Starship is Go...

Oldfart1939 · 2019-09-25 08:11:03

New Teslarati article and interview with Musk regarding the reentry flight profile of Starship!

https://www.teslarati.com/spacex-elon-m … 0b4eef1133

louis · 2019-09-25 13:27:58

Interesting read.

One side note - so there will be 400KwHs of batteries on each Starship to actuate the fins...so with six Starships, you will have 2,400 KwHs of battery capacity.

Once recharged on the surface, probably enough to run a hab for 50 sols on extreme minimal power (2Kws constant) or 10 sols at a much more laid back 10Kws constant.

Oldfart1939 wrote:

New Teslarati article and interview with Musk regarding the reentry flight profile of Starship!
https://www.teslarati.com/spacex-elon-m … 0b4eef1133

Last edited by louis (2019-09-25 13:59:04)

louis · 2019-09-25 18:55:54

Brilliant time-lapse video showing the Starship segments being moved and readied for final assembly! Aren't we lucky to be alive witnessing this!!?

https://www.youtube.com/watch?v=C2Q9okKNfJE

Last edited by louis (2019-09-25 18:56:11)

louis · 2019-09-26 18:24:26

It's Felix time again!

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

Hell - that Berry...that's a big crane - reaching over 600 feet!

Very good video! We can now see the methane pipes running down the rocket side.

But Musk apparently think of going with heat resistant tiles which apparently are working well.

Glad to see that Musk is talking about aerobrake manoeuvres to slow down the Starship on its return to Earth. I always suggested that was a strong possiblity but some people were rude about that!

Re the Saturday presentation...I am really hoping Musk is going to confirm that a 2024 Mars Mission is now a definite target and not just aspirational.

Last edited by louis (2019-09-26 18:25:37)

GW Johnson · 2019-09-26 22:41:50

I just put another article up on "exrocketman". I used the latest version of my liquid rocket engine and nozzle ballistics spreadsheet to reverse-engineer very realistic performance for Spacex's "Raptor" engine, in the 40:1 expansion form that can be used from sea level. I got about 333 sec Isp at sea level, and 360 sec Isp in vacuum. A sort of ballpark average from sea-level to vacuum might be 355 sec.

Then I got out another spreadsheet and did Bob Clark's favorite thing: estimating the SSTO potential of "Starship" alone, no booster. I did this with claimed 85 ton inert mass and 1100 ton propellant mass, and ZERO payload. I used summed dV's for orbit, deorbit, and landing, appropriately factored-up for losses.

I got just over 9 km/s dV available from the vehicle, and just under 9 km/s required of the mission. So if the inert mass doesn't grow much in the early suborbital flight testing, then it is likely "Starship" could reach orbit without its booster for flight test, if flown with no payload.

GW

louis · 2019-09-27 02:45:37

What are the implications of that? Do you mean literally no payload or could it be used to take billionaires on a single orbit joy ride? And could you put in passengers for sub-orbital trans-global "airline" flights.

GW Johnson wrote:

I just put another article up on "exrocketman". I used the latest version of my liquid rocket engine and nozzle ballistics spreadsheet to reverse-engineer very realistic performance for Spacex's "Raptor" engine, in the 40:1 expansion form that can be used from sea level. I got about 333 sec Isp at sea level, and 360 sec Isp in vacuum. A sort of ballpark average from sea-level to vacuum might be 355 sec.
Then I got out another spreadsheet and did Bob Clark's favorite thing: estimating the SSTO potential of "Starship" alone, no booster. I did this with claimed 85 ton inert mass and 1100 ton propellant mass, and ZERO payload. I used summed dV's for orbit, deorbit, and landing, appropriately factored-up for losses.
I got just over 9 km/s dV available from the vehicle, and just under 9 km/s required of the mission. So if the inert mass doesn't grow much in the early suborbital flight testing, then it is likely "Starship" could reach orbit without its booster for flight test, if flown with no payload.
GW

GW Johnson · 2019-09-27 11:42:55

Louis:

I loaded 6 tons payload and got dV demanded equal to dV available. At 7 tons, dV available fell short. That's for a weight statement that reads 85 m.tons inert, 6 m.tons payload, 1100 m.tons propellant, for a liftoff weight of 1191 m.tons.

