So the Air Force has found a concept that allows them to maximize system cost while minimizing the advantages? I mean... What should a two stag concept be good for? You replace a simple and scalable booster with an expensive SABRE design just to then add a second stage? Why???
Quote from: pippin on 03/03/2016 11:00 pmSo the Air Force has found a concept that allows them to maximize system cost while minimizing the advantages? I mean... What should a two stag concept be good for? You replace a simple and scalable booster with an expensive SABRE design just to then add a second stage? Why???Because a two stage system gives greater design margins. A lot of experienced people believe Skylon has a lot of design risk because it's single-stage to orbit. With two stages, there's more margin to work with, so the design doesn't have to push the edge of what's possible in so many ways, and there's more margin for making it more cost-effective.
Anyone else building precoolers other than Reaction Engines?. Here hoping this isn't an attempt by the air force to replicate Reaction Engine technologies in the US without Reaction engine involvement.
Plus, with two stages you can get the same payload to orbit with a smaller overall vehicle, or a larger payload to orbit with the same size vehicle. Smaller size means lower cost, which can more than offset the additional complexity of having two stages.
Because a two stage system gives greater design margins.
A lot of experienced people believe Skylon has a lot of design risk because it's single-stage to orbit. With two stages, there's more margin to work with, so the design doesn't have to push the edge of what's possible in so many ways, and there's more margin for making it more cost-effective.
The current Skylon user manual gives a GTOW of 325 tones for a 15 tonne payloadThat's a payload fraction of 4.6% Which is better than a Delta IV, the nearest big LH2 LV around and probably better than an F9, given SX are remarkably secretive about such things.
Saying Skylon is *better* than a working system is nonsense. Maybe some day it might but I wouldn'tbet on it. The user manual for a non-existent system is science fiction.
Surely someone has to think "it is better" of a non-existent thing before they could be bothered to get out of bed and make it real? Did the SpaceX founders think their non-existent clean sheet implementation would be better?
A slight shortfall in the performance of the former or underestimation of the mass of the latter could reduce its SSTO performance from 15 tons to not reaching orbit at all with zero payload.
intellectually dishonest.
Skylon is a concept remarkably short of actual full scale technology demonstration of either propulsion orvehicle structure and TPS.
A slight shortfall in the performance of the former or underestimation of themass of the latter could reduce its SSTO performance from 15 tons to not reaching orbit at all with zeropayload.
To state the obvious: This thread is in Advanced Concepts. So off the bat we know that: 1] it doesn't exist yet, 2] people are interested in discussing the concept, and if/how it might come to exist. So posts that point out it doesn't exist, and/or rush to conclude that it won't ever exist, or isn't worth discussing, really aren't moving the conversation forward very far...
According to my calculations, based on the numbers in the 2014 NISSIG presentation*, total payload loss would require one of: A) an 11.6% Isp loss across both engine modes, B) a 12.2% rocket Isp loss with no airbreathing performance loss, C) a 72% loss of airbreathing Isp with no rocket performance loss, D) 30.5% dry mass growth, or E) some combination of the above....
I see. So Skylon lacks a full scale demonstration because no one has built a Skylon yet. That alone makes you a doubter rather than a skeptic. Your name suggests you deal with logic devices. Do you understand the concept of a circular argument?
Funny. I've seen plenty of semiconductor documentation marked "provisional." In some cases I doubt they have even done the floor planning for the chip before telling the world it'll be available by next April, or whenever, yet they behave as if it will happen, and a lot of the time it does.
LOX-LH2 rocketry is a sufficiently mature tech that a large shortfall is ISP seems unlikely, even with the novel pump arrangement. Which, presuming their engineers have done their jobs right, leaves substantial performance margins before complete loss of payload.
Taking the above as reliable, the biggest uncertainty may be maintenance requirements between flights. Uncontained inspection and repair costs might render the whole system uneconomic even if full performance is delivered.
So posts that point out it doesn't exist, and/or rush to conclude that it won't ever exist, or isn't worth discussing, really aren't moving the conversation forward very far...
Quote from: Hanelyp on 03/08/2016 04:38 pmLOX-LH2 rocketry is a sufficiently mature tech that a large shortfall is ISP seems unlikely, even with the novel pump arrangement. Which, presuming their engineers have done their jobs right, leaves substantial performance margins before complete loss of payload. The design of the SSME was off it's predicted Isp by about 3 secs. Note this was only the 2nd staged combustion engine built in the US and the first (and only) LH2 engine. That's 0.66% for a first of a kind (SC of LH2) design. This suggests the rocket part at least is fairly well understood.
"The company plans to test the engines this year"
There's a new article about Skylon and Sabre at The Verge website:http://www.theverge.com/2016/3/8/11174670/rel-skylon-spaceplane-announced-jet-engine-rocket-propulsionOne bit of info was new to me:Quote"The company plans to test the engines this year"This is exciting news if true.