Fictional Apollo 18(+) Missions

In article ,
TVDad Jim wrote:
I believe it was so far out of plane that it was taxing fuel requirements.

I'm no whiz-bang at orbital mechanics, but couldn't the Apollo stack
have been inserted into lunar orbit on a trajectory other than
equatorial? How much more fuel would that have cost?

To a first approximation, you can reach any lunar-orbit inclination for
about the same cost, provided you don't insist on getting there on a
free-return trajectory. (A free-return trajectory confines you to sites
very near the equator, which is why the initial "Apollo zone" was there.)
Several of the later flights did indeed use orbits at substantial
inclinations.

Looked at more closely, though, some orbits are slightly more expensive
than others to reach... and Apollo's margins were always very thin at LOI
time, when considerable fuel had to be reserved against contingencies
(e.g. a possible need to use less-precise backup navigation methods
later). In fact, it was usually necessary to violate at least one of the
official mission constraints to make the LOI maneuver feasible; planning
for that maneuver was complex.
--
"Think outside the box -- the box isn't our friend." | Henry Spencer
-- George Herbert |

(Henry Spencer) wrote:
In article ,
Pat Flannery wrote:
You know where they should have sent a crew? The crater Alphonsus...

It was short-listed for both 16 and 17, but didn't make the final cut
for either.
--
"Think outside the box -- the box isn't our friend." | Henry Spencer
-- George Herbert |
What was the reason for Alphonsus not making the cut for either 16 or 17?



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(Henry Spencer) wrote:
In article , Matt Wiser
wrote:
I read in Chalkin's book that when Tycho was suggested as a landing site
for one of the later Apollos, Jim McDivitt (who had some veto power over
sites for safety) is supposed to have said "You are going to Tycho over
my
dead body."

Tycho kept being crossed off the list due to unacceptable operational
problems, and kept being added back because of very strong scientific
interest. By unanimous consent it got put at the end of most of the
lists, in hopes that the operational constraints would ease up with time.
As they in fact did, but not enough to make Tycho a serious candidate.

Wasn't Jack Schmitt lobbying for a farside landing? He argued that with
comsats
put in lunar orbit and in a relay position, the crew would not be out of
communication with Earth. It was shot down, but it was considered.

During the post-Apollo-13 hiatus, he argued for picking spectacular
targets to try to regain public attention; specifically, he proposed
sending the (then) four J missions to Tycho, Mare Orientale (on the
western edge of the nearside), the north pole, and the farside. But
money was tight and upper management was nervous about possibly losing
a crew, so doing something daring was not in the cards.

Site selection for Apollo 17 did revisit various previously-discarded
targets on general principles, and the farside idea got brought up again,
but there simply wasn't money for the necessary relay satellite.
--
"Think outside the box -- the box isn't our friend." | Henry Spencer
-- George Herbert |
What were the candidates for Apollo 17's landing? Taurus-Littrow was site
chosen, but what other site(s) were on the table for Apollo's finale?


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(Henry Spencer) wrote in message ...

To a first approximation, you can reach any lunar-orbit inclination for
about the same cost, provided you don't insist on getting there on a
free-return trajectory. (A free-return trajectory confines you to sites
very near the equator, which is why the initial "Apollo zone" was there.)
Several of the later flights did indeed use orbits at substantial
inclinations.

Again, I'm not good at the math here, but I thought there were
opportunities at the La Grange Point #1 where Apollo could adjust the
inclination angle somewhat. I know it's not the same as changing an
orbital inclination (which would involve expending almost as much
energy as a second launch) but I'm not sure how much energy would be
involved in changing the entry angle at L1. Isn't the entry cone
something like a lever, where it costs more energy at the base than at
the tip to change inclination? (with L1 being the tip of the cone).

/Somewhere, Kepler's grave has switched to 78 rpm...

In article , Matt Wiser wrote:
You know where they should have sent a crew? The crater Alphonsus...
It was short-listed for both 16 and 17, but didn't make the final cut...

What was the reason for Alphonsus not making the cut for either 16 or 17?

It was close enough to Mare Imbrium to have a fair chance that its
original pre-Imbrium surface had been contaminated by Imbrium ejecta.
There was a strong desire for ancient samples, as ancient as possible.

