Author Topic: Reusable Falcon vs Skylon  (Read 95849 times)

Offline ArbitraryConstant

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Re: Reusable Falcon vs Skylon
« Reply #40 on: 01/11/2013 05:43 pm »
Spacex are stating $54m for 13150Kg to LEO, which is of course peanuts relative to Skylon's $1Bn price tag and $6m/flight service costs, including propellant at 2002 NASA prices (sorry I have no more recent reference).
the currentbreak even point is 21 launches, where it's cheaper to buy a Skylon than buy another Spacex F9 ELV launch.
That's only the case if it's actually possible to buy a Skylon, which it isn't.

What if I tell you my flying saucer will launch the entire state of Nevada for a penny? Now I win the comparison.

Except I don't. Because my claim isn't credible. Skylon isn't credible either until they get a lot farther along in their development.

You're addressing critics as though they don't understand how lovely it would be if the PowerPoint slides became reality, which is missing the point. It would be lovely, agreed. The more serious issue is that there's a very good chance Skylon will never fly. Falcon 9 has gone to orbit multiple times, a Skylon LV hasn't even had metal bent, if you want to compare things you can buy, Skylon isn't even applicable.

SpaceX wants to do a reusable launcher. If you want to advance deeply speculative technologies that may never fly, that would be a more appropriate basis for comparison. And you should compare not only the promised price, but the probability for successfully flying at all.

Offline aero

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Re: Reusable Falcon vs Skylon
« Reply #41 on: 01/11/2013 07:18 pm »
At the risk of offending someones I will point out that this is the "Advanced Concepts" forum. It is not for existing hardware, if it were, it would not be "Advanced."

Further, this thread addresses the Advanced Concept of "Reusable Falcon vs Skylon." Discussions of existing expendible rockets are off topic except for supporting data they may offer. Skylon? Skylon still falls under "Advanced Concepts" per decisions of the Moderators.
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Offline ArbitraryConstant

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Re: Reusable Falcon vs Skylon
« Reply #42 on: 01/11/2013 08:28 pm »
Further, this thread addresses the Advanced Concept of "Reusable Falcon vs Skylon." Discussions of existing expendible rockets are off topic except for supporting data they may offer.
I agree.

My basic point is that we should evaluate based not only on the magnitude of the promise but on the likelihood of success, and if we are to compare Skylon to Falcon, it should be a reusable version and not the existing one that has already flown.

A reusable Falcon 9 may offer less potential, but has a higher likelihood of success. The technology needed is closer to reality, and the company doing it is largely self-funding. I think that's the main differentiator.

Offline Robotbeat

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Re: Reusable Falcon vs Skylon
« Reply #43 on: 01/11/2013 08:37 pm »
I disagree. I think the reusable Falcon 9 has just as much potential for cost reduction, if not more.
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Offline john smith 19

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Re: Reusable Falcon vs Skylon
« Reply #44 on: 01/11/2013 09:55 pm »
Meanwhile, you missed the word "reusable":
Yes and no. I went with the expendable because a) Musk has said reusability will halve the payload over the ELV version so hands and I wanted to  get a quick and dirty worst case comparison (for Skylon) b)Prices and payload are listed on the Spacex website. But RLV pricing is unknown.

In marketing pricing (not costing. I don't think anyone outside Spacex knows what their real costs are. In accounting terms price is like cost the way stress is like strain. IOW it's not) is a sales tool.

You go with F9(r) (or whatever it's called). Do you pay full cost for 1st launch because you pay for the the whole thing to be built? Do spacex lower the cost for multiple launches (ops and new 2nd stage at least to begin with)? How much (and will it vary by how many payloads you want up to their reuse limit). Can you get a cash back every time the 1st stage you bank rolled gets re-used by another customer? I'm not being whimsical. At least for the 1st launch 2 stages have to get built that are as big as the existing F9. As a customer I take a 50% payload size reduction. What's my incentive to do this?

Obviously if they move to full reusability the game changes again. But I've still taken that 50% payload hit over an ELV whatever they manage to raise the ELV payload to (I fully expect F9 1.1 to be better. But how much?) At full current F9 pricing I'm paying c$4000/lb for that privilege. Keeping that level I'm looking at $24m/launch. But I now know Spacex are re-using both stages. So I'd be feeling seriously gouged at that level.
What's my incentive to not stack 2 of my payloads on 1 F9 ELV and have done with it (if I can get away with that)? Selling on will be a big issue. How many people will need all the re-uses (10 AFAIK) that Spacex are planning for their 1st stage.

