SSME based SSTO’s.

[RCgothic]

What is the point of an SSTO? Cheap access to orbit? An expendable 2 stage will *always* be cheaper than the advanced engineering required for an SSTO.

Reuse? A reusable TSTO will always have more margin available than an equivalently engineered SSTO. Always.

[tater]

24 minutes ago, RCgothic said:

What is the point of an SSTO? Cheap access to orbit? An expendable 2 stage will *always* be cheaper than the advanced engineering required for an SSTO.

Reuse? A reusable TSTO will always have more margin available than an equivalently engineered SSTO. Always.

Yeah, the only good use case for any SSTO that I can imagine is RAPID reuse. No stacking required, gas and go. Since there are virtually no satellite payloads where this makes sense, it's gotta be crew... and currently there is no need to haul crew up to space on a "multiple times a day" sort of time frame. I'm just not seeing it, and even if you built a station so that commuting to orbit was desirable for such a vehicle, building that station would require a super heavy lift capability like SS/SH (or larger).

I'm not seeing the magical reduced cost aspect at all.

[sevenperforce]

3 hours ago, tater said:

Yeah, the only good use case for any SSTO that I can imagine is RAPID reuse. No stacking required, gas and go. Since there are virtually no satellite payloads where this makes sense, it's gotta be crew... and currently there is no need to haul crew up to space on a "multiple times a day" sort of time frame. I'm just not seeing it, and even if you built a station so that commuting to orbit was desirable for such a vehicle, building that station would require a super heavy lift capability like SS/SH (or larger).

I'm not seeing the magical reduced cost aspect at all.

I agree.

The only argument for SSTO over TSTO is that an SSTO can loop around to the launch site and land, while a TSTO either has to land downrange (and be transported back) or expend extra propellant for RTLS. The former option takes time and the latter is inefficient.

But I think it can probably be mathematically proven that you get more payload to LEO with a reusable TSTO, including RTLS boostback inefficiency, than with a reusable SSTO.

[RCgothic]

The only edge case I can think of is of the SSTO is landing somewhere fuel is available but a booster stage for a TSTO isn't.

If there's a booster available, TSTO is always better. If there's no fuel available then it's not rapidly reusable as SSTO Twice (without refuelling) isn't a thing on Earth.

Bit niche.

[tater]

5 minutes ago, sevenperforce said:

But I think it can probably be mathematically proven that you get more payload to LEO with a reusable TSTO, including RTLS boostback inefficiency, than with a reusable SSTO.

Yeah, and it's always important to remember what the role of a given vehicle is, and design for that goal. If a vehicle is to be a jack of all trasdes, it better be capable of "all trades," and ideally it should be cost effective.

The suggestion in the OP, even if cheap and expendable is that there is a market for small sats—and cheap can't possibly be a factor with even a single SSME on the bottom, the expendable SSTO would cost more to get a few tons to LEO than you could buy a F9 for.

This is in effect a smallsat launcher, and that market while filled with companies working towards competing, cannot possibly support more than a couple, and even those are moving to launch larger payloads as their customers are gobbled up by cheaper SpaceX launches.

Imagine the expendable option that gets a few tons to LEO for some amount of money equal to "just" the cost of a lightweight tank and very high I_sp engine. Some millions. A million a ton ($1000/kg)? That's cheap, but SS might drop that by more than an order of magnitude. There tends to be a group of people who talk about things like SS in terms of being "too big for normal payloads." All that matters if cost to target orbit.

[Nothalogh]

On 6/22/2021 at 6:45 PM, magnemoe said:

SSTO is an pipe dream / money sink until we get much better engines or launch systems. 

The only credible SSTO ever proposed was Project Orion

[Exoscientist]

8 hours ago, RCgothic said:

What is the point of an SSTO? Cheap access to orbit? An expendable 2 stage will *always* be cheaper than the advanced engineering required for an SSTO.

Reuse? A reusable TSTO will always have more margin available than an equivalently engineered SSTO. Always.

It’s the same reason why launch companies want to increase their payloads to orbit even with multistage rockets. SpaceX spent a great deal of  time and money doubling the payload to LEO of the F9 with the F9 Full Thrust.

