Starship is Go...

GW Johnson · 2024-04-03 09:35:39

Ductility is a problem for ALL materials at cryogenic temperatures, particularly the harsh ones like hydrogen. Ductility is important for the risk of debris impact, such as ice chunks, or even birds (ice is by far worse, except for frozen chickens shot from a cannon, but that's another tale).

The area under the stress-strain curve is the energy the material can absorb per unit of material volume. That is quite low due to very poor elongation cold, almost regardless of what happens to yield or even ultimate strengths. That easy, sudden fracture without any warning is what we perceive as cold-induced embrittlement.

The problem I have with propellant tanks made of any composite materials is their inherent porosity. You MUST put some kind of a liner in there to stop the propellant from just weeping right through the material. The matrix does NOT penetrate hardly at all into the yarns, only the spaces between yarns. Everybody forgets to include that liner in their weight and volume comparisons.

The smaller molecules are the worst about leaking through any porosity, which is why hydrogen is notorious for even weeping through a steel welding gas bottle over time-measured-in-months. Methane is much worse than oxygen about that, but not as bad as hydrogen. Things like propane and butane, even ammonia, are more-or-less comparable to oxygen, about that weep tendency.

The liner that you add to a composite cryogenic propellant tank, be it a film or a coating, must inherently strain at the same rate as the tank shell under pressure, and with thermal contraction and expansion. The liner will need a cryogenic elongation greater than that of the tank shell, or it WILL crack in service! There is no way around that requirement.

Metal tanks need no such liners, other than for corrosive effects, such as that of oxygen. Which is why 304/304L stainless is so popular for cryogenic tanks. It resists corrosion when used to contain oxygen, it needs no liner even for hydrogen, hydrogen embrittlement is not so much a problem as it is with other steels, and it has pretty good area under the stress-strain curve for impact resistance, all the way down to liquid hydrogen, or even liquid helium, temperatures. All the helium Dewars I ever saw were 304/304L construction.

Clearly no one property or characteristic is going to decide this material selection. It's just bloody complicated, and the specific details really do matter. Every class of designs will be different.

It gets really complicated, when your cryogen tank wall also gets exposed to heat! As in a recoverable stage doing re-entry. None of the matrix materials in any organic composites are any good much past the boiling point of water, although I remember using one epoxy in experimental laboratory rocket motors that went as high as 290 F. Aluminum is "junk" past about 300-350 F, except for one odd alloy that has titanium alloyed into it, and also the aluminum-lithium alloys. Those go a tad higher, maybe 400-450 before they are junk.

Despite common but incorrect beliefs otherwise, titanium is NOT a high-temperature material! Its max recommended service temperature is the same as plain mild carbon steel at 750-800 F. And titanium is notoriously harder to work, since alpha-phase titanium cannot be worked, only carved.

The alloy steels, martensitic stainlesses, and 300-series austenitic stainlesses do better at "1200 F plus", some as high as 1800 F. Those hot limits are inherently fuzzy, too. It depends upon how much strength loss when hot that you can tolerate. Or upon the formation of unacceptable corrosion, or scale.

All in all, good impact resistance cold, no need for a liner, no hydrogen embrittlement, no corrosion internally, and at-least-decent strength to 1200 F, without forming surface scaling and corrosion, is exactly why 304/304L has been so popular for propellant tanks. That's been the baseline for many decades, and it is really hard to beat.

GW

edit update same day:

Aluminum alloy is the other propellant tank baseline, as we all know. It has a much more modest service life than the 304, though. Stands less heat, fewer fatigue cycles. Corrodes easier, too. But for limited re-use life, it also works great, as long as your re-entry speeds are under about Mach 2.5 to 3, meaning about 0.75 to 0.90 km/s, presuming speed of sound near 300 m/s. The difference in heat resistance is why the Falcon cores require an entry burn to slow down for entry, while the Superheavy apparently does not.

