[alma-config]Reconfiguration Times

[John Conway]

Hi,


 I have been studying the timeline document Max Kraus
left on a 'strawman' scheme for reconfiguration using 2 
transporters which then gives a total of  4 moves per work day 
(i.e. 2 moves/antenna/day). This scheme  assumes 1 hour driving 
time (or 20km if the desired loaded speed or 20km/hr is 
achieved).  

Members of the configuration group wondered 
how the claimed move  rate of 2ant/day/transporter 
fitted in with the spec of 20- 30 minutes to pick up and set 
down antennas. According to Project book section 4.2.14
the requirement is that 

'....when the transporter arrives to 
pick up a maximum 20 minutes elapses before the transporter
leaves loaded with an antenna, and when it sets down a maximum
of 30 min is allowed between when the transporter arrives 
at a pad and when it is ready to depart...'. 
 

In fact the estimate Max gives (see details below) is more or 
less consistent with 
that spec  (he allows 30 min dead time for the transporter at 
both set up and set down), if we also  assume a drive time of 1hour
for the transporter.
In his scheme, he has two driver teams  and two antenna
teams, one such team dedicated to  preparation of an antenna 
for moving prior to transporter arrival and then loading onto 
transporter the other team doing unloading and installation.
 

The two specialised teams travel quickly from pad to pad 
doing their specialised functions. This saves man-hours - having 
fixed teams associated with each transporter wastes man-hours
since they have to spend the time in the cab while the transporter moves
from pad to pad.  In Max's scheme all the personnel work 6hrs 
at the site, though they  start  at staggered times. I have adapted 
his scheme slightly, I have included time for the specialised teams 
to move between pads, also I have included time for the transporter 
to move to the first pad at the start of the day.


-----------------------------------------------------------------------

Proposed Reconfiguration schedule, moving 4 antennas per day
using two transporters.

Each symbol between hyphens is assumed to take 0.5hrs.


Prep/Load team         Tr-Pr-L1-Tr-Pr-L2-Tr-Pr-L3-Tr-Pr-L4

Transporter 1          Tu-Tu-L1-Tl-Tl-U1-Tu-Tu-L3-Tl-Tl-U3

Transporter 2                   Tu-Tu-L2-Tl-Tl-U2-Tu-Tu-L4-Tl-Tl-U4
       
Unload/Install team                   U1-In-Tr-U2-In-Tr-U3-In-Tr-U4-In  

-----------------------------------------------------------------------

Key 

Pr - prep team  'shuts down'  antennaprepares antenna for arrival of 
     transporter.

In - Install team sets up  new antennas (i.e. get it ready for observations
     after transporter leaves)

Tr - prep or install team travels - uses fast vehicle (30-40km/hr)

Ln - Load antenna 'n' onto transporter. 
Un - Unload antenna 'n' onto pad.

Tu - Transporter travels to next pad -  unloaded
Tl - Transporter travels to next pad -    loaded


Using the above scheme all crews/drivers work 6hrs at the site 

-------------------------------------------------------------------


One can question whether Preparation of antenna for move 
and Installation  take less than 0.5 hrs assumed - it would be
nice to decide the spec for that. I didn't see anything in the 
project book, maybe there is something in the Antenna design 
documents. These in any case however don't effect the reconfiguration 
rate until  'Pr' and 'In' exceed half the drive time. Also the target 
goal for unloaded transporter motion twice that for 
loaded motion (50km/hr)  so 'Tu'
could be reduced. However  the work sequences of the eams 
have to synchronised or the man-hours and operations costs go up 
- hence  small adjustments like that don't effect the overall 
reconfiguration time.

Fundamentally in the above scheme there are 2 moves/ant/day 
because for each move there is  1hr travel (unloaded), 0.5hr pick 
up,  1hr travel (loaded), 0.5hr set down = 3hrs/move and a 6hr
work day at the site.

Its important to understand the travel time numbers
for  the compact array, how careful do we have to drive?
To go 200m at walking pace 5km/hr takes only 2 minutes.
All the time lost is in  acceleration-deceleration,
aligning on approach lasers, checking that 
blocking antennas are moved out of the way etc, etc. 
Despite the small distance I can't
believe that the drive time in the crowded compact array 
when we are moving between antennas with metre 
clearance can safely be lower than 0.5hrs?? In this 
case we can achieve 3 moves/transporter/day - and we 
probably need another preparation/installation crew.

If the time to load and unload an antenna on a transporter
can be reduced to 15 minutes and in the compact array 
drive times are 30 minutes, then we can achieve 
one reconfiguration per transporter in 90 minutes
or 4 moves/trans/day - and we probably need 4 
preparation/installation crews (unless these
functions can be reduced from the estimates of 30 minutes
which Max has  to 15 minutes in which case we make do with 
2 crews)


--------------------------------------------------------

Is a total of 4 moves/day enough??

For the largest configurations whether the proposed scheme 
is OK depends critically on what 
loaded speed  be achieved. In a Y+ design the longest moves
are 10-12km, so a speed greater than 10km/hr is needed. The
desired target loaded speed of 20km/hr is then well within 
requirements. However In memo 280 (Radford) for instance 
an 'effective' (including  detours, start and stop)   
loaded speed of  7.5km/hr and a ring array 
was assumed which then argued for more transporters to make the 
reconfigurations for the largest arrays in a reasonable time.


Using continuous reconfiguration in most intermediate 
configurations  a rate of reconfiguration 
of 4 antennas/move day is adequate. A 'Full cycle' in and
out - takes of order 306 moves (see todays memo 419 
by Otarola and Holdaway). Hence at 4 ant/move day, going 
full speed the array can go through all configurations
in 76 days (4.8 cycles/year!). More realistically I think would be 
to make 4 moves every 2 - 2.5 days, which realistically allows  two 
full cycles per year. The other days the transporter
and crews could be used to ferry antennas to the OCF 
or do general maintainence.

 However in the compact arrays from the configuration
point of view it may be  desirable to have significantly larger 
move rates (i.e. 6 - 8  moves/day). The reason is that 
the intermediate configurations between say the most compact 
and the first N-S extended array may not be as useful as 
for the intermediates.