 By using alt.comp. on existing engines and lightweight tanks can can also double the payload to orbit.  As a byproduct of that you also get an SSTO with the first stage that can more cheaply launch the smaller payloads, not needing the upper stage.

   Robert Clark

[tater]

7 minutes ago, Exoscientist said:

 By using alt.comp. on existing engines and lightweight tanks can can also double the payload to orbit.  As a byproduct of that you also get an SSTO with the first stage that can more cheaply launch the smaller payloads, not needing the upper stage.

If F9 lightened could fly some small cargo to LEO with just the booster, what would be gained? Throw away 9 engines to get a cubesat to LEO? (whatever, something small)

Right now, F9 gets many tons to LEO while only expending 1 engine, and one small tank.

Any technique used to lighten a booster for SSTO use could instead be used to improve S2 cost/mass, and just throw that away, instead, reusing the booster completely.

[Spacescifi]

1 hour ago, Nothalogh said:

The only credible SSTO ever proposed was Project Orion

 

Sort of...the orginal Orion had no way to return to Earth without shuttlecraft. All it was good for was boosting to orbit and boosting to other orbits.

 

It's an SSTO orbiter, since landing is not what it is made for.

 

Not to say you could not make an SSTO that could SSTO to orbit and land, it just needs modifications.

 

Design: A massive thick disc spaceship with rocket engines under the bell alobg the perimeter. A pusher plate is centrally located atop the disc, suspended by piston beams and shock absorbers.

 

Launch: Rockets boost clear of launch center, ship flips over and engages orion to orbit.

Reentry: Refuel the orion rocket engines in orbit with a tanker, use orion pusher plate to slow reentry speed before hitting atmosphere hard. Otherwise you take so much reentry damage that reusuability suffers.

 

Landing: Flip to engage rocket engines.

 

 

Why not just put rocket engines below around the perimeter and a pusher plate below in the center?

 

I thought about that,  and thought that perhaps doing that would damage the rocket nozzles from the bomb blast, since obviously the orion plate would not cover as far as ship's perimeter.

 

So I thought flipping may be better in any case where the plate is not as wide as the the ship.

Edited June 27, 2021 by Spacescifi

[RCgothic]

8 hours ago, Exoscientist said:

By using alt.comp. on existing engines and lightweight tanks can can also double the payload to orbit.  As a byproduct of that you also get an SSTO with the first stage that can more cheaply launch the smaller payloads, not needing the upper stage.

In SpaceX's particular case, that's just traded expending a cheap 2nd stage for expending the entire first stage. And the first stage also costs more than usual because of advanced!materials. That's not a good trade.

If utilising different engines and lightweight materials would make a big difference to turn a regular rocket into an SSTO (and note that several of them technically can already SSTO with extremely small payloads but never do), it would also make a big difference to a TSTO as well.

The only possible way an SSTO makes sense is if you want to reuse everything. And to reuse everything, everything needs a heat shield. Everything needs enough control authority for re-entry. All the extras need to be taken to orbit and back (eating potential payload).

Whereas to fully reuse a TSTO only the upper stage needs the extra bits, and the first stage can be much more lightweight.

SpaceX in particular aren't daft, and for starship they've taken the single best way to get to orbit fully reusable with a lot of payload. If SSTO made more sense, they'd have done that.

 

Finally, note that although SSMEs and RL10 are extremely efficient *engines*, their propellant tanks are larger, more insulated, more expensive, and heavier than the tanks required for alternative propellants. Storing hydrogen is hard.

Engine efficiency gives a linear benefit to the rocket equation. Mass fraction gives an exponential benefit. Depending on the application it can be better to optimise dry mass fraction than engine efficiency. A hydrogen powered stage might get more mass from LEO to the moon, but because of the better mass fraction a methane powered stage could send more mass from LEO out of the solar system entirely.

This is just one example to show why rockets don't always use "the best" even if they could. Hydrogen usually needs side boosters to get off the ground. Aluminium orthogrid may be lighter than steel, but it's more expensive, more time consuming to produce, and needs more heat shield than welded steel, for instance.

"Best" can mean many different things. Throwing better engines and materials on a rocket doesn't necessarily improve it if it makes the whole thing more expensive than the benefit.

