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.
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.
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).