Author Topic: Starship Single Stage Earth Point to Point  (Read 100921 times)

Offline FutureSpaceTourist

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Starship Single Stage Earth Point to Point
« on: 05/30/2019 09:21 am »
Think this warrants a new thread:

twitter.com/PPathole/status/1134020370984366080

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I guess the whole SSTO idea doesn't work because of lift off thrust. Raptor is powerful, but with a full propellant load Starship has a TWR under 1. It would need two more engines to have any shot at it. Starship thrust is appropriately scaled for what it's supposed to do.

https://twitter.com/elonmusk/status/1134023034908446723

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Add 2 to 4 more Raptors for Starship point to point on Earth. You can go surprisingly far, even with low lift/drag. This was an unexpected result.

twitter.com/13ericralph31/status/1134023297056686080

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Ah, so single-stage point-to-point? That sounds way better.

https://twitter.com/elonmusk/status/1134025184942313473

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Yeah, *way* better. Dramatically improves cost, complexity & ease of operations. Distances of ~10,000 km with decent payload seem achievable at roughly Mach 20.
« Last Edit: 05/30/2019 09:26 am by FutureSpaceTourist »

Online OneSpeed

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Re: Starship Single Stage Earth Point to Point
« Reply #1 on: 05/30/2019 09:49 am »
An engine arrangement something like this could be good for ballistic P2P. Max thrust at sea level would be more important than Isp in a vacuum.
« Last Edit: 05/30/2019 10:29 am by OneSpeed »

Offline gosnold

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Re: Starship Single Stage Earth Point to Point
« Reply #2 on: 05/30/2019 10:09 am »
Any estimate of the payload of a single stage starship for a 8 km/s delta-v (7 km/s for a 10 000km range plus 1km/s for gravity losses)?

Getting rid of the booster and especially the booster stacking would make Starship-only service feasible without any major infrastructure, the crane for booster stacking was massive.
« Last Edit: 05/30/2019 10:16 am by gosnold »

Offline Yggdrasill

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Re: Starship Single Stage Earth Point to Point
« Reply #3 on: 05/30/2019 10:13 am »
An engine arrangement something like this could be good for P2P. Max thrust at sea level would be more important than Isp in a vacuum.
Might make sense to divide the Raptors into separate cells and space them out as much as possible, so that failure of one engine is unlikely to affect the other engines. Safe operation will be quite important.
« Last Edit: 05/30/2019 10:14 am by Yggdrasill »

Offline speedevil

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Re: Starship Single Stage Earth Point to Point
« Reply #4 on: 05/30/2019 10:22 am »
Quote from: Elon
Yeah, *way* better. Dramatically improves cost, complexity & ease of operations. Distances of ~10,000 km with decent payload seem achievable at roughly Mach 20.
[/quote]

The number mentioned is mach 20 - assuming for the moment he is referring to mach 20 in the atmospheric speed of sound at altitude (the dear.moon presentation does this) this is about 6km/s.
At 6km/s, in order for 'lift' to be relevant, he must be talking of propulsively aided trajectories - unaided glide is not great and will not exceed lift:drag of 1:1 unless BFS has changed radically again.

At 7.8km/s outward acceleration in an orbit equals g.
At 6km/s, you need 0.4* the weight of the vehicle thrust to remain at a constant altitude.
If we were to assume sea-level mach numbers, and 6.8km/s, it's 0.25.

'hovering' for 1000km extra in the middle of your trajectory costs 400 or 600m/s of propellant.
Or 10 or 15 tons.

And of course, there is the question of 'add 2-4 more raptors' - and 'legs/flaps are changing again' raised in the tweetstorm.
Adding 4 raptors is pretty much what you'd want to do for SSTO attempts as well - but he seems to be ruling that out.
The heatshield required for suborbital is practically equivalent due to the increased entry angle.

Mach 20 (6 or 6.8km/s) needs 1-1.6km/s to get to orbit - 30-45 tons of propellant.

If he is actually saying the vehicle can't do SSTO, this pretty much caps the 'decent payload' he is talking about at this figure, plus (say) ten tons or whatever he considers a useful SSTO payload.

The strong 'no SSTO' statement is surrounded by what could be called by the optimistic 'weasel words'.
'actual work' 'not beneficial'.

Is this in context of 'cannot launch 6 tons to LEO at the launch sites inclination', or 'I really think we can get SH up and running faster than anyone envisioned, so let's not bother trying'.


