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SpaceX video showing Falcon 9 stages and Dragon performing avertical landing



 
 
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  #1  
Old October 1st 11, 04:40 PM posted to sci.space.policy
Space Cadet[_1_]
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Posts: 99
Default SpaceX video showing Falcon 9 stages and Dragon performing avertical landing

On Sep 29, 4:15*pm, Jeff Findley wrote:
SpaceX video showing Falcon 9 stages and Dragon performing a vertical
landinghttp://www.youtube.com/watch?v=p176UpWQOs4&feature=player_embedded

SpaceX Reusable Planshttp://nasawatch.com/archives/2011/09/spacex-reusable.html

So, this shows VTVL for a reusable TSTO (Falcon 9) plus Dragon landing
vertically.

For the first stage, it looks like they're using propulsion from three
of the engines to head back to KSC where it would land vertically on one
engine. *Since there is only TPS on the very end of the first stage, it
does not look like they're using any hypersonic lift to gain cross-
range.

For the second stage, the TPS looks like it extends further down the
side of the stage on one side. *This would indicate that they plan on
using hypersonic lift to gain cross-range and/or more accurately control
the landing location. *Similar to the first stage, the video shows the
second stage landing vertically under power of its engine.

In other words, their approach is a fully reusable VTVL TSTO. *I wish
them luck. *Since their test vehicle is reportedly based on the Falcon 9
first stage, it would appear that they're going to implement reusability
on it first. *This is *exactly* what I've been advocating for an
incremental approach to developing a fully reusable launch vehicle. *

As for landing Dragon under rocket power, this is a plus because (as
I've said in other posts) it eliminates the costs associated with
landing and recovery in the ocean. *Besides the costs associated with a
recovery ship, dunking a spacecraft in salt water might not be good for
reusability. *There would be costs associated with cleaning off the salt
water and verifying that it didn't get anywhere it shouldn't. *On top of
that, there would be the additional cost of testing and re-certifying
anything on the spacecraft that was exposed to salt water.

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


The part that shows the Dragon landing, I couldn't help but wondering,
where all the fuel is stored for landing or how much does that eat up
in payload?

Just my $0.02

Space Cadet

Moon Society - St. Louis Chapter

http://www.moonsociety.org/chapters/stlouis/

The Moon Society is a non-profit educational and
scientific foundation formed to further scientific
study and development of the moon.
  #3  
Old October 3rd 11, 07:34 PM posted to sci.space.policy
Jochem Huhmann
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Posts: 606
Default SpaceX video showing Falcon 9 stages and Dragon performing a vertical landing

Jeff Findley writes:

In article 73112da4-3bed-482e-a546-01c02f3a48f3
@d28g2000vby.googlegroups.com, says...

The part that shows the Dragon landing, I couldn't help but wondering,
where all the fuel is stored for landing or how much does that eat up
in payload?


The landing engines only need to slow the capsule from its terminal
velocity to zero. We're not talking about "a lot" of fuel here.


Doesn't matter how fast the thing is falling down -- Dragon weights
about 15000 lb when returning, so you need engines with 15000 lbf thrust
to hover. The existing OMS/RCS engines (Draco) have 4x90 lbf. You'd need
fourty of them to brake the thing.

And of course you'd need fuel not only for slowing down vertically. Even
if you can target reentry and descent to about a mile around the landing
pad you still need to nudge the capsule around quite a bit in the last
stages of descent. Without any kind of control surfaces you'll need to
expend fuel for that.

Also, parachutes "eat up" payload too.


True. But if the landing engines and fuel are meant to serve also as a
"pusher" escape system for manned launches you'll need to carry a
parachute anyway if you don't want to have the capsule plummet down to
the ground with empty fuel tanks afterwards.

And if they're really serious about that kind of escape system, they
will need to be able to accelerate with more than 1 g in case of a
catastrophic booster failure. 10 g would require 150000 lbf thrust, or
the equivalent of 400 Draco engines. And the fuel to feed them.


Jochem

--
"A designer knows he has arrived at perfection not when there is no
longer anything to add, but when there is no longer anything to take away."
- Antoine de Saint-Exupery
  #4  
Old October 3rd 11, 08:06 PM posted to sci.space.policy
Jeff Findley[_2_]
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Posts: 1,388
Default SpaceX video showing Falcon 9 stages and Dragon performing a vertical landing

In article , says...

Jeff Findley writes:

In article 73112da4-3bed-482e-a546-01c02f3a48f3
@d28g2000vby.googlegroups.com,
says...

The part that shows the Dragon landing, I couldn't help but wondering,
where all the fuel is stored for landing or how much does that eat up
in payload?


The landing engines only need to slow the capsule from its terminal
velocity to zero. We're not talking about "a lot" of fuel here.


Doesn't matter how fast the thing is falling down -- Dragon weights
about 15000 lb when returning, so you need engines with 15000 lbf thrust
to hover. The existing OMS/RCS engines (Draco) have 4x90 lbf. You'd need
fourty of them to brake the thing.


