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#776 2020-07-24 12:05:14

Oldfart1939
Member
Registered: 2016-11-26
Posts: 1,897

Re: Starship is Go...

kbd512-
My principal objection to your proposal is lugging along the SRBs, since we're talking about getting an big increase in vehicle velocity, and I'm not sure those SRBs have adequate exhaust velocity to push the vehicle fast enough. SRBs have a lotta thrust for getting heavy loads in motion, but not necessarily good for getting to escape velocity.
I'll shut up now and let GW make the definitive statement on this topic.

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#777 2020-07-27 04:23:39

elderflower
Member
Registered: 2016-06-19
Posts: 1,260

Re: Starship is Go...

how will this proposal satisfy the pork barrel lobbies?  If it doesn't the money will not flow that way. Musk is right to maximise the work in house.

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#778 2020-07-27 08:28:17

GW Johnson
Member
From: McGregor, Texas USA
Registered: 2011-12-04
Posts: 4,078
Website

Re: Starship is Go...

There's no fundamental limitations in flight velocity achievable with any given exhaust velocity,  except mass ratio and number of stages.  You can go as fast as you need with a solid.  I offer as examples the 3-stage solid that was Minuteman 1 through 3,  and the 4-stage solid satellite launcher Scout,  capable of geosynchronous transfer with small satellites. 

The real thing here is what Elderflower said about porkbarrel cash.  NASA itself has had little influence over what projects it must undertake since about 1970.  Congress sets those priorities.  Politics and pork is everything,  technical soundness is nothing. As proof:  SLS is the rocket to nowhere that no one can afford to use.  Gateway is the destination that gives SLS an actual purpose. And shuttle became a kluged cluster instead of a two-stage airplane system. 

Apollo worked as well as it did because Congress had not yet taken over mission and vehicle designs to be allowed,  only at that time where NASA facilities would be located.  Now Congress runs every detail,  and we go nowhere,  except what JPL can contrive and get through Congress.

GW

Last edited by GW Johnson (2020-07-27 08:33:05)


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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#779 2020-07-29 10:46:42

kbd512
Administrator
Registered: 2015-01-02
Posts: 3,723

Re: Starship is Go...

Oldfart1939,

Well, that's what I'm trying to do.  I want to get that heavy booster in motion a bit faster so that additional fuel can be devoted to accelerating rather than landing it.  Boosting is mostly about raw thrust, not specific impulse.  The SRBs have an abundance of thrust to provide to get that freight train moving.  It's actually funny to think about it that way, but getting a Saturn V class rocket going is like making a short freight train takeoff vertically and accelerate to Mach 7 (while getting much lighter very quickly, obviously).

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#780 2020-07-31 17:58:40

SpaceNut
Administrator
From: New Hampshire
Registered: 2004-07-22
Posts: 19,699

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#781 2020-07-31 18:02:02

kbd512
Administrator
Registered: 2015-01-02
Posts: 3,723

Re: Starship is Go...

Yay!

Finally, some good news!

smile

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#782 2020-08-03 20:52:00

SpaceNut
Administrator
From: New Hampshire
Registered: 2004-07-22
Posts: 19,699

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#783 2020-08-07 13:16:26

Oldfart1939
Member
Registered: 2016-11-26
Posts: 1,897

Re: Starship is Go...

Slow to report and respond here!

EVEN SILOS CAN FLY! Success on Tuesday's second attempt! All goals of SN-5 were achieved!

https://www.youtube.com/watch?v=s1HA9Ll … e=youtu.be

An after flight tweet by Elon Musk indicated that subsequent landing legs will be 60% longer on the next iteration, and probably have external legs for a wider landing stance on rough terrain; very similar to the Falcon 9 geometry.

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#784 2020-08-07 13:53:17

kbd512
Administrator
Registered: 2015-01-02
Posts: 3,723

Re: Starship is Go...

Oldfart1939,

What this really means is that we can now transport the entire grain silo to places that have starving people.

Packaging product into bags at a factory, cranes, trucks, more cranes, shipping, weeks of waiting, rinse and repeat at the destination port?

That sounds like too much work.  A few hundred tons of grain, a few hundred tons of LNG, a few full-flow staged combustion rocket engines, a 10 minute hop across the ocean, and we're done.  Screw efficiency, we're just sending the entire grain silo.  It's probably best not to stand in the landing area.  Seriously, though, this could work for medical supplies and water.

Ships: 10 days
Aircraft: 10 hours
Rocket: 10 minutes

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#785 2020-08-12 20:31:56

GW Johnson
Member
From: McGregor, Texas USA
Registered: 2011-12-04
Posts: 4,078
Website

Re: Starship is Go...

You have to look at more than 1 source's video to understand these two things. 

