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Brokedownclimber
Trad climber
Douglas, WY
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Topic Author's Reply - Jun 16, 2016 - 10:29pm PT
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The real key to making space travel happen, is reusability of the hardware, not having it all reside at the bottom of the Atlantic Ocean. That's why I'm excited at the approach SpaceX has taken. The number of recovered first stage boosters now stands at 4, and the reliability of landing them should only increase. The problem is Enthalpy available for re-landing them before running out. The concept of fuel and oxidizer densification is a good one, which reduces the physical size (hence, weight) of the tankage required. SpaceX has announced that later versions of the Falcon 9 may use liquefied and densified methane instead of RP-1 Rocket Propellant grade Kerosene. Supercooled liquid Oxygen is the oxidizer in the fuel/oxidizer combination, and there is a large surplus of Oxygen available to ensure complete kerosene combustion. Things will only get better for the Falcon 9 system once the new methane rated Merlin engines become available. Recovery of these booster first stages costing $16 million a whack, is a step in the right direction. Mission fuel costs are at $200,000.
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healyje
Trad climber
Portland, Oregon
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Jun 16, 2016 - 10:31pm PT
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Could you elaborate on 'methane rated'?
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Brokedownclimber
Trad climber
Douglas, WY
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Topic Author's Reply - Jun 16, 2016 - 10:37pm PT
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My understanding is, there are several small design changes required in order to enable regenerative cooling of the engine to be accomplished properly, along with modifications to the turbopumps feeding the fuel supply at different rates than RP-1. I'm sure there are different injector nozzles into the combustion chamber, as well. Methane also has a higher specific impulse than RP-1, which will result in even more thrust being available.
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healyje
Trad climber
Portland, Oregon
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Jun 16, 2016 - 10:42pm PT
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Can you list potential fuels / mixes by their [densified] energy (specific impulse?)
Seems like they'll need to do much better in the future.
I don't know squat about all this aspect of things...
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Brokedownclimber
Trad climber
Douglas, WY
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Topic Author's Reply - Jun 16, 2016 - 11:07pm PT
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Of the non toxic fuels available:
#1: Liquid Hydrogen
#2: liquid methane
#3: RP-1
There are problems associated with using liquid Hydrogen, since it has an extremely low boiling point--super cryogenic; it also causes metal embrittlement. It is also not very dense and requires larger storage tnaks which are insulated. The best compromise fuel seems to be liquid methane
Elon Musk has been planning all along to use methane, since it is easily manufactured from the Carbon Dioxide Martian atmosphere. That's really the concept first proposed by Dr. Robert Zubrin in his book The Case for Mars, and was extensively studied at Lockheed-Martin in the early 1990s.
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healyje
Trad climber
Portland, Oregon
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Jun 16, 2016 - 11:12pm PT
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The Mars Colonial Transporter seems unfathomably large. They said they'll need a whole new pad and system for it - maybe Texas as Canaveral pads are too small. Can't imagine standing one up; hard to picture it as any sort of tilt-up job like the Falcon 9. Also, a launch escape system for a payload like that (100 people) would be an interesting affair.
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Brokedownclimber
Trad climber
Douglas, WY
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Topic Author's Reply - Jun 17, 2016 - 09:19am PT
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After healyje's question about various fuel possibilities, I dug out one of my very old Aeronautical Engineering textbooks; Definitions for the record:
Specific Impulse, I (subscript, sp), is defined as the"number of seconds a pound of propellant can deliver a pound of thrust. "Units then, are "seconds," or "s."
Thrust= (propellant mass flow) x (exhaust velocity) = T, expressed mC.
The higher the exhaust velocity, the more thrust can be derived from a given propellant mass flow.
Exhaust velocity may be determined by multiplying I (sub sp) by g, the Earth's gravitational constant (32 feet per second per second).
Specific impulse for various propellant combinations are: 450 s for Hydrogen/Oxygen, 200 s for Hydrazine/oxygen, and 350 s for RP-1 kerosene/oxygen. Methane/oxygen is around 400 s. These are low compared to Nuclear-thermal systems developed in the 1970s at the end of the Apollo program, of 900 s. Chemical propulsion is currently the only option available with sufficient thrust & specific impulse to accomplish deep space missions. Moving beyond Mars to the Asteroid belt, in deep space exploration, Nuclear Thermal must be exploited. The NERVA system developed in the 1960s had developed thrusts of 250,000 pounds (1.1 million Newtons), with a specific Impulse of 825 s, almost twice that of the best chemical powered rocket engines. NERVA:(Nuclear Engines Rocket Vehicle Application). NERVA type engines produce radioactive exhaust products, essentially discouraging their use for first stage of rockets; deep space is no problem.
