Author Topic: Operating the ITS spaceship or tanker as an SSTO launch vehicle.  (Read 10262 times)

Offline envy887

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By popular demand, I'm splitting this topic from the SFR thread, which started wandering here:

https://forum.nasaspaceflight.com/index.php?topic=36508.msg1592782#msg1592782

I'll link some interesting simulations here for reference:

https://forum.nasaspaceflight.com/index.php?topic=36508.msg1626668#msg1626668

Also a video of a hypothetical 12-Raptor BFS simulated launch trajectory, credit to OneSpeed:


Online Robotbeat

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Looking good. Yeah, something like this would be great for bulk passenger launch to LEO, especially if you could afford some sort of escape system with the mass you can get to orbit.
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Offline RocketmanUS

Two version options for the BFS SSTO based on the BFS tanker
1 ) 9 sea level Raptors
2 ) 12 sea level Raptors

Option 1 would be the simpler change by exchanging 6 vacuum Raptors for 6 sea level Raptors and lowering them down to were their bell nozzles would match the 3 center sea level engine bell nozzles.

Option 2 would need new plumbing , thrust structure , and a little more dry mass.

Would these changes and low production rate raise the per unit cost?
How many units per year were expected to get the per unit cost SpaceX had for their tanker and crew version?

As these are modified BFS tankers there is still room at top for cargo, the propellant tanks are taller for the tanker version compared to the crew version. A hatch or cargo bay doors would need to be add in the top area of the BFS. Cargo bay doors similar to the space shuttle would seem the easiest way to get cargo in and out of the cargo bay. A hatch near the top were cargo could be slid in and out would be another option. Smaller opening, possibly easier to cover when placing cargo in before launch and keep it clean. If using doors like the shuttle then something like shuttle had might be needed out at the launch pad to load cargo.
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Online OneSpeed

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Option 2 would need new plumbing , thrust structure , and a little more dry mass.

Yes, I had estimated an extra 10mT for 12 Raptor 80 vs. 3 Raptor 50 + 6 Raptor Vac. That seems to line up pretty well with envy887's assessment here: https://forum.nasaspaceflight.com/index.php?topic=41809.msg1628146#msg1628146

Offline RocketmanUS

Option 2 would need new plumbing , thrust structure , and a little more dry mass.

Yes, I had estimated an extra 10mT for 12 Raptor 80 vs. 3 Raptor 50 + 6 Raptor Vac. That seems to line up pretty well with envy887's assessment here: https://forum.nasaspaceflight.com/index.php?topic=41809.msg1628146#msg1628146
What is the expected thrust , ISP ( SL , vac ), and dry mass of the Raptor 80?

Looking at that other post it looks like the 12-Raptor 80 BFS could be a little more than 10mt added dry mass.
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Offline envy887

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Option 2 would need new plumbing , thrust structure , and a little more dry mass.

Yes, I had estimated an extra 10mT for 12 Raptor 80 vs. 3 Raptor 50 + 6 Raptor Vac. That seems to line up pretty well with envy887's assessment here: https://forum.nasaspaceflight.com/index.php?topic=41809.msg1628146#msg1628146
What is the expected thrust , ISP ( SL , vac ), and dry mass of the Raptor 80?

Looking at that other post it looks like the 12-Raptor 80 BFS could be a little more than 10mt added dry mass.

Based on some old RPA simulations (I'll have to re-run these to double check):
A plausible mission architecture that requires minimal additional development could based on the development of a SSME-style nozzle for Raptor, with an expansion ratio of 80:1 and diameter of 2.3 m,. This could enable SL trust of 3080 kN at 330 s ISP and vac thrust of 3300 kN at 374 s ISP.

And based on some extrapolation from Merlin, using SSME as an extra data point (these are SWAGs, take for what that's worth):
I'm estimating that SL Raptors will mass around 2,500 kg and vac raptors about 3,000 kg, while a 80:1 vac engine would mass ~2,800 kg.

So by my rough estimates, replacing six vac engines with nine 80:1 engines adds 8,100 kg.

Offline RocketmanUS

Option 2 would need new plumbing , thrust structure , and a little more dry mass.

Yes, I had estimated an extra 10mT for 12 Raptor 80 vs. 3 Raptor 50 + 6 Raptor Vac. That seems to line up pretty well with envy887's assessment here: https://forum.nasaspaceflight.com/index.php?topic=41809.msg1628146#msg1628146
What is the expected thrust , ISP ( SL , vac ), and dry mass of the Raptor 80?

Looking at that other post it looks like the 12-Raptor 80 BFS could be a little more than 10mt added dry mass.

Based on some old RPA simulations (I'll have to re-run these to double check):
A plausible mission architecture that requires minimal additional development could based on the development of a SSME-style nozzle for Raptor, with an expansion ratio of 80:1 and diameter of 2.3 m,. This could enable SL trust of 3080 kN at 330 s ISP and vac thrust of 3300 kN at 374 s ISP.

And based on some extrapolation from Merlin, using SSME as an extra data point (these are SWAGs, take for what that's worth):
I'm estimating that SL Raptors will mass around 2,500 kg and vac raptors about 3,000 kg, while a 80:1 vac engine would mass ~2,800 kg.

So by my rough estimates, replacing six vac engines with nine 80:1 engines adds 8,100 kg.
RL10A-4-2 ( 368 lb )
RL10B-2    ( 611 lb )
B version has a large extension nozzle, that could be the big increase in mass. The Raptor vac. have a much larger nozzle than the sea level Raptors. The vac. version could have a much greater mass. I think it best to ask a forum expert on rocket engines what the masses might be and for their mount point and plumbing masses.

For just the 9 sea level Raptors ( expansion ratio 40 ) BFS it looks like it should be possible to deliver a Cygnus ( enhanced version ) to ISS and bring it down again.
https://en.wikipedia.org/wiki/RL10
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Online guckyfan

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For a minimal design change version, how would a vehicle with only six Raptor 80 work, leaving the 3 central sea level Raptor unchanged? That would work without changing plumbing and thrust structure for maximum commonality with the standard ITS.

Online OneSpeed

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For a minimal design change version, how would a vehicle with only six Raptor 80 work, leaving the 3 central sea level Raptor unchanged? That would work without changing plumbing and thrust structure for maximum commonality with the standard ITS.

I've run a quick simulation of your suggestion, and the results look like this:

ConfigurationMass to 300 x 300Vehicle massPayload
9 x Raptor 400 mT89 mT0mT
9 x Raptor 50190 mT90 mT28mT
3 x Raptor 50 + 6 x Raptor 80196 mT92 mT32mT
12 x Raptor 80240 mT100 mT67mT

So, perhaps an extra 4mT to orbit, but you would have the extra cost of development of the Raptor 80.
« Last Edit: 01/12/2017 11:41 AM by OneSpeed »

Offline Bynaus

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Interesting. Wouldn't that be a fully reusable replacement for the Falcon 9? At least the ones going to LEO?

