Ten perilous steps to heaven.

louis · 2020-05-31 19:11:01

Space X's ability to get the Crew Dragon safely to LEO suggests they should be able eventually to achieve the same with a Starship...But that is just the first step. Made me think there are ten perilous steps that Space X have to take, with each one being firm and assured so that the next can succeed:

Step 1

Get a human passenger Starship to LEO

Step 2

Refuel a Starship in LEO

Step 3

A successful transit from LEO to Mars orbit.

Step 4

Land a Starship on the surface of Mars.

Step 5

Ensure humans survive on Mars for a minimum of two years

Step 6

Find water and manufacture propellant.

Step 7

Successfully refuel a Starship on the Mars surface.

Step 8

Launch a Starship from the Mars surface to LMO.

Step 9

Successfully transit back to Earth orbit.

Step 10

Safely land humans back on Earth.

Ten perilous steps! I'd say possibly steps 7 and 8 are the riskiest and the most challenging to us.

Last edited by louis (2020-05-31 19:11:26)

Void · 2020-06-02 07:15:19

Louis,

I think that if they can get Starship to LEO as a freighter, that is the most important first step, because then they can launch satellites from it. Of course those may need a propulsion unit to get them to a useful place.

Starlink has electric krypton thrusters, so that's a beginning. Starship then begins to pay for its existence.

After that then perhaps to be able to bring materials to a space station, and possibly from a space station.

From the appearances so far, Falcon9/Dragon, can get people to and from that space station.

After that, if it were mine, I would develop a starship with automated laboratories and leave it in orbit as a temporary space station.
They might get customers to put experiments, or even production of materials. The Lab Starship would hang out in LEO for a period of time.

After that they would launch two automated starships, and practice docking. I think that would be necessary prior to any attempt to dock with the ISS. But yes if they got to that point, they might make money by delivering and retrieving things from the starship.

After that, they could send a Lab Starship, to dock with the ISS, so that if a human intervention in the Labs process were useful it could be done.

Those are all potentially $$$ giving activities, and also ways to shake out the wrinkles.

Then some kind of refueling in orbit.

After that space tourism. Although at that point the starship could not be fully trusted to bring people to and from LEO, you could have an activity where a Dragon carries the people to a Starship, after it is in orbit, and the dragon then carries them back from orbit. So, in that way you begin to test out the Starship for crew and tourists, without yet risking people in the transit of Starship through the Earths atmosphere.

And then after that you begin to try to build up to full capabilities, as it becomes assured that the Starship can be trusted.

Last edited by Void (2020-06-02 07:25:20)

GW Johnson · 2020-06-02 17:36:37

I think the plan is to fly Starship suborbitally, alone (without the booster stage), starting with very modest flights, and working up to very demanding suborbital flights.

As those suborbital flights get demanding, the reentry and heat protection issues get increasingly addressed to the point where readiness to fly orbitally is no longer in question.

The biggest weakness in that approach is the big first stage booster. I have seen no way proposed to fly that booster without a second stage Starship. That makes the first boosted flight an all-up test. Which is a leap of faith.

GW

Void · 2020-06-03 07:15:08

Of course I think you are well close to what is required.

I have seen hints that a Starship SSTO, is possible, but it could not have a heat shield or legs, and would carry very little or no cargo.
It could become modules for a space station. Don't know if the engines could or should be recycled to the Earth. Balance of cost would be the decider there I would think.

And such a method would be incremental, to prove the ship's ability to get to LEO. So you would have that. Then you might work on how to gear up the landing methods, when super heavy finally came on line.

As for the Super Heavy, I would think they might consider a "Dummy" starship at first. Just a shape and a weight. I would be dumped into the ocean, I would think. So your dummy load would not endanger the Super Heavy too much, with a malfunction of it's own.

Still I expect they may have their own ideas.

Last edited by Void (2020-06-03 07:20:07)

SpaceNut · 2020-06-03 16:50:10

Post #1 before man can use a starship for Mars we must test steps 1 through 4 near earth unmanned before going to Mars with a crew we will also need to do a long duration use flight.
At a minimum an unmanned test of 5 through 10 is required to prove system before men should be put to the task of Mars.
Step 5 requires resources to make use of with a plan for crew safety for return home health with reduced risk. With follow up mission looking to use more of Mars with each new crew. Its the transition of supplied to in situ that will happen with the initial work to dig in before refueling with mats sources.

louis · 2020-06-03 18:24:41

I think steps 5-10 can be adequately tested in the Earth-Moon system. You have to take some risks with this mission - Apollo took incredible big risks with their missions. These would be small risks in comparison.

