Simpler in-line SDLV

I havent seen this idea, so here goes:

Take one traditional side mounted SDLV.
Get rid of the ET's LOX tank.
Replace the cargo can with a Delta IV hydrogen tank, modded for LOX.
Stage II and the payload go where the old LOX tank went.
The intertank becomes the interstage. The stack gets a lot shorter
that the ATK proposal, and you dont get the off center thrust of, say,
Zurbin's Ares.

The launch pad remains the same.

Now there must be a reason why this has not been seriously proposed -
any thoughs?

Duncan Young wrote:
I havent seen this idea, so here goes:

Take one traditional side mounted SDLV.
Get rid of the ET's LOX tank.
Replace the cargo can with a Delta IV hydrogen tank, modded for LOX.
Stage II and the payload go where the old LOX tank went.
The intertank becomes the interstage. The stack gets a lot shorter
that the ATK proposal, and you dont get the off center thrust of, say,
Zurbin's Ares.

The launch pad remains the same.

Now there must be a reason why this has not been seriously proposed -
any thoughs?

This doesn't save any infrastructure development
effort because the launch pad would still have
to be heavily modified. The rotating service
structure, used to insert payloads into the
orbiter, would not be able to access the payload
area on this vehicle. Better to go either totally
in-line or totally payload side-mount that matches
existing pad structures, IMO.

- Ed Kyle

This doesn't save any infrastructure development
effort because the launch pad would still have
to be heavily modified

Is the intent to add payloads at the pad for an inline design? (or any
SDLV, for that matter). I would presume all the stacking would occur
in the VAB. The rotating sevice structure isnt that important for an
expendable.

For the ATK inline, you need an entirily new mobile pad structure. For
this proposal (side mounted LOX and SSMEs) you can use the exactly the
same. pad. That would seem to be a considerable saving.

Duncan Young wrote:
This doesn't save any infrastructure development
effort because the launch pad would still have
to be heavily modified

Is the intent to add payloads at the pad for an inline design? (or any
SDLV, for that matter). I would presume all the stacking would occur
in the VAB. The rotating sevice structure isnt that important for an
expendable.

Even if the payloads were stacked in the VAB, there
would have to be some type of service tower at the pad
that could provide access for arming separation charges,
etc.. Unlike SLC 41, which has an integration building
very close to the pad, the Complex 39 pads are 3 or so
miles from the VAB. It takes an entire day to do a
roll out (or roll back). If a battery suddenly needs
replaced, it would be nice to have a pad tower rather
than requiring a roll back, which could cost a week.
The RSS provides that function for shuttle, in addition
to serving as a payload installation clean room. A
new mobile access structure would be needed for an
in-line expendable.


For the ATK inline, you need an entirily new mobile pad structure. For
this proposal (side mounted LOX and SSMEs) you can use the exactly the
same. pad. That would seem to be a considerable saving.

I think you would need a new tower structure for this
concept, for the reasons mentioned above. As for the
mobile platforms themselves, they were modified from
the Saturn V launch setup to the Shuttle launch
configuration. They could be modified again for an
in-line launcher. The costs could be offset by the
long-term savings provided by the additional payload
capacity of an in-line launcher.

- Ed Kyle

Even if the payloads were stacked in the VAB, there
would have to be some type of service tower at the pad
that could provide access for arming separation charges,
etc..

Some good points, but you dont need a full RSS to do this. Saturn
certainly didn't. And a semi-inline is shorter than a full inline by
the height of the ET's LOX tank, so it is easier to make these mods to
the exiting tower.

The costs could be offset by the
long-term savings provided by the additional payload
capacity of an in-line launcher.

Right, but with a semi-inline you get that additional payload without
having to modify the pad. (I'm presuming here that the big payload
advantage of the inline comes from the addition of a second cryogenic
stage, and not through simplifying the aerodynamics or the ability to
add more SSMEs at launch).

Duncan Young wrote:
Even if the payloads were stacked in the VAB, there
would have to be some type of service tower at the pad
that could provide access for arming separation charges,
etc..

Some good points, but you dont need a full RSS to do this. Saturn
certainly didn't.

Sure it did:

"http://www.hq.nasa.gov/office/pao/History/ap11ann/kippsphotos/69-H-1050.jpg"

The Saturn V Mobile Service Tower was one of the
largest moving objects ever built. But it was
scrapped long ago.

... but with a semi-inline you get that additional payload without
having to modify the pad. (I'm presuming here that the big payload
advantage of the inline comes from the addition of a second cryogenic
stage, and not through simplifying the aerodynamics or the ability to
add more SSMEs at launch).

Much of the payload advantage of an inline comes
from the elimination of mass associated with the
side-mounted engines, which require a strong
thrust transfer structure, longer propellant
feedlines, etc. The advantage is substantial.

- Ed Kyle

The Saturn V Mobile Service Tower was one of the
largest moving objects ever built

Ouch. Obviously before my time.

Much of the payload advantage of an inline comes
from the elimination of mass...

Uncle. I would be interested in the breakdown of improvments in
performance between the ability to stage and carrying a side mount.

The inline is clearly the worse option. It requires developing more new
stuff, which is not the way to do the job quickly with minimal risk and
cost. (Recall the stunning successes of the X-33 project.) The
parallel stack also benefits from having all engines running at liftoff,
which avoids the disaster of an SSME failing to start at altitude.

On Sun, 31 Jul 2005 22:26:06 -0500, richard schumacher
wrote:

The inline is clearly the worse option. It requires developing more new
stuff, which is not the way to do the job quickly with minimal risk and
cost.

On the other hand, the inline would offer many more opportunities to
streamline assembly and pad operations, using lessons learned from the
Shuttle. I'm not sure how much "new" development it would really need,
anyway. There's nothing radical about inline SDLV.... it's essentially
a giant Atlas 5-Heavy or Delta IV-Heavy, afterall, with the hardest
parts (big boosters attached the sides) already a known commodity. But
it does offer a way to completely overhaul the pad for smoother
operations.

Brian

Duncan Young wrote:
Much of the payload advantage of an inline comes
from the elimination of mass...

Uncle. I would be interested in the breakdown of improvments in
performance between the ability to stage and carrying a side mount.

The ATK Thiokol designs offer one comparison.
ATK proposed a side mount and an inline design
that both used a pair of 5-segment SRBs. The
side mount LEO payload was projected to be
90.7 metric tons while a 109 metric ton payload
was projected for the inline design. A "starter"
side mount shuttle derived vehicle that used
standard 4-segment SRBs could lift 77 metric
tons.

For what its worth, ATK also showed a 5-segment
single SRB "Stick" design that could orbit
29.5 metric tons - more than any other launch
vehicle in the world today.

- Ed Kyle