Author Topic: Why the lack of SSTO projects?  (Read 20651 times)

Offline Vultur

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Why the lack of SSTO projects?
« on: 01/19/2017 06:20 AM »
There are a ton of "new space" companies right now, and many of them are working on or planning new launch vehicles - Blue Origin, Virgin Galactic, and many smaller operations like RocketLab. But there seems to be a lack of interest in SSTOs, except for Skylon, which while incredibly cool and possibly world-changing if successful has much more "novelty factor"/technical risk/development cost than a nearly-off-the-shelf standard "pure rocket" VTVL SSTO.

OK, nearly-off-the-shelf may be an overstatement, but I think every or nearly every part needed is demonstrated now.

The mass fractions needed have been demonstrated since the early 60s (and in fact well exceeded, given that modern engines have far better performance than Titan II's or Mercury-Atlas's).

 Vertical landing used to be a huge unknown, but  SpaceX and Blue Origin have demonstrated that it's now quite solvable.

The TPS IMO is the remaining large uncertainty -- but it may also be solved now. Depends how good PICA-X really is (that data isn't public, right?)

Offline savuporo

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Re: Why the lack of SSTO projects?
« Reply #1 on: 01/19/2017 06:34 AM »
Huge investment with massive risk of unproven system for what market ? Investors need the chance of enormous upside - where does the upside come from ? Has to be something that existing rockets can't do equally well.
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Offline Hobbes-22

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Re: Why the lack of SSTO projects?
« Reply #2 on: 01/19/2017 07:07 AM »
IIRC a Falcon 9 first stage can get to orbit on its own, but with 0 payload. So any low-risk developments would be pointless, which leaves the high-risk path of Skylon.

Offline Bynaus

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Re: Why the lack of SSTO projects?
« Reply #3 on: 01/19/2017 07:19 AM »
The ITS spaceship or at least the ITS tanker could be considered a first step towards a VTVL SSTO. If that works out, perhaps SpaceX could (should?) even branch off a variant which can be used for intercontinental point-to-point flights.

Other than that, its an application in search for a market with high upfront costs. Not really what investors are looking after...

Offline Nilof

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Re: Why the lack of SSTO projects?
« Reply #4 on: 01/19/2017 08:52 AM »
The big issue with SSTO's is that their smaller payload hurts economic viability if they aren't reusable, and reuse is an all-or-nothing endeavour. This runs counter to the incremental development strategy that most of the new space actors are aiming for.
« Last Edit: 01/19/2017 12:47 PM by Nilof »
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 Katana

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Re: Why the lack of SSTO projects?
« Reply #5 on: 01/19/2017 12:10 PM »
The big issue with SSTO's is that their lower payload hurts economic viability if they aren't reusable, and reuse is an all-or-nothing endeavour. This runs counter to the incremental development strategy that most of the new space actors are aiming for.
Even reuseable SSTO are inferior to full reuseable TSTO on payload and booster life. Only the second stage have to suffer orbital reentry in reuseable TSTO.

Offline Oli

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Re: Why the lack of SSTO projects?
« Reply #6 on: 01/19/2017 12:51 PM »

With SSTO you have several times the GLOW for the same payload even with crazy ITS-like mass fractions (meaning a much larger/heavier vehicle with a lot more engines).

Offline Proponent

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Re: Why the lack of SSTO projects?
« Reply #7 on: 01/19/2017 01:01 PM »
I see two fundamental barriers to the development of SSTO:  development risk and demand.

The development risk comes from the great sensitivity of payload to vehicle mass.  Consider the Atlas V 401, which can loft about 9400 kg to 400 km circular due East from the Cape.  The dry mass of the first stage is 21,054 kg.  Typically, 1 kg of mass added to a first stage reduces LEO payload by about 0.1 kg.  So imagine that the first stage runs over its mass budget by 1%, i.e., 210 kg.  Then the payload will be reduced by about 21 kg, i.e., 0.22%.

Now look at the second stage, which has a dry mass of 2243 kg.  On a final stage, a 1-kg overrun on the mass budget deducts 1 kg from the payload.  So if the second stage is overmass by 1%, then the payload takes a hit of 22 kg, i.e., 0.24%.

For an SSTO, we might hope (following Bruce Dunn: see the 3rd attachment to this post; I'm working with the un-sub-cooled lox/RP-1 case), that a vehicle with a dry mass of 46,620 kg could orbit a payload of 16,640 kg.  If the vehicle exceeds its mass budget by 1%, then the payload drops by 456 kg, i.e., 4.9%.

In other words, an SSTO is about 20 times more sensitive to the mass budget than is a conventional TSTO launch vehicle.  And that's using a very optimistic SSTO design (payload is about 2% of GLOM; more regularly one sees figures of maybe 0.5%).

The other thing about an SSTO is that its performance to a slightly more challenging orbit -- a little higher or at an non-optimal inclination -- will be really lousy, because the vehicle itself makes up so much of the mass injected into orbit.  Any foreseeable Earth-based SSTO will fly to and from a particular low-Earth orbit.  So there will have to be a lot of traffic to that one destination.  I'm thinking of a rate measured in launches per week, at the outside, rather than launches per year.  The traffic might be generated by a busy space station or propellant depot or by a low-cost, reusable tug which takes (a lot of) payloads to other orbits, or a combination of these.  But none of them exists yet or is even on the horizon.

EDIT:  Deleted redundant "we might hope" in 4th paragraph.
« Last Edit: 01/20/2017 11:49 AM by Proponent »

Online Robotbeat

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Re: Why the lack of SSTO projects?
« Reply #8 on: 01/19/2017 01:34 PM »
If I were starting a medium/small sat launch company, I'd consider an expendable SSTO to prove initial capability.

You could launch all the way to orbit without any staging events and with everything ground lit (and checked out before launch commit and clamp release). No deployments, no fairings, no recontact worries, no ullage motors, almost nothing.

Operationally, you'd end up using staging to get good performance, but for initial tests, expendable SSTO might be an interesting option.

« Last Edit: 01/19/2017 01:58 PM by Robotbeat »
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Offline scienceguy

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Re: Why the lack of SSTO projects?
« Reply #9 on: 01/19/2017 08:43 PM »
Are there any studies of SSTO's made of more modern, lighter materials like carbon fiber?
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Offline Toast

Re: Why the lack of SSTO projects?
« Reply #10 on: 01/19/2017 09:59 PM »
Are there any studies of SSTO's made of more modern, lighter materials like carbon fiber?
VentureStar and Skylon. VentureStar was cancelled, Skylon is still in development. Both are liable to start "lively" discussions around here.

Online Robotbeat

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Re: Why the lack of SSTO projects?
« Reply #11 on: 01/19/2017 10:14 PM »
And ITS, which Musk says is barely an SSTO in some variant by itself.

But yeah, X-33 was the venturestar sub scale prototype and had a carbon fiber tank which caused major headaches.

DeltaClipper, too. DC-X (its subscale prototype), was partly carbon fiber and DC-XA had aluminum-lithium alloy for tank structure.

Even Shuttle had carbon fiber parts.
« Last Edit: 01/19/2017 10:20 PM by Robotbeat »
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Offline Darkseraph

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Re: Why the lack of SSTO projects?
« Reply #12 on: 01/19/2017 10:25 PM »
The lack of projects is mostly due to the withdrawal of government support for such projects. The Sabre Engine is being slowly funded and that is pretty much it. SSTOs are expensive bleeding edge machines that are nowhere near as technologically mature as TSTO-RLV's. They would take possibly decades and billions to just get to a demonstration system. I can't see private companies jumping at this by themselves.

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Online Robotbeat

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Re: Why the lack of SSTO projects?
« Reply #13 on: 01/19/2017 10:41 PM »
The lack of projects is mostly due to the withdrawal of government support for such projects. The Sabre Engine is being slowly funded and that is pretty much it. SSTOs are expensive bleeding edge machines that are nowhere near as technologically mature as TSTO-RLV's. They would take possibly decades and billions to just get to a demonstration system. I can't see private companies jumping at this by themselves.
What is ITS, if it's not SpaceX trying to jump into what is essentially a SSTO?

And by the way, Virgin Galactic Branson wants long distance point to point transport in a rocket ship, which is nearly the same performance as SSTO.

Government can and likely will encourage and help such projects along, but I'm not sure we need to rely on government to lead any such efforts.
« Last Edit: 01/19/2017 10:46 PM by Robotbeat »
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Offline Darkseraph

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Re: Why the lack of SSTO projects?
« Reply #14 on: 01/19/2017 11:01 PM »
^ The dearth of SSTO projects in the private sphere relative to TSTO speaks for itself. Even the bleeding edge ITS is being designed as a two stage system. Technologies that are essential for SSTO tend to be very beneficial for TSTO and the gradual development and maturation of those in more modest two-stage systems may make it much more credible in the future for a private company to attempt SSTO. Or a future program similar to Darpa's XS-1 for SSTO could jump start it.. 

AFAIK, Branson is investing in more practical supersonic jets, not point-to-point suboribtal travel any time soon.
"For a successful technology, reality must take precedence over public relations, for Nature cannot be fooled." R.P.Feynman

Online Robotbeat

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Re: Why the lack of SSTO projects?
« Reply #15 on: 01/19/2017 11:12 PM »
He recently mentioned point to point. In ADDITION to the much slower supersonic jet.
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Offline Katana

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Re: Why the lack of SSTO projects?
« Reply #16 on: 01/20/2017 03:02 AM »
Are there any studies of SSTO's made of more modern, lighter materials like carbon fiber?
VentureStar and Skylon. VentureStar was cancelled, Skylon is still in development. Both are liable to start "lively" discussions around here.
Skylon is also shifting to TSTO.

Offline A_M_Swallow

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Re: Why the lack of SSTO projects?
« Reply #17 on: 01/20/2017 05:32 AM »
Reusable SSTO is viable on the Moon and possible on Mars. Concentrate your effort on those.

Offline ChrisWilson68

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Re: Why the lack of SSTO projects?
« Reply #18 on: 01/20/2017 06:24 AM »
The answer to the question in the title is simple: it's a bad idea.  Take any credible SSTO system using whatever optimistic technological progress you like for the foreseeable future and you can take those same technologies and make a TSTO system that gives you a better performance/cost and performance/risk trade-off.

Staging is a fantastic technology.  Yes, there are some costs and risks associated with staging, but with Earth's gravity, chemical engines, and foreseeable materials technology, removing staging just introduces greater costs and risks in other parts of the system for an equal payload.

That's true for expendable systems (expendable TSTO is better than expendable SSTO), and it's true to an even greater extent for reusable systems (reusable TSTO is better than reusable SSTO).
« Last Edit: 01/20/2017 06:25 AM by ChrisWilson68 »

Offline KelvinZero

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Re: Why the lack of SSTO projects?
« Reply #19 on: 01/20/2017 06:50 AM »
For a long time I wondered the exact opposite of the OP:

Why are there these hugely extravagant NASA reusable vehicle projects that fail instead of just doing an incremental approach, eg starting with TSTO and reusable boosters?

Then SpaceX came along, and Blue Origin, but I really wonder why we couldn't have done this almost mundane approach first, way back in the 70s.

Admittedly I was mostly thinking of things like the fly-back booster that the airforce was looking at. And I never considered that a commercial company would do this rather than NASA which specifically has budgets for developing things beyond the current state of the art, and doesn't need commercial success at each step.

Offline john smith 19

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Re: Why the lack of SSTO projects?
« Reply #20 on: 01/20/2017 07:31 AM »
Then SpaceX came along, and Blue Origin, but I really wonder why we couldn't have done this almost mundane approach first, way back in the 70s.
2 reasons.

1) NASA under Nixon suffered a 90% reduction in it's budget as a proportion of total government spending.
With such a cut down there was little reason to explore reusing existing stages, especially as the biggest (the Saturn V) had already ceased production by 1968.

2)Because in fact it's not "mundane". It took SX 5 years from F9's first flight to delivering a 1st landing of the 1st stage despite having the Grasshopper test vehicle to practice on and processors about 450x more powerful than those on the early Shuttle flights. That is from no more than a top speed of M10. 

Musk ruled out making the 2nd stage reusable (which is the final velocity an SSTO would have to achieve) at all.

So even partial reusability has turned out to be quite tough. The key seems to be recognizing that engine TVC alone can't do it.  Something it seems none of the 60's stage reuse concepts considered at all.
« Last Edit: 01/20/2017 07:34 AM by john smith 19 »
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Offline Nomic

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Re: Why the lack of SSTO projects?
« Reply #21 on: 01/20/2017 10:09 AM »
Always liked the idea of dual mixture ratio hydrolox for any one crazy enough to try reusable SSTO. Start off running LOX rich, switch to fuel rich at the equivalent of staging. Bulk density similar to methlox, but with full flow staged combustion ISP of 360 at sea level LOX rich going to 460 fuel rich ISP in the vacuum. LOX rich tan mentioned by JonGoff on the other thread is an interesting variation, lower pressure injection of the extra TAN LOX reducing the delta in pumping requirements between fuel rich and LOX rich modes.  Would still pose some interesting pump design problems.

For a smallsat SSTO, the original rotary rocket idea could be an option. Only scales up to 1000kg, maybe less. Wonder if it could be combined with a dual mixture ratio hydrolox, would probably have to sacrifice rotor blade aerofoil performance to get a large enough hydrogen line through it.

Offline Proponent

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Re: Why the lack of SSTO projects?
« Reply #22 on: 01/20/2017 01:05 PM »
Always liked the idea of dual mixture ratio hydrolox for any one crazy enough to try reusable SSTO. Start off running LOX rich, switch to fuel rich at the equivalent of staging. Bulk density similar to methlox, but with full flow staged combustion ISP of 360 at sea level LOX rich going to 460 fuel rich ISP in the vacuum.

I had a quick look at  variable-mixture-ratio lox-hydrogen SSTO a while ago but was underwhelmed by the results.

Online Robotbeat

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Re: Why the lack of SSTO projects?
« Reply #23 on: 01/20/2017 01:32 PM »
Theoretically, it's a nearly perfect solution as oxygen is very dense. This allows you to adjust the mixture to match the velocity. This is how you can get an energy efficiency at lower speeds.

Variable mixture SSTO is especially interesting if you're limited by energy, i.e. If propellant costs are significant.
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Offline john smith 19

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Re: Why the lack of SSTO projects?
« Reply #24 on: 01/20/2017 07:35 PM »
Always liked the idea of dual mixture ratio hydrolox for any one crazy enough to try reusable SSTO. Start off running LOX rich, switch to fuel rich at the equivalent of staging.
The J2 did this. Sacrificing Isp to improve payload seems counter intuitive but it's the concept of putting less KE into the remaining mass of the vehicle.

In a era of much lighter and faster computer control the logical move is to step profile the O2 O:F ratio as you rise.

BTW Aerojet seemed to have been quite fond of this tactic in many of their design studies. I think they went as high as 12:1. It's another of those "low hanging fruit" you should be looking at if you're going to do SSTO.

IRL the joker is you run oxidizer rich, which makes US developers very nervous, and you transition through the stoichometric  (maximum temperature) range. Obviously if you can scan through that range quickly enough without triggering combustion instability that's not a problem but I don't think anyone's ever really done that.  :(
"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 Robotbeat

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Re: Why the lack of SSTO projects?
« Reply #25 on: 01/20/2017 07:41 PM »
Maybe introduce the oxygen down-stream for lift-off, like in a thrust-augmented nozzle. That way, the combustion chamber conditions remain largely unchanged.

You'd probably want a separate lower pressure, higher mass flow turbopump just for the thrust-augmenting liquid oxygen.

