Author Topic: ITS Development Updates and Discussion Thread  (Read 99857 times)

Offline b0objunior

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Re: ITS Development Updates and Discussion Thread
« Reply #20 on: 09/30/2016 03:47 AM »
Comparing sizes again:

Also excluding panorama window, shuttle orbiter have bigger individual windows than ITS.
Made myself one also. Sea Dragon for fun.

Offline Jim

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Re: ITS Development Updates and Discussion Thread
« Reply #21 on: 09/30/2016 03:48 AM »
I would assume for the propellant refrigeration system?

What propellant refrigeration system?

Offline Seer

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Re: ITS Development Updates and Discussion Thread
« Reply #22 on: 09/30/2016 04:06 AM »
How is the heat from the heatshield rejected from the spacecraft during entry, especially on Mars entry which is hotter and where the atmosphere on the surface won't conduct heat away very quickly?

How will the heatshield be inspected in for damage either in space or on Mars after entry? Imagine having to replace one of the PICAX panels on this thing when its on the surface of Mars.

Online zodiacchris

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Re: ITS Development Updates and Discussion Thread
« Reply #23 on: 09/30/2016 04:24 AM »
I was wondering, given that the spaceship can just about make LEO on it's own, without the booster, would it be conceivable to launch an early prototype into LEO, stripped down to the bare essentials, and then refuel it using repeated FH tanker flights? That would allow shake down cruise in earth orbit or further out, maybe cis-lunar, and EDL. If it has life support, a Dragon 2 could even bring crew up, and take them down again, before the autonomous landing of the BFS. ???
Anybody done the numbers?

Offline Seer

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Re: ITS Development Updates and Discussion Thread
« Reply #24 on: 09/30/2016 04:26 AM »
I was wondering, given that the spaceship can just about make LEO on it's own, without the booster, would it be conceivable to launch an early prototype into LEO, stripped down to the bare essentials, and then refuel it using repeated FH tanker flights? That would allow shake down cruise in earth orbit or further out, maybe cis-lunar, and EDL. If it has life support, a Dragon 2 could even bring crew up, and take them down again, before the autonomous landing of the BFS. ???
Anybody done the numbers?

I think the propellant fraction of the upperstage is around 85%, much less than the >90% needed for SSTO.

Offline docmordrid

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Re: ITS Development Updates and Discussion Thread
« Reply #25 on: 09/30/2016 04:43 AM »
I would assume for the propellant refrigeration system?

What propellant refrigeration system?

I would assume using densified propellants in Raptor means chilling them on Mars and in transit.
DM

Offline Dante80

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Re: ITS Development Updates and Discussion Thread
« Reply #26 on: 09/30/2016 05:12 AM »
Question: Why launch the spaceship first, then the tankers.

I think that launching the spaceship first allows more time to fettle the most important launch, the one with the humans on it, so it can be as perfect as possible. It's also going to take more time to load cargo and people than fuel. Given the long launch windows possible with this thing there is time to fix any problems with the spaceship, if there is a problem with a tanker just switch it for another one.

Thoughts?

Launching the spacecraft first requires the least number of vehicles; booster, spacecraft, and tanker.

If there was a fuel depot, then the tanker flights could fill up the depot first and the spacecraft could be the last launch, but that would require a depot or second tanker. With these vehicles costing hundreds of millions of dollars, that's a big jump in cost.

Lets say that you need 4 tanker flights to refuel the spaceship. There are three ways to do this when starting the endeavor.

1. 1x booster, 1x tanker, 1x spaceship

Flight 1: Spaceship goes up with passengers
Flights 2-3-4-5 Tankers refuel the Spaceship.

2. 1x booster 2x tanker, 1x spaceship

Flight 1: Tanker goes up.
Flights 2-3-4: Tankers refuel the tanker.
Flight 5: Spaceship goes up with passengers and refuels from the tanker.

3. 1x booster, 1x tanker, 2x spaceship

Flight 1: Spaceship goes up unmanned.
Flights 2-3-4-5 Tankers refuel the Spaceship
Flight 6: Spaceship goes up and transfers passengers.

Between the three, the first approach allows for the leanest start hardware, the second allows you to use a tanker as a fuel depot and limit the time passengers spend on the staging area and the third is simply a contigency approach Elon described if the refueling process is not as rapid (2-3 weeks) as assumed.

Interestingly enough, the second approach points to the introduction of a staging area depot in the future (it simply scales operations better as you add hardware to the system). Especially since you limit the number of rendevous and fuelling operations for the fully manned Spaceship, as well as the time the passengers have to spend on the ship before departure (using the ships' supplies).

