Author Topic: The Reaction Engines Skylon Master Thread (5)  (Read 420892 times)

Offline 93143

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Re: The Reaction Engines Skylon Master Thread (5)
« Reply #1500 on: 04/23/2016 08:27 PM »
Part of the subcooling is for pump design reasons.  The rest is so the vehicle can sit on the runway for two hours without venting.  And I imagine the densification doesn't hurt...  (Just realized I probably overestimated the amount of kerosene/LOX that would fit into the tank volume, though I suppose you could densify that too...)
« Last Edit: 04/23/2016 11:42 PM by 93143 »

Offline lkm

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Re: The Reaction Engines Skylon Master Thread (5)
« Reply #1501 on: 04/24/2016 04:53 PM »
Mark Thomas will be a speaker at this conference in May:
http://www.aerosociety.com/Events/Event-List/2197/What-Price-Speed

Offline knowles2

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Re: The Reaction Engines Skylon Master Thread (5)
« Reply #1502 on: 04/25/2016 11:22 AM »
Mark Thomas will be a speaker at this conference in May:
http://www.aerosociety.com/Events/Event-List/2197/What-Price-Speed
May be we will get something new, they been quiet since December.

Offline francesco nicoli

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Re: The Reaction Engines Skylon Master Thread (5)
« Reply #1503 on: 05/11/2016 08:21 AM »
any progress of late? we would very much appreciate some update status from REL, if any REL-affiliated person is reading this...

Offline john smith 19

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Re: The Reaction Engines Skylon Master Thread (5)
« Reply #1504 on: 05/11/2016 12:10 PM »
Read elsewhere that the hydrogen is subcooled to 16K. If the tank pressure is reduced to 1 atm during flight then NPSH drops to about 0.7atm minus all the losses on the way to the pump inlet. The turbopump guy is not going to be very happy about this.
Running the properties for H2 from the NIST data book

http://webbook.nist.gov/cgi/fluid.cgi?TLow=14&THigh=20&TInc=1&Applet=on&Digits=5&ID=C1333740&Action=Load&Type=SatP&TUnit=K&PUnit=atm&DUnit=mol%2Fl&HUnit=kJ%2Fmol&WUnit=m%2Fs&VisUnit=uPa*s&STUnit=N%2Fm&RefState=DEF

Give saturation conditions for H2 at 16K of 0.2atm.

I'd suggest REL have had ample time to model flow losses through the pipework and turbopump design has advanced somewhat since days of the RZ20 and J2.

[EDIT The ability to pump 2 phase LH2/GH2 was part of the J-2S programme so a stage could relight after a long period on orbit (by the end they'd cracked the valve sequencing necessary to maintain low enough back pressure on the pumps to dispense with the starter cartridges, opening the way to unlimited starts). Designs capable of pumping a 50% gas flow had IIRC been mfg. AFAIK the design reports are still in the NASA archives ]
« Last Edit: 05/11/2016 12:25 PM by john smith 19 »
"Solids are a branch of fireworks, not rocketry. :-) :-) ", Henry Spencer 1/28/11  Averse to bold? You must be in marketing."It's all in the sequencing" K. Mattingly.  STS-Keeping most of the stakeholders happy most of the time.

Offline Hankelow8

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Re: The Reaction Engines Skylon Master Thread (5)
« Reply #1505 on: 05/11/2016 12:30 PM »
At the moment I believe SABRE 3 is very thirsty and SABRE 4 is "obese"

Could this mean a SABRE 3.5 !

Offline dror

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Re: The Reaction Engines Skylon Master Thread (5)
« Reply #1506 on: 05/11/2016 02:44 PM »
Part of the subcooling is for pump design reasons.  The rest is so the vehicle can sit on the runway for two hours without venting.  And I imagine the densification doesn't hurt...  (Just realized I probably overestimated the amount of kerosene/LOX that would fit into the tank volume, though I suppose you could densify that too...)

