Apollo Hypothetical Question (CSM Tracking)

In message , James Anatidae
writes
Something I've been wondering about since seeing "The Crawling Hand". If,
on its way to moon, one of the Apollo CSM's stopped transmitting suddenly,
would have NASA had any other way of figuring out were it was besides what
it's trajectory had been before the loss of communications? Or would it
have it been lost?

They'd be able to see it. The explosion on Apollo 13 was seen from
Earth, and even the Lunar Orbiters were photographed (magnitude 12-15,
though they were oriented to point the solar panels to Earth for the
picture)
--
"Forty millions of miles it was from us, more than forty millions of miles of
void"
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"Jonathan Silverlight" wrote
in message news
In message , James Anatidae
writes
They'd be able to see it. The explosion on Apollo 13 was seen from
Earth, and even the Lunar Orbiters were photographed (magnitude 12-15,
though they were oriented to point the solar panels to Earth for the
picture)
--
"Forty millions of miles it was from us, more than forty millions of miles
of
void"
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There was one ground based telescope that actually caught the "event".
Apparently it had been pointed at the projected location of the ship and had
the image displayed on a monitor. I do not know if it could actually see
the ship at that range in real time, but when the "event" occurred there
appeared a small "smudge" on the monitor, that was the cloud of liquid
oxygen reflecting sunlight. I read this years ago and have no idea what
telescope it was. Perhaps someone could fill in the details.


--
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In article ,
James Anatidae wrote:
Something I've been wondering about since seeing "The Crawling Hand". If,
on its way to moon, one of the Apollo CSM's stopped transmitting suddenly,
would have NASA had any other way of figuring out were it was besides what
it's trajectory had been before the loss of communications?

Not a good one. Some optical tracking of the CSMs was done, by amateurs
and experimentally -- as others have noted, the Apollo 13 tank burst was
in fact seen -- but it was not integrated with Apollo operations. Witness
the significant uncertainty in the impact location of Apollo 16's S-IVB
(which lost electronics power before lunar impact), a rather larger target
than a CSM.
--
MOST launched 1015 EDT 30 June, separated 1046, | Henry Spencer
first ground-station pass 1651, all nominal! |

In article ,
Doug... wrote:
There were radars that could skin-track a CSM at lunar distances, but I
don't know if they would have been available (or set up to do so).

References? I doubt that there was anything capable of routinely doing
that, not at 400,000km. There still isn't, as far as I know.

(The record for radar skin tracking of a spacecraft is 1.5Mkm -- the
detection of SOHO during the period when it was out of service -- but that
was a radar-astronomy tour de force, practical only because SOHO was
within the limited region of sky accessible to Arecibo, not a routine
capability of operational tracking systems.)

I'm
pretty sure the tracking was done by measuring the strength and location
of the radio signals from the CSM...

More precisely, by measuring their Doppler shift and the delay out and
back. The CSM's transmissions were phase-locked to the signal it was
receiving from Earth, so accurate ranging could be done. It wouldn't have
been nearly as good if they'd had to just listen, instead of sending a
signal up and listening for the CSM to (essentially) echo it back.

(Delay gives you range, of course. Doppler shift gives you rate of change
of range... but more important, watching how the Doppler shift changes as
Earth rotates gives you *direction* much more accurately than you could
determine it by just looking at antenna pointing.)

But I bet they'd be able to figure out roughly where the CSM was going,
if there was a complete comm loss. I'm pretty sure they could determine
that it still existed in one piece, anyway.

I think that might actually be a bit difficult... Of course, the crew
could still come home, because Apollo's on-board optical navigation system
didn't need Earth's help. (The original navigation-system requirement was
to be capable of flying the entire mission, including lunar landing, with
zero help from Earth, not even a voice link. That was later relaxed -- as
radio tracking got better, Cold-War worries about malicious interference
faded, and the CSM software started bumping up against memory limits -- to
merely being able to abort to a safe return at any time with zero help.)
--
MOST launched 1015 EDT 30 June, separated 1046, | Henry Spencer
first ground-station pass 1651, all nominal! |

Some NASA workers went looking for the apollo 11 LM ascent stage and found it
wasnt in lunar orbit and must of crashed.

I believe this was radar tracking..

In message , Hallerb
writes
Some NASA workers went looking for the apollo 11 LM ascent stage and found it
wasnt in lunar orbit and must of crashed.

I believe this was radar tracking..

He's still doing his "of", but without further evidence I'd guess they
went for optical detection. For one thing, how do you distinguish the
return from the LM from the rather bigger target which is probably also
in the beam?
--
"Forty millions of miles it was from us, more than forty millions of miles of
void"
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(Henry Spencer) wrote in message ...
In article ,
Doug... wrote:
There were radars that could skin-track a CSM at lunar distances, but I
don't know if they would have been available (or set up to do so).