I think it'd work. Someone should try it! :)

Edit: the Aerojet patent expires in 4 years...
« Last Edit: 01/20/2017 07:43 PM by Robotbeat »
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Offline KelvinZero

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Re: Why the lack of SSTO projects?
« Reply #26 on: 01/20/2017 09:10 PM »
Then SpaceX came along, and Blue Origin, but I really wonder why we couldn't have done this almost mundane approach first, way back in the 70s.
2)Because in fact it's not "mundane". It took SX 5 years from F9's first flight to delivering a 1st landing of the 1st stage despite having the Grasshopper test vehicle to practice on and processors about 450x more powerful than those on the early Shuttle flights. That is from no more than a top speed of M10.
I just meant basics, eg TSTO reusability before SSTO reusability. Not making it also immediately and always manned to _really_ tie potential for innovation and experimentation in knots. Not having the bizarre configuration of solids burning next to a massive hydrogen tank and engine. 4 things that have to separate sideways instead of 2 or 3 vertically.

And they did have unmanned landings. And that is a good place to invest development anyway. Less effort on the other issues would have solved these ones faster. And I was actually imagining flyback boosters, or in any case not the pretty miraculous thing SpaceX did of taking a fairly conventional rocket without particularly special physical characteristics such as throttling and just using incredible computing power to get a hoverslam type solution working.

I think NASA could have achieved a lot if it was allowed to do a sensible two (or 1.5) stage unmanned launcher, just a workhorse like F9, only concentrate on reuse of the first stage or boosters at first, but know you would not have to go back to the drawing board for the entire rocket if you decide to later consider upper stage reuse, or a "dreamchaser" like space plane in any case.

I know a lot of it was politics.

Offline ChrisWilson68

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Re: Why the lack of SSTO projects?
« Reply #27 on: 01/20/2017 11:04 PM »
Musk ruled out making the 2nd stage reusable (which is the final velocity an SSTO would have to achieve) at all.

Musk didn't rule it out.  He decided the economics of it don't make sense for now.  That's an important difference.

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Re: Why the lack of SSTO projects?
« Reply #28 on: 01/20/2017 11:43 PM »
Indeed. His comments leave open the possibility of 2nd stage reuse, just not right now. From what I've heard from spiiice on reddit, he's kind of obsessed with the idea of 2nd stage reuse.
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Offline clongton

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Re: Why the lack of SSTO projects?
« Reply #29 on: 01/20/2017 11:44 PM »
Basic answer to the basic question:
Chemical propulsion just cannot provide enough power long enough to enter orbit with any kind of meaningful payload. At least in earth's gravity well. It just costs too much money to produce a vehicle that will never be able to pay for itself. You won't see a useful SSTO vehicle until the stupid phobias against nuclear power are lifted.
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Offline john smith 19

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Re: Why the lack of SSTO projects?
« Reply #30 on: 01/21/2017 12:17 AM »
I think NASA could have achieved a lot if it was allowed to do a sensible two (or 1.5) stage unmanned launcher, just a workhorse like F9, only concentrate on reuse of the first stage or boosters at first, but know you would not have to go back to the drawing board for the entire rocket if you decide to later consider upper stage reuse, or a "dreamchaser" like space plane in any case.
The rules under which Shuttle was developed were as follows.
1)No more than $1Bn per year.
2)No money can be rolled over to the next year.
3)There is no increase to allow for inflation (during the 1970's which was a period of high US inflation)
4)There is no contingency allowance for cost overruns.

To put this in perspective that was viewed as enough to develop 1 new rocket engine and 1 new complete "stage" IE Orbiter.

You might almost think Nixon didn't want NASA to succeed in developing a new launch vehicle. :-|

The result being the aircraft + huge RATO packs + monster drop tank architecture.

Once you know that background you realize STS had very few choices to get anything flying.  :(
« Last Edit: 01/21/2017 12:32 AM by john smith 19 »
"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.

Offline Vultur

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Re: Why the lack of SSTO projects?
« Reply #31 on: 01/21/2017 12:19 AM »
IIRC a Falcon 9 first stage can get to orbit on its own, but with 0 payload.

That's about right (IIRC it was too small to be useful, maybe a few hundred kg, not quite 0). But...

Quote
So any low-risk developments would be pointless, which leaves the high-risk path of Skylon.

...that doesn't follow, because F9 first stage is optimized as a first stage. It carries <100 (IIRC) tons of second stage, as well as the payload. If you added that 100ish tons as more fuel (minus whatever the extra tank weight would be) its delta-v would be significantly higher.

IIRC mass ratio of 30 was mentioned for Falcon Heavy side booster, at least at one point. With that tank stretch the mass ratio could end up extremely good.

Huge investment with massive risk of unproven system for what market ?

The investment wouldn't be that huge.

OK, over a hundred million (F1 was $90 million, an F1 payload class SSTO would be more) but on the scale of space projects or large corporations, not so huge.

And the risk is not that big since there is really no 'out there' technology.

A really reusable "gas and go" SSTO would make space cheap - far more so than a semireusable (Shuttle or F9) system could ever achieve, probably significantly more than a two-stage fully reusable.

Basic answer to the basic question:
Chemical propulsion just cannot provide enough power long enough to enter orbit with any kind of meaningful payload. At least in earth's gravity well.

I just don't see the evidence for that. When I run the rocket equation with Merlin 1D's known Isp and the best demonstrated structural mass fractions, I get something very good.

Remember that Mercury-Atlas was almost an expendable SSTO (swap out those engines with modern ones and it would easily be a true SSTO) and it reached orbit in 1961.

Quote
You won't see a useful SSTO vehicle until the stupid phobias against nuclear power are lifted.

NERVA style nuclear rockets are too low TWR for practical Earth liftoff, IIRC. A nuclear lightbulb might work but that's way more unknown technology.

Project Orion would do it easily, of course, but there are other objections to that one than the fission products. Wouldn't it fry a whole bunch of existing satellites.

Offline john smith 19

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Re: Why the lack of SSTO projects?
« Reply #32 on: 01/21/2017 12:39 AM »
The thing with all proposed VTO SSTO's is they sacrifice payload for simplicity.

So far 3-4% of GTOW on 2 (or sometimes more) stages has outweighed the benefits of 1% (or thereabouts) on 1 stage.

That's been the ball park for reusable VOTL SSTO  proposals.

So maybe an expendable SSTO could do better (1.5%? 2%?)

But bottom line More GTOW / less payload --> higher $/lb to orbit.

I could see an existing stage design being adapted to an expendable SSTO, but would the development cost be recouped by the number of launches it would make in it's lifetime?
« Last Edit: 01/21/2017 12:40 AM by john smith 19 »
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Offline Vultur

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Re: Why the lack of SSTO projects?
« Reply #33 on: 01/21/2017 03:20 AM »
The thing with all proposed VTO SSTO's is they sacrifice payload for simplicity.

So far 3-4% of GTOW on 2 (or sometimes more) stages has outweighed the benefits of 1% (or thereabouts) on 1 stage.

That's been the ball park for reusable VOTL SSTO  proposals.

Well 'outweighed the benefits' might not be quite the situation. 2/3STO (or 'halfway' approaches like the Shuttle and Mercury-Atlas where there are discarded parts but the "upper stage" engines light on the ground) have always been chosen historically, yeah.

But there are factors other than pure engineering benefits in those decisions, like risk aversion & "irrational" government budgeting limits (Shuttle), and political pressure to reuse pre-existing hardware (eg SLS).

Quote
But bottom line More GTOW / less payload --> higher $/lb to orbit.

I doubt that. All else being equal, sure - but all else is definitely not equal.

Total cost probably doesn't go up linearly with size, even if materials costs do (F1 cost $90 million to develop, the original version of F9 cost $300 million to develop - even if we count much of the F1 cost into F9's because of heritage/experience, that's still about x4 development cost for about x10 size).

So the difference between 1% of GTOW and 3-4% of GTOW is 3-4x vehicle size for the same payload... but less than 3-4x cost.

And a reusable SSTO should be able to fly way more than 4x more often... even 10x would be pretty unimpressive.

EDIT: fixed quote tag
« Last Edit: 01/21/2017 03:21 AM by Vultur »

Online Robotbeat

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Re: Why the lack of SSTO projects?
« Reply #34 on: 01/21/2017 05:21 AM »
Falcon booster, full thrust and densified should get at least 3-6 tons to LEO equatorial expendable SSTO. That's not insignificant. Particularly the stretched version for FH (that has now changed to non-stretched).
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Offline Katana

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Re: Why the lack of SSTO projects?
« Reply #35 on: 01/21/2017 07:02 AM »
Indeed. His comments leave open the possibility of 2nd stage reuse, just not right now. From what I've heard from spiiice on reddit, he's kind of obsessed with the idea of 2nd stage reuse.
2nd stage reuse is always simpler than reuseable SSTO or shuttle architecture on the same conditions. TPS of large rockets is a great pain.

Offline Katana

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Re: Why the lack of SSTO projects?
« Reply #36 on: 01/21/2017 07:13 AM »
I think NASA could have achieved a lot if it was allowed to do a sensible two (or 1.5) stage unmanned launcher, just a workhorse like F9, only concentrate on reuse of the first stage or boosters at first, but know you would not have to go back to the drawing board for the entire rocket if you decide to later consider upper stage reuse, or a "dreamchaser" like space plane in any case.
The rules under which Shuttle was developed were as follows.
1)No more than $1Bn per year.
2)No money can be rolled over to the next year.
3)There is no increase to allow for inflation (during the 1970's which was a period of high US inflation)
4)There is no contingency allowance for cost overruns.

To put this in perspective that was viewed as enough to develop 1 new rocket engine and 1 new complete "stage" IE Orbiter.

You might almost think Nixon didn't want NASA to succeed in developing a new launch vehicle. :-|

The result being the aircraft + huge RATO packs + monster drop tank architecture.

Once you know that background you realize STS had very few choices to get anything flying.  :(
The shuttle program spended more than 50% the total cost of Apollo program and reinvented a launch system sending 100 tons into orbit , only 20% are useful payload.

Even more expensive than resuming the Saturn/Apollo/Skylab series could cost.

Saturn shuttle with F1/J2 engines and shuttle C for cargo are cancelled.

Offline john smith 19

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Re: Why the lack of SSTO projects?
« Reply #37 on: 01/21/2017 08:39 AM »
2nd stage reuse is always simpler than reuseable SSTO or shuttle architecture on the same conditions. TPS of large rockets is a great pain.
That's certainly an interesting PoV.

Most people who've looked at the problem note a large vehicle (IE one that keeps its tanks) has a large surface area but a low ballistic coefficient, so its entry interface is higher. That means it can lose more energy at a lower rate, enabling a lower temperature TPS. IOW Shuttles problem was not that it was too big, it was too small.

The thing is all SSTO proposals I'm aware of have been designed to do SSTO and to return. They side stepped the control issues of high aspect ratio, relatively flexible standard launch stages. Given SX had to fit grid fins to finally make it possible to work that seems like a smart move.

I look forward to SX demonstrating 2nd stage reuse.  I look forward even more to seeing at what price they will offer such a vehicle at.
"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.

Offline john smith 19

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Re: Why the lack of SSTO projects?
« Reply #38 on: 01/21/2017 09:04 AM »
Well 'outweighed the benefits' might not be quite the situation. 2/3STO (or 'halfway' approaches like the Shuttle and Mercury-Atlas where there are discarded parts but the "upper stage" engines light on the ground) have always been chosen historically, yeah.

But there are factors other than pure engineering benefits in those decisions, like risk aversion & "irrational" government budgeting limits (Shuttle), and political pressure to reuse pre-existing hardware (eg SLS).
Unfortunately IRL those also count as "benefits."  :(
Quote
Quote
But bottom line More GTOW / less payload --> higher $/lb to orbit.

I doubt that. All else being equal, sure - but all else is definitely not equal.

Total cost probably doesn't go up linearly with size, even if materials costs do (F1 cost $90 million to develop, the original version of F9 cost $300 million to develop - even if we count much of the F1 cost into F9's because of heritage/experience, that's still about x4 development cost for about x10 size).

So the difference between 1% of GTOW and 3-4% of GTOW is 3-4x vehicle size for the same payload... but less than 3-4x cost.
You have the problem backwards. If you don't have the "Bank of Elon" behind you you have to convince financiers this is a good idea.

They will do due diligence by plugging in that vehicle size into their aerospace cost model, where cost is roughly proportional to GTOW.
Result "Your SSTO will give this much to orbit, but a TSTO will give 2-4x that amount for the same GTOW. Funding refused."
This demonstrates 2 points.

If you do what you always do you'll get what you always got.

Being able to match a TSTO ELV in payload fraction matters. No historical SSTO had managed this.

These cost models are also the ones that reckon the budget to do F1 and up to the first F9 launch would be $2Bn, about 6.6x the known figure.
Quote
And a reusable SSTO should be able to fly way more than 4x more often... even 10x would be pretty unimpressive.

EDIT: fixed quote tag
Historically this has been something of a circular argument.  An SSTO with 1/3 to 1/4 of the payload of a TSTO ELV has to fly 3-4x more often. Personally I think it is possible and I don't think there are many payloads that cannot be broken up into reasonable sized modules for on orbit assembly. Of course what "reasonable sized" means is open to wide interpretation.  :)
"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.

Offline Katana

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Re: Why the lack of SSTO projects?
« Reply #39 on: 01/21/2017 11:38 AM »
2nd stage reuse is always simpler than reuseable SSTO or shuttle architecture on the same conditions. TPS of large rockets is a great pain.
That's certainly an interesting PoV.

Most people who've looked at the problem note a large vehicle (IE one that keeps its tanks) has a large surface area but a low ballistic coefficient, so its entry interface is higher. That means it can lose more energy at a lower rate, enabling a lower temperature TPS. IOW Shuttles problem was not that it was too big, it was too small.

The thing is all SSTO proposals I'm aware of have been designed to do SSTO and to return. They side stepped the control issues of high aspect ratio, relatively flexible standard launch stages. Given SX had to fit grid fins to finally make it possible to work that seems like a smart move.

I look forward to SX demonstrating 2nd stage reuse.  I look forward even more to seeing at what price they will offer such a vehicle at.
Both stages of F9 are large and hollow structures with similar low ballistic coefficient, thus require similar TPS thickness.

But the absolute scale and cost of first stage is much larger, a large stage suffering orbital reentry would increase total cost.

Anyway, a TSTO first stage could live a happy long life with moderate reentry velocity.
« Last Edit: 01/21/2017 11:51 AM by Katana »

Offline IsaacKuo

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Re: Why the lack of SSTO projects?
« Reply #40 on: 01/21/2017 01:53 PM »
Not that it necessarily helps enough, but if we assume ISRU source of propellant in space, a reusable upper stage could actively cancel out its orbital velocity before reentry. This could greatly reduce the TPS mass that must be carried all the way to orbit and back.

Alternatively, ISRU resupplied lox might be used to open cycle cool the TPS during reentry, directing the hot oxygen out nozzles for additional braking thrust. (Lox might be harvested in LEO via atmospheric scooping.) Same practical effect of minimizing TPS mass, but you only need to resupply oxidizer.

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Re: Why the lack of SSTO projects?
« Reply #41 on: 01/21/2017 02:59 PM »
Better to use nitrogen in that case instead of oxygen. There's like 4x as much nitrogen, and it's nearly inert.
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Offline Proponent

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Re: Why the lack of SSTO projects?
« Reply #42 on: 01/21/2017 04:07 PM »
Always liked the idea of dual mixture ratio hydrolox for any one crazy enough to try reusable SSTO. Start off running LOX rich, switch to fuel rich at the equivalent of staging.
The J2 did this. Sacrificing Isp to improve payload seems counter intuitive but it's the concept of putting less KE into the remaining mass of the vehicle.

I just had another look at the mixture-ratio data in Apollo by the Numbers, and I'm a bit puzzled.  First of all, for each burn of each stage, two O/F figures are given:  one corresponding to the start of the burn and the other supposedly the change during the burn.  But the latter figure, however, is generally larger than the former, which implies that O/F more than doubled during the burn.  That seems very unlikely, so I assume the second number is actually the O/F at shut-down.

With that assumption, it seems that the O/F gets leaner (higher) during most if not all burns.  But don't we expect just the opposite, namely getting richer (more hydrogen) to increase specific impulse as the burn proceeds?

