Why wasn't escape tower used on Gemini?

I was just watching the gemini DVD again. It said that an ejection
from the capsule probably wouldn't have been survivable because of the
speed. why didn't Gemini use the escape tower like Mercury and
Apollo?

On Sun, 26 Nov 2006 02:07:11 GMT, wrote:

I was just watching the gemini DVD again. It said that an ejection
from the capsule probably wouldn't have been survivable because of the
speed. why didn't Gemini use the escape tower like Mercury and
Apollo?

Henry Spencer answered this several years ago. Hopefully it's OK
for me to simply repost what he wrote then:

From: Henry Spencer
Date: Wed, Apr 19 2000 12:00 am

In article ,
Cletus Scharle wrote:

The story put out at the time was that the hypergolic propellants of the
Titan II would not detonate as quickly or with the brissance of
LOX/hydrocarbon propellants, therefore making the ejection seats
sufficient.
Any comments, Henry?

"Well, the hypergolic propellants made ejection seats *feasible* -- just --
as an escape method. Since they ignite on contact, it's hard for them to
form an explosive mixture and then go boom; this reduces the probable
violence of a Titan II accident.

Very early Gemini concept drawings do in fact show an escape tower. No
surprise, given that Gemini began as Mercury Mark II.

The switch to ejection seats apparently was motivated mostly by saving
weight. The seats took a lot of time and hassle to develop, but they were
a lot lighter than having a great hulking brute of a solid rocket on top.
They also eliminated the requirement for a backup parachute and its
associated hardware, since if the main parachute failed, the crew could
always just eject.

Something that doesn't get mentioned so often is *why* saving weight was
considered so important. Gemini never had a real weight crisis. But
there was a quiet ulterior motive: Gemini's designers had their eyes on
missions beyond LEO, and wanted to keep as much performance reserve in
hand as possible. "

Dale wrote:

I was just watching the gemini DVD again. It said that an ejection
from the capsule probably wouldn't have been survivable because of
the speed. why didn't Gemini use the escape tower like Mercury
and Apollo?

Henry Spencer answered this several years ago. Hopefully it's OK for
me to simply repost what he wrote then:

The switch to ejection seats apparently was motivated mostly by
saving weight....

There's no doubt that using ejection seats saved weight, but was that
the *main* reason?

According to Jim Chamberlin (chief designer of the Mercury Mark II and
Gemini's first project manager), much of it was motivated by his
personal distaste for the complexity of the Mercury escape tower and
associated automatic sequencing system, the large amount of time
required to check out the system before flight, and associated penalties
regarding reliability. See:

On The Shoulders of Titans
http://history.nasa.gov/SP-4203/ch2-5.htm

The new design attacked a number of other Mercury trouble spots. Perhaps
the most troublesome was the sequencing system. Chamberlin argued that
one of his chief motives for keeping systems in the new design separated
was to avoid the endless complications Mercury experienced because so
many sequentially controlled operations were built into it.

.....

What may have been the most complex sequencing of all was demanded by
the automatic abort modes in Mercury, which depended on a
rocket-propelled escape tower to pull the capsule away from the booster
in an emergency during or just after liftoff. In Chamberlin's mind,
"the sequencing of the escape system was one of the major problem areas
in Mercury in all its aspects - its mechanical aspects in the first part
of the program, and the electronic aspects later."

....

[Chamberlin's] active distaste for escape towers made him eager to
include ejection seats in his design.

....

Titan II had power to spare, its total thrust being almost two and a
half times that of Atlas. Not only could it easily lift the heavier
spacecraft, but it could also carry the redundant systems that would
make it a safer booster for manned space flight.

....

Ejection seats not only promised to relieve a major source of trouble by
getting rid of the escape tower, but they also furthered the concept of
modularization, keeping each spacecraft system, so far as possible,
independent. "The paramount objective in the program," according to
Chamberlin, "was to dissociate systems." Ejection seats, in what he
called "very happy coincidence that was fully realized at the time,"
also fitted in nicely with another design change, substituting
paraglider for parachute recovery.

- - -

So, the Titan II and its propellants made it possible and the weight
savings were a bonus, but it appears that the Chamberlin's desire to
simplify Mercury systems, particularly the automatic sequencer, that
persuaded him to replace the escape tower with ejection seats.

--
Dave Michelson

wrote:

I was just watching the gemini DVD again. It said that an ejection
from the capsule probably wouldn't have been survivable because of the
speed. why didn't Gemini use the escape tower like Mercury and
Apollo?



