Scots engineers prove space pioneer's 25-year-old theory (displaced orbits for satellites)

University of Strathclyde ^ | July 26, 2010 | Unknown

[decimon]

When American space pioneer, Dr Robert L Forward, proposed in 1984 a way of greatly improving satellite telecommunications using a new family of orbits, some claimed it was impossible.

But now engineers at the University of Strathclyde's Advanced Space Concepts Laboratory have proved that Forward was right.

The late Dr Forward - a renowned physicist who worked in the United States and from his second home in Scotland - believed it was possible to use 'displaced orbits' to deploy more satellites to the north or south of the Earth's equator, helping to meet the growing demand for communications.

He proposed that the orbit of a geostationary satellite could be pushed above - or below - the usual geostationary ring around the Earth, which follows the line of the equator, by using a large solar sail propelled by the pressure of sunlight. However, critics later claimed that such 'displaced orbits' were impossible due to the unusual dynamics of the problem.

Now graduate student Shahid Baig and Professor Colin McInnes, Director of the Advanced Space Concepts Laboratory, have shown that Forward was in fact correct, in a new paper published in the Journal of Guidance, Control and Dynamics.

Professor McInnes said:"Satellites generally follow Keplerian Orbits, named after Johannes Kepler - the scientist who helped us understand orbital motion 400 years ago. Once it's launched, an unpowered satellite will 'glide' along a natural Keplerian orbit.

"However, we have devised families of closed, non-Keplerian orbits, which do not obey the usual laws of orbital motion. Families of these orbits circle the Earth every 24 hours, but are displaced north or south of the Earth's equator. The pressure from sunlight reflecting off a solar sail can push the satellite above or below geostationary orbit, while also displacing the centre of the orbit behind the Earth slightly, away from the Sun."

Although the displacement distance above or below the equator is small - of the order of 10 to 50 km - work on hybrid solar sails, which use both light pressure and thrust from a conventional electric propulsion system, is underway and aims to improve the displacement distance.

Professor McInnes added: "Other work is investigating 'polar stationary orbits', termed 'pole-sitters' by Forward, which use continuous low thrust to allow a spacecraft to remain on the Earth's polar axis, high above the Arctic or Antarctic. These orbits could be used to provide new vantage points to view the Earth's polar regions for climate monitoring."

###

Shahid Baig and Professor Colin McInnes' work has been funded by the National Centre for Physics, Quaid-i-Azam University, and VISIONSPACE, an Advanced Investigator grant from the European Research Council, respectively.

The Advanced Space Concepts Laboratory is a world leader in frontier research on visionary space systems. Opened in 2009, the Laboratory's researchers are investigating how new space technologies can be used to deliver radically new space services, such as increased telecommunications capacity and new orbits for Earth observation and space science missions. More information at: www.strath.ac.uk/space

Notes to Editors:

1. The papers described in this press release are:

R L Forward, Light-levitated geostationary cylindrical orbits using perforated light sails, can be found in the Journal of the Astronautical Sciences, Vol.32, Apr-June, pp.221-226, 1984.

S Baig and C R McInnes, Light-Levitated Geostationary Cylindrical Orbits are Feasible, Journal of Guidance, Control and Dynamics, Vol. 33, No. 3, pp. 782-793, 2010.

A pre-print of the new paper is available at: http://strathprints.strath.ac.uk/18865/

[SunkenCiv]

Thanks decimon! And thanks also to KD for the additional ping (see Forward's talk about space tethers). This is one of those collateral interest topics for the String Theory ping list, and because the late Dr. Robert L. Forward wrote "Future Magic" which must be around here somewhere, and I can't remember how, but there's a catastrophism connection in that book. Somehow. :')

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[SunkenCiv]

Thanks decimon! And thanks also to KD for the additional ping.

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[Eaker]

um...that is going to take a long extension cord...

Home Depot.

[patton]

Ther is a Home Depot in orbit?

Huh. Must be between the two Starbucks.

[patton]

...and are there illegal aliens in the parking orbit?

[wastedyears]

I figured we had satellites already orbiting like that.

[krb]

Are you kidding? They are going to be able to cram many times as many satellites up there if this thing works like it’s supposed to.

[Eaker]

Lord knows they are everywhere else.

[patton]

“Lord knows they are everywhere else.”

Starbucks? Yeah, I heard that their latest plan to increase revenue is to open a Starbucks within every existing Starbucks. Sort of a quantum warp Starbucks, or something.

Now, can somebody explain to me what an electric rocket drive is?

Because I have issues with suspension of disbelieve.

This thread went to Freeper Island, and nobody even noticed when the ship set sail.

Just smile and wave, boys, just smile and wave.

[Squawk 8888]

I expect they used “climate monitoring” because that’s the buzzword needed to attract funding. The pole-sitters would be extremely useful for real-time weather imagery and other forms of surveillance.

[Squawk 8888]

Thanks- I’ve just placed a hold at my library for that title.

[Squawk 8888]

Nope- a stable orbit without thrusters must be focused on the centre of the earth, so geosynchronous orbits are only possible over the equator. Satellites that orbit above or below the equator actually cross the equator at an angle twice during each orbit; the angle at which it crosses will be the same as the maximum north and south lattitude over which it will orbit.

[PA Engineer]

However it's just going to be used for/funded by more climate garbage.

It may have been the only way to get it funded. When my Wife was doing her Fellowship at the NIH everything was AIDS. If you put AIDS in the proposal it was funded. Researches began to figure that out fast. "Government Science" is indeed always corrupted now, however some real research gets though by playing the game. I think that is a possibility in this case.

[Erasmus]

Starbucks? Yeah, I heard that their latest plan to increase revenue is to open a Starbucks within every existing Starbucks. Sort of a quantum warp Starbucks, or something.

They're going to call it "Starbucks Inception."

[Erasmus]

Nope- a stable orbit without thrusters must be focused on the centre of the earth, so geosynchronous orbits are only possible over the equator. Satellites that orbit above or below the equator actually cross the equator at an angle twice during each orbit; the angle at which it crosses will be the same as the maximum north and south lattitude over which it will orbit.

Pardon, but a slight quibble with the terminology. An inclined orbit at geosynchronous altitude is still geosynchronous (although noone would call it "geostationary"). From a fixed point on the earth, as you imply, the satellite appears to wander north and south of the equatorial plane. Throw in a slight eccentricity in the orbit, and the north-south deviation becomes a figure eight.

TV stations, along with other geosync satellite users, have to use dishes that are dynamically steered through small angles in alt/azimuth (larger than their beamwidth) to track these satellites.

A friend who had to install a number of ground stations was told by the satellite people that it cost the satellite less station-keeping fuel to have an orbit like that, implying a longer satellite life.

[Publius6961]

bookmark

[Eaker]

can somebody explain to me what an electric rocket drive is?

Yes I can, but I am tied up right now writing a good rap song.

[bruin66]

I don’t think any commsats are geostationary. Station-keeping is too labor intensive, when it’s not required for operational effectiveness.