Last edited by GW Johnson (2024-04-03 12:28:05)

Calliban · 2024-04-06 19:00:31

Elon Musk's speech to Boca Chica employees is worth listening to.
https://m.youtube.com/watch?v=OffMED-KXIs

The scale of his ambitions are certainly inspiring.

RGClark · 2024-04-08 13:57:25

The full video is here:

Elon Musk Starship Presentation: IFT-4 Master Plan, Starship V2 & V3, Raptor V3, Mars, IFT-3 & More.
https://youtu.be/z3B0XIImf_w

About 31 minutes in Elon suggests the current version V1 would be capable of 40 to 50 tons to orbit. This is bad because SpaceX sold NASA on the idea the Starship HLS could serve as an Artemis lander based on 150 tons to orbit reusable and “10ish” refueling flights. If the capability is max 50 tons, then it would take “30ish” refueling flights.

If they intend to use version V2 then this is bad because it would require further qualification flights for the larger version and more importantly further qualification of the more powerful Raptor 3 engine needed.

This last is doubly bad because I’d be willing to bet dollars to donuts that they never informed NASA that the current version couldn’t do it and further development would be required for the larger version.

Bob Clark

kbd512 · 2024-04-08 22:38:44

SLS has been through over 15 years of continuous vehicle development, but the first version of SLS that NASA launched was a 77t launch vehicle, according to NASA, not a 130t launch vehicle. Raptor-I was quickly replaced by Raptor-II, which will itself be replaced by Raptor-III. Starship is a work in progress. Falcon-9 ultimately wound up at the Block V variant. That means the very first version of the vehicle that flew successfully wasn't the final iteration of the design. There was Delta-I, Delta-II, Delta-III, Delta-IV, and Delta-IV Heavy. Atlas-V wasn't the first version of Atlas, either, and was dramatically more capable than the first version of Atlas that ever flew into space. Starship is undergoing launch vehicle evolution, plain and simple. Assuming that NASA's aerospace engineers cannot estimate lift capabilities for a given launch vehicle design, after SpaceX has shared detailed vehicle design information with them, is a little hard to believe.

SpaceX has more experience designing, building, and actually flying reusable launch vehicles than any other group of people on this planet. If they can't do the job, since nobody else has ever flown a single reusable launch vehicle to orbit and back to Earth again, it's probably not going to happen. After 300+ successful orbital flights, it's a reasonably safe assumption that they know what they're doing. You can get lucky here and there, but 300 launches in a row is not luck, it's skill and experience, whether we like their methods, design choices, or leadership, or not. This is as good as it gets.

Void · 2024-04-09 13:13:41

I thought that it was important that Elon Musk said that most Starships would likely stay on Mars. Technically those ships are themselves cargo. Same for ships that stay on the Moon.

I think that for the Moon it may be desirable to have a smaller ship, perhaps one that could ride in the starship. I have wondered today if Falcon 9 2nd stage might be converted over to a different fuel and of course Oxygen. The ship is light weight, so then would be a good machine to use for it perhaps.

If most starships are to stay on Mars, then I wonder if you do at some point develop a large ship, to bring people back and fourth, after Mars is self-sufficient to a large degree.

The Starship is perhaps best suited to go Earth<>LEO, but it happens that with a lot of trouble it could also go to Mars and the Moon.

That does not prohibit eventual hardware developments that are a better fit.

As kdb512 has indicated, this seems to be the only serious path to Mars. NASA might go to Mars in a century to grab some rocks and prance a bit and then hang it up after that, I would expect.

Done

Last edited by Void (2024-04-09 13:20:14)

RGClark · 2024-04-11 10:38:43

SpaceX should withdraw its application for the Starship as an Artemis lunar lander, Page 3: Starship has radically reduced capability than promised.
https://exoscientist.blogspot.com/2024/ … ation.html

Robert Clark

SpaceNut · 2024-04-11 11:34:29

I got to wonder if Space x has been launch with dead weight mass to compensate for all of the crew's resources that still must be designed and put into practice. To say nothing of the resource to keep the crew alive for the duration of supposed use.