Edited June 27, 2021 by RCgothic

[Exoscientist]

 Jet engines have used variable nozzles since the 70's:

 

 As a total WAG they might improve performance by, say, 10%. But used on a rocket engine it can improve payload 100%. Yet they have not been used on rocket engines.

   Robert Clark

[RCgothic]

They weigh and cost a lot more, and the weight doesn't matter because generally the wings on a jet is holding them up and they're fully reusable.

 

Using them in a rocket, ISP is optimal at SL and in a vacuum, so a small bit of ISP is gained just before the first stage separates. But late in the burn it's carrying way too much dry tank mass. The engines also have to shut or throttle down to stay within structural limits and become additional dead mass.

Comparatively, the Two Stage design has slightly worse ISP just before separation. It is also carrying more more engine and staging mechanism mass, but only early in the flight where that matters less. Later where it matters most it has less tank mass, fewer engines, and the engines weigh comparatively less than a compensating design.

Two stage still wins.

 

You want a compensating engine when you are constantly moving between different altitudes, throttle settings, and not trying to minimise dry mass. A rocket has just two regimes, one of which it stays in very briefly (SL), and dry mass is very important. It's a better optimization to go with a staging event 

Edited June 28, 2021 by RCgothic

[Exoscientist]

 Using high performance engines or adding altitude compensation plus lightweight tanks can triple the payload of the current Delta IV Heavy to ~70 tons to LEO:

 SSME based SSTO’s. UPDATED, 6/28/2021 - Extension to the Delta IV Heavy.

https://exoscientist.blogspot.com/2021/06/ssme-based-sstos.html

 Note this brings it into the payload range of the Falcon Heavy. Missions such as Robert Zubrins’s Moon Direct that require 3 launches of the Falcon Heavy for the cargo portions of the mission could be done by this upgraded Delta IV Heavy.

 Also, I discuss in the update that the ~20 ton payload to LEO of the upgraded Delta IV means it could get the same payload as a partially reusable Falcon 9, so could compete with SpaceX for the lucrative commercial satellite market.

 

  Robert Clark

[tater]

1 hour ago, Exoscientist said:

 Using high performance engines or adding altitude compensation plus lightweight tanks can triple the payload of the current Delta IV Heavy to ~70 tons to LEO:

 SSME based SSTO’s. UPDATED, 6/28/2021 - Extension to the Delta IV Heavy.

https://exoscientist.blogspot.com/2021/06/ssme-based-sstos.html

 Note this brings it into the payload range of the Falcon Heavy. Missions such as Robert Zubrins’s Moon Direct that require 3 launches of the Falcon Heavy for the cargo portions of the mission could be done by this upgraded Delta IV Heavy.

The current DIVH costs $350M - $400M. With the cheap engines, and cheap tank. 1 FH—expended—is $150M.

RS-68 engines are ~$20M. So DIVH with RS-25s would add $240M to the 350-400M cost. $590M to $640M. 4-5 FHe launches. Such savings! That's without "lighter tanks" so assume that costs zero.

 

1 hour ago, Exoscientist said:

 Also, I discuss in the update that the ~20 ton payload to LEO of the upgraded Delta IV means it could get the same payload as a partially reusable Falcon 9, so could compete with SpaceX for the lucrative commercial satellite market.

LOL, no.

DIV medium (no SRBs) costs more than an expended FH right now. An "increased price" version is not going to compete, ULA cannot compete with Atlas V.

 

PS-the satellte market is not all that lucrative, the total global market is ~$20B.

[magnemoe]

On 6/28/2021 at 10:06 PM, RCgothic said:

They weigh and cost a lot more, and the weight doesn't matter because generally the wings on a jet is holding them up and they're fully reusable.

 

Using them in a rocket, ISP is optimal at SL and in a vacuum, so a small bit of ISP is gained just before the first stage separates. But late in the burn it's carrying way too much dry tank mass. The engines also have to shut or throttle down to stay within structural limits and become additional dead mass.

Comparatively, the Two Stage design has slightly worse ISP just before separation. It is also carrying more more engine and staging mechanism mass, but only early in the flight where that matters less. Later where it matters most it has less tank mass, fewer engines, and the engines weigh comparatively less than a compensating design.

