Starship is Go...

tahanson43206 · 2021-05-12 06:43:19

For RobertDyck re #1175

SearchTerm:Pencil simulation of landing a rocket
SearchTerm:Heavy landing without legs, discussion of
SearchTerm:Wind effect upon control systems for Super Heavy attempting to "dock" in a tube in wind

As the StackExchange discussion cited a few posts back pointed out, a launch does NOT need to be performed on a day when winds are too strong at the landing site, unless the customer is so in need of delivery they are willing to pay for replacement of the booster.

A wind break could be constructed to have variable resistance to the wind, using vanes under computer control.

Such a system could make near-instantaneous adjustments to compensate for variations in wind velocity.

I note that I have never seen a science fiction story that thought about this issue. The authors seem to have regarded the details of landing vertically a given in the minds of the audience, and spent no time on it.

(th)

Oldfart1939 · 2021-05-12 09:47:50

I understand the pencil model argument. Unfortunately, Starship isn't a pencil, and weighs 100 tons and is 9 meters in diameter. It's basic physics and analytical mechanics at play. There is such a thing called Inertia and mass is involved. Moving a 100 ton spacecraft
instantaneously just isn't within the possible domain of physics as I understand things. Huge amounts of energy are required and in milliseconds time scale to keep things from ending in an RUD of the spacecraft AND the catching tower.

I consider the landing angle from the vertical as a "crabbing movement," and unfortunately the recovery needs to be instantaneous. It isn't likely that this problem will be solved anytime soon.

RobertDyck · 2021-05-12 10:03:18

Oldfart1939, why do you not understand that my example is intended to prove your point? We're in agreement.

tahanson43206 · 2021-05-12 10:29:29

For Oldfart1939 .... your doubt about the ability of modern electronic systems to achieve millisecond response times is concerning to me.

The movement of SpaceX rocket engines can be seen in real time in videos of descending rockets, as well as in animation.

I am confident you would discover (if you had access to the engineers who are managing those descents) that millisecond response times are routine in that system (those systems).

The demonstration of "balancing a broomstick" weighing many tons is ** right there ** for anyone to see.

My guess is that the SpaceX engineers are not worried about random gusts of wind because they've already demonstrated to their satisfaction the ability to deal with cross winds during the descent of (by now) many Falcon 9 first stages.

Winds aloft above the open ocean are not likely to be identical to winds near the ocean surface.

Sensors in the navigation package are likely to be sensing vectors at microsecond precision, and systems are (quite likely) responding in milliseconds.

Edit later: The SpaceX engineers need not be constrained by the same limits as NASA engineers must deal with ...

A wind break for a Super Heavy can be mobile ... It can operate in a circular track around the perch for the descending stage.

It can regulate flow of air from the prevailing wind direction by adjusting the position of vanes as needed to achieve a desired wind velocity, and that wind velocity can be communicated to the control systems in the descending stage.

If the entire system is mounted on a platform at sea, then the track could be installed at the perimeter of the platform.

(th)

Oldfart1939 · 2021-05-12 10:29:45

OK, I understand now that you've pointed that out to me. I kinda thought you were making an argument supporting "rocket catching."
Thanks for your clarification.

GW Johnson · 2021-05-12 18:47:52

RE: landing under automatic control in wind turbulence. --

I am no control systems engineer, but I did have to learn enough to talk with them in order to work with them. What I think you will find is that both the gains in the system logic and the forces required to correct attitude are much larger for the wind turbulence problem than for the general hit-the-mark control problem.

These gains will have to be adaptive (the control system must "learn" what gain to use from its prior experience, and they will be a function of azimuth (larger along the wind direction, smaller at other azimuth angles).

Screw that up, and your higher wind-direction gains applied off the wind direction could easily put you into overcontrol instability with positive feedback. Plus, there is the physical dynamic reaction time lag, when you have so little time actually available in a vertical propulsive rocket landing. A control that cannot keep up is worse than no control at all.

RE: windbreaks --

Such thing might help, but there is also a downside. Wind turbulence is a spectrum that varies with altitude, and not only is generated by terrain, but also responds to changes in terrain. Obstructions also generate turbulence that often has an organization to it, so your windbreak may control the gusts, but it also generates other turbulence, sometimes an alternating vortex "street".

Going from gusty air above the the windbreak to a different turbulence type behind the windbreak is going to act to upset the balance of the vehicle as maintained by whatever automatic flight control system it may have. Have you considered that?

