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From: Henry Spencer <>
Subject: staging (was Re: TSTO vs SSTO)
Date: Sun, 9 Jun 1996 04:39:21 GMT

In article <LFLekx.01ey@Booster.TCN.NET> LFLekx@Booster.TCN.NET (Len Lekx) writes:
>> Note that classical staging inherently can't be tested incrementally.  I
>> am told -- I don't have details -- that recent work suggests that *most*
>> past reusable-TSTO designs would have had separation problems ranging from
>> serious to catastrophic.
>    Did the X-Planes have separation problems?  I don't recall hearing of any.

The X-planes separated at subsonic speed... and their separation was studied
*very* damn carefully before it was tried, aided by the relative ease of
doing wind-tunnel tests for such low speeds.  In addition to which, they
were just a little bit lucky.  Separation problems *have* occurred with
seemingly-straightforward, and much smaller, things like bombs and drop 

Separation at high supersonic speeds is poorly explored and little known,
as witness the loss of one of the M-12s (the drone-carrier variants of
the A-12 Blackbird, precursor of the SR-71) and its crew due to a separation 

It is possible to do TSTO separation at subsonic speeds, but that severely
limits the benefits available from the lower stage.  It is also possible
to postpone staging until you're in vacuum, but that involves its own
compromises, especially if you're trying to use airbreathing engines.
If we feared danger, mankind would never           |       Henry Spencer
go to space.                  --Ellison S. Onizuka |

From: Henry Spencer <>
Subject: Re: Is New Atlas an SSTO?
Date: Mon, 22 Jul 1996 17:45:32 GMT

In article <> Michael Walsh <> writes:
>> True,  an optimal staging fraction means not making orbit,
>> but making orbit may well increase mission success rates.
>I don't believe this statement.  An optimized staging altitude would 
>certainly be above the thickest part of the atmosphere and so staging 
>should be accomplished at low dynamic pressures.  On what basis do you 
>believe boosting the upper stage into orbit will increase success rates?

I would conjecture that Pat's point is the same others have made:  orbit
is a much more benign environment for staging, with less time pressure
and more time to troubleshoot problems.  For example, note that the
Intelsat bird that Endeavour's first mission salvaged was the victim of,
essentially, a staging failure.  It was salvageable only because the
staging failure occurred in orbit.

>I don't believe that an economical two stage launch vehicle will put the 
>Centaur stage in orbit before it separates and fires its engines.

I don't think there is much doubt about that, if only because I'm pretty
sure that the new Atlas core can't put a fully-fuelled Centaur in orbit.

Besides, the new Atlas is still basically heir to the artillery-rocket
tradition of US rocketry, in which performance is all-important and
reliability will be made adequate -- not great, just adequate -- by
throwing money and effort at the problem.  This is doing the new Atlas a
bit of an injustice, mind you, because some of the changes are directed at
higher reliability via reduced complexity... but the mindset is still
there.  The idea of *sacrificing* performance for reliability is foreign
to that tradition; the reduced complexity of the new Atlas is being
justified on the grounds that performance is going up anyway. 
 ...the truly fundamental discoveries seldom       |       Henry Spencer
occur where we have decided to look.  --B. Forman  |

From: (Henry Spencer)
Subject: Re: Saturn launch/staging photography
Date: Thu, 10 Feb 2000 19:37:03 GMT

In article <>,
Justin Wigg <> wrote:
>There is a shot similar the famous sequence taken from the S-II looking back
>at the S-IC falling away which shows what looks like a Titan II first stage
>separating and getting the crap knocked out of it (it's pretty much
>destroyed) by the second stage's exhaust...

Titan II first stages, in fact, sometimes explode during staging.  The
reason is that in Titan staging, second-stage ignition comes *before*
separation, so the first stage takes much more punishment.  The Saturns
separated first, and ignited only after achieving a reasonable gap, so
their lower stages survived much better.
The space program reminds me        |  Henry Spencer
of a government agency.  -Jim Baen  |      (aka

From: (Henry Spencer)
Subject: Re: New Venturestar Layout
Date: Mon, 3 Apr 2000 01:55:10 GMT

In article <>,
Roy Stogner <> wrote:
>>During separation, the most critical case, it's the likelihood
>>that the interference effects will cause the two vehicles to collide.
>Design the system so that each rocket experiences lift away from the

Unfortunately, this is a lot easier said than done.  Particularly when
separating at supersonic speeds and non-trivial dynamic pressures (in an
abort, if nothing else), two objects flying in close formation do *not*
act as if the other wasn't there.  The aerodynamics of such a combination
can be sensitive to the separation; it's not at all inconceivable to have
lift away from the centerline when joined, which vanishes or even reverses
after the first couple of meters of separation.

