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BFR early next year.



 
 
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  #11  
Old March 14th 18, 12:32 AM posted to sci.space.policy
Alain Fournier[_3_]
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Default BFR early next year.

On Mar/13/2018 at 6:09 PM, Niklas Holsti wrote :
On 18-03-13 23:01 , Alain Fournier wrote:
Â*Â* ...
I would be very surprised if BFS had anything close to SSTO capability.
It is a spaceship not a launch vehicle.


Musk has said the BFS can do SSTO. Quotes from Musk's answer at
https://www.teslarati.com/elon-musks...bfs-spaceship/,
section headed "DEVELOPMENT SCHEDULE":

--- start quote:

Q: ... Will we see BFS hops or smaller test vehicles similar to
Grasshopper/F9R-Dev? Facilities being built? Propellant plant testing?
etc. etc.

A (Elon): Will be starting with a full-scale Ship doing short hops of a
few hundred kilometers altitude and lateral distance. Those are fairly
easy on the vehicle, as no heat shield is needed, we can have a large
amount of reserve propellant and don’t need the high area ratio, deep
space Raptor engines.

Next step will be doing orbital velocity Ship flights, which will need
all of the above. Worth noting that BFS is capable of reaching orbit by
itself with low payload, but having the BF Booster increases payload by
more than an order of magnitude. Earth is the wrong planet for single
stage to orbit. No problemo on Mars.

--- end quote.


Thanks for that. The web page you cited is very interesting.


Alain Fournier
  #12  
Old March 14th 18, 12:39 AM posted to sci.space.policy
Fred J. McCall[_3_]
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Default BFR early next year.

JF Mezei wrote on Tue, 13 Mar 2018
17:01:25 -0400:

On 2018-03-13 05:53, Jeff Findley wrote:

BFS. It could be that the first BFS would be similar to Grasshopper or
Enterprise in that it won't have all the systems necessary for
supporting a crew in space. Automated testing only.


Thanks. Hadn't thought of that.

Does the ability to land on Earth absolutely imply the ability to take
off from Earth? (I know BFS is to be able to take off from Mars).


It can certainly take off from Earth. Remember, it's intended to be
able to do transcontinental flight without a booster. It's also
intended to be able to take off from Mars into TEI and then do the
insertion and land on Earth.


(I realise the prototype will be empty shell and much lighter so usable
for tests, just curious about whether the ability to take off from Earth
comes automatically with ability to land on Earth).


For some definition of 'take off' it does, but in this case BFR
Spaceship is capable of flying to orbit (if it has all its engines)
without a booster. I question the 'empty shell' assumption. Musk has
stated that it probably won't have the vacuum engines installed, since
they're not needed initially.


I know that spaceX has been pushing composite tank size limits by a huge
margin for the first stage. Is the 2nd stage/BFS also beyond current
"commodity" tech for tanks?


I'm guessing, but I would say yes. BFR Spaceship carries 1,000 tonnes
of fuel and oxidizer.



You can do a partial fill for short "hops". Does your car's gas tank
need to be full to make a trip to the grocery store?


Thinking in terms of keeping the methane liquid long enough in such a
large tank. Will the tanks be pressurized to maintain the methane
liquid, or will it be a "reduce the boiling rate and vent excess
pressure" on pad like for shuttle's ET?


There will presumably be some boil off, although that's more
manageable given the liquification point of propane as compared to
hydrogen. The bulk of the fuel in the tanks will still be liquid,
right up until you're out of fuel entirely.


Note: you car may not worry about fuel sloshing around in a small car
tank, but fuel trucks worry very much about it when the tanks are not
full, which is why they have separate tanks in the big one, and each of
those smaller tanks have baffles to reduce movement as truck
accelerates/brakes/turns.


The rocket is under acceleration. Fuel won't 'slosh' much, if at all.


--
"Some people get lost in thought because it's such unfamiliar
territory."
--G. Behn
  #13  
Old March 14th 18, 12:43 AM posted to sci.space.policy
Jeff Findley[_6_]
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Default BFR early next year.

In article ,
says...

On 2018-03-13 05:53, Jeff Findley wrote:

BFS. It could be that the first BFS would be similar to Grasshopper or
Enterprise in that it won't have all the systems necessary for
supporting a crew in space. Automated testing only.


Thanks. Hadn't thought of that.

Does the ability to land on Earth absolutely imply the ability to take
off from Earth? (I know BFS is to be able to take off from Mars).


It had better, otherwise what's the point? How else would you do these
short test flights like Grasshopper did.