More specific Impulse may be utilized in 2 ways: reduction of travel times, or increased payloads, or realistically, some combination thereof.
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Brokedownclimber
Trad climber
Douglas, WY
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Topic Author's Reply - Jun 17, 2016 - 09:30am PT
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As an addendum to my previous post, the increase in specific impulse gained by going from RP-1 kerosene to liquid methane will result in a 14% increase in performance by the Falcon 9 vehicles, allowing a higher recovery rate of the launch vehicles. This may be equated to 14% more burn time available, allowing for better deceleration on reentry of the atmosphere and landing.
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Brokedownclimber
Trad climber
Douglas, WY
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Topic Author's Reply - Jun 17, 2016 - 09:18pm PT
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For those interested in rocket launches: There is to be a launch of Blue Origin's New Shepard suborbital spaceship early this Sunday morning beginning at 06:45 PDT. This will be the 4th flight of the particular hardware, having landed successfully on 3 previous flights. The webcast, beginning at 09:45 EDT, and 06:45 PDT may be accessed at:
http://www.blueorigin.com
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healyje
Trad climber
Portland, Oregon
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Jun 17, 2016 - 09:44pm PT
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Hell, it looked like a 2% bump would have successfully brought that baby home the other day - that close...
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Brokedownclimber
Trad climber
Douglas, WY
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Topic Author's Reply - Jun 17, 2016 - 09:55pm PT
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Correct. If the RP-1 could be cooled down another 10 to 15 degrees C, to -17 to -22 degrees C, that would have made enough difference in fuel availability to stick the landing. Recover another $16 million booster!
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Brokedownclimber
Trad climber
Douglas, WY
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Topic Author's Reply - Jun 20, 2016 - 07:10am PT
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HFCS-
It DOES resemble a phallus, though....but no jokes allowed.
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High Fructose Corn Spirit
Gym climber
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Jun 20, 2016 - 08:57am PT
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bdc, I don't know if you've followed Burt Rutan and SpaceShipOne over the years but the contrast between the two plans to get citizens to space is really something to watch and to think about. In hindsight particularly, clearly it seems Blue Origin is the more streamlined and safer approach and all things considered the better way.
I guess Burt Rutan retired in 2011 anyway. Black Sky: Race for Space is excellent documentary nonetheless. It sure fired me up back in 2006.
I wonder what Richard Branson is thinking about all these latest developments. I haven't been paying attention. He invested heavily in Rutan's operation.
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Brokedownclimber
Trad climber
Douglas, WY
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Topic Author's Reply - Jun 20, 2016 - 12:05pm PT
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If I were a betting man... I'd be betting heavily for Elon Musk and SpaceX to become the first private company to take humans to space. The Dragon 2 is scheduled for test flights in early 2017, with astronauts to the ISS in 2018. I also wouldn't be betting against Blue Origin; they are highly secretive w/r their timeline for suborbital tourist junkets to space above the Karman line.
I've already seen the Earth's curvature from an Air Force jet flying at nearly 50,000 feet.
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High Fructose Corn Spirit
Gym climber
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Jun 20, 2016 - 04:04pm PT
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Yeah, I'm ready to break through the Karman line!
I wonder how soon their projecting first customer launches after such amazing success so far? and the price tag? for 10 minutes of such fun?
I'll have to look into it. Sure was pretty though start to finish.
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Interesting:
"Due to atmospheric drag, the lowest altitude at which an object in a circular orbit can complete at least one full revolution without propulsion is approximately 150 km (90 mi), whereas an object can maintain an elliptical orbit with perigee as low as about 130 km (80 mi) with propulsion."
http://en.wikipedia.org/wiki/K%C3%A1rm%C3%A1n_line
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Brokedownclimber
Trad climber
Douglas, WY
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Topic Author's Reply - Jun 21, 2016 - 07:02am PT
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The most recent SpaceX satellite launch was successful, but the landing was unsuccessful due to...Liquid Oxygen (LOX) depletion in the last few seconds.
https://youtu.be/p5_hvVbxAAo
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