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From: Henry Spencer <>
Subject: Re: Apollo Block I (was:Reliability of Shuttle...)
Date: Mon, 26 Aug 1996 12:50:53 GMT

>> I've never understood the infatuation with lifting bodies.  I'd go for an
>> enlarged Gemini -- Gemini was operationally a better spacecraft than
>> Apollo -- including development of the paraglider for land touchdowns. 
> Why was Gemini a better spacecraft? 

Basically, because it was designed with benefit of hindsight from Mercury,
which Apollo was not (due to the lead time involved).  In particular, both
Mercury and Apollo were outer shells with equipment stuffed inside them,
meaning that almost all preparation and maintenance work had to be done
from *inside*.  This severely limited access, because the cramped interior
meant that few people could work simultaneously.  Almost all the Gemini
equipment was accessible from *outside*.  Gemini was originally conceived
as "Mercury done right", and was enlarged to a two-man spacecraft almost
as an afterthought (although the enlargement turned out to be crucial to
getting it funded).

> What would an enlarged Gemini have looked like?

The same only bigger. :-)  Well, the adapter section would also have been
revised to match the launcher used.

> Would there have been ways to put an airlock on it?

Yes.  The MOL project put a hatch in a Gemini, between the astronauts'
heads, for pressurized access to a larger module attached on the rear.
(Yes, the hatch went through the heatshield -- this was flight-tested
on an unmanned Gemini, and it worked.)  It would have been easy enough 
to put an airlock module, or even a small habitation module, in an 
enlarged adapter section, with access via a similar hatch.

> And another thing: how would this improved Gemini have handled
> docking? Would it need to do EVA style transfers of crews?

The simplest thing would probably be to put a docking assembly on the base
of the adapter module.  With the MOL-style hatch to get you into the
adapter, no EVA would have been needed.  That's more or less how Hermes
was going to do things. 
 ...the truly fundamental discoveries seldom       |       Henry Spencer
occur where we have decided to look.  --B. Forman  |

From: (Henry Spencer)
Subject: Re: Question about Gemini
Date: Wed, 19 Apr 2000 03:58:15 GMT

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
>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.
"Be careful not to step                 |  Henry Spencer
in the Microsoft."  -- John Denker      |      (aka

From: (Henry Spencer)
Subject: Re: Question about Gemini
Date: Wed, 19 Apr 2000 14:12:01 GMT

In article <8djrdb$3boa$>,
Daniel D Waltimire <> wrote:
>Actually the Titan's propellants were pretty lethal.  In the event of a
>major accident on the pad, I've always suspected that if a Gemini crew
>had succeeded in ejecting, they may very well have succumbed to the
>deadly red cloud of toxic gas spewing from their wrecked launcher, long
>before they could be rescued.
>Parachutes pretty much tend to land down wind after all.

For an on-pad ejection, there would be no time for any significant wind
drift, because the period of parachute descent would last only a few
seconds.  They'd land where the seats carried them -- quite some distance
away, bearing in mind that the seats have to get the crew clear of a
worst-case fireball -- and it's merely necessary to be sure that the seats
aren't aimed downwind.  I don't have positive information, but I'd be
surprised if this wasn't a constraint on wind direction at launch time.
"Be careful not to step                 |  Henry Spencer
in the Microsoft."  -- John Denker      |      (aka

From: (Henry Spencer)
Subject: Re: Question about Gemini
Date: Thu, 20 Apr 2000 05:28:46 GMT

In article <>,
Justin Wigg <> wrote:
>Any references as to how far away from the Titan a Gemini ejection seat
>would take a crewmember in an on pad abort?

About 600ft, reaching a maximum altitude of about 350ft.

>If it is any great distance,
>how did the seat get enough altitude to allow for that much horizontal
>distance and to allow the parachute time to unfurl properly?  Did it pitch
>up after exiting the spacecraft or something?

The initial catapult took the seat out of the spacecraft on rails, but the
rocket thrust (the most powerful rocket ever used in an ejection seat) was
angled upward to provide altitude as well as distance.  There was no
active attitude control of the seat, it was just very carefully balanced.

As usual in ejection seats, the parachute was hauled out by a mortar
rather than waiting for it to deploy in its own good time.

>"...The statistic was that 75% of ejections were successful, and the
>definition of successful was the guy didn't get *killed*!"

Pretty much correct.  The Gemini seats were at the very limits of human
acceleration tolerance, with a high probability of some injury accepted.

>I would have been distinctly nervous about ejecting from a Gemini.

Well, realistically, no pilot is going to eject unless the alternative
most definitely looks worse.  Even aircraft ejection is a very violent
process; broken bones and spinal injuries are not uncommon.
"Be careful not to step                 |  Henry Spencer
in the Microsoft."  -- John Denker      |      (aka

From: (Henry Spencer)
Subject: Re: Solids on Manned Systems
Date: Tue, 2 May 2000 16:59:11 GMT

In article <>,
Kelly McDonald <> wrote:
>>It's very hard to escape from a solid booster under thrust.  Atlas and
>>Titan II had very manageable escape environments.
>The Gemini system was designed for launch pad aborts, it wasn't a full

The Gemini system was designed to provide crew survival throughout ascent;
that's not the same thing as immediate ejection at any time.  (Even in
fighter aircraft, there are situations where it is assumed that you stay
with the aircraft until conditions are more favorable -- for example, at
high speed in thick air, ejection survival is very doubtful unless you can
stay with the aircraft long enough to slow down a bit first.)

>>if it goes boom, can you get out anyways?  With a liquid, that's fairly
>>easy to set up.  With a solid, it can be impossible.
>Not really, since its almost impossible for a solid booster to

On the contrary, solid-rocket failures are *almost always* catastrophic,
as witness what happens when a Titan III/IV SRB fails:  KABOOM.  Liquid
rocket engines, on the other hand, usually fail benignly, given some small
degree of intelligence on the vehicle's part (like, for example, stopping
the engines if the pumps are about to start sucking air).
"Be careful not to step                 |  Henry Spencer
in the Microsoft."  -- John Denker      |      (aka

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