None of those inert or propellant mass figures are in the least certain yet! But assuming they are correct, only 6 m.tons of payload is tolerable to reach orbit with Starship as an SSTO (no booster). And the takeoff thrust/weight is under about 1.1, so it's a slow, sluggish takeoff.

For humans going into space, there's the weight of the person, the weight of his space suit or two, and the weight of the food, air, and water necessary to keep him going for x days, whatever x is. It works out to about a ton per person for a mission measured in several days, especially if a real EVA suit is considered. That means ONLY 6 people on board: 1 pilot and at most 5 tons cargo, or that 1 pilot and at most 5 passengers.

I'm sorry, Louis, the numbers are harsh, but they don't lie. It's just physics.

The weakest thing about the whole analysis is the true inert mass of an operational "Starship". I noticed Musk is tweeting the Mk.1 flight test vehicle has not 85 tons inert and 1100 tons propellant, but 100 tons "dry" (whatever that really means) and 1200 tons propellant. For 1300 m.tons at ignition.

At 1300 tons liftoff mass, thrust to weight (with all 7 Raptors at sea level max thrust) is only 1.074. That's REALLY pokey! Net vertical upward acceleration at liftoff is 0.074 gee, or only 0.725 m/sec^2 = 72.5 cm/sec^2. The mk.1 test vehicle has only 3 Raptors installed.

That thing with 3 Raptors installed simply CANNOT lift off at all with a big propellant load.

Sea level max thrust of one Raptor is 440,000 lb = 1,960,000 N (and that's at 4400 psia chamber pressure, which they have yet to achieve in engine tests). The mass that has 1,960,000 N for its Earth weight is only 199,900 kg, or 199.9 m.tons. That's thrust/weight equal to 1.00, for zero upward acceleration (meaning it WILL NOT lift off)!

If the inert mass is 100 tons as Musk says in his tweet, they cannot carry more than about 80 or 90 tons of propellant and still lift off at all in that 3-engine mk.1 test vehicle.

80 or 90 tons of propellant? At sea level Isp=330 sec and 3 Raptors at full sea level thrust (again, still to be demonstrated at all!), the propellant flow rate is near 1.81 metric tons per second. You reach dry tanks in something like 44-50 seconds. That's a VERY short ride!

Do you now understand just how limited these early experimental test vehicles really are? And just how far away from a usable vehicle Spacex really is? What these early test vehicles can do has VERY LITTLE resemblance to the "Starship" designs in the presentations.

All that presentation stuff is nothing but groundless hype until some (more advanced) experimental test vehicle can actually demonstrate feasibility of each separate facet of the performance and physical characteristics claimed for "Starship". And this kind of thing is hellishly expensive to do, and it takes a bunch of time to do and evaluate each test! There is NO way around that!

Them's just the facts of life for flight vehicle development and experimental flight test.

GW

Last edited by GW Johnson (2019-09-27 11:52:44)

louis · 2019-09-27 16:15:24

5 passengers at $ 20 million a time? Sounds like it could be profitable. There are probably at least 5,000 people around the planet who would pay that to be able to boast about their experience at the dining table for the next 10 years... $100 billion in revenue.

Yes, I think I realise these early Mk vehicles are more about ensuring "flightability" if I can coin a word...I am guessing they are checking whether the whole thing can be guided and not fall apart, essentially. I presume the logic is that if you can do a 25Km test flight, you can then with confidence move on to a full attempt at orbital flight.

I must say it has been fascinating watching the Starship develop out in the open...am I right in saying there has been nothing like this "open development" in the history of space flight before? I can't anything similar.

I am remain optimistic about the development programme on the basis that for a lot of the Starship technology Space X will be scaling up existing Falcon 9 technology re guidance and landing. Clearly though a lot remains to be finalised.