1. The flaming debris flying into the air at SN-5 launch is pieces from the test stand from which it was launched.  That does not detract from the successful flight.  But it does speak to a fundamental misunderstanding of jet blast in the vicinity of launches and landings.  In some videos you can see the brief flash of fire from the ruptured methane line at that damaged launch stand.

2. After landing,  the "silo" is sitting out of plumb around a couple of degrees.  That wasn't enough to topple it over,  but it is evidence that the 6-leg landing pad approach at the 9 m diameter is inadequate even on a reinforced concrete pad.  I have spoken elsewhere to landing stability and soil bearing problems that Spacex has yet to address.  You just saw my worries confirmed. 

Which applies to the upcoming flight tests and orbital operations under the scenario of an unanticipated abort-to-surface,  leading to a landing on soft,  rough ground,  with way too much propellant still on board.  Which is EXACTLY why Musk is finally tweeting about bigger landing legs with a bigger pad span.

He (and they) still haven't figured out how to abort to surface,  when the landing weight exceeds the max thrust available.  Much less what to do when weight/pad area exceeds soil bearing capacity,  or when surface slope exceeds about 5 degrees,  based on pad span versus cg height.

I know most of you don't want to hear this,  but I told you so.  Some 2 years ago. And multiple times since. 

And I also told you all how these issues could be fixed.  I posted every bit of this on "exrocketman" some time ago.

GW

Last edited by GW Johnson (2020-08-12 20:36:33)


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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#786 2020-08-12 22:36:22

kbd512
Administrator
Registered: 2015-01-02
Posts: 3,723

Re: Starship is Go...

GW,

I recall some of those early landing attempts on the drone ships where the booster almost landed vertically, but then toppled over because it didn't settle onto the pad quite as perfectly as it needed to.

Would it be possible to keep the vehicle upright using gyros in the event of a slightly off-nominal landing, or would the gyro be prohibitively heavy?

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#787 2020-08-13 12:09:43

GW Johnson
Member
From: McGregor, Texas USA
Registered: 2011-12-04
Posts: 4,078
Website

Re: Starship is Go...

Kbd512:

Honestly,  I dunno.  Nobody has tried using that kind of a stability-enhancing gyro system, to my knowledge.  I would hazard the guess that wider-stance legs with bigger pads could be had for less weight growth and a lower cost,  plus fewer possible failure modes. But I dunno for sure.

If you hit crooked,  there is one leg that touches first,  and it gets the whole impact load.  Unless you plan on that,  you will under-design the strength of the legs.  Then that first-to-hit leg gets bent-up in the touchdown.  Too much,  and it fails,  and the craft topples over.  And that seems likely (to me) to be the scenario for the bad barge landings.

GW


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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#788 2020-08-13 19:14:10

louis
Member
From: UK
Registered: 2008-03-24
Posts: 5,868

Re: Starship is Go...

Been a bit out of circulation recently.  Brilliant to see the "grain silo" (love the nickname) on manouvres!! What a fantastic achievement by Space X and it keeps alive the rather emaciated hope that we might see humans on Mars in 2024.


Let's Go to Mars...Google on: Fast Track to Mars blogspot.com

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#789 2020-08-13 19:20:58

louis
Member
From: UK
Registered: 2008-03-24
Posts: 5,868

Re: Starship is Go...

GW Johnson wrote:

You have to look at more than 1 source's video to understand these two things. 

1. The flaming debris flying into the air at SN-5 launch is pieces from the test stand from which it was launched.  That does not detract from the successful flight.  But it does speak to a fundamental misunderstanding of jet blast in the vicinity of launches and landings.  In some videos you can see the brief flash of fire from the ruptured methane line at that damaged launch stand.

2. After landing,  the "silo" is sitting out of plumb around a couple of degrees.  That wasn't enough to topple it over,  but it is evidence that the 6-leg landing pad approach at the 9 m diameter is inadequate even on a reinforced concrete pad.  I have spoken elsewhere to landing stability and soil bearing problems that Spacex has yet to address.  You just saw my worries confirmed. 

Which applies to the upcoming flight tests and orbital operations under the scenario of an unanticipated abort-to-surface,  leading to a landing on soft,  rough ground,  with way too much propellant still on board.  Which is EXACTLY why Musk is finally tweeting about bigger landing legs with a bigger pad span.

He (and they) still haven't figured out how to abort to surface,  when the landing weight exceeds the max thrust available.  Much less what to do when weight/pad area exceeds soil bearing capacity,  or when surface slope exceeds about 5 degrees,  based on pad span versus cg height.

I know most of you don't want to hear this,  but I told you so.  Some 2 years ago. And multiple times since. 

And I also told you all how these issues could be fixed.  I posted every bit of this on "exrocketman" some time ago.

GW


Let's Go to Mars...Google on: Fast Track to Mars blogspot.com

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#790 2020-08-13 19:25:19

louis
Member
From: UK
Registered: 2008-03-24
Posts: 5,868

Re: Starship is Go...