Two stage still wins.

 

You want a compensating engine when you are constantly moving between different altitudes, throttle settings, and not trying to minimise dry mass. A rocket has just two regimes, one of which it stays in very briefly (SL), and dry mass is very important. It's a better optimization to go with a staging event 

This an fighter jet do loads of mission profiles, mostly its high attitude over watch or escort at modest velocity. But you also have high speed intercepts and low level penetration 
And the last two is the reason for fighter jets 

[Exoscientist]

On 6/29/2021 at 2:34 PM, tater said:

The current DIVH costs $350M - $400M. With the cheap engines, and cheap tank. 1 FH—expended—is $150M.

RS-68 engines are ~$20M. So DIVH with RS-25s would add $240M to the 350-400M cost. $590M to $640M. 4-5 FHe launches. Such savings! That's without "lighter tanks" so assume that costs zero.

LOL, no.

DIV medium (no SRBs) costs more than an expended FH right now. An "increased price" version is not going to compete, ULA cannot compete with Atlas V.

PS-the satellte market is not all that lucrative, the total global market is ~$20B.

  Knowledgeable observers of the space program know how the game is played: charges to the government for launches can be twice or more higher than for commercial launches. SpaceX is now learning the game:

Air Force, SpaceX mum about sky-high rocket costs.
Elon Musk’s promises of a cheaper alternative haven’t yet been realized.
By John M. Donnelly
Posted September 23, 2020 at 7:00am
But the company’s bid of $316 million for one launch in fiscal 2022 is roughly double its usual price. And it is nearly double ULA’s per-launch bid for this round of launches of $169 million.
https://www.rollcall.com/2020/09/23/air-force-spacex-mum-about-sky-high-rocket-costs/

 

 Here’s a list of all launches by ULA of the Delta IV and Delta IV Heavy:

https://en.m.wikipedia.org/wiki/Delta_IV#Delta_IV_launches_in_chronological_order

 All but the first were government launches. ULA could charge half as much for commercial launches than the price they charge to the government and still make a profit.

 As I mentioned, I would advise using alt.comp on the Delta IV and Delta IV Heavy to get high performance engines from the current RS-68 to improve payloads and produce a SSTO.

 About the current commercial launch market, it’s much higher than the government market and ULA would love to get a portion of it. 

   Robert Clark

Edited June 30, 2021 by Exoscientist
Clarity

[Exoscientist]

On 6/28/2021 at 4:06 PM, RCgothic said:

They weigh and cost a lot more, and the weight doesn't matter because generally the wings on a jet is holding them up and they're fully reusable

  New advances in ceramics also are allowing lightweight components to jet engines:

Ceramic matrix composites in aircraft engines projected to double over five years, Stratview Research predicts.

2018-07-30 COURTNEY E. HOWARD

Aerospace engineers are opting for CMC components in best-selling aircraft to reap such intrinsic advantages as temperature resistance up to 260 degrees Celsius higher than nickel alloys at just one-third the weight. Continuous replacement of nickel alloys with CMCs in both low-pressure and high-pressure engine zones will help drive the double-digit growth rate over the next five years. Increasing aircraft deliveries and demand for fuel-efficient aircraft will further propel the demand for CMC in aircraft engines, analysts predict.

An F-16 Fighting Falcon F100 engine exhaust nozzle with five A500 ceramic matrix composite (CMC) divergent seals, identified by the yellow arrows. Air Force Research Laboratory and industry are partnering to test the ceramic materials as candidates to replace nickel-based superalloys currently used in exhaust nozzles. (U.S. Air Force photo)

https://www.sae.org/news/2018/07/ceramic-matrix-composites-in-aircraft-engines-projected-to-double-over-five-years-stratview-research-predicts

  The use of such lightweight materials in rockets would have an even more important effect since lightweight and increased performance are even more paramount for rockets.

