APOLLO's Run Highlights
APOLLO runs are at present scheduled in consolidated chunks, so that
members of the collaboration can be present at the observatory for the
run. Ultimately, APOLLO telescope time will be scheduled in short (1 hour
or less) blocks throughout the month for optimal sampling of the lunar
orbit. The highlights below pertain to the once-monthly, few-day visits
to the observatory. Each time, we set new records and become more efficient
at getting outstanding laser returns from the moon.
APOLLO started getting "sky time" in July 2005a combination of engineering time and director's discretionary time. Snippets of time in
July, August, and September allowed us to hone our technique and develop the
software resources we needed to be successful on our first "real"
run in October, when we first installed the signal-boosting microlens array.
The run summary picks up here.
- first APOLLO ranges; see detailed
- successful ranges on three successive nights
- peak rate: 0.3 photons per pulse
- best run: 677 photons in 5000-shot (4 minute) run
- ranges comparable to JPL model within 0.1 ns (1.5 cm one-way)
- successful ranges on the last night (2-hour block) of run
- 1500 photons in roughly one hour span
- Successful ranges on two successive nights
- peak rate > 0.6 photons per pulse
- best run: 2150 photons in 12.5 minutes, pictured below
- total net on 12/08/05: 3700 photons
- in best run, 3 shots with 7-photon detections (and 7 shots
with 6 photons, 10 with 5, 40 with 4, 77 with 3, 272 with 2)
- half of the 2150 return photons in the best run were bundled in multi-photon detection events (the APD array is vital!)
- on the last night, acquired unambiguous signal in poor seeing within 10 seconds of start (and only 5 minutes into scheduled time)
Example run from December, 2005. The lunar return signal
is strikingly strong amidst the noise. The bursty nature is due in part
to manipulations of pointing as we try to optimize the signalsometimes
we steer completely off of it for a bit.
- only 2 out of the 12 scheduled hours were useful for ranging (weather)
- harvested 7000 photons in this brief period
- peak rate > 0.6 photons per pulse (and seeing not great, at > 1.5 arcsec)
- best run: > 2500 photons in 10000-shot (8 minute) block, hands-free
- recorded one event with 8 photons in return pulse
- building confidence in acquisition technique
- mostly weathered out, plus some software growing pains
- the short time we did get on the telescope had horrible seeing (3 arcsec), and
thus no acquisition
- both nights 100% clouded out, but substantial improvements to
overall capabilities were realized (closer to remote operability,
interleaved fiducial measurements)
- engineering effort resulted in stabilized clock
- much consternation over bad weather, but successful acquisition on
- having stabilized the clock, achieved interleaved fiducials (returns
from internal corner cube), and conducting periodic calibrations of the
TDC, this run represents the first science-quality data from APOLLO.
Prior data was good at the 12 centimeter level (not bad!), but we
now should be able to deliver millimeter-quality data.
- Let's not talk about May
- So far in 2006, we've been able to use 7.2 hours of 57 scheduled because
of weather. Less than six of these hours had decent seeing conditions.
- Nonetheless, we failed to acquire on a couple of decent nights in May.
- Enough about May
- A key breakthrough in understanding an anomalous 2 arcsecond
beam offset puts us on the path to efficient acquisition
- Found Apollo 15 quickly even in shadow (a first)
- Acquired Apollo 11 from Apollo 15 in less than a minute
- Saw a peak sustained photon rate of 0.2 photons per pulse on Apollo 11!
- Acquired Apollo 14 from Apollo 11 in less than two minutes (in dark)
- Good signal on all three Apollo reflectors within 15 minute period
- In second June run, verified our handle on acquisition (first night
found in ten seconds!)
- Established practical seeing limit at 2.02.5 arcsecondsbeyond
which acquisition is not assured. Luckily the seeing is rarely this bad.
- Operated from the control room: we are finally able to run the system
"remotely," opening the door for operations from our home
- Expanded beam to cover primary mirror more fully
- Installed notch filter in our CCD, allowing us to watch the target while ranging
Let the campaign begin...
Starting in the Fall of 2006,
APOLLO time is scheduled to occur more frequently as we
begin the science campaign in earnest.
Status updates now appear in tabular format
for each lunar month.
A running summary of APOLLO milestones appears below:
- As many as 9 photons in a single pulse
- Peak rate of about 0.8 photons per pulse (over several seconds)
- Sustained rate of about 0.35 photons per pulse (over several minutes)
- All four reflectors in a one-hour period (2650 photons total)
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