It probably a great ship for other uses just not to leave orbit due to all of the refueling requirements to use it.

Void · 2024-04-11 13:10:11

Rocketry is not my field, so this is worth as much as that.

But I feel that for now a capacity of 50 tons +/-? is not that bad.

The thing to do is "Do it at all". They have not gotten there yet, so they don't have a complete evaluation of the characteristics of the machines.

After you "Do it at all" then you can try to make it more elegant.

They are probably overbuilt in many ways. That would make sense because they don't know where they might dare cut corners.

50 tons +/-? to LEO, and a full evaluation of a complete flight and successful recovery are what is needed before deciding how to improve the ship. 50 tons +/-? to LEO may allow them to start servicing the Starlink with the ships. That could be a sort of payday.

But I think he said that that eventually the ships will do 200 tons to LEO. If it gets somewhere between 100 and 200 tons, to LEO, I think that would be a good machine.

Lunar Starships are a questionable factor in the first place. A Mini Starship will eventually make more sense. But when setting up a base, the trouble of lots of refilling's may not be that much of an issue.

He hinted at most Starships staying on Mars also. For Mars it will make sense later to have a special ship that does not land, and some kind of a Mini-Starship that can do the atmospheric passages. That is my opinion.

But SpaceX cannot afford to create two new ships at one time.

NASA will just have to wait or get Blue Origin to replace the Lunar activity. Maybe they could get Boeing to make them something

It makes no sense to kill the idea of eventually being able to land a Starship on the Moon, as that will be a good tool whenever it does show up.

Done

Last edited by Void (2024-04-11 13:20:58)

SpaceNut · 2024-04-11 13:53:08

The Falcon 9 heavy can already lift 63 mT to orbit and then some and does it quite well. So, what would a modified version of the of this rocket take to get it to the moon for a second stage change.

GW Johnson · 2024-04-11 17:32:55

It is far too early to be saying that Starship has a reduced payload capacity. It is still in early development testing. The track record of test vehicles is not, and never has been, a reliable indicator of what the final design will accomplish.

GW

Calliban · 2024-04-12 08:31:41

Each Starship flight to Mars must be supported by 6-10 on orbit refuelling missions. This suggests to me a strong cost incentive for developing a reusable interplanetary ship, propelled by a high ISP propulsion system. Although upfront cost will be high, replacing 10 tanker flights with just 1 tanker containing argon electric thruster propellant, represents a dramatic reduction in operating costs. Establishing orbital greenhouses that can convert effluents back into food and fresh water, provides a further reduction to operating costs. Ultimately, the only things we want to be shipping to Earth orbit using Starship are people and high value industrial equipment.

Last edited by Calliban (2024-04-12 08:35:33)

GW Johnson · 2024-04-12 09:20:36

Despite what Musk says, the laws of physics dictate that Starship/Superheavy is first and foremost a re-usable transport to low Earth orbit (LEO). Period. If it really works at all, that is what the experimental tests are all about.

To go elsewhere, where "elsewhere" includes even just high elliptical orbit, it must be refilled in LEO. To one extent or another. That requires tanker flights. No way around that. How much re-fill depends upon the mission. But to be reusable and abortable, it still must have enough propellant on board when it reaches LEO to deorbit and to land. It may have to be able to do that while carrying payload, which "ups" the amount needed to deorbit and land.

If you believe the propellant capacity of the Starship is 1200 tons, and its deliverable payload is 200 tons, then a first good guess is 6 tanker flights for a full refill, except that it may still have aboard something like 20-50 tons. For only a half-refill (less demanding mission), that would be 3 tanker flights, except for the 20-50 tons still aboard.

Now, if instead you believe the payload capacity is nearer only 100 tons, that doubles the number of tanker flights in any scenario.