(I realise the prototype will be empty shell and much lighter so usable
for tests, just curious about whether the ability to take off from Earth
comes automatically with ability to land on Earth).


Why would they do that? The only thing that was grossly wrong on
Grasshopper was the landing gear, which was over engineered so as not to
lose the test article on a relatively "hard" landing. Again, they'll
build it as close to the "real thing" as they can.

Note that is what NASA did with Enterprise. Enterprise was originally
going to be "refitted" to be space-worthy. But the cost was higher than
starting with the Structural Test Article, so that became Challenger.
Enterprise was not built to be a museum piece after the approach and
landing tests.

I know that spaceX has been pushing composite tank size limits by a huge
margin for the first stage. Is the 2nd stage/BFS also beyond current
"commodity" tech for tanks?


They built a full scale tank two years ago and pressure tested it:

http://www.businessinsider.com/space...nk-ocean-ship-
test-2016-11

Asking in a context of wondering how much new tech needs to be ready to
make first flight possible. (aka: how far ahead SpaceX is in developping
the new tech that makes the scaling to BFR possible).


Raptor is the "long pole in the tent", IMHO.

You can do a partial fill for short "hops". Does your car's gas

tank
need to be full to make a trip to the grocery store?


Thinking in terms of keeping the methane liquid long enough in such a
large tank. Will the tanks be pressurized to maintain the methane
liquid, or will it be a "reduce the boiling rate and vent excess
pressure" on pad like for shuttle's ET?


It will almost certainly be cryogenic just like the LOX in order to
maximize density and minimize tank mass.

Note: you car may not worry about fuel sloshing around in a small car
tank, but fuel trucks worry very much about it when the tanks are not
full, which is why they have separate tanks in the big one, and each of
those smaller tanks have baffles to reduce movement as truck
accelerates/brakes/turns.


BFR/BFS isn't a tanker truck, but sloshing is one of the potential
problems. That's why launcher tanks typically have anti-slosh baffles
in them.

Jeff
--
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These posts do not reflect the opinions of my family, friends,
employer, or any organization that I am a member of.
  #14  
Old March 14th 18, 12:52 AM posted to sci.space.policy
Fred J. McCall[_3_]
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Default BFR early next year.

Jeff Findley wrote on Tue, 13 Mar 2018
18:40:53 -0400:


The prototypes had better be close to BFR/BFS in many ways, or it
wouldn't be very useful would it?


It will probably fly without the vacuum engines or a heat shield, as
those aren't necessary for 'grasshopper' tests. However, Musk is
talking quickly moving to orbital testing, where both those things ARE
necessary.


--
"The reasonable man adapts himself to the world; the unreasonable
man persists in trying to adapt the world to himself. Therefore,
all progress depends on the unreasonable man."
--George Bernard Shaw
  #15  
Old March 14th 18, 01:26 AM posted to sci.space.policy
Alain Fournier[_3_]
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Posts: 548
Default BFR early next year.

On Mar/13/2018 at 5:01 PM, JF Mezei wrote :
Does the ability to land on Earth absolutely imply the ability to take
off from Earth? (I know BFS is to be able to take off from Mars).

(I realise the prototype will be empty shell and much lighter so usable
for tests, just curious about whether the ability to take off from Earth
comes automatically with ability to land on Earth).


Not really. You land with the tanks nearly empty. If you have only
enough thrust to land with nearly empty tanks, you won't have enough
thrust to take off with tanks full.


Alain Fournier
  #16  
Old March 14th 18, 08:22 AM posted to sci.space.policy
Niklas Holsti
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Posts: 168
Default BFR early next year.

On 18-03-14 00:36 , Jeff Findley wrote:
In article ,
lid says...

...
For small, Grasshopper-like hops, it would be enough to mount just one
of the two (or are there now more than two?) BFS sea-level engines.


Agreed. Two, from this pictu


On the other hand, at
https://www.teslarati.com/elon-musks...bfs-spaceship/,
Musk is quoted as follows (in the section headed "Raptor and rocket
propulsion"):

"If you just have two engines that do everything, the engine complexity
is much higher and, if one fails, you’ve lost half your power. Btw, we
modified the BFS design since IAC to add a third medium area ratio
Raptor engine partly for that reason (lose only 1/3 thrust in engine
out) and allow landings with higher payload mass for the Earth to Earth
transport function."

(Gosh, perhaps the "Earth to Earth transport function" is to be taken
seriously...)