It also seems to be the case that the second S-IVB burn is on average leaner than the first (I say "seems to be," because the average during the burn isn't necessarily the average of the intial and final values).  Rocket-equation-wise, this too seems counterintuitive, though maybe it's a way of maximizing stage performance in the face of hydrogen boil-off.

What gives?

Quote
BTW Aerojet seemed to have been quite fond of this tactic in many of their design studies. I think they went as high as 12:1.

That sounds interesting -- do you have any pointers as where to find these studies?

BTW, attached is a Rocketdyne study of a variable-mixture-ratio lox-hydrogen engine.

Offline IsaacKuo

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Re: Why the lack of SSTO projects?
« Reply #43 on: 01/21/2017 06:23 PM »
Better to use nitrogen in that case instead of oxygen. There's like 4x as much nitrogen, and it's nearly inert.

That's true, assuming you can use liquid nitrogen in one (or both) of the propellant tanks.

Offline Katana

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Re: Why the lack of SSTO projects?
« Reply #44 on: 01/22/2017 02:22 AM »
Always liked the idea of dual mixture ratio hydrolox for any one crazy enough to try reusable SSTO. Start off running LOX rich, switch to fuel rich at the equivalent of staging.
The J2 did this. Sacrificing Isp to improve payload seems counter intuitive but it's the concept of putting less KE into the remaining mass of the vehicle.

I just had another look at the mixture-ratio data in Apollo by the Numbers, and I'm a bit puzzled.  First of all, for each burn of each stage, two O/F figures are given:  one corresponding to the start of the burn and the other supposedly the change during the burn.  But the latter figure, however, is generally larger than the former, which implies that O/F more than doubled during the burn.  That seems very unlikely, so I assume the second number is actually the O/F at shut-down.

With that assumption, it seems that the O/F gets leaner (higher) during most if not all burns.  But don't we expect just the opposite, namely getting richer (more hydrogen) to increase specific impulse as the burn proceeds?

It also seems to be the case that the second S-IVB burn is on average leaner than the first (I say "seems to be," because the average during the burn isn't necessarily the average of the intial and final values).  Rocket-equation-wise, this too seems counterintuitive, though maybe it's a way of maximizing stage performance in the face of hydrogen boil-off.

What gives?

Quote
BTW Aerojet seemed to have been quite fond of this tactic in many of their design studies. I think they went as high as 12:1.

That sounds interesting -- do you have any pointers as where to find these studies?

BTW, attached is a Rocketdyne study of a variable-mixture-ratio lox-hydrogen engine.
Variations of mix ratio are too small to be meaningful.

Offline A_M_Swallow

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Re: Why the lack of SSTO projects?
« Reply #45 on: 01/22/2017 04:06 AM »
For a reusable TSTO can the upper stage and the capsule's service module be merged?

Offline HMXHMX

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Re: Why the lack of SSTO projects?
« Reply #46 on: 01/22/2017 04:23 AM »
For a reusable TSTO can the upper stage and the capsule's service module be merged?

Indeed it could.  There are some interesting configurations that can be explored along those lines.  The "Mainstage" (as I call it) would perform a once-around mission, never entering orbit, while the spacecraft with at least a few hundred m/s of delta V circularizes, raises orbit, etc. on its own.

Offline RotoSequence

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Re: Why the lack of SSTO projects?
« Reply #47 on: 01/22/2017 04:23 AM »
For a reusable TSTO can the upper stage and the capsule's service module be merged?

If you extrapolate the design of SpaceX's Interplanetary Transport System architecture to its logical conclusion, I don't see why you couldn't perform an arbitrary amount of systems integration into a launch vehicle's second stage as weight allows.
« Last Edit: 01/22/2017 04:25 AM by RotoSequence »

Offline Vultur

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Re: Why the lack of SSTO projects?
« Reply #48 on: 01/22/2017 12:30 PM »
\
Unfortunately IRL those also count as "benefits."  :(
Quote
Well, sure, but more for NASA/government projects... I was asking more about the lack of SSTO projects among the "new"/commercial space companies.

Quote
You have the problem backwards. If you don't have the "Bank of Elon" behind you you have to convince financiers this is a good idea.

They will do due diligence by plugging in that vehicle size into their aerospace cost model, where cost is roughly proportional to GTOW.

But where does this assumption ("cost proportional to GTOW") come from? It seems not to be true, or at least to be avoidable.

Quote

Being able to match a TSTO ELV in payload fraction matters. No historical SSTO had managed this.

But why is payload fraction the relevant metric? Cost per flight is more important.


Historically this has been something of a circular argument.  An SSTO with 1/3 to 1/4 of the payload of a TSTO ELV has to fly 3-4x more often.

Yeah but it ought to be able to fly >10x more often - early on. Once the market expands and the technology matures >>100x. 1 flight per vehicle every day or two doesn't really seem that unreasonable... IF you computerize the thing to the max, so there's no human inspections between flights unless the vehicle's computers flag a problem.

High flight rate and low cost per flight will be dependent on low labor costs and therefore heavily automated systems. Also probably not using existing ground infrastructure.

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Re: Why the lack of SSTO projects?
« Reply #49 on: 01/22/2017 01:22 PM »
In other words, ITS.
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Offline john smith 19

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Re: Why the lack of SSTO projects?
« Reply #50 on: 01/23/2017 06:32 AM »
Variations of mix ratio are too small to be meaningful.
Check the paper
"Enhancing the Saturn V translunar payload capability." by Logsdon & Africano.

The paper describes how NASA increased the payload to the Moon over the life of the Moon launches by 5%, at a time when the cost of that mass per unit to LLO was higher than Gold without hardware changes to the vehicle (essentially by doing, for want of a better phrase, "better maths"). That's about 5 tonnes.

They estimate that 1/2 of that improvement was due to MR control, which could not be applied to the first stage (which probably would have been even better).

MR control can give significant benefits and if you're dealing with a VTO rocket only SSTO you'd better be looking at as much "low hanging fruit" as you can get given the high sensitivity to engine under performance and structural weight growth.

IMHO the paper should be on any LV designers must read list. Sadly I can't find the planned follow up paper on propellant biasing for maximum payload to orbit.  :(
« Last Edit: 01/23/2017 06:33 AM by john smith 19 »
"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.

Offline QuantumG

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Re: Why the lack of SSTO projects?
« Reply #51 on: 01/23/2017 06:40 AM »
2nd stage reuse is always simpler than reuseable SSTO or shuttle architecture on the same conditions. TPS of large rockets is a great pain.

Ummm.. the reentry system of Sea Dragon was the pressure vessel. Never flew, obviously, but I don't think anyone really argues there's much doubt it wouldn't work. Big fluffy things reenter intact even when you don't want them too. It's small things that need painful TPS.
Jeff Bezos has billions to spend on rockets and can go at whatever pace he likes! Wow! What pace is he going at? The slowest possible.

Offline Nomic

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Re: Why the lack of SSTO projects?
« Reply #52 on: 01/23/2017 08:55 AM »
BTW Aerojet seemed to have been quite fond of this tactic in many of their design studies. I think they went as high as 12:1. It's another of those "low hanging fruit" you should be looking at if you're going to do SSTO.

IRL the joker is you run oxidizer rich, which makes US developers very nervous, and you transition through the stoichometric  (maximum temperature) range. Obviously if you can scan through that range quickly enough without triggering combustion instability that's not a problem but I don't think anyone's ever really done that.  :(

Aerojets work on the OTV engine touched on using mixture rations up to 13:1, some of the problems discussed  on page 108 onwards, and  solutions including gold platting the MCC (page 115) and platinum baffles. Idea behind the high mixture ratios was to use Lunar regolith as source of ISRU LOX. Don't think anyone has ever run an engine at these sort of mixture ratios though.

Offline john smith 19

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Re: Why the lack of SSTO projects?
« Reply #53 on: 01/23/2017 03:33 PM »
Aerojets work on the OTV engine touched on using mixture rations up to 13:1, some of the problems discussed  on page 108 onwards, and  solutions including gold platting the MCC (page 115) and platinum baffles. Idea behind the high mixture ratios was to use Lunar regolith as source of ISRU LOX. Don't think anyone has ever run an engine at these sort of mixture ratios though.
Exactly.  And check that expansion ratio. 1200.  :o

This is clearly not going to be operating anywhere near sea level.
"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.

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Re: Why the lack of SSTO projects?
« Reply #54 on: 01/23/2017 03:36 PM »
That's the neat thing about Thrust Augmented Nozzles. The expansion ratio for the main engine can be huge, but because you're adding a bunch of propellant downstream when at low altitudes, you don't get flow separation.
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Offline Patchouli

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Re: Why the lack of SSTO projects?
« Reply #55 on: 01/23/2017 04:51 PM »
That's the neat thing about Thrust Augmented Nozzles. The expansion ratio for the main engine can be huge, but because you're adding a bunch of propellant downstream when at low altitudes, you don't get flow separation.

One reason I think a SSME with TAN  might be the prefect engine for a simple near term SSTO.
Right now the nozzle is a compromise for sea level and  vacuum performance that uses a lot of tricks to prevent flow separation.
But a TAN nozzle could have an expansion ratio that is better optimized for both sea level and vacuum operation.

« Last Edit: 01/23/2017 04:54 PM by Patchouli »

Offline Nilof

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Re: Why the lack of SSTO projects?
« Reply #56 on: 01/23/2017 05:08 PM »
The other advantage of TAN of course is that it is one way to implement a tripropellant engine. For SSTO's, the increased payload fraction that can potentially be afforded by a tripropellant engine is difficult to understate.

Among the SSTO's that got somewhat serious consideration, I believe the MAKS spacecraft was the one that had the most margin, entirely due to the amazing performance of the RD-701.
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 #57 on: 01/25/2017 04:39 PM »
Ummm.. the reentry system of Sea Dragon was the pressure vessel. Never flew, obviously, but I don't think anyone really argues there's much doubt it wouldn't work. Big fluffy things reenter intact even when you don't want them too. It's small things that need painful TPS.
True.

Shuttle would have been a very different, and bigger design had they incorporated the ET into its design. It would also have had to deal with the issue of cycle life for the main fuel tanks over the life of the vehicle. Instead of which they opted to recover "just the engines" and deal with a highly temperamental TPS instead.  :(

50 years on and it seems both Arianespace and ULA are planning to adopt the same plan, with a small dense module that will fall deep into the atmosphere before hitting air dense enough to slow it down.

One reason I think a SSME with TAN  might be the prefect engine for a simple near term SSTO.
Not that near term. Look at what proportion of thrust comes from TAN. It's not just filling the bell to stop flow sep. At SL SSME is about 384Kbls. Aerojet were talking 50-100% of that. IE 190-384 Klbs That's a pretty major pump installation that's either got to run off it's own power system or tap the existing SSME turbine drive.
Quote
Right now the nozzle is a compromise for sea level and  vacuum performance that uses a lot of tricks to prevent flow separation.
Which are? The only "trick" I'm aware of the very high chamber pressure, coupled with some care in keeping the interior of the bell clean.
Quote
But a TAN nozzle could have an expansion ratio that is better optimized for both sea level and vacuum operation.
I think the term you're looking for is more adaptable to both SL and vacuum. You can get individual nozzles that are very well adapted to either condition already, the problem is when you want it to do both.
"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.

Offline Archibald

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Re: Why the lack of SSTO projects?
« Reply #58 on: 01/25/2017 06:37 PM »
it is a crying shame nothing happened with TAN over the last decade.

Offline john smith 19

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Re: Why the lack of SSTO projects?
« Reply #59 on: 01/25/2017 07:08 PM »
\
Unfortunately IRL those also count as "benefits."  :(
Well, sure, but more for NASA/government projects... I was asking more about the lack of SSTO projects among the "new"/commercial space companies.
Because as "any fule know" a VTO SSTO has to sacrifice payload. A TSTO ELV is normally in the 3-4% of GTOW. Historically the VTO SSTO's that Philip Bono described were expected to hit 1-1.5% GTOW as payload.

That means you either a)Have to fly 3-4 flights to put the same mass in LEO or b) Make it 3-4x bigger.
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You have the problem backwards. If you don't have the "Bank of Elon" behind you you have to convince financiers this is a good idea.

They will do due diligence by plugging in that vehicle size into their aerospace cost model, where cost is roughly proportional to GTOW.

But where does this assumption ("cost proportional to GTOW") come from? It seems not to be true, or at least to be avoidable.
Cost data is collected by several organizations and essentially the information is graphed and a best fit curve found, much as data is collected on software development projects to update the COCOMO II cost model for large project development.

There are several problems with these models (as a google on the sci.space.* newsgroups would show you over the last 20 years).
They are mostly based on government LV and aircraft programmes. These tend to over run their costs, which moves the "centre of gravity" of the cost curve upward. I cannot guess what the F35 programme will do for the estimated cost of a fighter programme of X lbs payload and Y mph top speed for example.   :(

For aircraft lowering GTOW is a good idea, as it lightens the landing gear, increases range etc. In LV systems it encourages you to go to LH2. I think the key difference is that in launch the spec is always set at Orbital speed and altitude high enough to not immediately re-enter. Everything below that is sub orbital, and a failure.

These were the models that NASA checked against SX's internal accounts to conclude F1 and F9 up to first launch as a NASA contract under BAU rules would have cost $3.977Bn and $1.695bn under "more commercial" procurement rules.  :(
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Being able to match a TSTO ELV in payload fraction matters. No historical SSTO had managed this.

But why is payload fraction the relevant metric? Cost per flight is more important.
Not to sound repetitive but if you don't have an angel investor then you have to deal with commercial investors. They will hire someone to do "due diligence" who will probably plug your plan for payload and GTOW into one of those models.

As of now there is only 1 design concept that has voluntarily undergone detailed 3rd party inspection and passed.

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Yeah but it ought to be able to fly >10x more often - early on. Once the market expands and the technology matures >>100x. 1 flight per vehicle every day or two doesn't really seem that unreasonable... IF you computerize the thing to the max, so there's no human inspections between flights unless the vehicle's computers flag a problem.
The problem is the budget you're going to need to build that vehicle.  The LV business is strange.
No other transportation system has basically the same company make the vehicles and operate them. Ship builders don't run container liners. Locomotive mfg's don't run railroads. Volvo (who own Mack in the US) don't run a trucking company.

The business model for mfg is completely different from operators (in every other transportation system)  yet in the LV they are basically the same. As long as this model persists it seems impossible for the mfg to ever recoup the cost of their vehicles development through the  open market.  The only reason this has not been a problem is because historically development has been under written by a government, or a consortium of governments.  :(
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High flight rate and low cost per flight will be dependent on low labor costs and therefore heavily automated systems. Also probably not using existing ground infrastructure.
True. 
IIRC there's about 400 staff standing behind each airline takeoff.That's about 2 orders of magnitude smaller than Shuttle (and the size of that standing army is very important to the running costs).

Various techniques were developed (but not deployed) to radically lower inspection and repair costs for shuttle.

In some ways the key thing is to start backward, with the cost target, and then look at what can give you that.
"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.

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Re: Why the lack of SSTO projects?
« Reply #60 on: 01/25/2017 08:30 PM »
it is a crying shame nothing happened with TAN over the last decade.
It's nearly out of patent protection!
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Offline jongoff

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Re: Why the lack of SSTO projects?
« Reply #61 on: 01/25/2017 11:24 PM »
it is a crying shame nothing happened with TAN over the last decade.

No joke.

~Jon

Offline john smith 19

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Re: Why the lack of SSTO projects?
« Reply #62 on: 01/25/2017 11:49 PM »
it is a crying shame nothing happened with TAN over the last decade.
It's nearly out of patent protection!
A quick check suggests "Melvin Bulman" is the key person behind TAN (he's also the author of the papers from Aerojet on it).
US6568171 B2  priority date  July 5th 2001, published  2003
US 7823376 B2 (TAN in plug and E/D nozzles)  priority date 2005. Published 2010.

So it does look TAN will be free to use for bell nozzles around July 6th 2021.

