Quote from: saaopl on 04/10/2017 11:26 pmI actually shared Musk's view towards conventional air-launch approaches. In the AQ section of the following page, brief comments on two conventional air launch by plane and by balloon approaches have already been included.http://saaopl.net/index.php/features/One major reason that two conventional air launch are not promising, and yet to be mentioned by Musk, is that none of them are reusable, or neither of them can be an ideal candidate to develop a reusable launch system.Actually, if you'll read the quote above from Musk it doesn't mention reusability at all. Musk's point is valid even if you have full reusability.Musk's point is that an aircraft-launched system essentially makes the aircraft an additional stage. You have all the cost and complexity of an additional stage, but it's an additional stage that gives you much less benefit than a rocket stage. The same is true for an airship-assisted launch system -- the airship is an additional stage, but one that gives you much less benefit than a rocket first stage.You didn't address this point in your reply.
I actually shared Musk's view towards conventional air-launch approaches. In the AQ section of the following page, brief comments on two conventional air launch by plane and by balloon approaches have already been included.http://saaopl.net/index.php/features/One major reason that two conventional air launch are not promising, and yet to be mentioned by Musk, is that none of them are reusable, or neither of them can be an ideal candidate to develop a reusable launch system.
Quote from: ChrisWilson68 on 04/13/2017 09:32 pmQuote from: saaopl on 04/10/2017 11:26 pmI actually shared Musk's view towards conventional air-launch approaches. In the AQ section of the following page, brief comments on two conventional air launch by plane and by balloon approaches have already been included.http://saaopl.net/index.php/features/One major reason that two conventional air launch are not promising, and yet to be mentioned by Musk, is that none of them are reusable, or neither of them can be an ideal candidate to develop a reusable launch system.Actually, if you'll read the quote above from Musk it doesn't mention reusability at all. Musk's point is valid even if you have full reusability.Musk's point is that an aircraft-launched system essentially makes the aircraft an additional stage. You have all the cost and complexity of an additional stage, but it's an additional stage that gives you much less benefit than a rocket stage. The same is true for an airship-assisted launch system -- the airship is an additional stage, but one that gives you much less benefit than a rocket first stage.You didn't address this point in your reply.The cost and complexity of designing and constructing an airplane and an airship are at different level.
The launch platform used in SAAOPL system can be much simpler than a conventional HAA at the same level. Structurally, it is a mix of an airship and balloon, with the maximum speed close to 40m/s at approximate 22km altitude, which is substantially lower than the maximum airplane speed of 200+ m/s at 10km. This difference alone already can save a lot of aerodynamic complexities.
Another thing to be emphasized that SAAOPL is an unconventional launching system. It is not a wisdom choice to isolate each components in the system and compare with conventional stages individually, rather than comparing systems as a whole.
Taking the launch platform for example, if simply comparing it with conventional first stage in the scenario of launching an conventional upper stage, it doesn't worth at all, since it adds zero delta-V, lifts very limited altitude and doesn't boost reliability. However, within SAAOPL system, the launch platform brings SLSS out of dense part of atmosphere (significantly boost the performance of SLSS),
and provide the crucial altitude redundancy that SLSS needs to dump its fuel in the scenario of immediately-after-launch engine failure.
As a novel system, delivering a cargo to space orbit using SAAOPL system conceptually can be like sending a cargo to another continent using Boeing 747.
The design of SAAOPL system have placed reusability, reliability and short-launch cycle in the key positions since the beginning.
The cost and complexity of designing and constructing an airplane and an airship are at different level.......
How is this better than what DARPA is doing with the XS-1?
Quote from: whitelancer64 on 08/16/2017 09:15 pmHow is this better than what DARPA is doing with the XS-1?Not very familiar with technical details of XS-1. It seems XS-1 still is a vertical take-off vehicle, like what SpaceX did. SAAOPL is quite different. It is novel launching system which combines stratospheric launch and HTHL.
I'd recommend replacing RS-25 with either Merlin or BE-3 because RS-25 cannot do air-start or restart. If it could, Ares I would probably be flying today. XS-1 is ground launched (partly) because of this limitation.How do you propose to target the booster at a runway after separation? If it cannot restart, it will be limited to launch azimuths that are within it's crossrange capability to a runway, but that still keep the upper stage ground track away from populated areas. This might work for some launch sites and inclinations, but it is a significant limitation that needs analysis.I'd also recommend doing a detailed analysis to see how much larger the first stage (suborbital spaceship) has to be to do VTHL and put the same upper stage/payload to Mach 12 (por alternatively, what the payload reduction is with the same booster doing VTHL). This will give a mathematical basis for the claim that the balloon "stage" is worth the expense.
