Author Topic: Problems of SSTO and technologies to solve these  (Read 50276 times)

Offline john smith 19

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Re: Problems of SSTO and technologies to solve these
« Reply #180 on: 01/13/2019 01:24 pm »
.. and don't forget the solution in The Rocket Company - an elevator stage to take you above 100km, your "SSTO" launches from there permitting a vacuum optimized nozzle and it lands under a parafoil.

Almost the original Kistler plan.


Wow, look how far we've come.

Modern animation is so much more convincing than that old stuff.

Still no closer to reality though.  :(

This was the original plan as conceived by a group of young, keen graduate types before the funders (a VC group that stumped up c$900m) thought "We need to hire ex-NASA engineers, as they are the only people who know how to do this."

In the sense they ran it like an unlimited funds cost plus project they were correct.  :(
BFS. The worlds first Methane fueled FFORSC engined CFRP structured A380 sized aerospaceplane tail sitter capable of flying in Earth and Mars atmospheres. BFR. The worlds biggest Methane fueled FFORSC engined CFRP stainless steel structured booster for BFS. First flight to Mars by end of 2022. Forward looking statements. T&C apply. Believe no one. Run your own numbers. So, you are going to Mars to start a better life? Picture it in your mind. Now say what it is out loud.

Offline TrevorMonty

Re: Problems of SSTO and technologies to solve these
« Reply #181 on: 01/13/2019 05:25 pm »
The actual historical problems of SSTO go something like this.

Developer:  I want to build a VTOVL SSTO that will deliver X Klbs to a 100nm Orbit. It will weigh Y Klbs  and I need I need $Zm to do it
Funder (after due diligence): But for the same budget we can fund a startup to make a TSTO ELV that can take 3x that payload into orbit
Developer:  But then you will have to build another to launch the same payload again, whereas with our concept it just needs to be refubished.
Funder (after due diligence): But there is no precedence for the materials you want to use to be refurbishable. VTOVL is extremely sensitive to weight gain in design and there is a significant technical risk it cannot be made to work.

TL;DR. Funders can get more, with lower technical risk for the same GTOW (which cost estimating relationships use as a proxy for cost). But if you do what you always did you get what you always got.

So if you want to have a shot at serious funding for an SSTO.

1) Deliver what a similar size ELV can deliver in terms of payload and orbit, not 1/3 or 1/2 of that.
2) Find a way to test as much as possible of the concept in stages, preferably without leaving the ground, rather than an all up everything-must-work test flight.
Trying to go from TSTO ELV to SSTO RLv is too big a jump for our current knowledge base. There are no short cuts, we need to work through the intermediates steps. Which are partially reuseable TSTO then fully reuseable TSTO, with flight experience from these two LVs and flight proven engines then jump to a SSTO RLV can be made.

The market for SSTO RLV also doesn't exist yet, they need high flight rate to fix LEO destination eg spacestation or fuel depot.

Offline RobLynn

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Re: Problems of SSTO and technologies to solve these
« Reply #182 on: 01/13/2019 07:40 pm »
SpaceX's Raptor is inferred to have a Thrust to weight of up to 200:1 (SpaceX comments about it challenging  Merlin for the record).  For SSTO it's 'averaged' Isp would be around 340s.  For dense fuels like methalox you need about 9100m/s for an Equator to LEO launch.  That means you can orbit about 6.5% of your takeoff mass.

Stainless steel balloon tanks like Atlas used on a 'fluffy' vehicle with low re-entry area loading or transpiration cooling of skin using LH2 (integral skin cooling passage structure can take tank pressure loads too) to avoid need for heavy TPS.  Such tanks can have fuel:tank mass ratio of >300:1

So tanks+engines for Stainless steel construction SSTO can likely mass as little as about 1.5% of takeoff mass.

Need a little extra mass for Engine TPS, RCS, avionics, thrust structures, payload aero shells etc, but can still likely have half of dry mass as payload (2-3% of lift-off mass).  Payload bay only requires TPS if it is to bring payload back to earth.

No-weight addition landing system can be accomplished with multiple helicopter stringing nets between them:
https://www.youtube.com/watch?v=hyGJBV1xnJI?t=14  have net moving downwards at high speed at point of catch to reduce impact.  Multiple net drone systems that can fly it high speeds can cover a large area for reduced or no need for reentry aerodynamic trajectory control.

