Author Topic: Why the lack of SSTO projects?  (Read 48347 times)

Offline CameronD

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Re: Why the lack of SSTO projects?
« Reply #80 on: 01/30/2017 10:13 pm »
Oh, sure, but with heavy automation you ought to be able to get the people who actually directly work on the vehicle down very low. It would almost all be "spread out" fleet stuff - working on whichever vehicle happened to be 'in the shop' at the moment.
It already is in terms of turning around a large aircraft for another flight.

FWIW, I think you'll find the numbers required to turn around a large aircraft operated by a large airline anywhere in the world are about as low as you'll ever get - "heavy automation" included(*).  Due to fierce competition with the next guy, it isn't in their commercial interest to have any more hires than absolutely necessary.

* = People are expensive and automation isn't, but there are a great many specialist jobs that for various reasons simply can't be automated.. and even if they could be (eg. the aircraft itself) you still need people (eg. the pilots) standing by in case anything goes wrong.
With sufficient thrust, pigs fly just fine - however, this is not necessarily a good idea. It is hard to be sure where they are
going to land, and it could be dangerous sitting under them as they fly overhead.

Offline tdperk

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Re: Why the lack of SSTO projects?
« Reply #81 on: 01/31/2017 10:09 am »
You may find this interesting. From the Advanced Topics thread "Finding the actual speed limit of a conventional ramjet powered vehicle."

Thank you.

Offline john smith 19

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Re: Why the lack of SSTO projects?
« Reply #82 on: 01/31/2017 05:57 pm »
Drawbacks of TAN: afterburning occurs at modest to low pressure and extremely short time scale (supersonic). While successful thrust have been proved, Isp of afterburning portion is still worse than independent high pressure booster engines or even SRB.
Now that you mention it the velocity down stream of the throat will be (should be) several Mach.
TBH TAN seems better as a way of running a much larger nozzle (300+?) at Earth sea level without getting flow separation. The logical tactic is to use LOX injection and create an "inverse afterburner" from the fuel rich main exhaust. Although in Russian terminology in a staged combustion (where what the US calls the Main Combustion Chamber) this would be an after-after-burner.  :)
Quote

RBCC concepts are shifting back to independent rocket + ramjet stream (IRS) too, as the mixing of rocket stream and incoming air needs more duct length and structure weight than independent engines.
https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19990081112.pdf

Anyway, the inherent low mixing efficiency in supersonic flow is a painful physical limit. This phenomenon is fully realized until CFD tools later than 1990s made Scramjets finally possible (but still feeble), and the information spread to industry even later.

Besides, among all architectures, VTVL airbreathers (looks exotic? but easier than winged) have best overall performance, either for SSTO or TSTO.

Comparative System Analysis of Reusable Rocket and Air-Breathing Launch Vehicles

http://drum.lib.umd.edu/bitstream/handle/1903/2939/umi-umd-2731.pdf

The result : simply strap up some (old) ramjets for Mach 1 to 5 ?
I think the author is now  the head of Reaction Engines Limited US Office.

As he notes HTOL benefits from higher takeoff speed and a Hydrogen final stage has a milder reentry heating cycle.

In fact SABRESkylon is the vehicle that meets all the criteria for an ideal vehicle.
MCT ITS BFR SS. The worlds first Methane fueled FFSC engined CFRP SS structure A380 sized aerospaceplane tail sitter capable of Earth & Mars atmospheric flight.First flight to Mars by end of 2022 TBC. T&C apply. Trust nothing. Run your own #s "Extraordinary claims require extraordinary proof" R. Simberg."Competitve" means cheaper ¬cheap SCramjet proposed 1956. First +ve thrust 2004. US R&D spend to date > $10Bn. #deployed designs. Zero.

Offline Vultur

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Re: Why the lack of SSTO projects?
« Reply #83 on: 02/01/2017 12:51 am »
However you're correct if you don't have an angel investor with deep pockets funding is an issue. And as I noted historically VTOL SSTO has required a vehicle 3x-4x bigger than a conventional TSTO to achieve the same result in 1 launch.  Funders tend to note that.

Yeah, I think the way to do it would probably need to be incremental where you can get revenue before you get to the full SSTO (unless it was a pet project of a multibillionaire).

The most plausible path, IMO, is incremental improvement of a suborbital reusable VTVL, from something like New Shepard (straight up and down to the Karman Line) to maybe trans-Atlantic suborbital to orbital. Problem is that would lock you into human-rated from the beginning and you might not want to start with that extra expense.

