A shroud of multi-layer insulation keeps the temperature within the telescope stable, and surrounds a light aluminum shell in which the telescope and instruments sit.. 
This led to an increased warming rate for the instrument and reduced its original expected Lifetime of 4.5 years to about 2 years.Ìranṣe ìṣàtúnṣe 3a servicing mission 3a, Flown by Discovery, took place in December 1999, and was a split-off from servicing mission 3 after three of the six onboard oṣóscopes had treaty.. 