Author Topic: Idea: Reusable second stage for reliability testing  (Read 3183 times)

Offline su27k

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Given the recent mishap and the discussion on CRS-7 thread, I was thinking a fully reusable system could really help right now, since you can fly test flights cheaply to verify possible root causes, and later confirm the fix actually works. It could also be used to test future upgrades without endangering customer's payload, and its test flights can be used to build up customer confidence.

Obviously this is not possible right now since 2nd stage is not reusable, so the question is: how hard would it be to develop some addons to 2nd stage to make it reusable just for reliability testing purposes? The difference from a production reusable 2nd stage is that the testing version is not required to put a payload to orbit, and depending on the test requirements, it itself may not need to reach orbit. The main requirement would be: a. it can be reused cheaply; b. it mirrors production 2nd stage design and flight profile as closely as possible.

Offline RonM

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Re: Idea: Reusable second stage for reliability testing
« Reply #1 on: 07/15/2015 01:22 pm »
Since a test second stage would not be carrying a payload, that would leave a lot of mass available to make a test second stage reusable. Put an inflatable heat shield on the front for reentry and whatever system is needed for landing as the payload. Then it would be a production stage. Problem is that the stage would be going through reentry stresses not seen on a normal flight, confusing structural results.

Offline 411rocket

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Re: Idea: Reusable second stage for reliability testing
« Reply #2 on: 07/16/2015 05:16 am »

Obviously this is not possible right now since 2nd stage is not reusable, so the question is: how hard would it be to develop some addons to 2nd stage to make it reusable just for reliability testing purposes? The difference from a production reusable 2nd stage is that the testing version is not required to put a payload to orbit, and depending on the test requirements, it itself may not need to reach orbit. The main requirement would be: a. it can be reused cheaply; b. it mirrors production 2nd stage design and flight profile as closely as possible.

I was thinking, initially at least, fit a M1D prototype for a 1st stage & basic legs on it. Perform tanking tests at increasing pressures & durations, before test flights out of SPA. May need a few of them, as these could very well be test, until destruction. Before attaching to a actual 1st stage, for a "normal" flight profile, maybe with a previously flown Dragon, on top.

It would be interesting, to see at what pressure a seam will split, or a COPV / attachment fails. Possibly, use an oversized shake table as well. Similar to what is used for earthquake tests, in building construction research.

Online meekGee

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Re: Idea: Reusable second stage for reliability testing
« Reply #3 on: 07/16/2015 05:12 pm »
You wouldn't need a heat shield even.

After half the dV is achieved, turn the stage around, and slow it down with a second burn so it enters at zero velocity.  The parachute it into the water, since it doesn't need to fly again.

Is this a "flight-like" experiment?  Kind of.  Will it provide useful data?  Quite possibly.

Is it needed if they figured out the root cause?  Not needed, but can be helpful to confirm various aspects of the design.

It would be cool if they ever do this.
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Offline wannamoonbase

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Re: Idea: Reusable second stage for reliability testing
« Reply #4 on: 07/17/2015 09:54 pm »
I'd like to see a F9 re-useable upper stage developed.  I realize this would have limited use, likely only FH flights to LEO. 

I don't know that it would ever be justified on financial terms.  But instead justified on the technical development and experience of the required systems and operations to make it reuseable.

Final added benefit is that until there is an appropriate Meth/LOx US engine that this reuseable FH US could be an available and functioning US for a mini-BFR/Raptor powered F9 replacement. 
Wildly optimistic prediction, Superheavy recovery on IFT-4 or IFT-5

Offline john smith 19

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Re: Idea: Reusable second stage for reliability testing
« Reply #5 on: 07/20/2015 05:16 pm »
Given the recent mishap and the discussion on CRS-7 thread, I was thinking a fully reusable system could really help right now, since you can fly test flights cheaply to verify possible root causes, and later confirm the fix actually works. It could also be used to test future upgrades without endangering customer's payload, and its test flights can be used to build up customer confidence.
Interesting idea. Several reasons why it's not going to happen.

Musk has stated upper stage reusability is off the table till the vehicle after the FH. That will be Methane so any development work here is known to be a dead end.

Grasshopper was basically a first stage with fewer engines. than normal added. They might not have installed various items not necessary for first stage the thrusters to flip the stage end over end (not necessary in the GH test programme). That said the closer to the flight configuration the more of the vehicle analysis you could have used to model its behaviour (those thrusters and their tanks would have been point mass loads on the structure. Would that have changed it's load response? Possibly, possibly not).

So GH could essentially be taken off the mfg line part way through and have a few bits added and be ready for testing.