SpaceNut wrote:

Post #1 before man can use a starship for Mars we must test steps 1 through 4 near earth unmanned before going to Mars with a crew we will also need to do a long duration use flight.
At a minimum an unmanned test of 5 through 10 is required to prove system before men should be put to the task of Mars.
Step 5 requires resources to make use of with a plan for crew safety for return home health with reduced risk. With follow up mission looking to use more of Mars with each new crew. Its the transition of supplied to in situ that will happen with the initial work to dig in before refueling with mats sources.

GW Johnson · 2020-06-04 08:08:20

The basic Starship design that Musk has recently presented and which is shown on the Spacex website has 6 engines. 3 of these are sea level Raptors that are gimballed for thrust vector control, and 3 of these are vacuum Raptors that are essentially fixed-mounted.

You must understand that a vacuum Raptor cannot be successfully fired at sea level atmospheric pressure. The flow will separate from the nozzle bell, and it just won't generate much thrust, if indeed the throat chokes at all. It may never successfully ignite.

The design thrust level of a sea level Raptor at sea level atmospheric pressure is 440,000 pounds = 1.957 MN, at the max chamber pressure that they have yet to demonstrate in test. There are three of them, for a total max sea level thrust of 5.87 MN.

Now, Starship's inert mass is currently running 120 metric tons, per Musk during his Boca Chica presentation in front of one of the prototypes. The max propellant capacity is 1200 metric tons, per the website data. Set payload to zero, for an ignition mass of 1320 metric tons. On Earth that weighs 12.94 MN.

That's more than twice the takeoff thrust that's available.

Even if you put 6 sea level Raptors in the rear of the Starship (reducing its Isp performance exoatmospheric), you only have 11.74 MN of thrust, still less than the max takeoff weight. You need takeoff thrust/weight 1.1 to 1.5 for decent takeoff flight performance.

If you offload propellant to reduce take-off weight, that reduces delta-vee. That shoots you in the foot, too. You are already short on the effective 8.8 km/s needed to reach LEO, and that's using the vacuum Raptors exoatmospherically.

I don't really think there is any potential in the second-stage Starship design for functioning as an SSTO vehicle.

I did revisit performance estimates for Starship/Superheavy, using the latest data I could find. I'm showing Spacex's "100+ metric tons to LEO" to be about 149 metric tons, assuming the same 120 ton inert mass as currently. I'm also showing 8 to 9 tanker flights to fully refill one Starship on-orbit in LEO.

If they succeed in lowering the inert mass, every ton of weight savings goes into payload increase, at the same performance levels. Musk's Boca Chica presentation indicated he hopes they can eventually get down to 100 tons inert. That's only a 20 ton change, and it has little impact on surface launch thrust/weight for Starship alone without Superheavy.

The Starship/Superheavy system estimates are posted over at "exrocketman" as an article dated 5-30-2020 and titled "2020 Reverse-Engineering Estimates for Starship/Superheavy".

GW

Last edited by GW Johnson (2020-06-04 08:09:56)

Void · 2020-06-04 08:22:40

I hesitate to continue, I understand your arguments pretty much, and concede that you are right, in the sense that Starship would be for bringing cargo to the Moon and Mars.

However, Elon Musk did say that he thought Starship could go SSTO, if you stripped it down, no legs, no heat shield, no cargo. I am quite certain that he and SpaceX are not interested in it for those reasons.

But, supposing for some reason, it would be useful to make space stations out of propellant tanks, in LEO.

And supposing the engine section somehow could be disconnected as a unit, put into a cargo Starship, to return to ground.

Supposing that as much of the Starship to be part of a space station, were more or less just propellant tanks, except for gear which must be included in order to have a rocket. Engines, AI, ect.

But I will agree that it might then make better sense to use the Super Heavy, but I am just seeking the far limits of possibility.

If it were possible, then of course the question is "Is it worth it"?

It would then be necessary to upgrade the canister with life support equipment, and I suppose lab equipment, and most likely that would come from the Earth in a cargo Starship using Super Heavy.