Another possibility would be to start with a 'half' SSTO (droppable engines like Mercury-Atlas LV, or boosters to get off the ground, whatever) and then refine it to a true SSTO.

Offline corneliussulla

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Re: Why the lack of SSTO projects?
« Reply #84 on: 02/01/2017 07:48 am »
ITS is a SSTO, problem is u have to start on Mars

Offline Katana

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Re: Why the lack of SSTO projects?
« Reply #85 on: 02/01/2017 10:56 am »
Now that you mention it the velocity down stream of the throat will be (should be) several Mach.
TBH TAN seems better as a way of running a much larger nozzle (300+?) at Earth sea level without getting flow separation. The logical tactic is to use LOX injection and create an "inverse afterburner" from the fuel rich main exhaust. Although in Russian terminology in a staged combustion (where what the US calls the Main Combustion Chamber) this would be an after-after-burner.  :)

TAN vs conventional nozzle = Scramjet vs conventional ramjet, or worse.

The scramjet limitation, long mixing length and low supersonic mixing efficiency, also applies to TAN operating conditions.

Modern high pressure engines (SSME or RD180) already have high expansion ratio and high efficiencies, leaving little margin to earn, lot to loose.

Offline Katana

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Re: Why the lack of SSTO projects?
« Reply #86 on: 02/01/2017 11:02 am »
However you're correct if you don't have an angel investor with deep pockets funding is an issue. And as I noted historically VTOL SSTO has required a vehicle 3x-4x bigger than a conventional TSTO to achieve the same result in 1 launch.  Funders tend to note that.

Yeah, I think the way to do it would probably need to be incremental where you can get revenue before you get to the full SSTO (unless it was a pet project of a multibillionaire).

The most plausible path, IMO, is incremental improvement of a suborbital reusable VTVL, from something like New Shepard (straight up and down to the Karman Line) to maybe trans-Atlantic suborbital to orbital. Problem is that would lock you into human-rated from the beginning and you might not want to start with that extra expense.

Another possibility would be to start with a 'half' SSTO (droppable engines like Mercury-Atlas LV, or boosters to get off the ground, whatever) and then refine it to a true SSTO.
X-33/Venturestar with SRB could be a good replacement when failed to reach SSTO.

NASA wasted lots of efforts after shuttle, changing from X-30 to X-33 and further to SLI or "next generation shuttle" before swinging back to rockets, Ares I/V and finally SLS.

Repetitive swinging between rockets and spaceplanes caused greater potential waste.

If NASA stick to improvements of Saturn I/V without wings, VTVL reuse could be realized long before Falcon 9. And the 1989 SEI Mars plan of George Bush may (start earlier before end of cold war and) came to real.
« Last Edit: 02/01/2017 11:24 am by Katana »

Offline Robotbeat

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Re: Why the lack of SSTO projects?
« Reply #87 on: 02/01/2017 01:02 pm »
X-33 was not designed to reach orbit. Odd as it may seem, the ITS BFS will have higher performance than X-33 would've.
« Last Edit: 02/01/2017 01:03 pm by Robotbeat »
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Offline john smith 19

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Re: Why the lack of SSTO projects?
« Reply #88 on: 02/01/2017 09:21 pm »
ITS is a SSTO, problem is u have to start on Mars
The earth gravity field has always been the problem with SSTO. If life had evolved on Mars the common question would probably "Why didn't they go SSTO like we did."
TAN vs conventional nozzle = Scramjet vs conventional ramjet, or worse.
That seems harsh. However now you mention it the flow conditions are somewhat similar, although I think the exhaust density is somewhat higher.
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The scramjet limitation, long mixing length and low supersonic mixing efficiency, also applies to TAN operating conditions.

Modern high pressure engines (SSME or RD180) already have high expansion ratio and high efficiencies, leaving little margin to earn, lot to loose.
Expansion ratio is still relatively limited on engines if you want them to start at Seal Level. TAN (theoretically) gives you an expansion ratio of 100s. Other options to do this rely on aerodynamics (n-bell nozzle) or mechanical (nozzle vents). TAN and vented nozzles are (in principal) testable at full scale at SL.
The most plausible path, IMO, is incremental improvement of a suborbital reusable VTVL, from something like New Shepard (straight up and down to the Karman Line) to maybe trans-Atlantic suborbital to orbital. Problem is that would lock you into human-rated from the beginning and you might not want to start with that extra expense.
Then we'll have to see how Blue does with this.
MCT ITS BFR SS. The worlds first Methane fueled FFSC engined CFRP SS structure A380 sized aerospaceplane tail sitter capable of Earth & Mars atmospheric flight.First flight to Mars by end of 2022 TBC. T&C apply. Trust nothing. Run your own #s "Extraordinary claims require extraordinary proof" R. Simberg."Competitve" means cheaper ¬cheap SCramjet proposed 1956. First +ve thrust 2004. US R&D spend to date > $10Bn. #deployed designs. Zero.