GW Johnson wrote:

Louis:
I loaded 6 tons payload and got dV demanded equal to dV available. At 7 tons, dV available fell short. That's for a weight statement that reads 85 m.tons inert, 6 m.tons payload, 1100 m.tons propellant, for a liftoff weight of 1191 m.tons.
None of those inert or propellant mass figures are in the least certain yet! But assuming they are correct, only 6 m.tons of payload is tolerable to reach orbit with Starship as an SSTO (no booster). And the takeoff thrust/weight is under about 1.1, so it's a slow, sluggish takeoff.
For humans going into space, there's the weight of the person, the weight of his space suit or two, and the weight of the food, air, and water necessary to keep him going for x days, whatever x is. It works out to about a ton per person for a mission measured in several days, especially if a real EVA suit is considered. That means ONLY 6 people on board: 1 pilot and at most 5 tons cargo, or that 1 pilot and at most 5 passengers.
I'm sorry, Louis, the numbers are harsh, but they don't lie. It's just physics.
The weakest thing about the whole analysis is the true inert mass of an operational "Starship". I noticed Musk is tweeting the Mk.1 flight test vehicle has not 85 tons inert and 1100 tons propellant, but 100 tons "dry" (whatever that really means) and 1200 tons propellant. For 1300 m.tons at ignition.
At 1300 tons liftoff mass, thrust to weight (with all 7 Raptors at sea level max thrust) is only 1.074. That's REALLY pokey! Net vertical upward acceleration at liftoff is 0.074 gee, or only 0.725 m/sec^2 = 72.5 cm/sec^2. The mk.1 test vehicle has only 3 Raptors installed.
That thing with 3 Raptors installed simply CANNOT lift off at all with a big propellant load.
Sea level max thrust of one Raptor is 440,000 lb = 1,960,000 N (and that's at 4400 psia chamber pressure, which they have yet to achieve in engine tests). The mass that has 1,960,000 N for its Earth weight is only 199,900 kg, or 199.9 m.tons. That's thrust/weight equal to 1.00, for zero upward acceleration (meaning it WILL NOT lift off)!
If the inert mass is 100 tons as Musk says in his tweet, they cannot carry more than about 80 or 90 tons of propellant and still lift off at all in that 3-engine mk.1 test vehicle.
80 or 90 tons of propellant? At sea level Isp=330 sec and 3 Raptors at full sea level thrust (again, still to be demonstrated at all!), the propellant flow rate is near 1.81 metric tons per second. You reach dry tanks in something like 44-50 seconds. That's a VERY short ride!
Do you now understand just how limited these early experimental test vehicles really are? And just how far away from a usable vehicle Spacex really is? What these early test vehicles can do has VERY LITTLE resemblance to the "Starship" designs in the presentations.
All that presentation stuff is nothing but groundless hype until some (more advanced) experimental test vehicle can actually demonstrate feasibility of each separate facet of the performance and physical characteristics claimed for "Starship". And this kind of thing is hellishly expensive to do, and it takes a bunch of time to do and evaluate each test! There is NO way around that!
Them's just the facts of life for flight vehicle development and experimental flight test.
GW

Last edited by louis (2019-09-27 16:20:40)

SpaceNut · 2019-09-27 16:24:17

Placing small solids around the base of the rocket to give brute force for the start would allow a quicker rise as the shuttle did with its main engines throttled back at ignition. Something like the atlas and delta would use. The solids do not cut into the payload mass and they can be made disposable to allow them to be made cheaply.

louis · 2019-09-28 08:47:45

Interesting idea - never heard of that before!

SpaceNut wrote:

Placing small solids around the base of the rocket to give brute force for the start would allow a quicker rise as the shuttle did with its main engines throttled back at ignition. Something like the atlas and delta would use. The solids do not cut into the payload mass and they can be made disposable to allow them to be made cheaply.

GW Johnson · 2019-09-28 09:39:41

For all 2-stage vertical launches, of "whatever" vehicle from "whomever" manufacturer, the staging velocity will be in the vicinity of 3 to 3.5 km/s at an altitude near 40-60 km. That first stage flight path is initially vertical, gradually pitching over in a classic gravity turn to rather near horizontal (maybe 10-20 degrees upward of horizontal) at staging. That's just the physics of launch of ballistic vehicles as we currently know them.

What that means is for the majority of that first stage burn, you are accelerating near-vertically upward, and it really is vertically upward during the initial portion, when you vehicle is at its very heaviest weight. It loses some weight due to propellant burnoff as you rise, but there is the enormous weight of the fully-fueled second stage-and-payload as the "payload" of this first stage (your first stage burnout weight is still fairly high). That “dilutes” the weight burnoff effect for you.