So, again, is it worth it even if it could be done?

https://space.stackexchange.com/questio … e-to-orbit
Quote:

Previously in 2018 Musk had stated on Twitter that Starship would be technically capable of SSTO, but only with no payload (making it entirely pointless to try to use Starship that way). Later in May 2019 he reiterated that Starship could do SSTO, but only with the heat shield, landing propellant, and legs stripped off. (Meaning no way to get back to Earth after launch.)

So, I don't believe that SpaceX or Elon Musk are interested in it, and that's fine with me. The other objectives are much more important.

But, I may not necessarily be thinking of SpaceX, I might be looking a bit at Vulcan. I believe that the intention there is to return the engines and avionics, and to discard the propellant tanks to burn up. That then allows a 2nd stage to go to orbit.

But if a system were designed with the intention of building space stations out of propellant tanks and no 2nd stage, well then any potential to achieve that? I think that would cause more trouble getting the engines and avionics back to Earth, because they would be traveling at a higher speed than for the real Vulcan.

But I will be honest, at least for now I would be more interested in a Starship as a microgravity laboratory/production unit, With all the ability to return to Earth after a stay in space. Of course I even understand that in that case Super Heavy is required.

I just like to find the absolute limits.

I am really not trying to annoy you. I understand that you are the authority.

Done.

Last edited by Void (2020-06-04 08:44:59)

GW Johnson · 2020-06-04 11:42:47

I'm no "authority", but I do know high-performance flight vehicles, new product development, rockets, ramjets, and stuff like that. It's what I once did for a living, and I was very good at it.

Spacex is the authority on their vehicles, but they are a bit cagey about what data they publish. I presume that is so people like me cannot reverse-engineer their designs so easily.

The dramatic price decrease to LEO in the satellite launch business has been driven by Spacex more than any other outfit. I think most folks would agree with that statement. Simplifying the logistics of building and launching vehicles is a huge part of that. The reusability is another big piece of that, partial though it is in the Falcons. There is also an economy-of-scale effect of very significant impact: larger vehicles prove cheaper to operate, all else equal. This shows up in the price per ton to LEO with Falcon-Heavy versus Falcon-9.

Given those facts, I completely understand why Spacex wants to (1) build a huge transport to LEO, and (2) wants to make that vehicle fully reusable. I rather doubt they would willingly do anything to give up on either of those features.

Now, there are discrepancies between the operating Starship concept and the prototypes we have so far seen. For one thing, there appeared to be no nested "header tanks" inside the propellant tanks of S/N 4 that blew up. For early testing, you don't need them. But for routine operation you do, especially for long missions.

The header tank holds your next burn supply, surrounded by the empty tank that is both extra insulation and a sunshade to hold down evaporation of cryogenic propellant. It'll need some kind of cryocooler, regardless. That stuff will get tested in later prototypes, I would expect.

Meanwhile, what good as a space station module is a bare uninsulated tank shell contaminated with methane? Especially if it has another, considerably smaller tank nested inside? It's not fit to pressurize for human habitation. That requires degassing, then insulation, and some sort of external meteoroid protection. Those things are hard enough to do down here on Earth. We have no experience doing that in microgravity and vacuum.

It's only an opinion, but I see more utility to the idea of simply launching to LEO the station modules we want, ready to use, as payloads, and then docking them together. We already know how to do that.

Just my 2 cents' worth.

GW

Last edited by GW Johnson (2020-06-04 11:47:29)

Void · 2020-06-04 11:48:57

I see you as authority.

Thanks for responding.

I will fall back as to return the benefits of the SSTO as I suggested, to be marginal at best, or less than desirable.

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#1 2020-05-31 19:11:01

Ten perilous steps to heaven.

#2 2020-06-02 07:15:19

Re: Ten perilous steps to heaven.

#3 2020-06-02 17:36:37

Re: Ten perilous steps to heaven.

#4 2020-06-03 07:15:08

Re: Ten perilous steps to heaven.

#5 2020-06-03 16:50:10

Re: Ten perilous steps to heaven.

#6 2020-06-03 18:24:41

Re: Ten perilous steps to heaven.

#7 2020-06-04 08:08:20

Re: Ten perilous steps to heaven.

#8 2020-06-04 08:22:40

Re: Ten perilous steps to heaven.

#9 2020-06-04 11:42:47

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#10 2020-06-04 11:48:57

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