Mobile version

Topex/Poseidon Orbits

The orbit configuration was chosen to optimise the study of temporal large-scale ocean variability and avoid aliasing different tidal constituents to the same frequency.

A high orbit altitude was also selected to minimise atmospheric drag and gravity forces acting on the satellite, and to make orbit determination easier and more accurate.

On 15 September 2002 Topex/Poseidon assumed a new orbit midway between its original ground tracks. The former Topex/Poseidon ground tracks are now overflown by Jason-1. This tandem mission demonstrated the scientific capabilities of a constellation of optimised altimetry satellites.

 T/P on its new orbit, situated at one half the Jason-1 track spacing. Cycle 369, which began on Friday 20 September 2002, was the first full cycle in the new orbit. Download Google Earth file to visualise <media 13049 - download>Jason-1</media> and T/P ground tracks.

The exact altitude enabling the orbit to satisfy these constraints and fly over two verification sites located in the Mediterranean Sea (Lampedusa Island, Italy) and at the Harvest oil rig platform (California, USA) was 1 336 km. An inclination of 66° was selected - i.e. the inclined orbit sampled from 66° north to 66° south - so as to cover most of the world's oceans (~ 90%). The orbit was non-sun-synchronous and prograde. A repeat period of 9.916 days was chosen (ie; the satellite passed vertically over the same location, to within 1 km, every ten days) as the best compromise between spatial and temporal resolutions. The distance between successive tracks was of the order of 315 km at the equator. The local time of successive passes shifted by nearly two hours per cycle.

A satellite orbit slowly decays due to air drag, and has long-period variability due to the Earth's heterogeneous gravity field, solar radiation pressure, and other lesser forces. Periodic manoeuvres are therefore required to keep the satellite on its orbit. The frequency of these manoeuvres depends primarily on the solar flux affecting the Earth's atmosphere, but there is generally expected to be one manoeuvre (or series of manoeuvres) every 40 to 200 days. The process usually takes from 20 to 60 minutes. Manoeuvres should wherever possible be performed at the end of a 10-day cycle, preferably when the satellite is overflying land in order not to disrupt precise orbit determination. Science data are not acquired when orbit maintenance manoeuvres are being performed.

Orbit parameters

Main characteristics
Semi-major axis 7714.4278 km
Eccentricity 0.000095
Argument of perigee 270.8268°
Inclination (non-sun-synchronous) 66.039°
Auxiliary data
Reference altitude (equatorial) 1,336 km
Nodal period 6,745.72 seconds
(112'42" or 1h52')
Repeat cycle 9.9156 days
Number of passes per cycle 254
Ground track separation at Equator 315 km
Acute angle at Equator crossings 39.5°
Longitude at Equator of pass 1 99.92°
98.51° since Sept. 2002
Orbital velocity 7.2 km/s
Ground scanning velocity 5.8 km /s
Rss feedsContactPartnersFAQLexiconMobile
You must enable cookies in your browser preferences to save the modifications
You are using an older version of Internet Explorer, please update to take full advantage of Aviso+ features

Customize the home page

View all widgets
Reduce display
Public profile
User profile

Select/Deselect widgets

Discover AVISO+

Customizable home, reading tools, products search guide, etc.. Discover step by step the features of the new site AVISO+.

Customizable homepage

This home page is composed of blocks called "widgets".

Rearrange the blocks with a "Click & Drop".

Hide a widget with the cross at the top right. Reset or add a widget with the "wrench" icon. The "User" and "Public" profiles offer a predefined organization.

All the modifications are automatically saved as cookies on your machine so as to enable you to have your own specific AVISO+.

Reading tools

Ease your reading by choosing the page background colour (black/white) and/or by modifying the font size.

Browsing menu and breadcrum trail

To ease your browsing through AVISO+, you can use at any time the main banner items with the interactive submenus or use the browsing menu on the left side of the screen (it is open by default). For more readiness of the page contents, you can fold and unfold the browsing menu by clicking on the tab. At any time you can know where you are thanks to the browsing menu or the breadcrum at the top of the page.

Products search guide

The first submenu of the "Data" banner item leads you to a new search form enabling you to find quickier the product that suits your needs. The list of results is updated according to your selection criteria.

AVISO+ Multimedia

The first submenu of the "Multimedia" banner item leads you to AVISO+ collections of images and videos linked to altimetry and its applications. Have a nice visit!