My point is that you must have thrust greater than initial weight to lift off at all, and you need the burnoff-of-weight effect, at that large takeoff thrust level (!!!), in order to continue to achieve acceptable acceleration levels, as the drag forces build with speed down in the atmosphere. Relief only comes as the atmosphere thins down above roughly 30-40 km and the trajectory really starts to bend over appreciably from vertical. This is where any solid strapons usually stage-off, and your speed is still typically only about ~1km/s: you are still a very long way away from staging speed! The thrust greater than takeoff weight requirement applies all through this interval! Any throttle-backs for whatever reasons are minor in amount.

Once more or less exoatmospheric and bent over from vertical appreciably, you can decrease thrust if desired (implemented as stage-off of strap-ons), or if an SSTO shedding inert weight to increase mass ratio, such as the staging-off of two now-inactive engines with the original Atlas of the 1950's and 1960's. The real requirement is still accelerating hard to staging speed, before the trajectory bends over too far in its gravity turn. From there the second stage completes the gravity turn to its burnout point essentially in vacuum (which zeroes its drag losses), and more-or-less horizontally (which reduces its gravity losses to near zero).

Any SSTO, such as a "Starship" prototype flight test vehicle, has these very same thrust constraints as the 2-stage vehicle. Thrust needs to be greater than liftoff weight to AT THE VERY LEAST the exoatmospheric / 45-degree point at about 1 km/s velocity, and PREFERABLY all the way to the nominal stage point of 3-3.5 km/s at ~50 km and near-horizontal. This is as true for suborbital flights of intercontinental range as it is for orbital flights.

Using solid strapons is a way to accomplish this with an underpowered SSTO design, but solid strapons are not very reusable, as we learned with shuttle SRB's. It is a feasible flight test demonstration approach, though, if you recognize it for the dead end it really is, when your finished vehicle design’s goal is full reusability.

My other point is, these solid strapons that you might "put around the base" of a 3-engine "Starship" prototype, cannot be "small" items. Their total thrust must make up for the missing 4 Raptor engines, which assumes 7 Raptors would be adequate. This 7-engine design assumption is true only up to about 1300 m.tons at liftoff, given the design thrust level of 440,000 lb per engine. That per-engine thrust is still yet to be demonstrated in ground tests!

That means your solids must total to something like 1.8 million pounds of thrust or more (more gets you better trajectory kinematics), and that ain't "small". You are looking at the equivalent of a shuttle SRB, split into at least 2 motors. Those will be all-alongside, not just “around the base”. Those prototypes are not designed for attachment forces like that.

As I have tried to point out in other threads, these experimental prototypes for "Starship" inherently bear little resemblance to the finished design. That is just inherent in experimental flight testing to develop a new vehicle from scratch, which this "Starship" thing is. That design will continue to evolve in very major ways as these test flights proceed! Drawing conclusions from these experimental vehicles about what "Starship" will actually be is nonsense, and way-premature nonsense at that.

As for 6 landing legs mounted in the base, yes, that is possibly more landing pad area. But not enough, the increase being only factor 2 vs the factor 10 needed to land on fine loose sand and launch from the same. And base-mounted landing pads reduces the span between opposite pads, thus vastly decreasing topple-over stability with an already-vulnerable tall and narrow design. Spacex's engineers still have a very long way to go before they have thought this issue through correctly.

Right now they are stuck in a rut: trying not to do the fold-out surfaces from the fin trailing edges that they will eventually need, in order to save the weight of the associated mechanisms and hydraulics. But they already have the hydraulics to work the folding-fin mechanism for relieving massive aero forces on the fins during entry! The weight of the fold-out pad surfaces is nonzero, but relatively trivial compared to the folding fin mechanisms.

They have no rough field capability on Earth to support abort emergencies, much less rough field landing capabilities on Mars or the moon. Once they think-through the true costs of a lost vehicle and crew, even just here on Earth making an abort landing, that design will change to something more practical.

With so far to go, and so much experimental flight testing to do, and respond-to in their designs, I think the schedule projections for when a “Starship” might actually fly an operational mission to Earth orbit, much less Mars, are still nonsense. You can only speed things up a little by throwing a lot more money at it, not speed it up a lot. Trying to go too fast guarantees crashes, and lost crews if manned. The engineers at Spacex know that, even if Musk doesn’t (and he doesn’t, or Musk time wouldn’t differ from real time by around a factor of 2).

