[00:00] Why can't we fly a plane into space
[00:03] what stops it from just flying higher and
[00:05] higher until it in space.
[00:08] well there are several issues but
[00:10] assuming we are in something like a
[00:12] normal jet airliner then one of the main
[00:14] problems is the air or lack of it as we
[00:18] get closer to space.
[00:19] a plane flies because it is propelled
[00:22] forward the wings which shaped to make
[00:25] the air flow faster of the top of them
[00:27] rather than the bottom generate lift as
[00:30] the plane goes faster the wings create
[00:33] more lists when the lift is greater than
[00:36] the weight to the plane it will climb into
[00:38] the air. As our playing climbs higher and
[00:41] higher into the atmosphere the air
[00:43] becomes less and less dense the plane to
[00:46] fly faster to create more iift until
[00:49] eventually it reaches an altitude where
[00:51] the engines either cease to function
[00:53] correctly because of the lack of oxygen
[00:55] or the air is too thin to create enough lift.
[00:59] Just as we need air to breathe then the
[01:02] engine need oxygen to burn to create
[01:05] thrust to propel the plane forward just
[01:07] engines however engines can work at higher
[01:09] altitudes than people. We humans have a
[01:11] limit about 8,000 meters or 26,000 feet
[01:14] above which is what climbers
[01:17] call the "Death Zone", this is where there
[01:20] is not enough oxygen for humans to
[01:22] survive for sustained period. The summit
[01:26] of Mount Everest is 29,000 feet high in
[01:29] the air density there is about
[01:31] 33%  of that at sea level.
[01:34] This means that with each breath you
[01:36] take you're only getting
[01:38] 33% of the oxygen. If you want to
[01:40] stay at this altitude without additional
[01:43] oxygen you would suffer from a condition
[01:45] called hypoxia were due to a lack of
[01:48] oxygen to the body starts to slow shut
[01:51] down and die.
[01:53] At 12,000 meters or 40,000 feet which is
[01:57] the upper limit for most modern
[01:59] airliners the air density is about
[02:01] 18% of that at sea level. If you
[02:04] were in a plane that had a rapid
[02:06] decompression at 40,000 feet you'll have
[02:09] about five maybe ten seconds to get your
[02:13] emergency oxygen mask on before you
[02:15] became unconscious. The highest flying
[02:18] jet plane in level flight was the
[02:21] Lockheed SR-71 blackbird with a height
[02:24] of 85,069 feet 42,929 meters
[02:30] and where the a density is just 2% of
[02:35] that sea level. At that height it's
[02:38] traveling at mach 3.2 or 2190 miles an
[02:43] hour. The SR-71 pilots had to wear a full
[02:47] pressure suit with its own oxygen supply
[02:49] in case of a cockpit decompression or
[02:52] emergency ejection and this was put to the
[02:55] test when you 1966 an SR-71 piloted by
[02:58] Bill Weaver disintegrated that mach 3.1
[03:02] at an altitude the 78,000 feet as it was
[03:06] performing a test flight to ironically
[03:08] optimizing performance. At that altitude
[03:11] your blood will boil in a similar way to
[03:14] when you open a bottle of fizzy drink as
[03:16] the nitrogen in your blood to the gas in
[03:19] the low-pressure atmosphere. The pressure
[03:21] suit work and Weaver survived the
[03:24] descent from 78,000 feet but tragically
[03:27] the navigator Jim's Zwayer died of a broken
[03:30] neck resulting from  break of the
[03:32] plane. Now while you would think that the
[03:34] SR-71 soft to get into space you need to
[03:38] reach what is called "escape velocity"
[03:40] this is where you are traveling faster
[03:43] than gravity is pulling you back to work
[03:46] and that is 25,020 miles an
[03:49] hour or 40,270 km/h and
[03:53] and if that wasn't a problem there's
[03:54] also to recognized altitude at where
[03:57] space starts at  328,000 ft
[03:59] or 100,000 meters
[04:02] well over three times the
[04:05] highest flight of the SR-71. Normal jet
[04:09] engines like those in the SR-71 have a
[04:12] maximum air speed limits for around
[04:13] about Mach 3.5 or 2695 miles now beyond
[04:18] that the air pressure and temperature
[04:20] becomes too high for compresses and the
[04:22] engine to effectively. For hypersonic
[04:25] speeds, experimental unmanned aircraft
[04:28] like NASA X-43 use what is called a scramjet
[04:32] engine. The  X-43 is currently the fastest
[04:36] free flying air-breathing aircraft in
[04:38] the world having flown at mach 9.6 or  7310
[04:44] miles an hour in November of 2004.