You can simply start a more dedicated depot by bringing a tanker up with some solar arrays and added insulation to make the propellants space storable for a much larger time.
« Last Edit: 09/30/2016 05:32 AM by Dante80 »

Offline Dante80

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Re: ITS Development Updates and Discussion Thread
« Reply #27 on: 09/30/2016 05:39 AM »
I was impressed with robustness and redundancy of the engine configuration on the BFS. I have been imagining how the ship would fare if engines were lost and doing some rough calculations. I think it could probably land on Mars with any 2 engines out and land on Earth with perhaps 3 out (as long as they are not all Sea Level Raptors).

This 6-3 engine set-up seems optimized to be a minimum engine configuration to get a maximum redundancy level. But I really don't know how to quantify it.

The only engines that gimbal on the spaceship are the three atmo optimized Raptors. The only engines that gimbal on the booster are the inner 7 engines.

Btw...here is a thought. I think that the spaceship engine configuration for Mars landing is designed so that each engine gimbals slgihtly towards the fins on the very final approach so as to clear the ground for the feet at touchdown. This would introduce some cosine losses, but also make the landing on unprepared surfaces easier I think (as well as protect from debris impacting the spaceship).
« Last Edit: 09/30/2016 06:50 AM by Dante80 »

Offline biosehnsucht

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Re: ITS Development Updates and Discussion Thread
« Reply #28 on: 09/30/2016 06:34 AM »
Those cosine losses give you effectively even lower than 20% throttle, which might be also useful on it's own. They're not likely to need 3x 100% on the last seconds of landing burn...

Offline Snake

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Re: ITS Development Updates and Discussion Thread
« Reply #29 on: 09/30/2016 07:06 AM »
A 600 t BFS landing on Mars would have a weight of 3.8 x 600 = 2,280 kN. Raptor SL engines have a max. thrust of 3,050 kN, so any or all of them could be used to land.

And yes, gimballing the engines outwards while landing on an unprepared site seems like it would help reduce blowback.
« Last Edit: 09/30/2016 07:13 AM by Snake »

Offline Dante80

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Re: ITS Development Updates and Discussion Thread
« Reply #30 on: 09/30/2016 07:31 AM »
A 600 t BFS landing on Mars would have a weight of 3.8 x 600 = 2,280 kN. Raptor SL engines have a max. thrust of 3,050 kN, so any or all of them could be used to land.

And yes, gimballing the engines outwards while landing on an unprepared site seems like it would help reduce blowback.

SL Raptors on Mars surface have more than 3050 kN of thrust. If we assume that they use the same 40:1 nozzle area ratio with the BFR Raptors, then the derived thrust according to the available information should be somewhere between 3,285 kN and 3,333 kN (138 MN / 42 engines or (31MN - 6x3,500kn) /3 engines), or a little less.
« Last Edit: 09/30/2016 07:45 AM by Dante80 »

Offline Snake

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Re: ITS Development Updates and Discussion Thread
« Reply #31 on: 09/30/2016 07:56 AM »
A 600 t BFS landing on Mars would have a weight of 3.8 x 600 = 2,280 kN. Raptor SL engines have a max. thrust of 3,050 kN, so any or all of them could be used to land.

And yes, gimballing the engines outwards while landing on an unprepared site seems like it would help reduce blowback.

SL Raptors on Mars surface have more than 3050 kN of thrust. If we assume that they use the same 40:1 nozzle area ratio with the BFR Raptors, then the derived thrust according to the available information should be somewhere between 3,285 kN and 3,333 kN (138 MN / 42 engines or 31MN - 6x3,500kn) /3 engines), or a little less.

Yes, thanks, the Raptor will have a higher thrust than I said. But even at 3,333 kN, you could still throttle low enough to land a full payload on all 3 Raptor SLs, (even without gimballing cosine losses), if desired.

Offline TheTraveller

Re: ITS Development Updates and Discussion Thread
« Reply #32 on: 09/30/2016 08:26 AM »
Tim Urban has a new article about the ITS up. The title contains an easily guessable "F" word, so I won't be writing it here.

He had a discussion about it with Elon Musk several months ago, and kept quiet about it until today.

Interesting timeline attached.

1st uncrewed ITS to be launched Dec 2022!
« Last Edit: 09/30/2016 08:29 AM by TheTraveller »
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Offline TheTraveller

Re: ITS Development Updates and Discussion Thread
« Reply #33 on: 09/30/2016 09:11 AM »
Can the ITS tanker version of the spaceship do SSTO to allow orbital testing before the ITS booster files?

