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TSTO spaceplanes
by IKE - 19-4-2006

Boeing (Scramjet)

This derivative of Boeing's proposal the carrier is identical with the version already described but it has two SSME engines in the back.

The orbiter is also a winged aircraft but it has a scramjet engine instead of a rocket. The scramjet uses the atmosphere's oxygen as oxidizer so the aircraft needs only tanks for fuel. It also has an auxiliary rocket engine for orbital maneuvering.

The flight profile is quite different because the scramjet needs to be inside the atmosphere in order to function properly. The two vehicles jointed take off using only the jet engines and again at 30.000ft and 0,85 mach the two rocket engines are ignited. When reaching 80.000ft and 2,5 mach the scramjet is starting to produce thrust and with the 2 rocket engines the joint aircrafts reach a velocity of 3,3 mach at only 90.000ft (the other version needs to climb at 103.000ft to reach that speed). At this altitude and speed the separation process is initiated and it is the same as described above.

After the separation the carrier heads for landing. The orbiter needs to remain below 40 miles of altitude because of the scramjet, so it accelerates to reach a velocity in excess of the required 25.700ft/s. When reaching the upper boundaries of the atmosphere the orbiter is moving at 26.200ft/s and while the scramjet shuts down due to lack of oxygen the orbiter uses its momentum to ascent at an altitude of almost 100 miles and enter to orbit. In this stage it also uses the auxiliary rocket engine to sustain orbit and to maneuver in space. After it accomplishes its task it re-enters the earth's atmosphere and sails to landing.

conclusions for both versions

This system is very flexible, both vehicles are completely reusable and need minimal pre-launch preparations before or after their flight. It can place cargo or people into orbit in short notice and repeat the same task in a very short period of time. No complex ground establishment or equipment is needed in contrast with the space shuttle or other vertically launched rockets which requires a lot of ground gear and personnel to support their launch and landing. There isn't also the handicap of the optimum equatorial launch coordinates that most rockets are facing. The system can transit to a place close to equator by using its jet engines and launch the orbiter with a minimum penalty in rocket fuel consumption.

Apart from the scramjet engine which is still in early experimental development stage, almost the entire technology that this project needs is not only operational but almost 25 years in use (the F101 and SSME engines for example). Of course the integration and final design of such a vehicle will be a very elaborate task. This proposal never reached production or early development stage (officially at least) some of its core design elements seems to derive or being used in the -unofficially named- Blackstar system.
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This very simple engine is essentially a tube with a central bulge and fuel injectors. Air enters with a high velocity at the front and is compressed because of the gradually reduced volume while fuel injectors enriched it with fuel. Later it ignites and the decompression produces forward thrust.

Ramjets are efficient in supersonic cruise but the inlet decelerates the airflow in subsonic speed in order for the engine to function properly.

This type of engine is used from the early years of aviation from a variety of vehicles in speeds higher than 2 mach.

This engine is a similar in principle with the ramjet engine. The main difference is that the flow inside the engine remains supersonic and the shockwaves contributes sustantially in the overhaul compression ratio.

It is very difficult to sustain a flame front under these flow conditions and most engines are still in the early experimental stage (like NASA/Boeing's X-43 and Qinetiq's HyShotIII).

If however they reach operational status scramjets can operate efficiently in hypersonic velocity (~10+mach) and high altitudes while scramjet equipped aircraft can be lighter in comparison to the equivalent rocket powered because there is no need for onboard oxidiser as the scramjet receives oxygen from the atmosphere


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