Aerojet might still get something funded in the mean time. They did a certain amount of this using IR&D funding.
« Last Edit: 01/26/2017 09:20 AM by john smith 19 »
"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.

Offline Katana

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Re: Why the lack of SSTO projects?
« Reply #63 on: 01/26/2017 03:32 AM »
Intergrated mfg and operation is not that terrible.

United Airlines and Boeing and Pratt Whitney are fomerly intergrated.
https://en.m.wikipedia.org/wiki/History_of_United_Airlines#Beginnings

Offline john smith 19

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Re: Why the lack of SSTO projects?
« Reply #64 on: 01/26/2017 09:09 AM »
Intergrated mfg and operation is not that terrible.

United Airlines and Boeing and Pratt Whitney are fomerly intergrated.
https://en.m.wikipedia.org/wiki/History_of_United_Airlines#Beginnings
People always bring up Boeing.  Boeing. P&W and UAC were demerged in 1934

If it was such a good idea shouldn't most aircraft mfg or engine mfgs have bought up an airline?

Or why didn't airlines buy up engine mfgs or aircraft mfg to serve as an in house supplier, perfectly adapted to their needs?

As your link show's it was not anti-trust laws that caused it to split, although the relevant law would have prevents such a formation in the US. there was AFAIK no equivalent law anywhere else in the world. BOAC or BEA in the UK could have (for example) bough Rolls Royce, or Bristol engines. Yet neither did.

The fact the Boeing/P&W/UAC example is the only one people can come up with suggests it's a pretty bad model and unlikely to encourage the growth of either the airplane or travel markets.

Integration is the (extreme) exception in the airliner/airline market and the market is huge.

Integration in the ELV market is the norm (with Sea Launch and Arianespace slightly more decoupled).
In terms of mass moved, number of movements (launches) its tiny. A fairly small regional airport moves more mass in a day than the entire ELV launch business moves in a year.   :(

That doesn't explain why there are so few SSTO projects. It may explain why there so few LV projects.
« Last Edit: 01/28/2017 06:39 AM by john smith 19 »
"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.

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Re: Why the lack of SSTO projects?
« Reply #65 on: 01/26/2017 01:32 PM »
It does explain, though. Think about it. SSTO is good enough to get to LOW orbit, but doing reusably is super hard. You need a big upfront effort to deal with TPS while getting very good mass fraction. To justify this, you need super high flight rate, but you'll be stuck in LEO until you develop ANOTHER system. So you can only address a fraction of the total launches, which is currently less than 100 flights per year GLOBALLY among all classes, all countries, all orbits, and all companies. You'd need about that many launches, in a single class (and probably country at least to start, given how dual-use this technology is), and to a single orbit (until another vehicle is developed).

Whereas TSTO is (basically) enough for all orbits right out of the box. Global launch is intrinsically segregated enough that it probably makes the most sense to do an expendable TSTO. And if you do reuse, it's even harder to make the case for upper stage reuse than first stage.

tl;dr: Low total mass moved globally makes the economic difficulty of an SSTO rLV even worse than typical for a launch vehicle.
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Offline Jim

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Re: Why the lack of SSTO projects?
« Reply #66 on: 01/26/2017 02:09 PM »

The fact the Boeing/P&W/UAC example is the only one people can come up


TWA and Hughes.

Eastern (Florida Airways and Pitcairn Aviation and GM)

American (Robertson Aircraft Corporation and Colonial Air Transport)

So your point is wrong.

Offline tdperk

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Re: Why the lack of SSTO projects?
« Reply #67 on: 01/26/2017 03:04 PM »
it is a crying shame nothing happened with TAN over the last decade.
It's nearly out of patent protection!

Given the work of Foa, Lockwood, the RBCC concept--this smacks of patenting prior art.  Sweetman made a good case it is flying in the Aurora.

It does seem to me that the like permits relatively nonexotic lifting airframes to achieve SSTO with an acceptable payload fraction.

Offline john smith 19

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Re: Why the lack of SSTO projects?
« Reply #68 on: 01/26/2017 07:25 PM »
TWA and Hughes.
AFAIK Hughes Aircraft never built an airliner. The closest it got was the H4 Spruce Goose. 1 made and [EDIT crashed 70 feet altitude on maiden (and only) flight.] The link is tenuous. Howard Hughes was involved in both.
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Eastern (Florida Airways and Pitcairn Aviation and GM)
I presume you mean the chopping and changing around North American Aviation (a GM subsidiary in the 30's, something I was unaware of). Again NAA made no civilian transport aircraft that Pitcairn, eventually Eastern, used.
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American (Robertson Aircraft Corporation and Colonial Air Transport)
Again I cannot find any reference for situations where the aircraft mfg supplied the airline.
Quote

So your point is wrong.
Only partly. I note none of those conglomerates has lasted. AFAIK none of the mfg ever supplied the airline arm of the group with their products, other than Boeing.  In fact only Pitcairn seems to have made a notable aircraft mfg business, solely for airmail aircraft. It ended in 1933.

In the LV market the operator only uses the product from its mfg arm (Arianespace being the sole exception).

In aircraft the mfg/operator business model is obsolete. It never seems to have taken off as a way of doing business at all in any other transport industry.

People should ponder that, along with the fact that the annual amount of material put in LEO (after 60 years) is still measured in tonnes.  :( [EDIT while commercial aircraft traffic movements and payload move are in the millions and aircraft freight rates are 1000-10000x lower than LV costs on a $/Kg basis

http://siteresources.worldbank.org/EXTAIRTRANSPORT/Resources/515180-1262792532589/6683177-1268747346047/air_cargo_ch4.pdf Page 9  ]
« Last Edit: 01/28/2017 08:03 PM by john smith 19 »
"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.

Offline Vultur

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Re: Why the lack of SSTO projects?
« Reply #69 on: 01/27/2017 11:58 PM »
Not to sound repetitive but if you don't have an angel investor then you have to deal with commercial investors. They will hire someone to do "due diligence" who will probably plug your plan for payload and GTOW into one of those models.

Well sure. Needing a funding source outside of traditional investors is an issue... but doesn't completely explain why we haven't seen more in this direction IMO.

And we see a lot of "new space" concepts which seem to have little to no hope of getting the funding to get past the concept stage, but SSTOs are poorly represented even among those.

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As long as this model persists it seems impossible for the mfg to ever recoup the cost of their vehicles development through the  open market.

Why does the operator & manufacturer being the same company prevent recouping development costs? I thought that was more a flight rate (and labor cost per flight, secondarily) issue. 


Quote
True. 
IIRC there's about 400 staff standing behind each airline takeoff.That's about 2 orders of magnitude smaller than Shuttle (and the size of that standing army is very important to the running costs).

Yeah. And IMO with modern automation you ought to be able to get well below 400.

Offline john smith 19

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Re: Why the lack of SSTO projects?
« Reply #70 on: 01/28/2017 06:51 AM »
Quote
As long as this model persists it seems impossible for the mfg to ever recoup the cost of their vehicles development through the  open market.

Why does the operator & manufacturer being the same company prevent recouping development costs? I thought that was more a flight rate (and labor cost per flight, secondarily) issue. 
Because once you go full reusable the pricing levels to buy a vehicle sharply diverge from the price you can realistically charge for a launch.
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Except "flight rate" is an operations concept. Selling a turn key fully reusable RLV  separates the mfg from any concern about what the operator uses it for. It also separates them from the "standing army" of staff to support the vehicle.

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True. 
IIRC there's about 400 staff standing behind each airline takeoff.That's about 2 orders of magnitude smaller than Shuttle (and the size of that standing army is very important to the running costs).

Yeah. And IMO with modern automation you ought to be able to get well below 400.
As I noted with Shuttle there were a number of ideas for significantly speeding up the process and reducing the head count.

400's for a an airliner carrying passengers. In principle cargo planes should have smaller support teams. Also note that AFAIK that number includes service staff split across all vehicles in an airlines fleet.  bigger the fleet, smaller the fraction of those staff carried by any particular vehicle.
« Last Edit: 01/29/2017 12:36 AM by john smith 19 »
"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.

Offline Archibald

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Re: Why the lack of SSTO projects?
« Reply #71 on: 01/28/2017 08:41 AM »

Quote
AFAIK Hughes Aircraft never built an airliner. The closest it got was the H4 Spruce Goose. 1 made and crashed on maiden flight. The link is tenuous. Howard Hughes was involved in both.

It didn't crashed and still exist at the evergreen aviation museum.

Offline Vultur

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Re: Why the lack of SSTO projects?
« Reply #72 on: 01/29/2017 02:27 AM »
Except "flight rate" is an operations concept. Selling a turn key fully reusable RLV  separates the mfg from any concern about what the operator uses it for. It also separates them from the "standing army" of staff to support the vehicle.

But if the vehicle can't be operated at a profit, even taking in the recouping of development costs baked into the vehicle's sale price, then operators won't buy it (once they find out, anyway).

I still don't see how that changes the fundamental issues -- which IMO are 1) finding the initial funding and 2) per-flight cost, which is going to be driven by maintenance / personnel needs largely.

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As I noted with Shuttle there were a number of ideas for significantly speeding up the process and reducing the head count.

Sure but you could do way better than even that.

Shuttle was way expensive IMO both because the engine and TPS were at the edge of what 70s technology could handle and because of government funding limitations which led to choosing high-operating-cost options because development cost was limited.

Also VTHL is an inherently more complex design. I don't know if you could have done VTVL back then, but modern software can definitely handle it.

Quote
Also note that AFAIK that number includes service staff split across all vehicles in an airlines fleet.  bigger the fleet, smaller the fraction of those staff carried by any particular vehicle.

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.

Offline Katana

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Re: Why the lack of SSTO projects?
« Reply #73 on: 01/30/2017 11:24 AM »
 Why launchers should be comparable to airliners on the market sense? All of them except Shuttle (national assets) and F9R (not yet reused) are expendable.

Operators of something expendable are NOT operators any more, they become distributors. And the tiny numbers of customers render distributors unnecessary.

TWA and Hughes.
AFAIK Hughes Aircraft never built an airliner. The closest it got was the H4 Spruce Goose. 1 made and [EDIT crashed 70 feet altitude on maiden (and only) flight.] The link is tenuous. Howard Hughes was involved in both.
Quote
Eastern (Florida Airways and Pitcairn Aviation and GM)
I presume you mean the chopping and changing around North American Aviation (a GM subsidiary in the 30's, something I was unaware of). Again NAA made no civilian transport aircraft that Pitcairn, eventually Eastern, used.
Quote
American (Robertson Aircraft Corporation and Colonial Air Transport)
Again I cannot find any reference for situations where the aircraft mfg supplied the airline.
Quote

So your point is wrong.
Only partly. I note none of those conglomerates has lasted. AFAIK none of the mfg ever supplied the airline arm of the group with their products, other than Boeing.  In fact only Pitcairn seems to have made a notable aircraft mfg business, solely for airmail aircraft. It ended in 1933.

In the LV market the operator only uses the product from its mfg arm (Arianespace being the sole exception).

In aircraft the mfg/operator business model is obsolete. It never seems to have taken off as a way of doing business at all in any other transport industry.

People should ponder that, along with the fact that the annual amount of material put in LEO (after 60 years) is still measured in tonnes.  :( [EDIT while commercial aircraft traffic movements and payload move are in the millions and aircraft freight rates are 1000-10000x lower than LV costs on a $/Kg basis

http://siteresources.worldbank.org/EXTAIRTRANSPORT/Resources/515180-1262792532589/6683177-1268747346047/air_cargo_ch4.pdf Page 9  ]

Offline Katana

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Re: Why the lack of SSTO projects?
« Reply #74 on: 01/30/2017 11:36 AM »
Shuttle got almost UNlimited budget (and fat size) from USAF, enabled re-inventing new engines and use too much advanced technology.

Original conservative plan, Saturn-Shuttle:

https://en.m.wikipedia.org/wiki/Saturn-Shuttle

Quote from: Vultur link=topic=42079.msg1636485#msg1636485  date=1485660464
Except "flight rate" is an operations concept. Selling a turn key fully reusable RLV  separates the mfg from any concern about what the operator uses it for. It also separates them from the "standing army" of staff to support the vehicle.

But if the vehicle can't be operated at a profit, even taking in the recouping of development costs baked into the vehicle's sale price, then operators won't buy it (once they find out, anyway).

I still don't see how that changes the fundamental issues -- which IMO are 1) finding the initial funding and 2) per-flight cost, which is going to be driven by maintenance / personnel needs largely.

Quote
As I noted with Shuttle there were a number of ideas for significantly speeding up the process and reducing the head count.

Sure but you could do way better than even that.

Shuttle was way expensive IMO both because the engine and TPS were at the edge of what 70s technology could handle and because of government funding limitations which led to choosing high-operating-cost options because development cost was limited.

Also VTHL is an inherently more complex design. I don't know if you could have done VTVL back then, but modern software can definitely handle it.

Quote
Also note that AFAIK that number includes service staff split across all vehicles in an airlines fleet.  bigger the fleet, smaller the fraction of those staff carried by any particular vehicle.

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.
« Last Edit: 01/30/2017 12:34 PM by Katana »

Offline Katana

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Re: Why the lack of SSTO projects?
« Reply #75 on: 01/30/2017 12:18 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.

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 ?
it is a crying shame nothing happened with TAN over the last decade.
It's nearly out of patent protection!

Given the work of Foa, Lockwood, the RBCC concept--this smacks of patenting prior art.  Sweetman made a good case it is flying in the Aurora.

It does seem to me that the like permits relatively nonexotic lifting airframes to achieve SSTO with an acceptable payload fraction.
« Last Edit: 01/30/2017 12:24 PM by Katana »

Offline tdperk

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Re: Why the lack of SSTO projects?
« Reply #76 on: 01/30/2017 12:43 PM »
The result : simply strap up some (old) ramjets for Mach 1 to 5 ?

I think current materials would permit a few minutes operation of non-supersonic ramjets up to M = 8 ~ 10.

But yes, VTVL seems now to be a given.

Offline john smith 19

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Re: Why the lack of SSTO projects?
« Reply #77 on: 01/30/2017 08:10 PM »

Quote
AFAIK Hughes Aircraft never built an airliner. The closest it got was the H4 Spruce Goose. 1 made and crashed on maiden flight. The link is tenuous. Howard Hughes was involved in both.

It didn't crashed and still exist at the evergreen aviation museum.
I updated my original post. I noted that it made a single flight that reached 70 feet. but from the PoV of the thread it never entered service and it was never part of any airline service.
"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.

Offline john smith 19

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Re: Why the lack of SSTO projects?
« Reply #78 on: 01/30/2017 09:21 PM »
But if the vehicle can't be operated at a profit, even taking in the recouping of development costs baked into the vehicle's sale price, then operators won't buy it (once they find out, anyway).

I still don't see how that changes the fundamental issues -- which IMO are 1) finding the initial funding and 2) per-flight cost, which is going to be driven by maintenance / personnel needs largely.
It expands the market from what the mfg/operator can handle on their own to what how ever many operators there are can handle. It also means the mfg can access markets (for LV) that would never consider using a US launch provider. 

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.
Quote
Sure but you could do way better than even that.

Shuttle was way expensive IMO both because the engine and TPS were at the edge of what 70s technology could handle and because of government funding limitations which led to choosing high-operating-cost options because development cost was limited.
Part of that was the insistence it carry about 3x what NASA had wanted it to carry and partly because parts of NASA wanted to do a staged combustion engine. The funding mean the more rational TSTO concepts were binned.
Quote
Also VTHL is an inherently more complex design. I don't know if you could have done VTVL back then, but modern software can definitely handle it.
Most of the SSTO concepts back then were VTOL but with rather squat, low AR designs. SX's problems with making high AR stages land right (until they fitted grid fins) indicates people were right to be worried that it would be difficult, but not impossible.
Quote
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.
Shuttle got almost UNlimited budget (and fat size) from USAF, enabled re-inventing new engines and use too much advanced technology.