GW

Last edited by GW Johnson (2019-09-28 09:47:26)

Oldfart1939 · 2019-09-28 10:09:46

Thanks for the analysis, GW!
In the world of non-engineering lingo, this is a Reality Check. The optimism of landing such a large vehicle on rough and perhaps sloping terrain is ridiculous, but I'm sure there are engineers at SpaceX who understand this problem. The only answer is outrigger legs, as are found on Falcon 9. and that are folded along almost the entire length of this monster vehicle.
On Reddit, earlier today, Elon confided to the interviewer that this was strictly the first iteration of the final design, and although this vehicle could probably attain orbit "as is," there would be no remaining fuel, nor could it carry any thermal protection or upgraded landing legs. This particular vehicle will make the 20 km ascent and make a landing attempt on a hard surface landing pad. If this were placed in orbit, it would strictly be a throwaway SSTO.
This is strictly an experimental engineering test vehicle--as was Starhopper. I suspect that the Starship Mark II in Florida, will incorporate quite a few upgrades once this particular critter has flown.
What can we learn from such a test hop? How running multiple new Raptor engines can be accomplished, and how to land a much larger vehicle than Falcon 9. Software engineering will be challenged. Control efficacy will be challenged. Fueling, and defueling a large bipropellant rocket with cryogenic liquified gas fuels will be interesting scale-up.
SpaceX will learn a lot doing these tests, and they will find more new questions than answers.

Last edited by Oldfart1939 (2019-09-28 10:12:10)

louis · 2019-09-28 13:06:55

We know various teams have identified rocky plateaus with less than 5% gradient. Satellite observation can identify individual rocks and boulders, even down to 6 inches I think it is.

Oldfart1939 wrote:

Thanks for the analysis, GW!
In the world of non-engineering lingo, this is a Reality Check. The optimism of landing such a large vehicle on rough and perhaps sloping terrain is ridiculous, but I'm sure there are engineers at SpaceX who understand this problem. The only answer is outrigger legs, as are found on Falcon 9. and that are folded along almost the entire length of this monster vehicle.
On Reddit, earlier today, Elon confided to the interviewer that this was strictly the first iteration of the final design, and although this vehicle could probably attain orbit "as is," there would be no remaining fuel, nor could it carry any thermal protection or upgraded landing legs. This particular vehicle will make the 20 km ascent and make a landing attempt on a hard surface landing pad. If this were placed in orbit, it would strictly be a throwaway SSTO.
This is strictly an experimental engineering test vehicle--as was Starhopper. I suspect that the Starship Mark II in Florida, will incorporate quite a few upgrades once this particular critter has flown.
What can we learn from such a test hop? How running multiple new Raptor engines can be accomplished, and how to land a much larger vehicle than Falcon 9. Software engineering will be challenged. Control efficacy will be challenged. Fueling, and defueling a large bipropellant rocket with cryogenic liquified gas fuels will be interesting scale-up.
SpaceX will learn a lot doing these tests, and they will find more new questions than answers.

Oldfart1939 · 2019-09-28 14:01:54

Louis, I'm aware of the features which a camera can detect, and the hi-rise camera is primarily responsible for the most accurate photos we currently have. The pixel size is what determines what can and cannot be seen; the pixel size is a lot more than 6 inches.

That said, I wouldn't be willing to ride Starship to a rough terrain landing as presently configured. I'll just wait and fly the same one as Elon as a co-passenger with him. My bet is--it will have substantial outriggers for tip-over prevention!

P.S. Next local chapter meeting of the Rocky Mountain Mars Society, I'll ask the designer of the hi-rise camera about what can and cannot be seen by orbiters. It was built by Ball Research, in Boulder, Colorado. The chief engineer and optical designer is one of our members.

Last edited by Oldfart1939 (2019-09-28 14:06:41)

GW Johnson · 2019-09-28 14:06:59

Louis:

The same data that you quote also show that there are a vast preponderance of sites that have rocks larger than your 6 inch figure. And 5% slope is too large for a vehicle whose center-of-gravity height-to-footprint width ratio exceeds 1, much less the 3 of "Starship" as proposed. The bulk of Mars is "slopier" than 5 degrees, and it is essentially "soft fine sand". THAT'S what the data says from the probes so far.

