Jules Verne creeps up on ISS

The European Space Agency's "Jules Verne" Automated Transfer Vehicle is slowly but surely creeping up on the International Space Station prior to a docking scheduled for 3 April. Artist's impression of the ATV approaching the ISS. Pic: ESA The ATV space truck will today strut its stuff on the second of two "demonstration days …

[BigTim]

GPS in space Uh?

How does that work then? Surely the ISS isn't at a lower orbit than the GPS satellites?

Paris is as clueless as me.

[Paul R]

re: GPS in space Uh?

Yup. ISS orbits at around 400KM height, GPS satellites at around 20,000KM height. :)

[Anonymous Coward]

GPS in space

There are two options:

ISS and JV *are* in lower orbits than the GPS constellation.

or

The GPS satellites don't transmit unidirectionally.

[Paul Crolla]

Re: GPS in space uh?

Having a quick scan of the web, GPS satellites orbit at 12000 km, which is a geostationary orbit, ISS is at approximately 340km (max of 440km). Therefore, probably with a little adjustment, GPS could be used.

[Anonymous Coward]

re. GPS in space Uh

The GPS sattelites are a lot further out than the ISS, about 12,000 miles, but you will need a special receiver.

Get one here: http://www.rokar.com/products/gps_spacenav.htm

[Anonymous Coward]

GPS in Space

Considering the altitude of a GPS satellite (which is geostationary) is some 35,786km from Earth, and the altitude of the ISS is 350-460 km, you would appear to be very very wrong. It is most definitely orbiting lower than GPS satellites, about 35,300km lower.

[Anonymous Coward]

Jules Verne?

One of the greatest imaginations ever and his name is given to a cargo truck?

Couldn't we call it the L Ron Hubbard and celebrate each time it's consigned to fiery oblivion?

[Anonymous Coward]

ElRon

The ESA probably doesn't want to get sued by the Co$.

The alien because LOLXenu.

[Tim Russell]

HEO, MEO and LEO

high earth orbit (HEO)

Geostationary or communications satellites PARKED @ 22,300 miles

medium earth orbit (MEO)

GPS satellites ORBIT at a height of about 12,000 miles

low earth orbit (LEO)

LEO includes orbits having apogees (high points) and perigees (low points) between about 100 km and 1,500 km. The space shuttle and the international space station are in a low earth orbit (LEO) to avoid the Van Allen radiation belts.

Source and more information: http://www.reformation.org/geostationary-satellites.html

[Jaster]

GPS in space

As said above the GPS satellites are a lot further out than the ISS

and anyway this is relative GPS - i.e. The Space truck does not care where it is, and does not care where the ISS is, it just cares where it is relative to the ISS - i.e. about to dock or about to crash into it ....

[G R Goslin]

@GPS in space

Ermm no!!! The GPS satellites are not in geostationary orbit, otherwise they would always be in the same place (as, say the orbital television satellites) and all the satellites would lie in the same plane, rather than covering the sky.

[Steve]

NOT geostationary

Although much higher than the ISS (~12,500 statute miles or ~20000km) the GPS satelites are not geostationary. Call up the satellite diagram of a GPS receiver and you can see them move (one orbit in 12 hours, IIRC).

[Elmer Phud]

White Van Man

Sorry Mike, can't call it the 'El Ron'* as it learning to drive it would involve having to do several meaningless courses at great expense.

But it does come with a free 'personality check' for all at the ISS.

(*El Ron - legendary bandit who stole from the poor and gave to the really rich)

[Robert Woodhead]

GPS basic facts

GPS constellation altitude is 20,200km. This is below geosyncronous orbit level; in fact, GPS sats make exactly 2 orbits a day. Furthermore, they are in highly inclined orbits, as opposed to communications satellites, which are in equatorial orbits.

GPS sats beam their signals in fairly tight beams down to the earth's surface (for efficiency purposes), but there is enough spillover that it can be used without problems in low earth orbit. The major modification that is needed to a standard GPS unit to work on the ISS is to remove the "sanity checking" code in the GPS ("gee, I'm several hundred kilometers high, and moving along at over 10,000km/hr. I must be broken!").

Ham radio enthusiasts put a GPS in one of their recent "Oscar" amateur satellites. They found it was even possible to get GPS to work above the level of the constellation, there is enough leakage of signal outwards (and you can detect GPS signals from sats near the edge of the earth) to get good readings.

With a decent antenna, you could get GPS to work on the moon -- well, the parts facing the earth, anyway.

[Mage]

GPS

Not Geostationary, just high up.

Geo is about 45,000km /22,500Miles.

In theory with a special receiver you could use GPS at an Altitude ABOVE the GPS, as long as you pick up at least 3 of them. Different software in receiver needed.

Quote:

The height of the orbits is then about 20200 km. Orbits in this height are referred to as MEO – medium earth orbit. In comparison, geostationary satellites like ASTRA or Meteosat – satellites orbit the earth at 42300 km, which is about twice the distance of GPS satellites.

http://www.kowoma.de/en/gps/orbits.htm

The ISS and Iridium Sat phone are LEO (Low Earth Orbit).

