rockets .. upside down ?

In article ,
Oren Tirosh wrote:
...Basically it's the original Atlas design with a
lightweight pressure-stabilized tank and staging by dropping engines.
But there is one notable difference: the payload is now below the
tanks... ...There is no tower. Everything can be serviced
at ground level because anything higher up is just passive tank
structure.

You can get much of that benefit, at least with unmanned payloads, just by
organizing your operations right. Proton has no tower, and neither does
Ariane 5; there simply is no access to the payload after rollout. Upper
stages either are fueled before rollout, or there are built-in plumbing
runs up the side of the lower stages for fueling the upper stages.

The vehicle can be statically tested by lashing it to a
test rig that resembles the bottom of the tank. This could potentially
make development faster and cheaper. Even production units could be
burned-in to get past the sharp drop in the bathtub curve.

Not terribly hard to do with conventional designs. Even LOX/LH2 stages
can be filled and drained many times without any particular difficulty.
This is more a matter of how much people feel like spending on testing and
reliability.

Some potential problems I can already see are center of gravity issues

Not a big problem, at least for an expendable. During the atmospheric
part of the flight, which is when you mostly care about center of mass,
the vehicle's mass is dominated by fuel. Any detailed control you need
can be had by having multiple tanks and draining them in sequence.
Having the payload's mass aft is undesirable but not very important.

and a possibly harsher payload environment so close to the engines.

Definitely an issue. The shuttle has problems with this.
--
MOST launched 30 June; first light, 29 July; 5arcsec | Henry Spencer
pointing, 10 Sept; first science, early Oct; all well. |

(Henry Spencer) wrote in message ...
In article ,
Oren Tirosh wrote:
...Basically it's the original Atlas design with a
lightweight pressure-stabilized tank and staging by dropping engines.
But there is one notable difference: the payload is now below the
tanks... ...There is no tower. Everything can be serviced
at ground level because anything higher up is just passive tank
structure.

You can get much of that benefit, at least with unmanned payloads, just by
organizing your operations right. Proton has no tower, and neither does
Ariane 5; there simply is no access to the payload after rollout.

How about rolling out in a vertical position? Without tanks, an
Atlas-class vehicle can fit on a flatbed truck vertically. No need for
tall vehicle assembly buildings or massive erectors (I just watched
some pictures from the rollout of the Delta IV heavy). Drive to the
launch pad, lift it with a harness and crane and lower it onto the
pad. Lift the empty tank to vertical position with the same crane and
lower it onto the cradle on the top of the vehicle.

The vehicle can be statically tested by lashing it to a
test rig that resembles the bottom of the tank. This could potentially
make development faster and cheaper. Even production units could be
burned-in to get past the sharp drop in the bathtub curve.

Not terribly hard to do with conventional designs. Even LOX/LH2 stages
can be filled and drained many times without any particular difficulty.

Testing pieces is not quite the same as testing the integrated entire
vehicle (modulu the tank). Parallel staging helps testing all engines.
A compact vehicle make it easier to put the whole vehicle on the test
stand (again, vertically).

and a possibly harsher payload environment so close to the engines.

Definitely an issue. The shuttle has problems with this.

Putting the payload in a helium tent should help a bit. The impedance
mismatch between air and helium means only 17% of the acoustic energy
is transmitted through.

Oren

(Henry Spencer) wrote in message ...
In article ,
Oren Tirosh wrote:
...Basically it's the original Atlas design with a
lightweight pressure-stabilized tank and staging by dropping engines.
But there is one notable difference: the payload is now below the
tanks... ...There is no tower. Everything can be serviced
at ground level because anything higher up is just passive tank
structure.

You can get much of that benefit, at least with unmanned payloads, just by
organizing your operations right. Proton has no tower, and neither does
Ariane 5; there simply is no access to the payload after rollout.

How about rolling out in a vertical position? Without tanks, an
Atlas-class vehicle can fit on a flatbed truck vertically. No need for
tall vehicle assembly buildings or massive erectors (I just watched
some pictures from the rollout of the Delta IV heavy). Drive to the
launch pad, lift it with a harness and crane and lower it onto the
pad. Lift the empty tank to vertical position with the same crane and
lower it onto the cradle on the top of the vehicle.

The vehicle can be statically tested by lashing it to a
test rig that resembles the bottom of the tank. This could potentially
make development faster and cheaper. Even production units could be
burned-in to get past the sharp drop in the bathtub curve.

Not terribly hard to do with conventional designs. Even LOX/LH2 stages
can be filled and drained many times without any particular difficulty.

Testing pieces is not quite the same as testing the integrated entire
vehicle (modulu the tank). Parallel staging helps testing all engines.
A compact vehicle make it easier to put the whole vehicle on the test
stand (again, vertically).

and a possibly harsher payload environment so close to the engines.

Definitely an issue. The shuttle has problems with this.

Putting the payload in a helium tent should help a bit. The impedance
mismatch between air and helium means only 17% of the acoustic energy
is transmitted through.

Oren

"johnhare" wrote in message
. ..
You might consider a 7 cluster with the 6 outside tanks just that. The
center
unit containing the engine, payload and stuff. Possibly tanks 2,3,5 and 6
containing LOX with 1 and 6 carrying fuel. Drop in pairs. This way the
outer
units have no intertank structure.

That suggested, I don't believe this is a really good idea. Tankage fluffs
the reentry profile for easier TPS. You still have the downrange drop
zones. You are carrying untested hardware each flight. You are carrying
a lot of extra engine later in the launch phase. But I am often wrong.

Just thought that its worth to mention:
I wasnt aware of how long history iedas of SSTOs augmented with drop tanks
have. All the way back to 1969, Bono's ROOST and ROMBUS vehicles.
http://www.spacefuture.com/archive/h..._systems.shtml

Its also worth to mention that Armadillo is considering cabin-at-bottom
designs for their future vehicles, essentially leaving only fuel tanks on
top of the vehicle.

-kert