You cannot govern where you come down well enough to "guarantee" that you will not hit 5-degree-plus and no-more-than-soft, fine-sand hardness. Period. End of issue. Spacex WILL have to deal with that before it ever sends a "Starship" to Mars, or the moon, for that matter, which is actually similar in those surface characteristics, if not actually rougher in both slopes and boulder size.

Plus, the great bulk (BY FAR !!!) of Mars is equivalent to "soft fine sand" in character. There are almost NO hard, AND FLAT(!!!), hard rock outcrops. So far, what we know says this Martian "fine soft sand" is no different from Earthly "fine soft sand". The allowable bearing pressure for Earthly fine soft sand is quoted in Marks' Mechanical Engineering Handbook (and a variety of other sources the civil engineers use) as 0.1 to 0.2 MPa. Period. End of issue.

Unless you already have soil test data for your site, and I mean REAL engineering test data (!!!), you MUST use the LOW end of that range for your estimates! Not doing so is a violation of engineering ethics that can get your engineering license revoked, if not also putting you in jail, and deservedly so.

Now, "Starship" landing weights are some 6-ish times lower than its takeoff weights, even on Mars. That's the mass ratio they seem to be able to achieve (and I personally won't believe THAT until I see it actually done in a flying vehicle). But the engineering standard is to multiply static weight to be supported by about 2 (sometimes 3) for dynamic effects of touching down transiently.

Still, if the Starship is ever to re-launch, it MUST support the full launch weight. And to land-only one-way (!!!), something only a factor of 2-to-3 lower! For re-launch, that's the Martian weight of something in the neighborhood of 1200 metric tons, perhaps higher, who yet knows? THAT governs landing pad size, period! At 1200-1300 metric tons loaded for launch, the min landing pad area is about 10 times larger than anything I have seen proposed by Spacex so far, at something like 40-50 sq.m. total pad area actually in contact with the dirt.

Louis, you cannot fight physics, and you cannot fight the ethical application of engineering standards that so many died to establish. Some of us know how this really has to be done. I am one such.

GW

Last edited by GW Johnson (2019-09-28 14:12:37)

Oldfart1939 · 2019-09-28 14:29:28

Given the fantastic pace with which Starship Mk. I was built, it's actually within the realm of possibility that a smaller pioneer ship could be built utilizing what is learned from this prototype. I would caution Elon that big isn't always better, and that something of an intermediate step is required before sending a vessel with the payload capacity, and hence, the total vehicle weight of Starship. A vessel 25% the size and mass strikes me as reasonable, although it could be a one-way trip for a prototype ship carrying supplies and equipment. A total mission crew of 25, broken down between scientists and construction technicians seems only logical. I would break it down to 17-18 construction types and 7 or 8 scientists.

Do the soils analysis. Do some landing site preparation. Construction of habitats, and build the fuel production plants. Build a greeenhouse, and have scientists become on-site mark Watney's.

Last edited by Oldfart1939 (2019-09-28 14:31:07)

louis · 2019-09-28 14:42:34

By comparing and processing multiple satellite images of the same area, you achieve higher resolutions:

"By stacking and matching pictures of the same area taken from different angles, Super-Resolution Restoration (SRR) allows objects as small as 5cm (about 2 inches) to be seen from … stacks of between four and eight 25cm images of the Martian surface taken using the NASA HiRISE camera…"

http://www.planetary.org/blogs/guest-bl … aging.html

Oldfart1939 wrote:

Louis, I'm aware of the features which a camera can detect, and the hi-rise camera is primarily responsible for the most accurate photos we currently have. The pixel size is what determines what can and cannot be seen; the pixel size is a lot more than 6 inches.
That said, I wouldn't be willing to ride Starship to a rough terrain landing as presently configured. I'll just wait and fly the same one as Elon as a co-passenger with him. My bet is--it will have substantial outriggers for tip-over prevention!
P.S. Next local chapter meeting of the Rocky Mountain Mars Society, I'll ask the designer of the hi-rise camera about what can and cannot be seen by orbiters. It was built by Ball Research, in Boulder, Colorado. The chief engineer and optical designer is one of our members.

louis · 2019-09-28 14:47:29

Not sure I understand your proposal - a smaller Starship to Mars? How does that work? Are you suggesting a 25-person crew for Mission One. Sounds way too big for me. For me 6 is the right number, 3 riding in each of two human passenger Starships.