Note that will my comments might sound a little hectoring IRL I have huge admiration for Spacex's progress and I'm sure (well as sure as anyone outside Spacex can be short of rifling their filing cabinets or hacking their servers  :) ) that they know all this already and have a plan. I think Spacex work their business model as hard as they work their trajectory model  :) but I've no clue what their plan is.

OTOH if you just sell the vehicle to someone else it's all their problem.  :)
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Offline Hauerg

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Re: Reusable Falcon vs Skylon
« Reply #45 on: 01/11/2013 10:09 pm »
There are 2 problems I see with the Skylon and similar RLV concepts:
a) you have a BIG investment before flight #1
b) if you lose one vehicle early on you might be out of business.

Both issues are not a problem with the SpaceX approach.

That's just plain wrong. Most of the cost of development is in the intellectual property, not the vehicle.
Thanks for confirming my point: skylon has to spend ALL of its development money before the can start making money. For them it s everything or nothing at all. There is no expendable or partially reusable Skylon IIRC.

Offline Rugoz

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Re: Reusable Falcon vs Skylon
« Reply #46 on: 01/11/2013 10:44 pm »
^

I expect skylon to be "sponsored" by government money like spacex is.


I couldn't care less about who succeeds, as long as I can afford a seat  ;D
« Last Edit: 01/11/2013 10:45 pm by Rugoz »

Offline Elmar Moelzer

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Re: Reusable Falcon vs Skylon
« Reply #47 on: 01/11/2013 11:19 pm »
^

I expect skylon to be "sponsored" by government money like spacex is.


I couldn't care less about who succeeds, as long as I can afford a seat  ;D
Well SpaceX has invested quite a significant amount of their own money...
Just saying.

Offline grondilu

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Re: Reusable Falcon vs Skylon
« Reply #48 on: 01/12/2013 12:06 am »
Thanks for confirming my point: skylon has to spend ALL of its development money before the can start making money. For them it s everything or nothing at all. There is no expendable or partially reusable Skylon IIRC.

Well, LAPCAT uses the same engine as Skylon so it could be seen as a partial implementation of Skylon.

Offline ArbitraryConstant

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Re: Reusable Falcon vs Skylon
« Reply #49 on: 01/12/2013 01:18 am »
You go with F9(r) (or whatever it's called). Do you pay full cost for 1st launch because you pay for the the whole thing to be built? Do spacex lower the cost for multiple launches (ops and new 2nd stage at least to begin with)? How much (and will it vary by how many payloads you want up to their reuse limit). Can you get a cash back every time the 1st stage you bank rolled gets re-used by another customer? I'm not being whimsical. At least for the 1st launch 2 stages have to get built that are as big as the existing F9. As a customer I take a 50% payload size reduction. What's my incentive to do this?
I'm not aware of any charter transportation service that front loads the cost of the vehicle on the first customer and then reimburses them over time later. The provider sets a rate that they believe will amortize the vehicle and make a profit in its expected service life. Companies deal with unexpected losses with insurance or self-insurance and try to have a high enough success rate that the failures don't take the company down.

Even now with expendables the customer doesn't buy the vehicle, they buy launch services. It's still a charter transportation service, except with an expendable the vehicle has to be amortized on its first flight.

Your incentive to use this is that that payload will be cheaper to launch with an F9R, and if that doesn't happen, the reusability concept will be a failure.

Well, LAPCAT uses the same engine as Skylon so it could be seen as a partial implementation of Skylon.
I think if LAPCAT were flying that would be a very important demonstration of the engine concept and would make it seem significantly less speculative.

I expect skylon to be "sponsored" by government money like spacex is.
SpaceX is getting limited payments for limited milestones. The total money received to date is much less than Skylon expects to need, and by the time it gets close it will be after many cargo deliveries and possibly crewed flights.

The SpaceX development cycle that they got money for was extremely short and to the point.

