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#132 - Celia Payne-Gaposhkin - Orbits

"The reward of the young scientist is the emotional thrill of being the first person in the history of the world to see something or understand something. Nothing can compare with that experience"Cecilia Helena Payne-Gaposchkin

Cecilia Helena Payne-Gaposchkin born OTD May 10, 1900 in British was an American astronomer and astrophysicist who in her 1925 doctoral thesis said the stars were composed primarily of hydrogen and helium

But when Payne's dissertation was reviewed, astronomer Henry Norris Russell, dissuaded her from concluding that, because it would contradict the current scientific consensus that the elemental composition of the Sun and the Earth were similar. Payne consequently described her results as "spurious"

A few years later, astronomer Otto Struve described her work as "the most brilliant PhD thesis ever written in astronomy" Russell also realized she was correct when he derived the same results. In 1929, he published his findings in a paper that admiringly acknowledged Payne's earlier work and discovery; nevertheless, he is often credited for the conclusions she reached

She taught Frank Drake, and loads of others

Her interest in astronomy began after attending a lecture by Arthur Eddington on his 1919 expedition, She was not awarded her degree from Cambridge as they didn’t give degree to woman till 1948

She met Shapley, the Director of the Harvard College Observatory, where he had just established a graduate program in astronomy, she left England in 1923. This was made possible by a fellowship to encourage women to study at the observatory. He persuaded her to do a PHD thesis, and she became the first Doctor of Astronomy from Radcliff, now part of Harvard.

In 1931, Payne became an American citizen. On a tour through Europe in 1933, she met Russian-born astrophysicist Sergei I. Gaposchkin in Germany.

So if you ever talk about variable stars, stella composition, Galactic Structure, stella evolution, then mention Cecilia a trail blazing legend of astronomy.

#SSOW Space Science of the Week – Orbits

When we talk about orbits lots of phrases pop up time and time again so I thought we’d tackle that once and for all so here is the IP guide to Orbits.

First of all you can define an orbit by what body it is orbiting, and this reminds me a little bit of the English collective nouns like a murder of crows, although to be fair it makes a lot more sense than that.

Earth orbits can be described by their altitude

Also the world is spinning about an axis, a spacecraft can orbit at an angle to plane of spin so imagine spinning a dinner plate then tilting it, this is known as the Inclination. 0° represents an equatorial orbit, and 90° represents a polar orbit.

Other cool orbits!

Tundra orbit: A synchronous but highly elliptic orbit with significant inclination (typically close to 63.4°) and orbital period of one sidereal day (23 hours, 56 minutes for the Earth). Such a satellite spends most of its time over a designated area of the planet. The particular inclination keeps the perigee shift small, we talked about this way back on Podcast 36 when a Soyuz rocket successfully delivers EKS-2 early-warning satellite to rare orbit

Molniya orbit: A semi-synchronous variation of a Tundra orbit. For Earth this means an orbital period of just under 12 hours. Such a satellite spends most of its time over two designated areas of the planet. An inclination of 63.4° is normally used to keep the perigee shift small.

Areosynchronous orbit (ASO): A synchronous orbit around the planet Mars with an orbital period equal in length to Mars' sidereal day, 24.6229 hours.

Areostationary orbit (AEO): A circular areosynchronous orbit on the equatorial plane and about 17,000 km (10,557 miles) above the surface of Mars. To an observer on Mars this satellite would appear as a fixed point in the sky.

More on Sun-synchronous,

A Sun-synchronous orbit is achieved by having the osculating orbital plane precess (rotate) approximately one degree eastward each day with respect to the celestial sphere to keep pace with the Earth's movement around the Sun, This precession is achieved by tuning the inclination to the altitude of the orbit such that Earth's equatorial bulge, which perturbs inclined orbits, causes the orbital plane of the spacecraft to precess with the desired rate.

The plane of the orbit is not fixed in space relative to the distant stars, but rotates slowly about the Earth's axis.

Typical Sun-synchronous orbits around Earth are about 600–800 km in altitude, with periods in the 96–100-minute range, and inclinations of around 98°. This is slightly retrograde compared to the direction of Earth's rotation: 0° represents an equatorial orbit, and 90° represents a polar orbit.

Sun-synchronous orbits can happen around other oblate planets, such as Mars. A satellite around the almost spherical Venus, for example, will need an outside push to maintain a Sun-synchronous orbit.

What about the circular and elliptical nature of orbits!!! The more elliptical the more eccentric.

Circular orbit: An orbit that has an eccentricity of 0 and whose path traces a circle.

• Elliptic orbit: An orbit with an eccentricity greater than 0 and less than 1 whose orbit traces the path of an ellipse.

o Geostationary or geosynchronous transfer orbit (GTO): An elliptic orbit where the perigee is at the altitude of a low Earth orbit (LEO) and the apogee at the altitude of a geostationary orbit.

o Hohmann transfer orbit: An orbital maneuver that moves a spacecraft from one circular orbit to another using two engine impulses. This maneuver was named after Walter Hohmann.

o Ballistic capture orbit: a lower-energy orbit than a Hohmann transfer orbit, a spacecraft moving at a lower orbital velocity than the target celestial body is inserted into a similar orbit, allowing the planet or moon to move toward it and gravitationally snag it into orbit around the celestial body.

Other Cool orbits terms!

Prograde orbit: An orbit with an inclination of less than 90°, or equivalently, an orbit that is in the same direction as the rotation of the primary.

Retrograde orbit: An orbit with an inclination of more than 90°, or equivalently, an orbit counter to the direction of rotation of the planet. Apart from those in Sun-synchronous orbit, few satellites are launched into retrograde orbit because the quantity of fuel required to launch them is much greater than for a prograde orbit. This is because when the rocket starts out on the ground, it already has an eastward component of velocity equal to the rotational velocity of the planet at its launch latitude. A gravity assist around the moon can reduce the fuel premium

Halo orbits and Lissajous orbits: These are orbits around a Lagrangian point. Lagrange points are shown in the adjacent diagram, and orbits near these points allow a spacecraft to stay in constant relative position with very little use of fuel. Orbits around the L1 point are used by spacecraft that want a constant view of the Sun, such as the Solar and Heliospheric Observatory. Orbits around L2 are used by missions that always want both Earth and the Sun behind them. This enables a single shield to block radiation from both Earth and the Sun, allowing passive cooling of sensitive instruments. Examples include the Wilkinson Microwave Anisotropy Probe and the upcoming James Webb Space Telescope. L1, L2, and L3 are unstable orbits[6], meaning that small perturbations will cause the orbiting craft to drift out of the orbit without periodic corrections.

P/2 orbit, a highly-stable 2:1 lunar resonant orbit, that will be used for the first time with the spacecraft TESS (Transiting Exoplanet Survey Satellite) in 2018.

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