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Zed_Noir
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« Reply #60 on: 07/15/2012 07:57 PM » |
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That is about 13.6 mT for LaucherOne. IMO Ed's propellant mass fraction estimate is a bit optimistic.
For a 13.6 tonne vehicle, the following are possibilities to get 500 lb to LEO.
Option 1
Stg1: 11.4 tonnes, PMF 0.89, ISPavg = 285s
Stg2: 1.8 tonnes, PMF 0.89, ISP = 325
Option 2
Stg1: 11.5 tonnes, PMF 0.89, ISPavg = 285s
Stg2: 1.7 tonnes, PMF 0.88, ISP = 330
Option 3
Stg1: 11.5 tonnes, PMF 0.88, ISPavg = 295s
Stg2: 1.7 tonnes, PMF 0.88, ISP = 330
Option 4
Stg1: 11.5 tonnes, PMF 0.88, ISPavg = 295s
Stg2: 1.7 tonnes, PMF 0.87, ISP = 337
... and so on. Payload is of course most sensitive to second stage PMF and ISP.
As Jim pointed out in another thread. Any air-launched stages will have to into consideration of being carry horizontally loaded with propellants. Also there are movable aerodynamic surfaces. So I think more structure mass fraction are required in comparison to a vertically ground launched rocket.
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Zed_Noir
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« Reply #61 on: 07/15/2012 08:05 PM » |
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That is about 13.6 mT for LaucherOne. IMO Ed's propellant mass fraction estimate is a bit optimistic.
I wonder why they choose a vehicle that is 3.4mT below the max WK2 payload. Is it because WK2 needs an extended range to drop the LauncherOne over the ocean, thereby limiting its max payload?
Maybe that extra 3.4 mT is allocated for the LOX venting off during the climb to launch altitude. I don't think Virgin Galactic is planning on replenishing the LOX inflight. The WK2 don't appear to have a high rate of climb.
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edkyle99
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« Reply #62 on: 07/15/2012 10:24 PM » |
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That is about 13.6 mT for LaucherOne. IMO Ed's propellant mass fraction estimate is a bit optimistic.
For a 13.6 tonne vehicle, the following are possibilities to get 500 lb to LEO.
Option 1
Stg1: 11.4 tonnes, PMF 0.89, ISPavg = 285s
Stg2: 1.8 tonnes, PMF 0.89, ISP = 325
Option 2
Stg1: 11.5 tonnes, PMF 0.89, ISPavg = 285s
Stg2: 1.7 tonnes, PMF 0.88, ISP = 330
Option 3
Stg1: 11.5 tonnes, PMF 0.88, ISPavg = 295s
Stg2: 1.7 tonnes, PMF 0.88, ISP = 330
Option 4
Stg1: 11.5 tonnes, PMF 0.88, ISPavg = 295s
Stg2: 1.7 tonnes, PMF 0.87, ISP = 337
... and so on. Payload is of course most sensitive to second stage PMF and ISP.
As Jim pointed out in another thread. Any air-launched stages will have to into consideration of being carry horizontally loaded with propellants. Also there are movable aerodynamic surfaces. So I think more structure mass fraction are required in comparison to a vertically ground launched rocket.
Compared to a vertically launch liquid rocket, yes, but the penalty may not be as big as you might expect. Consider that Pegasus XL first stage PMF is better than 0.91, and that includes the wing and fins, etc. - Ed Kyle
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vulture4
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« Reply #63 on: 07/16/2012 06:06 AM » |
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Solid propellant may be a bit more dense than liquids.
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edkyle99
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« Reply #64 on: 07/16/2012 01:13 PM » |
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Solid propellant may be a bit more dense than liquids.
Traditionally, solid motors have had lower propellant mass fractions than RP/LOX stages. The gap has closed with the development of composite solid motor cases, but now more and more composites are being used on liquid rockets too (interstages, etc.), and aluminum lithium is a possible way to make the tanks even lighter, so the gap may still exist. - Ed Kyle
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iamlucky13
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« Reply #66 on: 07/17/2012 03:01 AM » |
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LauncherOne will be powered by a two-stage, liquid-fueled rocket, now in initial development by Virgin Galactic. The same rocket also is intended to ultimately replace the non-reusable RM2 hybrid motor that will power the SS2 to suborbit, Virgin says.
Non-reusable? I thought it had a re-usable casing and frame so you could pull out a spent motor, stick a fresh one in, and send the spent motor back Sierra Nevada to have a fresh load of fuel cast into it? By the way, has anything been said about desired orbits for Planetary Resources Arkyd 100's? I presumed they were fairly agnostic in that regards, and would be launched as secondaries, so the LauncherOne announcement took me by surprise.
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QuantumG
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« Reply #67 on: 07/17/2012 03:13 AM » |
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Non-reusable? I thought it had a re-usable casing and frame so you could pull out a spent motor, stick a fresh one in, and send the spent motor back Sierra Nevada to have a fresh load of fuel cast into it?
Maybe after decades of people saying "refurbish-able isn't the same thing as reusable" when talking about the Shuttle SRBs, it's actually starting to get through?