If instead you change the propellant capacity, say, to 1400 tons, you just added another tanker (at 200 tons) for a full refill, or two tankers at only 100 tons, for that same full refill.

My point is that interplanetary transport (or any other missions more demanding than LEO) is NOT the prime function of this design. Those more-demanding missions can be performed with it at the cost of needing the tankers. With all the risks and expenses that implies. But if NOBODY ELSE offers the mission capability, then this Starship/Superheavy thing is the only game in town. So far, nobody else is actually developing any vehicles to offer the capability that SpaceX is attempting to provide.

And SpaceX has not yet succeeded in supplying it! Starship/Superheavy is still at this time a highly experimental test program, flying prototypes that bear only a superficial resemblance to the final product. Not even SpaceX yet knows what that final product will really look like, or what its capabilities will really turn out to be. Nobody yet knows because nobody can know: it hasn't happened yet.

And that's my other point.

GW

Last edited by GW Johnson (2024-04-12 09:25:45)

Void · 2024-04-12 09:54:40

Since you two are rather professional, I will risk a question.

What if a ship for Mars was initiated by a Nuclear Thermal Tug with Hydrogen as propellant, and it pushed a nuclear electric rocket towards Mars. Could you avoid the need for a heat shield to achieve Mars orbit? I typically talk about Ballistic Capture and that possibly could be involved, or not. The thing about electric is it takes a long time to get up to speed, but if you gave it an initial nuclear thermal boost, could then electric then get the ship to Mars orbit without the need for an aero-burn.

The propellants could be Hydrogen for the Nuclear Thermal, and Argon for the Electric. Argon could be resupplied from Mars if you had a lander.

The two being more efficient than Metha Lox, then I anticipate less LEO tankers to orbit. But Hydrogen is hard to store, so perhaps you would tank up the argon to the Mars ship first, and then tank up the tug with the Hydrogen and then set off on the mission.

I am wondering what you might give as thinking on such a thing.

Done

Void · 2024-04-12 12:00:33

As it happens this video seems to address it: "The Angry Astronaut, A new, nuclear powered plan to put humans on Mars from NASA and Lockheed Maratin!"

Well, bing being how it is, the video does not show up yet. But here is something: https://www.lockheedmartin.com/en-us/ne … -ever.html

The Angry video mentions 3 products in development. (4 months to Mars).
1) Nuclear Thermal, probably with Hydrogen.
2) "Jetson", which is nuclear electric.
3) Nuclear power plants to land on the Moon.

So, that's pretty nice.

Jetson: https://www.space.com/space-nuclear-pow … propulsion.

So, if SpaceX can get some sort of Starship functional, the ability to lift propellants for these nuclear types of rockets would certainly be helpful.

Done

Last edited by Void (2024-04-12 12:05:48)

GW Johnson · 2024-04-12 14:09:26

Void:

You said "get to Mars orbit", so I am interpreting that you want to examine some sort of orbit-to-orbit ship that is propelled with electric propulsion. An orbit-to-orbit design is certainly a feasible notion for electric propulsion. The escape from Earth is 4-5 months spiralling out, meaning you are exposed for months to hard radiation transiting the Van Allen belts. The arrival at Mars is a couple of months spiralling-in, with no radiation belts to worry about. The return to Earth is similar: a couple of months spiralling-out from Mars, and 4-5 months spiralling-in at Earth.

Note that I did NOT invoke any aerobraking at either end of the journey. Such would be feasible and perhaps attractive for returning to Earth, although the vehicle design is greatly complicated by the need to have a full entry-capability heat shield. Such is not so feasible for arriving at Mars, because the upper atmosphere density varies erratically by factors exceeding 2 at entry-type altitudes.

You must be prepared to make some sort of arrival burn than constitutes the majority of the dV, should the densities be factor-2 lower than you expected. And electric propulsion cannot do that job, it has to be conventional rocket at quite high thrust, because time is of the essence. If you fail to slow, you are literally lost in space.

