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  #11  
Old December 24th 17, 02:57 PM posted to sci.space.policy
Alain Fournier[_3_]
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Posts: 548
Default Lunar Lander

On Dec/23/2017 Ã* 7:20 PM, JF Mezei wrote :
On 2017-12-22 18:26, Fred J. McCall wrote:


You'd have to design a new upper stage that allowed refueling plus a
tanker stage to refuel it from. If you could refuel it, the existing
RP1/LOX upper stage might even have the capability for lunar work. But
we're talking hardware that would be, as yet, only a gleam in
someone's eye, unlike SLS.


What about the possibility of sending a the parts separately, but
already fueled such that refueling is not necessary?

Launch 3rd stage, service module, lander and capsule as separate launchs
(perhaps combining capsule with lander), assemble pre-fueled components
in orbit then go to the moon.

You could also potentially combine 3rd stage with service module to
reduce the weight of extra engine and use service module (with bigger
tanks) for TLI.

I think BFR Spaceship might be too heavy for other boosters, but you
could just use it with BFR. BFR Spaceship refueled in orbit is the
whole works. It can fly to the Moon, land, take off, and return to
Earth.


Reality check question: Apollo managed to get a capsule that fell from
the Moon to re-enter earth. NASA got Shuttle to re-enter earth from as
high as Hubble orbit. Space-X has gotten Stage-1 to re-enter from
suborbital speed/altitude. (same with Virgin Galactic).

Considering BFR will be a long fat stick instead of capsule or "space
plane", how does it expect to re-enter at high speeds and remain
structurally sound?


Being big helps for re-entry or aero-capture. If you're big and fluffy
you can spread the heat load and air pressure over a larger area. That
isn't to say that re-entry of BFR will be easy. It isn't easy for a
capsule, it isn't easy for a space plane and it won't be easy for BFR.

Is this a question of using engines to slow down such that re-entery
interface is done engine first like Falcon 9 stage-1 and engines firing
long enough to slow it down to sub orbital speeds before hitting
atmosphere?


No, heat shields are more efficient than engines for slowing down.

Would coming back from Mars create far higher speeds than coming back
from the Moon, or would "catching up to Earth" result in slower speeds?


You will have higher speeds coming back from Mars.


Alain Fournier
  #12  
Old December 24th 17, 10:57 PM posted to sci.space.policy
Fred J. McCall[_3_]
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Posts: 10,018
Default Lunar Lander

JF Mezei wrote:

On 2017-12-22 18:26, Fred J. McCall wrote:

You'd have to design a new upper stage that allowed refueling plus a
tanker stage to refuel it from. If you could refuel it, the existing
RP1/LOX upper stage might even have the capability for lunar work. But
we're talking hardware that would be, as yet, only a gleam in
someone's eye, unlike SLS.


What about the possibility of sending a the parts separately, but
already fueled such that refueling is not necessary?


Not enough grunt.


Launch 3rd stage, service module, lander and capsule as separate launchs
(perhaps combining capsule with lander), assemble pre-fueled components
in orbit then go to the moon.


You're talking an entire new stage, then. That's certainly an
alternative to refueling a stage.


You could also potentially combine 3rd stage with service module to
reduce the weight of extra engine and use service module (with bigger
tanks) for TLI.


So now you need a bigger Service Module engine, as well, and you're
taking a bunch of excess dry mass into lunar orbit.



I think BFR Spaceship might be too heavy for other boosters, but you
could just use it with BFR. BFR Spaceship refueled in orbit is the
whole works. It can fly to the Moon, land, take off, and return to
Earth.


Reality check question: Apollo managed to get a capsule that fell from
the Moon to re-enter earth. NASA got Shuttle to re-enter earth from as
high as Hubble orbit. Space-X has gotten Stage-1 to re-enter from
suborbital speed/altitude. (same with Virgin Galactic).

Considering BFR will be a long fat stick instead of capsule or "space
plane", how does it expect to re-enter at high speeds and remain
structurally sound?


The same way anything else does.


Is this a question of using engines to slow down such that re-entery
interface is done engine first like Falcon 9 stage-1 and engines firing
long enough to slow it down to sub orbital speeds before hitting
atmosphere?


BFR Spaceship is intended to come in nose-first. They even added some
little delta fins to give it better stability.


Would coming back from Mars create far higher speeds than coming back
from the Moon, or would "catching up to Earth" result in slower speeds?


You can still kill most of the velocity with aerobraking. BFR
Spaceship has a low enough density on return that a normal PICA-X heat
shield on the underside is sufficient. Shuttle needed the special
tiles because it was large, dense, and flying using wings and lifting
body shape (all of which add drag and increase heat loads when
reentering).


--
"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
  #13  
Old December 26th 17, 01:34 PM posted to sci.space.policy
Alain Fournier[_3_]
external usenet poster
 
Posts: 548
Default Lunar Lander

On Dec/24/2017 at 4:57 PM, Fred J. McCall wrote :
[snip]
You can still kill most of the velocity with aerobraking. BFR
Spaceship has a low enough density on return that a normal PICA-X heat
shield on the underside is sufficient. Shuttle needed the special
tiles because it was large, dense, and flying using wings and lifting
body shape (all of which add drag and increase heat loads when
reentering).


Being large and dense is the big culprit for the high heat loads
of the Shuttle. Not the added drag due to the body shape. In fact
you want to have lots of drag in a re-entry vehicle, for two reasons.
First and most importantly, if the re-entry vehicle has a blunt shape,
air doesn't flow away as much as with an aerodynamic shape. So in
effect, you have an air cushion around the vehicle and the heated shock
layer (where you have the most heat) is away from the vehicle. Second,
if you have a blunt shape, you will decelerate more during the earlier
phase of re-entry and your speed will be lower when you reach thicker
layers of the atmosphere.