--
Niklas Holsti
Tidorum Ltd
niklas holsti tidorum fi
. @ .
  #18  
Old March 14th 18, 11:24 AM posted to sci.space.policy
Jeff Findley[_6_]
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Posts: 2,307
Default BFR early next year.

In article ,
lid says...

On 18-03-14 00:36 , Jeff Findley wrote:
In article ,
lid says...
...
For small, Grasshopper-like hops, it would be enough to mount just one
of the two (or are there now more than two?) BFS sea-level engines.


Agreed. Two, from this pictu


On the other hand, at
https://www.teslarati.com/elon-musks...bfs-spaceship/,
Musk is quoted as follows (in the section headed "Raptor and rocket
propulsion"):

"If you just have two engines that do everything, the engine complexity
is much higher and, if one fails, you?ve lost half your power. Btw, we
modified the BFS design since IAC to add a third medium area ratio
Raptor engine partly for that reason (lose only 1/3 thrust in engine
out) and allow landings with higher payload mass for the Earth to Earth
transport function."

(Gosh, perhaps the "Earth to Earth transport function" is to be taken
seriously...)


This is all very fluid right now, isn't it?

Jeff
--
All opinions posted by me on Usenet News are mine, and mine alone.
These posts do not reflect the opinions of my family, friends,
employer, or any organization that I am a member of.
  #19  
Old March 14th 18, 11:28 AM posted to sci.space.policy
Jeff Findley[_6_]
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Posts: 2,307
Default BFR early next year.

In article ,
says...

On 2018-03-13 18:40, Jeff Findley wrote:

They built a full scale composite tank and pressure tested it to
destruction a couple years ago.
http://www.businessinsider.com/space...nk-ocean-ship-
test-2016-11


But correct to state that the destructive test was only a few months
ago? I seem to recal some tank video that was much more recent than 2016.

The prototypes had better be close to BFR/BFS in many ways, or it
wouldn't be very useful would it?



Depends on the goal of that test flight. It could very well be that a
real BFS ship is ready to be built with the structural aspects all done,
but will go without payload (the crew compartment)

On the other hand, there maty be PR/marketing pressres to have a flight
early, at which point engineers are told to focus on engines/tanks and
just build a epty shell around iot that looks like BFS. (the real
structsures/shell can be designed/built later).

Or, we could see naked engines/tanks go up and down. It really depends
on how far they are in the design.


The article was dated November 16, 2016 and said:

SpaceX announced on Wednesday that it had successfully completed
a critical test of a huge piece of its Mars spaceship ? a giant
and potentially explosive black orb.

Also, the Twitter video of them loading the tank on the barge is dated
16 months ago. That is consistent with the news article being put out
in November 2016.

So, it was only 16 months ago, not two years. Still, the tank was built
and was tested. That "retired" much of the risk of using such large
composite tanks. At least their shape is simple compared to the failed
X-33 tanks (which was a geometrically complex multi-lobed design).

Jeff
--
All opinions posted by me on Usenet News are mine, and mine alone.
These posts do not reflect the opinions of my family, friends,
employer, or any organization that I am a member of.
  #20  
Old March 14th 18, 08:02 PM posted to sci.space.policy
Fred J. McCall[_3_]
external usenet poster
 
Posts: 10,018
Default BFR early next year.

Niklas Holsti wrote on Wed, 14 Mar
2018 09:22:15 +0200:

On 18-03-14 00:36 , Jeff Findley wrote:
In article ,
lid says...

...
For small, Grasshopper-like hops, it would be enough to mount just one
of the two (or are there now more than two?) BFS sea-level engines.


Agreed. Two, from this pictu


On the other hand, at
https://www.teslarati.com/elon-musks...bfs-spaceship/,
Musk is quoted as follows (in the section headed "Raptor and rocket
propulsion"):

"If you just have two engines that do everything, the engine complexity
is much higher and, if one fails, you’ve lost half your power. Btw, we
modified the BFS design since IAC to add a third medium area ratio
Raptor engine partly for that reason (lose only 1/3 thrust in engine
out) and allow landings with higher payload mass for the Earth to Earth
transport function."

(Gosh, perhaps the "Earth to Earth transport function" is to be taken
seriously...)


Yeah, I thought all the later drawings and such that I'd seen showed 3
atmospheric engines vice 2. I believe it can still land on a single
engine, though.


--
"The reasonable man adapts himself to the world; the unreasonable
man persists in trying to adapt the world to himself. Therefore,
all progress depends on the unreasonable man."
--George Bernard Shaw
 




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