Original conservative plan, Saturn-Shuttle:

https://en.m.wikipedia.org/wiki/Saturn-Shuttle
ARe you sure you're not conflating Shuttle with the X30?  Shuttle had severe budgetary limits on it set by the OMB at the time. 

In contrast the USAF were very open with their X30 (had they been less so they would have spotted a number of glaring errors in the project pitch).  :(
"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.

Offline john smith 19

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Re: Why the lack of SSTO projects?
« Reply #79 on: 01/30/2017 09:36 PM »
The result : simply strap up some (old) ramjets for Mach 1 to 5 ?

I think current materials would permit a few minutes operation of non-supersonic ramjets up to M = 8 ~ 10.

But yes, VTVL seems now to be a given.
You may find this interesting. From the Advanced Topics thread "Finding the actual speed limit of a conventional ramjet powered vehicle."
Maybe Aero's claim that basic theory will get you to 3Km/s (about M8.8 )   is correct  but given the results of the X30 programme what I'm suggesting is a flight programme.

I think I noted that Glenn Olson (of the old alt-accel website) had spoken to enough ex-ramejt engineers to come away pretty confident that a well-designed subsonic combustion ramjet could reach speeds in a bit excess of Mach-8 and for the most part (unlike many of the folks riding "theory" till it auguered into the ground in the form of the SCramjet :) ) couldn't see many "good" reasons to go faster even if most of them thought Mach-10 was possible given the right propellant and design :)

And really what DOES air-breathing to @Mach-5+ get you if its "cheap" and "easy" enough over the alternatives?

(I'd suggest hitting up the "Ex-Rocketman's Take" blog to see some of the work he's done as one of "those" engineers :) )

Randy
So M8-9 with subsonic combustion seems viable.
"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.

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.
"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.

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

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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 »

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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.
Quote
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.
"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.

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

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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.
"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.

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.
"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.

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.
"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.

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.
"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.

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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

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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).
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Re: Why the lack of SSTO projects?
« Reply #100 on: 02/07/2017 04:03 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.

Launching from 4-5km altitude launch site in Ecuador can gain about 15-20s in average Isp, and gives reduced aero and gravity losses with higher optimal lift-off acceleration, as well as a slightly lower deltaV to achieve orbit from equator.  Mass in LEO could be increased by as much as 10-20%, with payload possibly doubled so it would make a lot of sense for SSTO if political and infrastructure support issues could be overcome.
https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20030022661.pdf
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Offline john smith 19

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Re: Why the lack of SSTO projects?
« Reply #101 on: 02/07/2017 10:04 PM »
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.
Except in an air breather that reaction mass would be the atmosphere and an air breath (while air breathing) is good for an Isp maybe 6x that of the best viable (IE LH2/LO2) propellant.
« Last Edit: 02/07/2017 10:04 PM by john smith 19 »
"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.

Offline R7

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Re: Why the lack of SSTO projects?
« Reply #102 on: 02/08/2017 09:46 AM »
Launching from 4-5km altitude launch site in Ecuador can gain about 15-20s in average Isp, and gives reduced aero and gravity losses with higher optimal lift-off acceleration, as well as a slightly lower deltaV to achieve orbit from equator.  Mass in LEO could be increased by as much as 10-20%, with payload possibly doubled so it would make a lot of sense for SSTO if political and infrastructure support issues could be overcome.
https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20030022661.pdf

From your link;

Launch altitude (km)Increase in payload (%)
531.2%
1060.2%
1584.3%
20104.9%
25122.5%

Seems tempting but when you weigh the restrictions, politics and technical challenges against gains a simple pop-up launch assist platform a la Kistler will soon look more tempting.

Also something odd in that paper;

Quote
Propellant (Fuel/Oxidizer) Liquid hydrogen (LH2) Liquid Oxygen (LOX)
Mixture ratio 3.4: 1
Specific gravity 260kg/m3 (1 6.231bm/ft3)

Specific heat ratio 1.26
Chamber temperature 2959K (4866F)
Chamber pressure 20.26MPa (2939psia)
Engine throttled to limit acceleration to 3g; Throttle range 20-100%.

Whaat?
AD·ASTRA·ASTRORVM·GRATIA

Offline Katana

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Re: Why the lack of SSTO projects?
« Reply #103 on: 02/08/2017 11:09 AM »
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.
Except in an air breather that reaction mass would be the atmosphere and an air breath (while air breathing) is good for an Isp maybe 6x that of the best viable (IE LH2/LO2) propellant.
Maybe some expendable ramjet boosters? They could provide at least marginal thrust gain, no dead weight to orbit, and dirt cheap.

Offline Proponent

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Re: Why the lack of SSTO projects?
« Reply #104 on: 02/08/2017 01:00 PM »
The thing is, the time you most need thrust is at take-off, when ramjets are useless.

Offline Katana

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Re: Why the lack of SSTO projects?
« Reply #105 on: 02/08/2017 02:20 PM »
The thing is, the time you most need thrust is at take-off, when ramjets are useless.
Of course.

However when marginal performance improvement such as 5% isp or 5km launch pad height are concerned , more thrust during halfway could have equal effects.

If more thrust at take-off is necessary, just add a few small solid boosters instead of ramjet.

Offline Katana

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Re: Why the lack of SSTO projects?
« Reply #106 on: 02/08/2017 02:45 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.

Launching from 4-5km altitude launch site in Ecuador can gain about 15-20s in average Isp, and gives reduced aero and gravity losses with higher optimal lift-off acceleration, as well as a slightly lower deltaV to achieve orbit from equator.  Mass in LEO could be increased by as much as 10-20%, with payload possibly doubled so it would make a lot of sense for SSTO if political and infrastructure support issues could be overcome.
https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20030022661.pdf
Or something opposite: launch to suborbital trajectory very close to orbit and recover first stage on ship.

Let the payload (may be a Dragon with more fuel for Superdracos) do final orbit insertion themselves, similar to the shuttle.

The shuttle jettisoned ET before orbit insertion with OMS.

Besides, this prove large hydrogen tanks could not survive reentry intact (being able to reuse) natually, though some small debris could survive.

Offline envy887

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Re: Why the lack of SSTO projects?
« Reply #107 on: 02/08/2017 04:58 PM »
...
Besides, this prove large hydrogen tanks could not survive reentry intact (being able to reuse) natually, though some small debris could survive.

NASA wanted the ET to break up during entry, to avoid hitting anything on the ocean with a gigantic orange tank. It was a lot fluffier than the orbiter, so it would have been much easier to get through reentry if there was any reason to do so.

Online Lars-J

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Re: Why the lack of SSTO projects?
« Reply #108 on: 02/08/2017 09:18 PM »
Or something opposite: launch to suborbital trajectory very close to orbit and recover first stage on ship.

Let the payload (may be a Dragon with more fuel for Superdracos) do final orbit insertion themselves, similar to the shuttle.

The shuttle jettisoned ET before orbit insertion with OMS.

But there is no free lunch... The delta-V needs to come from somewhere. And the Shuttle suborbital trajectory (pre-OMS burn) was only a few handfuls of m/s short of orbital velocity.

If you want to make the suborbital trajectory much less energy intensive, you pretty much have to make each payload be its own upper stage... Which is fine, but then you are now a two-stage launch system and no longer SSTO.

Offline john smith 19

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Re: Why the lack of SSTO projects?
« Reply #109 on: 02/09/2017 06:43 PM »
The thing is, the time you most need thrust is at take-off, when ramjets are useless.
True.  The closest you come is a shroud. This unit accelerates some of the atmosphere. IIRC NASA found this could give you a minimum 15% (of gross takeoff) thrust increase up to 50% up around M2.

This, like TAN is at the point of maximum mass. The joker in both cases is does the thrust increase over the period it works outweigh the hardware mass increase.
"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.

Offline Katana

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Re: Why the lack of SSTO projects?
« Reply #110 on: 02/10/2017 10:58 AM »
The thing is, the time you most need thrust is at take-off, when ramjets are useless.
True.  The closest you come is a shroud. This unit accelerates some of the atmosphere. IIRC NASA found this could give you a minimum 15% (of gross takeoff) thrust increase up to 50% up around M2.

This, like TAN is at the point of maximum mass. The joker in both cases is does the thrust increase over the period it works outweigh the hardware mass increase.
RBCC shroud is large and heavy, more heavier than ramjets and enlarged main engines.

Offline john smith 19

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Re: Why the lack of SSTO projects?
« Reply #111 on: 02/10/2017 02:58 PM »
RBCC shroud is large and heavy, more heavier than ramjets and enlarged main engines.
Shroud is probably not the best word for this. In hindsight I maybe referring to a diffuser.

a casing that's wrapped around the end of a rocket nozzle to to draw in more airflow by the venturi effect. More airflow --> more thrust.

In principle a fairly simple structure and because of it's location at relatively low temperature. Putting inlet holes on the skirt around the bottom of the first stage would also be in this class.

As I noted this gives at least 15% of GTOW at takeoff, which is not to be sniffed at for a VTO SSTO.

If you're dead set on SSTO and you don't have anything better than a rocket engine to do it this seems like another of those (relatively) low hanging fruit you would be looking at.

"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.

Offline Archibald

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Re: Why the lack of SSTO projects?
« Reply #112 on: 02/20/2017 05:31 PM »
it is a crying shame nothing happened with TAN over the last decade.

Well, I was wrong. I've just found this

Variable Element Launch by the same Melvin Bulman of Aerojet.

http://enu.kz/repository/2009/AIAA-2009-4983.pdf

Offline john smith 19

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Re: Why the lack of SSTO projects?
« Reply #113 on: 02/20/2017 11:22 PM »
it is a crying shame nothing happened with TAN over the last decade.

Well, I was wrong. I've just found this

Variable Element Launch by the same Melvin Bulman of Aerojet.

http://enu.kz/repository/2009/AIAA-2009-4983.pdf
Ingenious. I'd not realized that TAN allows you to build a biamese where both stages are well matched in size and weight. This underscores how important a good engine with good Isp is.

[EDIT SSTO (or anything close to full reusability) requires you "square the circle" of a very tough design problem coupled with delivering a development budget closer to that of an TSTO ELV. 

A very tough combination. ]
« Last Edit: 02/20/2017 11:30 PM by john smith 19 »
"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.

Offline Asteroza

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Re: Why the lack of SSTO projects?
« Reply #114 on: 02/21/2017 07:20 AM »
it is a crying shame nothing happened with TAN over the last decade.

Well, I was wrong. I've just found this

Variable Element Launch by the same Melvin Bulman of Aerojet.

http://enu.kz/repository/2009/AIAA-2009-4983.pdf

Interesting takeaway here is they reused knowledge from dual mode ramjet/scramjet work to make a LOx/LH2 main combustion rocket engine with LOx/RP-1 TAN, so this means successful tripropellant case here as well.

Offline john smith 19

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Re: Why the lack of SSTO projects?
« Reply #115 on: 02/21/2017 12:59 PM »
Structurally the question I've always had about "wet wing" designs is they put quite a lot of weight on the thickness of the wing, rather than the surface of the wing, where it would normally be counter balanced by the lift the wings generate.

I wonder if the "tail sitters" of the 1950's were wet wing designs or if they kept the fuel in the body?
"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.

Offline Katana

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Re: Why the lack of SSTO projects?
« Reply #116 on: 02/24/2017 03:45 AM »
it is a crying shame nothing happened with TAN over the last decade.

Well, I was wrong. I've just found this

Variable Element Launch by the same Melvin Bulman of Aerojet.

http://enu.kz/repository/2009/AIAA-2009-4983.pdf
The author did not mentioned anything about isp sl in TAN mode.
And kerosene combustion seems to be happening outside nozzle.

Offline Archibald

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Re: Why the lack of SSTO projects?
« Reply #117 on: 02/24/2017 06:02 AM »
The paper also confirm the key difference between Salkeld / Beichel / RD-701 research (1970 - 1990)  and TAN. The difference is, the "secondary" fuel is injected, not in the combustion chamber, but in the nozzle, (somewhat like a jet engine afterburner when you think about  it !)

RD-701 and Beichel tried to have a common combustion chamber for kerosene and LH2, not an easy feat when their respective temperatures and densities are polar opposites (kerosene and hydrogen are too different: room temperature vs - 270°C )
Or separate combustion chambers, one for hydrogen, the other for kerosene. Easier, but heavier and more complex.
TAN cut the issue is half: hydrogen in the combustion chamber, kerosene in the nozzle (or vice versa).




Offline HMXHMX

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Re: Why the lack of SSTO projects?
« Reply #118 on: 02/27/2017 05:03 AM »
The paper also confirm the key difference between Salkeld / Beichel / RD-701 research (1970 - 1990)  and TAN. The difference is, the "secondary" fuel is injected, not in the combustion chamber, but in the nozzle, (somewhat like a jet engine afterburner when you think about  it !)

RD-701 and Beichel tried to have a common combustion chamber for kerosene and LH2, not an easy feat when their respective temperatures and densities are polar opposites (kerosene and hydrogen are too different: room temperature vs - 270°C )
Or separate combustion chambers, one for hydrogen, the other for kerosene. Easier, but heavier and more complex.
TAN cut the issue is half: hydrogen in the combustion chamber, kerosene in the nozzle (or vice versa).


To my recollection, all of Rudi's dual-fuel engines used separate combustion chambers for each fuel.

Offline RanulfC

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Re: Why the lack of SSTO projects?
« Reply #119 on: 03/06/2017 09:58 PM »
JS19: The word or system you're looking for it "RENE" or "Rocket Engine Nozzle Ejector" system that was played with during the mid-60s. Katana, it's NOT an RBCC but an ejector shroud that while yes it mass' a bit was much less than SRBs or what they called a TAN-system back then. (You all DO recall it was mentioned that TAN has been patented multiple times since the late-50s?)

You end up with something similar to the Atlas 1.5 stage system, (duct drops off around Mach-2) with around double the nominal payload-to-orbit. The same concept gave the Soviet GNOM pretty much the same payload/range of a Minuteman at half the size/mass. Performance peaks between Mach-1 and Mach-1.5 and tops out at Mach-2 unless you have a non-fixed inlet geometry which gets heavy fast. You get better performance at the top end with fuel-rich or fuel injection but need a bit longer duct or active injectors again which adds complexity but not much mass.

One thing that was not looked at in any studies directly but highly suggestive in past studies, (mid-to-late-60s) was "pre-cooling" intake air, (various methods but an interesting 'passive' system used a lightly insulated LH2 tank structure) to increase the mass flow through the ejector duct. A water injection system integral to the duct was suggested and I'd note that that can increase static thrust of a standard jet engine by 2 or more so there would be no reason to think it wouldn't work similarly in an ejector or ramjet duct. (This would be somewhere around 100 or so pounds of water if I recall the figures correctly for the whole take-off-to-Mach-2 flight)

Again those this is NOT an "SSTO" in a purist sense, but add some parachutes and recover down-range it is a VERY simple, cheap and effective 'boost' option for a NEAR-SSTO vehicle.

Randy
From The Amazing Catstronaut on the Black Arrow LV:
British physics, old chap. It's undignified to belch flames and effluvia all over the pad, what. A true gentlemen's orbital conveyance lifts itself into the air unostentatiously, with the minimum of spectacle and a modicum of grace. Not like our American cousins' launch vehicles, eh?