Most engine failures result in RUD.
Quote from: TrevorMonty on 08/19/2017 07:36 pmMost engine failures result in RUD.That is exactly what the design of SAAOPL system wants to solve. If an engine malfunction was detected, engine can be shut down immediately. SLSS will dump all its fuel into the air and glide back.
Even in the scenario of engine explosion, a layer of Kevlar between engine and SLSS can protect SLSS from serious damage. SLSS and its payload still can be survived and recovered.
SLP also helps SLSS start its engine before separation.
Quote from: envy887 on 08/18/2017 01:18 pmI'd recommend replacing RS-25 with either Merlin or BE-3 because RS-25 cannot do air-start or restart. If it could, Ares I would probably be flying today. XS-1 is ground launched (partly) because of this limitation.How do you propose to target the booster at a runway after separation? If it cannot restart, it will be limited to launch azimuths that are within it's crossrange capability to a runway, but that still keep the upper stage ground track away from populated areas. This might work for some launch sites and inclinations, but it is a significant limitation that needs analysis.I'd also recommend doing a detailed analysis to see how much larger the first stage (suborbital spaceship) has to be to do VTHL and put the same upper stage/payload to Mach 12 (por alternatively, what the payload reduction is with the same booster doing VTHL). This will give a mathematical basis for the claim that the balloon "stage" is worth the expense.Stratospheric launch platform (SLP) stables itself in the relative slow and steady airflow in stratosphere. Azimuth and pitch angle of SLP does not necessarily to be same as what are required by stratospheric-launched suborbital shuttle (SLSS). By controling length of tether cables beneath SLP, azimuth and pitch angle of SLSS is set to the predetermined values before separation. SLP also helps SLSS start its engine before separation.Given the chilly ambient temperature in stratophere, RP-1 is not ideal fuel for SLSS. Comparing with vertical lift-off rockets, One advantage of SAAOPL system is its reliability. SAAOPL has conceptual goal 1000 launches per year for single SAAOPL system. Hence, engine failure is a scenario that the design of SAAOPL must consider. If engine failure occurs soon after lift-off, both vertical lift-off rocket and its payload will be lost. However, that would be different for SAAOPL system. If engine failures occurs after being launched from SLP, SLSS has sufficient altitude redundancy, which is provided by SLP, to safely dump all its fuel and glide to an airfield nearby with its payload.
Quote from: sevenperforce on 04/04/2017 05:29 pmAye, the only meaningful advantage of launching from altitude is the ability to use near-vacuum-optimized engines from the startAre there any advantages to having a much more benign aerodynamic environment (e.g., far lower max Q)? Would that allow a lighter structure for the actual vehicle, and thus better performance? If one doesn't have to worry about dense atmosphere, and thus streamlining, does that allow different form factors for the vehicle rather than a slender tube?
Aye, the only meaningful advantage of launching from altitude is the ability to use near-vacuum-optimized engines from the start
Firstly, I should put a note here that this is more a conceptual representation than a detailed design. Secondly, SLSS, as the third word of its name (Suborbital) states, doesn't reach orbital speed. For example, in a sample simulation for regional flight profile, SLSS reaches around 15 Mach speed and 112 km altitude at burn-out. Thanks for your interest and question!
Quote from: saaopl on 04/03/2017 01:26 amFirstly, I should put a note here that this is more a conceptual representation than a detailed design. Secondly, SLSS, as the third word of its name (Suborbital) states, doesn't reach orbital speed. For example, in a sample simulation for regional flight profile, SLSS reaches around 15 Mach speed and 112 km altitude at burn-out. Thanks for your interest and question!1 - the first time you mentioned SLSS was in this post in reply to mine, so how was I supposed to know it's suborbital?2 - actually, this is quite confusing, as the other name (your forum nickname) clearly has the word ORBITAL.3- so, is it ORBITAL or SUBorbital?4 - if itīs ORBITAL, how can it achieve a 30 km/s delta-v? Fuel tanks seem undersized by an order of magnitude at least.