetry about their long axis (if you don't consider internals or smaller features not obvious from a distance). A ...
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Why "strap-on" boosters, and how do other people say it?

This came up for me in the context of translating something into German. Everybody throws around terms like "strap-on boosters", although they aren't actually held on by straps. It's not even meant ...
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Has any other term been used for a solar day on a solar system body besides "sol" on Mars?

My interest was piqued by this question and answer. For several reasons NASA needed to refer frequently and extensively to a Martian solar day, and "sol" became the nom du jour. There have been ...
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1answer
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What is a Beam Waveguide dish and why do deep space communications stations use them?

NASA Spaceflight.com's Deep Space Network upgrades and new antennas increase vital communication capabilities says: NASA’s Deep Space Network, commonly referred to as the DSN, has welcomed a new dish,...
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1answer
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How often did launch vehicles have a "Stage 0", and what does it mean exactly?

While trying to do some reading for the question Need help understanding staging shown in infographic of Titan launch of Hexagon satellites I ran across the Wikipedia article for Titan III. This ...
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1answer
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What is the difference between "body drag", "frictional drag" and "pressure drag" for astronaut or aerobot atmospheric locomotion in microgravity?

Complaints below my answer to Would a higher air pressure on the ISS or elsewhere make it easier to “swim” in microgravity? about my spherical-cow estimate of how fast an astronaut can accelerate by &...
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What is the difference between docking and berthing on the ISS?

People often talk about docking and berthing. They both seem to be connecting a spacecraft to the ISS, yet seem to be very different. Why?
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Is the air "sucked out" or "blown out" into space when the hatch opens?

In a somewhat famous Star Trek: The Next Generation quote Data corrects Riker on the 'correct term' for a scenario where a hatch on a space capsule breaks open and all the crew are killed. Riker: &...
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Why do they say "go" and "no go"

I'm sure we're all familiar with the go/no go standard phrasing for reporting whether something is OK or not. Having a standard phrasing clearly makes comprehension easier and more reliable, ...
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What distinguishes a sounding rocket from a suborbital flight?

What are the differences between a sounding rocket and a suborbital flight? Sounding rockets have long been used for science purposes. Some of them have trajectories elliptic enough to do ...
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What term can we use to describe a planet's or dwarf planet's nearest distance to Earth?

Is there a single term that completes this sentence: "at its _____, Pluto is about 27AU from Earth." peri- something...?
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Is "medihelion" a word?

"Medihelion" is what I call the two points on a solar elliptical orbit where distance from the sun is the same as the ellipse's semi-major axis. These two points also correspond to the end-points of ...
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Name for geostationary orbit around another planet

A geostationary orbit is a circular orbit in Earth's equatorial plane whose rotation period matches that of the Earth. The "geo" in "geostationary" means Earth, so is there another term to designate ...
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What is the "specific impulse"?

One of the most important values when talking about rocket engines is the so-called specific impulse. I have read the Wikipedia article but still have trouble understanding what it really is and what ...
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1answer
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Did NASA use metric units for the Mercury missions?

Did NASA use metric or English units for Project Mercury? For example, did they measure delta-v in meters/second or in feet/second?
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1answer
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What was the procedure to stop the descent engine on the Apollo 11 LEM?

What was the correct procedure to stop the descent engine on the Apollo 11 LEM? When the LEM had a contact light on Apollo 11, there was some terminology spoken that I'm assuming is important (and ...
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1answer
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What is the difference between a "Suicide burn" and a "Hoverslam"?

As far as I can tell, the terms Suicide burn and Hoverslam have both been invented rather recently (with SpaceX themselves coining Hoverslam and the Kerbal Space Program community loosely credited ...