Offline john smith 19

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Re: Why the lack of SSTO projects?
« Reply #120 on: 03/07/2017 10:10 AM »
JS19: The word or system you're looking for it "RENE" or "Rocket Engine Nozzle Ejector" system that was played with during the mid-60s.
Noted. And welcome back.
Quote from: RanulfC

You end up with something similar to the Atlas 1.5 stage system, (duct drops off around Mach-2) with around double the nominal payload-to-orbit. The same concept gave the Soviet GNOM pretty much the same payload/range of a Minuteman at half the size/mass. Performance peaks between Mach-1 and Mach-1.5 and tops out at Mach-2 unless you have a non-fixed inlet geometry which gets heavy fast. You get better performance at the top end with fuel-rich or fuel injection but need a bit longer duct or active injectors again which adds complexity but not much mass.
This suggests the best simple approach for reusability would be to close the duct off this Mach range.
Quote from: RanulfC

One thing that was not looked at in any studies directly but highly suggestive in past studies, (mid-to-late-60s) was "pre-cooling" intake air, (various methods but an interesting 'passive' system used a lightly insulated LH2 tank structure) to increase the mass flow through the ejector duct. A water injection system integral to the duct was suggested and I'd note that that can increase static thrust of a standard jet engine by 2 or more so there would be no reason to think it wouldn't work similarly in an ejector or ramjet duct. (This would be somewhere around 100 or so pounds of water if I recall the figures correctly for the whole take-off-to-Mach-2 flight)
A 100lbs is pretty small. I guess it depends what the thrust of the base engine was.
Quote from: RanulfC

Again those this is NOT an "SSTO" in a purist sense, but add some parachutes and recover down-range it is a VERY simple, cheap and effective 'boost' option for a NEAR-SSTO vehicle.
Good point. SSTO (especially VTOL) has always been tightly constrained by both the mass ratio and the Isp, and it's a vicious combination, with the best Isp coming from the propellant with traditionally the worst T/W.

As always the question is could these (perhaps coupled with HTOL) be enough to do SSTO with more or less a conventional rocket engine?
« Last Edit: 03/07/2017 11:10 PM by john smith 19 »
"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.

Offline Rei

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Re: Why the lack of SSTO projects?
« Reply #121 on: 03/07/2017 11:21 AM »
Last time I looked into the concept (it's been a while), the duct tends to be a mass-limiting factor, hence the reason for getting rid of it when it's no longer needed, rather than just closing it off.

The water cooling concept makes no sense to me. How is the effect of an injection amount of water supposed to have a significant cooling effect on incoming air unless its mass is somewhat comparable to the incoming air (wherein the mass penalty would be large)? And if you're going to bring something with high specific heat, why not hydrogen, which in addition to being much colder, and much easier to mix rapidly, has a far lower molecular weight, aka more moles of light gas in the exhaust?

I do like the concept of thrust augmentation with air in general, though. It reminds me of the optimization issues one encounters with propellers. You get more thrust per unit power with a larger prop than a smaller prop because the larger one moves much more air, at a slower speed, to yield the same thrust; the slipstream is at lower velocity, and thus less energy is wasted to creating a fast slipstream.  It seems to be the same sort of optimization here: increase the thrust to power ratio by swapping mass for velocity.


Offline RanulfC

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Re: Why the lack of SSTO projects?
« Reply #122 on: 03/07/2017 10:48 PM »
Last time I looked into the concept (it's been a while), the duct tends to be a mass-limiting factor, hence the reason for getting rid of it when it's no longer needed, rather than just closing it off.

Exactly, but I'll point out that in some cases it was suggested that keeping the duct, (only loosing part of it to allow altitude compensation as an expander duct for the rocket array) was quite effective. It was studied under the "Reusable NOVA" (ReNOVA) concept and helped with the recovery of the stage by protecting the rocket engines on the way down. (ReNOVA's front end and aft expansion cone had it recovering like a the Mercury capsule it looked like)

Quote
The water cooling concept makes no sense to me. How is the effect of an injection amount of water supposed to have a significant cooling effect on incoming air unless its mass is somewhat comparable to the incoming air (wherein the mass penalty would be large)? And if you're going to bring something with high specific heat, why not hydrogen, which in addition to being much colder, and much easier to mix rapidly, has a far lower molecular weight, aka more moles of light gas in the exhaust?

A little water goes a long way or so the studies said :) A surprisingly long way but highly dependent on the airflow, vaporization, particle size and injection position which despite MIPCC being a 90s concept was actually studied and figured out in the early-60s. The concept later in flight injected liquid oxygen, (again a small amount compared to a rocket of course) to increase cooling at higher Mach, (2 to 4 in the original concept, here probably 1.5 to 2 if required at all, it was actually found that liquid nitrogen had a similar effect if you weren't needing the combustion chamber stabilization) and stabilize the combustion chamber temperature and combustion stability. Might not need that for a booster concept such as this.

Frankly one of the advantages is simply pushing more mass through the system and of course the more mass flow, which you get by 'cooling' the intake air to any degree, the better so you COULD use whatever you're using for fuel to burn with the air but if you're running fuel rich that's going to be overkill so why not use something dense, easy to store and easy to inject? The entire concept is based on historic use of water-injection in early turbojet engines, the trick was/is to use it in front of the compressor rather than in the exhaust providing more thrust, more air ingested, AND a higher compressor face Mach range. (The last has no place in the booster of course :) )

Quote
I do like the concept of thrust augmentation with air in general, though. It reminds me of the optimization issues one encounters with propellers. You get more thrust per unit power with a larger prop than a smaller prop because the larger one moves much more air, at a slower speed, to yield the same thrust; the slipstream is at lower velocity, and thus less energy is wasted to creating a fast slipstream.  It seems to be the same sort of optimization here: increase the thrust to power ratio by swapping mass for velocity.

That's the reason we have 'high-bypass' turbofans instead of turbojets :) The fans provide a much higher mass flow for less fuel consumption. Problem is, (like the propellers they resemble-ish :) ) they present a much larger area and so getting them to go faster is proportionally more difficult as the drag builds up. Hence we use low-or-medium bypass turbofans in aircraft we want to be able to go fast and high bypass in ones we don't need to.

Randy
From The Amazing Catstronaut on the Black Arrow LV:
British physics, old chap. It's undignified to belch flames and effluvia all over the pad, what. A true gentlemen's orbital conveyance lifts itself into the air unostentatiously, with the minimum of spectacle and a modicum of grace. Not like our American cousins' launch vehicles, eh?

Offline RanulfC

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Re: Why the lack of SSTO projects?
« Reply #123 on: 03/09/2017 02:02 AM »
Oh hullnuts! While we were all talking up the past we TOTALLY forgot to suggest the DIY method!
http://quantumg.net/mockingbird.pdf

You, a couple of buddy's, your CnC and 3D printer, a pickup truck and your personal 10kg to LEO SSTO! Sure it's PROBABLY going to be a bit on the expensive side and you'll PROBABLY find all sort of governments after your hide after a few launches but that's the FUN part, right?

Hey but that's not all! Switch things up a bit and you can probably milk at least half as much payload through various methods:
(I'm guessing since google is coming up empty no matter which keywords I use Dr. Dunn's alternate SSTO propellant paper is finally gone away :( )

Alternate propellants! Sure H2O2/Kerosene is nice and dense and needs no insulation but switch it out for LOX and Cryo-Propane instead! Bit trickier to work with but still well within the DIY range! And you can tell the authorities it's JUST for a barbecue! (Yes LOX cooking IS a thing :) )

Hey this baby is compact enough you really CAN use some "small" SRBs for it!
(https://engineering.purdue.edu/~propulsi/propulsion/rockets/solids.html)
Sure it's now an "assisted" SSTO but the motors for an AIM-9 or AMRAAM burn out pretty quick so they might fall in a friendly neighbors back-yard. Make space launch a community event!

Hey what about RENE, (Rocket-Engine-Nozzle-Ejector) for some extra "oomph" in your launch! Some re-arranging of parts and more of a "near-SSTO" effort and you can have your very own Mini-Me-NOVA... ER that is Mini-RE-NOVA! As in "reusable NOVA"!
(http://up-ship.com/blog/?p=9462)
You 'might' have to lose some of the shroud on the way up but maybe not as adding a water or liquid nitrogen intake cooling system might make up for the initial launch inefficiency. Don't forget to put a return address and postage on that main stage though as it will come down quite a ways down range! And then a small 'kick' motor on the payload puts it into orbit! But how to get it back? Well don't fret because in the late 60s a sintered carbon nosecap underwent an HOUR of reentry level heating cooled only by a couple of ounces of water and transpiration cooling and we're WAY more capable today! (And as per usual all my sites with that note are no longer valid, the paper used to be on tethers.com but no luck)

Lets face it the ability to get into loads of trouble at the drop of a launch vehicle is very much in range of todays DIY crowd so lets get out there and get launching!

Randy
From The Amazing Catstronaut on the Black Arrow LV:
British physics, old chap. It's undignified to belch flames and effluvia all over the pad, what. A true gentlemen's orbital conveyance lifts itself into the air unostentatiously, with the minimum of spectacle and a modicum of grace. Not like our American cousins' launch vehicles, eh?

Offline john smith 19

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Re: Why the lack of SSTO projects?
« Reply #124 on: 03/10/2017 09:27 PM »
Oh hullnuts! While we were all talking up the past we TOTALLY forgot to suggest the DIY method!
http://quantumg.net/mockingbird.pdf
Kare's powerpoint was certainly comprehensive both in the how and the why you would do it.  :) He definitely had access to Whiteheads work on pumped propulsion.
Quote from: RanulfC
You, a couple of buddy's, your CnC and 3D printer, a pickup truck and your personal 10kg to LEO SSTO! Sure it's PROBABLY going to be a bit on the expensive side and you'll PROBABLY find all sort of governments after your hide after a few launches but that's the FUN part, right?

Depending on launch site in the CONUS I'd expect a visit within 2 hours of a whole of USG departments, several of them with guns.
Quote from: RanulfC
Hey but that's not all! Switch things up a bit and you can probably milk at least half as much payload through various methods:
(I'm guessing since google is coming up empty no matter which keywords I use Dr. Dunn's alternate SSTO propellant paper is finally gone away :( )

Alternate propellants! Sure H2O2/Kerosene is nice and dense and needs no insulation but switch it out for LOX and Cryo-Propane instead! Bit trickier to work with but still well within the DIY range! And you can tell the authorities it's JUST for a barbecue! (Yes LOX cooking IS a thing :) )
Really? turning "Flambe" up to 11?
IIRC the standout from Dunn's paper was MethylAcetylene, or Propyne to give it its systemic name. The strained ring added several seconds to the Isp over Butane and Propane. Unfortunately I'm not sure they've ever cleared it from being carcinogenic.  :(
I think peroxide Propulsion in Sweden are still in business so a cat pack is potentially not too big a challenge (although work on Meso scale cat packs for cubesats suggests getting a small design right is tricky).
Quote from: RanulfC
Hey this baby is compact enough you really CAN use some "small" SRBs for it!
(https://engineering.purdue.edu/~propulsi/propulsion/rockets/solids.html)
Sure it's now an "assisted" SSTO but the motors for an AIM-9 or AMRAAM burn out pretty quick so they might fall in a friendly neighbors back-yard. Make space launch a community event!
True, but quite tough to get hold unless you're on an actual AFB.
Quote from: RanulfC
Hey what about RENE, (Rocket-Engine-Nozzle-Ejector) for some extra "oomph" in your launch! Some re-arranging of parts and more of a "near-SSTO" effort and you can have your very own Mini-Me-NOVA... ER that is Mini-RE-NOVA! As in "reusable NOVA"!
(http://up-ship.com/blog/?p=9462)
You 'might' have to lose some of the shroud on the way up but maybe not as adding a water or liquid nitrogen intake cooling system might make up for the initial launch inefficiency. Don't forget to put a return address and postage on that main stage though as it will come down quite a ways down range! And then a small 'kick' motor on the payload puts it into orbit! But how to get it back? Well don't fret because in the late 60s a sintered carbon nosecap underwent an HOUR of reentry level heating cooled only by a couple of ounces of water and transpiration cooling and we're WAY more capable today! (And as per usual all my sites with that note are no longer valid, the paper used to be on tethers.com but no luck)
 
 
I could have sworn those tests were done sometime in the mid 70's.  The problem has always seemed to be distributing the water and finding some kind of feedback mechanism to increase the flow to the hotter parts. I though of it as an "artificial sweat gland," but I've never seen any design that can implement it.  :(
Quote from: RanulfC
Lets face it the ability to get into loads of trouble at the drop of a launch vehicle is very much in range of todays DIY crowd so lets get out there and get launching!
Ah but the real challenge is bringing it down afterward.  :(

Mockingbird used a sort of TPS "umbrella" to substantially raise the the surface area and hence the re-entry altitude.

At this scale my instinct is that TPS and GNC are the biggest problems. GPS will shut down due to DoD restrictions (unless you want to home brew a GPS receiver. Quite feasible given a published design for a Transputer based unit needed about 10MIPS over 20 years ago). Likewise the challenge of a light but robust (ideally flexible) TPS. I note that NASA have developed flexible versions of its PICA and SIRCA ablatives. There's also something called "stunt gel"which is basically 99% water. I'll also note today high end brake pads are made of RCC.

The other issue that the Whitehead team noted was the lack of a small size high pressure thrust chamber as most had been inherited from pressure fed hypergolic designs for station keeping on comm sats. That suggests this is a key missing element for pump fed systems, going to 1000-1500psi 
« Last Edit: 03/11/2017 01:57 PM by john smith 19 »
"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.

Offline strangequark

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Re: Why the lack of SSTO projects?
« Reply #125 on: 03/10/2017 09:46 PM »
Oh hullnuts! While we were all talking up the past we TOTALLY forgot to suggest the DIY method!
http://quantumg.net/mockingbird.pdf

You, a couple of buddy's, your CnC and 3D printer, a pickup truck and your personal 10kg to LEO SSTO! Sure it's PROBABLY going to be a bit on the expensive side and you'll PROBABLY find all sort of governments after your hide after a few launches but that's the FUN part, right?

Hey but that's not all! Switch things up a bit and you can probably milk at least half as much payload through various methods:
(I'm guessing since google is coming up empty no matter which keywords I use Dr. Dunn's alternate SSTO propellant paper is finally gone away :( )

Alternate propellants! Sure H2O2/Kerosene is nice and dense and needs no insulation but switch it out for LOX and Cryo-Propane instead! Bit trickier to work with but still well within the DIY range! And you can tell the authorities it's JUST for a barbecue! (Yes LOX cooking IS a thing :) )

Hey this baby is compact enough you really CAN use some "small" SRBs for it!
(https://engineering.purdue.edu/~propulsi/propulsion/rockets/solids.html)
Sure it's now an "assisted" SSTO but the motors for an AIM-9 or AMRAAM burn out pretty quick so they might fall in a friendly neighbors back-yard. Make space launch a community event!

Hey what about RENE, (Rocket-Engine-Nozzle-Ejector) for some extra "oomph" in your launch! Some re-arranging of parts and more of a "near-SSTO" effort and you can have your very own Mini-Me-NOVA... ER that is Mini-RE-NOVA! As in "reusable NOVA"!
(http://up-ship.com/blog/?p=9462)
You 'might' have to lose some of the shroud on the way up but maybe not as adding a water or liquid nitrogen intake cooling system might make up for the initial launch inefficiency. Don't forget to put a return address and postage on that main stage though as it will come down quite a ways down range! And then a small 'kick' motor on the payload puts it into orbit! But how to get it back? Well don't fret because in the late 60s a sintered carbon nosecap underwent an HOUR of reentry level heating cooled only by a couple of ounces of water and transpiration cooling and we're WAY more capable today! (And as per usual all my sites with that note are no longer valid, the paper used to be on tethers.com but no luck)

Lets face it the ability to get into loads of trouble at the drop of a launch vehicle is very much in range of todays DIY crowd so lets get out there and get launching!

Randy

Working with vehicles almost exactly the size of Mockingbird, and knowing the masses of the various parts makes it amazingly hilarious to read through.
Don't flippantly discount the old rules of this industry. Behind each one lies a painful lesson learned from broken, twisted hardware. Learn those lessons, and respect the knowledge gained from them. Only then, see if you can write new rules that will meet those challenges.

Offline Proponent

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Re: Why the lack of SSTO projects?
« Reply #126 on: 03/11/2017 09:52 AM »
I'd like to turn the question in the OP around and ask not why there is so little interest in SSTO now but why there was so much interest in the 1990's.  If it was thinkable then, shouldn't it be even plausible now, with the benefit of 25 years' worth of technological advances?

