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SpaceX Dragon spacecraft for low cost trips to the Moon.



 
 
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  #1  
Old February 12th 12, 09:10 AM posted to sci.space.policy,sci.astro,sci.physics,sci.space.history,rec.arts.sf.science
Robert Clark
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Posts: 1,150
Default SpaceX Dragon spacecraft for low cost trips to the Moon.

Just saw this discussed on Nasaspaceflight.com

Elon Musk on SpaceX’s Reusable Rocket Plans.
February 7, 2012 6:00 PM
Quote:
The key, at least for the first stage, is the difference in
speed. "It really comes down to what the staging Mach number would
be," Musk says, referencing the speed the rocket would be traveling at
separation. "For an expendable Falcon 9 rocket, that is around Mach
10. For a reusable Falcon 9, it is around Mach 6, depending on the
mission." For the reusable version, the rocket must be traveling at a
slower speed at separation because the burn must end early, preserving
enough propellant to let the rocket fly back and land vertically. This
also makes recovery easier because entry velocities are slower.
However, the slower speed also means that the upper stage of the
Falcon rocket must supply more of the velocity needed to get to orbit,
and that significantly reduces how much payload the rocket can lift
into orbit. "The payload penalty for full and fast reusability versus
an expendable version is roughly 40 percent," Musk says. "[But]
propellant cost is less than 0.4 percent of the total flight cost.
Even taking into account the payload reduction for reusability, the
improvement is therefore theoretically over a hundred times."
http://www.popularmechanics.com/scie...-plans-6653023

Then for the Falcon 9, the payload would be reduced from 10 mT to 6
mT. If the reduction in payload really is this high, then maybe it
would be better to recover the first stage at sea. The loss in payload
is coming from the reduction in the speed of staging as well as the
need to retain a portion of the fuel for the return to base.
Recovering at sea would not have these disadvantages because you could
let the first stage make its usual trajectory at returning to the sea
but use just small amount of propellant for the final slowdown before
the sea impact.
In this article Musk does mention that returning back to the launch
point allows the turnaround time at least for the first stage to be
just hours. But will we really need that short a turnaround time at
this stage of the game? A turnaround time of a few days would seem to
be sufficient.
Perhaps the idea that retrieval at sea would be so expensive comes
from the experience of the shuttle with the SRB's. But these were
quite large and heavy at ca. 90 mT dry compared to that of the Falcon
9 first stage at less than 15 mT. Also, it is well known the labor
costs for the shuttle were greatly inflated compared to a privately
funded program.
The only additional requirement is that you would need a cover that
could be extended to cover the engine section and would be watertight.


Bob Clark

  #2  
Old February 13th 12, 08:51 PM posted to sci.space.policy,sci.astro,sci.physics,sci.space.history,rec.arts.sf.science
Jeff Findley[_2_]
external usenet poster
 
Posts: 1,388
Default SpaceX Dragon spacecraft for low cost trips to the Moon.

In article ba228d9e-b64d-475a-801e-
,
says...

Just saw this discussed on Nasaspaceflight.com

Elon Musk on SpaceX?s Reusable Rocket Plans.
February 7, 2012 6:00 PM
Quote:
The key, at least for the first stage, is the difference in
speed. "It really comes down to what the staging Mach number would
be," Musk says, referencing the speed the rocket would be traveling at
separation. "For an expendable Falcon 9 rocket, that is around Mach
10. For a reusable Falcon 9, it is around Mach 6, depending on the
mission." For the reusable version, the rocket must be traveling at a
slower speed at separation because the burn must end early, preserving
enough propellant to let the rocket fly back and land vertically. This
also makes recovery easier because entry velocities are slower.
However, the slower speed also means that the upper stage of the
Falcon rocket must supply more of the velocity needed to get to orbit,
and that significantly reduces how much payload the rocket can lift
into orbit. "The payload penalty for full and fast reusability versus
an expendable version is roughly 40 percent," Musk says. "[But]
propellant cost is less than 0.4 percent of the total flight cost.
Even taking into account the payload reduction for reusability, the
improvement is therefore theoretically over a hundred times."
http://www.popularmechanics.com/scie...-plans-6653023

Then for the Falcon 9, the payload would be reduced from 10 mT to 6
mT. If the reduction in payload really is this high, then maybe it
would be better to recover the first stage at sea.


Oh hell no! Dunking a launch vehicle in salt water is not a good idea.
This introduces a host of new problems related to salt water corrosion.
That's on top of the expense of maintaining the boat(s) necessary to
recover the first stage. All of this adds up to additional cost.

The only additional requirement is that you would need a cover that
could be extended to cover the engine section and would be watertight.


Don't forget the requirement for recovery boat(s), divers, and assorted
other trained crew members.

Jeff
--
" Ares 1 is a prime example of the fact that NASA just can't get it
up anymore... and when they can, it doesn't stay up long. "
- tinker
 




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