References? I doubt that there was anything capable of routinely doing
that, not at 400,000km. There still isn't, as far as I know.

(The record for radar skin tracking of a spacecraft is 1.5Mkm -- the
detection of SOHO during the period when it was out of service -- but that
was a radar-astronomy tour de force, practical only because SOHO was
within the limited region of sky accessible to Arecibo, not a routine
capability of operational tracking systems.)

Any planetary radar could probably find an SM around the moon,
provided of course that the antenna can point at the moon. Due to the
r^4 dependence of radar, it's at least 100 times easier to do this at
lunar distances than at SOHO's. Goldstone and Haystack (both fully
steerable) were doing asteroid radar work in 1968 and could presumably
have been used. And for obvious reasons, these radars are set up to
do ranging and velocity on skin-track targets.

http://echo.jpl.nasa.gov/asteroids/P...r.history.html

The only problem I can see is that the moon may be *too close*. Some
of these radars switch between transmit and receive by physically
moving one feed out of the way and placing another at the focus. The
speed of this operation sets a limit to the closest target that can be
observed. It's no big deal for planets but can make it tough to
observe something as close as the moon, and these radars are
presumably not designed for anything closer.

To work around this problem (and maybe anyway for accuracy) they could
also do bi-static observations. Use one of the big transmitters to
illuminate the SM, then receive on all ground stations that have the
SM in view. The doppler shifts and time delays, combined with the
station locations and the earth's rotation, all known, will give you a
very accurate position and velocity. This is basically how the DSN
works today for spacecraft tracking. All the equipment needed for
this certainly existed at the time of Apollo, but I don't know about
the software and procedures. I'll bet something could have been
improvised if it was really, really needed.

Lou Scheffer

In article ,
Doug... wrote:
References? I doubt that there was anything capable of routinely doing
that, not at 400,000km. There still isn't, as far as I know.

Any planetary radar could probably find an SM around the moon,
provided of course that the antenna can point at the moon. Due to the
r^4 dependence of radar, it's at least 100 times easier to do this at
lunar distances than at SOHO's. Goldstone and Haystack (both fully
steerable) were doing asteroid radar work in 1968 and could presumably
have been used...

Thanks, Lou. I knew the capability existed.

But if it existed, *why* wasn't it used?

There *were* cases where electronics failures caused loss of tracking on
objects that people wanted tracked, like Apollo 16's S-IVB. None of them
was skin-tracked. This seems to contradict the claim that such a
capability was available then.

To me, it looks like the capability did *not* exist. It might possibly
have been put together, with significant improvisations, but it wasn't
available on request.

Goldstone and Haystack tracked Icarus at its closest approach in 1968.
Icarus was about 15 times the distance of the Moon, which hurts by a
factor of about 50,000, but it is about 250 times the diameter of an
Apollo, which helps by a factor of about 63,000. So Icarus is not really
any harder to track than Apollo, and may have been somewhat easier.
--
MOST launched 1015 EDT 30 June, separated 1046, | Henry Spencer
first ground-station pass 1651, all nominal! |

On Tue, 23 Sep 2003 20:30:50 GMT, (Henry Spencer)
wrote:

Icarus was about 15 times the distance of the Moon, which hurts by a
factor of about 50,000, but it is about 250 times the diameter of an
Apollo, which helps by a factor of about 63,000.

I make it (1400m / 3.9m) about 360 times the diameter. T-shirt?

Chris

--
"War is the state's killer app" - Ken MacLeod
[peacetime .sig will return when apposite]

(Lou Scheffer) wrote in message . com...
(Henry Spencer) wrote in message ...
In article ,
Doug... wrote:
There were radars that could skin-track a CSM at lunar distances, but I
don't know if they would have been available (or set up to do so).

References? I doubt that there was anything capable of routinely doing
that, not at 400,000km. There still isn't, as far as I know.

Any planetary radar could probably find an SM around the moon,

Backing this up a little, from
http://www.news.cornell.edu/releases/May96/arecibo.html
an article talking about the Arecibo upgrade, "the radar could detect
a steel golf ball at the distance of the moon."

Of course this is the post-upgrade performance, which would not have
been available in 1968. However, from the same page: "The new system
increases the telescope's sensitivity by a factor of about 20 for
radar studies of the solar system". Since Apollo was a lot bigger
than 20x the area of a golf ball (even end on it was roughly 5,000x
bigger), the old pre-upgrade radar could easily find an SM. The other
planetary radars that existed at the time were not quite as powerful,
but they were competitive, and should not have had problems either.

Lou Scheffer