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#1101 2021-05-02 11:33:36

RobertDyck
Moderator
From: Winnipeg, Canada
Registered: 2002-08-20
Posts: 6,484
Website

Re: Starship is Go...

GW Johnson,

Yea, that's why I was never comfortable with SpaceX initial plans to land Crew Dragon propulsively. It would have been better to use the parachute, then land propulsively. What's terminal velocity for a parachute on Earth? Quick Google... this says "5–6 meters per second (roughly 20 km/h or 12 mph)". Propulsive landing from that should be easy. After all, Soyuz capsules have done it for how many years? Soyuz capsules do not have landing legs, instead seats inside of shock absorbers. One Canadian astronaut reported landing in a Soyuz felt like a car crash. Landing legs with shock absorbers would be far preferable. If you want the vehicle to steer toward a landing pad, you could use a parafoil.

Propulsive landing for Falcon 9 core boosters is fine. That's just a rocket stage, if it fails there's no loss of life, and no high value payload. And Falcon 9 uses landing legs with a wide stance. that's minimum for stability. I assume the composite legs positioned at an angle provide some flex, so act as the shock absorber.

Starship is too big for a parachute. I would really like this to work. Elon promised Starship would bring total cost down to $2 million per flight. Not $2 million per unit mass, but per launch. Of course that's cost to SpaceX; expect price to customer to be higher. Still, that would be a dramatic game changer! Even if they never achieve human flight reliability, just as a cargo launch vehicle that would be amazing! As I posted elsewhere, Starship could launch a spacecraft for Mars, then crew could rendezvous with a Dragon capsule. The capsule could stay attached as an emergency escape pod when returning to Earth. If SpaceX does get Starship to work, with reliability sufficient for Earth-to-Earth passengers? I would be pleased.

Starship is not what I would have designed for a large passenger rocket. I would have designed something like VentureStar. Remember, NASA 1968 plans for a Shuttle were fully reusable Two-Stage-To-Orbit. Bids from contractors were Shuttle LS A based on X-24 lifting body shape, and Shuttle MDC based on HL-10.
sts70lc.jpg stslbmd7.jpg

Still, I hope they get Starship to work. It is the best design for a Mars shuttle: surface to Mars orbit and back. And for Earth, it would be a game changer.

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#1102 2021-05-02 13:21:35

louis
Member
From: UK
Registered: 2008-03-24
Posts: 6,300

Re: Starship is Go...

At $20 per kg it's a hell of a game changer! Even if they add on a $10 mark-up, it's still only $30 per kg. Seeing the speed they are building these things at, the built-in reusability and the fact they are made of cheap steel and use cheap methane for fuel, then I can believe the $2 million flight price.


RobertDyck wrote:

Starship is too big for a parachute. I would really like this to work. Elon promised Starship would bring total cost down to $2 million per flight. Not $2 million per unit mass, but per launch. Of course that's cost to SpaceX; expect price to customer to be higher. Still, that would be a dramatic game changer! Even if they never achieve human flight reliability, just as a cargo launch vehicle that would be amazing! As I posted elsewhere, Starship could launch a spacecraft for Mars, then crew could rendezvous with a Dragon capsule. The capsule could stay attached as an emergency escape pod when returning to Earth. If SpaceX does get Starship to work, with reliability sufficient for Earth-to-Earth passengers? I would be pleased.


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#1103 2021-05-02 14:58:22

SpaceNut
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From: New Hampshire
Registered: 2004-07-22
Posts: 21,841

Re: Starship is Go...

Shuttle landings already proved that dead mass in the 100mt are possible with the heat shield opening to make the landing gear come out just fine so that makes any fuel on the starship just a means to get accross to another airport....that means also a higher payload to orbit since the mass of fuel is not needed to vertically land.

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#1104 2021-05-04 07:00:48

louis
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From: UK
Registered: 2008-03-24
Posts: 6,300

Re: Starship is Go...

Launch scheduled for today (4 May) , it seems.

https://www.youtube.com/watch?v=diEdOGhC8p0


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#1105 2021-05-04 14:09:58

louis
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From: UK
Registered: 2008-03-24
Posts: 6,300

Re: Starship is Go...

Seems the plans for a test flight of SN15 today were scrubbed. Mention was made of fog earlier - might have been a factor after the last fogbound mishap.


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#1106 2021-05-04 14:20:00

louis
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From: UK
Registered: 2008-03-24
Posts: 6,300

Re: Starship is Go...

Apparently the problem was a potential steering issue with the rear fin.


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#1107 2021-05-05 09:04:48

louis
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From: UK
Registered: 2008-03-24
Posts: 6,300

Re: Starship is Go...