I didn't read this thread for a while,
Why do you mention kerosene in relation to Skylon?
"If we crave some cosmic purpose, then let us find ourselves a worthy goal. "
Carl Sagan, Pale Blue Dot

Offline 93143

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Offline Alf Fass

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Re: The Reaction Engines Skylon Master Thread (5)
« Reply #1508 on: 05/12/2016 06:46 AM »
Carryover from another thread:

http://forum.nasaspaceflight.com/index.php?topic=40066.msg1521829#msg1521829



Meanwhile, much more "traditional" SSTO proposals can get similar or higher margins and less payload uncertainty with way fewer new technologies and a more reasonable development budget...

Analysis or citation please.  This statement is preposterous on its face.

Actually, if a Skylon vehicle used dense propellants, conventional high t/w rocket engines and was launched vertically, it would place somewhere between 2 and 4 times more payload into orbit for its empty weight (obviously swapping out the SABRE engines for rocket engines).  I've done this calculation for several different iterations of the published Skylon empty mass, so don't wish to bother to hunt up the link here on NASAspaceflight at the moment.  But using published info on Skylon anyone can repeat the calculation.

The calculation illustrates Skylon's real technical risk (beyond the engines working as planned).  No surprise, but its mass fraction is quite high, higher than I'd be comfortable proposing for a LOX-hydrocarbon vehicle, even VTOL.  It just looks low due to the larger amount of LH2 it employs.  But PMF calculations always must be normalized to propellant density, not weight, since that is the proper metric.

I wrote this 5 years ago:
Quote
After running through the mass numbers for Skylon that Reaction Engines offers, I'm left believing that they've got an engine that will theoretically get them to orbit in one stage, but only by them making unrealistic assumptions about the structural weight of the rest of the vehicle, total dry mass 53 tonnes, engine thrust 270 tonnes, engine T/W 14 therefore mass of engines ~19 tonnes, therefore mass of the rest of the vehicle ~34 tonnes. 34 tonnes for a winged vehicle that's 83 meters long, carries all its landing gear to orbit, it has a propellant volume around 1400^3 meters, it uses cryogenic propellants and it has to endure re-entry. I know they're promoting Skylon as having revolutionary construction materials and methods, but it seems to me they've had to make some excessively optimistic assumptions about the structural weight to get the numbers to come together  so they can continue with their pet project - the engines.

Looking at it another way: The combined propellant tank volume by my math (with a few assumptions on the current LH2:LOX ratio) would have enough volume to hold 500 tonnes of LH2/LOX at a 1:6 ratio, lets allow structural weight growth of 20% for the heavier take-off weight making structural wt 40.8 tonnes, 2 SSME's (or easily maintained equivalent) is + 6.4 tonnes, so total unladen weight is 47.2 tonnes, add a P/L of 15 tonnes and also the 500 tonnes LOX/LH2 and you get a take-off weight of 562.2 tonnes, at engine shut off weight is 62.2. Mo/M1 is 9.03, delta V at Ve 4500 m/s is 9907m/s.

While I was obviously too optimistic about the achievable exhaust velocity from SSME's lifting from the ground, I see no reasons in the rebuttals to Gary's comments to revise my skepticism of Skylon, that version of Skylon had a fuselage physically larger than an A380 that weighs less than 34 tons. Why aren't we building all out jet aircraft using the aeroshell that RE plans? Think of the fuel savings that could be had by cutting the weight of aircraft by over 50%!
When my information changes, I alter my conclusions. What do you do, sir?
John Maynard Keynes

Offline john smith 19

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Re: The Reaction Engines Skylon Master Thread (5)
« Reply #1509 on: 05/12/2016 09:58 PM »
While I was obviously too optimistic about the achievable exhaust velocity from SSME's lifting from the ground, I see no reasons in the rebuttals to Gary's comments to revise my skepticism of Skylon, that version of Skylon had a fuselage physically larger than an A380 that weighs less than 34 tons. Why aren't we building all out jet aircraft using the aeroshell that RE plans? Think of the fuel savings that could be had by cutting the weight of aircraft by over 50%!
So you don't really know anything, but you're sure the number have been fudged. Is that about it?

And you really can't figure out any reason all aircraft are made from this material?

Passenger aircraft don't have to deal with skin temperatures of 1100c. They can get by with Aluminum and composites. The skin material is likely to be more expensive and certainly has less usage history than either, so they won't use it as there is no compelling need for it.