    Robert Clark

Edited June 30, 2021 by Exoscientist
Clarity

[tater]

4 hours ago, Exoscientist said:

  Knowledgeable observers of the space program know how the game is played: charges to the government for launches can be twice or more higher than for commercial launches. SpaceX is now learning the game:

Air Force, SpaceX mum about sky-high rocket costs.
Elon Musk’s promises of a cheaper alternative haven’t yet been realized.
By John M. Donnelly
Posted September 23, 2020 at 7:00am
But the company’s bid of $316 million for one launch in fiscal 2022 is roughly double its usual price. And it is nearly double ULA’s per-launch bid for this round of launches of $169 million.
https://www.rollcall.com/2020/09/23/air-force-spacex-mum-about-sky-high-rocket-costs/

 

One, they have also charged as low as $35M for an F9 launch for NASA.

Two, the above quote includes the vertical payload integration facilites, and I think the extended fairing.

Three, there is ZERO reason for SpaceX to reduce costs when none of the competitors are (since they can't in the case of ULA).

 

Quote

 Here’s a list of all launches by ULA of the Delta IV and Delta IV Heavy:

https://en.m.wikipedia.org/wiki/Delta_IV#Delta_IV_launches_in_chronological_order

 All but the first were government launches. ULA could charge half as much for commercial launches than the price they charge to the government and still make a profit.

 As I mentioned, I would advise using alt.comp on the Delta IV and Delta IV Heavy to get high performance engines from the current RS-68 to improve payloads and produce a SSTO.

 About the current commercial launch market, it’s much higher than the government market and ULA would love to get a portion of it. 

   Robert Clark

The only commercial launches ULA has coming up (and the only commercial launches for a few years now, the last was in 2018) are for Amazon—a gimme contract from Bezos because he doesn't have a rocket, BO owes ULA some engines, and he would not buy from SpaceX even if a better deal. ULA is simply not competitive. If they could reduce prices and get commercial contracts, they might. So I'd say ULA would not "love" to get any part of it—they are not even trying. They just are not. SpaceX is already cheaper than ULA, and SpaceX can go cheaper still (and has). SpaceX competitively bid Starship for a cubsat contract. Like 6 cubesats. They didn't lose on price I think, but possible schedule risk (sensible, it's not a thing yet).

 

Regardless, the entire premise of this thread makes zero sense WRT commercial launches. I maintain the only use case is crew—and cost is not really much of a concern there.

1. There is no plausible route to useful SSTO cargoes at reduced prices with extant ULA rockets as the starting point (and I'm not sure there is even clean sheet). Particularly since the payloads are in the "smallsat" class, a market filled with new players. Your SSTO would need to fly for well under $10M per flight. Astra is $2.5M. Beat that or don't bother.

2. The market doesn't support many launches, it's tiny. Larger players like ULA are not interested. The only one that is eating that market is... SpaceX with rideshare. An 830kg rideshare is $4.15M. If Astra starts flying more... that could go down (the prices they have seem designed to compete with RocketLab ($7.5M)).

 

Edited July 1, 2021 by tater

[sevenperforce]

Trying to use more advanced materials to make an SSTO use case close is like adding spoilers to a UPS truck in hopes of making deliveries faster. 

Literally any advancements that could make an SSTO closer to workable would make a TSTO architecture significantly more workable. 

[tater]

33 minutes ago, sevenperforce said:

Trying to use more advanced materials to make an SSTO use case close is like adding spoilers to a UPS truck in hopes of making deliveries faster. 

Literally any advancements that could make an SSTO closer to workable would make a TSTO architecture significantly more workable. 

Particularly WRT reusable SSTO concepts.

Solving rapid reuse from orbit means that your TSTO rocket is now also fully reusable. The only downside would be operational concerns (stacking)—but in the real world, unless you are some nut that wants to colonize Mars (lol), there's no reason to turn around fast enough that the stacking delays matter, and of course in return you get way more payload.

[Hannu2]

On 6/25/2021 at 10:40 AM, Exoscientist said:

No. That’s the point I’m making. By using high performance engines such as the SSME’s and lightweight tanks such as with carbon fiber, then an expendable SSTO can even match the ca. 3% payload fraction of current expendable multistage rockets.

That is highly speculative option. SpaceX tried to make fuel tanks from composites and failed. It is clearly very non trivial task. No on knows how much development takes money or time and what results eventually are. Just take strenght of lightest composite and calculate some values is not very credible.