Further engine Isp increase and aero loss reduction (and reduced mass aeroshell) can be achieved by launching from high altitude equatorial site like 5-6km high up on Chimborazo in Ecuador.

Is summary: economic SSTO is probably possible with available technologies.  But would it be able to compete with TSTO?
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Offline john smith 19

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Re: Problems of SSTO and technologies to solve these
« Reply #183 on: 01/13/2019 08:51 pm »
Trying to go from TSTO ELV to SSTO RLv is too big a jump for our current knowledge base. There are no short cuts, we need to work through the intermediates steps. Which are partially reuseable TSTO then fully reuseable TSTO, with flight experience from these two LVs and flight proven engines then jump to a SSTO RLV can be made.
Only if you have engines that can deliver Isp's in the 100s of secs, rather than the 1000s, and you insist on starting with a VTO TSTO ELV to begin with, and you have to do substantial amounts of new science before you realize you can't make it work.
Quote from: TrevorMonty
The market for SSTO RLV also doesn't exist yet, they need high flight rate to fix LEO destination eg spacestation or fuel depot.
Actually they need a design that you can buy and operate independently of the mfg that delivers a payload equal to a TSTO.

We are as far away from that as ever.
« Last Edit: 01/13/2019 09:03 pm by john smith 19 »
BFS. The worlds first Methane fueled FFORSC engined CFRP structured A380 sized aerospaceplane tail sitter capable of flying in Earth and Mars atmospheres. BFR. The worlds biggest Methane fueled FFORSC engined CFRP stainless steel structured booster for BFS. First flight to Mars by end of 2022. Forward looking statements. T&C apply. Believe no one. Run your own numbers. So, you are going to Mars to start a better life? Picture it in your mind. Now say what it is out loud.

Offline KelvinZero

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Re: Problems of SSTO and technologies to solve these
« Reply #184 on: 01/14/2019 01:33 am »
One can dream.

A nuclear saltwater rocket could get us a viable SSTO.

Tell me what planet we should fly it from, though.
I have always been a fan of some sort of beamed energy propulsion system.* Just saying. I interpret the topic as that it really has to be about chemical, and fixing the issues in what we already have that is moderately close to viable SSTO. I think that from today it simply has to be reusable as well. That goes without saying IMO.

*Especially one that could exploit the atmosphere for most of the propellant. This gets close to the dream of an "away shuttle" that could land on a planet and return to an orbiting carrier later. The bit that stays in orbit would have the massive lasers and solar power collectors etc.
« Last Edit: 01/14/2019 01:41 am by KelvinZero »

Offline john smith 19

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Re: Problems of SSTO and technologies to solve these
« Reply #185 on: 01/15/2019 07:25 pm »
Returning to the thread title...


Another big issue is the TPS from orbit.

When you do an accurate physics calculation (g varies with altitude, actual speed of sound at a booster separation altitude), a calculation any competent High School Physics student can do,  you find that the amount of Kinetic and Potential Energy per unit mass for a 200Km LEO orbit is about 11.3 x as big as the amount a booster has to lose before returning to Earth.

So if you want your second stage to survive reentry N times that's N x 11.3

Not looking good for ablatives, is it? Unless of course can make "LEO grade" ablative that's 11.3x better (or more) than the regular kind for the same mass, so you won't have to change it every flight.

And that's before we factor in the shift from at least a 6:1 (the pressure stabilized Atlas was more like 13:) trade of structural fraction to payload down to the 1:1 trade of the US.

Reusable TPS is looking like the way to go.

And then of course there is the fact that gravity rises as you fall, so your rate of accelerating rises as you fall . Staying as high as possible as you decelerate should pay very serious dividends (if you can manage it).

[EDIT A few further facts to consider.

Air pressure (or drag) is the biggest disturbance force on a satellite below 1000Km altitude. Normal parachute grade nylon weighs about 70g/m^2.

So (hypothetically) you could deploy a parawing that would support a stage vertically while the air molecules gradually slowed it down (with any TPS being on the side into the wind.

In the ideal world the stage will have lost nearly all its KE by the time it passes over the landing site and it begins to descend, minimizing the amount of propellant to handle the landing.

