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Hmmm, Ed, I can't say I would agree with your opinion even if it wasn't based on mistaken premise- you cannot seriously claim that the only use for these massive, reusable spaceships is to carry large numbers of people to Mars. Musk just updated his plan for financing those flights and it including many different ways to gather value from a vehicle that can bring 150 tons to orbit. 

If it's capable and tasked to handle duties that F9/FH might handle, and is fully re-usable, why would it make SpaceX less competitive? Actually, how could SpaceX be less competitive with a reusable BFR? I'm scratching my head here on your opinion about this.
SpaceX presentations show heavy lift to Mars, including human transport, as the primary mission for BFR.  If SpaceX intended only to be commercially competitive, it would develop a launch vehicle designed to launch 6 tonne comsats to GTO in the most cost efficient manner.  That launch vehicle would have maybe only 1/4th or 1/3rd the BFR GLOW (assuming a reusable design) and would cost as much less to develop and fly.

 - Ed Kyle

Building GTO-focused LV might be a method of being commercially competitive in the launch business, but it's most certainly not the only one. I seem to remember many discussions around here about the lack of sufficient 6+ tonne launch requests to support the flight rate that a reusable vehicle requires at a compelling price. Building a new reusable vehicle to accomplish only that task would almost certainly not be a path to profitability. Also, as other have noted, SpaceX has no intentions of being only commercially motivated.

Musk was pretty clear that the BFR had important secondary uses, and that his plans to fund the vehicle involved deriving revenue from those other uses. A multipurpose vehicle has significantly most revenue possibilities than a uni-tasker (paraphrasing Alton Brown).

Still though, you haven't addressed my question- how could SpaceX be less competitive with a reusable BFR? I understand that they could fail to achieve that goal, but assuming they do (and it will be high priority for a company that intends to both land and take-off again from Mars with the same vehicle), how could having a BFR make them less competitive?
General Discussion / Re: Paul Weitz has passed away
« Last post by ZachS09 on Today at 07:03 PM »
RIP Paul Weitz.

You will be missed forever.  :'(
In-Space Hardware Section / Re: 3-D Printing in Space
« Last post by oldAtlas_Eguy on Today at 07:00 PM »
The re-fabricator tech is a piece of the puzzle to make going to Mars and elsewhere easier and cheaper by reducing the required mass needed and also being able to expand the ability to replace broken parts far beyond the normal idea of supplies required to support a moderately risky endeavor and make it a lower risk endeavor.
Advanced Concepts / Re: Lunar-capable shuttle
« Last post by SweetWater on Today at 06:59 PM »
I've been trying to design a lunar capable shuttle for awhile now and I've hit a road block.does anyone know what the fuel usage per second is for the SSME's?And could a LO2/LH2 tank fuel it in a 15 by 20 ft space?

The SSME was throttleable from (I believe) 65% to 109% of rated power. The rate of consumption of fuel and oxidizer would depend on what level of thrust you were trying to achieve. My understanding of rocket engines is limited, but I believe that while percentage of thrust and fuel/oxidizer consumption are related, they do not scale precisely linearly (i.e. consumption at 75% of rated thrust is NOT 75% of consumption at 100% of rated thrust).

As for whether SSMEs could run using the LO2/LH2 in a 15 x 20 foot tank, my guess would be not for a very long time.

I'm curious as to why you want to use the shuttle as a basis for a lunar-capable vehicle. The wings, for example, are a lot of mass that is useless on/around the moon but needs to be propelled there (and, presumably, back) anyway. Shuttle TPS wasn't designed to re-enter at lunar velocities, the SSME required a lot of ground support equipment to start and couldn't be re-started in space.

Also, FWIW, if you are going down this rabbit hole, you might want to read up on Shuttle Centaur if you haven't already. It would probably help you ballpark how much LO2/LH2 could be fit into an insulated tank in the cargo bay, if you really wanted to try.
A few photos of OCISLY from last Thursday by user 'pin2hot' on Reddit: :o
SpaceX have stated several times in the media that they have to recoup most of the $1 Billion+ they invested in F9R before steep discounts on launches are possible. Schedule improvement rather than large discounts are the current incentive SpaceX is using to sell reused cores to their customers. 