RE: unrealistic expectations for capabilities of automatic control systems. --

Many newer airliners now feature very nearly automatic landing control features. So far these demonstrably cannot deal with a sudden gust upset at touchdown. If they could, we would have already developed and fielded such equipment. There is no such equipment out there. The successful landings in turbulent, high-wind conditions are still hand-flown by human pilots. Ones both experienced and practiced at it.

Plus, the runways are quite wide, so that there is room to miss the centerline without leaving the pavement. And gusty cross winds are exactly why they are designed that way.

GW

Last edited by GW Johnson (2021-05-12 18:57:22)

louis · 2021-05-12 19:45:03

Re landing aircraft on Earth I have certainly read before now that planes can land automatically - better than pilots on average - but public perception doesn't like it. I suspect that's right: the computer will beat the average pilot but maybe not the best pilot when it comes to landing in heavy cross winds.

GW Johnson wrote:

RE: landing under automatic control in wind turbulence. --
I am no control systems engineer, but I did have to learn enough to talk with them in order to work with them. What I think you will find is that both the gains in the system logic and the forces required to correct attitude are much larger for the wind turbulence problem than for the general hit-the-mark control problem.
These gains will have to be adaptive (the control system must "learn" what gain to use from its prior experience, and they will be a function of azimuth (larger along the wind direction, smaller at other azimuth angles).
Screw that up, and your higher wind-direction gains applied off the wind direction could easily put you into overcontrol instability with positive feedback. Plus, there is the physical dynamic reaction time lag, when you have so little time actually available in a vertical propulsive rocket landing. A control that cannot keep up is worse than no control at all.
RE: windbreaks --
Such thing might help, but there is also a downside. Wind turbulence is a spectrum that varies with altitude, and not only is generated by terrain, but also responds to changes in terrain. Obstructions also generate turbulence that often has an organization to it, so your windbreak may control the gusts, but it also generates other turbulence, sometimes an alternating vortex "street".
Going from gusty air above the the windbreak to a different turbulence type behind the windbreak is going to act to upset the balance of the vehicle as maintained by whatever automatic flight control system it may have. Have you considered that?
RE: unrealistic expectations for capabilities of automatic control systems. --
Many newer airliners now feature very nearly automatic landing control features. So far these demonstrably cannot deal with a sudden gust upset at touchdown. If they could, we would have already developed and fielded such equipment. There is no such equipment out there. The successful landings in turbulent, high-wind conditions are still hand-flown by human pilots. Ones both experienced and practiced at it.
Plus, the runways are quite wide, so that there is room to miss the centerline without leaving the pavement. And gusty cross winds are exactly why they are designed that way.
GW

Calliban · 2021-05-12 23:08:06

Some background information on automated landing assist systems.
https://en.m.wikipedia.org/wiki/Autoland

Oldfart1939 · 2021-05-12 23:14:48

Landing any airplane in gusty and crosswind conditions is a real art, and pilots spend hours practicing these a lot. I flew out of Casper, WY (KCPR) for most of the years while I still had a medical certificate. Crosswind landings are moderately difficult themselves, but when gusty conditions are added to the equation, it's a whole new ballgame. Every pilot develops a set of personal guidelines as to how windy it can get and still safely take off and land the airplane

GW is correct that there isn't any autoland system capable of landing ANY airplane under gusty conditions, but routine landings under standard conditions are routinely done by the landing system computer--with a pilot having hands on the controls to deal with sudden and unexpected gusts.

TH--I am well aware of the electronic control systems response time being in the millisecond range; it's not possible to make physical systems respond fast enough; especially as big as they are getting.

tahanson43206 · 2021-05-13 06:05:18

For Oldfart1939 re #1184 ... Thanks for your follow up regarding electronic response time compared to physical actuator response time.

The flight computer (in the case of the Super Heavy) has a lot to ** think ** about as it manages the forces at work in descending from rapid forward motion (to deliver the first stage to staging point) to arriving safely back at the docking tower.

It can use (and I expect will receive) floods of data about atmospheric conditions at all elevations through which it will be passing.

The issue we are addressing in this recent series of (to me quite interesting) posts is what effect (if any) a gust of wind at ground level might have on a multi-ton cylinder descending at a decreasing rate might have.

