Re: Why did it take so long to reach the moon

On Mar 3, 11:34 pm, terry <tfm...@xxxxxxxxxxxxxx> wrote:
On Mar 4, 5:50 pm, BradGuth <bradg...@xxxxxxxxx> wrote:

On Mar 3, 12:02 pm, terry <tfm...@xxxxxxxxxxxxxx> wrote:

On Mar 4, 2:02 am, BradGuth <bradg...@xxxxxxxxx> wrote:

On Mar 3, 4:18 am, terry <tfm...@xxxxxxxxxxxxxx> wrote:

On Feb 26, 2:15 am, P...@xxxxxx wrote:

I was just looking at the Apollo 15 DVD set. It showed them flying
over their landing site at GMT 96 hours and something. that's 4 whole
days after launch. If they were traveling at 25,000 MPH, they should
have made it in about 10 hours. Did they slow down along the way? Do
they orbit earth a few times to check things out or head for the moon
as soon as they're in the right position?

25,000 mph is about the speed to escape the earths gravity, then the
craft just coasts , gradually losing speed until the moons gravity is
stronger and it begins to accelerate again. Actually the time of
flight to the moon is a very strong function of the injection speed.
the flight time chosen for Apollo missions was about 72 hrs which
required an injection speed of about 10.84 km/sec. Increasing the
injection speed to just 11.2 km /sec would have reduced the flight
time to only 32 hours. It is all a balance of the wt of fuel
required versus the extra supplies for life support.
The above figures come from " fundamentals of astrodynamics" by Bate,
Mueller and White. I highly reccommend it for explaining the maths of
various spaceflight trajectories.
Terry

Obviously there wasn't sufficient fuel for retro-thrusting on behalf
of getting there any sooner than they supposedly did. Of course
robotics have little of anything that isn't rad-hard to start off
with, so there's no great hurry.

Coasting through the moon's L1 as slow as possible is by far the most
fly-by-rocket efficient alternative, and that should be rather easily
simulated.

The minimum injection speed is 10.82 km/sec, which will give a flight
time of 120 hrs. anything less than this speed, the craft will not
make it and fall back to earth. same ref as given earlier)
terry

In other words, that initial 10.82 km/s is going to become just
slightly better than zero meters/sec velocity or speed of advance as
arriving into the moon's L1. Is that it?
. - Brad Guth- Hide quoted text -

yep that would be my interpretation.

Of course that low of SOA, as per coasting efficiently into the moon's
L1, as accomplished without applied retrothrust is going to take
somewhat longer than those NASA/Apollo missions had taken place, but
otherwise such a near zero velocity at this Earth-Moon L1 zone of
mutual or null gravity would have been an extremely energy efficient
application of fly-by-rocket deployment, as well as for accommodating
whatever Clarke Station like station-keeping format if that was ever
the intent of a given mission.

Too bad there's no such public simulators (especially of nothing in 3D
interactive eye-candy format) available for running off various
payloads simulations, as per trekking through this gravity nullified
oasis.
.. - Brad Guth
.

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