[04:47] Scramjets do away with the turbine
[04:50] compressors  of the jet engine so they
[04:52] have no moving parts instead they use
[04:55] shock waves in the engine to compress
[04:57] the raise the temperature in the engine to
[05:00] burn fuel and create trust an in theory
[05:03] they can fly up to Mach 20 and possibly
[05:06] beyond. The problem with this is that
[05:09] they won't work at speeds of less than
[05:12] around Mach 5 so they have to be
[05:14] brought up to speed by rocket engine
[05:16] booster before they can operate, which is
[05:19] how NASA x43 worked. They also won't
[05:23] work in space because there is no air
[05:25] with oxygen in to combust the fuel
[05:28] So this why space vehicles are
[05:31] launched by Rockets. Rockets can have
[05:33] much more power and can operate from a
[05:36] speed of zero on the launchpad to Mach 33 and
[05:39] beyond which is the escape velocity of
[05:41] Earth. One of the earliest experimental
[05:44] space planes was the North American X-15
[05:47] which reached a height of 353,000 feet
[05:51] or 107,000 meters 1963 and was
[05:56] powered by a liquid rocket danger but it
[06:00] had to be carried up to 45,000 feet
[06:02] attached to the underside with B-52
[06:04] bomber before being released. Then of
[06:07] course we've had space shuttle the
[06:09] Soviet version of the Space Shuttle
[06:10] the "Buran", SpaceShipOne and the Boeing X-37,
[06:14] all of which were examples of space
[06:17] planes but we're really just rocket powered gliders.
[06:20] Rocket differ from Jets
[06:23] because they bring their own oxygen to
[06:26] burn the fuel and don't rely on the
[06:28] atmospheric oxygen.
[06:29] This means that they can working space
[06:31] equally as well as in the atmosphere. The
[06:34] problem with rockets is that because they
[06:36] need to bring the oxidizer with they makes
[06:38] them very heavily. Look at the space
[06:41] Shuttle for example, the external fuel
[06:43] and the tanks to hold it along with the two
[06:46] solid rocket boosters weighed 1,940 metric
[06:51] tonnes at liftoff and that's without the
[06:54] space shuttle. All of which has to be
[06:56] carried along with the shuttle to the
[06:58] edge of space where they are they
[07:00] jettisoned. The maximum payload the shuttle
[07:03] could deliver it into a low earth orbit was
[07:05] 27.5 metric tons, which as a payload
[07:10] fraction is just 1.3% of the total
[07:15] take off weight.
[07:16] Rockets however can create huge amount
[07:19] of power, so they can achieve the
[07:21] speed that is need to escape the pull
[07:24] of gravity and go into orbit and Beyond.
[07:27] But what of the future, will we ever get
[07:30] planes that can take off from an
[07:32] aircraft runway, fly into space and then
[07:35] return back to a runway. There are
[07:38] still considerable technical issues to
[07:40] overcome but one design which looks
[07:42] promising is the Skylon. This is an SSTO
[07:47] or Single Stage To Orbit design meaning
[07:50] that unlike a rocket, it stays in one
[07:52] piece rather than having a separate main
[07:55] booster stage which detaches and return
[07:57] to Earth and then a smaller second stage
[08:00] which one goes on to orbit. The key
[08:02] technology makes Skylon work is the  SABRE or
[08:05] Synergetic Air Breathing Rocket Engines.
[08:08] Now these are kind of hybrid jet rocket
[08:11] engine which can take off like a normal
[08:14] jet engine, breathe air upto 93,000 feet
[08:18] and at a speed up to Mach 5.4 when then
[08:22] switches to rocket mode and can fly
[08:24] into space for up to 800 kilometers 500
[08:28] miles above the earth. It would then
[08:31] return to the Earth's atmosphere and
[08:34] land as normal air-breathing plane to be
[08:37] checked, refueled and ready for launch.
[08:40] Because it uses more efficient engines
[08:43] and the lift of the wings it would use
[08:46] only 20% of the fuel compared
[08:48] to a conventional rocket. It would still
[08:50] need to bring it oxidizer for the rocket
[08:53] portion of the journey but a lot less
[08:55] that will be required for a normal
[08:56] rocket. This allows for a larger payload
[08:59] when compared to the total weight around
[09:01] 5.5% compared to the shuttles 1.3%.
[09:05] Unmanned flight test of the Skylon
[09:07] could be happening by 2025, if all goes
[09:11] well but a
[09:13] potentially large flying in ointment is the
[09:15] recent advances in reusable rockets like
[09:18] SpaceX Falcon f9r and the Blue Origin
[09:22] New Shepherd. These could make the
[09:24] development costs to the Skylon
[09:26] expensive for satellite deployment and
[09:28] supplying the International Space
[09:30] Station. One thing which could come out
[09:33] though, is a rocket less version of the
[09:35] SABRE engine which could make hypersonic
[09:39] air travel more a viable option than using
[09:42] a scramjet.
[09:43] Only time will tell but this is an
[09:46] exciting time for both the future of air
[09:48] and space travel, so we may yet see the
[09:51] plane that can fly to space. So as always
[09:54] thanks for watching and please subscribe,
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