Seems like the flight is back on...

https://www.youtube.com/watch?v=NPNvB5ComFw

There was a discussion about landing legs.

Seems like Musk is determined to bring in legless landings for Earth (ie use a rocket capture system), to save on mass. Of course legs still required for first landings on Mars.


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#1108 2021-05-05 11:15:12

louis
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From: UK
Registered: 2008-03-24
Posts: 6,300

Re: Starship is Go...

WAI say it's about 2.5 hours to launch.


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#1109 2021-05-05 13:51:17

louis
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From: UK
Registered: 2008-03-24
Posts: 6,300

Re: Starship is Go...

Launch has not been cancelled so far but not looking great.  The weather is an issue for sure - quite high winds. Who does Space X's weather forecasting? They aren't very good!

Last edited by louis (2021-05-05 18:32:03)


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#1110 2021-05-05 16:51:02

louis
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From: UK
Registered: 2008-03-24
Posts: 6,300

Re: Starship is Go...

They did it!


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#1111 2021-05-05 16:53:14

louis
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From: UK
Registered: 2008-03-24
Posts: 6,300

Re: Starship is Go...

All legs extended...but fire.


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#1112 2021-05-05 16:55:07

louis
Member
From: UK
Registered: 2008-03-24
Posts: 6,300

Re: Starship is Go...

Those water cannon look pathetic! Can't they do better?  Get some robots in there with fire hoses.


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#1113 2021-05-05 17:00:21

louis
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From: UK
Registered: 2008-03-24
Posts: 6,300

Re: Starship is Go...

Stumpy legs worked!


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#1114 2021-05-05 17:02:25

louis
Member
From: UK
Registered: 2008-03-24
Posts: 6,300

Re: Starship is Go...

Incredible achievement to soft land SN15 like that.


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#1115 2021-05-05 17:04:44

louis
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From: UK
Registered: 2008-03-24
Posts: 6,300

Re: Starship is Go...

Any views on the fire? Where's it coming from...and how come the whole thing doesn't blow up if it's that bad.


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#1116 2021-05-05 17:08:32

louis
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From: UK
Registered: 2008-03-24
Posts: 6,300

Re: Starship is Go...

Took about 10 minutes to get the fire out.


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#1117 2021-05-05 17:11:02

louis
Member
From: UK
Registered: 2008-03-24
Posts: 6,300

Re: Starship is Go...

Elon Musk tweets the landing was nominal.

https://twitter.com/elonmusk/status/1390073153347592192


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#1118 2021-05-05 17:54:26

louis
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From: UK
Registered: 2008-03-24
Posts: 6,300

Re: Starship is Go...

It's a stunning achievement.  Not least, landing on little stumpy legs!

We are now fully on schedule for a 2026 human landing on Mars I would say, remembering that Apollo went from proof flighting to landing on the Moon within less than two years (Nov 67 to July 69).  A 2026 human landing implies a 2024 robotic cargo landing of course.


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#1119 2021-05-05 18:15:19

SpaceNut
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From: New Hampshire
Registered: 2004-07-22
Posts: 21,841

Re: Starship is Go...

For the moon or mars the potential fire is still problematic but at least they now have a unit to inspect to see what they are getting wrong.

The stubby legs worked on a hard surface flat and level of which the moon and mars are not totally going to work this stability issue...

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#1120 2021-05-05 18:33:47

louis
Member
From: UK
Registered: 2008-03-24
Posts: 6,300

Re: Starship is Go...

Is the fire being fed by onboard oxygen or the Earth atmosphere? If the latter, then that is not an issue on Moon or Mars.

SpaceNut wrote:

For the moon or mars the potential fire is still problematic but at least they now have a unit to inspect to see what they are getting wrong.

The stubby legs worked on a hard surface flat and level of which the moon and mars are not totally going to work this stability issue...


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#1121 2021-05-05 19:20:08

SpaceNut
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From: New Hampshire
Registered: 2004-07-22
Posts: 21,841

Re: Starship is Go...

The heat of the engines could for a period of time cause the soils to give up there oxygen and it would continue until the are had given up all that it could due to temperatures....So its good that they now have a complete unit to look at and test....

Engine bells are still slamming into each other not only at shutoff but also during restarts
https://youtu.be/z9eoubnO-pE

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#1122 2021-05-06 08:32:06

GW Johnson
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From: McGregor, Texas USA
Registered: 2011-12-04
Posts: 4,358
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Re: Starship is Go...

Spacenut:

Makes me wonder if the post-landing fires are methane leaks from cracked engine bells (from slamming together).  The methane fuel is the regenerative coolant.  I guess it could be just the methane vapor vent catching fire,  though. 