I will say this in addition: it has to be a full capability heat shield! You cannot sidestep that by "skimming" through the upper atmosphere,
because you WILL NOT get any appreciable deceleration! You WILL get full entry heating before you penetrate deep enough to get the necessary deceleration. You can see this in a simple direct entry: the peak heating pulse always precedes the peak deceleration pulse!

You can use a space tug to shorten the spiralling-out/spiralling-in times at Earth, and/or at Mars. I have looked at that. The tug cannot give you the full escape dV from LEO, its max speed must be a tad lower than escape, to stay in an elongated elliptical orbit for practical recovery and reuse. The minority of the escape dV must come from the orbit-to-orbit vehicle, but if electric, that's very little propellant, really. And the spiral-out time from that condition is much shorter, too.

The same arguments apply at Mars, although the infrastructure to operate a tug there would have to be put into place first. Such tugs could be nuclear or chemical. I've looked at that, too.

GW

Last edited by GW Johnson (2024-04-12 14:12:43)

Void · 2024-04-12 19:07:32

Dr. Johnson,

Thank you for giving me this useful information. I am very interested in orbit to orbit with various methods.
I seems to me that between the NASA-Lockheed Martin devices and SpaceX, some interesting things might be done.

I seems to me that with these tools, Mars activities might be divided into 3 parts.
1) Initiation. In this case you do not yet have resources from the surface to give to the effort, so you have to develop them.
2) Bulk Cargo transfers.
3) People moving. Immigrants, not professionals space crews.

I want to explore #2 at this time. Bulk Cargo transfers. What I will suggest cannot so much be done until #1 is reasonably complete, and you probably have to have some very professional people involved as well in #1, #2, and #3.

From post #1814, Quote:

1) Nuclear Thermal, probably with Hydrogen.
2) "Jetson", which is nuclear electric.
3) Nuclear power plants to land on the Moon.

If you are doing robotic transfers, then you may only need the "Jetson" device, coupled with a Starship. You don't need to be concerned about the Van Allen Belts.

So, I suggest modifying that Starship to be compatible with a "Jetson" device.
-Perhaps the Header Tanks can be removed.
-And do not load any Methane or Oxygen to the ship. Perhaps put a propellant into a Starship tank though, perhaps Argon.

I believe that Elon Musk thinks it would be nice to have a major settlement on Mars by 2050. So, there is plenty of time for this assembly to spiral to Mars and down to a low orbit. Perhaps bring a lot of extra cargo along, too much to put in the cargo compartment. Strap some of it to the leeward side of the Starship.

There should be a propellant depot in orbit of Mars with Methane, Oxygen, and perhaps Argon kept on board. It also should have heat shield repair services. Now disconnect the "Jetson" device and also the external cargo. Fill the Starship with Methane and Oxygen, sufficient to land.

Also perhaps connect some "One-Time" landing legs onto the Starship. These legs could have ablative and perhaps where needed active cooling heat shield methods.

Land the ship if you can and unload the cargo.

So, far, the story is that most Starships will stay on Mars as habitat and materials for resources. But this may be a Ship that could fly to orbit perhaps 5 times or more, I am guessing, with minor maintenance. If it does not pass examination, then it can be grounded. When it launched to orbit it may leave its landing legs behind as materials to make resources out of.

Each time it would fly to orbit it could carry Methane, Oxygen, and Argon to the propellant depot. Each time it was at the propellant depot, it could have its heat shield examined and repaired. Also, perhaps new landing legs put on it.

If a Starship crashes, then it becomes scrap materials. Hopefully it would not damage anything on the ground. Eventually statistics might indicate how many times a Starship should be used before retiring it to use, perhaps as habitat and factory space.

The previous story I am aware of was that you landed them and then they usually stayed planted as things to repurpose or recycle. This, I think makes more sense because you may well have a perfectly good tool that can have reuses before being retired.

