Ascension Island

mcat ascension island and inset map
The NASA MCAT 1.3m Telescope and Observatory is located on the coast of Ascension Island
in the remote mid Atlantic Ocean near the equator.
Ascension Island Topics of Interest
Location Climate Conditions
Animal Habitat Vegetation
Observing Qualities Observing Challenges



Ascension Island is an isolated volcanic island in the equatorial waters of the South Atlantic Ocean, around 1,000 miles from the coast of Africa and 1,400 miles from the coast of Brazil. It is roughly midway between the horn of South America and Africa. It is remote and dark; simultaneously harsh and lush while providing magical opportunities for both wildlife and science.

Ascension Island is the new home of the 1.3m MCAT telescope, a cutting edge satellite and orbital debris tracking instrument for NASA.

The Ascension Island Observatory site is very different from most observatory sites in that it is less than 1/2 mile from the open ocean, and only 300 feet above sea level.

Climate Conditions:

Ascension has a tropical desert climate with temperatures at the coast ranging from 22 to 31°C (72 to 88°F), and about 5 to 6°C (9 to 11°F) cooler at the highest point. Rain showers may occur at any time during the year, but tend to be heavier between June and September.

In 1836, it was described as an arid, treeless island, with nothing growing near the coast. Mostly dry and barren, the island had little appeal for settlement.

Inland, however reveals a very different ecosphere. The strong water spring in the high interior of the island, in what is now called Breakneck Valley gives the impression of a dense, moist jungle.

Continuous trade winds carry volcanic pumice and high relative humidity. Ordinarily, pumice dust would just be a inconvenience, but can be quite detrimental to the maintenance of elaborate astronomical instrumentation.

The humidity factor is similar. Normally, not pervasive, but in relation to delicate instrumentation, it prompted the development of a dry air purge system for the optics and critical drive components of the MCAT.

Animal Habitat:

Ascension is a haven for sea birds providing refuge from predators and allowing uninhibited island nesting.

For example, the sooty tern, a bird common in the tropical oceans, breeding on islands throughout the equatorial zone can be found in excessive numbers on Ascension Island. It is known as the "wideawake tern" referring to the incessant calls produced by a colony of these birds. The wings and deeply forked tail are long, and it has dark black upperparts and white underparts with black legs and a black bill. The average life span is 32 years. Dishes using its eggs are considered a delicacy.

The largest native land animal is the large, bright yellow land crab. It grows to a width of 4.5 inches on Ascension Island.

Offshore, there is a variety of open-ocean fish, including sharks, wahoo, tuna, bonito, barracuda, marlin, blackfish and sailfish.

However, the protected green turtle is perhaps the most notable of the endemic fauna, coming ashore to lay their eggs on the sandy beaches from November to May. Tracks left by these enormous female turtles can be seen readily across the beaches of Ascension Island.


The island had its own native flora until Portuguese explorers released goats in the 1500s which ate much of it. The later introduction of rabbits, sheep, rats and donkeys, and over 200 imported species further marginalized the original flora.

By 1843 the island was barren with few plants. However, due to the introduction of species by the British, Ascension Island's Green Mountain is now one of the few large-scale planned forests, and is gradually growing with each year. Its highest point is at 2,817 feet.

In June 2005 the first National Park on Ascension Island, the Green Mountain National Park, was opened. Non-indigenous plants teem there, and the crown of Green Mountain is a lush halo of bamboo. Flanking one side is a large stand of tall Norfolk pine, trees planted by British mariners, which were to have been used as replacement masts for sailing ships.

Observing Qualities:

MCAT is a unique telescope, one of only two like it in the world – a double horseshoe mount telescope designed by DFM Engineering that allows NASA to track not just Geosynchronous Orbit (GEO) debris, but fast-moving low Earth orbit (LEO) debris.

NASA contends Ascension Island offers numerous advantages over other locations. It offers the benefits of location, weather and infrastructure.

The near equatorial location affords the opportunity to access under-sampled low-inclination orbits and new GEO longitudes. The Ascension Island location presents access to the sky from a unique latitude/longitude position for an optical telescope. It fills a key longitudinal gap in the GEODSS, the system of telescopes for Ground-based Electro-Optical Deep Space Surveillance.

Constant trade winds provide a steady laminar airflow over the island; a trait sought after to create stable atmospheric and good astronomical 'seeing' conditions with very low annual rainfall values. Ascension Island is a volcanic, desert island, receiving only 7 inches of rain per year on average at the observatory location.

With a US Air Force base presence, the necessary infrastructure and support for this scientific research already exists. And yet the total population of the island is estimated at less than 1,000. Light pollution is nearly non-existent and also contributes to good astronomical 'seeing' conditions.

Observing Challenges:

The Ascension Island location does bring a measure of challenge to maintaining an elaborate fast-tracking instrument such as the 1.3m MCAT telescope.

The same continuous trade winds that provide a steady laminar airflow over the island also carry volcanic pumice and high relative humidity. It is this harsh environment which prompted the development of a dry air purge system for the optics and critical drive components of the MCAT.

The remoteness of the island makes for inconvenient parts upgrades and the harshness of the climate expedites mechanical degradation which in turn demands ongoing maintenance.

However, the MCAT project scientist, Dr. Susan Lederer, joined the DFM team for the final 4 weeks of the installation to acquire as much hands-on experience as possible with installing and tuning the optics and mount. Her new insight and experience will play a large part in the future success of the project given the remoteness and harsh environment of the site.


NASA MCAT Installation

NASA MCAT Installation Images

The NASA MCAT Original Project Description

NASA MCAT Terminology and Acronyms

other noteworthy links . . .

Custom Telescopes

Observatory Design and Consulting

Another 1.3m Telescope Installation for IIA