Offline Jim

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Re: Why the lack of SSTO projects?
« Reply #89 on: 02/01/2017 09:26 pm »

If NASA stick to improvements of Saturn I/V without wings, VTVL reuse could be realized long before Falcon 9.

Unsubstanitated

Offline Katana

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Re: Why the lack of SSTO projects?
« Reply #90 on: 02/02/2017 05:27 am »
Expansion ratio is still relatively limited on engines if you want them to start at Seal Level. TAN (theoretically) gives you an expansion ratio of 100s. Other options to do this rely on aerodynamics (n-bell nozzle) or mechanical (nozzle vents). TAN and vented nozzles are (in principal) testable at full scale at SL.
SSME already have expansion ratio of 69:1 and isp vac of 452 seconds, being able to start at SL.
RL-10 have expansion ratio of 84:1 or 280:1 and isp vac of 450 or 465 seconds
TAN will at most earn 15 seconds on isp vac from bigger nozzles.

Quote
Then we'll have to see how Blue does with this.
BO uses 2 stages for LEO and 3 stages for GTO, even more stages than Space X, though with hydrogen upperstage.

Offline john smith 19

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Re: Why the lack of SSTO projects?
« Reply #91 on: 02/03/2017 09:32 pm »
SSME already have expansion ratio of 69:1 and isp vac of 452 seconds, being able to start at SL.
RL-10 have expansion ratio of 84:1 or 280:1 and isp vac of 450 or 465 seconds
TAN will at most earn 15 seconds on isp vac from bigger nozzles.
WRT to SSTO that 15 seconds would buy you an extra 0.8% of PMF. Historically SSTO concepts have expected to offer a usable payload of 1% of the structural weight.  IIRC the SSME with an expansion ratio of 77 delivered around 363sec at SL. 15secs at that Isp also increases the PMF by about 0.8% of GTOW.
Quote
Quote
Then we'll have to see how Blue does with this.
BO uses 2 stages for LEO and 3 stages for GTO, even more stages than Space X, though with hydrogen upperstage.
So somewhat OT for this thread.
MCT ITS BFR SS. The worlds first Methane fueled FFSC engined CFRP SS structure A380 sized aerospaceplane tail sitter capable of Earth & Mars atmospheric flight.First flight to Mars by end of 2022 TBC. T&C apply. Trust nothing. Run your own #s "Extraordinary claims require extraordinary proof" R. Simberg."Competitve" means cheaper ¬cheap SCramjet proposed 1956. First +ve thrust 2004. US R&D spend to date > $10Bn. #deployed designs. Zero.

Offline Katana

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Re: Why the lack of SSTO projects?
« Reply #92 on: 02/04/2017 03:46 am »
SSME already have expansion ratio of 69:1 and isp vac of 452 seconds, being able to start at SL.
RL-10 have expansion ratio of 84:1 or 280:1 and isp vac of 450 or 465 seconds
TAN will at most earn 15 seconds on isp vac from bigger nozzles.
WRT to SSTO that 15 seconds would buy you an extra 0.8% of PMF. Historically SSTO concepts have expected to offer a usable payload of 1% of the structural weight.  IIRC the SSME with an expansion ratio of 77 delivered around 363sec at SL. 15secs at that Isp also increases the PMF by about 0.8% of GTOW.
Quote
Quote
Then we'll have to see how Blue does with this.
BO uses 2 stages for LEO and 3 stages for GTO, even more stages than Space X, though with hydrogen upperstage.
So somewhat OT for this thread.
If 15s matters so much as to require exotic technology, the risk of project is already unmanageable for the probability of structure overweight.

Stage and half approaches are much less sensitive.

Offline john smith 19

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Re: Why the lack of SSTO projects?
« Reply #93 on: 02/04/2017 06:51 am »
If 15s matters so much as to require exotic technology, the risk of project is already unmanageable for the probability of structure overweight.

Stage and half approaches are much less sensitive.
Well strictly speaking it's more the idea that VTOL SSTO is more risky and you would want to do anything possible to improve the odds of success. For a rocket only single stage design I'd start with the best Isp engine I could get my hands on.

The key is the engine and how much PMF it needs, or can give you.

