[asac] Nutator Questions for Leiden Meeting

[Al Wootten]

Jeff Kingsley forwards some possible choices on subreflector options
for discussion in Leiden:

All,

Listed below are the questions I hope you can get answered at the ASAC
meeting later this week.   It is important that we get clear science
guidance on these issues so that they can be properly budgeted and work
can start on getting the nutator developed.  I have added a few possible
option for the nutator with rough estimated costs that I hope will be
useful in making the cost performance tradeoffs of the science
requirements.

1.) Do the nutator requirements listed below agree with the science
requirements?

Switching Rate:            1-10 Hz variable
Transition time:             10 msec
Throw:                        +/- 3 acrmin on sky
Reaction less:                Yes
Pointing requirement:    Meet all Antenna RFP pointing specifications
Multiaxis:                    ?
Budgeted Cost:            ?

2.) Are nutators required for the prototype antennas?

3.) How many nutator will be required for the full array?

4.) Several nutator options are listed below with the estimated
production cost.  What option best meets the science requirements
considering the cost trade off?  does the group have any alternate
option, idea or proposal for the nutator?

    A.) For a single axis reactionless nutator similar to the SMA but
scaled for ALMA is expected to to cost about a $100k for production
version.

    B.)   A simple multiaxis nutataor might use a reactionless nutator
similar to the SMA but scaled for ALMA along with a rotator about the
optical axis.   The rotator would have a range of about +/-90 with the
slow motion in rotation .  This type of multiaxis system would be the
most economical and simplest to implement. (The 12-meter at Kitt Peak
originally had a similar type system.)  The estimated cost of production
models of this system is about $160k.

    C.) Same as above but with full rotation about optical axis at a
fast rate of about 10 rpm. This system would require slip rings and cost
about $210k.

    D.) A gimbaled reactionless system similar to the JCMT could be
implement but the system would be very massive and might require
modification to the antenna feed legs and structure resulting in
additional antenna cost.   The estimated production cost is about $260k
not including possible antenna  modifications

    E.) A completely new reactionless hexapod nutator system could be
developed but this would be very expensive to develop.  The system would
be light weight and dynamically be very agile.   The production cost is
expected to be similar to items A or B but developmental cost would be
about $400k and take about 20 months.

The nutator options list above are rough estimates but the best that we
have right now.  Other option exist but have not yet been explored.  I
wanted to confirm with Simon on the above estimates but have been unable
to get a hold of him.   Once I talk with him I might revise the costing.

Good luck at the meeting and I look forward to hearing the results.


Best wishes,

Jeff