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.
Are there any studies of SSTO's made of more modern, lighter materials like carbon fiber?
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.
Quote from: scienceguy on 01/19/2017 08:43 pmAre 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.
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.
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.
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.
Quote from: KelvinZero on 01/20/2017 06:50 amThen 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.
Musk ruled out making the 2nd stage reusable (which is the final velocity an SSTO would have to achieve) at all.
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.
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.
Huge investment with massive risk of unproven system for what market ?
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.
You won't see a useful SSTO vehicle until the stupid phobias against nuclear power are lifted.
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.
But bottom line More GTOW / less payload --> higher $/lb to orbit.
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.
Quote from: KelvinZero on 01/20/2017 09:10 pmI 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.
2nd stage reuse is always simpler than reuseable SSTO or shuttle architecture on the same conditions. TPS of large rockets is a great pain.
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).
QuoteBut 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
Quote from: Katana on 01/21/2017 07:02 am2nd 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.
Quote from: Nomic on 01/20/2017 10:09 amAlways 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.
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.
Better to use nitrogen in that case instead of oxygen. There's like 4x as much nitrogen, and it's nearly inert.
Quote from: john smith 19 on 01/20/2017 07:35 pmQuote from: Nomic on 01/20/2017 10:09 amAlways 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?QuoteBTW 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.
For a reusable TSTO can the upper stage and the capsule's service module be merged?
\Unfortunately IRL those also count as "benefits." QuoteWell, sure, but more for NASA/government projects... I was asking more about the lack of SSTO projects among the "new"/commercial space companies.QuoteYou 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.QuoteBeing 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.
Well, sure, but more for NASA/government projects... I was asking more about the lack of SSTO projects among the "new"/commercial space companies.QuoteYou 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.QuoteBeing 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.
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.
Being able to match a TSTO ELV in payload fraction matters. No historical SSTO had managed this.
Variations of mix ratio are too small to be meaningful.
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.
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.
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.
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.
Quote from: john smith 19 on 01/21/2017 09:04 am\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.
\Unfortunately IRL those also count as "benefits."
QuoteYou 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.
QuoteBeing 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.
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.
it is a crying shame nothing happened with TAN over the last decade.
Quote from: Archibald on 01/25/2017 06:37 pmit is a crying shame nothing happened with TAN over the last decade.It's nearly out of patent protection!
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
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.
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 long as this model persists it seems impossible for the mfg to ever recoup the cost of their vehicles development through the open market.
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).
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.
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. QuoteQuoteTrue. 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.
QuoteTrue. 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.
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.
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.
As I noted with Shuttle there were a number of ideas for significantly speeding up the process and reducing the head count.
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.
Quote from: Jim on 01/26/2017 02:09 pmTWA 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. QuoteEastern (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. QuoteAmerican (Robertson Aircraft Corporation and Colonial Air Transport)Again I cannot find any reference for situations where the aircraft mfg supplied the airline.QuoteSo 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 ]
Quote from: john smith 19 on 01/28/2017 06:51 amExcept "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.QuoteAs 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.
Quote from: Robotbeat on 01/25/2017 08:30 pmQuote from: Archibald on 01/25/2017 06:37 pmit 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.
The result : simply strap up some (old) ramjets for Mach 1 to 5 ?
QuoteAFAIK 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.
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.
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.
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.
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: Katana on 01/30/2017 12:18 pmThe 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.
Quote from: john smith 19 on 08/16/2014 11:28 amMaybe 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
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.
Quote from: Vultur on 01/29/2017 02:27 amOh, 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.
You may find this interesting. From the Advanced Topics thread "Finding the actual speed limit of a conventional ramjet powered vehicle."
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.pdfAnyway, 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 Vehicleshttp://drum.lib.umd.edu/bitstream/handle/1903/2939/umi-umd-2731.pdfThe result : simply strap up some (old) ramjets for Mach 1 to 5 ?
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.
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 from: john smith 19 on 01/30/2017 09:21 pmHowever 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.
ITS is a SSTO, problem is u have to start on Mars
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.
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.
If NASA stick to improvements of Saturn I/V without wings, VTVL reuse could be realized long before Falcon 9.
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.
Then we'll have to see how Blue does with this.
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 secondsTAN will at most earn 15 seconds on isp vac from bigger nozzles.
QuoteThen 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.
Quote from: Katana on 02/02/2017 05:27 amSSME 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 secondsTAN 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. QuoteQuoteThen 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.
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.
Quote from: Nilof on 02/05/2017 09:27 am15 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.
Quote from: john smith 19 on 02/05/2017 10:16 pmFor 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_IIhttps://en.wikipedia.org/wiki/Graphite-Epoxy_MotorGEM 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).
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.
Actually Jeff Greason, when he was at XCOR, suggested something similar.
Quote from: john smith 19 on 02/05/2017 10:16 pmQuote from: Nilof on 02/05/2017 09:27 am15 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_IIhttps://en.wikipedia.org/wiki/Graphite-Epoxy_MotorGEM 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.
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
Propellant (Fuel/Oxidizer) Liquid hydrogen (LH2) Liquid Oxygen (LOX)Mixture ratio 3.4: 1Specific gravity 260kg/m3 (1 6.231bm/ft3)Specific heat ratio 1.26Chamber temperature 2959K (4866F)Chamber pressure 20.26MPa (2939psia)Engine throttled to limit acceleration to 3g; Throttle range 20-100%.
Quote from: Robotbeat on 02/06/2017 11:44 pmAlso, 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.
The thing is, the time you most need thrust is at take-off, when ramjets are useless.
Quote from: john smith 19 on 02/05/2017 10:16 pmQuote from: Nilof on 02/05/2017 09:27 am15 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
...Besides, this prove large hydrogen tanks could not survive reentry intact (being able to reuse) natually, though some small debris could survive.
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.
Quote from: Proponent on 02/08/2017 01:00 pmThe 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.
Quote from: john smith 19 on 02/09/2017 06:43 pmRBCC 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.
RBCC shroud is large and heavy, more heavier than ramjets and enlarged main engines.
Quote from: Archibald on 01/25/2017 06:37 pmit 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 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).
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.
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.
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.
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!
Oh hullnuts! While we were all talking up the past we TOTALLY forgot to suggest the DIY method!http://quantumg.net/mockingbird.pdfYou, 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
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.
Would the Mockingbird ever works ? I thought SSTOs scaled pretty bad.
Quote from: su27k on 03/11/2017 12:39 pmWell 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: su27kAlso 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: su27kIf 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
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.)
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.
Quote from: HMXHMX on 03/11/2017 04:17 pmSSTOs 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?Quote from: HMXHMX on 03/11/2017 04:19 pmIt'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.
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).
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.
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
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.
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.
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 tonnesAt 7800 m/s: 10.75 tonnesAfter landing (500 m/s): 9.22 tonnesSince 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.
Quote from: Asteroza on 03/23/2017 05:57 amSo 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.
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.
I always thought a single SSME with TAN based SSTO would be a nice low cost project
Quote from: Patchouli on 04/30/2017 05:04 pmI 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.
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.
Quote from: guckyfan on 04/30/2017 07:24 pmQuote from: Patchouli on 04/30/2017 05:04 pmI 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?