Downsides include needing to replace the parawing after ever flight (it won't survive much above maybe 80c) and (AFAIK) parachute deployment at orbital velocities is a complete unknown. ]
« Last Edit: 01/16/2019 08:50 pm by john smith 19 »
BFS. The worlds first Methane fueled FFORSC engined CFRP structured A380 sized aerospaceplane tail sitter capable of flying in Earth and Mars atmospheres. BFR. The worlds biggest Methane fueled FFORSC engined CFRP stainless steel structured booster for BFS. First flight to Mars by end of 2022. Forward looking statements. T&C apply. Believe no one. Run your own numbers. So, you are going to Mars to start a better life? Picture it in your mind. Now say what it is out loud.

Offline RobLynn

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Re: Problems of SSTO and technologies to solve these
« Reply #186 on: 01/17/2019 07:26 am »
spinning disk of stainless steel foil (or super thin wire mesh fabric).  Would act as a big parachute at <1kg/m˛ and if get overall loading down to <10kg/m˛ then <600°C peak re-entry temperatures which it could survive for reuse.  Could even convert to a parachute for landing at low speeds.
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Offline aceshigh

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Re: Problems of SSTO and technologies to solve these
« Reply #187 on: 01/18/2019 03:12 pm »
Yeah, I lost all hope in NASA ever advancing the state of the art in launcher technology after they cancelled DC-X in favor of X33 which ended in disaster. Thank god for some of the new space companies, or I would have lost all interest in space flight.

X33 did not end in disaster. The engineers even showed it was possible for making the tanks in aluminum.

However, there was no political will to pursue it, as the government had its eyes on Constellation, which could distribute much more money across many more states and garante many more retirement funds

Offline john smith 19

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Re: Problems of SSTO and technologies to solve these
« Reply #188 on: 01/20/2019 12:38 pm »
X33 did not end in disaster. The engineers even showed it was possible for making the tanks in aluminum.
But the assumption was a CFRP tank would be needed for the full size VentureStar and that would not have proved that a CFRP tank (even at X33 scale) was viable, which was one of the points of the whole programme, at least from NASA's PoV.
Quote from: aceshigh
However, there was no political will to pursue it, as the government had its eyes on Constellation, which could distribute much more money across many more states and garante many more retirement funds
In fact CxP didn't exist at this point and the push for it came from NASA, as the Augustine II commission found and as Jeff Greason explained in various lectures.

The problem  that (VTOL) SSTO faces (and it's a trivial calculation to make) is that it won't launch as much payload as a TSTO for the same development budget.

However the reverse idea, that a VTO rocket driven TSTO RLV will give you TSTO ELV performance is also implausible. That 2nd stage trades 1:1 payload with structural mass fraction. So IRL the TSTO RLV is not likely to deliver the same payload either.
« Last Edit: 01/23/2019 07:10 am by john smith 19 »
BFS. The worlds first Methane fueled FFORSC engined CFRP structured A380 sized aerospaceplane tail sitter capable of flying in Earth and Mars atmospheres. BFR. The worlds biggest Methane fueled FFORSC engined CFRP stainless steel structured booster for BFS. First flight to Mars by end of 2022. Forward looking statements. T&C apply. Believe no one. Run your own numbers. So, you are going to Mars to start a better life? Picture it in your mind. Now say what it is out loud.

Online libra

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Re: Problems of SSTO and technologies to solve these
« Reply #189 on: 01/22/2019 06:51 am »
Mister "TAN" is Mel Bulman, a veteran from Aerojet. At Aerojet Bulman knew Rudi Beichel, anothet tripropellant supporter, who was Robert Salkeld friend.
Hence Salkeld, Bulman and Beichel, the three major pioneers in tripropellant technology, knows each other pretty well.
Since Beichel has died and Salkeld retreated, Bulman has taken the helm. TAN first (2006) and later his Variable Element Launch system"

https://www.google.com/search?client=firefox-b-ab&ei=gMpGXMfoD46lUqbhq4gP&q=%22variable+element+launch%22&oq=%22variable+element+launch%22&gs_l=psy-ab.3...7074.7074..7438...0.0..0.74.74.1......0....1..gws-wiz.HX-z9Gdc1Ys
« Last Edit: 01/22/2019 06:51 am by libra »

Offline aceshigh

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Re: Problems of SSTO and technologies to solve these
« Reply #190 on: 01/22/2019 02:14 pm »
X33 did not end in disaster. The engineers even showed it was possible for making the tanks in aluminum.
But the assumption was a CFRP tank would be needed for the full size VentureStar and that would not have proved that a CFRP tank (even at X33 scale) was viable, which was one of the points of the whole programme, at least from NASA's PoV.

yes, this problem is addressed in this video, starting at around 6:30 to 9:30.

the irony is that in 2004, only 3 years after the project was cancelled, Northrop Grumman announced they had solved the composite fuel tanks problem.