Offline envy887

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Interesting. Wouldn't that be a fully reusable replacement for the Falcon 9? At least the ones going to LEO?

Kind of. The payload disappears really fast for higher orbits. It's can't deliver anything directly to SpaceX's planned constellation. But it could work very well using transfer orbits with the payload doing circularization. For lower SSO like Iridium, and for LEO like Orbcomm it would be good.

It's kind of a kludge for Dragon launches. Might work, but doesn't seem worthwhile since F9 can already do booster RTLS on those.

A human rated SSTO dedicated as an LEO taxi, with a large (~100) capacity and full cabin abort abilities, is probably feasible based on this concept. That would be awesome, but would take a fair amount of modifications and development work.

Online Robotbeat

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The constellation sats are solar-electric. They could raise the orbit themselves.
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Offline Bynaus

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Quote
It's kind of a kludge for Dragon launches. Might work, but doesn't seem worthwhile since F9 can already do booster RTLS on those.

Yes - but you also lose an upper stage each time you use a F9 instead of a ITS-SSTO. The later needs more fuel, but fuel is cheap. Could ITS-SSTO do ISS crew missions? You wouldn't have to do 100 crew - only 6 or so (which doesn't mean that there wouldn't be a market for a 100 pax SSTO...).

Online Robotbeat

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I think the main point of a ship like this would be as a people mover either to LEO (as you can do it safer as a single stage and perhaps even afford an abort system) or possibly even (cargo?) point to point.
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Offline RocketmanUS

For a minimal design change version, how would a vehicle with only six Raptor 80 work, leaving the 3 central sea level Raptor unchanged? That would work without changing plumbing and thrust structure for maximum commonality with the standard ITS.

I've run a quick simulation of your suggestion, and the results look like this:

ConfigurationMass to 300 x 300Vehicle massPayload
9 x Raptor 400 mT89 mT0mT
9 x Raptor 50190 mT90 mT28mT
3 x Raptor 50 + 6 x Raptor 80196 mT92 mT32mT
12 x Raptor 80240 mT100 mT67mT

So, perhaps an extra 4mT to orbit, but you would have the extra cost of development of the Raptor 80.
Raptor 50? Or should that just  be Raptor 40?

The 9 Raptor 40 should get payload to orbit.

Interesting. Wouldn't that be a fully reusable replacement for the Falcon 9? At least the ones going to LEO?
Not for Dragon or direct to GTO,GSO, or escape. However cargo that could fit in the cargo bay could take a ride to LEO and then SEP could take the payload to it's needed orbit. Propellant for SEP tugs and satellite refueling could be delivered by the BFS SSTO.

Crew would need an escape system added.
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Offline drzerg

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one of the applicatioun for SSTO ITS spaceship is to test it on orbit separately of booster developement. testing includes orbit operations and atmospheric landings (heat shield optimisations)
« Last Edit: 01/12/2017 08:29 PM by drzerg »

Online Robotbeat

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You can do that without a useful SSTO capability. Just like X-33, you can test those things Suborbitally.
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Online OneSpeed

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The 9 Raptor 40 should get payload to orbit.

Perhaps it depends on what you are assuming is the SL thrust of the Raptor 40? I'm using the figures from the Reddit AMA: Approx 360s vacuum Isp and 290 mT of thrust. So, thrust to weight at liftoff is 290 x 9 / 2590 or 1.01. The simulation of launch is excruciating to watch. It takes 27 seconds just to clear the tower, by which time over 200mT of fuel has been burnt, and only 15 m/s of velocity has been gained. I get about 150mT to 300 x 300 kms, compared with 190mT using Raptor 50s. I suspect that 40mT difference would cancel the 28mT payload, as well as 12mT of the fuel required for landing.


Offline envy887

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There's no point in using a 40:1 nozzle on the BFS. Musk's presentation clearly showed it with only 200:1 and 50:1 nozzles, so there is plenty of room for bigger nozzles.

The only point of the 40:1 is packing 42 of them tightly under BFR. That's not an issue on BFS.

Offline RocketmanUS

There's no point in using a 40:1 nozzle on the BFS. Musk's presentation clearly showed it with only 200:1 and 50:1 nozzles, so there is plenty of room for bigger nozzles.

The only point of the 40:1 is packing 42 of them tightly under BFR. That's not an issue on BFS.
Were in his presentation does it show a 50:1 nozzle for the BFS?
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Offline envy887

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Here are the engines from the full vehicle cutaway image, overlaid next to each other. There is no perspective distortion, as you can tell from the 12m main tank diameters matching perfectly. The "sea level" nozzles on the spaceship are clearly more expanded than those on the booster. Measuring the image gives a value of about 20% larger.

Perhaps this is meaningless overanalysis, but I don't think so. And it does make sense to have larger nozzles on the spaceship, for reasons noted above.

Online OneSpeed

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Yes, by comparing the IAC Mexico images with those generated using a simple rendering program:

Raptor 40, 1.51m
Raptor 50, 1.78m
Raptor Vac, 3.8m
« Last Edit: 01/13/2017 09:51 PM by OneSpeed »

Offline dglow

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Good to see! I pointed this out back in October but nobody took the bait.  ???

Offline RocketmanUS

Are the images to scale?

Slide 36 from the SX PDF on ITS
Quote:
" 3 Sea-Level - 361s ISP "
" 6 Vacuum - 382s ISP "

When it says 3 Sea Level that is referring to three sea level engines. I believe those are the vacuum ratings for both engines.

Slide 26 does show the BFS sea level engine bell larger than the BFR sea level engine. However this image might not be to scale. Compare the length and diameter of the BFS and the BFR.

We would need to hear from SpaceX on this.

Anyway Raptor 80 could possible give the best mass to orbit if it's specs are correct.
Sea level thrust and ISP?
Vacuum thrust and ISP?
Chamber pressure?
Dry mass.
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Offline envy887

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Are the images to scale?

Slide 36 from the SX PDF on ITS
Quote:
" 3 Sea-Level - 361s ISP "
" 6 Vacuum - 382s ISP "

When it says 3 Sea Level that is referring to three sea level engines. I believe those are the vacuum ratings for both engines.

Slide 26 does show the BFS sea level engine bell larger than the BFR sea level engine. However this image might not be to scale. Compare the length and diameter of the BFS and the BFR.

They are to scale in the image I posted: the tank diameters are identical and there is no perspective distortion.

Quote
We would need to hear from SpaceX on this.

Anyway Raptor 80 could possible give the best mass to orbit if it's specs are correct.
Sea level thrust and ISP?
Vacuum thrust and ISP?
Chamber pressure?
Dry mass.

From a RPA sim using LOX/LCH4 at 300 bar, 3.800 O/F, 80:1 expansion from .0582 m2 throat, 100% bell nozzle length and 99.50% reaction efficiency, the expected actual performance (not theoretical best performance, which is a couple percent higher) is:
SL: 3005 kN at 323.2 s
Vacuum: 3479 kN at 372.2 s

My mass estimate is ~2800 kg
. Mvac sans nozzle is ~600 kg at 934 kN, and mass scales roughly with thrust, which would put the R80 at 2230 kg. I'm adding ~570 kg for the 80:1 nozzle and added mass penalties of FFSC cycle compared to GG and methalox compared to kerolox.