I'm told that if you use modern analysis on historic TSTO concepts, many
of them would likely have had serious trouble separating.

>>Also, I think you'll find that all serious VTVL SSTO concepts to date
>>have assumed a special launch pad (with flame trenches, etc.) and
>>stand ...
>But then, wouldn't you want a VTVL SSTO to land on a similar pad?  The
>idea of having an SSTO take off and land on the same pad would allow
>drastically reduced turnaround times.

Moving the thing from landing pad to launch stand is not difficult or
time-consuming, and landing on the launch stand is problematic without
plenty of hover fuel.  It's much easier to land somewhere where a few
meters of misalignment doesn't matter.
"Be careful not to step                 |  Henry Spencer
in the Microsoft."  -- John Denker      |      (aka

From: (Henry Spencer)
Subject: Re: Interstage differences between East and West
Date: Tue, 9 May 2000 17:02:10 GMT

In article <>,
Jeffrey A Pleimling <> wrote:
>In general, the West has solid skirts for the interstage area on rockets
>while a lot of 'East' rockets (USSR (Russia), China, North Korea) use
>open gridwork.
>Is one technically superior or is it just a design-shop decision?

This is probably mostly due to a difference in staging philosophy:  grid
interstages tend to go along with fire-in-the-hole staging, where the
upper stage is lit *before* separation.  (A Western example is Titan,
which doesn't have a grid interstage but does have large vents in its
interstage ring.)

As for the difference in staging philosophy...  I think that's mostly a
question of which set of problems a particular design shop historically
prefers.  Fire-in-the-hole staging means the upper stage is under power
throughout staging, which simplifies control, but engine ignition in close
proximity to the lower stage can be problematic.  Ignition after
separation is less worrisome, but then you've got relatively weak control
of the stage motions during separation.
"Be careful not to step                 |  Henry Spencer
in the Microsoft."  -- John Denker      |      (aka

From: (Henry Spencer)
Subject: Re: Interstage differences between East and West
Date: Wed, 10 May 2000 21:19:12 GMT

In article <8F303A55damonhalcyoncom@>,
Damon Hill <> wrote:
>>...Fire-in-the-hole staging means the upper stage is under power
>>throughout staging, which simplifies control, but engine ignition in close
>>proximity to the lower stage can be problematic...
>I realized this way back during the Gemini missions...
>Possibly the most spectacular staging I've ever seen; it appeared the
>first stage upper tank literally blew up and filled the frame of view with

The Titan first stage wasn't *supposed* to come apart after the second
stage lit, but once in a while it did.

Mind you, the Saturn V staging was spectacular even without that, with a
huge sheet of flame erupting sideways as first-stage retros, second-stage
ullage rockets, and shaped-charge separation system all fired more or less
"Be careful not to step                 |  Henry Spencer
in the Microsoft."  -- John Denker      |      (aka

From: (Henry Spencer)
Subject: Re: Aerial Propellant Transfer Revisited
Date: Wed, 28 Jun 2000 23:44:05 GMT

In article <8j4g4h$rtn$>,
John A. Gregor, Jr. <> wrote:
>the orbiter is mated underneath a fairly minimal structure that
>consists primarily of the propellant probe(s) and a pair of canards.
>After the orbiter was tanked up, this structure would separate from the
>orbiter and remain attached to the propellant hose(s)...
>1. The propellant probe(s) can be large and accessible without worrying
>about retracting or insulating them for reentry.

Of course, you've got to retract or insulate whatever fittings they attach
to.  Still might be useful, but the benefit is reduced.

>I think the separation would be fairly easy.  Since the canards are
>applying a pitch-up moment to the orbiter, at separation the orbiter's
>nose would drop and it would fly below the tanker plane while the
>canard/probe structure would climb away from the orbiter.

The aerodynamics of such separations are not necessarily intuitive.  It's
tricky enough separating objects like bombs, which don't have lifting
surfaces; military-aircraft designers spend a lot of wind-tunnel time and
a lot of flight tests making sure that the bombs don't go up and hit the
aircraft.  (Yes, it can happen.)

>So, what obvious things am I missing?

That separation maneuver is going to be very exciting.  Especially the
very first time it's tried.  The nice thing about flight refueling, even
with exotic liquids, is that every step can be tried a little bit at a
time; there are no big "oh God, this better work" moments when you're
trying something you've never come anywhere close to before.
Microsoft shouldn't be broken up.       |  Henry Spencer
It should be shut down.  -- Phil Agre   |      (aka

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