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U.S. astronauts are climbing back into space capsules. Here's howthey've improved over the past 50 years



 
 
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  #21  
Old September 25th 17, 12:19 AM posted to sci.space.policy
Fred J. McCall[_3_]
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Default U.S. astronauts are climbing back into space capsules. Here's how they've improved over the past 50 years

Jeff Findley wrote:

In article ,
says...

JF Mezei wrote:

On 2017-09-23 13:33, Fred J. McCall wrote:

down. I think it's funny that NASA lets astronauts ride on Soyuz,
which relies on power at landing on dirt for them to survive, yet is
being obstructionist to safety certify Dragon V2 for fully powered
landings on dirt.


A rare instance where I agree with you.

But being devil's advocate: At the time NASA started to purchase seats
on Soyuz, it had already proven itself and it ability to land. Also,
they had no choice since Soyuz was also the escape pod in case of emergency.

And during post Columbia stand down and after permanent shutdown of
Shuttle, NASA had no choice either.


True, but doesn't address the issue. Why not let SpaceX prove powered
landing?


Higher (perceived) risk for returning payloads.


But most don't return payloads. Why obstruct those?


--
"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
  #22  
Old September 25th 17, 12:22 AM posted to sci.space.policy
Fred J. McCall[_3_]
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Default U.S. astronauts are climbing back into space capsules. Here's how they've improved over the past 50 years

JF Mezei wrote:

On 2017-09-24 08:43, Jeff Findley wrote:

itself during descent, even when the Super Dracos aren't firing. This
is quite similar to Falcon 9 first stage landings where the Merlin
engines only fire briefly for boost back, reentry, and landing.


And how many stage 1s were lost before SpaceX got it right?


Irrelevant. The problem with Falcon core is the engines aren't deeply
throttleable. Dragon V2 with Super Draco doesn't have that problem.


In terms of landing accuracy, can landing from a full orbit altitude be
as accurate as landing after a 3 minute flight where speed during
re-entry is much lower so minute deviations in angles etc have far
lesser impact?


Of course it can. Dragon isn't just a rock coming back.


--
"Some people get lost in thought because it's such unfamiliar
territory."
--G. Behn
  #23  
Old September 25th 17, 12:27 AM posted to sci.space.policy
Fred J. McCall[_3_]
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Posts: 10,018
Default U.S. astronauts are climbing back into space capsules. Here's how they've improved over the past 50 years

JF Mezei wrote:

On 2017-09-24 16:34, Jeff Findley wrote:

From above article:

"The reason we decided not to pursue (powered landings) heavily
is it would have taken a tremendous amount of effort to qualify
that for safety, particularly for crew transport," Musk said.


Ok, so was Dragon gonna do powered re-entry like Stage 1, or be like
Soyuz with lifting re-entry, parachutes and powered "cushion" very near
ground?


More like the former.


I was told it was to be a powered one like stage I, where fuel available
becomes critical. (and validating software a bigger challenge).


No. The only reason there were 'issues' with the Falcon Core is that
the engines can't be deeply throttled. That's not the case with
Dragon V2.


was a management/engineering trade-off and appears to be SpaceX's call,
not NASA's.


Suspect origimally NASA, then SpaceX realised water landings not as bad
as thought.


Why is it so hard to safety certify? Because NASA doesn't want to
certify it.



Yes. Dragon flies a lifting reentry and therefore has some cross-range
capability. This was also true of both Gemini and Apollo (and Russian
Soyuz and Chinese Shenzhou).


Does "cross range" refer to only left/right, or also forward/backward?
(aka, a narrow elipse or a full circle as possible landing locations?


Capsule is round. Why would it be limited to only 'left/right'
control?


--
"Some people get lost in thought because it's such unfamiliar
territory."
--G. Behn
  #24  
Old September 25th 17, 08:53 AM posted to sci.space.policy
Fred J. McCall[_3_]
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Posts: 10,018
Default U.S. astronauts are climbing back into space capsules. Here's how they've improved over the past 50 years

JF Mezei wrote:

On 2017-09-24 19:27, Fred J. McCall wrote:

No. The only reason there were 'issues' with the Falcon Core is that
the engines can't be deeply throttled. That's not the case with
Dragon V2.


Whatever the reason, it took a number of attempts before they fine tuned
the software to make it work. And one should expect Dragon to have
similar failures at first.