Edit: the nozzle exit diameter for this specific configuration would be 2.43 meters. The throat diameter is the same as the 200:1 engine.
« Last Edit: 01/14/2017 01:34 PM by envy887 »

Offline john smith 19

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This is highly entertaining but I've yet to see any definition on how this stage will reenter and land the key issues.

Isp is obviously important, as is how it varies on altitude. So is heating rate as that will set the amount of TPS you have to carry (or fuel you stream through the bells in the early stages of reentry).

It's known that all Vertical Takeoff & Landing SSTO concepts are critically dependent on Isp and structural mass fraction.

The SSME bells were IIRC 77:1 but Raptor should be able to do better. That matters if you're tracking Isp change with altitude and you plan to use a straight single position Rao nozzle.
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Offline envy887

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I don't think any modifications have been proposed that would significantly affect the EDL sequence as described in the IAC presentation. EDL should work essentially the same for SSTO ITS as TSTO ITS.

Online Robotbeat

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It's known that all Vertical Takeoff & Landing SSTO concepts are critically dependent on Isp and structural mass fraction.
...
This is true whether vertical, horizontal, or diagonal takeoff/landing SSTO RLV.

Even true for Skylon, which has to have ridiculously* good mass fraction (from a volumetric perspective).


*but perhaps still achievable
« Last Edit: 01/16/2017 05:03 PM by Chris Bergin »
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Online OneSpeed

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...
We would need to hear from SpaceX on this.
...

Here are the Raptor figures I'm using in SpaceSim. Most of these figures have been published by SpaceX or mentioned in the Reddit AMA. I've simply interpolated to get my Raptor 80 figures. The mass estimates are envy's, they sound pretty reasonable to me.

   Cycle            Full-flow staged combustion
   Oxidiser         Subcooled liquid oxygen
   Fuel            Subcooled liquid methane
   Chamber pressure   300 bar or 30 MPa
   Throttle capability 20% to 100% thrust

   Sea-level Nozzle
      Expansion Ratio   40
      Thrust (SL)      2,842 kN
      Thrust (Vac)   3,061 kN
      Isp (SL)      333s
      Isp (Vac)      360s
      Diameter      1.51m
      Mass         2400 kg
      
      Expansion Ratio   50
      Thrust (SL)      3,094 kN
      Thrust (Vac)   3,333 kN
      Isp (SL)      334s
      Isp (Vac)      361s
      Diameter      1.78m
      Mass         2500 kg
      
      Expansion Ratio   80
      Thrust (SL)      3,200 kN
      Thrust (Vac)   3,400 kN
      Isp (SL)      336s
      Isp (Vac)      368s
      Diameter      2.4m
      Mass         2800 kg
      
   Vacuum Nozzle
      Expansion Ratio   200
      Thrust         3,500 kN
      Isp            382s
      Diameter      3.8m
      Mass          3000 kg

Offline RocketmanUS

...
We would need to hear from SpaceX on this.
...

Here are the Raptor figures I'm using in SpaceSim. Most of these figures have been published by SpaceX or mentioned in the Reddit AMA. I've simply interpolated to get my Raptor 80 figures. The mass estimates are envy's, they sound pretty reasonable to me.

   Cycle            Full-flow staged combustion
   Oxidiser         Subcooled liquid oxygen
   Fuel            Subcooled liquid methane
   Chamber pressure   300 bar or 30 MPa
   Throttle capability 20% to 100% thrust

   Sea-level Nozzle
      Expansion Ratio   40
      Thrust (SL)      2,842 kN
      Thrust (Vac)   3,061 kN
      Isp (SL)      333s
      Isp (Vac)      360s
      Diameter      1.51m
      Mass         2400 kg
      
      Expansion Ratio   50
      Thrust (SL)      3,094 kN
      Thrust (Vac)   3,333 kN
      Isp (SL)      334s
      Isp (Vac)      361s
      Diameter      1.78m
      Mass         2500 kg
      
      Expansion Ratio   80
      Thrust (SL)      3,200 kN
      Thrust (Vac)   3,400 kN
      Isp (SL)      336s
      Isp (Vac)      368s
      Diameter      2.4m
      Mass         2800 kg
      
   Vacuum Nozzle
      Expansion Ratio   200
      Thrust         3,500 kN
      Isp            382s
      Diameter      3.8m
      Mass          3000 kg
First thanks  :) .

First we have this quote-
Questions and Answers from the I am Elon Musk, ask me anything about becoming a spacefaring civ! AMA on the /r/spacex Reddit site pertaining to reentry and landing:


https://www.reddit.com/r/spacex/comments/590wi9/i_am_elon_musk_ask_me_anything_about_becoming_a/d94vcmw/?context=3
Quote
Question from __Rocket__

ITS Spaceship design question II.:

The ITS Spaceship has two mystical spherical tanks, marked green in this slightly edited image. The whole tank design looks very exciting, and there's rampant speculation on this sub about the purpose of those spherical tanks:

    are they for landing fuel?
    ... or are they storing 'hot' gaseous propellants as part of the autogenous propellant pressurization system?
    ... or are they used for on-orbit propellant densification to store vapor before it's liquefied again?

All of the above perhaps?



Answer from /u/ElonMuskOfficial

Those are the header tanks that contain the landing propellant. They are separate in order to have greater insulation and minimize boil-off, avoid sloshing on entry and not have to press up the whole main tank.


https://www.reddit.com/r/spacex/comments/590wi9/i_am_elon_musk_ask_me_anything_about_becoming_a/d94vdk1/?context=3
Quote
Question from /u/_rocketboy

Also, why does the booster only have one in 1 tank?



Answer from /u/ElonMuskOfficial

The liquid oxygen transfer tube serves as the header tank for ox

https://www.reddit.com/r/spacex/comments/590wi9/i_am_elon_musk_ask_me_anything_about_becoming_a/d94v8p8/?context=3
Quote
Question from /u/FoxhoundBat

    Overall is the landing architecture of ITS booster and distances needed to be covered to be same as Falcon 9s? Boostback, re-entry burn, landing burn?

    Could you give us nuggets on what changes the final Falcon 9 version (v1.3) you mentioned will have? Uprated engines obviously from 170k to 190k lbf, but what else? Is it mostly geared towards reusabilty over performance?

    Gwynne mentioned 2 weeks ago that F9 v1.2 will be reused only once or twice while v1.3 should be reused up to 10 times. Can you talk about what are the limiting factors for Falcon 9 reuse?



Answer from /u/ElonMuskOfficial
The big booster will have an easier time of things than Falcon, as the mass ratio of the stages is lower and it will have lower density. Net result is that it won't come in quite as hot and fast as Falcon, so Falcon should be a bounding case on the big booster.

