All air breathing SSTO systems suffer from a serious basic rocket equation problem: Mass Ratio.One can treat a launch to orbit as two conic sections: Either 1 stage and 2nd stage (for TSTO), or atmosphere/vacuum for atmosphere breathing SSTO solutions.Falcon 9 gets the second conic section started at 2.3km/sec at 65km altitude. Similar for Starship/Booster.A fantasy air breathing scramjet can get at most 3km/sec at 40km altitude (X-43 did it for 10 seconds). so about 1.5x the energy. (But most real-life proposals are less energy, topping out at Mach 5.).The mass ratio of a large aircraft is on the order of 3 or less. Usually a lot less. Wings weigh a lot, as do the air breathing engines, landing gear, and airframe that ties them all together. Which is great if you are flying around in an atmosphere, but terrible if you are trying to fly in a vacuum.The mass ratio of the Falcon second stage is about 18 (6.5 for Starship).There is no fuel that can make up for the lack of mass ratio in the second conic section. The Isp of such a fuel would have to be 1.7x to make up for the difference in mass ratio of a Starship (or an Isp of 633) and 2.6x for Falcon 9 (an Isp of 910). The only thing in that range is nuclear thermal, and that'll make the mass ratio even worse.One could crank up the size of the atmosphere breathing SSTO in order to get a usable cargo mass, but then there would be no landing gear physically possible that would be able to land such a monster.It amuses me every time I see fantasy drawings and even funding for startups that can't pass a very basic rocket equation scrutiny.
All air breathing SSTO systems suffer from a serious basic rocket equation problem: Mass Ratio.
In context here this wasn't an "air-breathing SSTO" but an "near-SSTO with air-breathing engines" in that it was planned to be launched into near-orbit using large SRB and then using the air breathing engines after reentry as pretty much a 'normal' aircraft.The version without any air-breathing engines removed them to make way for more propellant and better rocket engines so it could actually make orbit once the SRB burned out.Randy
During the 1980s Rockwell International envisaged the MRCC (Multi Role Common Core) trans-atmospheric vehicle for the USAF to be used as a suborbital/orbital replacement for the F-111 fighter-bomber. The MRCC spaceplane would have been powered by one large rocket engine and two turbojets, with the option to remove and replace the turbojets with more rocket propellant and OMS-type engines. Unsurprisingly, the Rockwell International military TAV proposal was not proceeded with, given that the engine technology proposed for this spaceplane surely would have faced insurmountable technical and financial hurdles. This link can be consulted for technical data regarding the MRCC trans-atmospheric vehicle project:https://www.secretprojects.co.uk/threads/rockwell-international-mrcc-multi-role-common-core-tav.1615/
Are there any technical specifications or extant Rockwell International project documents for the MRCC spaceplane in the Boeing archives?
Final report BOEING TRANSATMOSPHERIC VEHICLE (TAV) CONCEPTS DEFINITION (PHASE I)Battelle Columbus Laboratories (Subcontract No. A-3089(6697)-288)USAF Contract No. F33615-83-C-0132, Task 6December 22, 1983 Report Number D180-27669-4> The study requested The Boeing Company to describe two or more Transatmospheric Vehicle (TAV) concepts that could provide 5,000 lb to 30,000 lb in low Earth orbit utilizing horizontal takeoff (HT0). A brief list of system requirements and goals were defined in the statement of work.https://apps.dtic.mil/sti/pdfs/ADB216503.pdfhttps://apps.dtic.mil/sti/citations/ADB216503