Multiple Engines???

In article ,
Mike Miller wrote:
I suspect the TSTO can glide back. Even at mach 8 separations, is the
first stage all that far down range, more than 100-200 miles?

For an orthodox trajectory, a Mach 8 separation will bring it down more
like 300mi from the launch site. That tends to require powered return.
And that's not a particularly high separation speed.

It'll
have a lot of energy from altitude and speed that can be spent turning
around and gliding back.

Not unless it has truly excellent aerodynamic performance, which is
another nasty can of worms. It's not all that high up by the time it
can get turned around.
--
MOST launched 30 June; first light, 29 July; 5arcsec | Henry Spencer
pointing, 10 Sept; first science, early Oct; all well. |

In article ,
Mike Miller wrote:
I suspect the TSTO can glide back. Even at mach 8 separations, is the
first stage all that far down range, more than 100-200 miles?

For an orthodox trajectory, a Mach 8 separation will bring it down more
like 300mi from the launch site. That tends to require powered return.
And that's not a particularly high separation speed.

It'll
have a lot of energy from altitude and speed that can be spent turning
around and gliding back.

Not unless it has truly excellent aerodynamic performance, which is
another nasty can of worms. It's not all that high up by the time it
can get turned around.
--
MOST launched 30 June; first light, 29 July; 5arcsec | Henry Spencer
pointing, 10 Sept; first science, early Oct; all well. |

In article ,
David Shannon wrote:
But how do you get the first stage back?

...It staged at T+105 seconds at 83,175' and 2,900 ft/sec.
Even so, it was then only 10.5 nautical miles laterally from the pad.

Unfortunately, this is more like a boosted SSTO than a TSTO; staging at
only Mach 3, the upper stage is doing almost all of the work.

Worse, 83kft is comfortably within the atmosphere, so we're talking about
staging at high dynamic pressure -- an idea that makes design engineers
cringe while aerodynamics researchers rub their hands in glee. (As a
point of comparison, the Saturn V staged at twice that altitude.)
--
MOST launched 30 June; first light, 29 July; 5arcsec | Henry Spencer
pointing, 10 Sept; first science, early Oct; all well. |

In article ,
David Shannon wrote:
But how do you get the first stage back?

...It staged at T+105 seconds at 83,175' and 2,900 ft/sec.
Even so, it was then only 10.5 nautical miles laterally from the pad.

Unfortunately, this is more like a boosted SSTO than a TSTO; staging at
only Mach 3, the upper stage is doing almost all of the work.

Worse, 83kft is comfortably within the atmosphere, so we're talking about
staging at high dynamic pressure -- an idea that makes design engineers
cringe while aerodynamics researchers rub their hands in glee. (As a
point of comparison, the Saturn V staged at twice that altitude.)
--
MOST launched 30 June; first light, 29 July; 5arcsec | Henry Spencer
pointing, 10 Sept; first science, early Oct; all well. |

Henry Spencer wrote:
David Shannon wrote:
Consider the design path where the stages are externaly identical
(eg General Dynamics "Triamese"...
This approach has theoretical limitations that are outweighed by
practical advantages. You only have to spend skull-sweat on the orbiter -
the boosters are simplified variants (no OMS, less TPS, etc, etc)

The practical problem with biamese and triamese is that almost anything
you do to simplify the boosters starts you off down the slippery slope of
building two different vehicles. It's very hard to stop that.

Just leaving systems out looks easy, but often it means a lot of extra
engineering to assess what *happens* when you leave those systems out,
and what drives development cost is not materials but engineering effort.
Later on, when weight is excessive or there's a bit of a performance
shortfall, well, we're already building two different configurations, so
we'll just make them a little *more* different...

Biamese or triamese is a win only if the boosters are the *same* as the
orbiter. Same TPS; if it doesn't get as hot, that's nice. Same OMS;
okay, we can leave its tanks empty on the boosters. Same systems, all of
them. Maybe we fill the boosters' cargo bays with tanks, but if so, any
permanent fittings we need to add go in the orbiters too. It takes very
strong engineering leadership to make this work.

I would pushback from that some. But the sentiment is clearly
thinking smart.

If you're trying to do highly commonal biamese/triamese, I would
lay down some groundrules:
1) Same airframe structure. That means same parts, same holes,
same brackets, the whole nine yards.
2) Same TPS, per Henry.
3) Same systems for power, control, guidance, etc.
4) Same mechanisms (control surfaces, doors, gear, etc).
5) Same wiring harness.
6) Same main engines powerhead; a different nozzle is acceptable
between the orbital and booster models, but one should be able to
put a box over the nozzle end and tape cover any other identifying
markings and stump a tech on whether it's the long or short nozzle
model engine.