So if they had gone forwards with the X33 aluminum fuel tanks, only 3 years later they would have had the composite fuel tanks needed for the full size Venture Star.


ps: I know Constellation had not yet been announced. I meant it in irony, in the sense NASA (or the men pulling the strings behind) were feeling Venture Star would dry the cash cow.

Offline Nighthawk117

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Re: Problems of SSTO and technologies to solve these
« Reply #191 on: 01/28/2019 02:28 am »
Luckily, XS-1 is the spiritual successor to X-33.

Online libra

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Re: Problems of SSTO and technologies to solve these
« Reply #192 on: 01/28/2019 10:33 am »
The X-33 was a disaster, in the sense that by 1997 top speed was to be mach 15 but in the end the thing was so heavy, it would barely goes past mach 10 or even lower...  Lockheed had already downrated top speed to mach 12 before cancellation.
A SSTO needs Mach 25 and X-33 was to be a demonstrator to Venture Star.
Sure, i can understand "demonstrator" > for rapid turnaround, LH2 handling, maintenance, all those things the Shuttle failed at.
But the crux of a SSTO is the propellant mass fraction, 0.92 is the absolute minimum to get 9 km/s  and Earth orbit.
X-33 was 0.79, fine  -it was a demonstrator - but then it didn't solved that major issue.

I remember all too well in July 1996, I was only 14 but already a space nerd that knew a SSTO (or orbital speed, same thing) was mach 25 or burst.
I then found absurd that the X-33, even a demonstrator, stopped at Mach 15 and did not tackled the PMF issue.

By the way when one looks at Maxwell Hunter / MDD approach to a SSTO, the DC-X obviously was the subsonic demonstrator, then the DC-Y was their very own X-33, suborbital (hence the Y-, as in YF-16)

It usually works that way
X = experimental, prototype (think X-29 )
Y = pre-serie, not entirely frozen (YF-16)
and then the production vehicle. (F-16A)

but there was to be a third and last prototype, fully SSTO and fully orbital, before production started.

The DC-Y is frequently mixed with the final orbital vehicle, but this is wrong - there was to be a third, separated vehicle (I can't remember its name, damn it).

Ah, here it is. DC-X, DC-Y, DC-1. Wikipedia, not a good source, but I've seen that detail elsewhere (Flight International archive).
https://en.wikipedia.org/wiki/McDonnell_Douglas_DC-X
« Last Edit: 01/28/2019 10:42 am by libra »

Offline ZachF

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Re: Problems of SSTO and technologies to solve these
« Reply #193 on: 01/28/2019 05:04 pm »
The reason SSTO is being abandoned in favor of two stage RLVs is a function of simple math applied to physics and economics.

-An SSTO is going to weigh more per unit of mass of payload.

-An SSTO is going to have to deliver, and return, it's entire mass to and from orbital speed, compared to less than half that of a two stage vehicle. This is going to increase the cost of the delivery vehicle per unit of mass it weighs.

-An SSTO is also more mass sensitive, meaning it is again going to raise the cost of the delivery vehicle per unit of mass by using more expensive materials to meet weight targets. Conversely, because it is so mass sensitive, that means options that can increase durability at the expense of payload aren't on the table in many circumstances, This means that service life will likely be lower.

-Most of the payload an SSTO delivers to orbit will be the weight of the SSTO craft, meaning it will likely use more fuel per unit of payload delivered than a two stage option.

-An SSTO is very ISP sensitive. While fuel cost is not a large percentage of operational costs for LVs it will be a larger chunk of the pie for reusable vehicles. Hydrolox fuel is roughly 10x more expensive per kg than dirt cheap methalox fuels 2 stages RLVs are moving towards.

