Author Topic: ITS Development Updates and Discussion Thread  (Read 84341 times)

Offline TheTraveller

Re: ITS Development Updates and Discussion Thread
« Reply #40 on: 09/30/2016 04:35 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.

Interesting the atmo Raptors have a 361 Isp on the BFS spec sheet, which is higher than the stated atmo Isp of 334 and lower than the Vac Isp of 382 on the Raptor engine spec sheet. Just maybe they can burn all 9 engines in atmo to get a combined 361 Isp and a combined thrust of around 2,800mT?

Elon did say that on Earth, the BFS was the Launch Abort System, so the 9 x BFS Raptors much have the capacity to get the BFS away from the BFR.
« Last Edit: 09/30/2016 04:42 PM by TheTraveller »
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Offline wrvn

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Re: ITS Development Updates and Discussion Thread
« Reply #41 on: 09/30/2016 04:44 PM »
Interesting the atmo Raptors have a 361 Isp on the BFS spec sheet, which is higher than the stated atmo Isp of 334 and lower than the Vac Isp of 382 on the Raptor engine spec sheet.

Could it be that 361 Isp figure is for Mars atmosphere?

Offline Dante80

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Re: ITS Development Updates and Discussion Thread
« Reply #42 on: 09/30/2016 04:50 PM »
Here is how it works.

1. SL Raptor with 40:1 ratio nozzle

SL Isp: 334s
Vac Isp: 361s

2. Vac Raptor with 200:1 ratio nozzle

Vac Isp 382s

Both the booster and the spaceship use the same SL Raptors (in the Booster, the inner 7 have gimbals, and in the spaceship all three).The booster has an additional 35 SL Raptors that cannot gimbal, and the spaceship has six Vac Raptors that cannot gimbal.
« Last Edit: 09/30/2016 04:52 PM by Dante80 »

Offline TheTraveller

Re: ITS Development Updates and Discussion Thread
« Reply #43 on: 09/30/2016 05:02 PM »
Here is how it works.

1. SL Raptor with 40:1 ratio nozzle

SL Isp: 334s
Vac Isp: 361s

2. Vac Raptor with 200:1 ratio nozzle

Vac Isp 382s

Both the booster and the spaceship use the same SL Raptors (in the Booster, the inner 7 have gimbals, and in the spaceship all three).The booster has an additional 35 SL Raptors that cannot gimbal, and the spaceship has six Vac Raptors that cannot gimbal.

The BFS spec sheet shows atmo Raptor Isp of 361 which as all 9 BFS Raptors need to fire up to do Earth side LAS, would suggest that 361 is the averaged Isp of 3 atmo bell and 6 Vac bell Raptors running at the same time.
« Last Edit: 09/30/2016 05:02 PM by TheTraveller »
"As for me, I am tormented with an everlasting itch for things remote. I love to sail forbidden seas.”
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Offline MP99

Re: ITS Development Updates and Discussion Thread
« Reply #44 on: 09/30/2016 05:02 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

But what if the engine needs sub-cooled propellants?

Cheers, Martin


Offline IRobot

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Re: ITS Development Updates and Discussion Thread
« Reply #45 on: 09/30/2016 05:13 PM »

Look at shipping technology in Europe. When all you had to do was cross the Mediterranean, the ships were pretty lame—they couldn’t cross the Atlantic. So commerce basically had short-range vessels. Without the forcing function, shipping technology didn’t improve that much—you could do the same things with ships, pretty much, around the time of Julius Caesar as you could around the time of Columbus. 1,500 years later, you could still just cross the Mediterranean. But as soon as there was a reason to cross the Atlantic, shipping technology improved dramatically. There needed to be the American colonies in order for that to happen.
Actually, the Atlantic sailing vessels (Caravels) were developed by the Portuguese 40-50 years before Columbus, in incremental steps to be able to sail against the wind on the African coast.
Ships would be sent, they would fail, then after 2-3 years they would try with some modified ships.

The real drive for development was the discovery of the maritime path to India, America's discovery was an "accident". There were no european colonies in India, so the analogy is not correct.