The flight computer can be given information about wind conditions upwind for as great a distance as is needed to insure it can compensate so that when the vehicle arrives where the predicted wind arrives it will have canted the vehicle just exactly right so that the wind blows it back to vertical.

My guess is that the engineers managing the descent programming will have accumulated a high level of confidence based upon (by now many) successful landings of the Falcon 9 first state.

So, in specific response to your (of course correct) observation, the flight computer can (and will) move the massive thrust machinery in plenty of time so that the predicted effect of wind is exactly compensated for at each point in the descent.

That does NOT mean a wind break would not be a good idea.

And, as the StackExchange correspondents pointed out (in the posts reported earlier in ** this ** topic) the flight can be postponed if wind conditions at the landing site would exceed the safety margin for the vehicle in question.

***
In re-reading your post, I noted the observation that a "real" intelligence (a human pilot) can learn how to deal with transient events through practice.

The flight assist systems that exist today (I am confident) are programmed by humans who try to anticipate what the program will have to deal with, but (to the best of my knowledge) ** those ** programs are not designed to learn. True AI systems are coming, and I would expect Elon Musk to apply them to the SpaceX division just has he has (apparently) been doing in the Tesla division.

The "learning" by each descending Super Heavy can be immediately copied to each other vessel in the fleet (by copying the entire set of bits), so the entire fleet can accumulate experience at a faster rate than any individual vessel.

The Mars connection here is that the same learning capability could be designed into Mars landing systems.

(th)

louis · 2021-05-13 07:00:15

I'm sure we've all had the experience of being hit suddenly by wind force when driving and also seeing overturned trucks in high wind conditions. If you didn't instantly respond, maybe within a couple of milliseconds, your vehicle would slide into the next lane. Has anyone ever experimented with laser beams in directing landings? I'm thinking the rocket would lock on to the laser beams. Perhaps they are unnecessary but I am not sure what is guiding the rocket to the landing pad - is it radio transmitters or a visual idendtification performed by onboard computer or maybe both? I know we've been told here before that radio transmitters cut out as the rocket gets close to the ground. Lasers might help in course corrections. Also, I was just wondering if you had maybe 8 weather vanes around the landing pad with a chequered circular guage painted on the ground that could help the rocket anticipate wind conditions in the next few metres as it got closer to the ground. The onboard computer could instantly convert the guage readings below to wind direction(s).

There are some coastal regions that are infamous for their crosswinds. I wonder if Boca Chica is one.

tahanson43206 wrote:

For Oldfart1939 re #1184 ... Thanks for your follow up regarding electronic response time compared to physical actuator response time.
The flight computer (in the case of the Super Heavy) has a lot to ** think ** about as it manages the forces at work in descending from rapid forward motion (to deliver the first stage to staging point) to arriving safely back at the docking tower.
It can use (and I expect will receive) floods of data about atmospheric conditions at all elevations through which it will be passing.
The issue we are addressing in this recent series of (to me quite interesting) posts is what effect (if any) a gust of wind at ground level might have on a multi-ton cylinder descending at a decreasing rate might have.
The flight computer can be given information about wind conditions upwind for as great a distance as is needed to insure it can compensate so that when the vehicle arrives where the predicted wind arrives it will have canted the vehicle just exactly right so that the wind blows it back to vertical.
My guess is that the engineers managing the descent programming will have accumulated a high level of confidence based upon (by now many) successful landings of the Falcon 9 first state.
So, in specific response to your (of course correct) observation, the flight computer can (and will) move the massive thrust machinery in plenty of time so that the predicted effect of wind is exactly compensated for at each point in the descent.
That does NOT mean a wind break would not be a good idea.
And, as the StackExchange correspondents pointed out (in the posts reported earlier in ** this ** topic) the flight can be postponed if wind conditions at the landing site would exceed the safety margin for the vehicle in question.
***
In re-reading your post, I noted the observation that a "real" intelligence (a human pilot) can learn how to deal with transient events through practice.
The flight assist systems that exist today (I am confident) are programmed by humans who try to anticipate what the program will have to deal with, but (to the best of my knowledge) ** those ** programs are not designed to learn. True AI systems are coming, and I would expect Elon Musk to apply them to the SpaceX division just has he has (apparently) been doing in the Tesla division.
The "learning" by each descending Super Heavy can be immediately copied to each other vessel in the fleet (by copying the entire set of bits), so the entire fleet can accumulate experience at a faster rate than any individual vessel.
The Mars connection here is that the same learning capability could be designed into Mars landing systems.
(th)

