Multiple Engines???

(Henry Spencer) wrote in message ...

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.

Alright, back to powered flybacks for first stages. Are jet engines
worth the trouble of extra systems? Could one of several main rocket
engines be used frugally to keep the stage up to speed during its
return flight, and some or all of the weight that would've gone to jet
engines be used for additional rocket fuel?

I can see some issues like a possible need for an alternate or unusual
fuel pump system to feed the main engine during level flight and, of
course, a big rocket engine uses fuel pretty quickly.

Mike Miller, Materials Engineer

(Henry Spencer) wrote in message ...

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.

Alright, back to powered flybacks for first stages. Are jet engines
worth the trouble of extra systems? Could one of several main rocket
engines be used frugally to keep the stage up to speed during its
return flight, and some or all of the weight that would've gone to jet
engines be used for additional rocket fuel?

I can see some issues like a possible need for an alternate or unusual
fuel pump system to feed the main engine during level flight and, of
course, a big rocket engine uses fuel pretty quickly.

Mike Miller, Materials Engineer

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.

I believe the study's focus was specifically a
no-TPS glide-return-to-base 1st stage for a LHOx TSTO.

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.

I believe the study's focus was specifically a
no-TPS glide-return-to-base 1st stage for a LHOx TSTO.

The fixed proportion of stage sizes constrains the staging point to a
specific value around Mach 3-4.

My calculations optimise around 2,200 m/sec - Mach 8+?

Bimese requires crossfeed. ... Crossfeed ... is quite complex.

Ah, yes.

... the crossfeed flow be shut down and the feed system switch to the
internal tanks while the engines keep running.

Ah, no.
Crossfeed to the next stage's tanks, not its engines.
(This implies the pump-fed type.)

A true bimese configuration forces the duplication of wholly unnecessary
systems on the two stages.

So don't do "true biamese".
Use the same components where feasible, and simpler/deleted
substitutes where it makes engineering sense.
Some parts will be overbuilt, but the devil's in the details.

An optimally designed orbiter can get by with a T/W of 1 or
less at staging. Therefore, forcing commonality puts more engines on the
orbiter than it really needs.

I'll trade optimality for the ability to abort-to-launch from the pad.

For more on this subject, see "Selection of Lockheed Martin's Preferred TSTO
Configurations for the Space Launch Initiative" paper number IAC-02-V.4.03
from the 2002 World Space Congress

Where can I download a copy?

The fixed proportion of stage sizes constrains the staging point to a
specific value around Mach 3-4.

My calculations optimise around 2,200 m/sec - Mach 8+?

Bimese requires crossfeed. ... Crossfeed ... is quite complex.

Ah, yes.

... the crossfeed flow be shut down and the feed system switch to the
internal tanks while the engines keep running.

Ah, no.
Crossfeed to the next stage's tanks, not its engines.
(This implies the pump-fed type.)

A true bimese configuration forces the duplication of wholly unnecessary
systems on the two stages.

So don't do "true biamese".
Use the same components where feasible, and simpler/deleted
substitutes where it makes engineering sense.
Some parts will be overbuilt, but the devil's in the details.

An optimally designed orbiter can get by with a T/W of 1 or
less at staging. Therefore, forcing commonality puts more engines on the
orbiter than it really needs.

I'll trade optimality for the ability to abort-to-launch from the pad.

For more on this subject, see "Selection of Lockheed Martin's Preferred TSTO
Configurations for the Space Launch Initiative" paper number IAC-02-V.4.03
from the 2002 World Space Congress

Where can I download a copy?

"David Shannon" wrote in message
om...

An optimally designed orbiter can get by with a T/W of 1 or
less at staging. Therefore, forcing commonality puts more engines on the
orbiter than it really needs.

I'll trade optimality for the ability to abort-to-launch from the pad.

