Waiting for First Light
September 2006
As MRO approaches its first
Martian year of science operations, from November 2006 through November
2008, one of the key activities of the CRISM team is preparing for
"cover opening."
When CRISM was being built, tested, and integrated onto the MRO
spacecraft, cleanliness was Job 1. The same was true for all of the
optical instruments on MRO - CRISM, HiRISE, CTX, and MARCI.
As any camera user knows, keeping dirt off the lens is of first
importance for taking clear, sharp pictures. For example, the picture
below shows CRISM being tested after it was built. The engineers
working on it (1) wore "bunny suits" to contain loose hairs, skin flakes, and sneezes.
The opening in the telescope was covered with a bag made of special
plastic (2) to keep out dust. And a small plastic tube (3) was attached to the instrument to blow ultra-clean nitrogen into the interior to "push out" moisture from the air.
Cleanliness is even more critical with CRISM because some of the
wavelengths of light measured in its hyperspectral images are
particularly sensitive to the tiny amounts of water or organic material
in airborne dust and chemicals. So CRISM has gone a step further than
the other optical instruments on MRO by including a one-time deployable
cover over the telescope (below). Many spacecraft optical instruments
use covers like this because once the spacecraft is on its launch
vehicle, the countdown and launch can create a surprisingly dirty
environment. So does the early part of interplanetary spaceflight.
Rocket exhaust or chemicals that boil off a spacecraft in the vacuum of
deep space can condense into a film on camera optics and make the
images blurry. That actually happened on the NEAR and Stardust missions.
CRISM's cover has stayed closed since launch to protect the optics during the major burn for Mars Orbit Insertion, and during aerobraking when the spacecraft body gets heated and volatile chemicals may be driven off.
The scheduled day for cover-opening is September 26, 2006. CRISM will
turn on the previous day and undergo a series of tests to be sure that
engineering functions are nominal. Then, while Mars is being
imaged, the cover will be deployed half-way through the image. Mars
popping into view provides the ultimate validation that deployment
went smoothly - literally, "first light."
NASA |
