Term
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Definition
| period of time when we can launch a spacecraft directly into a speficied orbit from a given launch site |
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Definition
| marking the time between the Sun's successive passages above a certain point by observing shadows on a sundial |
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Definition
| since the Earth rotates on an ellipse, each apparent solar day's length varies; to compensate for this variation, we take the average of the lengths for one year to get a "mean solar day;" little more than 360 degrees; exactly 24 solar hours |
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| Greenwich Mean Time (GMT) |
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Definition
| the local mean time solar time at the Prime Merdian, as the 0 degree longitude line as the international reference point to start the 24 time zones around the world |
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Definition
| the angle between a longitude line and the vernal equinox; "related to the stars" |
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Definition
| the successive passages of the vernal equinox over a specific longitude; exactly 360° rotation; little less than 24 solar hours |
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| Local Sidereal Time (LST) |
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Definition
| the time since the vernal equinox last passed over the local logitude |
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Definition
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Term
| How to solve for Time in Degrees |
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Definition
| Time (hours) x 15 degrees/hour |
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| How to solve for Time in Hours |
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Definition
| Time (degrees) / [15 degrees/hour] |
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Term
| If Lo = i, how many launch opportunities per day? |
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Definition
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Term
| If Lo < i on a prograde orbit, how many launch opportunities per day? |
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Definition
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Term
| If Lo < 180° - i on a retrograde orbit, how many launch opportunities per day? |
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Definition
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Term
| Launch Window Sidereal Time (LWST) |
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Definition
| the degrees between the vernal equinox direction (I vector) to the point where the launch site passes through the orbital plane; function of Ω and δ (launch window location) |
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Term
| Ascending-node opportunity |
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Definition
| the launch site opportunity closer to the ascending node |
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Term
| Descending-node opportunity |
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Definition
| the launch site opportunity closer to the descending node |
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Term
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Definition
| triangle on the surface of a sphere; different from planar triangles |
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Term
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Definition
| Inclination auxiliary angle; angle between the equator and ground trace of the orbit at the ascending node |
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Term
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Definition
| launch-direction auxiliary angle; angle between the lauch site longitude line and ground trace of the orbit |
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Term
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Definition
| launch-window location angle; along the equator, between the node closest to the launch opportunity being considered and the longitude where the orbit crosses the lauch site latitude |
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Term
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Definition
| launch-site latitude; the length of the local longitude line between the launch site and the equator |
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Term
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Definition
| launch azimuth; the direction to launch; angle from true north at the launch site, clockwise to the launch direction |
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Term
| Computing β and LWST depends on what 3 things? |
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Definition
1. Direct or indirect orbit
2. Ascending node or descending node
3. Launch-site in northern or southern hemisphere |
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Term
| If Lo > i how many launch opportunities per day? |
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Definition
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Term
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Definition
| changes in COEs caused to unintentional outside forces |
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Term
| Which 2 COEs change to atmospheric drag and how do they change? |
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Definition
| a (smaller); e (smaller, AKA tried to become a circle) |
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Term
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Definition
| Because Earth is spinning on an axis, and is mostly comprised of water, it is not actually spherical; instead it is "squashed" or "oblate" |
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Term
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Definition
| J2 is a constant describing the size of the bulge in the mathematical formulas used to model the oblate Earth |
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Term
| What 2 COEs change due to Earth's oblateness and how? |
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Definition
| Ω, at its nodal regression rate which causes it to decrease in prograde orbits and increase in retro grade orbits (also increases if the orbit is low in altitude and low in inclination, no affect on polar orbits); ω, at its perigee rotation rate (usually given) |
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Term
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Definition
| takes advantage of eastward nodal progression in order to make the orbital plane maintain the same orientation to the Sun |
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Term
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Definition
| Russian for "quick as lightening;" inclination is 63.4° so that the ω doesn't change due to Earth's oblateness, and was useed to get great coverage of the Northern hemisphere where the apogee is |
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Term
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Definition
| can cause long-term orbital perturbations and unwanted spacecraft rotation |
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Term
| third-body gravitational effects |
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Definition
| (Moon, Sun, planets, ect) can perturb orbits at high altitudes and on interplanetary trajectories |
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Definition
| cause by either outgassing or malfunctioning thrusters; can perturb orbits or cause spacecraft rotation |
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Definition
| the most fuel efficient transfer; uses an ellitptical transfer orbit tangent to the initial and final orbits |
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Term
| 4 assumptions to Hohmann transfers |
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Definition
2 instantaneous burns
tangential orbits
in the orbital plane
co-apsidal orbits (major axis aligned) |
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Definition
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Term
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Definition
| to get from 1 orbit to the transfer orbit, we change the orbit's energy (by an amount ΔV1) and then when the spacecraft gets to orbit 2, we change its energy again (by changing its velocity by an amount ΔV2) |
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