Sub-orbital spaceflight
Some sub-orbital flights have been undertaken to test spacecraft and launch vehicles later intended for orbital spaceflight.[3] By definition, a sub-orbital spaceflight reaches an altitude higher than 100 km (62 mi) above sea level.[4] The US military and NASA award astronaut wings to those flying above 50 mi (80 km),[5] although the U.S. State Department does not show a distinct boundary between atmospheric flight and spaceflight.Thus the net extra specific energy needed compared to just raising the spacecraft into space is between 0 andThe maximum speed in a flight is attained at the lowest altitude of this free-fall trajectory, both at the start and at the end of it.(If there were no atmospheric drag the theoretical minimum delta-v would be 8.1 km/s to put a craft into a 300-kilometer high orbit starting from a stationary point like the South Pole.)[citation needed] For sub-orbital spaceflights covering a horizontal distance the maximum speed and required delta-v are in between those of a vertical flight and a LEO.The maximum speed at the lower ends of the trajectory are now composed of a horizontal and a vertical component.Scaled Composites SpaceShipTwo which is under development will have a similar free-fall orbit but the announced maximum speed is 1.1 km/s (perhaps because of engine shut-off at a higher altitude).The minimum-delta-v trajectory for going halfway around the world corresponds to a circular orbit just above the surface (of course in reality it would have to be above the atmosphere).Increasing the speed to 7.9 km/s to attain any point on Earth requires a considerably larger missile because the amount of fuel needed goes up exponentially with delta-v (see Rocket equation).For an ICBM the atmospheric reentry phase takes about 2 minutes; this will be longer for any soft landing, such as for a possible future commercial flight.A partial failure caused it to instead follow a sub-orbital trajectory, reentering the Earth's atmosphere 43 hours after launch.[8] To calculate the time of flight for a minimum-delta-v trajectory, according to Kepler's third law, the period for the entire orbit (if it did not go through the Earth) would be:Using Kepler's second law, we multiply this by the portion of the area of the ellipse swept by the line from the centre of the Earth to the projectile:From the form involving arccosine, the derivative of the time of flight with respect to d (or θ) goes to zero as d approaches 20000 km (halfway around the world).[citation needed] Sub-orbital tourist flights will initially focus on attaining the altitude required to qualify as reaching space.The flight path will be either vertical or very steep, with the spacecraft landing back at its take-off site.The spacecraft will shut off its engines well before reaching maximum altitude, and then coast up to its highest point.[10][11] In late 1945, a group led by M. Tikhonravov K. and N. G. Chernysheva at the Soviet NII-4 academy (dedicated to rocket artillery science and technology), began work on a stratospheric rocket project, VR-190, aimed at vertical flight by a crew of two pilots, to an altitude of 200 km (65,000 ft) using captured V-2.[12] In 2004, a number of companies worked on vehicles in this class as entrants to the Ansari X Prize competition.The Scaled Composites SpaceShipOne was officially declared by Rick Searfoss to have won the competition on October 4, 2004, after completing two flights within a two-week period.It has since been completed with eight seats (one pilot, one co-pilot and six passengers) and has taken part in captive-carry tests and with the first mother-ship WhiteKnightTwo, or VMS Eve.Branson stated, "[w]e are going to learn from what went wrong, discover how we can improve safety and performance and then move forwards together.Scientific sub-orbital flights began in the 1920s when Robert H. Goddard launched the first liquid fueled rockets, however they did not reach space altitude.[15] Today there are dozens of different sounding rockets on the market, from a variety of suppliers in various countries.Research, such as that done for the X-20 Dyna-Soar project suggests that a semi-ballistic sub-orbital flight could travel from Europe to North America in less than an hour.[17] The main challenge lies in increasing the reliability of the different components, particularly the engines, in order to make their use for passenger transportation on a daily basis possible.[a] Private companies such as Virgin Galactic, Armadillo Aerospace (reinvented as Exos Aerospace), Airbus,[24] Blue Origin and Masten Space Systems are taking an interest in sub-orbital spaceflight, due in part to ventures like the Ansari X Prize.NASA and others are experimenting with scramjet-based hypersonic aircraft which may well be used with flight profiles that qualify as sub-orbital spaceflight.
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