Alain Fournier
  #14  
Old December 26th 17, 07:18 PM posted to sci.space.policy
Fred J. McCall[_3_]
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Posts: 10,018
Default Lunar Lander

Alain Fournier wrote:

On Dec/24/2017 at 4:57 PM, Fred J. McCall wrote :
[snip]
You can still kill most of the velocity with aerobraking. BFR
Spaceship has a low enough density on return that a normal PICA-X heat
shield on the underside is sufficient. Shuttle needed the special
tiles because it was large, dense, and flying using wings and lifting
body shape (all of which add drag and increase heat loads when
reentering).


Being large and dense is the big culprit for the high heat loads
of the Shuttle. Not the added drag due to the body shape. In fact
you want to have lots of drag in a re-entry vehicle, for two reasons.
First and most importantly, if the re-entry vehicle has a blunt shape,
air doesn't flow away as much as with an aerodynamic shape. So in
effect, you have an air cushion around the vehicle and the heated shock
layer (where you have the most heat) is away from the vehicle. Second,
if you have a blunt shape, you will decelerate more during the earlier
phase of re-entry and your speed will be lower when you reach thicker
layers of the atmosphere.


Drag generates lift. Since we don't live in a perfect universe, part
of the drag does not generate lift but generates waste heat. The
'draggier' you are the more lift (and heat) you will generate. If the
Shuttle didn't try to fly heat loads would be smaller. It's why wing
leading edges needed special insulators.


--
"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 December 26th 17, 07:52 PM posted to sci.space.policy
Alain Fournier[_3_]
external usenet poster
 
Posts: 548
Default Lunar Lander

On Dec/26/2017 at 1:18 PM, Fred J. McCall wrote :
Alain Fournier wrote:

On Dec/24/2017 at 4:57 PM, Fred J. McCall wrote :
[snip]
You can still kill most of the velocity with aerobraking. BFR
Spaceship has a low enough density on return that a normal PICA-X heat
shield on the underside is sufficient. Shuttle needed the special
tiles because it was large, dense, and flying using wings and lifting
body shape (all of which add drag and increase heat loads when
reentering).


Being large and dense is the big culprit for the high heat loads
of the Shuttle. Not the added drag due to the body shape. In fact
you want to have lots of drag in a re-entry vehicle, for two reasons.
First and most importantly, if the re-entry vehicle has a blunt shape,
air doesn't flow away as much as with an aerodynamic shape. So in
effect, you have an air cushion around the vehicle and the heated shock
layer (where you have the most heat) is away from the vehicle. Second,
if you have a blunt shape, you will decelerate more during the earlier
phase of re-entry and your speed will be lower when you reach thicker
layers of the atmosphere.


Drag generates lift. Since we don't live in a perfect universe, part
of the drag does not generate lift but generates waste heat. The
'draggier' you are the more lift (and heat) you will generate. If the
Shuttle didn't try to fly heat loads would be smaller. It's why wing
leading edges needed special insulators.


No. Go see https://en.wikipedia.org/wiki/Atmospheric_entry, read the
"Blunt body entry vehicles" section. The most relevant sentence is:
"In the United States, H. Julian Allen and A. J. Eggers, Jr. of the
National Advisory Committee for Aeronautics (NACA) made the
counterintuitive discovery in 1951[6] that a blunt shape (high drag)
made the most effective heat shield."

The draggier you are the less you need special insulators.


Alain Fournier
  #16  
Old December 27th 17, 12:33 AM posted to sci.space.policy
Fred J. McCall[_3_]
external usenet poster
 
Posts: 10,018
Default Lunar Lander

Alain Fournier wrote:

On Dec/26/2017 at 1:18 PM, Fred J. McCall wrote :
Alain Fournier wrote:

On Dec/24/2017 at 4:57 PM, Fred J. McCall wrote :
[snip]
You can still kill most of the velocity with aerobraking. BFR
Spaceship has a low enough density on return that a normal PICA-X heat
shield on the underside is sufficient. Shuttle needed the special
tiles because it was large, dense, and flying using wings and lifting
body shape (all of which add drag and increase heat loads when
reentering).

Being large and dense is the big culprit for the high heat loads
of the Shuttle. Not the added drag due to the body shape. In fact
you want to have lots of drag in a re-entry vehicle, for two reasons.
First and most importantly, if the re-entry vehicle has a blunt shape,
air doesn't flow away as much as with an aerodynamic shape. So in
effect, you have an air cushion around the vehicle and the heated shock
layer (where you have the most heat) is away from the vehicle. Second,
if you have a blunt shape, you will decelerate more during the earlier
phase of re-entry and your speed will be lower when you reach thicker
layers of the atmosphere.


Drag generates lift. Since we don't live in a perfect universe, part
of the drag does not generate lift but generates waste heat. The
'draggier' you are the more lift (and heat) you will generate. If the
Shuttle didn't try to fly heat loads would be smaller. It's why wing
leading edges needed special insulators.


No. Go see https://en.wikipedia.org/wiki/Atmospheric_entry, read the
"Blunt body entry vehicles" section. The most relevant sentence is:
"In the United States, H. Julian Allen and A. J. Eggers, Jr. of the
National Advisory Committee for Aeronautics (NACA) made the
counterintuitive discovery in 1951[6] that a blunt shape (high drag)
made the most effective heat shield."

The draggier you are the less you need special insulators.


True when you're talking about blunt objects, but only because they
create a compressed shockwave away from the vehicle that winds up
taking the heat load.


--
"Insisting on perfect safety is for people who don't have the balls to
live in the real world."
-- Mary Shafer, NASA Dryden
 




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