GW Johnson wrote:

You have to look at more than 1 source's video to understand these two things. 

1. The flaming debris flying into the air at SN-5 launch is pieces from the test stand from which it was launched.  That does not detract from the successful flight.  But it does speak to a fundamental misunderstanding of jet blast in the vicinity of launches and landings.  In some videos you can see the brief flash of fire from the ruptured methane line at that damaged launch stand.

2. After landing,  the "silo" is sitting out of plumb around a couple of degrees.  That wasn't enough to topple it over,  but it is evidence that the 6-leg landing pad approach at the 9 m diameter is inadequate even on a reinforced concrete pad.  I have spoken elsewhere to landing stability and soil bearing problems that Spacex has yet to address.  You just saw my worries confirmed. 

Which applies to the upcoming flight tests and orbital operations under the scenario of an unanticipated abort-to-surface,  leading to a landing on soft,  rough ground,  with way too much propellant still on board.  Which is EXACTLY why Musk is finally tweeting about bigger landing legs with a bigger pad span.

He (and they) still haven't figured out how to abort to surface,  when the landing weight exceeds the max thrust available.  Much less what to do when weight/pad area exceeds soil bearing capacity,  or when surface slope exceeds about 5 degrees,  based on pad span versus cg height.

I know most of you don't want to hear this,  but I told you so.  Some 2 years ago. And multiple times since. 

And I also told you all how these issues could be fixed.  I posted every bit of this on "exrocketman" some time ago.

GW


Let's Go to Mars...Google on: Fast Track to Mars blogspot.com

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#791 2020-08-13 19:35:21

kbd512
Administrator
Registered: 2015-01-02
Posts: 3,723

Re: Starship is Go...

Glad to see you're back, Louis.

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#792 2020-08-13 20:18:18

SpaceNut
Administrator
From: New Hampshire
Registered: 2004-07-22
Posts: 19,699

Re: Starship is Go...

kbd512 wrote:

Glad to see you're back, Louis.

Like wise....

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#793 2020-08-23 17:30:58

louis
Member
From: UK
Registered: 2008-03-24
Posts: 5,868

Re: Starship is Go...

So looks like we could have static fire on 23 August and a short hop flight before the end of the month! Exciting times!!


Let's Go to Mars...Google on: Fast Track to Mars blogspot.com

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#794 2020-08-24 10:50:47

Oldfart1939
Member
Registered: 2016-11-26
Posts: 1,897

Re: Starship is Go...

We did have the successful static firing--after two earlier aborts--on 23 August 2020. Looking forward now to another short hop test with SN6.

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#795 2020-08-24 14:43:21

louis
Member
From: UK
Registered: 2008-03-24
Posts: 5,868

Re: Starship is Go...

It's one short hop for the SN6, one giant leap for the Mars Mission. Fingers crossed it happens.

Oldfart1939 wrote:

We did have the successful static firing--after two earlier aborts--on 23 August 2020. Looking forward now to another short hop test with SN6.


Let's Go to Mars...Google on: Fast Track to Mars blogspot.com

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#796 2020-08-24 16:35:47

SpaceNut
Administrator
From: New Hampshire
Registered: 2004-07-22
Posts: 19,699

Re: Starship is Go...

I though that I had missed the flight of sn5 but its in the flying silo...
Aug 05, 2020 · SpaceX just flew a full-size prototype of its Starship Mars-colonizing spacecraft for the first time ever.. The Starship SN5 test vehicle took to the skies for about 40 seconds this afternoon....
SpaceX’s full-scale Starship prototype, the SN5, has successfully completed its first 150-m "hop" test, where its engines fired and lifted the spacecraft into the air for about 40 seconds before returning to land on its designated landing site.

Now I see that sn5 was just a test tank and not a full starship....If I was to only open my eyes to see the silo....

https://en.wikipedia.org/wiki/SpaceX_Starship

Furthermore, he stated that SN5 needs several repairs, and he believes SN6 will be ready for a flight test first

https://www.popularmechanics.com/space/ … 7-updates/

Aug 24, 2020 · SpaceX is iterating toward the final Starship vehicle through the SN prototypes. For example, the SN8 version, which is already under construction, will sport three Raptors and will fly much higher than SN5 and SN6 — eventually, all the way up to 12 miles (20 kilometers) above Earth’s surface, if all goes according to plan.

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#797 2020-08-24 19:13:55

louis
Member
From: UK
Registered: 2008-03-24
Posts: 5,868

Re: Starship is Go...

Every iteration brings us closer to the goal! They've overcome do many problems already - mission capability is getting stronger as every week passes. 