You've also ignored the fact that such a lightweight structural concept maybe possible because LH2 has such low density and the load is quite evenly distributed within the whole fuselage.

Rather like a soda can, which weighs 11g and carries around 330g,  but can support at least nine more sitting on top of it. IE a load of 3.3Kg sitting on an 11g, a 300:1 payload to structure ratio.

But you can't scale that performance up. The problem plays to the strengths of the materials used to create a solution that seems to be impossible.

Much like Skylon's structural concept.

"Solids are a branch of fireworks, not rocketry. :-) :-) ", Henry Spencer 1/28/11  Averse to bold? You must be in marketing."It's all in the sequencing" K. Mattingly.  STS-Keeping most of the stakeholders happy most of the time.

Offline Alf Fass

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Re: The Reaction Engines Skylon Master Thread (5)
« Reply #1510 on: 05/13/2016 01:37 AM »
While I was obviously too optimistic about the achievable exhaust velocity from SSME's lifting from the ground, I see no reasons in the rebuttals to Gary's comments to revise my skepticism of Skylon, that version of Skylon had a fuselage physically larger than an A380 that weighs less than 34 tons. Why aren't we building all out jet aircraft using the aeroshell that RE plans? Think of the fuel savings that could be had by cutting the weight of aircraft by over 50%!
So you don't really know anything, but you're sure the number have been fudged. Is that about it?

I didn't say fudged, rockets on the drawing board often don't turn out to be as good as the designers hoped, you and I are both in the situation of not really knowing anything, you're just trusting that this paper plane will work as well as its promoters imagine.
Quote
And you really can't figure out any reason all aircraft are made from this material?

Passenger aircraft don't have to deal with skin temperatures of 1100c. They can get by with Aluminum and composites. The skin material is likely to be more expensive and certainly has less usage history than either, so they won't use it as there is no compelling need for it.

And you know these facts from what?
Quote
You've also ignored the fact that such a lightweight structural concept maybe possible because LH2 has such low density and the load is quite evenly distributed within the whole fuselage.

So the vehicle has bulkheads in it to keep the H2 load evenly distributed even when the acceleration of the vehicle would make it unevenly distributed?
Quote
Rather like a soda can, which weighs 11g and carries around 330g,  but can support at least nine more sitting on top of it. IE a load of 3.3Kg sitting on an 11g, a 300:1 payload to structure ratio.

And if an ant were as big as an elephant it could lift 10 tons
Quote

But you can't scale that performance up. The problem plays to the strengths of the materials used to create a solution that seems to be impossible.

Much like Skylon's structural concept.

If the light weight Skylon fuselage is possible, it will be easy enough to build the tanks with that system to get to orbit with a reusable SSTO vehicle carrying the same PL, with the same vehicle dry mass, by using just plain old rocket engines.
« Last Edit: 05/13/2016 01:43 AM by Alf Fass »
When my information changes, I alter my conclusions. What do you do, sir?
John Maynard Keynes

Offline Elmar Moelzer

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Re: The Reaction Engines Skylon Master Thread (5)
« Reply #1511 on: 05/13/2016 01:59 AM »
rockets on the drawing board often don't turn out to be as good as the designers hoped
Like?

Offline Alf Fass

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Re: The Reaction Engines Skylon Master Thread (5)
« Reply #1512 on: 05/13/2016 02:15 AM »
rockets on the drawing board often don't turn out to be as good as the designers hoped
Like?

The Shuttle had growth problems throughout its development, wasn't it originally supposed to get 29.5 tons into LEO, but couldn't in practice?
When my information changes, I alter my conclusions. What do you do, sir?
John Maynard Keynes

Offline 93143

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Re: The Reaction Engines Skylon Master Thread (5)
« Reply #1513 on: 05/13/2016 04:04 AM »
So the vehicle has bulkheads in it to keep the H2 load evenly distributed even when the acceleration of the vehicle would make it unevenly distributed?

No, I don't think so.  Actually, I think he misspoke there; it's not "even" distribution as much as it is a particular distribution that makes the structural concept work.  (Note that to help maintain trim, they drain the rear tanks first.)