And why is that?


Why is it so hard to safety certify? Because NASA doesn't want to
certify it.


Not hard, But it would take a few flights to prove it, diuring which you
can't return anything, at a time NASA was craving to return stuff.


Of course you can. Nothing requires ALL reentries to use propulsive
landing.


This is why I suggested SpaceX should have insisted the text flight land
on land to do that testing/certification/debugging.


That's a bad plan, because you've just done the very thing you said
was bad and prohibited returning anything until propulsive landing is
safety certified.


Considering it is likely they could do much of the testing/debiugging by
dropping it from 30,000 feet or lower, they could have done this at
faster rate than the space flight rate.


Nope. Things that are different aren't the same.



Capsule is round. Why would it be limited to only 'left/right'
control?


When you have 0 left/right speed, it is easy to use a bit of
aerodynamics at right time to creare left/right cross range.


Poppycock! You have to 'bend' your velocity vector and bending it one
way is just as difficult as bending it some other way.


But when you're coming in at 25,000km/h in forward speed, I would think
that any miscalculation could get capsule to land very far before or
after landing point.


You shouldn't think. It doesn't appear to be one of your core
competencies. The velocity vector isn't 'forward'; it's at a slant
downward. Hence 'reentry'. But it doesn't matter. To change the
landing point you need to 'bend' the velocity vector by applying lift.
Bending it left or right is no harder (or easier) than bending it up
or down. It's just a matter of how much 'lift' you apply and in which
direction.

[Actually you have slightly less authority 'up' and slightly more
authority 'down' because of this stuff called gravity, so landing
'shorter' is a little easier than landing 'longer', but it's not THAT
much harder.]


--
"Some people get lost in thought because it's such unfamiliar
territory."
--G. Behn
  #25  
Old September 25th 17, 11:06 AM posted to sci.space.policy
Jeff Findley[_6_]
external usenet poster
 
Posts: 2,307
Default U.S. astronauts are climbing back into space capsules. Here's how they've improved over the past 50 years

In article . com,
says...

On 2017-09-24 16:34, Jeff Findley wrote:

From above article:

"The reason we decided not to pursue (powered landings) heavily
is it would have taken a tremendous amount of effort to qualify
that for safety, particularly for crew transport," Musk said.


Ok, so was Dragon gonna do powered re-entry like Stage 1, or be like
Soyuz with lifting re-entry, parachutes and powered "cushion" very near
ground?


No. Parachutes would not have been used for a nominal powered landing.
Parachutes would have been necessary in case of an abort because the
abort burn would have used too much fuel to allow for a powered landing.

I was told it was to be a powered one like stage I, where fuel available
becomes critical. (and validating software a bigger challenge).


It's critical in the sense that you have to budget enough for landing,
but the terminal velocity of the capsule limits the amount of fuel
needed for landing, so it's not hard to make sure you have enough.

So, since it's not as important to Mars as SpaceX once thought it was,


I smell excuse here.


Funny, I saw a clear engineering/management trade-off.

The Mars plans were announced years after Dragon was designed. I suspect
this is more about SpaceX realising that the refurb costs for salt water
landings aren't as high as thought, so it is more economical to land in
water than to spend the extra money to develop/test land landings.

I suspect Mars landing will be different enough to not be applicable to
Earth landings.


We'll see what has changed with the next update from SpaceX on its Mars
plans. It could be that a (relatively simple) powered vertical landing
has been abandoned in favor of something else a tad more complicated.

was a management/engineering trade-off and appears to be SpaceX's
call, not NASA's.


Suspect origimally NASA, then SpaceX realised water landings not as bad
as thought.


Possible.

Yes. Dragon flies a lifting reentry and therefore has some cross-

range
capability. This was also true of both Gemini and Apollo (and Russian
Soyuz and Chinese Shenzhou).


Does "cross range" refer to only left/right, or also forward/backward?
(aka, a narrow elipse or a full circle as possible landing locations?


Roughly speaking, by rotating the capsule, you can direct the lift
vector anywhere along the circle that's normal to the velocity vector.
So in your terms, yes you can direct the lift vector left/right and/or
forward/backward.

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.
  #26  
Old September 25th 17, 11:11 AM posted to sci.space.policy
Jeff Findley[_6_]
external usenet poster
 
Posts: 2,307
Default U.S. astronauts are climbing back into space capsules. Here's how they've improved over the past 50 years

In article ,
says...

