Apollo post-TLI immediate return-to-earth possibilities

Apollo post-TLI immediate return-to-earth possibilities


I recall that the first crew and MCC actions after lunar touchdown
was to assess LM health, with the option of immediate liftoff and
return to lunar orbit. There was, I believe, a contingency procedure
for just such an emergency procedure.

But how about earlier in the flight, just after TLI from LEO using
the S4B? Were there ever any serious contingency plans for an
immediate turnaround and fast return back to Earth?

It seems it would have been pretty complex, requiring LM checkout
and firing the LM engine, then jettisoning it and firing the Apollo SPS.
That could have taken a LONG time -- a day or so, maybe more --
that pretty much would void any advantage of turning around versus
just doing an Apollo-13 style lunar fly-past.

Has anybody heard of any speculations -- even half-baked plans --
for such an immediate post-TLI abort and fast return to Earth?

Thanks!

In article ,
Jim Oberg wrote:
But how about earlier in the flight, just after TLI from LEO using
the S4B? Were there ever any serious contingency plans for an
immediate turnaround and fast return back to Earth?

Yes, there were abort options both during and after TLI.

During TLI, it would mean S-IVB shutdown, separation, a big SPS burn, and
a flight time of up to a few hours (possibly with a midcourse correction)
before reentry, depending on how far TLI had gotten. This was basically a
major-emergency procedure, for the case where something broke badly during
TLI.

For aborts immediately after TLI, there was a planned abort opportunity 90
minutes later -- again using a big SPS burn, and a flight time of a few
hours with a midcourse correction to fine-tune reentry. There were
similar opportunities later, with times chosen to put the spacecraft down
in ocean recovery areas. Only when they got fairly close to the Moon did
a free-return abort around the Moon start to look preferable.

It seems it would have been pretty complex, requiring LM checkout
and firing the LM engine, then jettisoning it and firing the Apollo SPS.

At least in the early missions, none of the abort plans involved using the
LM except in the event of SPS failure. As you say, it would take too long
to set up. Also, with a fully-loaded SM, I'd guess you wouldn't get a lot
of extra delta-V from the LM burn. (After LOI, with the SM nearly empty,
was a very different case.)

That could have taken a LONG time -- a day or so, maybe more --
that pretty much would void any advantage of turning around versus
just doing an Apollo-13 style lunar fly-past.

For Apollo 13, they actually briefly considered a turn-around abort, but
it would have required jettisoning the LM, which closed off too many
options.

Has anybody heard of any speculations -- even half-baked plans --
for such an immediate post-TLI abort and fast return to Earth?

See above. This isn't particularly obscure; it's discussed briefly in
some of the documents reprinted in the Apogee books, for example.
--
spsystems.net is temporarily off the air; | Henry Spencer
mail to henry at zoo.utoronto.ca instead. |

Jim Oberg wrote:
Apollo post-TLI immediate return-to-earth possibilities


I recall that the first crew and MCC actions after lunar touchdown
was to assess LM health, with the option of immediate liftoff and
return to lunar orbit. There was, I believe, a contingency procedure
for just such an emergency procedure.

But how about earlier in the flight, just after TLI from LEO using
the S4B? Were there ever any serious contingency plans for an
immediate turnaround and fast return back to Earth?

It seems it would have been pretty complex, requiring LM checkout
and firing the LM engine, then jettisoning it and firing the Apollo SPS.
That could have taken a LONG time -- a day or so, maybe more --
that pretty much would void any advantage of turning around versus
just doing an Apollo-13 style lunar fly-past.

Has anybody heard of any speculations -- even half-baked plans --
for such an immediate post-TLI abort and fast return to Earth?

Thanks!

Here is a description of the "TLI 90-minute abort" from an Apollo 11
press kit.

"http://www-lib.ksc.nasa.gov/lib/archives/apollo/pk/APOLLO11pt1.PDF"

pg 74-75

"Deep Space Aborts
Translunar Injection Phase --
Aborts during the translunar injection phase are only
a remote possibly, but if an abort became necessary during the
TLI maneuver, an SPS retrograde burn could be made to produce
spacecraft entry. This mode of abort would be used only in the
event of an extreme emergency that affected crew safety. The
spacecraft landing point would vary with launch azimuth and length
of the TLI burn. Another TLI abort situation would be used if a
malfunction cropped up after injection. A retrograde SPS burn
at about 90 minutes after TLI shutoff would allow targeting to land
on the Atlantic Ocean recovery line.

Translunar Coast phase --
Aborts arising during the three-day translunar coast
phase would be similar in nature to the 90-minute TLI abort.
Aborts from deep space bring into the play the Moon's antipode
(line projected from Moon's center through Earth's Center
to the surface opposite the Moon) and the effect of the Earth's
rotation upon the geographical location of the antipode. Abort
times would be selected for landing when the 165 degree west
longitude line crosses the antipode. The mid-Pacific recovery
line crosses the antipode once each 24 ho,_rs, and if a timecritical
situation forces an abort earlier than the selected
fixed abort times, landings would be targeted for the Atlantic
Ocean, West Pacific or Indian Ocean recovery lines in that order
of preference. When the spacecraft enters the Moon's sphere
of influence, a circumlunar abort becomes faster than an attempt
to return directly to Earth."

- Ed Kyle

"Jim Oberg" wrote in message
...

I recall that the first crew and MCC actions after lunar touchdown
was to assess LM health, with the option of immediate liftoff and
return to lunar orbit. There was, I believe, a contingency procedure
for just such an emergency procedure.

But how about earlier in the flight, just after TLI from LEO using
the S4B? Were there ever any serious contingency plans for an
immediate turnaround and fast return back to Earth?

Has anybody heard of any speculations -- even half-baked plans --
for such an immediate post-TLI abort and fast return to Earth?

There was much more than speculation. The abort scenarios for incomplete TLI
burns or emergencies during translunar coast were worked out in detail. One
good reference is "Apollo Abort Planning," C.T Hyle, C.E Foggatt, B.D.
Weber, R. J. Gerbracht, and L.S. Diamant, 1970. This is AIAA Paper number
1970-94, available at www.aiaa.org or fine engineering libraries everywhere.
The paper includes plots of return trip time as a function of when a
translunar abort occurs and the maneuver delta-v imparted. There were some
constraints - notably that certain return orbits would result in entry
velocities which exceeded the capability of the TPS, and that trip time
correlates directly with landing location, so they tried to pick solutions
which put the landing site in the Pacific. Despite those issues, it looks
like there were options for return in as little as 12 hours if an abort was
called shortly after TLI. Apparently the crew were provided with translunar
abort guidance solutions for pre-determined times during the translunar
coast, so that in the event of a loss of communication with the ground they
would be able to perform them independently.

Josh Hopkins

Thanks for the valuable responses and leads
to this question -- it's for an article i'm
preparing on trans-MARS abort options.