Hubble to use moon as mirror to see Venus transit

Re:Hubble to use moon as mirror to see Venus transit by ggchappell on Sunday May 06, 2012 @05:51PM (#3936456)

A good question, to which I do not know the answer. I would imagine the problem is either that there are parts that cannot be allowed to get too hot, or that stray light might wreck optical sensors.

So I looked into it. Wikipedia[1] explains that the Sun is never allowed to illuminate any part of the Optical Telescope Assembly. And therefore Hubble never points within 50 degrees of the Sun. This is the "Solar Avoidance Angle". A forum on NasaSpaceFlight.com[2] has a message that adds more detail:

  In general the following viewing constraints apply:
  - 50 degree solar avoidance angle
  - 20 degree from illuminated Earth
  -  6 degree from dark Earth limb

So it seems very likely that the problem would be stray light wrecking optical sensors.

I don't know this, however. Further info from someone knowledgeable, would be nice.

[1] https://en.wikipedia.org/wiki/Hubble_space_telescope

[2] http://forum.nasaspaceflight.com/index.php?topic=17256.0

[ Parent | on HN ]

Re:Hubble to use moon as mirror to see Venus transit by DanBC on Sunday May 06, 2012 @06:03PM (#3936488)

(http://www.stsci.edu/hst/wfpc2/software/wfpc2-help-sun_angle...)

> Most HST observations are made when the target is roughly 90 degrees from the sun. However, scheduling constraints can force the observation into other sun angles.

> The brightest backgrounds result when sources in the ecliptic plane are observed close to the sun. If you are concerned about the worst-case sky background, you may wish to try setting "sun angle" to 50 degrees, which is the HST solar avoidance angle. Ecliptic longitudes less than 50 degrees are possible for sources far from the celestial equator, but for these sources the zodiaical light is already moderately low.

> The lowest backgrounds occur when sources are farthest from the sun, i.e., "sun angle" = 150 to 180 degrees.

[ Parent | on HN ]