Obviously those are too small. From what I've read, SpaceX plans on
using "Super Draco" engines for this purpose. The plan is that these
engines will double as launch escape and propulsive landing engines.

And of course you'd need fuel not only for slowing down vertically.

Even
if you can target reentry and descent to about a mile around the landing
pad you still need to nudge the capsule around quite a bit in the last
stages of descent. Without any kind of control surfaces you'll need to
expend fuel for that.


True.

Also, parachutes "eat up" payload too.


True. But if the landing engines and fuel are meant to serve also as a
"pusher" escape system for manned launches you'll need to carry a
parachute anyway if you don't want to have the capsule plummet down to
the ground with empty fuel tanks afterwards.


I'd also like to add that in a launch abort situation like this, it is
very likely that the capsule will come down in the ocean, so a parachute
seems like a more appropriate for a "splash-down".

And if they're really serious about that kind of escape system, they
will need to be able to accelerate with more than 1 g in case of a
catastrophic booster failure. 10 g would require 150000 lbf thrust, or
the equivalent of 400 Draco engines. And the fuel to feed them.


You're just being silly. Obviously the engineers at SpaceX have thought
of this.

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
  #5  
Old October 3rd 11, 09:50 PM posted to sci.space.policy
Jochem Huhmann
external usenet poster
 
Posts: 606
Default SpaceX video showing Falcon 9 stages and Dragon performing a vertical landing

Jeff Findley writes:

And if they're really serious about that kind of escape system, they
will need to be able to accelerate with more than 1 g in case of a
catastrophic booster failure. 10 g would require 150000 lbf thrust, or
the equivalent of 400 Draco engines. And the fuel to feed them.


You're just being silly. Obviously the engineers at SpaceX have thought
of this.


I surely hope so, but *what* did they think? ;-)

The point is that as clean and nice and easy all this looks in a video,
as soon as you look at the numbers all of this looks very dubious. And a
liquid fueled pusher escape system needs some engines with *massive*
thrust. If they use 400 Draco engines (obviously not really an option)
or just 4 new engines with each 100 times the thrust of a Draco engine,
the required thrust stays the same.

Squeezing something with 150000 lbf thrust into the bottom of a Dragon
capsule along with the fuel tanks for it just seems impossible to me.


Jochem

--
"A designer knows he has arrived at perfection not when there is no
longer anything to add, but when there is no longer anything to take away."
- Antoine de Saint-Exupery
  #6  
Old October 4th 11, 03:20 PM posted to sci.space.policy
Jeff Findley[_2_]
external usenet poster
 
Posts: 1,388
Default SpaceX video showing Falcon 9 stages and Dragon performing a vertical landing

In article , says...

Jeff Findley writes:

And if they're really serious about that kind of escape system, they
will need to be able to accelerate with more than 1 g in case of a
catastrophic booster failure. 10 g would require 150000 lbf thrust, or
the equivalent of 400 Draco engines. And the fuel to feed them.


You're just being silly. Obviously the engineers at SpaceX have thought
of this.


I surely hope so, but *what* did they think? ;-)

The point is that as clean and nice and easy all this looks in a video,
as soon as you look at the numbers all of this looks very dubious.


Really? And just where are these "dubious" numbers? Care to share?


Obviously SpaceX isn't going to share much, since that's all their
intellectual property. But having seen papers on landing using
propulsion, the numbers just aren't as bad as you're making them out to
be.

Yes you lose payload, but that's not the point. A launch vehicle can
afford to "lose payload" when it's being reused several times. LOX and
kerosene are a tiny fraction of today's launch costs. The lion's share
of today's launch costs are to replace the *entire launch vehicle* after
each and every flight.

And a
liquid fueled pusher escape system needs some engines with *massive*
thrust. If they use 400 Draco engines (obviously not really an option)
or just 4 new engines with each 100 times the thrust of a Draco engine,
the required thrust stays the same.


True, so it is a good thing LOX/kerosene rocket engines have excellent
thrust to weight ratios. The Merlin IC reportedly has a thrust to
weight ratio of nearly 100. Using that as a yardstick, 150,000 lbs of
thrust requires an engine weight of about 1,500 lbs.

Here is a report on the Apollo launch escape system:
http://klabs.org/history/apollo_expe...ports/tn-d7083
_apollo_launch_escape_propulsion.pdf

Curiously, it had a thrust of 155,000 lbs, which is just about what
you're saying Dragon would need, so this ought to be interesting. Total
impulse of the launch escape motor was 515,000 lb-sec, which works out
to about 3.3 seconds of thrust at 155,000 lbs.

The launch escape motor had a weight of 4850 lbs.

Now compare it to LOX/kerosene numbers:

According to Wikipedia, when configured for Falcon 1, Merlin IC's thrust
was 78,000 lbs at sea level, and its fuel consumption is about 300 lb of
propellant per second. Scaling that up to 155,000 lbs of thrust gives a
fuel consumption number of about 600 lbs per second which is about 2000
lbs for 3.3 seconds of thrust.

So, the total weight of LOX/kerosene engines plus propellant would be
3500 lbs, which is 1350 lbs lighter than the solid. Obviously we've got
to add in the weight of tanks, plumbing, and etc., so there may not be
much in the way of weight savings.