So, in the end, an SSTO, for every kilogram delivered to orbit, will almost surely:

1.Weigh more
2.Cost more for every pound it does weigh
3.Have a lower service life
4.Use more fuel
5.Use more expensive fuel

The math does not add up for SSTO.
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Offline john smith 19

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Re: Problems of SSTO and technologies to solve these
« Reply #194 on: 01/28/2019 09:28 pm »
The reason SSTO is being abandoned in favor of two stage RLVs is a function of simple math applied to physics and economics.

-An SSTO is going to weigh more per unit of mass of payload.
Assertion, not fact.
Quote from: ZachF
-An SSTO is going to have to deliver, and return, it's entire mass to and from orbital speed, compared to less than half that of a two stage vehicle. This is going to increase the cost of the delivery vehicle per unit of mass it weighs.
Which, may, or may not be totally irrelevant to development and/or operating cost.
Quote from: ZachF
-An SSTO is also more mass sensitive, meaning it is again going to raise the cost of the delivery vehicle per unit of mass by using more expensive materials to meet weight targets. Conversely, because it is so mass sensitive, that means options that can increase durability at the expense of payload aren't on the table in many circumstances, This means that service life will likely be lower.
You do realize you've only ever been talking about vertical takeoff SSTO's, right?
Quote from: ZachF
-Most of the payload an SSTO delivers to orbit will be the weight of the SSTO craft, meaning it will likely use more fuel per unit of payload delivered than a two stage option.
Because we all know what a big part of the operating costs the propellant is. Hint for F9 it's about 0.23% of the stated launch price.
Quote from: ZachF
-An SSTO is very ISP sensitive. While fuel cost is not a large percentage of operational costs for LVs it will be a larger chunk of the pie for reusable vehicles. Hydrolox fuel is roughly 10x more expensive per kg than dirt cheap methalox fuels 2 stages RLVs are moving towards.
And you got that figure for LH2 from where exactly?  I'd say it's more like 3x, and of course when you look a the actual mass of the LH2 stage I think cost wise it's much closer.
Quote from: ZachF
So, in the end, an SSTO, for every kilogram delivered to orbit, will almost surely:

1.Weigh more
2.Cost more for every pound it does weigh
3.Have a lower service life
4.Use more fuel
5.Use more expensive fuel

The math does not add up for SSTO.
All said without a single "IMHO"

Clearly you're not encumbered by false modesty.

But in fact you're blinkered because of you're (unstated) assumption that VTO is the only kind of SSTO possible.

And on the subject of this thread we get the problems already.

Do you actually have any solutions to these issues, other than "Try and make a reusable TSTO?"
BFS. The worlds first Methane fueled FFORSC engined CFRP structured A380 sized aerospaceplane tail sitter capable of flying in Earth and Mars atmospheres. BFR. The worlds biggest Methane fueled FFORSC engined CFRP stainless steel structured booster for BFS. First flight to Mars by end of 2022. Forward looking statements. T&C apply. Believe no one. Run your own numbers. So, you are going to Mars to start a better life? Picture it in your mind. Now say what it is out loud.

Offline aceshigh

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Re: Problems of SSTO and technologies to solve these
« Reply #195 on: 01/28/2019 11:10 pm »
Assuming NASA had solved the composite fuel tanks problem in time, and the project had gone forward... X33 had flown, and then NASA had gone ahead and built a Venture Star.

It was supposed to be a complete SSTO. 20 tons to LEO.

Is that really so bad? Would it suck (money) like the Space Shuttle?

If not, why so much animosity against SSTO?

A superficial analysis doesn´t indicate Venture Star to be such a bad deal... or Skylon for that matter. Is the problem the cost of building one? Developing one? Would Venture Star cost as much as SLS?

Offline whitelancer64

Re: Problems of SSTO and technologies to solve these
« Reply #196 on: 01/28/2019 11:19 pm »
Luckily, XS-1 is the spiritual successor to X-33.

No, it is not.
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Offline john smith 19

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Re: Problems of SSTO and technologies to solve these
« Reply #197 on: 01/29/2019 10:46 pm »
Assuming NASA had solved the composite fuel tanks problem in time, and the project had gone forward... X33 had flown, and then NASA had gone ahead and built a Venture Star.
Because they would not have. The concept was LM would have built it (rather like the concept of Commercial Crew and Cargo, but not NASA designed or controlled).
Quote from: aceshigh
It was supposed to be a complete SSTO. 20 tons to LEO.