Quote
If the light weight Skylon fuselage is possible, it will be easy enough to build the tanks with that system to get to orbit with a reusable SSTO vehicle carrying the same PL, with the same vehicle dry mass, by using just plain old rocket engines.

Skylon is a detailed design optimized for a specific load envelope and mixture ratio with hydrogen in the bulk of the volume and almost all the heavy stuff in the middle where the lift and thrust loads are.  You can't just hijack it for rocket mixture ratios, never mind different propellants or a different vehicle configuration, and expect the dry mass to stay the same.  Mark Hempsell already pointed this out.
« Last Edit: 05/13/2016 05:48 AM by 93143 »

Offline Alf Fass

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Re: The Reaction Engines Skylon Master Thread (5)
« Reply #1514 on: 05/13/2016 08:22 AM »

If the light weight Skylon fuselage is possible, it will be easy enough to build the tanks with that system to get to orbit with a reusable SSTO vehicle carrying the same PL, with the same vehicle dry mass, by using just plain old rocket engines.

Skylon is a detailed design optimized for a specific load envelope and mixture ratio with hydrogen in the bulk of the volume and almost all the heavy stuff in the middle where the lift and thrust loads are.  You can't just hijack it for rocket mixture ratios, never mind different propellants or a different vehicle configuration, and expect the dry mass to stay the same.  Mark Hempsell already pointed this out.

Hudson says volume Hempsell says mass, how to choose, personally I'd start with volume and add in whatever reinforcing required to support the extra mass.

With "build the tanks with that system" I mean using the same truss system that's supposed to work so well for Skylon but used in a VTOHL configuration with the engines at the back, interestingly despite my earlier misgivings, Skylon's fuselage isn't hugely lighter in terms of mass ratio that the Shuttle ET, the big difference is the surviving re-entry bit.

Something with the ET's H2/LOX propellant and Skylon's structural mass/propellant ratio and reentry ability with the equivalent of 6 SSME's on the back end could do the round trip with a similar PL to Skylon.

SLWT mass: 26,500 kg
LOX mass: 630,000 kg
H2 mass: 106,000 kg
6 x SSME: 27,600 kg
Add in a bit for other: 6,000 kg*
Payload: 15,000

GLOW: 811,100 kg

Thrust at Lift off: 6 x 1860 kN = 11,160 kN
Orbital mass: 75,100 kg

M0/M1 10.8

Exhaust velocity: 3586 - 4430 m/s SL - vac,  average 4000 m/s?

Delta V: 9518 m/s.


* Other: wings, fins, giudance, landing gear (which would be far lighter than Skylon's in only having to support the landing of the propellant empty vehicle) payload compartment - all the things already included in Skylon's ~34,000 kg engineless weight.

If Skylon works, I credit it to its light weight yet still reusable structure, not the engines.

When my information changes, I alter my conclusions. What do you do, sir?
John Maynard Keynes

Offline francesco nicoli

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Re: The Reaction Engines Skylon Master Thread (5)
« Reply #1515 on: 05/13/2016 01:45 PM »
Anyway,
I updated my calculations for Skylon's operators and producers business case with very, very conservative assumptions.

Assumptions for the operator:
Skylon acquisition price: 2.3 BN Eur.  per Unit (4x original REL value)
operation costs per flight: 10 M eur per flight (2X original REL value)
market price of similar launcher category: 40 M eur per flight (SpaceX F9-1R)
Nr. of total flights: 200 (as stated by REL)
lifespan: 30 years (as stated by REL)
With this conservative assumptions, each Skylon operator closes the business case with at least 3 launches per year over 30 years, i.e. 90 launches in total in 30 years.


Assumptions for the builder:
Skylon development costs: 20 bn Eur (about 25% higher than REL estimates)
of which:
            10 BN put forward by investors
            10 BN through loan financing at 5%-year interest rate.

SKylon production cost (per unit) 300 M (unknown value)
Skylon selling costs (2.3 BN *unit) (about 4X original value).

Now, financing: assuming that:
1)  50% of the total develpment cost of Skylon (10 BN) is financed through 5% annual interest rate
2) 2/3 of each unit sold go to reduce that debt burden, while 1/3 goes to investors
3) REL pulls out 1 new skylon each year once the production kicks off

then, it will take 8/9 years for REL to completely repay the original debt burden without disappointing the investors. The entire amount put upfront by the investors (the other 10 BN) will be repaid in total 11 years.


