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Where does space begin?

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Glad New 12 months to all my readers and followers.

A lot of you’ll be conscious of the latest check flight of the Virgin Area Ship Unity. On 13 December 2018 it reached an altitude of 82.7 km and was extensively reported within the media, for instance the BBC news website, as reaching ‘the sting of area’.  Though no particular dates have been set, VSS Unity is the spacecraft on which Richard Branson’s Virgin Galactic group hopes to take price paying passengers into area later this yr.

Picture From https://www.virgingalactic.com/articles/first-space-flight

Though this can be a nice achievement for Virgin Galactic, the Virgin Galactic ‘astronauts’ didn’t get fairly excessive sufficient to succeed in area in line with probably the most extensively used definition of the place area begins.  The altitude of the place the Earth’s environment ends and area begins is considerably unclear.

Potential definitions of area

The Earth’s environment consists of gasoline and there may be clearly no mounted boundary the place it ends, and area begins. As we get larger in altitude its density falls till it will definitely reaches the very low density of 5 particles per cubic centimetre present in interplanetary area. Within the diagram under, I’ve illustrated some totally different altitudes and I’ll talk about whether or not every of them could possibly be thought-about to be in area.

eight.eight km – The summit of Mount Everest. At this altitude the air stress is just one third of that at sea stage and a younger match particular person acclimatised to excessive altitude couldn’t survive for greater than 30 minutes while not having further oxygen.

10.6 km – Boeing 747 cruising altitude. The air stress at this altitude is round 24% of that at sea stage and a human could be lifeless inside minutes from lack of oxygen. Even so, this altitude shouldn’t be usually thought-about to excessive sufficient to be outlined as in area.

20.7 km – Concorde most altitude. This was the utmost altitude which the supersonic aeroplane Concorde achieved and it occurred throughout a check flight in 1973. At this altitude air is so skinny that the sky is darkish blue in daytime and the air stress is simply 7.6% that of sea stage.

Concorde was in service between 1976 and 2003 and will journey at a pace of two,180 km/h – greater than twice the pace of sound. It had a most cruising altitude of 18.three km and was marketed as travelling ‘on the sting of area’.

At 20.7 km the boiling level of water is simply 30 levels Celsius so a human being whose physique temperature is generally 37 levels could be topic to an especially disagreeable destiny except they have been enclosed in an area swimsuit or a pressurized cabin – the water within the eyes, mouth, throat and the liner of the lungs would actually boil away. Due to this fact, it could possibly be argued that Concorde on this check flight was travelling in area.

41.four km – world balloon altitude report. This was achieved by Alan Eustace, a Senior Vice President of Google, in 2014. At this altitude the air stress is simply zero.237% of the ocean stage and the air density is so low that the sky seems black within the daytime. Though this altitude shouldn’t be usually thought-about to be excessive sufficient to be in area, Eustace felt that at he had reached area. On his return, he mentioned

‘..It was lovely. You could possibly see the darkness of area and you may see the layers of environment, which I had by no means seen earlier than.’

as quoted within the New York Times

100 km – an altitude often known as the Karman line which is normally taken because the boundary of area. I’ll talk about this later.

150 km – approximate minimal altitude for a satellite tv for pc to finish an orbit. At this altitude the Earth’s environment has about one billionth of its density at sea stage.

When a satellite tv for pc is in a low orbit across the Earth, its speedy motion by means of the very tenuous traces of the Earth’s environment ends in friction, which causes the satellite tv for pc to lose vitality and spiral again to Earth. The upper a satellite tv for pc’s orbit, the thinner the environment, which implies that there’s much less friction and it stays in orbit longer. At 150 km, the thickness of the environment is such typical satellite tv for pc would theoretically have the ability to full a single orbit however it will be spiralling down in the direction of the Earth fairly quickly.  At altitudes under 150 km, a typical satellite tv for pc wouldn’t have the ability to full a single orbit. In reality this minimal orbital altitude is simply approximate, as the quantity of friction slowing down a satellite tv for pc additionally is dependent upon the dimensions and form of the article. At an altitude of 150 km, a heavy streamlined satellite tv for pc may wait for longer than one orbit.