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vulture4
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« Reply #68 on: 07/18/2012 12:36 AM » |
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Non-reusable? I thought it had a re-usable casing and frame so you could pull out a spent motor, stick a fresh one in, and send the spent motor back Sierra Nevada to have a fresh load of fuel cast into it?
Maybe after decades of people saying "refurbish-able isn't the same thing as reusable" when talking about the Shuttle SRBs, it's actually starting to get through?
I heard the SRBs described as "salvageable" by someone who did it for a living. Rutan is a genius but not familiar with rocket propulsion. Hybrids had theoretical advantages but removing the fuel section and nozzle and replacing them, and assuring the quality of all the seals and attach points is time-consuming and costly, and you still have to deal with loading the oxidizer (LOX or NO) with significant hazards in either case. And of course with liquids you have the option of a pump-fed engine. Had the lox-kerosene powered X-34 not been canceled it would have set a benchmark for cost and hazards of reusable liquid-propelled air-launched rockets and Rutan might well have made a different decision with the Spaceship 1. It sounds like the "launcher" is primarily a test vehicle for reuse of the LOX/kerosene engine.
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RanulfC
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« Reply #69 on: 07/18/2012 05:08 PM » |
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17,500mph gets you one orbit in 90 mins, right? What's this 80,000mph about?
Still reading the thread but if no one else has "hit" on it yet the whole "80,000mph/around-the-world-in-80-minutes" thing is trying to PR reference "Around The World in 80 Days" by Jules Verne... (Given Sir Branson had a "bit" part in the last "re-make" version with Jackie Chan....  ) Randy
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docmordrid
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« Reply #70 on: 07/30/2012 01:04 AM » |
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NASA Watch @NASAWatch
RT @jeff_foust: Whitesides: anchor customers for LauncherOne have expressed interest in "dozens, if not hundreds" of launches.
#newspace2012
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Atlan
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« Reply #71 on: 07/30/2012 12:21 PM » |
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I just dont get it......why are there so many customers for a launch method so expensive (<10 Million for 225kg is just incredibly expensive as i understand it). Is the advantage of being the primary payload so huge?
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baldusi
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« Reply #72 on: 07/30/2012 12:34 PM » |
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I just dont get it......why are there so many customers for a launch method so expensive (<10 Million for 225kg is just incredibly expensive as i understand it). Is the advantage of being the primary payload so huge?
Because the lower end of the market is not driven by USD/kg, but by total amount of money spent. If you want to do a program under 20M, for example, you can't currently launch unless you do a secondary. Which prevents you from managing your launch dates, and might constraint you volumetrically. Not to mention that you might not find the orbit that you really want. A launcher of 1M for 15kg would have plenty of business, actually. You could put 10 cube sats, and each cost something like 200k with launch. At those prices you'd have a lot of demand.
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Danderman
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« Reply #73 on: 07/31/2012 02:25 PM » |
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I just dont get it......why are there so many customers for a launch method so expensive (<10 Million for 225kg is just incredibly expensive as i understand it). Is the advantage of being the primary payload so huge?
Because the lower end of the market is not driven by USD/kg, but by total amount of money spent. If you want to do a program under 20M, for example, you can't currently launch unless you do a secondary. Which prevents you from managing your launch dates, and might constraint you volumetrically. Not to mention that you might not find the orbit that you really want.
A launcher of 1M for 15kg would have plenty of business, actually. You could put 10 cube sats, and each cost something like 200k with launch. At those prices you'd have a lot of demand.
The economic term is for this is "unit cost". Sometimes, even $500 per pound is too expensive for a customer if the unit cost (the total price) is too high. A CubeSat customer typically will pay about $50,000 a kg, so they don't care about unit costs, only cost per kg; only prime customers really care about unit costs. Pegasus is really expensive per kg, but has a relatively low unit cost.
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HMXHMX
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« Reply #74 on: 07/31/2012 07:04 PM » |
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I just dont get it......why are there so many customers for a launch method so expensive (<10 Million for 225kg is just incredibly expensive as i understand it). Is the advantage of being the primary payload so huge?
Because the lower end of the market is not driven by USD/kg, but by total amount of money spent. If you want to do a program under 20M, for example, you can't currently launch unless you do a secondary. Which prevents you from managing your launch dates, and might constraint you volumetrically. Not to mention that you might not find the orbit that you really want.
A launcher of 1M for 15kg would have plenty of business, actually. You could put 10 cube sats, and each cost something like 200k with launch. At those prices you'd have a lot of demand.
The economic term is for this is "unit cost". Sometimes, even $500 per pound is too expensive for a customer if the unit cost (the total price) is too high.
A CubeSat customer typically will pay about $50,000 a kg, so they don't care about unit costs, only cost per kg; only prime customers really care about unit costs.
Pegasus is really expensive per kg, but has a relatively low unit cost.
I believe I heard the most recent Pegasus proposal was priced in the $40M range. That's 2/3rd the price of a Falcon 9, so unit cost is pretty extreme due to low flight rate.
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