NASA 的 JPL 回答「你們用的圓周率是 3.14 嗎?」的問題

NASAJPL 回答了他們所使用的圓周率:「How Many Decimals of Pi Do We Really Need?」。


For JPL's highest accuracy calculations, which are for interplanetary navigation, we use 3.141592653589793.

先拿目前離地球最遠的人造物 Voyager 1 來舉例,約 201 億公里 (125 億英里) 的距離,使用這個小數下 15 位的圓周率,與實際的圓周率算出來的誤差只有 3.81 公分 (1.5 英寸):

The most distant spacecraft from Earth is Voyager 1. It is about 12.5 billion miles away.

It turns out that our calculated circumference of the 25 billion mile diameter circle would be wrong by 1.5 inches. Think about that. We have a circle more than 78 billion miles around, and our calculation of that distance would be off by perhaps less than the length of your little finger.

另外還舉了地球與整個宇宙的數字來計算,需要的精確度沒有想像中那麼大 XD

2017 年將有新一季的 Star Trek...

剛剛看到 2017 年將會有最新一季的 Star Trek:「New Star Trek Series Premieres January 2017」。

Star Trek 在科技史上是部很重要的影集與一系列的電影,在 NASA 裡甚至有很多人是被 Star Trek 所影響才加入 NASA 的。

明年 2016 年將會有五十週年活動:

Star Trek, which will celebrate its 50th anniversary in 2016, is one of the most successful entertainment franchises of all time.

來等看看好了,之前有些 series 有點雷,新的不知道怎樣 XDDD


在「The International Space Station (Finally) Gets an Espresso Machine」這篇看到的,原始的報導出自「The International Space Station (finally!) gets an espresso machine」。

幾個重點 XDDD

The ISSpresso requires 120V DC power which is obtained at the Utility Outlet Panel (UOP) on the ISS.

很特別的電力,是 120V DC 而非 120V AC...

NASA 用雷射光傳送「蒙娜麗莎」圖片到月球上...

NASA 用雷射光將灰階「蒙娜麗莎」傳送到月球軌道上的 LOLA (Lunar Orbiter Laser Altimeter,看起來是台描繪地表用的儀器?):「NASA Beams Mona Lisa to Lunar Reconnaissance Orbiter at the Moon」。

Lunar Orbiter Laser Altimeter

傳輸速度是 300bits/sec (這數字讓人真感動 XD),傳送 152x200 的 4096 灰階圖片。這次測試其中一個目的是了解地球大氣層對光訊號的影響,可以看到左邊的 raw data 與右邊靠 2/3 RS code 修正的結果:

To clean up transmission errors introduced by Earth's atmosphere (left), Goddard scientists applied Reed-Solomon error correction (right), which is commonly used in CDs and DVDs. Typical errors include missing pixels (white) and false signals (black). The white stripe indicates a brief period when transmission was paused.

不過好像沒提到用多大台的雷射打到月球上... (雷射砲?)