I don't particularly mind leaving a podded OMS system off a booster
or sticking modular tanks (or, a flyback system) in a booster's cargo
bay area. I agree with Henry that if you put any dedicated
mountings for those in the cargo bay, it should be fleetwide.

Basically... there should be two sets of things. The Airframe,
which is structures and systems which are common, and those should
be *common*... the fitout for changing one model into the other
model should be not significantly more than normal minor overhaul.
And then modular equipment sets that change between the two
missions (or more, if you have low/hi/orbital rather than
booster/orbital). All the interfaces need to be common,
and you need to enforce on the design team (and ideally on
the operations team) that airframes are not going to be
shoehorned into either role. Establishing that in the
operations and maintenance schedule model would be great.


-george william herbert

Henry Spencer wrote:
David Shannon wrote:
Consider the design path where the stages are externaly identical
(eg General Dynamics "Triamese"...
This approach has theoretical limitations that are outweighed by
practical advantages. You only have to spend skull-sweat on the orbiter -
the boosters are simplified variants (no OMS, less TPS, etc, etc)

The practical problem with biamese and triamese is that almost anything
you do to simplify the boosters starts you off down the slippery slope of
building two different vehicles. It's very hard to stop that.

Just leaving systems out looks easy, but often it means a lot of extra
engineering to assess what *happens* when you leave those systems out,
and what drives development cost is not materials but engineering effort.
Later on, when weight is excessive or there's a bit of a performance
shortfall, well, we're already building two different configurations, so
we'll just make them a little *more* different...

Biamese or triamese is a win only if the boosters are the *same* as the
orbiter. Same TPS; if it doesn't get as hot, that's nice. Same OMS;
okay, we can leave its tanks empty on the boosters. Same systems, all of
them. Maybe we fill the boosters' cargo bays with tanks, but if so, any
permanent fittings we need to add go in the orbiters too. It takes very
strong engineering leadership to make this work.

I would pushback from that some. But the sentiment is clearly
thinking smart.

If you're trying to do highly commonal biamese/triamese, I would
lay down some groundrules:
1) Same airframe structure. That means same parts, same holes,
same brackets, the whole nine yards.
2) Same TPS, per Henry.
3) Same systems for power, control, guidance, etc.
4) Same mechanisms (control surfaces, doors, gear, etc).
5) Same wiring harness.
6) Same main engines powerhead; a different nozzle is acceptable
between the orbital and booster models, but one should be able to
put a box over the nozzle end and tape cover any other identifying
markings and stump a tech on whether it's the long or short nozzle
model engine.

I don't particularly mind leaving a podded OMS system off a booster
or sticking modular tanks (or, a flyback system) in a booster's cargo
bay area. I agree with Henry that if you put any dedicated
mountings for those in the cargo bay, it should be fleetwide.

Basically... there should be two sets of things. The Airframe,
which is structures and systems which are common, and those should
be *common*... the fitout for changing one model into the other
model should be not significantly more than normal minor overhaul.
And then modular equipment sets that change between the two
missions (or more, if you have low/hi/orbital rather than
booster/orbital). All the interfaces need to be common,
and you need to enforce on the design team (and ideally on
the operations team) that airframes are not going to be
shoehorned into either role. Establishing that in the
operations and maintenance schedule model would be great.


-george william herbert

(George William Herbert) wrote:
and you need to enforce on the design team (and ideally on
the operations team) that airframes are not going to be
shoehorned into either role.

That's going to be difficult-to-impossible to enforce. Any self
respecting scheduler/planner is going to grab a vehicle already in
configuration x in order to fly a mission with requirements x. His
boss, and his bosses boss are gonna give him attaboys for saving the
manhours. And they'll be right in doing so, over years and decades
of operation, those little savings add up.

Establishing that in the operations and maintenance schedule
model would be great.

Why? You waste manhours, and enforce slow degredation of the vehicles
by doing so. Other than academic satisfaction, there is utterly no
need for routine conversion between configurations. Conversions
should be driven by need, not ivory tower dictates.

D.
--
The STS-107 Columbia Loss FAQ can be found
at the following URLs:

Text-Only Version:
http://www.io.com/~o_m/columbia_loss_faq.html

Enhanced HTML Version:
http://www.io.com/~o_m/columbia_loss_faq_x.html

Corrections, comments, and additions should be
e-mailed to , as well as posted to
sci.space.history and sci.space.shuttle for
discussion.

(George William Herbert) wrote:
and you need to enforce on the design team (and ideally on
the operations team) that airframes are not going to be
shoehorned into either role.