It was thought that the less volatile propellants of the Titan II would
make a vehicle failure in flight less catastrophic than that of the
Atlas or Saturns.
Originally it was intended to recover Gemini on land using an inflatable
Rogallo parawing and skids, and the ejection seats would have allowed
the crew to escape if it didn't deploy correctly.
The proposed Saturn launched Lunar Gemini variants would have used an
escape tower.

Pat

Pat Flannery wrote:


Originally it was intended to recover Gemini on land using an
inflatable Rogallo parawing and skids, and the ejection seats would
have allowed the crew to escape if it didn't deploy correctly.


This wasn't from the beginning of the program which used parachutes for
recovery, but it did get as far as manned landing attempt which resulted
in a crash, so the concept got dropped. One fallout of this was the
horizontal landing attitude of the Gemini compared to the
heatshield-first landing of Mercury and Apollo.


Pat

On Sun, 26 Nov 2006 09:31:42 GMT, Dave Michelson wrote:

Dale wrote:

I was just watching the gemini DVD again. It said that an ejection
from the capsule probably wouldn't have been survivable because of
the speed. why didn't Gemini use the escape tower like Mercury
and Apollo?

Henry Spencer answered this several years ago. Hopefully it's OK for
me to simply repost what he wrote then:

The switch to ejection seats apparently was motivated mostly by
saving weight....

There's no doubt that using ejection seats saved weight, but was that
the *main* reason?

According to Jim Chamberlin (chief designer of the Mercury Mark II and
Gemini's first project manager), much of it was motivated by his
personal distaste for the complexity of the Mercury escape tower and
associated automatic sequencing system, the large amount of time
required to check out the system before flight, and associated penalties
regarding reliability.

snip

Maybe the real answer as to why they chose ejection seats is simply
because they could? It certainly simplified things, and added an escape
option at the end of the flight, should the envisioned parawing fail. It seems
to me that the experience gained with Mercury should have lessened the
automatic sequencing hassles to be expected with Gemini. But simplicity
is a virtue, regardless of whether or not an escape tower might have been
easier to apply to Gemini after the lessons learned with Mercury.

Ejection seats weren't an option with Apollo. Were the lessons learned
with the Mercury escape system readily applied to Apollo, or were the two
on separate but parallel design paths, and a lot of stuff had to be learned
all over again with the Apollo LES?

Dale

Maybe you'll get an "I corrected an old and unauthorized repost from Henry"
t-shirt, Dave

On Sun, 26 Nov 2006 03:54:11 -0600, Pat Flannery wrote:

Originally it was intended to recover Gemini on land using an
inflatable Rogallo parawing and skids, and the ejection seats would
have allowed the crew to escape if it didn't deploy correctly.

This wasn't from the beginning of the program which used parachutes for
recovery, but it did get as far as manned landing attempt which resulted
in a crash, so the concept got dropped. One fallout of this was the
horizontal landing attitude of the Gemini compared to the
heatshield-first landing of Mercury and Apollo.

At the beginning of the program, if the parawing hadn't been envisioned yet,
were the parachutes to be in the nose of the craft? If so, how far along did the
design get before the change? Was there any "fallout" from that?

Sorry if these are dumb questions...

Dale

On Sun, 26 Nov 2006 02:07:11 GMT, wrote:

I was just watching the gemini DVD again. It said that an ejection
from the capsule probably wouldn't have been survivable because of the
speed. why didn't Gemini use the escape tower like Mercury and
Apollo?

Sorry about posting about this yet again (but it is refreshingly on topic

The original poster's question raises a good point. While NASA might
have had in mind launch pad explosions as the primary need for escape,
from their limited previous experience- by the time the escape tower
was jettisoned from both Mercury and Apollo, the survival prospects for
guys instead being shot out from the capsule on ejection seats must have
been pretty grim. Was the escape envelope dangerously limited on ascent
during the Gemini missions, or could the capsule/adapter module fill the gap
and safely separate in the even of a late ascent problem?

Dale

It figures that Jim Chamberlin was/is Canadian...

Pat Flannery wrote:
Originally it was intended to recover Gemini on land using an inflatable
Rogallo parawing and skids, and the ejection seats would have allowed
the crew to escape if it didn't deploy correctly.

If it didn't deploy correctly, wouldn't they just be ejecting into the
failed parawing? All that cloth and the support lines would surely get
in the way of a safe ejection if it partially deployed.

Mark

wrote in message
oups.com...
Pat Flannery wrote:
Originally it was intended to recover Gemini on land using an inflatable
Rogallo parawing and skids, and the ejection seats would have allowed
the crew to escape if it didn't deploy correctly.

If it didn't deploy correctly, wouldn't they just be ejecting into the
failed parawing? All that cloth and the support lines would surely get
in the way of a safe ejection if it partially deployed.

No, since they could have ejected the failed parawing first.

Mark