Rocket engineering types have little trouble evaluating single and multistage VTO vehicles but the seem to have more trouble with winged HTOL designs. Even a design that gives you say 3000s over part of the trajectory can make a huge difference to what structure  fraction you need, while the wings can remove a lot of the gravity losses.

An air breather can give you "virtual staging." The question is wheather the weight gained is made up for they size and weight of the oxidizer you don't carry during air breathing and the huge (if temporary) increase in Isp over any known high thrust rocket engine.

But the increased technical risk and the (historically) low payload to orbit are probably the major factors why SSTO is not a common approach and has little support amongst armchair rocket engineers.
MCT ITS BFR SS. The worlds first Methane fueled FFSC engined CFRP SS structure A380 sized aerospaceplane tail sitter capable of Earth & Mars atmospheric flight.First flight to Mars by end of 2022 TBC. T&C apply. Trust nothing. Run your own #s "Extraordinary claims require extraordinary proof" R. Simberg."Competitve" means cheaper ¬cheap SCramjet proposed 1956. First +ve thrust 2004. US R&D spend to date > $10Bn. #deployed designs. Zero.

Offline Nilof

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Re: Why the lack of SSTO projects?
« Reply #94 on: 02/05/2017 09:27 am »
15 seconds is a sub-5% improvement in Isp. It can be worth it, but if it comes at the expense of T/W ratio, that gain in mass ratio can easily be eaten up by increased gravity losses, or increased engine mass fraction if you increase the number of engines.
For a variable Isp spacecraft running at constant power and constant acceleration, the mass ratio is linear in delta-v.   Δv = ve0(MR-1). Or equivalently: Δv = vef PMF. Also, this is energy-optimal for a fixed delta-v and mass ratio.

Offline john smith 19

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Re: Why the lack of SSTO projects?
« Reply #95 on: 02/05/2017 10:16 pm »
15 seconds is a sub-5% improvement in Isp. It can be worth it, but if it comes at the expense of T/W ratio, that gain in mass ratio can easily be eaten up by increased gravity losses, or increased engine mass fraction if you increase the number of engines.
For rocket only SSTO the fine details matter.  Anything that buys more Isp or improves T/W or lowers structural mass should be considered.  Sub cooled propellants, increasing the expansion ratio, changing the vehicle form factor.  Air breathing is the one that seems to offer the biggest Isp improvement, to the point where the required mass fraction moves from rocket stage level to more like aircraft. Winged lift means you can reduce thrust to < GTOW with HTOL.
MCT ITS BFR SS. The worlds first Methane fueled FFSC engined CFRP SS structure A380 sized aerospaceplane tail sitter capable of Earth & Mars atmospheric flight.First flight to Mars by end of 2022 TBC. T&C apply. Trust nothing. Run your own #s "Extraordinary claims require extraordinary proof" R. Simberg."Competitve" means cheaper ¬cheap SCramjet proposed 1956. First +ve thrust 2004. US R&D spend to date > $10Bn. #deployed designs. Zero.

Offline Katana

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Re: Why the lack of SSTO projects?
« Reply #96 on: 02/06/2017 04:20 am »
15 seconds is a sub-5% improvement in Isp. It can be worth it, but if it comes at the expense of T/W ratio, that gain in mass ratio can easily be eaten up by increased gravity losses, or increased engine mass fraction if you increase the number of engines.
For rocket only SSTO the fine details matter.  Anything that buys more Isp or improves T/W or lowers structural mass should be considered.  Sub cooled propellants, increasing the expansion ratio, changing the vehicle form factor.  Air breathing is the one that seems to offer the biggest Isp improvement, to the point where the required mass fraction moves from rocket stage level to more like aircraft. Winged lift means you can reduce thrust to < GTOW with HTOL.

Low combustion efficiency and low isp sl of TAN or dead weight of wings / airbreathers (to orbit) may eat back their merits.

For 5% more impulse without dead weight, GEM for Delta II works excellent with modest price.

https://en.wikipedia.org/wiki/Delta_II
https://en.wikipedia.org/wiki/Graphite-Epoxy_Motor
GEM 46, gross weight 19 tons, thrust 601kN (60 tons), burn 77 seconds.
9 of them used per one Delta II, implies modest unit cost.