That's going to be difficult-to-impossible to enforce. Any self
respecting scheduler/planner is going to grab a vehicle already in
configuration x in order to fly a mission with requirements x. His
boss, and his bosses boss are gonna give him attaboys for saving the
manhours. And they'll be right in doing so, over years and decades
of operation, those little savings add up.

Establishing that in the operations and maintenance schedule
model would be great.

Why? You waste manhours, and enforce slow degredation of the vehicles
by doing so. Other than academic satisfaction, there is utterly no
need for routine conversion between configurations. Conversions
should be driven by need, not ivory tower dictates.

D.
--
The STS-107 Columbia Loss FAQ can be found
at the following URLs:

Text-Only Version:
http://www.io.com/~o_m/columbia_loss_faq.html

Enhanced HTML Version:
http://www.io.com/~o_m/columbia_loss_faq_x.html

Corrections, comments, and additions should be
e-mailed to , as well as posted to
sci.space.history and sci.space.shuttle for
discussion.

In article ,
George William Herbert wrote:
Biamese or triamese is a win only if the boosters are the *same* as the
orbiter. Same TPS; if it doesn't get as hot, that's nice... It takes very
strong engineering leadership to make this work.

I would pushback from that some. But the sentiment is clearly
thinking smart.

I'm willing to consider backing off from absolutely identical hardware a
little bit, but it needs to be done *very* cautiously to avoid incurring
extra analysis. Even deleting something that looks like it will separate
cleanly can mean a new version of things like vibration analysis. (Almost
certainly, the reason why the Pogo oscillation on Apollo 6 was worse than
that on Apollo 4 was that Apollo 4's dummy LM was just a tub of ballast
while Apollo 6's dummy tried to simulate the real LM's properties.) You
really need to identify the deletions ahead of time and make sure they
get cranked into all the analyses, so you're deleting only in places
where variability is *expected*.

6) Same main engines powerhead; a different nozzle is acceptable
between the orbital and booster models, but one should be able to
put a box over the nozzle end and tape cover any other identifying
markings and stump a tech on whether it's the long or short nozzle
model engine.

Yes, that one's probably worth doing, if you're not using an engine which
does altitude compensation some other way.

...All the interfaces need to be common,
and you need to enforce on the design team (and ideally on
the operations team) that airframes are not going to be
shoehorned into either role. Establishing that in the
operations and maintenance schedule model would be great.

You can do this in a small way by planning that early orbiters (which may
not be up to the final standard, as Enterprise and Columbia weren't) will
eventually be demoted to use as boosters. What you really want, though,
is to build in some promotions from booster to orbiter -- that's the
direction that's easy to mess up.
--
MOST launched 30 June; first light, 29 July; 5arcsec | Henry Spencer
pointing, 10 Sept; first science, early Oct; all well. |

In article ,
George William Herbert wrote:
Biamese or triamese is a win only if the boosters are the *same* as the
orbiter. Same TPS; if it doesn't get as hot, that's nice... It takes very
strong engineering leadership to make this work.

I would pushback from that some. But the sentiment is clearly
thinking smart.

I'm willing to consider backing off from absolutely identical hardware a
little bit, but it needs to be done *very* cautiously to avoid incurring
extra analysis. Even deleting something that looks like it will separate
cleanly can mean a new version of things like vibration analysis. (Almost
certainly, the reason why the Pogo oscillation on Apollo 6 was worse than
that on Apollo 4 was that Apollo 4's dummy LM was just a tub of ballast
while Apollo 6's dummy tried to simulate the real LM's properties.) You
really need to identify the deletions ahead of time and make sure they
get cranked into all the analyses, so you're deleting only in places
where variability is *expected*.

6) Same main engines powerhead; a different nozzle is acceptable
between the orbital and booster models, but one should be able to
put a box over the nozzle end and tape cover any other identifying
markings and stump a tech on whether it's the long or short nozzle
model engine.

Yes, that one's probably worth doing, if you're not using an engine which
does altitude compensation some other way.

...All the interfaces need to be common,
and you need to enforce on the design team (and ideally on
the operations team) that airframes are not going to be
shoehorned into either role. Establishing that in the
operations and maintenance schedule model would be great.

You can do this in a small way by planning that early orbiters (which may
not be up to the final standard, as Enterprise and Columbia weren't) will
eventually be demoted to use as boosters. What you really want, though,
is to build in some promotions from booster to orbiter -- that's the
direction that's easy to mess up.
--
MOST launched 30 June; first light, 29 July; 5arcsec | Henry Spencer
pointing, 10 Sept; first science, early Oct; all well. |