Author Topic: 9m ITS Development Updates and Discussion Thread  (Read 257256 times)

Offline spacenut

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Re: 9m ITS Development Updates and Discussion Thread
« Reply #500 on: 08/25/2017 12:00 pm »
Would a tanker ITSy be sent to Mars to make fuel only, and be left there?  This would be near a proposed colony site.  This tanker ITS would go to Mars 2 years before ITS with a crew of 12 and cargo arrives.  Would a full ITS tanker be able to supply two ITS with fuel?  Then several tankers could be sent to have multiple colonies within an electric vehicle drive from each other.  I'm also assuming metholox flexible hoses to transfer fuel and lox several hundred yards away. 

Multiple colonies could then be made within a days drive of each other.  This would be kind of like how Americas counties were formed.  Each county seat was within a days horse and buggy ride of each other which is about 30 miles from each other.  Grids of Mars colonies could be made this way, especially if the rovers go less than 5 mph.  Some colonies may have more access to water ice and become food producing areas with excess water sent via a pipeline to the fuel depot ship to produce fuel. 

Offline GORDAP

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Re: 9m ITS Development Updates and Discussion Thread
« Reply #501 on: 08/25/2017 03:30 pm »
In a tweet talking about how well the Falcon 9 1st stage landed the barge, Elon Musk gave these figures:

Touchdown:
Vertical Velocity (m/s): -1.47
Lateral Velocity  (m/s): -0.15
Tilt (deg):  0.40 ​
Lateral position: 0.7m from target center


Then somebody asked:


What's the ITS landing mount lateral position constraints in m?

And Elon Musk replied:

Probably 2m or so

I guess they have their target defined.

The 2m spec would be effectively a margin of error that is 20% the diameter of the entire ITSy. That sounds extremely implausible without the use of some sort of active recovery mechanism, not that I want to open up that can of worms again...

Either an active mechanism to grab the core in an approximately 12-15m wide mount, or a sort of passive funnel that would require the stage to go through all new kinds of stresses from the centering process.

I don't know why this is shocking.  The landing that just occurred delivered essentially a 20% diameter of booster accuracy in x-y positioning.

Elon said in his talk that they expect to get better in x-y positioning with BFR than they currently are with the F9.  I believe he alluded to additional thrusters or some such.

Also, I think with the combination of a landing pad that is quite equipped to handle extensive flame thrust, combined with a probable ability to more deeply throttle, the BFR will be able to do more of a 'hover' and less of a 'slam' than the F9, if needed.  This would allow more time for the thrusters to center the stage up.  In addition, the BFR is probably more massive per unit of cross section area (square-cube law) and would thus be less sensitive to wind gusts.

Offline oldAtlas_Eguy

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Re: 9m ITS Development Updates and Discussion Thread
« Reply #502 on: 08/25/2017 03:30 pm »
In a tweet talking about how well the Falcon 9 1st stage landed the barge, Elon Musk gave these figures:

Touchdown:
Vertical Velocity (m/s): -1.47
Lateral Velocity  (m/s): -0.15
Tilt (deg):  0.40 ​
Lateral position: 0.7m from target center


Then somebody asked:


What's the ITS landing mount lateral position constraints in m?

And Elon Musk replied:

Probably 2m or so

I guess they have their target defined.

The 2m spec would be effectively a margin of error that is 20% the diameter of the entire ITSy. That sounds extremely implausible without the use of some sort of active recovery mechanism, not that I want to open up that can of worms again...

Either an active mechanism to grab the core in an approximately 12-15m wide mount, or a sort of passive funnel that would require the stage to go through all new kinds of stresses from the centering process.
Think about how the new docking mechanism for the ISS works. It uses a set of leaves to perform final fine alignment. The use of the same sort of method would allow 2m long leaves 4 each on the Booster and ground mount would perform this final alignment and have the mechanisms for a soft capture and also the ability to absorb just like the docking mechanism any vertical landing velocity reaming.

It would be a heavy duty docking adapter.

Offline Coastal Ron

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Re: 9m ITS Development Updates and Discussion Thread
« Reply #503 on: 08/25/2017 03:50 pm »
Think about how the new docking mechanism for the ISS works. It uses a set of leaves to perform final fine alignment. The use of the same sort of method would allow 2m long leaves 4 each on the Booster and ground mount would perform this final alignment and have the mechanisms for a soft capture and also the ability to absorb just like the docking mechanism any vertical landing velocity reaming.

It would be a heavy duty docking adapter.

OK, but with spacecraft docking with the ISS the spacecraft is physically moved to align with the ISS - and docking speeds are relatively slow.

Instead we're talking about a massive spacecraft doing what it can to stop it's fall from space just as it touches the landing platform. I have trouble envisioning how such a system would move an entire ITS 1-2m sideways in less than a second. That would have to be some pretty beefy areas on the ITS, which sounds like a lot of weight.

