Using the predicted count rates from § 3.0.3,
we can estimate telemetry rates and dump sizes required for the CUBIC \
science data.
We expect to be able to obtain 99% - 99.5%
charged particle rejection. In this case, the charged particle background
will only be 
count per second, and our data rate will be
dominated by the sky rate of 
2--5 counts per second.
For these calculations, we will assume an X-ray count rate of 4 cps.
Our telemetry packing algorithm uses 64 bits per photon.
The CCD frame headers add a substantial overhead, and
the ECC memory increases the science data by 50%.
The science data header adds nearly half a megabit,
and the pointer header, and synch words
add a small amount as well.
Without any additional reduction in data volume, we
would exceed the CUBIC T/M allocation of 20 Mbits
per T/M dump and the total CUBIC memory of 24 Mbits.
To ensure that CUBIC does not
fill its memory with useless data, we will use time-tagged serial
commands to tell the ICP when to process data (dark portion of the
orbit, unocculted by Earth, not in SAA) and when to ignore data
(see §4.4.15).
We expect to collect data for only 25% of the time after applying
the criteria mentioned above, and
this procedure should reduce the CUBIC data rate to roughly
29 Mbits/day.
As a further measure to avoid filling the memory with background events
during SAA passages, etc., the ICP will monitor the count rate and will
overwrite data collected during times of excessive count rate.
High count rates experienced during observations of bright sources
will be dealt with through a ``Bright Source Mode'', during which
time normal count rate ceilings on data processing will be ignored.
The excess memory above the amount usable for T/M dumps will be used
as spare memory in the event of a memory chip failure in flight.
We will transmit complete CCD frames at least once per day in order
to carefully track the performance of the CCDs.
This will be done during the orbits
with ground station contacts.
These frames will be compressed using a simple, fast algorithm in order to
reduce the data volume necessary to transmit this information.
Pixels with values less than 128 will be transmitted as bytes (with
a leading zero).
Pixels with values over 127 but under 4096 will be transmitted
as words in which the most significant nibble is set to hex 8 (0x8XXX).
Any pixels with values over 4095 (which can only occur if the baseline
subtraction and mean row correction produces negative values in some pixels)
are transmitted as 16 bit words without any masking of the upper nibble.
This permits the CPU to pack the pixels on a pixel-by-pixel basis during
the frame processing.
This compression scheme
requires 
million bits to transmit a single CCD frame, assuming
roughly 7000 pixels exceed the threshold value of 127
(this number is estimated by assuming 27 X-ray events occupying 5 pixels
each plus 700 cosmic ray events occupying 100 pixels each).
This will leave enough bits available to transmit normal
data for the remainder of the orbit (
Mbits).
We will transmit one CCD frame per orbit in this way during the
second and third orbits of each sequence of ground station contacts,
alternating detectors each orbit,
with an estimated data volume of 6.3 Mbits
for these dumps.
In Table 23 we show predictions for the data volume generated by CUBIC (assuming a count rate of 4 cps) for each pass in a single day.
Table 23: Predicted data volume for one day of CUBIC operations