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SpaceX's New Spin on Falcon 9

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Re: SpaceX's New Spin on Falcon 9

#81

Post by rbanffy »

jccooper wrote: post #45
rst wrote: post #26

Earlier quoted context omitted.

It's going to be cheaper, but still in the millions, and not just because you still need to pay for a new second stage. There's also nontrivial cost associated with range safety, payload setup, and so forth (which are operations that still involve lots of highly trained personnel, with limited opportunities for automation because, among other things, the payloads aren't all alike).

Millions would be great, as it's currently a matter of tens (or hundreds) or millions. Order of magnitude can make a big difference.

Any sufficiently large quantitative change becomes a qualitative change. Orders of magnitude usually do that.

Re: SpaceX's New Spin on Falcon 9

#82

Post by pqomdv »

Gravityloss wrote: post #59
pqomdv wrote: post #40

Earlier quoted context omitted.

I can't wait for junkyard micro-satellites equipped with an ion thruster. They are launched in the hundreds at a time, each locates their specific target, attaches and start a slow descend to burn in the atmosphere. This process is done automatically over a time-frame of months, since ion thrusters work slowly, which is great for automation.

there are even more efficient and cheaper ways for deorbiting than ion engines.

Can you elaborate?

Re: SpaceX's New Spin on Falcon 9

#83

Post by FiatLuxDave »

DanielBMarkham wrote: post #76
tsotha wrote: post #75

Earlier quoted context omitted.

>It is bittersweet for me, the opportunity lost to keep funding NASA at a reasonable level... We spent more than enough money on NASA to have been decades ago where SpaceX is today. Unfortunately, Congress sees NASA as a source of patronage funding and not a space agency. If it had been run as a space program the shuttle would have been cancelled in the early '80s when it became The Monster That Ate The Budget.

I may disagree about which programs should be cut or not, but I agree with your sentiment: we could have paid NASA 10x and not advanced significantly. It would have just all flowed into various Congressional districts. We're advancing in spaceflight because we have no other choice: the money's ran out -- years ago, really. Political systems of organization (organizations of people set up based on the desires of the e…

I agree that we need to build a mass launcher. However, I don't think we need to build it on the Earth. I think we need to build it on an airplane.

Seriously, the limiting factor in how small you can make an orbital launch packet is atmospheric drag. The more atmospheric drag, the more mass to surface area ratio you need to reduce the losses to an acceptable level. The smaller you can make the orbital packet, the smaller you can make the mass launcher. The smaller the mass launcher, the smaller the capital expense. A small mass launcher also fits on a smaller airplane.

We already have plenty of airplanes capable of flying in the stratosphere which can mount a mass launcher of a few tons weight. If the goal is getting mass up there, it doesn't matter whether it is 1000 launches of 1 kg each, or 1 launch of 1000 kg. But 1000 launches of 1 kg each could be done with much less capital expense.

The whole reason we don't have a mass launcher is because it is perceived as too expensive. Sea-level, or even mountain-level mass launchers need to launch large packets by their nature. But a high-flying airplane could launch many smaller packets with a cost which is actually doable.

Re: SpaceX's New Spin on Falcon 9

#85

Post by kllrnohj »

marktangotango wrote: post #67
kllrnohj wrote: post #61

Earlier quoted context omitted.

> This is an absurd level of improvement for an already mature, commercially successful rocket. What are you basing that on? And an absurd level of improvement can just as easily mean that V1 was just really bad, not that V2 is just that good. I mean, the Merlin-1D has really good thrust to weight ratio, but the actual amount of thrust and the ISP at sea level is lacking compared to, say, the space shuttle's main eng…

To bad people down voted you without commenting on why. Here's what I think: >>I mean, the Merlin-1D has really good thrust to weight ratio, but the actual amount of thrust and the ISP at sea level is lacking compared to, say, the space shuttle's main engines (even with +30% the 1D is going to come short of 1,000 kN thurst, whereas the RS-25 on the shuttle was 1,860 kN). The Saturn's F1 engine had an even lower Isp,…

Sure, but the Merlin 1D is still on the very low end of the spectrum for total thrust, which you seem to ignore.

You'll note I only focused on Isp for engines with similar or better thrust than the 1D. And you can't just blindly ignore this. The lower the Isp of the engine the more fuel you need and the worse the thrust-to-weight of the vehicle total ends up being.

Having a very light but very low Isp engine will not get you off the ground efficiently. And if your claim to fame is being cost-effective, efficiency is kinda important.

Or put another way, the RS-25 at 7,480lb each represents a tiny, tiny fraction of the shuttle's total launch weight of 4,400,000 lbs. Using a 5,000lb engine instead would change nothing. Similarly your claim they only ran at lift off to verify they'd start is wrong. The RS-25 represented 30% of the launch thrust.

Even on the fairly light and small Falcon 9, the total vehicle weight is 1,115,200 lbs. The engine weight here is important but far, far from being the single most important attribute. And with a higher Isp engine with enough thrust you could then carry less fuel. Pretty sure you could spend 10,000 lbs on the engines to save 240,000 lbs of fuel (Falcon 9 has ~822,000 lbs of propellant, the RS-25's Isp is +30% the 1D at sea level)

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