Final Falcon 9 has a lot of minor refinements that collectively are important, but uprated thrust and improved legs are the most significant.

Actually, I think the F9 boosters could be used almost indefinitely, so long as there is scheduled maintenance and careful inspections. Falcon 9 Block 5 -- the final version in the series -- is the one that has the most performance and is designed for easy reuse, so it just makes sense to focus on that long term and retire the earlier versions. Block 5 starts production in about 3 months and initial flight is in 6 to 8 months, so there isn't much point in ground testing Block 3 or 4 much beyond a few reflights.

https://www.reddit.com/r/spacex/comments/590wi9/i_am_elon_musk_ask_me_anything_about_becoming_a/d94ukv8/?context=3
Quote
Question from /u/termderd

We got a pretty good idea of what a Mars EDL looks like, but can you explain how the ITS and the Tanker plan to do an Earth EDL? Having talked with you at IAC about the Mars entry, we learned that there's very powerful thrusters that can handle attitude control. These work great for the Martian atmosphere, but what about on earth? There doesn't appear to be grid fins and the thrusters obviously have less authority here on earth, so what's the trick?

Thanks for your time!

    Tim Dodd, The Everyday Astronaut



Answer from /u/ElonMuskOfficial

Good question -- that wasn't shown at IAC. The spaceship and tanker would have split body flaps for pitch and roll. Probably just use the attitude control thrusters for yaw.

https://www.reddit.com/r/spacex/comments/590wi9/i_am_elon_musk_ask_me_anything_about_becoming_a/d94ub7h/?context=3
Quote
Question from /u/Tesla_X_City:
If I recall correctly on one of the slides it mentioned that there it will be 4-6 G's upon reentry. It does not specify, however, whether that will be during the landing burn or aerobreaking. It would be nice if that is clarified as well.



Answer from /u/ElonMuskOfficial

The spaceship would be limited to around 5 g's nominal, but able to take peak loads 2 to 3 times higher without breaking up.

Booster would be nominal of 20 and maybe 30 to 40 without breaking up.

https://www.reddit.com/r/spacex/comments/590wi9/i_am_elon_musk_ask_me_anything_about_becoming_a/d94u6zk/?context=3
Quote
Question from /u/TheVehicleDestroyer

Hi Elon. Ive got 3 questions on the ITS vehicle specs:

    Can you divulge what the Vacuum Thrust+Isp figures are for the Sea-Level Raptor variant?

    The ITS booster is able to hover. Will it ever use this capability to better ensure a successful landing at the expense of some small gravity losses, or is it hoverslams all the way?

    What is the expected maximum acceleration that the ITS booster can withstand during entry/landing?

Thanks for everything.



Answer from /u/ElonMuskOfficial

    Approx 360 sec vacuum Isp and 290 metric tons of thrust
    A high acceleration landing is a lot more efficient, so there wouldn't be any hovering unless it encountered a problem or unexpected wind conditions. A rocket that lands slowly is wasting a lot of fuel.
    Aiming for 20 g's


Then we have this quote-
Just noticed that SpaceX posted higher resolution photos of the raptor test fire on flickr than were attached to Elon's original tweets (as originally posted below). I can't see these higher resolutions posted earlier in this, or the previous ITS propulsion thread.

Quote from: Elmar Moelzer link=topic=34197.msg1588736#msg1588736
Elon Musk on Twitter:
SpaceX propulsion just achieved first firing of the Raptor interplanetary transport engine
https://twitter.com/elonmusk/status/780280440401764353

Production Raptor goal is specific impulse of 382 seconds and thrust of 3 MN (~310 metric tons) at 300 bar
https://twitter.com/elonmusk/status/780275236922994688
So what do you make of this?

As the Raptor 80 could give the best payload mass should we use it for the BFS SSTO ( tanker version modified to carry payload at it's top portion )? And double check the specs for this Raptor variant?
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Offline RocketmanUS

For a minimal design change version, how would a vehicle with only six Raptor 80 work, leaving the 3 central sea level Raptor unchanged? That would work without changing plumbing and thrust structure for maximum commonality with the standard ITS.

I've run a quick simulation of your suggestion, and the results look like this:

ConfigurationMass to 300 x 300Vehicle massPayload
9 x Raptor 400 mT89 mT0mT
9 x Raptor 50190 mT90 mT28mT
3 x Raptor 50 + 6 x Raptor 80196 mT92 mT32mT
12 x Raptor 80240 mT100 mT67mT

So, perhaps an extra 4mT to orbit, but you would have the extra cost of development of the Raptor 80.
OK , so I just subtracted the six vacuum Raptor engine thrust from the BFS total vacuum thrust and divided by three to get the vacuum thrust of the sea level engines. 333,333,333 N, so that is the same for your figures for the Raptor 50 , so will have to call it three versions for Raptor.

9 Raptor 50 at ~28 mt would be impressive.
12 Raptor 80 at ~67 mt would be even more impressive.
That is even after adding in the mass for a hatch ( or door ) along with a cargo bay the up/down payload mass.

What is the propellant mass at liftoff for the 9 and 12 Raptor 80 models?

Has anyone measured the volume of the BFS crew version propellant tanks? If so how much propellant can they hold by mass? How high will the tanks rise into the cargo area for these concept SSTO BFR's ( 9 and 12 engine versions ). This is to calculate how much possible volume is left for possible payload ( height of tank to top of BFS ).
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Offline john smith 19

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Since expansion ratio is quite important to this it might help to know what at what level flow separation is likely to take place.

A common rule of thumb is when the nozzle outlet pressure is < 0.4 of the ambient pressure. More accurate tests based on real nozzles reckon this is conservative and 0.34 of Pambient is safe.

At 300 bar with 1 Atm at 101326 Pa and 14.7psi to 1 Atm that's 4352 psi, close to double the SSME's chamber pressure.

That's suggests you could go higher than 80 expansion ratio at Earth SL takeoff, which is the critical limit for takeoff thrust, stresses etc.  Bigger expansion ratio is the #1 choice of engine designers when they want more Isp, but I don't have a feel for how chamber pressure scales with expansion ratio.

If you're going to chase the VTOL SSTO concept you need all the low hanging fruit you can get to make it work.

"Solids are a branch of fireworks, not rocketry. :-) :-) ", Henry Spencer 1/28/11  Averse to bold? You must be in marketing."It's all in the sequencing" K. Mattingly.  STS-Keeping most of the stakeholders happy most of the time.

Online OneSpeed

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Since expansion ratio is quite important to this it might help to know what at what level flow separation is likely to take place.

A common rule of thumb is when the nozzle outlet pressure is < 0.4 of the ambient pressure. More accurate tests based on real nozzles reckon this is conservative and 0.34 of Pambient is safe.

At 300 bar with 1 Atm at 101326 Pa and 14.7psi to 1 Atm that's 4352 psi, close to double the SSME's chamber pressure.