As for the legs, if they are not used as scrap, perhaps they can be refurbished and sent to orbit in a launching Starship. Presumably new heat shielding would be added to them.

This process should be less dangerous than coming in from interplanetary space. Coming from Low Martian Orbit should be a slower speed, and it should be possible to have extra propellants on board for the landing so that you don't have to land, "Running on fumes", so to speak.

I will be happy to have input on this if you have the time and patience for it.

Done.

Last edited by Void (2024-04-12 19:32:26)

GW Johnson · 2024-04-13 10:39:29

Void:

I like to think of planting things on Mars in 3 phases. First, there's a sort of surface exploration-and-scouting phase, in which you might, or might not, yet know exactly where you'd like to build a real settlement. Small numbers of people, perhaps at multiple sites, supplied from Earth, but exploring ways and means to live off the land. They do not stay permanently.

Second phase is setting up a permanently-occupied base, or maybe two of them. You don't do that until you have some success learning to live off the land. These people may still rotate in and out of Mars, but the stays are much longer. Still low numbers of people. They are exploring how to scale up the ways and means to live off the land, for larger populations, and they are emplacing some of the infrastructure needed to do this work. They are still supplied some things from Earth, but not nearly as much as in phase 1.

Third phase is turning the best of the bases into real settlements and growing them into actual cities. Now people generally come to stay permanently. Little supply from Earth is needed, phasing slowly into none, which would be all home-grown on Mars. This 3rd phase is Musk's vision, but he seems unwilling to go through the first two phases. Yet if you don't, it is quite unlikely you can actually succeed in building a city, jumping straight to phase 3. That's because it takes time to identify what is really required (and actually works) to live off the land on a fundamentally-hostile planet, and to figure out how to scale that up for larger populations. The odds favor that all our preconceived notions will turn out to be wrong! It also takes much time to emplace infrastructure to do these things, and to get it working right, and reliably. That's just life.

The transport means for all this stuff is likely not just one type! I would suspect that phase 1 (and some phase 2) cargoes would be delivered to a direct entry right off the interplanetary trajectory, without stopping in orbit. That's the minimum energy-expense way to send cargo on a 1-way trip to Mars, where the planet essentially runs over you from behind, but you can aerobrake-away most of your speed. People need to have the means to return. That's quite different, and there's 2 fundamentally-different schools of thought on how to accomplish that.

One is an orbit-to-orbit transport that carries landers using propellant sent from Earth in phase 1, and a combination of propellants made on Mars and sent from Earth in phase 2. It would be all local Mars propellant in phase 3. The other is landing without stopping in orbit (SpaceX's approach), and making all the return propellant on Mars from the first landings onward. That second one assumes the propellant technology works as advertised from the get-go. If it doesn't, you do not go home. You die there. And quite unpleasantly, I might add.

By the time you are ready to start phase 3, the return propellant thing should be well-settled and working at large scale. What supply deliveries still come from Earth, can be 1-way direct-entry deliveries, and SpaceX's Starship is one way to do that, although there are other similar 1-way means that do not require as sophisticated a vehicle design. It is the two-way Starships that make more sense: why waste such a sophisticated vehicle as a 1-shot throwaway item unless you are forced to (that would be if it is the only game in town).

I ran a trade study looking at simple cylindrical 1-way, 1-shot delivery vehicles. These would carry about 40 tons of cargo in a cylinder about 10 m dia and 20 m long. It enters blunt end first, with a minimal ablative heat shield, and internally-insulated bare metal sides and aft end. Side panels fold down after the rocket-braked landing, to be unload ramps, for humans with Mars-adapted electric-powered forklifts. These are sent with a transfer stage from low Earth orbit to direct aerobraking entry at Mars. I was estimating about 80 tons at entry interface, with a ballistic coefficient of about 850 kg/sq.m. No chutes, no time to use them, you come out of hypersonics at about 5 km altitude, about 10 sec from impact at local Mach 3. It's about 3 gees to decelerate to a soft landing.