But a 2nd stage test vehicle is exactly that. A test vehicle. It needs a full 1st stage just to fly it, and since none of those have been recovered yet conservatively that's a big expense on every test flight.

So you're going from a test programme that's either fairly cheap to run (Grass Hopper and the recovery flight tests on paid launches) to a test programme where your costs start with "Buy an F9 1st stage."

And of course it also fails the key criteria of not getting Elon to Mars faster/safer/cheaper.

As usual in seeing the benefits of a small part of the whole you have to keep the whole picture in sight.

Useful, yes.

Justifiable, no.
MCT ITS BFR SS. The worlds first Methane fueled FFSC engined CFRP SS structure A380 sized aerospaceplane tail sitter capable of Earth & Mars atmospheric flight.First flight to Mars by end of 2022 TBC. T&C apply. Trust nothing. Run your own #s "Extraordinary claims require extraordinary proof" R. Simberg."Competitve" means cheaper ¬cheap SCramjet proposed 1956. First +ve thrust 2004. US R&D spend to date > $10Bn. #deployed designs. Zero.

Offline wannamoonbase

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Re: Idea: Reusable second stage for reliability testing
« Reply #6 on: 07/24/2015 02:19 pm »
...Musk has stated upper stage reusability is off the table till the vehicle after the FH. That will be Methane so any development work here is known to be a dead end.

I disagree.  The technology and operational experience of developing a recoverable second stage would be beneficial and have real financial benefits.

As we've seen with the first stage recovery efforts it's not a slam dunk.  Lots to figure out with hardware, software and operations.  Developing these abilities with an existing, revenue generating vehicle would be cheap development and is what SpaceX is currently doing with the booster.

Other tangible benefits is that they would be able to better design a MethLOx upper stage.  It can be designed from the very start to be re-useable with the lessons learned reducing those development costs and all that experience . 

Further less exciting but equally important aspects, building confidence with costumers and the FAA takes years.  Best to get started.

They aren't going to have time for 2 or 3 years since SpaceX has their hands full with F9 v1.2, FH and Dragon 2.  However, I think there is a good chance this gets revisited as some of those development efforts are wrapping up and engineers are available.   
Wildly optimistic prediction, Superheavy recovery on IFT-4 or IFT-5

Offline LM13

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Re: Idea: Reusable second stage for reliability testing
« Reply #7 on: 07/24/2015 02:54 pm »
What if the Second Stage only needs to fly itself on a suborbital trajectory from the ground and back, as a qualification measure?

Suppose you replace the payload with a big set of legs (legs which attach to the top of the stage) and some SuperDracos.  The second stage itself is an article intended for orbital flight.  In Texas or New Mexico, the stage is fitted to this recovery package, launched off the ground as Grasshopper was, boosted into a sub-orbital trajectory and subjected to the same acceleration profile you'd get in flight, and then landed.  The stage is then de-mated from the recovery package, and trucked to a launch site with a "Flight-Tested" stamp. 

This would weed out defective stages in a fully-reusable manner, and doesn't seem that it should be more expensive than Grasshopper tests (the components are the same--fixed landing gear and a single Merlin engine). 

I'm just a student, but does this suggestion have merit?

Offline guckyfan

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Re: Idea: Reusable second stage for reliability testing
« Reply #8 on: 07/24/2015 03:27 pm »
The technology and operational experience of developing a recoverable second stage would be beneficial and have real financial benefits.

As we've seen with the first stage recovery efforts it's not a slam dunk.  Lots to figure out with hardware, software and operations.  Developing these abilities with an existing, revenue generating vehicle would be cheap development and is what SpaceX is currently doing with the booster.

Other tangible benefits is that they would be able to better design a MethLOx upper stage.  It can be designed from the very start to be re-useable with the lessons learned reducing those development costs and all that experience . 

They could beef up attitude control, maybe with aerodynamic surfaces. Add a PicaX heatshield and try to get it through reentry. It should not cost too much both in money and payload penalty. The would not get the stage back but they could learn a lot that could then be applied to a real reusable upper stage. Probably for MCT, if not for a reusable Falcon upper stage.

Offline su27k

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Re: Idea: Reusable second stage for reliability testing
« Reply #9 on: 07/24/2015 03:39 pm »
@RomM: See @meekGee's description of a suborbital hop, this is what I'm wondering, it would avoid the heat shield which is a pain. I would like the 2nd stage to be recovered and reused for additional testing though, so probably no dropping into water.

@411rocket, @LM13: I think it would need a first stage to make the flight profile as close to production as possible.

@wannamoonbase: a reusable 2nd stage that can be used in real launches would be pretty hard, I don't know if they'll do it but even if they do, it would be years down the line. I was thinking of something quick and dirty, like Grasshopper.