 

On 6/25/2021 at 10:40 AM, Exoscientist said:

 This is because the greatly improved Isp of the high performance engine radically improves total mass to orbit. Then when you add onto that the dry mass is greatly reduced by lightweight tanks, the expendable SSTO matches or even exceeds the payload fraction for the current multi-stage expendable.

But why we would not build two stage booster from those new advanced materials and get again benefits of multi stage rocket?

 

 

On 6/25/2021 at 10:40 AM, Exoscientist said:

 So you use the SSTO only for smaller payloads and the newly optimized TSTO for larger payloads or to GEO.

There is already significant competition in small launches. There are small conventional rockets and rockets launched from plane. And there is also a threat that when huge starship begin to work as intended it takes markets because fully reusable huge craft may be cheaper than small expendable rocket.

I am sure that those companies have investigates SSTO possibility but rejected it. It is like shuttle, many very advanced things are needed but no one knows how much it cost or take time to develop them. Governments may make overoptimistic decisions and keep programs running using loads of taxpayer's money even everything will not be realized as intended. But companies can not afford that.

 

[Exoscientist]

20 hours ago, sevenperforce said:

Trying to use more advanced materials to make an SSTO use case close is like adding spoilers to a UPS truck in hopes of making deliveries faster. 

Literally any advancements that could make an SSTO closer to workable would make a TSTO architecture significantly more workable. 

  I fully agree - but that’s precisely why such advancements should be done! SpaceX spent quite a bit of money doubling the payload of the Falcon 9 with the Falcon 9 Full Thrust. The changes made included given it a larger propellant tank and using supercooled propellant.

 I’m saying  an approx. doubling in payload could be accomplished by altitude compensating additions to the Merlins and lightweighting the existing tanks (the weight savings not as great here since they already use aluminum-lithium tanks) . So you wouldn’t need  larger tanks, or supercooled propellant. I’m asserting these changes would have been cheaper than the approach SpaceX took. The altitude compensation methods I described in the update to my blog post are technically simple. Any half decent garage tinkerer could make working prototypes of such attachments.

 Plus, you would then have a working SSTO. The payloads that the Falcon9 v1.1 had launched could be launched now by the first stage only, so for a lower cost not needing the upper stage.

 Or said another way, the current F9 FT, would also have its payload approximately doubled by applying these changes and much of the current launch market to LEO could be done by just the first stage of the F9, for a cheaper launch cost not needing the upper stage.

  Robert Clark

 

[tater]

1 minute ago, Exoscientist said:

 Plus, you would then have a working SSTO. The payloads that the Falcon9 v1.1 had launched could be launched now by the first stage only, so for a lower cost not needing the upper stage.

Except they would have to throw away that first stage with 9 engines.

So they could save the cost of 1 engine.

The hit on ASDS landing is ~20%, and RTLS landing is ~40%. There is no possible way that an SSTO F9 booster could possibly be recovered from orbit. You're talking about making it even less durable (lighter), with a small payload, so it can be thrown away. It makes zero sense.

[Exoscientist]

12 hours ago, Hannu2 said:

That is highly speculative option. SpaceX tried to make fuel tanks from composites and failed. It is clearly very non trivial task. No on knows how much development takes money or time and what results eventually are. Just take strenght of lightest composite and calculate some values is not very credible.

 More precisely, it did a trade that for the Starship when you take into account the weight of the thermal shielding  the ultra strong steel it decided on would be more heat resistant so less thermal shielding would be required.  Carbon fiber tanks are now a well-established technology.

That materials choice is perfectly OK. As I said in the blog post some ultra strong metals would save just as much weight in the tanks as carbon composites, so could also result in SSTO’s.

 

  Robert Clark

[Shpaget]

The problem you seem to have is that you think SSTO is some paragon of technological achievement, with the whole rocket science community struggling to make it work because it will revolutionize space travel.

The truth is that nobody* really cares about it. All the problems and complexities that come from TSTO configuration are already solved, not to mention they pale in comparison to performance gains that come from shedding mass.

*talking about launch providers, not dreamy eyed, scifi loving spectators. Also, clients are just interested in the final orbit.