Jeff Findley wrote:

In article ,
says...

Anthony Frost wrote:

In message
Jeff Findley wrote:

This has changed somewhat recently. Reportedly SpaceX is the one who
shelved development of Dragon V2 vertical landing. The reasons for this
aren't terribly clear, but there are hints from SpaceX that this is
because they've decided to change the (Mars) landing mode of their
(eventual) Mars vehicle.

Also apparently NASA weren't happy about cargo flights being used for
testing powered landings.


Why would they care? They get their cargo on the way up, not the way
down.


Because Dragon is the only way that NASA can get things like EMUs back
to earth for refurbishment. There have been articles on how few
functioning EMUs are left. Sorry for the word-wrap on the cites:


But most flights aren't carrying those (or anything else) back down.
So why is NASA apparently being obstructionist about landing the
'empties' propulsively?


I suspect that it's mostly the pointy haired bosses at NASA being
"cautious", not the engineers raising concerns. They've had it hammered
into their heads that "Failure is not an option", even though that's not
at all what was meant by that phrase during Apollo 13.

Like you said, if they lost a capsule or two (as long as it didn't carry
something critical to be refurbished like an EMU), it's not like it
would impact ISS safety in any way.


I think it's funny that NASA lets astronauts ride on Soyuz,
which relies on power at landing on dirt for them to survive, yet is
being obstructionist to safety certify Dragon V2 for fully powered
landings on dirt.


That's the rumor. Another rumor says Dragon V2 propulsive landings are
being dropped because SpaceX is going to be changing its landing mode
for Mars missions. I'm not sure how much stock I put in that, but we'll
just have to wait and see. SpaceX isn't afraid to change directions
when something isn't working out or when another more promising approach
surfaces.


Well, they could get smaller by removing the outer ring of engines.
That would reduce thrust to 1/4 of the original concept, which is
about four times what a Falcon Heavy delivers. But is that big enough
to support a real Mars colony?


Good question. A better question might be does a BFR that's only good
for Mars make economic sense when NASA is setting its sights on lunar
orbit and might very well buy launches since SLS is going to have an
abysmally low flight rate (at most twice per year).

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.
  #27  
Old September 25th 17, 11:14 AM posted to sci.space.policy
Jeff Findley[_6_]
external usenet poster
 
Posts: 2,307
Default U.S. astronauts are climbing back into space capsules. Here's how they've improved over the past 50 years

In article ,
says...

Jeff Findley wrote:

In article ,
says...

JF Mezei wrote:

On 2017-09-23 13:33, Fred J. McCall wrote:

down. I think it's funny that NASA lets astronauts ride on Soyuz,
which relies on power at landing on dirt for them to survive, yet is
being obstructionist to safety certify Dragon V2 for fully powered
landings on dirt.


A rare instance where I agree with you.

But being devil's advocate: At the time NASA started to purchase seats
on Soyuz, it had already proven itself and it ability to land. Also,
they had no choice since Soyuz was also the escape pod in case of emergency.

And during post Columbia stand down and after permanent shutdown of
Shuttle, NASA had no choice either.


True, but doesn't address the issue. Why not let SpaceX prove powered
landing?


Higher (perceived) risk for returning payloads.


But most don't return payloads. Why obstruct those?


Dragon is the only cargo vessel (US or otherwise) which returns to earth
from ISS. Because of this, it's a single point of failure for anything
which must be returned, which includes EMUs in need of refurbishing.
Unfortunately, return was a given when the shuttle was flying, so there
are quite a few things which were designed to be returned. Mostly
experimental results, but some hardware as well (which in some cases is
critical for failure analysis).

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.
  #28  
Old September 26th 17, 12:15 AM posted to sci.space.policy
Fred J. McCall[_3_]
external usenet poster
 
Posts: 10,018
Default U.S. astronauts are climbing back into space capsules. Here's how they've improved over the past 50 years

Jeff Findley wrote:

In article . com,
says...

On 2017-09-24 16:34, Jeff Findley wrote:

From above article:

"The reason we decided not to pursue (powered landings) heavily
is it would have taken a tremendous amount of effort to qualify
that for safety, particularly for crew transport," Musk said.


Ok, so was Dragon gonna do powered re-entry like Stage 1, or be like
Soyuz with lifting re-entry, parachutes and powered "cushion" very near
ground?


