Frequently Asked Questions

What does NEOSSat stand for?

NEOSSat is short for “Near Earth Object Surveillance Satellite.” NEOSSat searches for asteroids under a project called NESS, which is short for “Near Earth Space Surveillance.”

Do Near-Earth Objects include the space junk like old satellites orbiting Earth?

No, Near-Earth Objects (NEOs) are defined as asteroids and comets that orbit the Sun but have been gravitationally nudged into paths that take them into the neighbourhood of the inner planets. “Space junk” is another term for the collection of useless rocket or satellite debris that orbits the Earth.

What’s special about NEOSSat? Aren’t there already telescopes looking for asteroids?

Yes, there are other telescopes scanning the skies for asteroids, but these instruments are all Earth-based. (Visit for a list of these search programs.) NEOSSat is the first space telescope dedicated to finding and tracking asteroids. Observing from space means we can operate 24/7 and search the sky close to the Sun.

What’s the difference between NEOSSat and something like the Hubble Space Telescope?


Hubble Space Telescope
Credit: NASA/STSci

While both NEOSSat and Hubble are satellites in orbit around the Earth, they are very different (in more ways than we can list here but for example…)

  1. Size and Weight: Imagine a large suitcase (NEOSSat) floating in space next to a school bus (Hubble) and you get the idea. Plus NEOSSat only weighs 74 kg compared to Hubble’s 11,110!
  2. The Telescope: The mirror in NEOSSat’s telescope is 15 centimeters wide while Hubble’s main mirror is 2.4 metres in diameter.
  3. Power Requirements: NEOSSat and Hubble are both solar-powered but NEOSSat only requires 80 watts compared to Hubble’s 2800 watts.
  4. Mission: NEOSSat has one science mission – to find asteroids orbiting between the Earth and the Sun. Hubble’s mission is to take pictures and collect data on all kinds of objects ­– from the planets and moons of our solar system to distant, faint galaxies outside of our Milky Way.

What happens when NEOSSat finds an asteroid?

There are a couple of steps. First, we measure the asteroid’s coordinates in Right Ascension (RA) and Declination (DEC) as precisely as possible based on its position against the background stars. Second, we check asteroid databases to see if it’s a new discovery or a previously known asteroid. We also check its possible orbit to see if it’s a main belt asteroid (one that orbits between Mars and Jupiter) or an NEO.

If the asteroid is a new NEO, we want to follow up and extend its orbital arc. Whether it is a new discovery or a known asteroid, we send the coordinates to the Minor Planet Center near Cambridge,  Massachusetts. Then we re-task NEOSSat to image the asteroid again. Any additional observations help better determine its orbit. The final step is notifying ground-based asteroid follow-up telescopes so they can also observe the new object; this is done automatically by the Minor Planet Center as well as us.

How many asteroids do you think NEOSSat will discover?

Currently this is a difficult question to answer with precision, but some background first. The NESS project is using NEOSSat to complement the search efforts of ground-based telescopes. If we searched in a similar part of the sky as current efforts, we would find more asteroids, but the ground-based telescopes would soon find them as well, so our search effort would be redundant.

The NESS project searches for Near-Earth Objects near the Sun, which is difficult for ground-based telescopes to do. Searching near the Sun along Earth’s orbit is harder because a diffuse cloud of dust occurs there (observers call this cloud the zodiacal light) which brightens the sky and makes finding asteroids there more difficult. However, searching near the Sun also happens to be interesting scientifically as a specific orbital group, which goes by the name Atira, is most efficiently found with this strategy. (This orbital class is also known as Apohele or interior to Earth’s Orbit asteroids.) Atiras are asteroids whose orbits are entirely within the Earth’s.

As of January, 2013, there are only a dozen known Atira asteroids; if the NEOSSat telescope performed as designed, our simulations indicate that we would double that number in the first year of the mission. However, we currently have uncertainty in telescope performance due to electronic interference (discovered in late stage testing close to launch) from other components of the spacecraft. We will be reassessing instrument sensitivity during the commissioning period once on orbit and exploring how to best avoid interferences.

What are these asteroids made of? Are they special?


Itokawa Asteroid
Credit: JAXA

Asteroids are made of the same materials found on Earth – rock, metals, water, all ninety-two of the naturally occurring elements. So no, they’re not special in that sense. What makes asteroids very interesting to scientists is their great age and what can be learned from them about the origin of the Solar System.

Asteroidal resources are also interesting because of the great cost of launching material from the Earth. The asteroids that are dynamically closest to Earth are easiest to explore or exploit. Their small size makes their gravitational force much lower than the Earth’s and the Moon’s, meaning landing and take-offs would require almost no energy. All near-Earth asteroids hold great potential for useful resources, especially if we plan on exploring space on a larger scale.

Will the NESS project reduce the impact hazard on the Earth?

NEOSSat’s observations will probably reduce the impact hazard from unknown large NEO’s by a few per cent over its lifetime, but it isn’t designed to discover small asteroids near the Earth that may be on collision courses.

Such projects, such as the recently funded ATLAS, search a large fraction of the sky each night. The primary goal of the NESS project is to discover (and to determine orbits for) asteroids orbiting near the Sun. (These are known as Atira asteroids – orbit entirely inside Earth’s orbit – and Atens – orbit mostly inside Earth’s orbit.) Because of its design and vantage point in orbit around the Earth, NEOSSat can continuously search the sky near the Sun and is therefore more effective than ground-based telescopes at finding these objects. However, it only searches a very small area of sky each day with maximum sensitivity to find these objects – the opposite of what the ATLAS project will do. Even though NEOSSat’s search strategy is optimized for a scientific purpose rather than impact hazard reduction, it could nonetheless provide decades of warning if it were to detect a 1-km scale Aten class asteroid that posed a globally dangerous impact hazard.

Would NEOSSat have been capable of detecting the asteroid that fragmented in the skies over Chelyabinsk, Russia, on Feb.15, 2013?

No, the Chelyabinsk asteroid came out of the sky in the direction of the Sun so it would have been a very difficult target for any imaging sensor on or near Earth, including NEOSSat.