Oldfart1939 · 2021-05-13 10:24:23

Louis-

All major airports have elements of what is called the WAAS system, which is the acronym for Wide Area Augmentation System. This is composed of several strategically placed transponders on the ground to aid and assist the onboard GPS navigation system. My airplane had a Garmin 550 on board and was "WAAS enabled." This system is essential for landing aircraft to know their altitude with a high degree of accuracy. The transponders are surveyed in place with exact altitude included. GPS is great for position in map coordinates, but not good enough to land an airliner.

louis · 2021-05-13 12:10:28

It's definitely been stated here by someone that rockets interfere with radio transmissions as the rocket approaches landing.

Oldfart1939 wrote:

Louis-
All major airports have elements of what is called the WAAS system, which is the acronym for Wide Area Augmentation System. This is composed of several strategically placed transponders on the ground to aid and assist the onboard GPS navigation system. My airplane had a Garmin 550 on board and was "WAAS enabled." This system is essential for landing aircraft to know their altitude with a high degree of accuracy. The transponders are surveyed in place with exact altitude included. GPS is great for position in map coordinates, but not good enough to land an airliner.

GW Johnson · 2021-05-13 12:55:44

Guys, the simplest solution here is a wider landing pad, so that the chance of getting blown off its edge is far lower.

The "insurance" for that simpler solution is to start developing landing legs and "feet" that are designed to accommodate significant wind-induced sideways motion at touchdown, and which will not sink into the tidal mudflat if the pad gets missed.

And, BTW, sideways motion at touchdown is as big a risk for toppling over as is too steep a slope. It gets back to wide vs narrow stance in your landing leg design. What's worked before for dozens of landers on the moon and Mars is a center-of-gravity-height to stance-width ratio pretty close to 1.

GW

Last edited by GW Johnson (2021-05-13 12:58:51)

Calliban · 2021-05-13 13:12:32

How big does it need to be? Concrete and hard-core are cheap. Land is cheap in the Southern US.

SpaceNut · 2021-05-13 19:14:30

SpaceX plans to send Starship to Hawaii via space

FCC flight plan

The Booster stage will separate approximately 170 seconds into flight. The Booster will then perform a partial return and land in the Gulf of Mexico approximately 20 miles from the shore. The Orbital Starship will continue on flying between the Florida Straits.

BB1gHR7y.img?h=419&w=799&m=6&q=60&o=f&l=f

It will achieve orbit until performing a powered, targeted landing approximately 100km (~62 miles) off the northwest coast of Kauai in a soft ocean landing."So an upcoming Starship prototype, paired with a Super Heavy booster, will blast off from the SpaceX development site in Boca Chica, Texas. Super Heavy would then separate and land, perhaps on a ship, off shore while Starship continues on to orbit, flying east all the way to Hawaii for a splashdown in the Pacific. The entire flight, from liftoff to splashdown, is expected to last 90 minutes.

BB1gHJpi.img?h=419&w=799&m=6&q=60&o=f&l=f

SpaceX reveals first orbital Starship flight plan, launching from Texas and returning near Hawaii

The rocket initially launches on a "Super Heavy" booster, which makes up the bottom half of the rocket and stands about 230 feet tall. Together, Starship and Super Heavy will be nearly 400 feet tall when stacked for the launch.

BB1gHO2a.img?h=419&w=799&m=6&q=60&o=f&l=f

RobertDyck · 2021-05-13 21:00:02

Orbital Stage Landing
Event Timelines
Event: T+ time (seconds)
Liftoff: 0
MECO: 169
Stage Separation: 171
SES: 176
Booster Touchdown: 495
SECO: 521
Ship Splashdown: 5420 (90 minutes 20 seconds)

I added colons, the FCC exhibit has a table. And I added minutes/seconds.
Interesting they use the word "Touchdown" for Booster, but "Splashdown" for Ship. The Booster will "Touchdown" 20 miles from the shore, does that mean they'll attempt a drone ship landing? But Starship will simply splash in the ocean?

Calliban · 2021-05-14 02:29:57

Landing on a floating platform in the Gulf of Mexico greatly reduces the risk of damage if the booster were to crash on land. But it also imposes the need for very accurate landing. If the booster is off course by 10m, then it misses the landing platform. This would seem to be a design weakness to me. It is obviously much more difficult and expensive to widen a floating platform.

louis · 2021-05-14 05:51:48

I couldn't see any dates mentioned.