With these numbers, REL (or any producer) turns to profit if at least 11 skylons are built.

diffent assumptions:

1) 10% annual interest rate, 1 skylon produced per year: 11 years to fully repay debt, investors are paid off in 14 years
2) 10% annual interest rate, 2 skylon produced per year: 6 years to repay debt, 6 to repay investors
3) 5% annual interest rate, 2 skylon produced per year: 4 years to repay debt, 5 to repay investors

Concluding, we can consider that the quicker Skylon units are produced and built, the less expensive they become (because revenue can be used to repay part of the debt, therefore reducing the interest burden).
in turn, the pace Skylon units are built depend on the market absorption capacity. for 2 units per year to be built each year, the total skylon fleet would need to increase number of flights it does each year from 6 (3 per vehicle the first year) to 30 (still 3 per vehicle) the sixth year.

The flight pace would need to increase if the price per flight were to go below 40M per flight (which is the price of the best competitor).

« Last Edit: 05/13/2016 03:47 PM by francesco nicoli »

Offline john smith 19

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Re: The Reaction Engines Skylon Master Thread (5)
« Reply #1516 on: 05/14/2016 10:47 AM »
I didn't say fudged, rockets on the drawing board often don't turn out to be as good as the designers hoped, you and I are both in the situation of not really knowing anything, you're just trusting that this paper plane will work as well as its promoters imagine.
The topic of what design margins SABRESkylon has has been discussed at length on this thread.

What we know from Shuttle is that it's possible to go from no design base to a design (the SSME) that was within 3 secs of its Vacuum Isp target. IIRC SABRE would have to be 10s of seconds below it's rocket Isp and 100s of secs below its airbreathing Isp before Skylon would not be viable at its design masses. REL have also stated they are designing to international standards for fuselage weight growth so their design still works if it comes in 15% heavier than expected.
Quote
And you know these facts from what?
People have been learning how to work and use Aluminum alloys since the days of the Zeppelins. Every material has a much shorter usage history in the field. This is why both the French and the British opted to go with a Aluminum alloy for Concorde. That was viable at M2.2, not so at M3.
Quote
So the vehicle has bulkheads in it to keep the H2 load evenly distributed even when the acceleration of the vehicle would make it unevenly distributed?
Centre of Gravity (or "trim" as it's usually called in aircraft) is AFAIK SOP for all big aircraft such as the round the world Voyager, because other wise you need large control surfaces and/or large movements of those surfaces to make the vehicle change directions. But fast aircraft also have major Centre of Pressure shifts as they move through the Mach range. The B58 and Concorde certainly controlled the order and rate their tanks were used and I'd fully expect the SR71 and XB70 did as well.

Incidentally it's the location of the dead weight that matters, not tank stiffness, so pressure stabilization would not help this problem. People who design rockets have little understanding of this area as their brief is just to get the vehicle out of any atmosphere ASAP.
Quote
And if an ant were as big as an elephant it could lift 10 tons
Exactly. But I still find it a good yard stick to remind people there is what is possible (under certain conditions) and what people think is possible. Frequently the latter is very much less than the former.
Quote
If the light weight Skylon fuselage is possible,
Which it is, given the Wellington bomber was built with such construction. It's strong and light but was labor intensive to build in WWII.

I full expect that even fairly slow automation (operating 24/7) could build full fuselages and wing assemblies at an acceptable rate with much lower staff needs.
Quote
it will be easy enough to build the tanks with that system to get to orbit with a reusable SSTO vehicle carrying the same PL, with the same vehicle dry mass, by using just plain old rocket engines.
You appear to be conflating 2 separate idea.

The question "Can you build the fuselage at all" and "can you build the fuselage so it can take 100tonnes+ more weight," since that's an estimate of the LOX mass SABRE's save the vehicle having to carry.

The first is plausible.

The second is much less certain.
"Solids are a branch of fireworks, not rocketry. :-) :-) ", Henry Spencer 1/28/11  Averse to bold? You must be in marketing."It's all in the sequencing" K. Mattingly.  STS-Keeping most of the stakeholders happy most of the time.

