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?
Quote from: Alf Fass on 05/13/2016 02:15 amThe Shuttle had growth problems throughout its development, wasn't it originally supposed to get 29.5 tons into LEO, but couldn't in practice?The Shuttle is a special case to me and also only ONE example for this. You said "often". One is not "often".If I was to take one, then I could use Falcon 9 which is now way beyond the original designs capabilities.
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.
Quote from: Elmar Moelzer on 05/14/2016 03:46 pmQuote from: Alf Fass on 05/13/2016 02:15 amThe Shuttle had growth problems throughout its development, wasn't it originally supposed to get 29.5 tons into LEO, but couldn't in practice?The Shuttle is a special case to me and also only ONE example for this. You said "often". One is not "often".If I was to take one, then I could use Falcon 9 which is now way beyond the original designs capabilities.A. It applies to all rockets, not just shuttle, most fail to meet original specs. And it applies Falcon 9 toob. There were upgrades left on the table to help the shuttle meet original requirements. c. All vehicles have gone through upgrades. Nothing new about that.
. . . They get there, at least after upgrades.
The statistics I quoted 5 years ago are different to those I'm seeing today, most notably engine thrust, my original post had it at 270 "tons" thrust at a T/W of 14, wiki now has 2000 kN per engine, still at T/W of "up to 14"That difference would mean an increase in engine weight from 19 tons to over 28 tons, empty weight is still given as 53.4 tons, so that shrinks non engine empty weight from 34 to 25 tons.Maybe I've misinterpreted something, or maybe wiki's got it wrong, or maybe those growth problems are happening for Skylon.
Quote from: Alf Fass on 05/14/2016 10:51 pmThe statistics I quoted 5 years ago are different to those I'm seeing today, most notably engine thrust, my original post had it at 270 "tons" thrust at a T/W of 14, wiki now has 2000 kN per engine, still at T/W of "up to 14"That difference would mean an increase in engine weight from 19 tons to over 28 tons, empty weight is still given as 53.4 tons, so that shrinks non engine empty weight from 34 to 25 tons.Maybe I've misinterpreted something, or maybe wiki's got it wrong, or maybe those growth problems are happening for Skylon.You're using wiki as a source for something like this.....
Quote from: Alf Fass on 05/14/2016 10:51 pmThe statistics I quoted 5 years ago are different to those I'm seeing today, most notably engine thrust, my original post had it at 270 "tons" thrust at a T/W of 14, wiki now has 2000 kN per engine, still at T/W of "up to 14"That difference would mean an increase in engine weight from 19 tons to over 28 tons, empty weight is still given as 53.4 tons, so that shrinks non engine empty weight from 34 to 25 tons.Maybe I've misinterpreted something, or maybe wiki's got it wrong, or maybe those growth problems are happening for Skylon.Or we could use the figures from V 2.0 of the Skylon Users Manual figures. That has a GTOW of 325 Tonnes with air breathing minimum thrust of 163 tonnes up to 407 tonnes and a rocket thrust of 407 tonnes. Given this is a HTO vehicle thrust does not have to exceed mass. Typically GTOW for aircraft is 3x thrust. For Skylon it's about 2x thrust, given a substantially faster acceleration profile.
Quote from: Alf Fass on 05/14/2016 10:51 pmwiki now has 2000 kN per engine, still at T/W of "up to 14"Maybe I've misinterpreted something, or maybe wiki's got it wrong, or maybe those growth problems are happening for Skylon.I take it you failed to notice the "citation needed" note on the 14:1 statement in wikipedia's Skylon article?
wiki now has 2000 kN per engine, still at T/W of "up to 14"Maybe I've misinterpreted something, or maybe wiki's got it wrong, or maybe those growth problems are happening for Skylon.
Quote from: JCRM on 05/15/2016 10:23 amI take it you failed to notice the "citation needed" note on the 14:1 statement in wikipedia's Skylon article?Why would they not have a citation? Is it perhaps because with RE failing to provide a T/W ratio for the engines they've done the sensible thing and had to assume its the same as for the previous engine?If you think that an air breathing engine as complex as Sabre is can have a thrust ratio as high as 20/1, which would be far higher than any turbojet, well . . .
I take it you failed to notice the "citation needed" note on the 14:1 statement in wikipedia's Skylon article?
Sabre 3 engine mass was 10870 kg for both engines, Sabre 4 isn't necessarily a heavier engine as it losses the frost control mass. SABRE T/W is up to 14 over the air breathing mode as it varies with velocity and altitude, peeking around Mach 2. SABRE rocket mode is substantially higher thrust with a T/W of 28.That's my understanding from the information we have available to us.
Quote from: lkm on 05/15/2016 01:12 pmSABRE T/W is up to 14 over the air breathing mode as it varies with velocity and altitude, peeking around Mach 2. SABRE rocket mode is substantially higher thrust with a T/W of 28.That's my understanding from the information we have available to us.Which SABRE? do you have a source?Skylon user Manual 2.1 shows 2MN peak thrust for air breathing and 2MN thrust for rocket.
SABRE T/W is up to 14 over the air breathing mode as it varies with velocity and altitude, peeking around Mach 2. SABRE rocket mode is substantially higher thrust with a T/W of 28.That's my understanding from the information we have available to us.
Britain to announce the location of its first spacesport after tomorrow. http://www.parabolicarc.com/2016/05/15/reports-britain-announce-location-spaceport-wednesday/I believe that the only suited for Skylon is CampbellTown, right?
The spaceport isn't directly related to Skylon in any way, it's about developing the UK space sector through space tourism (virgin galactic etc) and eventually potential for a small polar launcher. Of course REL may well make use of the site for small-scale testing.