My guess is that the answer lies more in Keynes's animal spirits than in technology or economics:  the economic boom of the 1990's led people to dream a little more and worry a little less.  But maybe I'm wrong.  Were there, for example, specific technological or economic lessons learned from the projects in the nineties that have curtailed enthusiasm today?

Offline su27k

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Re: Why the lack of SSTO projects?
« Reply #127 on: 03/11/2017 12:39 PM »
I'd like to turn the question in the OP around and ask not why there is so little interest in SSTO now but why there was so much interest in the 1990's.  If it was thinkable then, shouldn't it be even plausible now, with the benefit of 25 years' worth of technological advances?

Well all the SSTO projects since then have crashed and burned may have something to do with it... Also back then NASA is still flying a partially reusable vehicle, it may be uneconomical but it is reusable, so a SSTO may be seen as a natural next step. Nowadays NASA has pretty much given up on reusable and retreated to throw away everything, so SSTO seems to be further away then ever if you just considering NASA and traditional aerospace.

If this hypothesis is true, I think we may see renewed interest in SSTO if current crop of partial reusable launch vehicles prove themselves.

Offline john smith 19

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Re: Why the lack of SSTO projects?
« Reply #128 on: 03/11/2017 01:53 PM »
Well all the SSTO projects since then have crashed and burned may have something to do with it...
Which ones were you thinking of?

I can only think of the X33, which was a masterclass in poor design selection compounded by poor staffing and uncaring management.
Quote from: su27k
Also back then NASA is still flying a partially reusable vehicle, it may be uneconomical but it is reusable, so a SSTO may be seen as a natural next step. Nowadays NASA has pretty much given up on reusable and retreated to throw away everything, so SSTO seems to be further away then ever if you just considering NASA and traditional aerospace.
Things may change.
Quote from: su27k
If this hypothesis is true, I think we may see renewed interest in SSTO if current crop of partial reusable launch vehicles prove themselves.
Unlikely for the same reason that existed then. VTOL SSTO delivers 1/3 to 1/2 the payload weight to orbit.  Only designs substantially outside the rocket paradigm can do better and that makes investors very nervous.

That won't change until a much better engine is tested.
Unlikely
"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.

Offline Archibald

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Re: Why the lack of SSTO projects?
« Reply #129 on: 03/11/2017 02:08 PM »
Would the Mockingbird ever works ? I thought SSTOs scaled pretty bad.

Offline HMXHMX

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Re: Why the lack of SSTO projects?
« Reply #130 on: 03/11/2017 04:17 PM »
Would the Mockingbird ever works ? I thought SSTOs scaled pretty bad.

SSTOs do scale badly.  I was always dubious about Mockingbird for a number of reasons but at the same time, in the early 1990s, having any one-stage reusable VTOL demonstrator was better than having none, so I supported it.  If it had been built, it would have had similar utility to DC-X, which was a much larger project.

(Bit of background: I was a hired consultant to Livermore's O-Group for the project, along with Max Hunter, Thor and S-IVB Chief Engineer, and George R. Sutton, yes, of Rocket Propulsion Elements.)

Offline HMXHMX

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Re: Why the lack of SSTO projects?
« Reply #131 on: 03/11/2017 04:19 PM »
Well all the SSTO projects since then have crashed and burned may have something to do with it...
Which ones were you thinking of?

I can only think of the X33, which was a masterclass in poor design selection compounded by poor staffing and uncaring management.
Quote from: su27k
Also back then NASA is still flying a partially reusable vehicle, it may be uneconomical but it is reusable, so a SSTO may be seen as a natural next step. Nowadays NASA has pretty much given up on reusable and retreated to throw away everything, so SSTO seems to be further away then ever if you just considering NASA and traditional aerospace.
Things may change.
Quote from: su27k
If this hypothesis is true, I think we may see renewed interest in SSTO if current crop of partial reusable launch vehicles prove themselves.
Unlikely for the same reason that existed then. VTOL SSTO delivers 1/3 to 1/2 the payload weight to orbit.  Only designs substantially outside the rocket paradigm can do better and that makes investors very nervous.

That won't change until a much better engine is tested.
Unlikely

It's not a better engine that is required since chemical engines are at the peak of their development and performance; it's a better propellant mass fraction.

Offline john smith 19

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Re: Why the lack of SSTO projects?
« Reply #132 on: 03/11/2017 10:40 PM »
SSTOs do scale badly.  I was always dubious about Mockingbird for a number of reasons but at the same time, in the early 1990s, having any one-stage reusable VTOL demonstrator was better than having none, so I supported it.  If it had been built, it would have had similar utility to DC-X, which was a much larger project.

(Bit of background: I was a hired consultant to Livermore's O-Group for the project, along with Max Hunter, Thor and S-IVB Chief Engineer, and George R. Sutton, yes, of Rocket Propulsion Elements.)
That suggests that any design choices should have been well informed although I recall Charles Pooley (microlaunchers) did note that scale down (for single or multi stage vehicles) is tough. 

On the upside the scale of such a vehicle opens up various mfg and materials possibilities.

What particular areas did you think Mockingbird was going to have trouble with?

It's not a better engine that is required since chemical engines are at the peak of their development and performance; it's a better propellant mass fraction.
If you're looking at a rocket powered SSTO then you need to put the whole structure into less than 10% of the GTOW. Not using LH2 may reduce the gravity losses (I normally knock 100m/s off) but OTOH you lose a substantial amount of Isp in the process, lowering the average Isp by quite a lot.

My instinct is that no pure rocket SSTO can deliver a payload fraction equal to a TSTO. That fact alone severely limits investor interest.  If you can't match a TSTO what does your vehicle do that outweighs that disadvantage?

Only moving away from a pure rocket system seems to offer a chance of delivering the kind of Isp that can accommodate a payload fraction at least equal to that of a TSTO.
"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.

Offline jongoff

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Re: Why the lack of SSTO projects?
« Reply #133 on: 03/11/2017 11:49 PM »
It's not a better engine that is required since chemical engines are at the peak of their development and performance; it's a better propellant mass fraction.

Well, engine T/W ratio and mission-averaged Isp are ones where there are still room for improvement, even if Isp at a specific exit condition has already neared practical limits. Engine T/W ratio is an important part of overall dry mass especially on SSTOs. But yeah, there are a lot of other areas that could use improvement.

~Jon

Offline HMXHMX

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Re: Why the lack of SSTO projects?
« Reply #134 on: 03/12/2017 12:46 AM »
SSTOs do scale badly.  I was always dubious about Mockingbird for a number of reasons but at the same time, in the early 1990s, having any one-stage reusable VTOL demonstrator was better than having none, so I supported it.  If it had been built, it would have had similar utility to DC-X, which was a much larger project.

(Bit of background: I was a hired consultant to Livermore's O-Group for the project, along with Max Hunter, Thor and S-IVB Chief Engineer, and George R. Sutton, yes, of Rocket Propulsion Elements.)
That suggests that any design choices should have been well informed although I recall Charles Pooley (microlaunchers) did note that scale down (for single or multi stage vehicles) is tough. 

On the upside the scale of such a vehicle opens up various mfg and materials possibilities.

What particular areas did you think Mockingbird was going to have trouble with?

It's not a better engine that is required since chemical engines are at the peak of their development and performance; it's a better propellant mass fraction.
If you're looking at a rocket powered SSTO then you need to put the whole structure into less than 10% of the GTOW. Not using LH2 may reduce the gravity losses (I normally knock 100m/s off) but OTOH you lose a substantial amount of Isp in the process, lowering the average Isp by quite a lot.

My instinct is that no pure rocket SSTO can deliver a payload fraction equal to a TSTO. That fact alone severely limits investor interest.  If you can't match a TSTO what does your vehicle do that outweighs that disadvantage?

Only moving away from a pure rocket system seems to offer a chance of delivering the kind of Isp that can accommodate a payload fraction at least equal to that of a TSTO.

Interestingly, there was a study done by some NASA Langley folks in the mid-1980s (can't place the time any better – memory fades) where they showed (to their, my and Hunter's satisfaction) that one-stage systems could directly match payload performance of two-stage systems to LEO, when a detailed analysis took into account the penalty of the mass of the interstage plus extra altitude engine propulsion mass.  What I don't recall is where the two concepts crossed over, but the basic message was to refute the "two stages are always better than one" assertion.  The analysis also required pretty high mass fractions, but not higher than what SpaceX and others have approached or achieved.  I do recall that the analysis was a briefed at pretty high levels in the gov't which helped kick off the program (SSRT) that became DC-X.  (And then DC-X didn't address the most critical issue, i.e., propellant mass fraction.)

I've wanted to write a formal paper on the matter for a long while but never had the time, and my motivation to do so is largely gone.  And first I'd have to find the hardcopy of their memo/briefing, which might be a near-impossible task.

Offline Katana

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Re: Why the lack of SSTO projects?
« Reply #135 on: 03/12/2017 02:39 AM »
Would the Mockingbird ever works ? I thought SSTOs scaled pretty bad.
In my own calculations, a tiny pump fed launcher capable of 10kg payload need 2.5 or 3 stages and 1~2 ton GTOW. Structure mass fractions of stages varies from 1/6 to 1/12 (instead of 1/20 of Mockingbird ) depending on propellants.

Electric pumps and batteries are light, but overall weight of all systems are heavy. Piston pumps of Mockingbird are heavier, especially more valves. 0.02 inch Al skin is also too thin to weld.

For using low weight traditional rocket as (expendable) SSTO, the old Atlas I with balloon tanks should be promising. The original version only jettison 2 engines and send 1.3t Mercury capsule to orbit with 120t GTOW, rather good. Replacing 1950s low isp kerosene engines with Merlin may make it complete SSTO.

Though less economic than F9R.
« Last Edit: 03/12/2017 05:23 AM by Katana »

Offline sevenperforce

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Re: Why the lack of SSTO projects?
« Reply #136 on: 03/22/2017 08:27 PM »
Just for the hell of it, how about I crunch the numbers on a mini-ITS SSTO powered by a production version of the 1000 kN dev Raptor with an ejector shroud?

Suppose the engine masses roughly 550 kg and develops 102 tonnes of thrust. Add an ejector shroud (mass: 2 tonnes) and the static thrust jumps to 117.3 tonnes thrust. Let's set GLOW at 100 tonnes exactly, both to have a nice round number and to give us a launch TWR of just under 1.2. The ITS tanker's carbon-fiber body has a structural tankage ratio of 97.4% including TPS. I'll drop that to 96% as an expected square-cube loss, but that means a "pure fuel" ship would give us 93.6 tonnes of fuel. So whatever we have left once we reach orbit, re-enter, and land is our round-trip payload.

Rather than trying to compute a pure mathematical solution, I'll just define the following discrete velocity regimes for thrust augmentation and compute iteratively:

under 170 m/s: 15% augmentation, eff isp 384.1 s
170 to 430 m/s: 25% augmentation, eff isp 417.5 s
430 to 670 m/s: 40% augmentation, eff isp 467.5 s
670 to 1500 m/s: 50% augmentation, eff isp 501 s
1500 to 2000 m/s: 40% augmentation, eff isp 467.6 s
2000 to 2500 m/s: 30% augmentation, eff isp 434.2 s
2500 to 3000 m/s: 20% augmentation, eff isp 400.8 s
3000 to 3400 m/s: 10% augmentation, eff isp 367.4 s
over 3400 m/s: 8% vacuum thrust boost, eff isp 361 s

landing: 0% boost, isp 334 s.

As the ship will rapidly gain speed due to the ejector duct, gravity drag losses will be minimal, but drag losses will be a little higher. I'll estimate 1.1 km/s total, with 100 m/s of drag added to each of the above acceleration regimes (300 m/s on the last one).

GLOW: 100 tonnes
At 170 m/s: 93.1 tonnes
At 430 m/s: 85.23 tonnes
At 670 m/s: 79.14 tonnes
At 1500 m/s: 65.49 tonnes
At 2000 m/s: 57.45 tonnes
At 2500 m/s: 49.89 tonnes
At 3000 m/s: 42.83 tonnes
At 3400 m/s: 37.27 tonnes
At 7800 m/s: 10.75 tonnes
After landing (500 m/s): 9.22 tonnes

Since our dry mass is 6.4 tonnes, this means the payload is 2.82 tonnes with a fully reusable SSTO at a GLOW of 100 tonnes.

Any further improvement...like SSME-derived altitude compensation to push up the vacuum specific impulse, or a parallel launch assist booster...makes this quite viable.

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).
This is precisely my feeling on the matter.

Quote from: Robotbeat
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).
Yeah, the curve for air augmentation or other airbreathing modes goes up with ram compression, then starts to drop as the forward airspeed approaches the exhaust velocity. There would be a very specific ascent profile for a partial airbreather.

Offline Arch Admiral

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Re: Why the lack of SSTO projects?
« Reply #137 on: 03/22/2017 08:49 PM »
The reason SSTO was so popular in the 1980s and the early 90s was that there was a high-priority national program that couldn't work without cheaper access to LEO -- namely the Strategic Defense Initiative. X-30/NASP and DC-X/DC-Y were directly funded by SDIO to launch and maintain anti-ICBM systems. ALS/NLS and X-33/VentureStar were less directly influenced by SDIO, but clearly considered orbital battle stations (like the Soviet Polyus) as a major part of their market.

The reason SSTO has dropped from sight since then is that those programs clearly showed that the idea was unworkable in the real world of real engineering (just like the proposed payloads). The preliminary work done on the test vehicles X-30, DC-X, and X-33 demonstrated that the operational versions NASP, DC-Y, and VentureStar would come out far to heavy to reach orbit.

Offline john smith 19

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Re: Why the lack of SSTO projects?
« Reply #138 on: 03/22/2017 11:08 PM »
The reason SSTO was so popular in the 1980s and the early 90s was that there was a high-priority national program that couldn't work without cheaper access to LEO -- namely the Strategic Defense Initiative. X-30/NASP and DC-X/DC-Y were directly funded by SDIO to launch and maintain anti-ICBM systems. ALS/NLS and X-33/VentureStar were less directly influenced by SDIO, but clearly considered orbital battle stations (like the Soviet Polyus) as a major part of their market.

The reason SSTO has dropped from sight since then is that those programs clearly showed that the idea was unworkable in the real world of real engineering (just like the proposed payloads).
Actually DC-X showed that with a properly designed vehicle you could turn it around in  26 hours (and that would have been about 9 if the range crew had been willing to work a bit later) without engine removal or dis assembly despite having the most difficult to handle (but highest Isp) fuel  available.

The X33 programme demonstrated only that NASA was that a company keen to retain the status quo could effectively game the NASA procurement process by making promises it had no intention of keeping then ensuring project failure by packing the staff with staff who lacked either the skills or the intelligence (or both) to make it succeed.

All the X33 programme demonstrated about SSTO was that if  you choose the most complex way to carry out a task, with the most amount of untested (and unnecessary) technology in the critical path you have a very high likelyhood of failure. Compound that by staffing the project with inexperienced or under qualified staff and you can practically guarantee failure.

Otherwise it demonstrated that LM are very good at extracting money from the USG.
Quote from: Arch Admiral
The preliminary work done on the test vehicles X-30, DC-X, and X-33 demonstrated that the operational versions NASP, DC-Y, and VentureStar would come out far to heavy to reach orbit.
I'd suggest you read TA Heppenheimers "Facing The Heat Barrier." What the X30 programme demonstrated is that without effective oversight a great deal of money can be wasted on something that, had the proper thermophysical properties been used from the onset, would probably have never been started. I'll leave others to speculate on how that came about.

DC-X did not in fact address vehicle weight. That was to be handled by DC-Y.  Curiously there seems to have been an anonymous campaign in Congress to prevent this from ever being funded, as described in G Harry Stine's "Half Way to Anywhere."
"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.

Offline Asteroza

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Re: Why the lack of SSTO projects?
« Reply #139 on: 03/23/2017 05:57 AM »

The other issue that the Whitehead team noted was the lack of a small size high pressure thrust chamber as most had been inherited from pressure fed hypergolic designs for station keeping on comm sats. That suggests this is a key missing element for pump fed systems, going to 1000-1500psi 

I wonder for the Rocketlabs Electron what the Rutherford engine's chamber pressure is a max electric pumping?