Wouldn't it be more likely that the landing platform is designed so that the ITS can land off-center and still be OK?
If we don't continuously lower the cost to access space, how are we ever going to afford to expand humanity out into space?

Offline oldAtlas_Eguy

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Re: 9m ITS Development Updates and Discussion Thread
« Reply #504 on: 08/25/2017 04:30 pm »
Think about how the new docking mechanism for the ISS works. It uses a set of leaves to perform final fine alignment. The use of the same sort of method would allow 2m long leaves 4 each on the Booster and ground mount would perform this final alignment and have the mechanisms for a soft capture and also the ability to absorb just like the docking mechanism any vertical landing velocity reaming.

It would be a heavy duty docking adapter.

OK, but with spacecraft docking with the ISS the spacecraft is physically moved to align with the ISS - and docking speeds are relatively slow.

Instead we're talking about a massive spacecraft doing what it can to stop it's fall from space just as it touches the landing platform. I have trouble envisioning how such a system would move an entire ITS 1-2m sideways in less than a second. That would have to be some pretty beefy areas on the ITS, which sounds like a lot of weight.

Wouldn't it be more likely that the landing platform is designed so that the ITS can land off-center and still be OK?
In order to move 1m in 1 second require .2m/s^2 of accelration. If you need both getting it going and then stopping the motion you will need ~.3m/s^2 for a .5 seconds flolwed by the same in the oposite direction for .5 seconds. A vehicle whose dry weight is 50mt that acceleration comes to a lateral load of 15mt. For a vehicle whose thrust structure must deal with 5000mt of thrust on liftoff, 15mt is well withing the basic structure's capability.

Additionally:
If strain gauges are use as instrumentation on the alignment fins the guidance system can then help by performing final maneuvering to help with the alignment lowering the loads on the actual fins. Once it gets to a certain very fine tolerance the capture mechanisms can then take out the remainder of the misalignment. But those values will be measured in centimeters not meters. So the fins get you from a 20% of diameter landing accuracy to a 2% of diameter landing accuracy. At that point many latching design work very well and reliably.

There is also alternative design I just thought of that may work extremely well for this problem and that is a cone and post alignment and capture design. A 2m diameter cone at four corner edges of the vehicle structure strongly reinforced. And four very sturdy pins on the pad will force the final alignment during the last few meters of descent. Once the posts reach a certain point a simple capture mechanism that capture the post head will then hold the vehicle in place even if it sways back and fort some after contact.

It will take some trade-offs to determine whether it is better to have the cones on the vehicle or on the pad. But basically a physical align and capture method is doable with a 20% of diameter misalignment tolerance on landing.

Now here is a real interesting item and that is could we see such a version installed and tested by a F9.
« Last Edit: 08/25/2017 04:56 pm by oldAtlas_Eguy »

Offline TomH

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Re: 9m ITS Development Updates and Discussion Thread
« Reply #505 on: 08/25/2017 04:57 pm »
If you're landing near the launch pad and a crane can move the S1 onto the pad, I don't see that a problem exists. OTOH, if you're trying to land with millimeter precision in a cradle on the launch pad, that's a different story. Not only do you have unknown winds, you also have rocket exhaust and unpredictable eddy swirls. Any attempt to grapple, capture, dock or whatever of the bottom of the stage must be coordinated with some method of vectored force to the top of the stage. This is not as simple as hitting (0,0) on one Cartesian grid. You have two planar Cartesian grids that have to reach (0,0) at approximately the same time: the bottom of the stage as well as the top of the stage. If the vehicle comes in close to vertical, but 3m off on the lower planar (x,y) coordinates, then some solid or fluid mechanism then pushes the bottom into position, it also pushes the fuselage away from being vertically plumb. Now you have a potential tipping problem. If you want to make the entire vehicle move sideways while remaining close to plumb, it needs to be pushed or pulled from both top and bottom by approximately equal forces.

In regards to docking leaves, this situation is dissimilar to micro-G vacuum maneuvering. That is done at a V differential of what, a mm/sec.? While inertia is the only force about which to be concerned. With the landing, we have a vehicle whose prop mass is constantly decreasing (and rapidly approaching zero-meaning no margin for error), a rocket engine whose thrust is not as constant as the inertia of a craft on orbit, unpredictable swirling of winds and engine exhaust, as well as a changing temperature of said leaves as the engine exhaust hits them. What will the heat do to them? Then there is the incredibly complex aerodynamics of the engine exhaust swirling around and between these leaves.

Maybe this can be done, maybe not, but it seems to involve a lot of complexity that could be avoided by landing on a flat slab then moving the vehicle a short distance with a crane.
« Last Edit: 08/25/2017 05:00 pm by TomH »

Offline philw1776

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Re: 9m ITS Development Updates and Discussion Thread
« Reply #506 on: 08/25/2017 05:37 pm »
SpaceX is trying to save the mass of the landing legs; thus the complexity
FULL SEND!!!!