Did you notice the landing leg about 1 m from the edge of the pad?  If it and 1 other had hit the soft dirt,  they'd sink in,  and topple the vehicle (a guaranteed explosion).  Lesson:  they nearly missed the hard pad,  located in an otherwise soft sea of mud.  That sort of landing leg is experimental-only.  They will soon need a real soft-dirt capability,  and will likely blow up at least a couple more,  before they finally learn that lesson. 

They do need better,  more-reliable camera coverage.  And (flight test 101) you do NOT do this stuff obscured by clouds!  You need ground-based photography,  too.  They obviously have NOT learned that lesson yet,  either.  Camera visuals really are your best diagnostic tool for problems,  especially the unexpected ones.

If this was the Boeing or Lockheed of half a century ago,  I'd say in 3 years they might reach operational orbital flight (if the Boeing or Lockheed of today,  NEVER!).  Spacex could probably beat that 3 years,  but not until they start learning flight test lessons faster. 

GW

PS/update:  I noticed two other things -- (1) the announcer said they intended to light 3 engines for the flip,  then shut down to 2 engines,  maybe even 1 engine,  for the landing.  Despite the unreliable camera footage,  I was able to tell that's not what actually happened.  They came out of the flip and made the landing on 2 engines.  It rather looks like they were only able to get 2 engines lit.  At least they started the flip early enough for the engine-out contingency to still get decelerated (they seem to have learned that lesson). 

Given the demonstrated likelihood of an engine-out,  one has to wonder if the post landing fires we have seen on SN-15 and SN-11 are in some way associated with fuel leaking from a failed engine.  Methane is sure venting from something.  It catches fire very easily with air.  And if oxygen should reach that:  Ka-Boom!

(2) I didn't see any engine bay fires during the ascent,  despite the unreliable camera coverage.  So it would appear they have found and fixed that problem.  The post-landing fires would thus appear to have a different cause.

Last edited by GW Johnson (2021-05-06 12:15:46)


GW Johnson
McGregor,  Texas

"There is nothing as expensive as a dead crew,  especially one dead from a bad management decision"

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#1123 2021-05-06 09:34:58

Oldfart1939
Member
Registered: 2016-11-26
Posts: 2,063

Re: Starship is Go...

I'm not sure the engine bells are slamming into each other. In order to do that, the gimbal system would have to be FUBAR. I think we're seeing the computer controlling them even though nothing is powering the rocket at the time.
The landing leg issue will undoubtedly be addressed soon; otherwise--more rapid unscheduled disassembly will occur.
Elon seems a bit stubborn about the leg issues, though.

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#1124 2021-05-06 09:41:18

Oldfart1939
Member
Registered: 2016-11-26
Posts: 2,063

Re: Starship is Go...

SN 15 is being moved this morning and is in the recovery phase. Now they can examine the plumbing to discover the source of the post-landing fires. It's great that they now can do a full post mortem on the recovered vehicle, and a lot more than they could from a pile of recovered junk.

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#1125 2021-05-06 09:47:17

louis
Member
From: UK
Registered: 2008-03-24
Posts: 6,300

Re: Starship is Go...

The difference between Starship and all other rocket development programmes I can think of is that Space X seem to have another one ready to go in days. This must speed up the programme even if they are making some major mistakes along the way.

Another thing I like about Space X is that once they crack a problem, they really do seem to crack it, so it doesn't resurface in a few months' time.

GW Johnson wrote:

Spacenut:

Makes me wonder if the post-landing fires are methane leaks from cracked engine bells (from slamming together).  The methane fuel is the regenerative coolant.  I guess it could be just the methane vapor vent catching fire,  though. 

Did you notice the landing leg about 1 m from the edge of the pad?  If it and 1 other had hit the soft dirt,  they'd sink in,  and topple the vehicle (a guaranteed explosion).  Lesson:  they nearly missed the hard pad,  located in an otherwise soft sea of mud.  That sort of landing leg is experimental-only.  They will soon need a real soft-dirt capability,  and will likely blow up at least a couple more,  before they finally learn that lesson. 

They do need better,  more-reliable camera coverage.  And (flight test 101) you do NOT do this stuff obscured by clouds!  You need ground-based photography,  too.  They obviously have NOT learned that lesson yet,  either.  Camera visuals really are your best diagnostic tool for problems,  especially the unexpected ones.

If this was the Boeing or Lockheed of half a century ago,  I'd say in 3 years they might reach operational orbital flight (if the Boeing or Lockheed of today,  NEVER!).  Spacex could probably beat that 3 years,  but not until they start learning flight test lessons faster. 

GW

Last edited by louis (2021-05-06 09:47:49)


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