No. Parachutes would not have been used for a nominal powered landing.
Parachutes would have been necessary in case of an abort because the
abort burn would have used too much fuel to allow for a powered landing.

I was told it was to be a powered one like stage I, where fuel available
becomes critical. (and validating software a bigger challenge).


It's critical in the sense that you have to budget enough for landing,
but the terminal velocity of the capsule limits the amount of fuel
needed for landing, so it's not hard to make sure you have enough.


Since Dragon V2 has internal fuel tanks and that fuel is pretty much
used only for the Super Draco engines (I think they use cold gas for
OMS now), you come down with virtually full tanks.

So, since it's not as important to Mars as SpaceX once thought it was,


I smell excuse here.


Funny, I saw a clear engineering/management trade-off.


That's because you know something about engineering and management and
Mayfly knows something about taking the trash out for Mom and the
living conditions in her basement.

The Mars plans were announced years after Dragon was designed. I suspect
this is more about SpaceX realising that the refurb costs for salt water
landings aren't as high as thought, so it is more economical to land in
water than to spend the extra money to develop/test land landings.

I suspect Mars landing will be different enough to not be applicable to
Earth landings.


We'll see what has changed with the next update from SpaceX on its Mars
plans. It could be that a (relatively simple) powered vertical landing
has been abandoned in favor of something else a tad more complicated.


I think they may have tripped over the same issue landing anything of
size on Mars has. The air is to thin for aerobraking adequately and
the gravity is too heavy for a pure propulsive landing.

was a management/engineering trade-off and appears to be SpaceX's
call, not NASA's.


Suspect origimally NASA, then SpaceX realised water landings not as bad
as thought.


Possible.


But there is the cost of the capsule recovery force.

Yes. Dragon flies a lifting reentry and therefore has some cross-

range
capability. This was also true of both Gemini and Apollo (and Russian
Soyuz and Chinese Shenzhou).


Does "cross range" refer to only left/right, or also forward/backward?
(aka, a narrow elipse or a full circle as possible landing locations?


Roughly speaking, by rotating the capsule, you can direct the lift
vector anywhere along the circle that's normal to the velocity vector.
So in your terms, yes you can direct the lift vector left/right and/or
forward/backward.


Yep.


--
"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
  #29  
Old September 26th 17, 04:19 AM posted to sci.space.policy
Greg \(Strider\) Moore
external usenet poster
 
Posts: 752
Default U.S. astronauts are climbing back into space capsules. Here's how they've improved over the past 50 years

"Jeff Findley" wrote in message
...

In article ,
says...

Jeff Findley wrote:

In article ,
says...

Anthony Frost wrote:

In message
Jeff Findley wrote:

This has changed somewhat recently. Reportedly SpaceX is the one
who
shelved development of Dragon V2 vertical landing. The reasons
for this
aren't terribly clear, but there are hints from SpaceX that this
is
because they've decided to change the (Mars) landing mode of their
(eventual) Mars vehicle.

Also apparently NASA weren't happy about cargo flights being used for
testing powered landings.


Why would they care? They get their cargo on the way up, not the way
down.


Because Dragon is the only way that NASA can get things like EMUs back
to earth for refurbishment. There have been articles on how few
functioning EMUs are left. Sorry for the word-wrap on the cites:


But most flights aren't carrying those (or anything else) back down.
So why is NASA apparently being obstructionist about landing the
'empties' propulsively?


I suspect that it's mostly the pointy haired bosses at NASA being
"cautious", not the engineers raising concerns. They've had it hammered
into their heads that "Failure is not an option", even though that's not
at all what was meant by that phrase during Apollo 13.

Like you said, if they lost a capsule or two (as long as it didn't carry
something critical to be refurbished like an EMU), it's not like it
would impact ISS safety in any way.

I'm going to say even then it doesn't matter.

Consider that they haven't been able to count on cargo return since Shuttle.
So, in a sense, bringing back a failed EMU and having it crash is really no
worse than not bringing it back in the first place.



Jeff


--
Greg D. Moore http://greenmountainsoftware.wordpress.com/
CEO QuiCR: Quick, Crowdsourced Responses. http://www.quicr.net
IT Disaster Response -
https://www.amazon.com/Disaster-Resp...dp/1484221834/

 




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