Offline oldAtlas_Eguy

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Re: 9m ITS Development Updates and Discussion Thread
« Reply #507 on: 08/25/2017 06:06 pm »
SpaceX is trying to save the mass of the landing legs; thus the complexity
The pros:
CRADLE: It saves mass on the vehicle.
CRADLE: Save processing time (probably).
NORMAL LANDING LEGS: Can handle significant tolerance in misalignment on landing including significant vertical velocity errors.

Cons:
CRADLE: If you have an excessive misalignment the system is not tolerant such that a crash and burn occurs LOV and possible loss of the cradle and other things nearby.
NORMAL LANDING LEGS: High mass penalty.
NORMAL LANDING LEGS: Significant handling processing in lifting, folding legs. Takes significant time to perform.

I would basically say that initially that the ITSy booster would have legs just like the F9 but at some point could transition to Cradle landing once the accuracy reliability on landing is refined. The probable LOV during the initial test phase of the Booster would result in many crashes if trying to land it on a Cradle at first. Use legs at first to eliminate faults during landing. Many of which will still result in a crash and burn but the landing facility is just a crude slab of concrete able to survive such events. Once the vehicle landing accuracies are high enough often enough with a low probability of LOV for Cradle landing then start doing Cradle landings. Meantime accept the payload penalty (one extra tanker flight or an X% less cargo/payload).


Offline AncientU

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Re: 9m ITS Development Updates and Discussion Thread
« Reply #508 on: 08/25/2017 07:48 pm »
If you're landing near the launch pad and a crane can move the S1 onto the pad, I don't see that a problem exists. OTOH, if you're trying to land with millimeter precision in a cradle on the launch pad, that's a different story. Not only do you have unknown winds, you also have rocket exhaust and unpredictable eddy swirls. Any attempt to grapple, capture, dock or whatever of the bottom of the stage must be coordinated with some method of vectored force to the top of the stage. This is not as simple as hitting (0,0) on one Cartesian grid. You have two planar Cartesian grids that have to reach (0,0) at approximately the same time: the bottom of the stage as well as the top of the stage. If the vehicle comes in close to vertical, but 3m off on the lower planar (x,y) coordinates, then some solid or fluid mechanism then pushes the bottom into position, it also pushes the fuselage away from being vertically plumb. Now you have a potential tipping problem. If you want to make the entire vehicle move sideways while remaining close to plumb, it needs to be pushed or pulled from both top and bottom by approximately equal forces.

In regards to docking leaves, this situation is dissimilar to micro-G vacuum maneuvering. That is done at a V differential of what, a mm/sec.? While inertia is the only force about which to be concerned. With the landing, we have a vehicle whose prop mass is constantly decreasing (and rapidly approaching zero-meaning no margin for error), a rocket engine whose thrust is not as constant as the inertia of a craft on orbit, unpredictable swirling of winds and engine exhaust, as well as a changing temperature of said leaves as the engine exhaust hits them. What will the heat do to them? Then there is the incredibly complex aerodynamics of the engine exhaust swirling around and between these leaves.

Maybe this can be done, maybe not, but it seems to involve a lot of complexity that could be avoided by landing on a flat slab then moving the vehicle a short distance with a crane.

EM said 2m precision was goal... not 2mm.
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Offline Ionmars

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Re: 9m ITS Development Updates and Discussion Thread
« Reply #509 on: 08/25/2017 10:04 pm »
It occurs to me that a 12m ITS tanker that could refill an ITSy 9m spaceship in one trip would replace 3 trips by a 9m tanker. That might be an initial economic argument for building the 12m tanker.

Offline oldAtlas_Eguy

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Re: 9m ITS Development Updates and Discussion Thread
« Reply #510 on: 08/25/2017 10:27 pm »
It occurs to me that a 12m ITS tanker that could refill an ITSy 9m spaceship in one trip would replace 3 trips by a 9m tanker. That might be an initial economic argument for building the 12m tanker.
But it would also need a 12m booster BFR.
 Once you have that then you have no reason to keep using the 9m ITSy but to use the 12m ITS.

Offline Ionmars

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Re: 9m ITS Development Updates and Discussion Thread
« Reply #511 on: 08/25/2017 10:45 pm »
It occurs to me that a 12m ITS tanker that could refill an ITSy 9m spaceship in one trip would replace 3 trips by a 9m tanker. That might be an initial economic argument for building the 12m tanker.
But it would also need a 12m booster BFR.
 Once you have that then you have no reason to keep using the 9m ITSy but to use the 12m ITS.
That's a good point. OTOH they wouldn't take all the ITSy spaceships out of commission immediately, so I'm thinking of an overlapping period where both are operational. The initial justification is only needed if they were trying to finance ITS at that time. They could put 12m tankers into operation while still developing the passenger and cargo versions.