That's suggests you could go higher than 80 expansion ratio at Earth SL takeoff, which is the critical limit for takeoff thrust, stresses etc.  Bigger expansion ratio is the #1 choice of engine designers when they want more Isp, but I don't have a feel for how chamber pressure scales with expansion ratio.

If you're going to chase the VTOL SSTO concept you need all the low hanging fruit you can get to make it work.

I agree that given the outstanding chamber pressure of the Raptor, the expansion ratio could be a little higher, although you would loose some of the ability to throttle deeply. The sims I've run so far indicate that going from 9 Raptor 50s to 6 Raptor 80s + 3 Raptor 50s gains you about 4mT to orbit. Going to say 9 Raptor 90s might gain you another couple of tons.

However, for SSTO, increasing thrust made a far bigger difference. Having 12 Raptor 80s added 39mT to the payload, mostly because of reduced gravity losses, rather than better Isp. I would argue that T/W is actually the low hanging fruit for SSTO of the ITS (not saying better Isp doesn't help).

Online guckyfan

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However, for SSTO, increasing thrust made a far bigger difference. Having 12 Raptor 80s added 39mT to the payload, mostly because of reduced gravity losses, rather than better Isp. I would argue that T/W is actually the low hanging fruit for SSTO of the ITS (not saying better Isp doesn't help).

But going to 12 Raptor would require a basically new thrust structure, almost a new rocket. Staying at 9 would be much less development intensive so a lot cheaper.

Online Semmel

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However, for SSTO, increasing thrust made a far bigger difference. Having 12 Raptor 80s added 39mT to the payload, mostly because of reduced gravity losses, rather than better Isp. I would argue that T/W is actually the low hanging fruit for SSTO of the ITS (not saying better Isp doesn't help).

But going to 12 Raptor would require a basically new thrust structure, almost a new rocket. Staying at 9 would be much less development intensive so a lot cheaper.

So what this basically means is.. if Raptor takes a similar development as the Merlin and increases its thrust by, say 50% over the first couple of years of using it, an ITS SSTO might be a reasonable thing to look for. I wouldnt count on that though since ITS might grow with the Raptor performance to maximize payload to Orbit.

Given your simulations OneSpeed, I dont think we will see an ITS SSTO and I agree with Guckyfan, a 12-Raptor version of the ITS is probably not going to happen. Time will tell of course.

Offline envy887

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Increasing expansion does eventually lead to seperation at sea level, at about 140:1, but SL thrust drops to 2715 kN per engine and ISP drops to 292s. On a thrust-limited design this is a poor trade-off, even though vacuum ISP is close to 380.

However, instead of nine 80:1 nozzles it might make sense to have a mix of 50:1 and 140:1. The former have much higher thrust and ISP at SL, and the latter have higher thrust and ISP in vacuum, but both are operable (if needed) across the entire flight. The 50:1 engines could be shut down to improve overall ISP once the vehicle is high enough (and light enough) that the 140:1 nozzles can maintain optimal acceleration.

Online OneSpeed

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Increasing expansion does eventually lead to seperation at sea level, at about 140:1, but SL thrust drops to 2715 kN per engine and ISP drops to 292s. On a thrust-limited design this is a poor trade-off, even though vacuum ISP is close to 380.

However, instead of nine 80:1 nozzles it might make sense to have a mix of 50:1 and 140:1. The former have much higher thrust and ISP at SL, and the latter have higher thrust and ISP in vacuum, but both are operable (if needed) across the entire flight. The 50:1 engines could be shut down to improve overall ISP once the vehicle is high enough (and light enough) that the 140:1 nozzles can maintain optimal acceleration.

That's an interesting concept, but for SL that gives:

(3 * 3,094 + 6 * 2,715) / 9.8 = 2609mT thrust.

So T/W = 2609 / 2590 = 1.01, the same as for 9 Raptor 40s. I suspect the gravity losses at low altitude would be similar, with a similar payload to a 300 x 300 km orbit (unfortunately none).

...
Given your simulations OneSpeed, I dont think we will see an ITS SSTO and I agree with Guckyfan, a 12-Raptor version of the ITS is probably not going to happen. Time will tell of course.

Actually I suspect the same, but I was asked to provide the sims, so I'm just trying to help where I can. More thrust is the only way I can see the SSTO having a chance, but even then, it seems more efficient to use the full BFR/BFS stack, and if small payloads are required, deliver more of them with each flight.

Offline john smith 19

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Actually I suspect the same, but I was asked to provide the sims, so I'm just trying to help where I can. More thrust is the only way I can see the SSTO having a chance, but even then, it seems more efficient to use the full BFR/BFS stack, and if small payloads are required, deliver more of them with each flight.
This has always been the issue with VTO SSTO.

VTO TSTO gives you 3-4% of GTOW. Historically people have been willing to accept 1% of GTOW for SSTO.  There is only one known architecture that can deliver a TSTO payload and that can't land on Mars.
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Online Robotbeat

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I fail to see how vertical or horizontal makes any difference there. The problem is the same.
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Offline RocketmanUS

For a minimal design change version, how would a vehicle with only six Raptor 80 work, leaving the 3 central sea level Raptor unchanged? That would work without changing plumbing and thrust structure for maximum commonality with the standard ITS.

I've run a quick simulation of your suggestion, and the results look like this:

ConfigurationMass to 300 x 300Vehicle massPayload
9 x Raptor 400 mT89 mT0mT
9 x Raptor 50190 mT90 mT28mT
3 x Raptor 50 + 6 x Raptor 80196 mT92 mT32mT
12 x Raptor 80240 mT100 mT67mT

So, perhaps an extra 4mT to orbit, but you would have the extra cost of development of the Raptor 80.
12 Raptor 80 how much propellant mass were you using?
What is the maximum propellant mass for the tanker for their propellant tank size?
SX PDF slide 36 show 2,500 mt propellant.
And shows 380 mt propellant delivered to orbit. I assume that was part of the 2,500 mt and not extra.
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Offline rakaydos

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I fail to see how vertical or horizontal makes any difference there. The problem is the same.
I'd argue that Airlaunch (horizontal takeoff TSTO) is different enough from traditional rocketry to merit a distinction, but that Horizontal SSTO suffers from the worst of both worlds.

Now, if we could get an airllaunch stage that could compete with the capability of even a RTLS Falcon 9 first stage... Upper atmoshphere with a high mach number, and all that. SCRAMjet and SABER may be possibiities in the future... as is, amusingy enough, certian blimp concepts.

Online OneSpeed

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12 Raptor 80 how much propellant mass were you using?
What is the maximum propellant mass for the tanker for their propellant tank size?
SX PDF slide 36 show 2,500 mt propellant.
And shows 380 mt propellant delivered to orbit. I assume that was part of the 2,500 mt and not extra.

I was assuming the same propellant mass as the maximum for the ITS tanker, i.e. 2500mT, for a GLOW of 2600mT. And yes, that the 380mT ITS Tanker payload would be residual from its 2500mT of propellant.