Offline john smith 19

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Re: The Reaction Engines Skylon Master Thread (5)
« Reply #1517 on: 05/14/2016 11:10 AM »
Anyway,
I updated my calculations for Skylon's operators and producers business case with very, very conservative assumptions.

Assumptions for the operator:
Skylon acquisition price: 2.3 BN Eur.  per Unit (4x original REL value)

Assumptions for the builder:
Skylon development costs: 20 bn Eur (about 25% higher than REL estimates)
This is a most interesting post but I think you're starting numbers are a bit off.

Despite being a UK company REL normally quote their development budget and Skylon pricing in US dollars, whcih I think ithe international standard for the launch services business.

IIRC their current development budget (including the Skylon Upper Stage) is $12Bn, that's 10.61Bn euros, so 25% higher would be about 13.27Bn. 20Bn Euros is about 88% higher. IIRC this is derived from the ESA cost model, which is very conservative, given it predicted the A380 cost to be about $3Bn higher than it actually was.

The LSE analysis performed for ESA used a price of $2Bn for a Skylon, which is about Bn1.77 Euros. Your figure is therefor about 30% higher than the LSE estimate, which I think was conservative to begin with.
« Last Edit: 05/14/2016 11:15 AM by john smith 19 »
"Solids are a branch of fireworks, not rocketry. :-) :-) ", Henry Spencer 1/28/11  Averse to bold? You must be in marketing."It's all in the sequencing" K. Mattingly.  STS-Keeping most of the stakeholders happy most of the time.

Offline francesco nicoli

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Re: The Reaction Engines Skylon Master Thread (5)
« Reply #1518 on: 05/14/2016 02:44 PM »
Anyway,
I updated my calculations for Skylon's operators and producers business case with very, very conservative assumptions.

Assumptions for the operator:
Skylon acquisition price: 2.3 BN Eur.  per Unit (4x original REL value)

Assumptions for the builder:
Skylon development costs: 20 bn Eur (about 25% higher than REL estimates)
This is a most interesting post but I think you're starting numbers are a bit off.

Despite being a UK company REL normally quote their development budget and Skylon pricing in US dollars, whcih I think ithe international standard for the launch services business.

IIRC their current development budget (including the Skylon Upper Stage) is $12Bn, that's 10.61Bn euros, so 25% higher would be about 13.27Bn. 20Bn Euros is about 88% higher. IIRC this is derived from the ESA cost model, which is very conservative, given it predicted the A380 cost to be about $3Bn higher than it actually was.

The LSE analysis performed for ESA used a price of $2Bn for a Skylon, which is about Bn1.77 Euros. Your figure is therefor about 30% higher than the LSE estimate, which I think was conservative to begin with.

I am aware I was extremely conservative. However, consider that prices were expressed in 2008 values, so inflation also is to be taken into account. Still, the numbers are higher than their own estimates precisely because I wanted to test whether the model is sustainable even in case of substantial costs overshots.

the verdict is that yes, it looks sustainable, as long as operators mantain an high price (spaceX 1R levels). If prices go substantially below, then each Skylon will need to launch much more frequently . The bottom price any commercial Skylon operator looks to be a price of 16M/flight, at the conditions they manage to fly it at least 7 times per year (for 30 years). this is the minimal condition to operate without losses. below that, the company is in red.
Ideally, if a Skylon operator would charge 25M/flight and fly 10 times per year, it would completely repay the investment in about 8-9 years, leaving  more than the half of the vehicle capaity for pure profit.
in that case, total expected revenue is about 5Bn in 18 years.
« Last Edit: 05/14/2016 02:49 PM by francesco nicoli »

Offline francesco nicoli

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Re: The Reaction Engines Skylon Master Thread (5)
« Reply #1519 on: 05/14/2016 02:52 PM »
A public operator willing to buy a Skylon to use as a public infrastructure would be able to charge as little as 10M/flight to keep it running, at the condition of writing off the initial investment (as it happens with nearly all public infrastructure projects, which are not done to create profit for the the State but to provide infrastructure).
personally, I believe that a State owning a Skylon and willing to charge only operating expenses to the customers would be able to give an incredible boost to its space industry.

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