Satellite TV, Thuraya Sat phones and World Space Radio all use Geo or Clarke Belt orbits.

[Chris Miller]

Oh dear

GPS orbital radius = 26,600 km (distance from the centre of the Earth)

Altitude = 20,200 km (distance from the surface of the Earth)

Geostationary orbital radius ~42,000 km

Quick check - orbital period at the surface of the Earth ~90 minutes, geostationary means an orbital period of 24 hrs, i.e. 16x greater. Kepler's law gives period squared proportional to radius (semi-major axis of you insist) cubed. 16^(2/3) ~ 6.4 Earth radii (~6,400 km) which gives 41,000 km (good enough).

Mines the anorak, ta.

[andrew mulcock]

Differential GPS

And just to comment on differential GPS, as opposed to standard GPS.

differential, you receive the same set of satellite on both receivers, one on the ISS one on Jules Verne. GPS gives you errors in location, but both the receivers should be getting the same error.

There for although you don't know your exact place, you very precisely know the difference between you in 3D, conceptually to a few mm, and so can navigate.

[Anonymous Coward]

GPS lotto

around 20,000KM

some 35,786km

at 12000 km,

about 12,000 miles,

12,500 statute miles or ~20000km

is 20,200km.

So who won?

[Michael]

Re: GPS in space .

Didn't the russians do something a bit similar with the PROGRESS supply vehicle?

(I've got a bad feeling about this)

[Anonymous Coward]

@Mage

> 45,000km /22,500Miles ???

Unless we're talking about nautical miles, and even then that's really stretching it (1 naut. mile = 1.8km)

> In theory with a special receiver you could use GPS at an Altitude ABOVE the GPS, as long as you pick up at least 3 of them

Nope, you need at least four signals. The reason being, you have 4 degrees of liberty: the conventional 3D coordinates + time (as in : the GPS satellites have a nucular clock onboard, but that's not the case for your receiver, so the exact time is treated as an unknown)

In other words, you sir/madam do not deverse the boffin's icon ! For shame.

The pedant's pedant.

[Mage]

Three.

You do only need three to get a 3D fix. More than 3 is better. It depends on the position & separation of the 3 signals as to how good your fix is. But the nearby ISS will have same error, so differential position really very good with 3.

[Tim]

Christ on a spacebike

Are you all reading different Wikipedia pages? You can't agree on geostationary orbit (may A.C.C. rest in peace), how many KMs there are in an M, or the altitude at which the GPS constellation orbits. (35,786km. Really, that specific eh? Above what? The perfectly smooth, flat surface of the Earth?)

I can't believe UK Gov's science budget cuts have taken effect so quickly.

[Smallbrainfield]

@The pedant's pedant

Oh dear. Wherever there is a pedant, there is usually another pedant standing ready to correct them. It's nuclear, not nucular.

Unless you are George W Bush.

/awaits minor punctuation mistake correction by previously unknown new species of super-pedant.

[The Other Steve]

@@The pedant's pedant('s pedant ?)

"/awaits minor punctuation mistake correction by previously unknown new species of super-pedant."

Wouldn't that be a hyper-pedant, since the reply you are being pedantic about is already one being pedantic about someone else pedantry ?

Is this meta-pedantry ? My latin-prefix-fu is weak today.

[b166er]

@@@The pedants' pedants' pedants' pedant

As you are now categorising pedants as a group and super-pedants another and so on, isn't it now appropriate to refer to them as groups of pedants, therefore requiring that the apostrophe follow the group?

BTW The Other Steve, does this make me an uber-pedant?

I'm confused, could you all be more pacific? :~)

[Anonymous Coward]

@Tim

Thanks mate!

Was having a really bad day, then I read the the muppet convention, but your reply tipped me over!!

The coat as I have pissed myself laughing so much!

[Anonymous John]

Looks a bit like a Star Wars X-Wing fighter to me.

Does the ISS have any defences?

[Anonymous Coward]

Geostationary

"(35,786km. Really, that specific eh? Above what? The perfectly smooth, flat surface of the Earth?)"

It's an altitude above mean sea level. Which yes, is a perfectly smooth flat sphere, even if it is 'imaginary'.

http://en.wikipedia.org/wiki/Geostationary

And there are ~3,281ft in a km & exactly 5,280ft in a mile, meaning 1 mile ~= 1.609...km. Nautical miles are different again, as was mentioned...

[Jim Brinton]

What's being overlooked in all this...

...is how close the ATV is to being a man-rated spacecraft. If pressurized, it could certainly serve as a taxi to the ISS; only one-way, though as it is not designed to survive re-entry. Speaking as a frustrated US-er, I wish the EU would fund a manned program; after all, you are most of the way there with the ATV, and frankly, I would like to see somebody put the boot up NASA's rear.

As for the sadly non-existent UK manned program, you can have the Earth when the rest of us have finished with it. As far as plans for reviving the Empire go, it's a bit long term, but workable.