Offline john smith 19

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I'd argue that Airlaunch (horizontal takeoff TSTO) is different enough from traditional rocketry to merit a distinction, but that Horizontal SSTO suffers from the worst of both worlds.
The classic question of air launch is "Does it let us remove a stage." Historically the answer has been "no," so you're down to other benefits like lower development costs (if you're using more or less existing stages, as Orbital did with Pegasus).

The upside of HTO is that wings let you build bigger vehicles as you need thrust which is 1/3 to 1/2 the GTOW. VTO needs thrust >1x GTOW (at least 1.1). Wheather that's enough of an advantage depends on how good your structural design is and if you can tuck the wing and other major parts in the structural budget. That's a known (but non trivial) problem for aircraft designers, but not so much for people used to the simpler shape of a rocket stage.
Quote
Now, if we could get an airllaunch stage that could compete with the capability of even a RTLS Falcon 9 first stage... Upper atmoshphere with a high mach number, and all that. SCRAMjet and SABER may be possibiities in the future... as is, amusingy enough, certian blimp concepts.
That's SCramjet and SABRE.

SABRESkylon is the joker in the pack. It's the only plan that designed to deliver TSTO payload in an SSTO design. It also gives you about 6x the Isp of a rocket in air breathing mode, allowing you to afford the structural mass that can make the system reusable.

Blimp concepts ( historically called rockoons) suffer from the problem that once the rocket separates you have a very short time to either vent the lift gas or ("magically") compress (or liquefy) it before your balloon rises so high the pressure differential splits it (or burst height).

If you can solve that problem you can make a reusable launch system. If you can't you won't. The problem is as you go higher the mass you can lift falls so the balloon size you need gets radically bigger, so you are into dealing with very large volumes of fairly low pressure gases quickly
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Online Robotbeat

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Air launch does kind of help you remove a stage. Taurus used an extra stage as Pegasus.

But sometimes adding an extra stage may be easier than the complications of air launch.
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Offline ZachF

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FWIW an SSTO ITS could be a pretty serious weapons platform. Even if it's payload is only 40 tons, 40 tons of GPS-guided tungsten rods at ~8km/s will be pretty deadly.

I kinda hope it doesn't though...

Offline rakaydos

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Blimp concepts ( historically called rockoons) suffer from the problem that once the rocket separates you have a very short time to either vent the lift gas or ("magically") compress (or liquefy) it before your balloon rises so high the pressure differential splits it (or burst height).
There's one group workign with a "blimp relay race" concept, where they design an upper atmsphere blimp that could never fly below 10 miles high, but that has a low enough envelope pressure that it can hold it's thin helium even against vacuum. (it is of course huge- over a KM long, to support itself with low pressure helium. Fortunately turbulance is negligable at that height) They intend to use this upper atmoshere blimp as first a launch platform, and later potentially an orbital vehical itself, if they can get certian drag reduction technoligies out of the lab and into real life.
They need to load it using conventional ground-to-high atmosphere blimps, but cargo transfer is gradual enough that you can compress gas to avoid popping the ferry balloon.

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Offline envy887

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To kind of return to the topic of ITS as an SSTO, I wonder how well the ITS design' mass fraction fare if it's scaled down. I think everything goes down pretty linearly

Pressure vessel mass scales directly with volume, which is linear with lift-off mass.
Engine mass scales with thrust which is linear with lift-off mass.
Landing legs scale with landing mass, so if everything else affecting mass fraction scales linearly they will as well.
TPS is a function of area/mass. A smaller vehicle has a better area/volume ratio and so should have a better area/mass ratio.

So a 1/10 mass scale of the tanker would be 1/101/3 in diameter and length, which is 5.6 m diameter by 23 m length. It could dry mass at 9 tonnes, hold 250 tonnes of subcooled methalox, and have 1 Raptor engine which could be optimized for SL to vacuum. Despite more air drag reach the ISS from the Cape with about 6.5 tonnes of payload while reserving 2% of its fuel for landing. 4 methalox RCS thrusters could provide a unity TWR at landing.

That's right about the performance of Falcon 5 for ISS missions, and it's also similar to SSO orbits and other LEO destinations, all in a 265 tonne at liftoff fully reusable SSTO. Could be very useful for transporting small payloads to a space station quite cheaply.


Online OneSpeed

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I did a similar simulation recently of a half scale BFS with two Raptor 80 engines. I got 7mT to 400 x 400 kms, perhaps I was more conservative on mass fractions and ullage.

Anyway, we're starting to build up quite a range of ITS alternative configurations. Some of these figures are projections from 300 x 300km simulations.

NameConfigurationMass to 400 x 400 kmsVehicle massPayload
Micro BFS SSTO1 x Raptor 5025.5 mT9 mT6.5 mT
Mini BFS SSTO2 x Raptor 8043 mT18 mT7 mT
BFS SSTO9 x Raptor 50187 mT90 mT25 mT
BFS SSTO3 x Raptor 50 + 6 x Raptor 80193 mT92 mT29 mT
FH Booster / Mini BFS27 x Merlin 1D + 2 x Raptor 5068 mT73 + 18 mT36.5 mT
BFS SSTO12 x Raptor 80236 mT100 mT63 mT
Mini ITS7 x Raptor 50 + 2 x Raptor 80116 mT50 + 18 mT80 mT
ITS Crew42 x Raptor 40 + 3 x 50 + 6 Vac578 mT275 + 150 mT300 mT

Edit: added FH Booster / Mini BFS

« Last Edit: 03/07/2017 12:40 AM by OneSpeed »

Online Robotbeat

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Nothing that HMXHMX hasn't talked about numerous times.
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Nothing that HMXHMX hasn't talked about numerous times.

True and Robot is now replying to a removed post, because we have rules about civility. Uncivil, post gets removed.

Offline Manabu

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Here are the Raptor figures I'm using in SpaceSim. Most of these figures have been published by SpaceX or mentioned in the Reddit AMA. I've simply interpolated to get my Raptor 80 figures. The mass estimates are envy's, they sound pretty reasonable to me.

   Cycle            Full-flow staged combustion
   Oxidiser         Subcooled liquid oxygen
   Fuel            Subcooled liquid methane
   Chamber pressure   300 bar or 30 MPa
   Throttle capability 20% to 100% thrust

   Sea-level Nozzle
      Expansion Ratio   40
      Thrust (SL)      2,842 kN
      Thrust (Vac)   3,061 kN
      Isp (SL)      333s
      Isp (Vac)      360s
      Diameter      1.51m
      Mass         2400 kg
      
      Expansion Ratio   50
      Thrust (SL)      3,094 kN
      Thrust (Vac)   3,333 kN
      Isp (SL)      334s
      Isp (Vac)      361s
      Diameter      1.78m
      Mass         2500 kg
      
      Expansion Ratio   80
      Thrust (SL)      3,200 kN
      Thrust (Vac)   3,400 kN
      Isp (SL)      336s
      Isp (Vac)      368s
      Diameter      2.4m
      Mass         2800 kg
      
   Vacuum Nozzle
      Expansion Ratio   200
      Thrust         3,500 kN
      Isp            382s
      Diameter      3.8m
      Mass          3000 kg
I don't know from where you got your Raptor 40 performance numbers. In the SpaceX presentation it is listed as SL 3,050 kN at 334 s while other people got via RPA numbers very close to that. Plus your nozzle diameter is also too small: it should be 1.7m to be consistent with the Raptor 200 and Raptor 80 nozzles. Although I admit it is inconsistent with measurements on the SpaceX slides/renders and 42 of those wouldn't fit under the booster... but it is better to be internally consistent with your numbers IMHO. The booster seem to be using a Raptor 32 while the BFS a Raptor 44...