This back of the envelope calculation shows that liquid fueled engines
for launch escape isn't ridiculous at first glance. I know that "the
devil is in the details", so this may be quite a challenge to work out.
Pluse, if these liquid fueled engines double as landing engines, that's
a "win" over a solid system which is simply discarded if it's not
needed.

Squeezing something with 150000 lbf thrust into the bottom of a Dragon
capsule along with the fuel tanks for it just seems impossible to me.


We'll see what SpaceX comes up with. Results are what will matter.

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
  #7  
Old October 5th 11, 09:59 AM posted to sci.space.policy
Jochem Huhmann
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Posts: 606
Default SpaceX video showing Falcon 9 stages and Dragon performing a vertical landing

Jeff Findley writes:

Curiously, it had a thrust of 155,000 lbs, which is just about what
you're saying Dragon would need, so this ought to be interesting. Total
impulse of the launch escape motor was 515,000 lb-sec, which works out
to about 3.3 seconds of thrust at 155,000 lbs.

The launch escape motor had a weight of 4850 lbs.


The Apollo CM had less mass than dragon with down payload, so to attain
about the same escape acceleration as Apollo, Dragon needs about the
same thrust, yes.

Now compare it to LOX/kerosene numbers:

According to Wikipedia, when configured for Falcon 1, Merlin IC's thrust
was 78,000 lbs at sea level, and its fuel consumption is about 300 lb of
propellant per second. Scaling that up to 155,000 lbs of thrust gives a
fuel consumption number of about 600 lbs per second which is about 2000
lbs for 3.3 seconds of thrust.

So, the total weight of LOX/kerosene engines plus propellant would be
3500 lbs, which is 1350 lbs lighter than the solid. Obviously we've got
to add in the weight of tanks, plumbing, and etc., so there may not be
much in the way of weight savings.


3500 lbs is about half of the Dragon down payload and a quarter of the
up payload. And you'll need turbopumps (which might be a bit slow to
spin up in an escape system and anyway heavy) or pressurized tanks
(which also are heavy). And plumbing and then there's the landing gear.
And getting away with about 30 seconds worth of fuel for a landing seems
to be a bit daring, too. Especially if you don't have any other way to
control your descent (like control surfaces), you'll need the fuel for
more than just breaking.

And for a manned landing there will be a very nasty black zone where
you're too low to switch to the backup parachute and still high enough
to have a failing engine or control system lead to loss of vehicle and
crew. But if you have thrust enough for accelerating with 10 g, you may
have got enough engines and redundancy to compensate for many failure
modes, OK.

This back of the envelope calculation shows that liquid fueled engines
for launch escape isn't ridiculous at first glance. I know that "the
devil is in the details", so this may be quite a challenge to work out.
Pluse, if these liquid fueled engines double as landing engines, that's
a "win" over a solid system which is simply discarded if it's not
needed.


I think solids are better for escape systems if you throw them away
unused nearly all the time. Just because they're probably cheaper.
Maybe more reliable, too. For a reusable capsule liquid fueled is
certainly a good idea.

Dragon is a great spacecraft and would totally deserve powered precision
landings. I'm just saying that this is nothing anyone would dare to try.
If it works out: Great!

Squeezing something with 150000 lbf thrust into the bottom of a Dragon
capsule along with the fuel tanks for it just seems impossible to me.


We'll see what SpaceX comes up with. Results are what will matter.


I'm certainly looking forward to that and in any case trying and failing
is totally better than not even trying.


Jochem

--
"A designer knows he has arrived at perfection not when there is no
longer anything to add, but when there is no longer anything to take away."
- Antoine de Saint-Exupery
  #8  
Old October 6th 11, 09:00 PM posted to sci.space.policy
Dr J R Stockton[_131_]
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Posts: 8
Default SpaceX video showing Falcon 9 stages and Dragon performing a vertical landing

In sci.space.policy message , Wed, 5 Oct 2011
10:59:39, Jochem Huhmann posted:


I think solids are better for escape systems if you throw them away
unused nearly all the time. Just because they're probably cheaper.
Maybe more reliable, too. For a reusable capsule liquid fueled is
certainly a good idea.


An escape TOWER is a waste of mass; there may be need for a light
fairing to protect the capsule.

The capsule should have a ring of motors at the bottom of its sides,
sized overall to give the necessary but uncomfortable escape thrust for
the escape period.

As soon as there is no need for such an escape system, or when the lower
stages have been dropped, or after a subsequent coast period, then those
motors should be used, a comfortable few at a time, for the final
insertion into orbit or for subsequent orbit raising.

Everything that lifts off the launch pad should be used before it is
abandoned.

--
(c) John Stockton, nr London, UK. Turnpike v6.05 MIME.
Web http://www.merlyn.demon.co.uk/ - FAQqish topics, acronyms and links;
Astro stuff via astron-1.htm, gravity0.htm ; quotings.htm, pascal.htm, etc.
No Encoding. Quotes before replies. Snip well. Write clearly. Don't Mail News.
 




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