Offline Dante80

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Re: ITS Development Updates and Discussion Thread
« Reply #46 on: 09/30/2016 05:14 PM »
The BFS spec sheet shows atmo Raptor Isp of 361 which as all 9 BFS Raptors need to fire up to do Earth side LAS, would suggest that 361 is the averaged Isp of 3 atmo bell and 6 Vac bell Raptors running at the same time.

I think it is pretty clear, and distinct. Read this slide.



3 seal level raptors = 361s
6 vacuum raptors   = 382s

And in another slide, it is shown that vac and SL Raptors are pretty much the same engine, with different nozzles.



If SpaceX added two lines in the second slide for sea level nozzle Raptor thrust and Isp performance in vacuum, this confusion would be averted.
« Last Edit: 09/30/2016 05:19 PM by Dante80 »

Offline TheTraveller

Re: ITS Development Updates and Discussion Thread
« Reply #47 on: 09/30/2016 05:26 PM »
The BFS spec sheet shows atmo Raptor Isp of 361 which as all 9 BFS Raptors need to fire up to do Earth side LAS, would suggest that 361 is the averaged Isp of 3 atmo bell and 6 Vac bell Raptors running at the same time.
If SpaceX added two lines in the second slide for sea level nozzle Raptor thrust and Isp performance in vacuum, this confusion would be averted.

And the sea level Isp for the vac Raptor nozzle would be?
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Offline Dante80

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Re: ITS Development Updates and Discussion Thread
« Reply #48 on: 09/30/2016 06:02 PM »
And the sea level Isp for the vac Raptor nozzle would be?

Irrelevant? Do you get an SL Isp for RL-10 or J-2X?

The vacuum Raptors are going to work strictly in vacuum, or near vacuum.Nowhere near Earth sea level with that huge nozzle.
« Last Edit: 09/30/2016 06:05 PM by Dante80 »

Offline Snake

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Re: ITS Development Updates and Discussion Thread
« Reply #49 on: 09/30/2016 06:06 PM »
And the sea level Isp for the vac Raptor nozzle would be?

Irrelevant? Do you get an SL isp for RL-10 orJ-2X?

The vacuum Raptors are going to work in vacuum.

The vacuum Raptors will work at or near sea level for some launch abort/escape sequences. I would like to know the engine's Isp at sea level for this reason alone.

Offline TheTraveller

Re: ITS Development Updates and Discussion Thread
« Reply #50 on: 09/30/2016 06:11 PM »
And the sea level Isp for the vac Raptor nozzle would be?

Irrelevant? Do you get an SL Isp for RL-10 or J-2X?

The vacuum Raptors are going to work strictly in vacuum, or near vacuum.Nowhere near Earth sea level with that huge nozzle.

All 9 BFS Raptors are used for Earth side LAS, Vac nozzles included.

BTW RPA Lite (free version):
http://www.propulsion-analysis.com/downloads.htm
calcs:

SL Nozzle (40 expansion) @ SL = 334 Isp, @ Vac = 360 Isp.
Vac Nozzle (200 expansion) @ SL = 253 Isp, @ Vac = 382 Isp.

Both at 300 bar chamber pressure, mixture ratio 2.7/2.8, fuel LCH4/LOX.
« Last Edit: 09/30/2016 06:14 PM by TheTraveller »
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Offline baldusi

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Re: ITS Development Updates and Discussion Thread
« Reply #51 on: 09/30/2016 06:14 PM »
And the sea level Isp for the vac Raptor nozzle would be?

Irrelevant? Do you get an SL isp for RL-10 orJ-2X?

The vacuum Raptors are going to work in vacuum.

The vacuum Raptors will work at or near sea level for some launch abort/escape sequences. I would like to know the engine's Isp at sea level for this reason alone.
Nope, you get flow separation issues on the 200 expanded nozzle, which might even created burn troughs. No SL ignition of vacuum optimized nozzles.

Offline TheTraveller

Re: ITS Development Updates and Discussion Thread
« Reply #52 on: 09/30/2016 06:17 PM »
And the sea level Isp for the vac Raptor nozzle would be?