Simple interpolation for getting Raptor 80 numbers is wrong, as it would be working much more over-expanded than the Raptor 40, that is already slightly over-expanded at SL. Envy887's numbers seem much better, but you seem to have used only his diameter and mass numbers, not the SL performance ones:
SL: 3005 kN at 323.2 s
Vacuum: 3479 kN at 372.2 s

I also don't know from where you got your Raptor 50 numbers, but they are suspicious as well, as any ER higher than about 32 should have smaller SL thrust and isp. Correct me if I'm wrong.

Plus, I'm doubtful if the BFS can throttle enough for landing with just Raptor 80 engines. I would leave the center cluster alone in those modifications.
« Last Edit: 03/05/2017 03:29 AM by Manabu »

Online OneSpeed

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I don't know from where you got your Raptor 40 performance numbers.

From the Reddit AMA, which was more recent than the IAC Mexico presentation. In the AMA Elon said the Raptor 40 has 290mT thrust at SL, less than the figure from the IAC presentation.

Plus your nozzle diameter is also too small: it should be 1.7m to be consistent with the Raptor 200 and Raptor 80 nozzles. Although I admit it is inconsistent with measurements on the SpaceX slides/renders and 42 of those wouldn't fit under the booster... but it is better to be internally consistent with your numbers IMHO. The booster seem to be using a Raptor 32 while the BFS a Raptor 44...

If the slides are from the CAD drawings, why would they be incorrect? It may be that the Raptor 40 has a slightly smaller throat, and the 1.51m and 40:1 ratio are correct.

Simple interpolation for getting Raptor 80 numbers is wrong, as it would be working much more over-expanded than the Raptor 40, that is already slightly over-expanded at SL. Envy887's numbers seem much better, but you seem to have used only his diameter and mass numbers, not the SL performance ones:
SL: 3005 kN at 323.2 s
Vacuum: 3479 kN at 372.2 s

Although I have great respect for Envy's expertise and analysis, I'm surprised that his Raptor 80 vacuum figure is only 21kN less than that for the Raptor 200, presumably for the same fuel flow. If that is accurate, there seems little reason for the larger 200:1 nozzle to exist. Perhaps he could respond separately?

I also don't know from where you got your Raptor 50 numbers, but they are suspicious as well, as any ER higher than about 32 should have smaller SL thrust and isp. Correct me if I'm wrong.

The Raptor 50 numbers are from the IAC Mexico slides. Where does your 32:1 figure come from? Wouldn't chamber pressure effect the point at which a nozzle becomes overexpanded?

Plus, I'm doubtful if the BFS can throttle enough for landing with just Raptor 80 engines. I would leave the center cluster alone in those modifications.

Leaving the centre three engines as Raptor 50s could certainly work, the difference in performance would be minimal. How many percent do you estimate the Raptor 80 could throttle to?

Offline Manabu

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From the Reddit AMA, which was more recent than the IAC Mexico presentation. In the AMA Elon said the Raptor 40 has 290mT thrust at SL, less than the figure from the IAC presentation.
In the reddit thread it is asked what are the *Vacuum* Thrust and Isp for the "Sea-Level Raptor" variant. So that 290mT is thrust at vacuum, not SL. But he does not specify if it is for Raptor 40 (that is indeed labeled as the SL variant in the IAC slides) or maybe the raptor variant used in the booster. Well, it doesn't add up for me anyway... This whole thing is strange, maybe result of fluctuating raptor performance figures...


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If the slides are from the CAD drawings, why would they be incorrect? It may be that the Raptor 40 has a slightly smaller throat, and the 1.51m and 40:1 ratio are correct.
Wouldn't that be a scaled down raptor then? A different engine?

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The Raptor 50 numbers are from the IAC Mexico slides. Where does your 32:1 figure come from? Wouldn't chamber pressure effect the point at which a nozzle becomes overexpanded?
I can't find any direct mention to a Raptor with 50 expansion ratio on the IAC slides. My 32:1 figure comes from analogy to other engines, like the Merlin 1D+ that has roughly a third of the chamber pressure and whose ideal SL expansion ratio would be 11.05. Scaling that linearly, you get around 30 for raptor actually. Or from AP3's analysis that I linked earlier, that estimates optimum expansion for the Raptor 40 is at 1.71km, 0.813 atm, so optimum SL expansion is something lower. I'm not sure about my number, but everything indicates something lower than 40 as optimum SL nozzle.

Just as a note, I understand that the optimum launcher nozzle is something bigger than that, because the average pressure it will work is much less than sea level.

Quote
Plus, I'm doubtful if the BFS can throttle enough for landing with just Raptor 80 engines. I would leave the center cluster alone in those modifications.

Leaving the centre three engines as Raptor 50s could certainly work, the difference in performance would be minimal. How many percent do you estimate the Raptor 80 could throttle to?
I don't really know how to estimate this, but if linear linear extrapolation could be used, then I would guess around 40~50% throttle.
« Last Edit: 03/05/2017 02:54 PM by Manabu »

Offline Manabu

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Note: By Raptor 40 below I mean the 1.7m one for consistency with the other ones, but I think it doesn't really matters much if it is slightly more or less expanded because the way they are used.

My original idea for a BFS SSTO was to substitute 2 or 3 of the Raptor 200 by a cluster of 3 x Raptor 40. The downside of this approach is that the remaining Raptor 200 can't be lit on the ground, plus are dead weight up to a certain altitude. But I think they eventually pay for their weight in ISP and added thrust middle flight. Needs simulation. Of course, this approach needs a new thrust structure and tank design, but the tank can even be a bit bigger and more mass efficient than before IMHO, because it can be rounder at the base.

If SpaceX is willing to make one new type of nozzle, a cluster of 2 x Raptor 80 + 1 x Raptor 40 fits perfectly in the space left from removing one Raptor 200, and provides for an even more rounded tank and better average ISP and thrust. This should give a slightly better payload to orbit.

And I have some feature requests for the simulation: it would be interesting to show in the left bar the total delta-v expended to reach orbit, including losses, and what is the average isp of the flight. Those numbers can then be put in the traditional rocket equation to estimate small changes more easily.

Increasing expansion does eventually lead to seperation at sea level, at about 140:1, but SL thrust drops to 2715 kN per engine and ISP drops to 292s. On a thrust-limited design this is a poor trade-off, even though vacuum ISP is close to 380.

