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The HST Observing Cycle
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During "Phase I" the observer has to:
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Choose one or more targets and what to investigate.

Figure out which instrument(s) would be useful.
(camera, spectrograph?)

Make sure that this has not already been done.
(check the HST data archive)

Figure out about how much time is needed on the telescope.

Write up a scientific justification and submit by annual deadline.
(exception: the observer can apply directly to the
Institute Director at any time for special circumstances)

Next the Telescope Allocation Committee (TAC) Meets
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This is actually several committees of scientists in different fields.

They review all the proposals in their field and identify the best
ones.

They make recommendations to the Director on which proposals to
accept.

If the observer is given time they move on to "Phase II" where they:
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Get an award letter from the Institute.

Get target information from the journals or other scientists.
(need approximate coordinates and magnitude)

Measure the target coordinates in HST guide star reference frame.
(on plates that were use to form the guide star catalog)

Figure out all the observations needed.

Group them into sets of observations that can be done together.
(we call these visits)

Figure out the details of each set of observations and put them
together in an order which uses the target visibility periods best.

Write up observations in special HST observation scripting language.
(language is documented in the Phase 2 Proposal Instructions)

Use APT software to check the program:
Is the syntax correct?
Is what was requested actually possible?
(filters, tape recorder usage, # of orbits, ...)
Is there a time of year that this could be done?

Submit program to Institute.


At the Institute the PCs do program preparation:
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Check that program reflects what was approved by the TAC.

Check that these observations have not already been done.

Prepare the program for flight.
(compile the script into what telescope will do)

Look for suitable guide stars throughout the year.

Check that the observation can schedule.
time of day: target occultation, south atlantic anomaly
time of year: sun, moon, target visibility, guide stars
observer imposed: orientation, timing or phase, visit ordering

The Long Range Planners then create a plan for the year using all the
programs.

An instrument scientist reviews the program.
(is it safe, will the target be acquired,
will it give them what they want?)

The next step is to schedule the visits for execution
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Start work about 11 days ahead.

7 days of visits must be bundled together to execute automatically.

It can be tricky fitting all the visits together to make
efficient use of the the telescope.
(like making a stone fireplace, there will always be gaps,
but the big gaps can be plugged with survey programs -
which contain lots of little observations that can go any time)


During and after execution
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Telescope slews to target.

Data is taken and recorded to the on board tape recorder.

The observations start and stop with each time the Earth occults the
target.

Later the telescope makes contact with a Tracking Data Relay Satellite
(TDRS) and data is down linked.

The actual path of the data is from HST to TDRS to Whitesands NM to a
domestic communications satellite to Goddard Space Flight Center to
the Institute.

Data is automatically processed for routine calibrations.

Raw and calibrated data is written to archive and tape if requested.

If requested, the tapes are mailed to the scientist, otherwise the
data can be gotten from the archive with a special password.

Scientist begins to reduce the data using various specialized software
packages. (some specific to HST data, others not)

Scientist draws conclusions or at least raises questions and presents
this as a scientific paper or a talk at a conference.