Edit: clarification
« Last Edit: 08/25/2017 10:52 pm by Ionmars »

Offline TomH

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Re: 9m ITS Development Updates and Discussion Thread
« Reply #512 on: 08/25/2017 10:47 pm »
EM said 2m precision was goal... not 2mm.

I was not responding to Elon, but to other posters here. Please explain how you are going to land this booster without landing legs, in a cradle, while being two meters off target?

That may as well be an oncological neurosurgeon excising a brain tumor, while being two meters off target.
« Last Edit: 08/25/2017 10:49 pm by TomH »

Offline Robotbeat

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Re: 9m ITS Development Updates and Discussion Thread
« Reply #513 on: 08/25/2017 11:30 pm »
EM said 2m precision was goal... not 2mm.

I was not responding to Elon, but to other posters here. Please explain how you are going to land this booster without landing legs, in a cradle, while being two meters off target?

That may as well be an oncological neurosurgeon excising a brain tumor, while being two meters off target.
The centering fins and the rest of the mechanism that we haven't seen yet. Think like a huge version of the probe and drogue system used for Soyuz docking and for aerial refueling. If you're ~6 inches off, it's fine. Scaled up to ITS, that ~6 inches is about 2 meters.
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Offline docmordrid

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Re: 9m ITS Development Updates and Discussion Thread
« Reply #514 on: 08/25/2017 11:32 pm »
EM said 2m precision was goal... not 2mm.
>
That may as well be an oncological neurosurgeon excising a brain tumor, while being two meters off target.

Questionable metaphor. Think of it as a percentage of stage diameter, not an absolute applicable to all scales. 2m is 22% of a 9m stage diameter.

More like a neurosurgeon needing 1.0mm accuracy to be perfect and achieving 1.22mm.
« Last Edit: 08/25/2017 11:45 pm by docmordrid »
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Offline AncientU

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Re: 9m ITS Development Updates and Discussion Thread
« Reply #515 on: 08/26/2017 01:01 am »
EM said 2m precision was goal... not 2mm.

I was not responding to Elon, but to other posters here. Please explain how you are going to land this booster without landing legs, in a cradle, while being two meters off target?


I'm not landing anything... Elon is. 
His 2meters.

Quote
What's the ITS landing mount lateral position constraints in m?
https://twitter.com/rupertdance/status/900953725841285120

Quote
Probably 2m or so
https://twitter.com/elonmusk/status/900954066292924417
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Offline Ionmars

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Re: 9m ITS Development Updates and Discussion Thread
« Reply #516 on: 08/26/2017 05:51 pm »
EM said 2m precision was goal... not 2mm.

I was not responding to Elon, but to other posters here. Please explain how you are going to land this booster without landing legs, in a cradle, while being two meters off target?

That may as well be an oncological neurosurgeon excising a brain tumor, while being two meters off target.
It requires a movable landing cradle, which is addressed in this thread:
https://forum.nasaspaceflight.com/index.php?topic=42131.0

My own proposal may be found in Replies #265-267, #275. #282. and #287.

Offline Bananas_on_Mars

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Re: 9m ITS Development Updates and Discussion Thread
« Reply #517 on: 08/26/2017 10:14 pm »
If we assume the ITS 1st stage is caught on some outer rim that only has the diameter of the rest of the stage, the stability radius is 4.5m. So with 2m landing accuracy you might get some pendulum swing when simply landing into a conical catch feature on the landing mount, but it should work just fine.

I think there's some engineering problems to solve with ITS, but the landing cradle should be a minor one if they consistently hit within their 2m bullseye.


Offline drzerg

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Re: 9m ITS Development Updates and Discussion Thread
« Reply #518 on: 08/27/2017 12:10 am »
if you want to make booster as light as possible it shoud touch landing cradle as gentle as you can make. so moving cradle.  from booster frame of reference cradle should just appear where it lands in ideal position. any weight that could be saved from booster shoud go to cradle.

any structure (conical ets.) that needs some aditional strength or equipement from the booster adds weight to the booster.

Offline AncientU

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Re: 9m ITS Development Updates and Discussion Thread
« Reply #519 on: 08/27/2017 10:42 am »
This is like saying it's "nonsensical" to get a car gas tank that can fit more than 20 miles of gas because most of your trips fit under that limit.

That's making a mockery of language.

I'm not interested in silly analogies. A fully reusable 10mt launcher would cost a small fraction of ITS and actually achieve a decent flight rate. If you see any promising markets for reusable super-heavy lift feel free to name them.

You are looking in the wrong direction... look that way -->  the future.
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