Offline Crispy

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Re: Starship Single Stage Earth Point to Point
« Reply #5 on: 05/30/2019 10:33 am »
And bear in mind that 10,000km is still not enough for all routes. It gets you things like London-USA(48 states) or LA-Tokyo, but LA-Sydney, NY-Mumbai or Auckland-Anywhere-Not-In Oceania are all too far for a single hop.

Offline FutureSpaceTourist

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Re: Starship Single Stage Earth Point to Point
« Reply #6 on: 05/30/2019 10:43 am »
And bear in mind that 10,000km is still not enough for all routes. It gets you things like London-USA(48 states) or LA-Tokyo, but LA-Sydney, NY-Mumbai or Auckland-Anywhere-Not-In Oceania are all too far for a single hop.

True, but much lower start-up - and on-going - cost to not need SH. So can expand to all routes later, with SH, if demand warrants it. Initially people could potentially do two flights on some route if there's demand. For example, NY-Tokyo via LA or London? It may be that SS on it's own can cover enough of the market that there isn't a business case to add in complexity of using SH too.

Offline rklaehn

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Re: Starship Single Stage Earth Point to Point
« Reply #7 on: 05/30/2019 11:19 am »
And bear in mind that 10,000km is still not enough for all routes. It gets you things like London-USA(48 states) or LA-Tokyo, but LA-Sydney, NY-Mumbai or Auckland-Anywhere-Not-In Oceania are all too far for a single hop.

They expect that raptor will get a better thrust to weight and slightly higher isp over time. That should be enough to go to 15000km.

Re: Starship Single Stage Earth Point to Point
« Reply #8 on: 05/30/2019 11:49 am »
Hi everybody! (First post here)

While single stage P2P can be great from the operations point of view, I would be concerned about passengers comfort during launch. With SH, they can use lower T/W during launch to lower the Gs that the passengers experience. They can assume some gravity loses since the whole system has so much total Delta-V that they will get there anyway. But to get far with only the SH will requiere higher accelerations during launch.

(I didn't run any numbers, that's just mental inequations)

Offline rakaydos

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Re: Starship Single Stage Earth Point to Point
« Reply #9 on: 05/30/2019 12:15 pm »
An engine arrangement something like this could be good for ballistic P2P. Max thrust at sea level would be more important than Isp in a vacuum.

It's tempting to have maximum gimbal for all engines, but I think that's a trap. I would expect the InterContinental Starship to expand the Aft Cargo Bays for rapid baggage loading/unloading.

Offline speedevil

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Re: Starship Single Stage Earth Point to Point
« Reply #10 on: 05/30/2019 12:21 pm »
They expect that raptor will get a better thrust to weight and slightly higher isp over time. That should be enough to go to 15000km.

Raptors weight falling to zero (from ten tons in twelve hundred or so) has almost no effect on performance.
Nor does gaining 10s in ISP.
10000 to 15000km is not a small improvement.
« Last Edit: 05/30/2019 12:23 pm by speedevil »

Offline CapitalistOppressor

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Re: Starship Single Stage Earth Point to Point
« Reply #11 on: 05/30/2019 12:36 pm »
So, assuming dragon wings are just regular wings, what would a proper wing look like that optimizes SSP2P and reentry without the need for a heat shield for suborbital, LEO and interplanetary mission profiles?

Is there one solution that solves that rather broad set of problems?

Offline Cheapchips

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Re: Starship Single Stage Earth Point to Point
« Reply #12 on: 05/30/2019 12:39 pm »
It'll be disappointing if platforms lack a Super Heavy.  I liked P2P as a sneaky way of building out mass BEO transit. Better to get a business going and build on it I suppose.

I'm sure they'll be a push for SH P2P flights from Gwynne. How else will she get home from Saudi Arabia in time for dinner?  :)


Offline RonM

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Re: Starship Single Stage Earth Point to Point
« Reply #13 on: 05/30/2019 03:19 pm »
And bear in mind that 10,000km is still not enough for all routes. It gets you things like London-USA(48 states) or LA-Tokyo, but LA-Sydney, NY-Mumbai or Auckland-Anywhere-Not-In Oceania are all too far for a single hop.

LA to Tokyo on SS gets you across the Northern Pacific. From Tokyo you can take SS to Sydney, Auckland, and Mumbai. For the Southern Pacific, Auckland to Santiago and then Santiago to LA.

10,000 km is enough with the right routes.

Offline Solex

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Re: Starship Single Stage Earth Point to Point
« Reply #14 on: 05/30/2019 03:53 pm »
Perhaps it is convenient to put the already proven organization of octaweb engines and in this way also gain luggage space for the passengers.

