Author Topic: Operating the ITS spaceship or tanker as an SSTO launch vehicle.  (Read 7384 times)

Online 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:


Offline 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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Offline 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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Online 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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Offline 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.

Offline 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?

Online 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.

Offline 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...).

Offline 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.
Chris  Whoever loves correction loves knowledge, but he who hates reproof is stupid.

To the maximum extent practicable, the Federal Government shall plan missions to accommodate the space transportation services capabilities of United States commercial providers. US law http://goo.gl/YZYNt0

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 »

Offline 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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Offline 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.


Online 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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