Oldfart1939 wrote:

Given the fantastic pace with which Starship Mk. I was built, it's actually within the realm of possibility that a smaller pioneer ship could be built utilizing what is learned from this prototype. I would caution Elon that big isn't always better, and that something of an intermediate step is required before sending a vessel with the payload capacity, and hence, the total vehicle weight of Starship. A vessel 25% the size and mass strikes me as reasonable, although it could be a one-way trip for a prototype ship carrying supplies and equipment. A total mission crew of 25, broken down between scientists and construction technicians seems only logical. I would break it down to 17-18 construction types and 7 or 8 scientists.
Do the soils analysis. Do some landing site preparation. Construction of habitats, and build the fuel production plants. Build a greeenhouse, and have scientists become on-site mark Watney's.

SpaceNut · 2019-09-28 16:11:37

Photo dithering is how pluto was found as that is what you are doing its just decernable its not a measurement persay.

Thanks GW for the starship analysis and how expendable solids are needed based on the engine count. which means for a fully populated 7 count engines to get more payload adding the solids does change the game.

louis · 2019-09-28 16:16:11

A pixel is not a "measurement" it's just a computer artefact. There is nothing to stop new computer artefacts being produced through new processing methods. The test is does the processed image match reality on the ground when we get up close having landed on the surface.

SpaceNut wrote:

Photo dithering is how pluto was found as that is what you are doing its just decernable its not a measurement persay.
Thanks GW for the starship analysis and how expendable solids are needed based on the engine count. which means for a fully populated 7 count engines to get more payload adding the solids does change the game.

elderflower · 2019-09-30 07:01:21

Well it wont be landing on fine sand. The exhaust will blow that away, together with all small pebbles and the not so big rocks. Nobody has any idea what will remain. Nasa got round this using a sky crane device for a large load and very small items can be landed with airbags, but not huge space vehicles!
My conclusion: there must be a pioneering mission to investigate, clear and consolidate a landing zone before a starship landing with tens of people can be risked.

louis · 2019-09-30 07:51:53

Space X's plan involves 4 cargo ships to Mars in 2022 and two human passenger craft in 2024. So the nature of the ground can be confirmed with great accuracy by the four cargo ships before humans venture forth. the four cargo ships can also act as transponders to determine with absolute accuracy the landing zone.

NASA and ESA have instruments that can detect the density of the material on the ground ie whether sand, mud or rock, so they will already have a very accurate idea about the nature of the surface.

elderflower wrote:

Well it wont be landing on fine sand. The exhaust will blow that away, together with all small pebbles and the not so big rocks. Nobody has any idea what will remain. Nasa got round this using a sky crane device for a large load and very small items can be landed with airbags, but not huge space vehicles!
My conclusion: there must be a pioneering mission to investigate, clear and consolidate a landing zone before a starship landing with tens of people can be risked.

GW Johnson · 2019-09-30 11:41:19

"Well it wont be landing on fine sand. The exhaust will blow that away, together with all small pebbles and the not so big rocks." -- That is NOT what happened on the moon! In vacuum (or Mars's near-vacuum), jet blast does NOT behave the way you would expect based on our experiences with jet blast in a dense atmosphere here on Earth.

In a vacuum, it's NOT a straight stream out the exit cone. The edges of the plume bend outward right at the exit lip to just a tad more than 90 degrees. This effect can be seen in the standard tables for Prandtl-Meyer flow in any text or source on compressible fluid mechanics.

While the plume is more-or-less straight out the exit exactly at the exit plane, just a tiny fraction of an inch past that exit plane, that exiting flow is a widely-spread-out fan from just past 90 degrees off centerline on one side through straight ONLY on exactly the centerline, to just past 90 degrees off centerline on the other side. The bulk of the plume is way, way off centerline, and expanded to essentially zero pressure.

The impact pressure of such a suddenly-widely-spread plume is proportional to it speed squared, and linearly proportional to its stream static pressure. Since that is suddenly-expanded to essentially zero, the jet blast wind pressure that can possibly be exerted is also now essentially zero.