By the time of site selection for 17, people understood that ancient
samples were not easy to come by anywhere, but going far away from Imbrium
still seemed likely to improve the odds. Also, another complication
intervened: Apollo 15 had observed and photographed what everyone thought
were young volcanic features in Taurus-Littrow. (Volcanic they are, but
young they aren't -- because the glass-rich ejecta deposits are
mechanically weak, they don't preserve craters as well as hard rock does,
so they look less cratered than they are.)
--
"Think outside the box -- the box isn't our friend." | Henry Spencer
-- George Herbert |

In article , Matt Wiser wrote:
Site selection for Apollo 17 did revisit various previously-discarded
targets on general principles, and the farside idea got brought up again,
but there simply wasn't money for the necessary relay satellite.

What were the candidates for Apollo 17's landing? Taurus-Littrow was site
chosen, but what other site(s) were on the table for Apollo's finale?

The short list was Alphonsus, Gassendi, and Taurus-Littrow. Alphonsus
seemed too close to Mare Imbrium to be uncontaminated old terrain, the
operations people thought Gassendi's floor was too rough and vetoed it,
and Taurus-Littrow was at the head of the scientists' list anyway because
of generally-ancient terrain with seemingly-young volcanic features (see
my other posting).
--
"Think outside the box -- the box isn't our friend." | Henry Spencer
-- George Herbert |

On Sun, 28 Nov 2004 19:35:38 -0600
Pat Flannery wrote:

Oh...now that does make sense; it is mighty far from the lunar equator
compared to the other Apollo landings.

Is the problem the plane change which takes place while the LM is on the surface? A 70 hour surface stay seems to result in a 37 degree shift for a polar orbiting vehicle, less for a vehicle orbiting to just reach the lattitude of tycho.
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Michael Smith wrote:


Is the problem the plane change which takes place while the LM is on the surface? A 70 hour surface stay seems to result in a 37 degree shift for a polar orbiting vehicle, less for a vehicle orbiting to just reach the lattitude of tycho.


I was wondering about the free return path of a polar orbit myself. But
as you point out, the polar orbit is far more influenced by lunar
rotation than the basically equatorial one, and this may rule it out as
a usable option- although earlier in the thread there was discussion
about a lunar polar landing, and that would suggest some sort of a
high-inclination orbital path for the mission, wouldn't it?

Pat

In article ,
Pat Flannery wrote:
I was wondering about the free return path of a polar orbit myself.

Basically not feasible -- a free-return trajectory requires doing LOI more
or less over the lunar equator, which gives you a roughly equatorial
orbit. What you can do, at some small cost, is start out on a free-return
trajectory, stay on it until you've got your spacecraft separated and
checked out, and then move to the desired trajectory -- the difference
will be small if you do the move soon after TLI. Some of the Apollos did
this. (By the end of the program, they were confident enough that they
didn't even start out on a free-return trajectory, although they were
still close enough to one to move to it with RCS burns in a pinch.)

...although earlier in the thread there was discussion
about a lunar polar landing, and that would suggest some sort of a
high-inclination orbital path for the mission, wouldn't it?

If the landing site itself is polar or almost exactly so, then *any* polar
orbit passes over it, and there's no need to fiddle with the orbit to keep
passing over the landing site.
--
"Think outside the box -- the box isn't our friend." | Henry Spencer
-- George Herbert |

In article ,
TVDad Jim wrote:
To a first approximation, you can reach any lunar-orbit inclination for
about the same cost, provided you don't insist on getting there on a
free-return trajectory...

Again, I'm not good at the math here, but I thought there were
opportunities at the La Grange Point #1 where Apollo could adjust the
inclination angle somewhat.

The Apollos didn't pass through the L1 point, actually.

The usual mental model of the situation -- spacecraft zooms out to
intercept a nearly-stationary Moon -- is *wrong*. It's actually more
accurate to think of the spacecraft, nearly stationary at the apogee of a
highly elliptical transfer orbit, being overtaken by the fast-moving Moon.

That being the case, whether the spacecraft passes over the lunar equator
(where an LOI burn gives an equatorial orbit), or a lunar pole (where an
LOI burn gives a polar orbit), or something in between, is a matter of
quite small adjustments in exactly where the transfer orbit's apogee is
and exactly when you get there. Only when you start studying the details
quite carefully do modest cost differences appear.
--
"Think outside the box -- the box isn't our friend." | Henry Spencer
-- George Herbert |