Blue Origin may have an advantage here in the extraodinary wealth of their founder. They could afford to offer steep discounts upfront with New Glenn, which is desgined for at least 100 launches. They would not even require to do anything unethical like sell below production cost, just sell sligthly above marginal cost per flight and defer the full recovery of dev costs. If the market grows rapidly in response to cheaper access to space, they can even recoup the costs quicker than expected. It would also put pressure on SpaceX and other competitors to follow suit and lower prices leading to a virtuous circle. Even if not, they can still use low costs to capture market share from SpaceX and others.

SpaceX will likely make up that $1B before New Glenn flies reliability. They will only need to average ~$10M savings per flight over the next 3 or 4 years, and are probably tripling that already.
It's just a fact of nature that kinetic energy generated in a moving reference frame will appear as greater in some other reference frames (and lesser in others). If any form of propellentless propulsion is possible at all, then you can amplify kinetic energy by judiciously creating it from within moving or rotating reference frames and harvesting it in another. It's no more 'free energy' that needs to be explained any more than a higher relative velocity due to relative motion has to be explained as 'free velocity'.

This is not about KE being different in different frames (it obviously is), but about the total change of KE as a result of some interaction in a system, which must be the same in ANY inertial frame to satisfy CoE.  When you switch frames, KE of all participating objects changes, but this does not give you free energy.  However, when some physical interaction causes the total KE to change in a way that is frame dependent (i.e. the difference is frame dependent), it becomes a problem since it allows free energy.

Can you relate what you said to the parameters of the proposed Proxima Centauri probe? How would that satisfy or not satisfy COE in your view. I know that if an object was falling through an infinite uniform gravitational field the kinetic energy it gained would be different to different observers but each would also calculate a different amount of work the field does on the accelerating mass because the constant force acts through different distances to each observer. The work done would identically match the gain in KE from each perspective. Some say the EMDrive as well as the MEGA drive essentially create an artificial gravity field that the device falls through which amount to the same effect. I think any form of PP would essentially act the same.

I have to think more about what you said but I believe what I said was true regardless but only useful for energy extraction if you have a true form of PP to actually put energy into a moving or rotating frame. In that case it acts similar to gravity. Otherwise it just becomes a classical energy/momentum conservation problem which implies that you never truly have a stable reference frame to work with. For the purposes of this discussion, my definition of a valid reference frame is a platform which doesn't have to locally conserve momentum as an object is accelerated within it or at least it's a frame, like an almost infinite planet in which you don't have to supply the energy and momentum to maintain the integrity of that frame. A working EMDrive or MEGA drive appears to allow this as it isn't reacting against anything in the local environment to accelerate (if it really works!!!).
Historical Spaceflight / Re: Apollo 11 coffee table
« Last post by Chris Bergin on Today at 06:51 PM »
Welcome to the site.

That is very cool! Never seen that before.

Where did you get it from?
Blue Origin / Re: Blue Origin's BE-4 Engine
« Last post by envy887 on Today at 06:49 PM »
Looks like a good, stable burn. Few artifacts, and more than enough to begin a considerable test program. Impressive even at 50% power. It wouldn't surprise if this engine surpasses RD-191 before the end of this year, and reaches 3MN before the next year is out.

I though they were targeting 2.45 MN as operational thrust. Is 122% a standard margin? Will they try to take it higher?

Yes - ULA needed considerably more thrust (and margin) than Blue was originally after, thus a larger engine and fewer for NG as a result. Would also expect that they are expecting to gradually increase chamber pressure beyond afterward.

(The engine seems "over scaled" for  what they want/claim for it.)

Blue was originally targeting 400 klbf (1800 kN). They upped it to 550 klbf (2450 kN) to sell it to ULA. Why would they need to fire it at 675 klbf (3000 kN)?

Agree that it does seem oversized for 2450 kN and Blue is probably reserving performance.
General Discussion / Paul Weitz has passed away
« Last post by astropl on Today at 06:48 PM »
Former NASA astronaut Paul Weitz has passed away today at the age of 85.
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