400 km – Worldwide Area Station (ISS).  At this altitude the atmospheric density is a miniscule half a trillionth (zero.000 000 000 000 5) of its density at sea stage, however this very tenuous gasoline nonetheless causes a small quantity of atmospheric drag on the ISS.  The ISS loses altitude on the charge of round 2 km per thirty days and wishes to fireside its personal rocket motors (or these on visiting spacecraft) a couple of occasions a yr to lift its altitude. If it didn’t do that, the ISS would proceed to lose altitude and would return to Earth in a couple of years, breaking apart within the course of.

1000 km – at this altitude the atmospheric density is so low satellite tv for pc will stay in orbit for over 1000 years with out returning to Earth.


Air density and stress at totally different altitudes


considerably affected  by photo voltaic exercise. The figures have been taken for low photo voltaic exercise.

The Karman Line

The Fédération Aéronautique Internationale (FAI), the worldwide physique setting requirements and preserving data within the discipline of aeronautics and astronautics, defines area as beginning 100 km above the floor of the Earth.  At this altitude the atmospheric density and stress are greater than one million occasions decrease than they’re at sea stage.  This altitude is named the Karman Line after the Theodore von Kármán (1881-1963), a Hungarian-American mathematician, aerospace engineer, and physicist.  He calculated that at roughly this altitude it will not be doable for an aeroplane to fly as a result of the air density is simply too low for sufficient carry to be generated by airflow over the plane wings (see the notes under for extra particulars).

Even so, this 100 km boundary is considerably arbitrary and isn’t accepted by everybody. Curiously, america Federal Aviation Authority (FAA)  defines area as beginning not on the Karman line however at 80 km above the Earth’s floor. Virgin Galactic due to this fact felt assured sufficient to state on their web site on 13 December that the check flight that day had reached area, having achieved 82.7 km, and that their pilots have been due to this fact astronauts:

The historic achievement has been recognised by the Federal Aviation Administration (FAA) who introduced as we speak that early subsequent yr they’ll current pilots Mark “Forger” Stucky and Frederick “CJ” Sturckow with FAA Industrial Astronaut Wings at a ceremony in Washington DC.  

Nevertheless, when it begins industrial operations Virgin Galactic will take area vacationers to a most altitude of 110 km, 10 km above the Karman Line. This can keep away from any argument about whether or not they have travelled excessive sufficient to succeed in area.  As described in a previous post the flight could have a price ticket of $250,000, which is slightly too costly for me.

Richard Branson the founding father of Virgin Galactic who has publicly said that he will likely be a passenger on the primary industrial spaceflight of VSS UnityMrs Geek feels that he significantly wants to vary his hairdresser 🙂


I want to thanks for studying and following my weblog – a few of you for the final 5 years – and want you a cheerful and profitable 2019.  To search out out extra in regards to the Science Geek’s weblog, click on here or on the Science Geek Home hyperlink on the high of this web page.



The movement of an plane by means of the air is ruled by 4 forces.

  • Thrust is the ahead power supplied by the engines which pushes the plane ahead.
  • Drag is the power brought on by air resistance because the plane strikes by means of the air. It slows the plane down.
  • Weight is the downward power attributable to gravity.
  • Raise is the upward power brought on by the truth that when an plane strikes by means of the air, the air stress is larger on the underside of the plane’s wing in comparison with the topside. This larger air stress on the underside pushes (or lifts) the plane upwards.

The carry (L) generated by airflow over the wings of an plane is given by the carry equation

L = ½ ρv2ACL

The place the phrases are as follows.

  • p is the atmospheric density
  • v is the plane’s velocity with respect to the encircling air
  • A is the floor space of the plane’s wings
  • CL is a quantity often known as the carry coefficient, which is dependent upon the dimensions and form of the wings and properties of the encircling environment.

For an plane to stay at a relentless altitude the quantity of carry generated have to be equal to the burden of the plane.

From the carry equation, because the density of the environment falls, an plane should transfer sooner to generate the identical quantity of carry.  At an altitude of round 100 km the atmospheric density is so low that an plane’s velocity must be larger than 28,200 km/h to offer sufficient carry. That is the rate wanted to get into orbit, so an plane shifting at altitude of 100 km would really be in orbit across the Earth and its passengers and crew could be weightless.





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