Is that right - no timeframe as yet?

GW Johnson · 2021-05-15 13:53:52

Just to let y'all know, I got my data recovered from the dead laptop. I still have no computer, but can use my wife's machine now and then.

I had been working on a new "exrocketman" article when the laptop died. I just finished it and posted it today. Date 15 May 2021, title "Evaluations of the Spacex Starship/Superheavy". This one catalogs and summarizes all the reverse engineering and risk assessments I had done the last few years on the Starship/Superheavy.

Just thought you'd like to know.

GW

Last edited by GW Johnson (2021-05-15 13:54:48)

louis · 2021-05-18 20:39:32

New video from Felix - interesting summary of where we are...

https://www.youtube.com/watch?v=-s_0fu-jEWA

Musk is so focussed on Mars - that's why they are talking about relaunching SN15.

louis · 2021-05-21 13:55:44

Another good video from Felix...

https://www.youtube.com/watch?v=ncBT-4hP81E

Or is he being over-confident?

louis · 2021-05-22 18:35:22

Weirdo robosound but interesting:

https://www.youtube.com/watch?v=_kU9LR6z1xg

louis · 2021-05-24 06:16:34

https://www.youtube.com/watch?v=scUj0UF-d-U

Interesting tanks...

Is this the sort of thing that could form part of the propellant production facility on Mars. It would be like Musk to kill two birds with one stone but (a) would they fit in a Starship and (b) even if they could how would you get them out to the surface but (c) could they stay inside the Starships but (d) why not just use the rocket propellant tanks in the Starships for storage?

I'm not making much sense am I!

GW Johnson · 2021-05-24 08:35:56

Those odd objects are shell-and-tube heat exchangers. They are not any kind of flyable hardware. They are the very heavy steel construction type of thing you see at chemical refineries. What Spacex needs them for, at Boca Chica, is a public unknown at this time.

Long term storage of manufactured cryogenic propellants requires insulated tanks, even on cold Mars. The cryogenics are far colder, especially the methane. The tanks on Starship are not insulated, so long-term storage is not feasible without the expenditure of enormous power. This is also a problem for months-long interplanetary voyages, for which we have yet to see any solution.

Any propellant plant, on Earth or Mars, will have to feature insulated storage tanks for the methane and for the oxygen, from which the tanks on the vehicle are filled right before launch. We have already seen this in action with the prototypes at Boca Chica. There is radiation heating of the tanks on surfaces and in space, and down on planetary surfaces, there is convective heating from the atmospheres (lower on Mars because of the low densities and lower temperatures), and conductive heating from the surface up the supports for the tanks.

That's just heat transfer physics, which NO ONE can get around. The in-space problem is less because there is only radiational heating to deal with. Some sort of cryocooler is the solution for that. But you do need the power to run it. For months at a time.

The videos whose links Louis so graciously provided do indeed deal with some of the problems we have seen so far in prototype testing. There is one problem no one is yet discussing: the troubles getting a relight on all intended engines. SN-15 was supposed to light 3 engines for the flip, then use 2 or even just 1 to touch down. The announcer said so during the ascent. That failed to happen: only 2 relit for the flip and touchdown.

I suspect without evidence that the failure to relight and the post-touchdown methane leak fires are related in some way. I may be wrong, but all the flights that have landed (even briefly) so far have had relight problems, and post-touchdown methane leaks.

GW

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#1176 2021-05-12 06:43:19

Re: Starship is Go...

#1177 2021-05-12 09:47:50

Re: Starship is Go...

#1178 2021-05-12 10:03:18

Re: Starship is Go...

#1179 2021-05-12 10:29:29

Re: Starship is Go...

#1180 2021-05-12 10:29:45

Re: Starship is Go...

#1181 2021-05-12 18:47:52

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#1182 2021-05-12 19:45:03

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#1183 2021-05-12 23:08:06

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#1184 2021-05-12 23:14:48

Re: Starship is Go...

#1185 2021-05-13 06:05:18

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#1186 2021-05-13 07:00:15

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#1187 2021-05-13 10:24:23

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#1188 2021-05-13 12:10:28

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#1189 2021-05-13 12:55:44

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#1193 2021-05-14 02:29:57

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#1194 2021-05-14 05:51:48

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#1195 2021-05-15 13:53:52

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