@john smith 19: Sorry, I should clarify that this assumes they'll use a recovered first stage to do the launch, this can complement or replace some of the reusable first stage test flights in New Mexico.
« Last Edit: 07/24/2015 03:45 pm by su27k »

Offline john smith 19

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Re: Idea: Reusable second stage for reliability testing
« Reply #10 on: 07/25/2015 07:27 am »
Obviously this is not possible right now since 2nd stage is not reusable,
And so far neither is the 1st stage, despite most peoples hopes Grassshopper had nailed down all the major stuff needed for a 1st stage recovery.
Quote
so the question is: how hard would it be to develop some addons to 2nd stage to make it reusable just for reliability testing purposes?
Re reading this I ask my self what exactly are you trying to test? New hardware for every copy of the stage (which is what would have been needed to pick up the strut failure SX say is the root cause), which is usually called a "proof" test, or testing the whole flight profile?
Quote

The difference from a production reusable 2nd stage is that the testing version is not required to put a payload to orbit, and depending on the test requirements, it itself may not need to reach orbit. The main requirement would be: a. it can be reused cheaply; b. it mirrors production 2nd stage design and flight profile as closely as possible.
"As closely as possible" means going to orbit. While the 180 flip/retro fire/180 flip looks to be the same process as stg1 the parameters defining the values involved for forces, Cg etc are very different. KE per Kg of stage mass will be about 4x that of the 1st stage, hence the PICA heat shield.

However IRL Musk has stated 2nd stage reuse for F9 or F9 derived vehicles is off the table.

SX have been very economical by doing their testing on stages that have already been bought (and used) by a customer. This is more of an X programme, which is not really justifiable by a commercial firm (especially one that's acquired some major new investors).

I hope SX will extend their testing to F9 stage 2 so they can more firmly anchor their simulations when they get to MCT and BFR size vehicles but the question is how well the results can be transferred to something  6x or 10x bigger.







What if the Second Stage only needs to fly itself on a suborbital trajectory from the ground and back, as a qualification measure?
Suppose you replace the payload with a big set of legs (legs which attach to the top of the stage) and some SuperDracos. 

The second stage itself is an article intended for orbital flight.  In Texas or New Mexico, the stage is fitted to this recovery package, launched off the ground as Grasshopper was, boosted into a sub-orbital trajectory and subjected to the same acceleration profile you'd get in flight, and then landed.  The stage is then de-mated from the recovery package, and trucked to a launch site with a "Flight-Tested" stamp. 

This would weed out defective stages in a fully-reusable manner, and doesn't seem that it should be more expensive than Grasshopper tests (the components are the same--fixed landing gear and a single Merlin engine). 

I'm just a student, but does this suggestion have merit?
It's generically called a "proof test," like firing a gun on a stand to make sure it does not blow up due to faulty workmanship.

Historically this has been one of the problems that there's no way to realistically test the upper stage except by flying it.  The problem with all expendable vehicles, or expendable parts. It's why the Atlas ICBM had drop engines but only a single set of tanks, to guarantee all needed engines would start (on the ground).

You're plan has at least 2 obvious flaws, one specific, one more of a "design pattern."

Specifically upper stages tend to have much higher expansion ratio nozzles as they work in near vacuum. Testing these engines at sea level means either a) running inside a sort of vacuum chamber called a diffuser or b)replacing it with a  much lower expansion ratio nozzle.

If you don't you typically get sever side loads on the nozzle (although it's not clear to me if that's due to the high expansion ratio or the Western nozzle optimization choices versus the Russian approach).

The "design pattern" is that stage and engine failures could be triggerd by the test hardware while under the real conditions the stage won't fail.

In your case that would include using a sea level nozzle instead of the vacuum design (increasing the number of nozzle swaps, possibly weakening the joint so it fails on the next swap IE in flight) or the shock loads as you try to land it on the super dracos (see "Frontiers of Space" for a similar proposal by Philip Bono for Saturn 1c recovery).

Reading your plan seems to be the closest thing to the spirit of the OP's question.
MCT ITS BFR SS. The worlds first Methane fueled FFSC engined CFRP SS structure A380 sized aerospaceplane tail sitter capable of Earth & Mars atmospheric flight.First flight to Mars by end of 2022 TBC. T&C apply. Trust nothing. Run your own #s "Extraordinary claims require extraordinary proof" R. Simberg."Competitve" means cheaper ¬cheap SCramjet proposed 1956. First +ve thrust 2004. US R&D spend to date > $10Bn. #deployed designs. Zero.

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