Is that really so bad? Would it suck (money) like the Space Shuttle?
X-programmes work best when they are designed to acquire a capability. They are not a prototype vehicle. They collect the data to design the prototype vehicle.
Quote from: aceshigh
If not, why so much animosity against SSTO?
Because if you insist on building a VTO SSTO it's very difficult to do and gives you less mass to orbit than a TSTO ELV.  Other options are much better but are not straight rockets.
Quote from: aceshigh
A superficial analysis doesn´t indicate Venture Star to be such a bad deal... or Skylon for that matter. Is the problem the cost of building one? Developing one? Would Venture Star cost as much as SLS?
Conflating X-33/VentureStar with Skylon demonstrates a truly remarkable level of ignorance of both.  :(

I'd suggest you start with the back issues of the space access societies newletter for the X33 story.

TL;DR. Sklyon is only as innovative as it needs to be. X-33's reason d'etre was to develop a whole bunch of unproven and high risk concepts which did little reach the goal of SSTO (compared with much simpler concepts) but all of which had to work (because of the design)

This thread runs over 10 pages. You might like to start by reading some of it.
« Last Edit: 01/29/2019 10:47 pm by john smith 19 »
BFS. The worlds first Methane fueled FFORSC engined CFRP structured A380 sized aerospaceplane tail sitter capable of flying in Earth and Mars atmospheres. BFR. The worlds biggest Methane fueled FFORSC engined CFRP stainless steel structured booster for BFS. First flight to Mars by end of 2022. Forward looking statements. T&C apply. Believe no one. Run your own numbers. So, you are going to Mars to start a better life? Picture it in your mind. Now say what it is out loud.

Offline aceshigh

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Re: Problems of SSTO and technologies to solve these
« Reply #198 on: 01/30/2019 03:21 am »
Quote
Conflating X-33/VentureStar with Skylon demonstrates a truly remarkable level of ignorance of both.  :(

thanks for all the complimenting.

I ONLY conflated both in the sense they were both SSTOs projects. And in the sense SOME people bash all and any SSTO project/idea, no matter if it's a VTO SSTO like Venture Star or an airbreathing horizontal take-off spaceplane like Skylon.

I can search the thread if you tell me exactly what was wrong in my sentence, aside saying what I see OTHER people generalizing about SSTOs.

Quote
Because if you insist on building a VTO SSTO it's very difficult to do and gives you less mass to orbit than a TSTO ELV

yes, just like I said. 20 tons to LEO was calculated. But what about the reusability? NOW, with SpaceX, Venture Star doesn´t look so good. But until SpaceX landed a first stage, the proposed reusability of Venture Star seemed to make it a good prospect, despite the relatively low payload to orbit.

Quote
X-programmes work best when they are designed to acquire a capability. They are not a prototype vehicle. They collect the data to design the prototype vehicle.

I ended the first sentence with "Venture Star". So my second quote was about Venture Star, not X33. X33 was designed to collect data to design Venture Star.

Maybe you are trying to say Venture Star's 20 tons to LEO, rapid reusability, etc, were wild guesses with very small chance of being proven by X33?

Offline Elmar Moelzer

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Re: Problems of SSTO and technologies to solve these
« Reply #199 on: 01/30/2019 06:46 pm »
-An SSTO is very ISP sensitive. While fuel cost is not a large percentage of operational costs for LVs it will be a larger chunk of the pie for reusable vehicles. Hydrolox fuel is roughly 10x more expensive per kg than dirt cheap methalox fuels 2 stages RLVs are moving towards.
SSTOs are more dry mass sensitive than ISP- sensitive. That is something that (among others) Bono and Gary Hudson realized, which is why they both considered SSTOs feasible, even with the engine technology available off the shelf at the time. Granted, some altitude compensating engine features (like altitude compensating nozzles, aerospikes and aeroplugs, etc) help, but they are not required. I think that a methalox based SSTO using Raptor turbo- machinery combined with an aeroplug would work sufficiently well.
Also, the cost of fuel is minor, even for hydrolox. AFAIK, hydrolox is more of an issue when it comes to total system weight than fuel cost.

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