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Application of trans-stage for a recoverable rocket?
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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 |
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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 |
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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 |
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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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