SpaceNut wrote:

I though that I had missed the flight of sn5 but its in the flying silo...
Aug 05, 2020 · SpaceX just flew a full-size prototype of its Starship Mars-colonizing spacecraft for the first time ever.. The Starship SN5 test vehicle took to the skies for about 40 seconds this afternoon....
SpaceX’s full-scale Starship prototype, the SN5, has successfully completed its first 150-m "hop" test, where its engines fired and lifted the spacecraft into the air for about 40 seconds before returning to land on its designated landing site.

Now I see that sn5 was just a test tank and not a full starship....If I was to only open my eyes to see the silo....

https://en.wikipedia.org/wiki/SpaceX_Starship

Furthermore, he stated that SN5 needs several repairs, and he believes SN6 will be ready for a flight test first

https://www.popularmechanics.com/space/ … 7-updates/

Aug 24, 2020 · SpaceX is iterating toward the final Starship vehicle through the SN prototypes. For example, the SN8 version, which is already under construction, will sport three Raptors and will fly much higher than SN5 and SN6 — eventually, all the way up to 12 miles (20 kilometers) above Earth’s surface, if all goes according to plan.


Let's Go to Mars...Google on: Fast Track to Mars blogspot.com

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#798 2020-08-24 19:18:09

SpaceNut
Administrator
From: New Hampshire
Registered: 2004-07-22
Posts: 19,699

Re: Starship is Go...

Not sure if you got the email but am glad you are back....

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#799 2020-08-24 19:42:43

Oldfart1939
Member
Registered: 2016-11-26
Posts: 1,897

Re: Starship is Go...

Tomorrow has road closures and the silo may fly...er...SN6 may fly.

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#800 2020-08-25 12:02:23

GW Johnson
Member
From: McGregor, Texas USA
Registered: 2011-12-04
Posts: 4,078
Website

Re: Starship is Go...

The one-engine birds like SN-5 ("the silo") have at max throttle 2 MN of thrust.  Using,  say,  factor 1.2 on takeoff weight for decent flight kinematics,  the takeoff weight cannot exceed 1.667 MN,  which corresponds to 170 metric tons.  Assuming that Musk's Boca Chica presentation number of 120 metric tons inert mass still applies,  they have "room" for only 50 tons of propellant. 

2 MN thrust at sea level Isp = 330 s means they are burning 6.06 metric tons per second.  That's an 8 s flight if all conducted at full thrust. Throttling back reduces the propellant burn rate,  which corresponds to what we saw.

Adding engines raises takeoff thrust.  That raises propellant loadable,  thus increasing the test flight time.  A 3-engine bird has 6 MN max thrust.  Use factor 1.2 again,  although Musk said he wants 1.5,  and the max test liftoff weight is 5 MN,  or 510 metric tons mass.  At no payload and 120 tons inert,  you can load 390 tons of propellant.  The max thrust flow rate is 18.18 tons/s,  for a test flight time no longer than 21.4 s,  unless you can throttle back to lower thrust as the mass burns off.

There's room to put 6 Raptors in the tail.  The intent,  as presented,  is 3 sea level Raptors,  and 3 vacuum Raptors,  which cannot be used at sea level. But if you put all 6 engines as sea level Raptors,  your max thrust is 12 MN.  At factor 1.2,  that's a max takeoff mass of 1000 metric tons.  At zero payload,  that's a max propellant load of 880 tons. 

The tanks are built for 1200 tons,  according to the website.  Therefore,  you will NOT see the Starship fly to orbit without the Superheavy booster.  It simply cannot lift its own weight,  if fully loaded with propellant,  even at zero payload and with 6 sea level engines.

Assume 120 tons inert.  1200 tons propellant.  Zero payload.  Takeoff mass 1320 metric tons,  which weighs 12.94 MN.  Factor that by 1.2 for takeoff kinematics.  You would need 15.53 MN thrust to take off and fly without the Superheavy booster.  At 2 MN per sea level Raptor,  you would need 8 such engines in the tail.  The mountings for that are not there,  and never planned to be there.

Musk said the goal was 100 tons inert.  The site says 100+ tons payload.  Use 100 inert,  100 payload,  a full load of 1200 tons propellant,  for a 1400 ton takeoff mass,  which weighs 13.73 MN.  At factor 1.2 for min kinematics,  you need 16.48 MN thrust,  which at 2 MN per sea level Raptor would require 8-9 engines.  That cannot fit!

At the factor 1.5 that Musk said was needed for acceptable flight kinematics,  the required thrust is 20.60 MN.  At 2 MN per sea level Raptor,  you would need 10-11 engines in the tail.  Nor can that fit!

Have I made my point?

You will see very limited test flights of Starship by itself,  until Superheavy is ready.  Then and only then will Starship go near,  or to,  orbit.  So says Sir Isaac Newton.

Which just goes to prove that there is a lot more to this than just Isp and the rocket equation.

GW

Last edited by GW Johnson (2020-08-25 12:26:27)


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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