However, instead of nine 80:1 nozzles it might make sense to have a mix of 50:1 and 140:1. The former have much higher thrust and ISP at SL, and the latter have higher thrust and ISP in vacuum, but both are operable (if needed) across the entire flight. The 50:1 engines could be shut down to improve overall ISP once the vehicle is high enough (and light enough) that the 140:1 nozzles can maintain optimal acceleration.
SpaceX is reportedly using a 150 expansion ratio for Raptor testings, but maybe because the test stand is a few hundred meters more above SL.

There are several more interesting raptor configurations. One can do a circle of 9 x 3m diameter Raptor 125 around the gimbaling cluster. Or something not as symmetrical with 6 x Raptor 140 + 4 x Raptor 57. In all those examples there is space for up to 4 x Raptor 40 engines in the gimbaling cluster if desired because the surrounding engines are smaller than the original Raptor 200.

Offline envy887

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Envy887's numbers seem much better, but you seem to have used only his diameter and mass numbers, not the SL performance ones:
SL: 3005 kN at 323.2 s
Vacuum: 3479 kN at 372.2 s

Although I have great respect for Envy's expertise and analysis, I'm surprised that his Raptor 80 vacuum figure is only 21kN less than that for the Raptor 200, presumably for the same fuel flow. If that is accurate, there seems little reason for the larger 200:1 nozzle to exist. Perhaps he could respond separately?
[/quote]

I got 3573 kN for the Raptor 200, because I was basing this on the R40 engine performance and not trying to match both... They aren't quite consistent with each other.

Offline Manabu

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I got 3573 kN for the Raptor 200, because I was basing this on the R40 engine performance and not trying to match both... They aren't quite consistent with each other.
From the thread I linked earlier they did the opposite, basing the Raptor 40 in the Raptor 200, and the next poster  said that if he varied the mixture ratio he would get better numbers for the SL version. Maybe that is the source of this inconsistency? Or maybe SpaceX numbers are just all over the place and we should round down to the lowest denominator...
« Last Edit: 03/05/2017 06:52 PM by Manabu »

Offline MikeAtkinson

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I would not be too concerned with consistency, the Raptor figures depend on various factors:

1. design aim (what performance the engineers are aiming to obtain).

2. estimated performance (what the design obtains on average).

3. measured performance (the current results obtained, perhaps extrapolated to larger engines or expansion ratios).

4. minimum guaranteed performance (below which an engine would be rejected).

5. performance after a set of known improvements.

6. ultimate performance after a set of known and unknown improvements.

Some of these performance figures will change over time as new data is gathered and the design of ITS is matured.

There is also the possibility that SpaceX are being deliberately misleading in giving consistent performance figures, perhaps for competitive reasons or to conform to ITAR.

Offline Manabu

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The fact that raptor performance is on flux don't precludes us from trying to be internally consistent when making our own predictions for fun over this paper rocket.

It also don't makes it right to claim that an ER of 80:1 is better than an ER of 40:1 for a Raptor SSTO because it's better thrust at SL, when the reason for that difference is that you are using a sub-scale raptor for your Raptor 40 and extrapolating the SL thrust in the wrong direction for the Raptor 80. It may be better, but that will be because it's vacuum characteristics, despite it's lower SL thrust.

I'm not trying to bash OneSpeed, I'm just trying to contribute to better simulations and learn in the process.

Online OneSpeed

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... I'm just trying to contribute to better simulations and learn in the process.

The figures I've posted above are those currently used in my simulations. I'm not asking anyone else to use them, they are purely FYI.

If you would like to try some alternatives, I'd suggest you download SpaceSim from https://github.com/zlynn1990/SpaceSim and plug in your own figures. That sounds more like fun to me.

Offline radozw

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I did a similar simulation recently of a half scale BFS with two Raptor 80 engines. I got 7mT to 400 x 400 kms, perhaps I was more conservative on mass fractions and ullage.

Anyway, we're starting to build up quite a range of ITS alternative configurations. Some of these figures are projections from 300 x 300km simulations.

NameConfigurationMass to 400 x 400 kmsVehicle massPayload
Micro BFS SSTO1 x Raptor 5025.5 mT9 mT6.5 mT
Mini BFS SSTO2 x Raptor 8043 mT18 mT7 mT
BFS SSTO9 x Raptor 50187 mT90 mT25 mT
BFS SSTO3 x Raptor 50 + 6 x Raptor 80193 mT92 mT29 mT
FH Booster / Mini BFS27 x Merlin 1D + 2 x Raptor 5068 mT73 + 18 mT36.5 mT
BFS SSTO12 x Raptor 80236 mT100 mT63 mT
Mini ITS7 x Raptor 50 + 2 x Raptor 80116 mT50 + 18 mT80 mT
ITS Crew42 x Raptor 40 + 3 x 50 + 6 Vac578 mT275 + 150 mT300 mT

Edit: added FH Booster / Mini BFS


I think there should be configuration as standard ITS + 2 side boosters F9.
That will solve T/W problem and reduce gravity loses.
It will complicate loading of fuel and launch pad configuration but it will enable testing of standard ITS and have usefull payload.
I can not do calculations

Offline envy887

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I think there should be configuration as standard ITS + 2 side boosters F9.
That will solve T/W problem and reduce gravity loses.
It will complicate loading of fuel and launch pad configuration but it will enable testing of standard ITS and have usefull payload.

The standard ITS spaceship won't be able to light it's vacuum engines at sea level, they are too expanded for that at 200:1. The nozzles would have to be trimmed back to about 135:1. If the average ISP to orbit for the 40:1 and 135:1 combined engine set is 355 seconds, the crewed ship would be able to barely get to orbit and back, with only a nominal payload of perhaps 10 tonnes. Assuming the F9 boosters land downrange.

The tanker ITS with the same F9 boosters and mods would get about 100 tonnes to low orbit and then return. A cargo-only version based on the tanker could get nearly that... it would be a little heavier with payload adapter and cargo doors etc.

Offline radozw

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I think there should be configuration as standard ITS + 2 side boosters F9.
That will solve T/W problem and reduce gravity loses.
It will complicate loading of fuel and launch pad configuration but it will enable testing of standard ITS and have usefull payload.

The standard ITS spaceship won't be able to light it's vacuum engines at sea level, they are too expanded for that at 200:1. The nozzles would have to be trimmed back to about 135:1. If the average ISP to orbit for the 40:1 and 135:1 combined engine set is 355 seconds, the crewed ship would be able to barely get to orbit and back, with only a nominal payload of perhaps 10 tonnes. Assuming the F9 boosters land downrange.

The tanker ITS with the same F9 boosters and mods would get about 100 tonnes to low orbit and then return. A cargo-only version based on the tanker could get nearly that... it would be a little heavier with payload adapter and cargo doors etc.

That sounds good. So for starters tanker and cargo ITS to test technology, reentry and have decent cargo capability so somebody can pay for launch.

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