From the attached maybe it can do so and even carry a small test crew, assuming 91t of fuel in LEO is enough to deorbit and land.
« Last Edit: 09/30/2016 09:13 AM by TheTraveller »
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Offline Dante80

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Re: ITS Development Updates and Discussion Thread
« Reply #34 on: 09/30/2016 09:18 AM »

From the attached maybe it can do so

Musk said it cannot.

Offline TheTraveller

Re: ITS Development Updates and Discussion Thread
« Reply #35 on: 09/30/2016 09:29 AM »

From the attached maybe it can do so

Musk said it cannot.

Pax SpaceShip, sure. But the tanker at 2,590t wet and 90t dry should be capable of SSTO with 91.7t of fuel to get home.

Rocket equation for the ITS SpaceShip makes it clear SSTO is not possible as max lift is 147t and SpaceShip dry mass is 150t as attached. Even if it did just make orbit, there is no fuel to get back home.

However it should be possible for the ITS Tanker to allow testing with a small crew prior to ITS Booster availability as the 90t Tanker can make orbit with 91.7t of fuel (181.7t total LEO mass) to get back home.
« Last Edit: 09/30/2016 10:01 AM by TheTraveller »
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Offline high road

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Re: ITS Development Updates and Discussion Thread
« Reply #36 on: 09/30/2016 10:02 AM »
For those who still have a hard time visualizing how to unload cargo from so far up, here is what Elon tweeted:

https://twitter.com/elonmusk/status/781206685553528833
Quote
@BArtusio:
@elonmusk How will occupants descend from the spacecraft?At 162 ft., appears too tall to utilize ladder w/  spacesuit. Especially repeatedly

@elonmusk:
@BArtusio Three cable elevator on a crane. Wind force on Mars is low, so don't need to worry about being blown around.

So basically slightly fancier version of this classic Tin-Tin crane.  :)

Is it just me or is there a certain 'redneck on Mars' vibe to using these? European depictions of 17th-18th century America always show hay attics with these cranes. And if you count similar cranes for ships, all harbour images going back thousands of years show them. Not that romanticism about going to Mars is a problem, if the people paying for it accept the associated injury (and some death) rate. Which would go a long way in bringing down the cost of a Mars mission anyway.

So I guess people on Mars would have to embark/disembark in a basket held by the crane? Is that the fastest, safest, most efficient form of ingress/egress? What if someone has a leak in their spacesuit? Hopefully the winch won't break down. For frequent ingress/egress it might be nicer to have one of those scissor-lift things:



They could even support vehicles easily:



This comes with a mass penalty because you need the center of mass to be low for stability, and maintenance issues because the crane has a lot more moving parts, that are now standing in Martian dust and on the outside of the biggest rigid pressurized area that wasn't constrained by having to be easy to set up on Mars. Oh, and that means loading them also becomes more difficult than a retractible beam.

Offline MP99

Re: ITS Development Updates and Discussion Thread
« Reply #37 on: 09/30/2016 10:45 AM »
I would assume for the propellant refrigeration system?

What propellant refrigeration system?
Elon seemed to say that they relied on subcooled prop to avoid various issues, including cavitation.

Is it possible for prop to remain sub-cooled over a multi month Mars transit?

ISTM the alternative is to let the prop reach boiling point, then manage boiloff?

Cheers, Martin

Offline Jim

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Re: ITS Development Updates and Discussion Thread
« Reply #38 on: 09/30/2016 12:56 PM »
I would assume for the propellant refrigeration system?

What propellant refrigeration system?
Elon seemed to say that they relied on subcooled prop to avoid various issues, including cavitation.

Is it possible for prop to remain sub-cooled over a multi month Mars transit?

ISTM the alternative is to let the prop reach boiling point, then manage boiloff?

Cheers, Martin

Use the boil off for attitude control and electrical power production

Offline OneSpeed

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Re: ITS Development Updates and Discussion Thread
« Reply #39 on: 09/30/2016 02:49 PM »
Can the ITS tanker version of the spaceship do SSTO to allow orbital testing before the ITS booster files?

From the attached maybe it can do so and even carry a small test crew, assuming 91t of fuel in LEO is enough to deorbit and land.

The SL Raptor has 3,050 kN of thrust at sea level, or 311 mT. If there are only 3 SL Raptors on the tanker, that is 933 mT of thrust, which from earth is not sufficient to launch a 2590 mT ship.

Tags: ITS Spaceship SpaceX