So for a mockingbird/bricklifter/3U cubesat lifter redux, the pump system and associated chamber get pretty important. At these scales though, what kind of pumping systems are available now that look attractive enough to use? Rocketlabs is bringing electric pump power source into vogue, but what about the physical pumps themselves? Whitehead advocated an advanced piston design. Some piston systems use a non-propellant high pressure drive gas (dump the gas as verniers?).  Rotaries range from traditional centrifugal to axial, plus rampressors and lobed rotors like gerotors/wankel/"liquid piston" inverse wankel. Other piston oddballs might include electric drive free pistons.

At these scales, is using active cooling to assist the pump cycle generally not worth it, or is it terribly application specific? Rutherford appears to use active cooling for the nozzle at least.

Offline john smith 19

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Re: Why the lack of SSTO projects?
« Reply #140 on: 03/23/2017 07:20 AM »

So for a mockingbird/bricklifter/3U cubesat lifter redux, the pump system and associated chamber get pretty important. At these scales though, what kind of pumping systems are available now that look attractive enough to use? Rocketlabs is bringing electric pump power source into vogue, but what about the physical pumps themselves? Whitehead advocated an advanced piston design. Some piston systems use a non-propellant high pressure drive gas (dump the gas as verniers?).  Rotaries range from traditional centrifugal to axial, plus rampressors and lobed rotors like gerotors/wankel/"liquid piston" inverse wankel. Other piston oddballs might include electric drive free pistons.

At these scales, is using active cooling to assist the pump cycle generally not worth it, or is it terribly application specific? Rutherford appears to use active cooling for the nozzle at least.
The actual question is between "turbine" pumps (centrifugal or axial) and positive displacement. The turbines need much more complex machining or mold making than the positive displacement types. Surface finish has to be very smooth and clearances very narrow at low thrust levels.

IIRC the crossover point was for roughly 5000lbs of thrust according to Whitehead, at which point the pistons and/or losses get too large and turbine designs can be mfg with surface finish levels and clearances that ordinary machine tools can manage. The blades are now big enough that they have enough thermal mass to not be burnt off by the drive gases.

An interesting hybrid option would be a piston pump driven, not by motors, but by solenoids, something like an old fashioned door bell. Instead of the striker hitting 2 bells it would pump 2 cylinders. In principal mechanically simpler than a rotary motor.

Note that Whitehead's pumps are patented. In particular the idea of cross coupling the two cylinders (electronics engineers will recognize this as a monostable multvibrator) as a way of synchronizing their operation.
"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.

Offline Proponent

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Re: Why the lack of SSTO projects?
« Reply #141 on: 03/23/2017 09:04 AM »
What the X30 programme demonstrated is that without effective oversight a great deal of money can be wasted on something that, had the proper thermophysical properties been used from the onset, would probably have never been started. I'll leave others to speculate on how that came about.

Someone once mentioned attending a morning session of a major space conference where the construction of the Shuttle orbiter Atlantis, then in progress, was discussed.  A cost around $2 billion was given.  In the afternoon, the same person attended a session on the X-30, where a development cost of $5 billion was given.  That the development of the an entirely novel kind of vehicle could be projected to cost only about twice as much as merely manufacturing one more of an existing type shows that the X-30 was not reality-based.

Offline sevenperforce

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Re: Why the lack of SSTO projects?
« Reply #142 on: 03/23/2017 01:17 PM »
Just for the hell of it, how about I crunch the numbers on a mini-ITS SSTO powered by a production version of the 1000 kN dev Raptor with an ejector shroud?

Suppose the engine masses roughly 550 kg and develops 102 tonnes of thrust. Add an ejector shroud (mass: 2 tonnes) and the static thrust jumps to 117.3 tonnes thrust. Let's set GLOW at 100 tonnes exactly, both to have a nice round number and to give us a launch TWR of just under 1.2. The ITS tanker's carbon-fiber body has a structural tankage ratio of 97.4% including TPS. I'll drop that to 96% as an expected square-cube loss, but that means a "pure fuel" ship would give us 93.6 tonnes of fuel. So whatever we have left once we reach orbit, re-enter, and land is our round-trip payload.

(snip)
At 3400 m/s: 37.27 tonnes
At 7800 m/s: 10.75 tonnes
After landing (500 m/s): 9.22 tonnes

Since our dry mass is 6.4 tonnes, this means the payload is 2.82 tonnes with a fully reusable SSTO at a GLOW of 100 tonnes.

Any further improvement...like SSME-derived altitude compensation to push up the vacuum specific impulse, or a parallel launch assist booster...makes this quite viable.
Two things that were missing from my earlier maths. First of all, the specific impulse would already be rising due to underexpansion pressure alone, which I didn't factor in. Second, a properly-designed ejector duct should be capable of boosting the vacuum specific impulse noticeably from the 361 seconds of the SL Raptor -- not to the 382 seconds of the Raptor Vacuum, but probably to about two thirds of that improvement.

With these increases, the 100-tonne GLOW devRaptor-derived SSTO would be able to reach orbit at a total mass of 11.17 tonnes and land at a total mass of 9.59 tonnes. This gives us our total fuel use -- 90.41 tonnes -- which allows us to set tankage and structural mass at 3.77 tonnes. The engine and the ejector shroud mass 2.55 tonnes, leaving a net payload of 3.27 tonnes.

I doubt there are any TSTOs on the market today boasting a payload fraction over 3%, much less a fully reusable one. IIRC, the highest in history was the Saturn V, at 4.33%, but that's not reusable. The Shuttle boasted 6.49%, but only if you include the mass of the orbiter as payload; its true payload fraction was under 2%.

Offline Katana

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Re: Why the lack of SSTO projects?
« Reply #143 on: 04/30/2017 01:36 PM »

So for a mockingbird/bricklifter/3U cubesat lifter redux, the pump system and associated chamber get pretty important. At these scales though, what kind of pumping systems are available now that look attractive enough to use? Rocketlabs is bringing electric pump power source into vogue, but what about the physical pumps themselves? Whitehead advocated an advanced piston design. Some piston systems use a non-propellant high pressure drive gas (dump the gas as verniers?).  Rotaries range from traditional centrifugal to axial, plus rampressors and lobed rotors like gerotors/wankel/"liquid piston" inverse wankel. Other piston oddballs might include electric drive free pistons.

At these scales, is using active cooling to assist the pump cycle generally not worth it, or is it terribly application specific? Rutherford appears to use active cooling for the nozzle at least.
The actual question is between "turbine" pumps (centrifugal or axial) and positive displacement. The turbines need much more complex machining or mold making than the positive displacement types. Surface finish has to be very smooth and clearances very narrow at low thrust levels.

IIRC the crossover point was for roughly 5000lbs of thrust according to Whitehead, at which point the pistons and/or losses get too large and turbine designs can be mfg with surface finish levels and clearances that ordinary machine tools can manage. The blades are now big enough that they have enough thermal mass to not be burnt off by the drive gases.

An interesting hybrid option would be a piston pump driven, not by motors, but by solenoids, something like an old fashioned door bell. Instead of the striker hitting 2 bells it would pump 2 cylinders. In principal mechanically simpler than a rotary motor.

Note that Whitehead's pumps are patented. In particular the idea of cross coupling the two cylinders (electronics engineers will recognize this as a monostable multvibrator) as a way of synchronizing their operation.
Positive displacement pumps need many smoothed sealing contacts, literally zero clearances. And they are VERY prone to cavitation at power density required for rockets, down to hundreds of lbs. Turbopumps are much simpler than imagine if you have a metal 3D printer. Just print it or cast it, similar to casted automobile turbocharger and small centrifugal water pumps. Tip clearances are not so crazy,  only the shaft needs smoothed sealing contacts.  All gas generator turbines, big or small,  runs under thermal equilibrium, drive gases are not hot enough to burn blades.

S2.711: 5000lb gas generator engine designed in 1960s for SAM-2 and launched more than 2000 missiles during the vietnam war.
http://www.b14643.de/Spacerockets/Specials/KB-Isayev_engines/index.htm


Regenertive cooling of high pressure chamber is normal for thrust down to this level, but infeasible under 1000lb, since the (surface area / flow rate) ratio becomes too high. Radiative or ablative cooling are required, unless use high fractions of film cooling (XCOR small thrusters).

Besides,  a small (NOT HUGE) vehicle could reentry easier with higher (surface area / weight) ratio, suppose the same structual mass fraction. Small titanium or CFRP helium bottles of space junk often land intact.
« Last Edit: 04/30/2017 03:18 PM by Katana »

Offline Patchouli

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Re: Why the lack of SSTO projects?
« Reply #144 on: 04/30/2017 05:04 PM »
I always thought a single SSME with TAN based SSTO would be a nice low cost project SSTO to pursue.
Don't have a specific payload target at first just make a flying demonstrator.

One advantage I think a kerosene TAN nozzle could have is wings on a  RLV for landing would no longer be dead weight on the way up as they can double as fuel tanks for the TAN nozzle.

Keeping hydrogen in a wing tank is difficult but kerosene is been there done that.

This also would apply to a hydrocarbon engine fuel RLV just burn the fuel in the wing tanks first so they don't have to be too different from standard airliner tanks.
« Last Edit: 04/30/2017 05:07 PM by Patchouli »

Offline john smith 19

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Re: Why the lack of SSTO projects?
« Reply #145 on: 04/30/2017 06:06 PM »
I always thought a single SSME with TAN based SSTO would be a nice low cost project SSTO to pursue.
Don't have a specific payload target at first just make a flying demonstrator.
As it happens I think the late Len Cornier mentioned that Boeing had proposed something similar to the USAF.  The concept was roughly a sled launch assisted looking like a scaled down Shuttle with tile and blankets but incorporating the results of programmes to design light weight LH2 tanks.

The really astonishing part about this project was that Boeing was so confident they had all the issues under control that they were prepared to do it on a $1Bn fixed price contract.

However IIRC this was before the X30 got started and $1Bn was viewed as just too high.  :(
"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.

Offline guckyfan

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Re: Why the lack of SSTO projects?
« Reply #146 on: 04/30/2017 07:24 PM »
I always thought a single SSME with TAN based SSTO would be a nice low cost project

Somehow I find SSME and low cost in one sentence weird. Maybe to NASA standards.

Offline john smith 19

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Re: Why the lack of SSTO projects?
« Reply #147 on: 05/01/2017 02:56 PM »
I always thought a single SSME with TAN based SSTO would be a nice low cost project

Somehow I find SSME and low cost in one sentence weird. Maybe to NASA standards.
Depends.

Over the years NASA spent a lot of money on SSME improvements. Had they implemented them it's efficiency would have been higher, it would have been more resistant to superheated steam attack and greatly reduced parasitic masses like the the 300lb GHe purge tank. They also spent a lot on VHM to bring about safe shut down.

A lot of SSME cost was in how NASA operated them. It took them a very long time to accept you did not have to remove them after every single use for example. That did not just add to cost it multiplies the costs. Likewise stripping it apart was very time consuming. Not just doing so but re-confirming the reassembly had  been done correctly and then certifying all the interfaces had been remade. If you don't break them you don't have to make them again (you also eliminate the risk of leaving something inside after you reassembled.

You should ask what's going to do the more damage? What I didn't find by not opening it up or what I caused by opening it up and dropping something there that need never have been there?
« Last Edit: 05/02/2017 09:06 AM by john smith 19 »
"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.

Offline hkultala

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Re: Why the lack of SSTO projects?
« Reply #148 on: 06/03/2017 07:12 AM »
Just for the hell of it, how about I crunch the numbers on a mini-ITS SSTO powered by a production version of the 1000 kN dev Raptor with an ejector shroud?

Suppose the engine masses roughly 550 kg and develops 102 tonnes of thrust. Add an ejector shroud (mass: 2 tonnes) and the static thrust jumps to 117.3 tonnes thrust.

umm.. why?

The static thrust should stay exactly the same.

Only when it has gained some speed, it should start to help.

And your other numbers are also way too optimistic.

Practically you don't want to travel fast in atmosphere, so you would be rising above the atmosphere very quickly(or, if you do want to travel in atmosphere quickly, you need to make your vehicle more aerodynamic, and use heat shielding also on ascnd, not just re-entry, causing extra weight).

And when you are high above atmosphere or in very thin atmosphere, you are not getting much augmentation.

Offline john smith 19

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Re: Why the lack of SSTO projects?
« Reply #149 on: 06/03/2017 02:26 PM »
umm.. why?

The static thrust should stay exactly the same.

Only when it has gained some speed, it should start to help.

And your other numbers are also way too optimistic.

Practically you don't want to travel fast in atmosphere, so you would be rising above the atmosphere very quickly(or, if you do want to travel in atmosphere quickly, you need to make your vehicle more aerodynamic, and use heat shielding also on ascnd, not just re-entry, causing extra weight).

And when you are high above atmosphere or in very thin atmosphere, you are not getting much augmentation.
AFAIK 15% thrust increase on a rocket with an ejector starting at zero speed was about what NASA thought. More importantly it's at takeoff, the exact time you want high thrust and (depending on your design) high acceleration to get you out of the dense atmosphere quickly.

I would agree that a T/W of > 200:1 does sound quite optimistic for a first generation SC engine.
"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.

Offline Hog

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Re: Why the lack of SSTO projects?
« Reply #150 on: 06/03/2017 08:49 PM »
I always thought a single SSME with TAN based SSTO would be a nice low cost project

Somehow I find SSME and low cost in one sentence weird. Maybe to NASA standards.
Depends.

Over the years NASA spent a lot of money on SSME improvements. Had they implemented them it's efficiency would have been higher, it would have been more resistant to superheated steam attack and greatly reduced parasitic masses like the the 300lb GHe purge tank. They also spent a lot on VHM to bring about safe shut down.

A lot of SSME cost was in how NASA operated them. It took them a very long time to accept you did not have to remove them after every single use for example. That did not just add to cost it multiplies the costs. Likewise stripping it apart was very time consuming. Not just doing so but re-confirming the reassembly had  been done correctly and then certifying all the interfaces had been remade. If you don't break them you don't have to make them again (you also eliminate the risk of leaving something inside after you reassembled.

You should ask what's going to do the more damage? What I didn't find by not opening it up or what I caused by opening it up and dropping something there that need never have been there?
Agreed. According to Mr Wayne Hale, "The block upgrade (from Phase II+ to Block I to Block II) took almost a decade and cost over $2B."

He then further illuminates us as to the why and the how of these upgrades and what some results of the upgrades were.

   "The intention was to provide a more robust engine, not just because of some pad abort that occurred.  The newer block engine had lower ISP (by about 1.5 sec) which required an increase in thrust from 104% RPL to 104.5%RPL to make up for the performance loss.  Neither engine was certified for 109% operation but that was certainly the intent for the Block II engine.  Both nominal flight and all intact aborts used the 104.5% RPL thrust level.  During testing to certify the 109% for aborts, it was found that there were components in the main propulsion piping in the orbiter which likely could not withstand the higher vibration environment associated with that flow rate.  Cracking of the metallic components could have lead to liberation of metal pieces into the engine inlet which would not have been good at the pumps.  So efforts to certify 109% or 111% were terminated.  109% throttles were authorized only in 'do or die' contingency abort scenarious which were multiple failures deep."



The following was taken from the SSME report for engines used on STS-104 Atlantis(her 24th flight)

https://www.jsc.nasa.gov/news/columbia/frr/sts-104/08_ssme.pdf

STS-104 was the first flight for Block-II SSME. The single Block II engine ME-2051 was flown in the ME#2 position(left engine), with Block-IIA engines 2056 and 2047 being flown in ME#1(center) and ME#3(right) engine positions.
· Integration of Pratt and Whitney HPFTP
completes evolution of SSME to Block II
configuration
 Reduced Maintenance
1) No need for turbopump removals
between flights
2) Inspections limited to borescope and
rotor torque checks

Paul

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