Reason they would not used such a system is they don't want to go to the moon or any crewed BLEO program. That has been the real reason we have been strung along. They had the option with Atlas V and DIV for Lunar before investing in the HLV.
Quote from: Downix on 08/29/2013 05:51 amI checked yours. You neglected the weight of the lander itself. No I didn't.Dry mass: 10458Payload mass: 43000Total mass at burnout: 53458Isp: 312Delta-v: 3107Apply the rocket equation, you get: 147579 in LEO.Subtract the payload, you get: 104579Subtract the dry mass, you get: 94121
I checked yours. You neglected the weight of the lander itself.
QuoteQuote from: QuantumGOnly in pixie land is that the cost of an SLS launch.That's the cost on-record.Perhaps you mean that's the marginal cost that they made up, including none of the development costs, all of which could be avoided by just not building the pointless monster rocket.
Quote from: QuantumGOnly in pixie land is that the cost of an SLS launch.That's the cost on-record.
Only in pixie land is that the cost of an SLS launch.
Quote from: Warren Platts on 08/29/2013 02:39 amIt only has an isp of about 312 s? For the sake of argument.
It only has an isp of about 312 s?
Well, having large quantities of toxic storables at the pad for fueling could be less than desirable, especially for a crewed launch. Hypergolics are expensive and difficult to handle, which is one of the several reasons I've read that Titan IV was retired and replaced with EELV's using cryogenics.
QuoteReason they would not used such a system is they don't want to go to the moon or any crewed BLEO program. That has been the real reason we have been strung along. They had the option with Atlas V and DIV for Lunar before investing in the HLV. they, they. who is they, btw ? the illuminatis ?
Everybody who launches stuff launches hypergolics as well, and knows how to handle them. There are (much) less toxic alternatives, but it's not enough of a problem to switch. As for crewed launches, Orion and Dragon both use hypergolics, as did the Shuttle. And the propellant for an EDS or lander need not be launched together with the crew. In fact, the ability to offload propellant without new technology development is a large part of the attractiveness of hypergolics for this application.
Unless I misunderstand what you mean there is no such tipping point.
You do misunderstand because every rocket performance list I've ever seen has given a maximum mass it can move to a certain orbit. So, just how big does propulsion stage have to be when its' own mass exceeds its ability to push that mass through TLI?
Quote from: Ben the Space Brit on 08/29/2013 09:48 pmYou do misunderstand because every rocket performance list I've ever seen has given a maximum mass it can move to a certain orbit. So, just how big does propulsion stage have to be when its' own mass exceeds its ability to push that mass through TLI?That limit is for a given size of the stage, but a larger stage will be able to move a larger payload, it's not related to the type of propellant per se.
Quote from: mmeijeri on 08/29/2013 09:50 pmQuote from: Ben the Space Brit on 08/29/2013 09:48 pmYou do misunderstand because every rocket performance list I've ever seen has given a maximum mass it can move to a certain orbit. So, just how big does propulsion stage have to be when its' own mass exceeds its ability to push that mass through TLI?That limit is for a given size of the stage, but a larger stage will be able to move a larger payload, it's not related to the type of propellant per se.Different propellent have different energies (Isp). There must be a mass where attempting to move it with the number of engines that a tank of that size can reasonably support will never add sufficient energy to the system to reach escape velocity before the propellent is exhausted. It could be that this figure is so large that it isn't a real issue but the limit must exist.
Different propellent have different energies (Isp). There must be a mass where attempting to move it with the number of engines that a tank of that size can reasonably support will never add sufficient energy to the system to reach escape velocity before the propellent is exhausted. It could be that this figure is so large that it isn't a real issue but the limit must exist.
Another way to say what Ben is saying: you'll need an engine for this big EDS stage that can produce sufficient thrust, what is it?
According to my math, please check me, I figure it would be about 10,458 kg dry and 104,579 kg when full. This would provide the 3107 m/s of delta-v to get through TLI, with the lunar insertion to be done by the lander (as in the NASA architecture).I know 105 tons sounds like a lot, but it's only two Falcon Heavy launches, and because we're using storable propellant there's no time pressure. If you really wanted to you could do it with Falcon 9 v1.1.