Offline envy887

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Re: Starship Single Stage Earth Point to Point
« Reply #15 on: 05/30/2019 04:01 pm »
And bear in mind that 10,000km is still not enough for all routes. It gets you things like London-USA(48 states) or LA-Tokyo, but LA-Sydney, NY-Mumbai or Auckland-Anywhere-Not-In Oceania are all too far for a single hop.

LA to Tokyo on SS gets you across the Northern Pacific. From Tokyo you can take SS to Sydney, Auckland, and Mumbai. For the Southern Pacific, Auckland to Santiago and then Santiago to LA.

10,000 km is enough with the right routes.

Sydney-Honolulu and Honolulu-New York are both about 8000 km. Landing and launching without disembarking should only add about 30 minutes to the flight, so a direct but not non-stop Sydney-Honolulu-New York flight would be about 1:15 instead of 45 minutes in the air. Much better than the current ~22 hours.

Offline envy887

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Re: Starship Single Stage Earth Point to Point
« Reply #16 on: 05/30/2019 04:05 pm »
It'll be disappointing if platforms lack a Super Heavy.  I liked P2P as a sneaky way of building out mass BEO transit. Better to get a business going and build on it I suppose.

I'm sure they'll be a push for SH P2P flights from Gwynne. How else will she get home from Saudi Arabia in time for dinner?  :)

Dubai - London - LA is one possibility. Or Dubai - Tokyo - LA. All those hops are less than 9,000 km and take ~25 minutes at Mach 20. A single refueling for 20,000 km still makes a very capable anti-podal transport system.

Offline envy887

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Re: Starship Single Stage Earth Point to Point
« Reply #17 on: 05/30/2019 04:07 pm »
Hi everybody! (First post here)

While single stage P2P can be great from the operations point of view, I would be concerned about passengers comfort during launch. With SH, they can use lower T/W during launch to lower the Gs that the passengers experience. They can assume some gravity loses since the whole system has so much total Delta-V that they will get there anyway. But to get far with only the SH will requiere higher accelerations during launch.

(I didn't run any numbers, that's just mental inequations)

Raptor can throttle and shut down / restart, so limiting acceleration is not a problem. Starship P2P would probably be limited to about 3 gees for passenger comfort.

Offline philw1776

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Re: Starship Single Stage Earth Point to Point
« Reply #18 on: 05/30/2019 04:56 pm »
And bear in mind that 10,000km is still not enough for all routes. It gets you things like London-USA(48 states) or LA-Tokyo, but LA-Sydney, NY-Mumbai or Auckland-Anywhere-Not-In Oceania are all too far for a single hop.

True, but much lower start-up - and on-going - cost to not need SH. So can expand to all routes later, with SH, if demand warrants it. Initially people could potentially do two flights on some route if there's demand. For example, NY-Tokyo via LA or London? It may be that SS on it's own can cover enough of the market that there isn't a business case to add in complexity of using SH too.

Agreed.  Silicone Valley (sic) approach is start soonest with minimum viable product.  Reveals design problems soonest and provides revenue soonest.  Revenue to pay the costs of launch facilities.
P2P starship will require expensive infrastructure at launch sites.  These sites will be expensive and offshore.  That infrastructure investment and permitting, q.v. Boring Company NIMBY reactions and delays, is the limiting factor for P2P.
Later, even a smaller SH 1st stage with ~19 engines* can greatly extend the single hops to reach the longer routes.
FULL SEND!!!!

Offline RonM

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Re: Starship Single Stage Earth Point to Point
« Reply #19 on: 05/30/2019 04:57 pm »
And bear in mind that 10,000km is still not enough for all routes. It gets you things like London-USA(48 states) or LA-Tokyo, but LA-Sydney, NY-Mumbai or Auckland-Anywhere-Not-In Oceania are all too far for a single hop.

LA to Tokyo on SS gets you across the Northern Pacific. From Tokyo you can take SS to Sydney, Auckland, and Mumbai. For the Southern Pacific, Auckland to Santiago and then Santiago to LA.

10,000 km is enough with the right routes.

Sydney-Honolulu and Honolulu-New York are both about 8000 km. Landing and launching without disembarking should only add about 30 minutes to the flight, so a direct but not non-stop Sydney-Honolulu-New York flight would be about 1:15 instead of 45 minutes in the air. Much better than the current ~22 hours.

Good point. Hawaii would make a great hub.

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