Newsgroups: sci.space.history
From: Henry Spencer <henry@zoo.toronto.edu>
Subject: Re: Stretching Apollo for more passengers
Date: Tue, 13 Jan 1998 03:59:17 GMT

In article <rmhg79s6sr.fsf@fluent.com>, John Stoffel  <jfs@fluent.com> wrote:
>Now in terms of increasing it's ferry capacity, wouldn't it be fairly
>simple to just add a cylindrical splice between the base (curved but
>fairly flat) and the cone of the top?

Alas, that wouldn't work.  The capsule reenters at an angle, necessarily
so to get some lift and hence achieve both a gentler reentry and a
controlled one.  It is essential that the upper body stay in the lee of
the base despite the tilt; that, and not streamlining on the way up, is
the crucial reason why the upper body is a cone.

Mind you, you can play interesting games with asymmetric shapes, since
the thing always flies with the tilt to the same side... but then you
get into worries about aerodynamic side forces during launch.

To get a greater capacity, you either rebuild the interior to give you
more room -- Apollo was not built as a maximum-capacity ferry -- or else
just enlarge the whole thing.  Semi-ballistic shapes are workable up to
quite large sizes.
--
Being the last man on the Moon                  |     Henry Spencer
is a very dubious honor. -- Gene Cernan         | henry@zoo.toronto.edu

Newsgroups: sci.space.history
From: Henry Spencer <henry@zoo.toronto.edu>
Subject: Re: Stretching Apollo for more passengers
Date: Tue, 13 Jan 1998 21:41:08 GMT

In article <rmg1mss565.fsf@fluent.com>, John Stoffel  <jfs@fluent.com> wrote:
>Is the upper body staying in the lee of the base an aerodynamic
>requirement, or is it a heat load requirement, or a combination of
>both? ...

Some of both.  The heatshield on the upper body was rather thinner, but
the aerodynamics were the key.  The thing has lift (sideways force)
because the nearly-flat base is tilted; anything sticking out beyond the
leading edge of the base reduces lift, and there isn't a lot to spare.
(The designers would have preferred a greater tilt for more lift, in fact,
but it was awkward to shift the center of mass as far as they wanted.)

>I do remember reading (or hearing) about Apollo capsule's
>actually have some cross range due to aerodynamic lift.

Correct.  It's not a lot; the crossrange is important mostly because it
gives you enough control for a moderately precise touchdown.  The major
importance of the lift, for a LEO reentry, is holding the capsule up in
thinner air longer, for more gradual deceleration and reduced G-forces.

>If it's an aerodynamic dominated problem, would just shifting in and
>up along the cone before inserting the cylindrical stretch work out?
>I'm sorta thinking something like the Gemini and Mercury Capsules,
>which necked down for a bit, then went straight again (I assume that
>was where the parachutes were held for the return)...

Yup, that's where the chutes were.  However, that cylindrical section
did limit the tilt angle that Gemini could fly at.  (Mercury did not
attempt a lifting reentry.)  Keeping the upper body in the lee is still
a requirement, so this doesn't really gain you much.

However...  What you *could* do, given that Apollo's CM was never offset
far enough to fully exploit its shape, is make the upper body longer --
a sharper cone.  Now you're talking major redesign, mind you, but it
does gain some interior space.

>> Mind you, you can play interesting games with asymmetric shapes, since
>> the thing always flies with the tilt to the same side... but then you
>> get into worries about aerodynamic side forces during launch.
>
>If you're going to stay with a fixed orientation for return, would it
>be possible to change the cone shape into an axe head design?

It's impractical to create the tilt by firing thrusters constantly; it
has to be done with aerodynamics and center-of-mass position.  So a given
design is indeed going to have a fixed tilt with respect to its velocity
vector, with the same point on the base's rim always the leading edge.
(Rotation *around* the velocity vector is cheap, and that's how you
control the thing during reentry.)

You couldn't do a full axe-head without having the sides stick out,
which would drive up their heating problems.  You do want the aft body
fully in the lee.  But you could bulge the sides of the cone out some
without causing severe problems, I'd think.  It would increase the side
forces caused by high-altitude winds on the way up, if the winds came
in from the wrong direction, and that can be troublesome.

The fully asymmetric shape *is* better.  Not only does it get you more
internal volume, but it helps provide a greater CM offset, which means
greater tilt and more lift.

>> To get a greater capacity, you either rebuild the interior to give
>> you more room -- Apollo was not built as a maximum-capacity ferry --
>> or else just enlarge the whole thing...
>
>I assume you'd want to keep the angle that the base makes with the
>cone fairly similiar to apollo's angle, so it would seem that just
>increasing the diameter of the base plate would give you a fairly
>substantial increase in interior volume.  You wouldn't even need to
>increase the diameter of the stage below, you'd just use a shroud like
>the Titan IV uses to neck down from the payload to the booster.

It *would* probably be simpler to just enlarge the whole thing, yes.  Then
you're dealing with a known shape with well-understood properties.

Given that Apollo didn't use nearly the full diameter of either the Saturn
IB or the Saturn V, you don't even need a Titan-style "hammerhead" fairing
if you're using Saturns for launch.  In fact, you could probably increase
the payload to orbit that way, by putting the capsule (and its mini-SM)
directly on top of the S-IVB rather than up on top of a long tapered
adapter section.
--
Being the last man on the Moon                  |     Henry Spencer
is a very dubious honor. -- Gene Cernan         | henry@zoo.toronto.edu

From: jamess@mcsummation.com (James Summers)
Newsgroups: sci.space.history
Subject: Re: Apollo Emergency Abort Reentry
Date: Mon, 25 May 1998 15:35:17 GMT

On Mon, 25 May 1998 11:17:51 GMT, savoyard999@mindspring.com (Bob
Danielson) wrote:
   <snip>
> the idea being that
>you want to reduce the complexity of plotting the reentry by getting the CM
>weight to where it's originally expected to be.
   <snip>

In order to do the reentry "maneuver" correctly, we had to know the
location of the CM's Center of Gravity prettly accurately.  Since
there was no way to recompute the CG after launch (in fact, it was
weighed in Downey and the CG computed before being taken to the Cape),
they had to put enough "ballast" to put it where we expected it.

The trajectory through the atmosphere was very dependent on the CG
position.  It took many hours to find the AS-202 CM because the CG
that was given to us by Rockwell was quite some distance from the
actual CG.

-----------------------
James Summers
IBM-ret, "old space guy".
Apollo 201, 202, 203 204, 1, & 9 Support.  Apollo 13 "back room".
Abort/Reentry trajectory prediction for all the Apollos.