Offline john smith 19

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Re: Reusable Falcon vs Skylon
« Reply #50 on: 01/12/2013 11:34 am »
I'm not aware of any charter transportation service that front loads the cost of the vehicle on the first customer and then reimburses them over time later. The provider sets a rate that they believe will amortize the vehicle and make a profit in its expected service life. Companies deal with unexpected losses with insurance or self-insurance and try to have a high enough success rate that the failures don't take the company down.
And that might well be how Spacex decides to charge it. I suggested the others as options. However unlike existing systems it's likely the first systems will only be partially reusable and the reusable parts will have strictly limited lives. I'm unaware of any systems that match those features.
Quote
Even now with expendables the customer doesn't buy the vehicle, they buy launch services. It's still a charter transportation service, except with an expendable the vehicle has to be amortized on its first flight.

Your incentive to use this is that that payload will be cheaper to launch with an F9R, and if that doesn't happen, the reusability concept will be a failure.
Well given it's 1/2 the size of the F9 it should be cheaper. The question is how much by?
Quote
I think if LAPCAT were flying that would be a very important demonstration of the engine concept and would make it seem significantly less speculative.
REL have made it clear they think hypersonic flight is significantly harder than launch. People have described hypersonic flight as like continuous reentry. REL are currently designing and building a sub scale SABRE engine which will also make it "significantly less speculative."
This should probably stay in the "Skylon master thread."
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Offline ArbitraryConstant

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Re: Reusable Falcon vs Skylon
« Reply #51 on: 01/12/2013 09:31 pm »
However unlike existing systems it's likely the first systems will only be partially reusable and the reusable parts will have strictly limited lives. I'm unaware of any systems that match those features.
Just because the number of flights might be lower than for an airliner doesn't mean SpaceX can't do math. Amortization isn't rocket science.

The only reason I can think of for SpaceX to expose cost and risk to the customer is if they were going for very steep discounts over many flights.

Offline grondilu

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Re: Reusable Falcon vs Skylon
« Reply #52 on: 01/12/2013 10:17 pm »
As far as I'm concerned, the reason why I am very skeptical about the reusable Falcon is that it looks a lot like one of the oldest rocket design:



And by this I mean:  rocket engineers had plenty of time to try to implement this design.  They even actually went quite close with the DC-X.



Nowadays several private companies perform such rocket-powered vertical-takeoff and landing:  Armadillo-aerospace, Masten aerospace and of course recently SpaceX.

Yet none of these things ever went out of the atmosphere, and made a landing from a substantially high altitude.  Why?

My guess is that it is just extremely difficult to do it because it requires a tremendous precision in the control of the descent trajectory.

I mean for take-off, the way a rocket must behave is quite simple:  just give out the maximum thrust and go up.  Sure you need to control the trajectory but if you make a mistake it is usually easy to make a correction:  it's not like there was a wall in front of you.  Hell, during the last Falcon9 mission the rocket even lost an engine and still managed to fulfill its main objectives.   The target is a speed:  as long as you reach the correct velocity you're probably good to go.

For landing, that's different:  the target is a speed AND a position (the ground).  Sure you have a large margin of error for latitude and longitude but as far as altitude is concerned, you need to reach almost zero speed at ground level.  There is very little tolerance on this.  For landing there is, literally, a wall in front of you.  Since your rocket only has a certain deceleration capacity, if you are going too fast at a given altitude, then you won't have enough thrust to reach the ground safely.  And even if you have enough thrust, you might not have enough fuel.   So basically you need to carefully control your speed depending on your altitude during all the descent.  That's very hard,  and the difficulty seems proportional to the length of the powered descent.  So even if a vehicle is capable of vertical landing from say 100 meters altitude, it's still a long way to go before it is capable of landing from higher atmosphere.

And since this is the RFalcon vs Skylon thread, I'll also say that it is why I think Skylon has more chance of success.  Skylon is a plane and we know how planes work.  Also, a winged reentry concept has been proven already by the NASA space-shuttle.  The only thing that was missing was the SABRE engine and ReactionEngines seems to have proven that it can work.  So when Alan Bond says he has absolutely no doubt that his concept will work, I believe it is not just wishful thinking.  He really thinks it will and I believe him.

I am no rocket engineer not even a scientist and this was just my humble opinion.

PS.  just after I wrote this, I remembered the old unix game I once played long time ago:  moon-lander.   This thing was so tough to land it was a nightmare.  I know that computers will do it for a RFalcon, but still...
« Last Edit: 01/12/2013 11:50 pm by grondilu »

Offline KelvinZero

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Re: Reusable Falcon vs Skylon
« Reply #53 on: 01/12/2013 10:46 pm »
Both of those images are for single stage to orbit rockets though. (and the Tintin one is nuclear)

But if Im getting the general gist of your argument, you are saying F9R probably won't work because it looks too simple and someone would have done it already if it were that easy.

