April 7, 2020

Astro-Event of the Week: 05.11.09: See STS-125 dock with Hubble!

First; the good news. This week’s potential launch of Atlantis on STS-125 for it’s much delayed servicing mission (the 4th and final) to the Hubble Space Telescope (HST) will provide spectacular views, both of the initial launch along the Space Coast of Florida and the dawn and dusk skies as it chases the orbiting observatory. Now for the bad; the current orbit of Hubble is positioned such that most of the northern hemisphere won’t see the action! The HST is inclined at a 28.5 degree orbit, far different than the normal 51.6 degree orbit the shuttle orbiters must attain to dock with the ISS.

Since we’re approaching lengthier days towards the summer solstice in the northern hemisphere, this means that the majority of passes over Europe and North America will occur in broad daylight. In the southern hemisphere, however, the reverse is true, and viewers based in Australia, South Africa, and South America all stand a good chance of spotting the pair during docking-undocking. Utilize your favorite satellite software or tracking site of choice, from Heavens-Above to Orbitron (our top pick!) to Spaceweather.com; just don’t forget to refresh those Two-Line Elements and that daylight savings thing. Atlantis is set to launch from the Kennedy Space center at 2:01 PM EDT, Monday the 11th; this is the beginning of a three-day window. If (The big IF) Atlantis slips a day or two, it may be just possible for viewers in the southern US to pick up the pair at dawn, towards the end of their eleven day mission. The next window opens up on May the 22nd, which will provide a slightly better geometry.  Endevour will be prepped and serve as a backup rescue vehicle in the event of an emergency. If it is not required, Endevour will then be headed off to the ISS in June. STS-125 is the ninth to last Shuttle flight planned before the fleet is retired next year. If you can’t see the pair pass overhead, be sure to watch the drama on NASA TV; and if the Shuttle doesn’t launch, you can at least watch the HST, in orbit for 20 years next year!

This week’s astro-term of the week is spherical aberration. Remember way back when in the early 1990′s when Hubble was first put into orbit? This was the optical flaw it was suffering from. Basically, when the figure of a lens or mirror isn’t ground precisely correct, it doesn’t bring all the light to one distinct point. Thus, the image cannot be brought into focus. The COSTAR device originally added “corrective lenses” to Hubble’s’ optics; subsequent replacement packages all account for this defect and now compensate for it.

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