A "quasi-SSTO" with low cost small boosters (booster GTOW < 0.5* sustainer GTOW) could be better than either pure SSTO (high tech, low margin) or typical TSTO (or 1.5 stage) systems (booster GTOW > 2 * sustainer GTOW).
« Last Edit: 02/06/2017 04:53 am by Katana »

Offline john smith 19

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Re: Why the lack of SSTO projects?
« Reply #97 on: 02/06/2017 06:19 am »
For rocket only SSTO the fine details matter.  Anything that buys more Isp or improves T/W or lowers structural mass should be considered.  Sub cooled propellants, increasing the expansion ratio, changing the vehicle form factor.  Air breathing is the one that seems to offer the biggest Isp improvement, to the point where the required mass fraction moves from rocket stage level to more like aircraft. Winged lift means you can reduce thrust to < GTOW with HTOL.

Low combustion efficiency and low isp sl of TAN or dead weight of wings / airbreathers (to orbit) may eat back their merits.

For 5% more impulse without dead weight, GEM for Delta II works excellent with modest price.

https://en.wikipedia.org/wiki/Delta_II
https://en.wikipedia.org/wiki/Graphite-Epoxy_Motor
GEM 46, gross weight 19 tons, thrust 601kN (60 tons), burn 77 seconds.
9 of them used per one Delta II, implies modest unit cost.

A "quasi-SSTO" with low cost small boosters (booster GTOW < 0.5* sustainer GTOW) could be better than either pure SSTO (high tech, low margin) or typical TSTO (or 1.5 stage) systems (booster GTOW > 2 * sustainer GTOW).
Actually Jeff Greason, when he was at XCOR, suggested something similar.

The only justification for an SSTO is that it delivers per unit mass price in a payload that the overall cost  is also affordable better than other systems.

The (potential) benefit of SSTO is you don't drop stuff over other peoples land. That's something you lose with boosters.

Greason also introduced the rule of thumb that average (Isp is Isp(SL) +2x Isp(vac))/3. Obviously this suggests Vac Isp is the most important unless you can get SL Isp much higher, IE not say the 15% of an ejector shroud (as NASA found for M0-2) but multiple times bigger.
MCT ITS BFR SS. The worlds first Methane fueled FFSC engined CFRP SS structure A380 sized aerospaceplane tail sitter capable of Earth & Mars atmospheric flight.First flight to Mars by end of 2022 TBC. T&C apply. Trust nothing. Run your own #s "Extraordinary claims require extraordinary proof" R. Simberg."Competitve" means cheaper ¬cheap SCramjet proposed 1956. First +ve thrust 2004. US R&D spend to date > $10Bn. #deployed designs. Zero.

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Re: Why the lack of SSTO projects?
« Reply #98 on: 02/06/2017 04:21 pm »
Actually Jeff Greason, when he was at XCOR, suggested something similar.

The quasi-SSTO, known as the Frequent Flyer, was actaully developed by Dan DeLong when he was at Teledyne Brown. There is a short blurb about it on a previous version of the website.
I tried it at home

Offline Robotbeat

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Re: Why the lack of SSTO projects?
« Reply #99 on: 02/06/2017 11:44 pm »
15 seconds is a sub-5% improvement in Isp. It can be worth it, but if it comes at the expense of T/W ratio, that gain in mass ratio can easily be eaten up by increased gravity losses, or increased engine mass fraction if you increase the number of engines.
For rocket only SSTO the fine details matter.  Anything that buys more Isp or improves T/W or lowers structural mass should be considered.  Sub cooled propellants, increasing the expansion ratio, changing the vehicle form factor.  Air breathing is the one that seems to offer the biggest Isp improvement, to the point where the required mass fraction moves from rocket stage level to more like aircraft. Winged lift means you can reduce thrust to < GTOW with HTOL.

Low combustion efficiency and low isp sl of TAN or dead weight of wings / airbreathers (to orbit) may eat back their merits.

For 5% more impulse without dead weight, GEM for Delta II works excellent with modest price.

https://en.wikipedia.org/wiki/Delta_II
https://en.wikipedia.org/wiki/Graphite-Epoxy_Motor
GEM 46, gross weight 19 tons, thrust 601kN (60 tons), burn 77 seconds.
9 of them used per one Delta II, implies modest unit cost.

A "quasi-SSTO" with low cost small boosters (booster GTOW < 0.5* sustainer GTOW) could be better than either pure SSTO (high tech, low margin) or typical TSTO (or 1.5 stage) systems (booster GTOW > 2 * sustainer GTOW).

Also, drag. You have to accelerate all that reaction mass from a standstill to near your flight speed, JUST like a regular launch vehicle except you have to use inlets to do so.

This is kind of a subtle point that I haven't seen many people actually grok (and interestingly, keeping the airflow supersonic like in a SCRAMjet doesn't actually help you much... Energy is conserved).
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

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