Interesting point. However we have tried things that are probably harder, such as the delta clipper. Its not like vertical takeoff and landing is something that people know is not worth attempting. People are always saying in hindsight that these projects were too difficult and took on too many new technologies at once, but for some reason we seemed to keep doing it, and not do the simpler sounding projects such as develop just a reusable booster or first stage to begin with, gain experience with that and move on.

It might just be that these projects were government funded. Part of their goal is to push the limits of technology, so a project that creates worthy problems in several fields, involving institutions across several states, is a popular one.

(edit: Sorry I know I am not dealing with the points you bring up later, Im just focusing on the "they havent done it, therefore something makes it hard")
« Last Edit: 01/12/2013 11:04 pm by KelvinZero »

Offline Elmar Moelzer

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Re: Reusable Falcon vs Skylon
« Reply #54 on: 01/12/2013 11:10 pm »
The DC-X was cancelled mostly for political reasons than technical reasons. NASA wanted the X-33 lifting body instead and that is why they cancelled the DC-X.

Offline Jim

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Re: Reusable Falcon vs Skylon
« Reply #55 on: 01/12/2013 11:16 pm »
No there is no proof that sabre will work.  And actually, F9R is closer to reality than Skylon.   The issue for F9R isn't can it happen but will it be a cost reduction.  Also landing isn't a big deal, it was done on the moon and mars and earth with DC-X

Offline grondilu

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Re: Reusable Falcon vs Skylon
« Reply #56 on: 01/12/2013 11:36 pm »
No there is no proof that sabre will work.  And actually, F9R is closer to reality than Skylon.

To me, being closer to reality does not mean having more chance of success.

Offline KelvinZero

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Re: Reusable Falcon vs Skylon
« Reply #57 on: 01/13/2013 12:43 am »
No there is no proof that sabre will work.  And actually, F9R is closer to reality than Skylon.

To me, being closer to reality does not mean having more chance of success.

This is what makes the comparison so hard though. We are comparing a near at hand thing with a probably better but possibly imaginary thing.

Neither of them quite seem to make sense for the current market so we are not only trying to compare current apples with future oranges, we also have to take into account that the market still has to be created also.

Rather than F9R vs Skylon, it seems to me almost certain that F9R will have its go first, and it may in fact be the F9R that opens the market that makes Skylon investment attractive. Maybe the success of F9R is what will give it a very short lifespan, something we will remember like those weird aircraft from the dawn of flight.

Im interested in both of them but not in think big projects. Both of them have think-small versions and these don't even overlap. Once a market for reusables exist things will probably advance quickly.

Offline Jim

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Re: Reusable Falcon vs Skylon
« Reply #58 on: 01/13/2013 01:12 am »
No there is no proof that sabre will work.  And actually, F9R is closer to reality than Skylon.

To me, being closer to reality does not mean having more chance of success.

Huh?  If it becomes reality, it is a success.
Sabre has nothing flying, F9 does. 
Sabre may never reach orbit, much less refly

Offline grondilu

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Re: Reusable Falcon vs Skylon
« Reply #59 on: 01/13/2013 01:29 am »
Huh?  If it becomes reality, it is a success.
Sabre has nothing flying, F9 does. 
Sabre may never reach orbit, much less refly

It really seems to me that when you mean "closer to reality", you mean something along the line of being tangible, or being in the demonstration phase.   When I wrote that when something is closer to reality it does not mean it has more chance of success, I was trying to make you understand what I mean.

I don't value the fact of having a prototype or "something flying" as much as you do.  Flying is not the difficult part.  I trust computer models, especially in the aeronautics field since for what I can see planes are designed mostly on computer and usually the first prototypes don't crash nowadays.   When the first A380 took off for the first time I'm pretty sure nobody was really scared.



Let me ask you this.  Imagine ReactionEngines had begun by making a full scale Skylon, with hydrogen tanks, the exact same shape and everything, but instead of SABRE engines, they would have put some conventional engines instead, and made some demonstrations of subsonic flights.  And then they would have said:  "we intend to replace these engines by dual-mode engines soon so we can fly hypersonic and eventually fly to orbit."

Do you think that would have changed anything to the chance of success?  I don't.
« Last Edit: 01/13/2013 01:52 am by grondilu »

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