One possibility that seems obvious is to have OMS pods that fit the same
slots as main engines. The unit used as booster has X engines with no OMS
pods, while the orbiter unit has X-1 engines plus the OMS pod. If it is a
designed in feature, weight and balance could be similar for both modes
without divergence of design or dead weight of non functional systems.

"David Shannon" wrote in message
om...

An optimally designed orbiter can get by with a T/W of 1 or
less at staging. Therefore, forcing commonality puts more engines on the
orbiter than it really needs.

I'll trade optimality for the ability to abort-to-launch from the pad.

One possibility that seems obvious is to have OMS pods that fit the same
slots as main engines. The unit used as booster has X engines with no OMS
pods, while the orbiter unit has X-1 engines plus the OMS pod. If it is a
designed in feature, weight and balance could be similar for both modes
without divergence of design or dead weight of non functional systems.

In message
(David Shannon) wrote:

My calculations optimise around 2,200 m/sec - Mach 8+?

Bimese requires crossfeed. ... Crossfeed ... is quite complex.

Ah, yes.

Could you explain why crossfeed is *required*?

... the crossfeed flow be shut down and the feed system switch to the
internal tanks while the engines keep running.

Ah, no.
Crossfeed to the next stage's tanks, not its engines.
(This implies the pump-fed type.)

Why not just optimise your tank sizes so that when full they hold enough
to take the orbiter vehicle from ground to orbit, then only partly fill
the booster vehicles tanks. You gain some weight from the larger tanks
required, but lose the complexity of the crossfeed. You also get a less
dense vehicle that will have an easier re-entry so may be able to win
back some more weight from the TPS.

Doing a quick back of an envelope calculation on something that
admittedly doesn't have flyback capability or re-entry shielding. A
trimese vehicle based on the S-II stage would have the same thrust to
weight ratio at take off as a Saturn V with a fully tanked core stage
and 60% loads in the two booster stages.

Dropping the booster fuel load to nearer 50% means you'd be separating
them after about 160 seconds, which is where the S-1C stage of a Saturn
V was exhausted. The core stage still has a 50% fuel load, or more if
you've kept the boosters running at 100% thrust and throttled down the
core, and could probably shut down some engines for the rest of the way
up.

A much smaller envelope suggests you could do something similar with
flyback S-1C stages, though using a bimese with 4 engines in each
vehicle or trimese with 3 would help matters.

Anthony

--
| Weather prediction will never be accurate until we |
| kill all the butterflies |

In message
(David Shannon) wrote:

My calculations optimise around 2,200 m/sec - Mach 8+?

Bimese requires crossfeed. ... Crossfeed ... is quite complex.

Ah, yes.

Could you explain why crossfeed is *required*?

... the crossfeed flow be shut down and the feed system switch to the
internal tanks while the engines keep running.

Ah, no.
Crossfeed to the next stage's tanks, not its engines.
(This implies the pump-fed type.)

Why not just optimise your tank sizes so that when full they hold enough
to take the orbiter vehicle from ground to orbit, then only partly fill
the booster vehicles tanks. You gain some weight from the larger tanks
required, but lose the complexity of the crossfeed. You also get a less
dense vehicle that will have an easier re-entry so may be able to win
back some more weight from the TPS.

Doing a quick back of an envelope calculation on something that
admittedly doesn't have flyback capability or re-entry shielding. A
trimese vehicle based on the S-II stage would have the same thrust to
weight ratio at take off as a Saturn V with a fully tanked core stage
and 60% loads in the two booster stages.

Dropping the booster fuel load to nearer 50% means you'd be separating
them after about 160 seconds, which is where the S-1C stage of a Saturn
V was exhausted. The core stage still has a 50% fuel load, or more if
you've kept the boosters running at 100% thrust and throttled down the
core, and could probably shut down some engines for the rest of the way
up.

A much smaller envelope suggests you could do something similar with
flyback S-1C stages, though using a bimese with 4 engines in each
vehicle or trimese with 3 would help matters.

Anthony

--
| Weather prediction will never be accurate until we |
| kill all the butterflies |