I’ve posted a video on youtube about this study. It’s of me giving a slide presentation about it. Search for “exrocketman1” on youtube. It’s one of about half a dozen videos posted there.

The tools to analyze the orbits for this, the entry descent and landing issues, the rocket vehicle sizing and performance, and for estimating rocket engine Isp, are in the "orbits+" course materials I created, and that Tahanson43206 posted in a drop box for us forums users. The links are in "interplanetary transportation" topic, under the "orbital mechanics traditional" thread. The stuff is designed for students to self-teach from, and the working tools are suppled with the course materials: spreadsheet files, already set up. Everything is there for anybody to run the kinds of design studies that I run. Nobody has to be a trained expert.

I’ve also posted a video on my youtube exrocketman1 channel about how to use the rocket engine estimator spreadsheet. There’s a version of that spreadsheet in one of the last lessons in the “orbits+” course package. Again, it’s just me giving a presentation about exactly how to use the spreadsheet.

Go take a look. You can do for yourself the same sorts of things that I do.

GW

Void · 2024-04-13 11:14:30

Thank You Dr. Johnson. I will take some time to investigate these things.

Done

Oldfart1939 · 2024-04-13 11:50:22

I too watched the Angry Astronaut interview with the PR guy from Lockheed Martin. The Nuclear Thermal vehicle is intended to go from LEO to a LMO and not itself be a lander. Instead, it's to provide a Mars Base in orbit and a return point from several short duration visits to the planetary surface.

GW Johnson · 2024-04-13 12:23:54

Orbit-to-orbit transports that never land are an unusually easy case to consider. They could be electric propulsion if you can tolerate the spiral out times and the Van Allen belt exposures, or they could be conventional chemical rocket, or they could be nuclear thermal. They could even be nuclear explosion drive, if built big enough to be efficient (10,000+ tons), AND IF you can tolerate the EMP on the surface below the thing when it fires up in orbit.

Except for electric, all those other propulsion types are easy enough to build to be "impulsive" burns that do not suffer from gravity losses in space. You can roughly-approximate the mass ratio-sizing dV from impulsive orbital mission numbers, just factored-up for those non-impulsive gravity losses, which are considerable for electric. I use a factor of 2, some others say 1.5. Either way, it's a big factor.

The hardest part is correctly accounting for 3-body effects when using only classical 2-body orbital mechanics equations. To get it "right" requires finite-difference trajectory codes. But the approximation good enough to get an accurate dV is easy: Vnear^2 = Vfar^2 + Vesc^2, where Vesc is figured at the altitude where you make the burn, not the surface. Vnear is your velocity "near" the planet at the burn altitude. Vfar is your velocity "far" from the planet with respect to the planet, figured from your speed with respect to the sun from 2-body transfer orbits, using the planet speed about the sun to shift axes. This accounts for the target planet pulling on you with its gravity, as you approach it. That speeds you up as you approach, or slows you down as you depart.

I put all this into the multiple lessons of the orbits+ course set, and much more besides (such as launch with losses, entry descent and landing, etc).

GW

Last edited by GW Johnson (2024-04-13 12:27:12)

SpaceNut · 2024-04-13 15:36:07

With this the requirements to build a station is now a requirement and we know how much the funds obsorbed would be just based on half of that mission design for the ISS. Mars station would require even more to accomplish.

GW Johnson · 2024-04-13 16:31:00

I don't know that a Mars orbit station is needed until very late in the colonization process. Any manned orbit-to-orbit transport is its own station, by definition.

GW

RGClark · 2024-04-14 23:52:39

A key issue now is I think NASA was blindsided by the low value of 40 to 50 tons payload capacity of the current version of Starship. The reason I think that is if you run the numbers for the SpaceX cited specifications for booster and ship dry and propellant mass, and for Raptor thrust and ISP the vehicle should easily make 100+ tons payload even as reusable.
So what accounts for the lower payload capacity for the current version? Either the dry mass values or the Raptor values or both must be significantly worse than those cited by SpaceX.

