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Application of trans-stage for a recoverable rocket?



 
 
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  #1  
Old March 2nd 14, 03:55 PM posted to sci.space.tech
Anthony Frost
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Posts: 253
Default Application of trans-stage for a recoverable rocket?

In message
David Spain wrote:

In this scenario, a smaller trans-stage is attached to the top

There are a couple of advantages to this approach:

1) The entire propellant load of the first stages could be used for ascent.


Not an advantage. You still need a similar amount of fuel for the
landing, all you've done is add extra tanks to hold it, increasing the
mass, and added more engines, also increasing the mass.

2) Simplification of the recovery effort of a multi-booster
configuration such as the Falcon-9 Heavy. Instead of having to manage
the recovery of three separate boosters, you only need deploy landing
legs on the three and have a single point-of-control for the active
recovery.


What are you proposing to use to hold the stages together, very long
bits of string? Consider why this wouldn't have worked to recover the
shuttle ET and SRBs as a single package...

Anthony


  #2  
Old March 2nd 14, 07:28 PM posted to sci.space.tech
Niels Jørgen Kruse
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Posts: 49
Default Application of trans-stage for a recoverable rocket?

Anthony Frost wrote:

In message
David Spain wrote:

In this scenario, a smaller trans-stage is attached to the top

There are a couple of advantages to this approach:

1) The entire propellant load of the first stages could be used for ascent.


Not an advantage. You still need a similar amount of fuel for the
landing, all you've done is add extra tanks to hold it, increasing the
mass, and added more engines, also increasing the mass.


But the main engines don't have to be restartable and the thrusting
engines are farther from the ground in landing, blowing up less
shrapnel.

--
Mvh./Regards, Niels Jørgen Kruse, Vanløse, Denmark

  #3  
Old March 3rd 14, 11:17 AM posted to sci.space.tech
David Spain
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Posts: 2,901
Default Application of trans-stage for a recoverable rocket?

On 3/2/2014 9:55 AM, Anthony Frost wrote:
In message
David Spain wrote:

2) Simplification of the recovery effort of a multi-booster
configuration such as the Falcon-9 Heavy. Instead of having to manage
the recovery of three separate boosters, you only need deploy landing
legs on the three and have a single point-of-control for the active
recovery.


What are you proposing to use to hold the stages together, very long
bits of string? Consider why this wouldn't have worked to recover the
shuttle ET and SRBs as a single package...


I'm answering your comment and question in reverse order.

I consider the SRB/ET-Shuttle as a TSTO system with the ET as part of
the 2nd stage not the first stage since it was never designed to be
recoverable. A very different system than an F9HR with recovery
capability on all three boosters. But done so independently. Thus
if/when F9HR becomes a reality there will be 3 separate boosters to
control on return rather than one.

No in this scenario the boosters don't separate at all, they go up as
one and come down as one. Yes you loose the advantage of cross-feed
propellant or engine throttle down on the core booster since at no time
does it fly standalone. So there is that reduction in performance as
well. I could speculate you *might* be able to make up that difference
by stretching the boosters a bit, but barring that you loose the
performance gain of a throttle down throttle up core booster OR it puts
significant additional burden on the 2nd stage. Perhaps too much of one?

From an engineering perspective it seems far easier (read less costly)
to eventually just build out a recoverable single BFR rather than deal
with the added complexity of recovering the multiple boosters of a
smaller rocket bundled together. I think that was the gist of the debate
in the other forum. This trans-stage option might have been one solution
to that problem. Albeit maybe not a very good solution.

But I am most interested in learning if this trans-stage option was
given any serious consideration in the past.

I guess the snide remark is that NO-ONE was giving rocket recovery any
serious consideration in the past. Folks just got too comfy with
governments footing the bill for what was nearly a monopoly market with
a single payer customer, with the occasional well-heeled commercial
client thrown in.

Dave


  #4  
Old March 3rd 14, 11:17 AM posted to sci.space.tech
David Spain
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Posts: 2,901
Default Application of trans-stage for a recoverable rocket?

On 3/2/2014 1:28 PM, Niels Jørgen Kruse wrote:
Anthony Frost wrote:

In message
David Spain wrote:

In this scenario, a smaller trans-stage is attached to the top

There are a couple of advantages to this approach:

1) The entire propellant load of the first stages could be used for ascent.


Not an advantage. You still need a similar amount of fuel for the
landing, all you've done is add extra tanks to hold it, increasing the
mass, and added more engines, also increasing the mass.


But the main engines don't have to be restartable and the thrusting
engines are farther from the ground in landing, blowing up less
shrapnel.


Yes I considered that as well. Shrapnel that could get into your firing
engines at a very inopportune time. But I would think that could be
easily avoided by keeping the landing pad clean and free of debris.

Anthony's observation about the additional mass is a good reason why
this is not a good option for a single booster. I really was only
thinking about it in terms of a multiple-booster cluster.

OTOH you have to view that against the added wet+dry mass of the
trans-stage. And the fact that the CG change during ascent possibly
moves along a line that is in a direction less favorable over time,
depending upon that wet+dry mass of the trans-stage versus the dry mass
of the boosters below.

I'll throw in one more what-if. And that would be what-if the
trans-stage used a different engine & fuel. One that offered much higher
ISP and with a denser fuel than the first stage could afford to use on
its own? That might swing the balance in the favor of this approach. But
then consider, who is going to give you that other rocket and fuel for
free? If you were a legacy company with lots of different rocket designs
sitting around that approach might make some sense. But if you are just
starting up, wouldn't it makes more sense to develop your best solutions
for the first stage and go with what you have there? As SpaceX is doing now?

Some things to mull over.

Dave

 




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