That behavior is quite distinct from the behavior of jet plumes released in an atmosphere of significant pressure, like Earth's. In that event, the jet plume stays very well collimated, and essentially still straight out of the exit, for a long way outside the nozzle. THAT is what we are all familiar with. That is TOTALLY UNLIKE vacuum behavior!

Its speed is the expansion speed, and its pressure is not zero. Since it is still well-collimated, before it has a chance to mix significantly with the surrounding air, the wind force it can exert is essentially the thrust of the nozzle that produced the plume. That behavior is UNLIKE what happens in vacuum IN EVERY WAY.

And THAT is why the video and camera footage made of Apollo LM jet blast hitting the moon during Apollo landings show only the merest traces of dust being blown away, and NO (!!!) excavation of sand or rocks, and NO (!!!) blast crater of any sort, underneath the LM. Plumes in vacuum (or near-vacuum) behave VERY differently from what we are inherently used to here on Earth!

So, yes, they WILL land on "soft fine sand:" over 90+% of Mars's surface is exactly that. Loose dry sand, sometimes with loose rocks in it, sometimes just sand. But loose!

"NASA and ESA have instruments that can detect the density of the material on the ground ie whether sand, mud or rock, so they will already have a very accurate idea about the nature of the surface." -- that works by inference, NOT by direct measurement of bearing strength. Thus it has inherent room for significant error.

The real ground truth is NOT known by those methods, but ONLY by direct experience! Density is NOT part of the bearing strength problem, an actual soil crush test result IS. It gives you a direct measurement of the allowable bearing pressure you may exert upon the soil. Weight divided by the area supporting it IS the bearing pressure you exert upon that soil. What you exert MUST be LESS than the soil crush strength, or your landing leg will bury itself into the soil. Simple as that.

What we are arguing about here gets to the real difference between a professional scientist and a professional engineer. If the scientist gets a wrong answer, he is temporarily embarrassed. If the engineer gets the wrong answer, people die.

Sorry to be such a thorn in your side about this rough field landing issue, but that (being a thorn in the sides of over-enthusiasts) was my job as an engineer! To ALWAYS get an answer that would not kill people! I did a whole lot of things no one had ever done before. NO ONE ever got hurt, much less killed, on my watch.

GW

Last edited by GW Johnson (2019-09-30 11:54:23)

louis · 2019-09-30 18:22:36

Well this is not what I get from the Workshops on landing sites exploration zones.

https://www.nasa.gov/feature/mars-human … entations/

The Mars orbital satellites and Rover data give v. accurate info on potential landing sites.

There are low dust rocky outcrops or plateaus on Mars which have under 5% slopes and can thus be used for landing.

But most importantly the Space X mission architecture requires us to land cargo ships. Even if some inexplicable error had been made about the landing zone, no human would be injured. You would just lose up to 4 cargo ships. But if no such disaster happened (and I doubt it will) then the cargo ships can be used to provide even more data about the landing site.

GW Johnson wrote:

"NASA and ESA have instruments that can detect the density of the material on the ground ie whether sand, mud or rock, so they will already have a very accurate idea about the nature of the surface." -- that works by inference, NOT by direct measurement of bearing strength. Thus it has inherent room for significant error.
The real ground truth is NOT known by those methods, but ONLY by direct experience! Density is NOT part of the bearing strength problem, an actual soil crush test result IS. It gives you a direct measurement of the allowable bearing pressure you may exert upon the soil. Weight divided by the area supporting it IS the bearing pressure you exert upon that soil. What you exert MUST be LESS than the soil crush strength, or your landing leg will bury itself into the soil. Simple as that.
What we are arguing about here gets to the real difference between a professional scientist and a professional engineer. If the scientist gets a wrong answer, he is temporarily embarrassed. If the engineer gets the wrong answer, people die.
Sorry to be such a thorn in your side about this rough field landing issue, but that (being a thorn in the sides of over-enthusiasts) was my job as an engineer! To ALWAYS get an answer that would not kill people! I did a whole lot of things no one had ever done before. NO ONE ever got hurt, much less killed, on my watch.
GW

Last edited by louis (2019-09-30 18:33:50)

SpaceNut · 2019-09-30 18:32:10

The issue for sending crew when the chances of cargo ship lose is a no go for safety even if they land whats to say that the crew ship will not have the issue even though the others landed safely....

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