Bob Clark

Last edited by RGClark (2024-04-15 05:51:08)

Void · 2024-04-15 08:29:31

Since better members have not commented yet, I will drag out "A half of a loaf is better than nothing".

I am guessing that SpaceX is focusing on getting the Starship to orbit and back down to the beginning of the Troposphere.

NASA also has a Blue Origin lander to despair about as well.

Supposing 50 Tons is all that Starship could even do in full recovery mode. If we believe that a launch is going to be more cost effective than the Falcon Heavy, then as I see it, progress has been made. The per Ton cost then is 2 or 3 times what was desired, but new capabilities have emerged.

But they apparently have a plan to seek to get beyond 50 Tons, so that is good. As soon as somebody else has a better functioning system then NASA can regret its investment in Starship.

I have my eye on Terran-R as well, a sort of a potential Moon Mini-Starship might emerge from that. It has some years to burn though before that could be considered. Probably 2026 at the earliest, I guess. But being of the same propellant usage as Starship, then it would be relatively easy for a Starship to refill it for a trip to the Moon. In the case where Starship never exceeds 50 Tons to LEO, Options for the Moon would exist. It would be tedious to send a Starship to the Moon in that case, but probably it could be done, which is more than what we have now.

More is better in this case. Patience is a virtue.

Done

Last edited by Void (2024-04-15 08:38:00)

RobertDyck · 2024-04-15 14:24:16

Competition is a real factor. Elon doesn't talk about Blue Origin because you don't give your competition advertising. You certainly don't remind your customers that someone else is an alternative. But Blue Origin is working in New Glenn. Design work began 2012, high level specifications revealed September 2016. SpaceX had always intended a heavy lift launcher, since the company was founded (or before). Mars Colonial Launcher was announced in 2012. In 2016 the name was changed to Interplanetary Transportation System. At that time it was going to use carbon fibre. But notice the announcements are an attempt to keep public focus on SpaceX, to take attention away from Blue Horizon. SpaceX also poached talent from Blue Horizon, slowing their work. New Glenn is listed on Wikipedia as 7 metre diameter, 98 metre tall, 2 stages, payload of 45 metric tonnes to LEO, launched from Cape Canaveral LC-36. Starship is 9 metre diameter, 121 metre tall, 2 stages, payload 150 to 200 metric tonnes to LEO, fully reusable. The ITS variant with carbon fibre in 2016 was claimed to be able to lift 300 metric tonnes to LEO, fully reusable. Change to stainless steel dramatically cut cost and sped development cycle, but halved payload capacity. So now the SpaceX website is saying it will lift 100-150 tonnes to LEO fully reusable, or 250 tonnes expendable.

Remember Blue Horizon surprised SpaceX by successfully landing New Shepard 2 in 2015. SpaceX was trying to land Falcon 9 on drone ships but failed every time. New Shepard succeeded in landing on its tail, on land, the second test flight. It's first test crashed. But this took attention away from SpaceX. So SpaceX landed Falcon 9 on land instead of a ship, and that did succeed. Since Falcon 9 was a orbital launcher while New Glenn was a suborbital joy ride, SpaceX kept attention on them.

Also realize SpaceX is dependent on the "capital market". That means they depend on investors. SpaceX is profitable, so they could continue without investors, but would not be able to continue rapid development of Starship without them.

Falcon Heavy was always intended, but realize Falcon Heavy is competition for New Glenn. Starship is the big rocket designed to eclipse New Glenn. And New Horizon hasn't stopped development, just slowed down. Once New Glenn is able to deliver paying cargo to orbit it will start to generate significant revenue. That will make them real competition. SpaceX wants Starship working before that.

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