Irrelevant? Do you get an SL isp for RL-10 orJ-2X?

The vacuum Raptors are going to work in vacuum.

The vacuum Raptors will work at or near sea level for some launch abort/escape sequences. I would like to know the engine's Isp at sea level for this reason alone.
Nope, you get flow separation issues on the 200 expanded nozzle, which might even created burn troughs. No SL ignition of vacuum optimized nozzles.

If so then how can the BFS engines work as LAS as Elon stated? The 3 atmo nozzled Raptors don't have enough lift for LAS.
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Offline Barrie

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Re: ITS Development Updates and Discussion Thread
« Reply #53 on: 09/30/2016 06:25 PM »
And the sea level Isp for the vac Raptor nozzle would be?

Irrelevant? Do you get an SL isp for RL-10 orJ-2X?

The vacuum Raptors are going to work in vacuum.

The vacuum Raptors will work at or near sea level for some launch abort/escape sequences. I would like to know the engine's Isp at sea level for this reason alone.
Nope, you get flow separation issues on the 200 expanded nozzle, which might even created burn troughs. No SL ignition of vacuum optimized nozzles.

Wouldn't you be quite happy to trash the nozzles for an abort?

Offline JasonAW3

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Re: ITS Development Updates and Discussion Thread
« Reply #54 on: 09/30/2016 06:26 PM »
Comparing sizes again:

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

Wonder if a Methalox Sea Dragon would be feasible?
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Offline notsorandom

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Re: ITS Development Updates and Discussion Thread
« Reply #55 on: 09/30/2016 06:39 PM »
Wouldn't you be quite happy to trash the nozzles for an abort?
Not if it creates asymmetric thrust that cannot be compensated for.

Offline rubicondsrv

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Re: ITS Development Updates and Discussion Thread
« Reply #56 on: 09/30/2016 06:49 PM »
Wouldn't you be quite happy to trash the nozzles for an abort?
Not if it creates asymmetric thrust that cannot be compensated for.

IMO that will be sorted out at some point.   this is still very early in the design process and many things can change.   

it would be quite possible to design a mechanism to shorten the nozzle in an abort if the overexpansion would not be tolerable for a few seconds.  however this would add weight to the engine

given how much remains to be done before production expect many changes to the final version before production.   

Offline DanielW

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Re: ITS Development Updates and Discussion Thread
« Reply #57 on: 09/30/2016 06:51 PM »
Wouldn't you be quite happy to trash the nozzles for an abort?
Not if it creates asymmetric thrust that cannot be compensated for.

There must be a way to pryo cut the nozzle in this case. Or release a band that holds it on.

Offline Robotbeat

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Re: ITS Development Updates and Discussion Thread
« Reply #58 on: 09/30/2016 08:03 PM »
And the sea level Isp for the vac Raptor nozzle would be?

Irrelevant? Do you get an SL isp for RL-10 orJ-2X?

The vacuum Raptors are going to work in vacuum.

The vacuum Raptors will work at or near sea level for some launch abort/escape sequences. I would like to know the engine's Isp at sea level for this reason alone.
Nope, you get flow separation issues on the 200 expanded nozzle, which might even created burn troughs. No SL ignition of vacuum optimized nozzles.

If so then how can the BFS engines work as LAS as Elon stated? The 3 atmo nozzled Raptors don't have enough lift for LAS.
Not enough thrust for pad abort, unless you severed the nozzle to prevent flow sep. but would still have enough thrust for some abort scenarios. With liquid rockets, you can reliably terminate thrust of the booster engines in case of abort.
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Offline RoboGoofers

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Re: ITS Development Updates and Discussion Thread
« Reply #59 on: 09/30/2016 08:15 PM »
lets not forget what abort means with ITS; propulsive landing or abort to orbit only. Without the vac bells, maybe only landing. with a full load of fuel, cargo and passengers, abort sounds about as comforting as 'aborting' an airplane into a forest.
« Last Edit: 09/30/2016 09:24 PM by RoboGoofers »

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