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ICESat: Frequently Asked Questions

ICESat: Frequently Asked Questions

What is NASA's ICESat orbit-lowering and re-entry plan?

NASA's ICESat satellite completed a very productive scientific mission earlier this year. In June, NASA's Science Mission Directorate approved a plan to lower the spacecraft's orbit so that it would re-enter the atmosphere by August-September 2010. A series of thruster burns on the spacecraft conducted June 23-July 14 slowly lowered ICESat's orbit, minimizing the time until it re-enters Earth's atmosphere and breaks up. Some pieces of the spacecraft, weighing collectively about 200 pounds, are expected to survive re-entry. The risk of harm coming to anyone on Earth from this debris is estimated to be very low.

When will the ICESat spacecraft re-enter the atmosphere and burn up?

NASA is planning to have ICESat re-enter the atmosphere and largely burn up sometime between mid-August and early September 2010.

What risks are there to people and property from falling pieces of ICESat?

There is a very low risk to people and property from pieces of ICESat that reach Earth's surface. Most of ICESat will burn up in the atmosphere during re-entry. Of the spacecraft's total mass (about 2000 lbs.), only a small percent will reach the surface of Earth. The largest single piece expected to survive, about the size of a large flat-screen television, weighs about 70 pounds. The chance that one of the surviving pieces will cause a personal injury is assessed to be less than 1 in 10,000.

Why has NASA decided to have ICESat re-enter so quickly?

It is NASA policy to lower the orbit of a satellite as much as possible once its mission has ended. For satellites that are at relatively high orbits and have little thruster fuel reserves needed to lower the orbit, spacecraft re-entry can often take years. ICESat orbited at a relatively low altitude and had a considerable amount of fuel remaining after its science mission was completed, which gave NASA the opportunity to plan for spacecraft re-entry in a matter of months rather than years. NASA chose to pursue a relatively rapid ICESat re-entry as a way to reduce the overall burden of orbital debris.

What is the sequence of activities involved in the ICESat re-entry?

Bringing ICESat out of orbit works in two stages: lowering the orbit and re-entry. First, ICESat performed a sequence of thruster firings begun on June 23 that changed the spacecraft's orbit from approximately 370 miles (600 km) above Earth to an orbit where the lowest point is just 124 miles (200 km) high. These firings were conducted in series separated by at least one day for NASA controllers to assess the results of the burns and look for any potential orbital hazards. Thruster firings concluded on July 14. All remaining fuel on the spacecraft is now depleted.

Where will any remains of ICESat likely reach Earth's surface?

ICESat circles the Earth from pole to pole, so the surviving debris could land almost anywhere on the planet. Due to natural variabilities in the near-Earth environment, a precise location of where spacecraft debris will re-enter cannot be forecast. The U.S. Space Surveillance Network, operated by the Department of Defense, will closely monitor the orbit of ICESat debris during its final days and issue periodic predictions of re-entry time and location.

How will NASA know that ICESat has finally re-entered?

NASA will know that ICESat has successfully re-entered by information provided by the U.S. Space Surveillance Network, which will likely be able to establish the actual re-entry area.

How often does orbital debris re-enter Earth's atmosphere?

On average, a piece of debris from rocket bodies and old satellites enters the atmosphere and burns up harmlessly every day.

How many NASA satellites, launch vehicles, and other large orbital debris re-enter Earth's atmosphere each year?

Recently, the number is about half a dozen.

How many of these re-entries have resulted in confirmed personal injury or major property damage?

None.

Will some of the ICESat spacecraft remain in orbit to contribute to orbital debris?

No. After the ICESat spacecraft has re-entered, there will not be any components remaining on orbit and will therefore not contribute to orbital debris.

When was the last time that a NASA science satellite re-entered Earth's atmosphere?

In January 2002, the Extreme Ultraviolet Explorer re-entered the Earth's atmosphere under conditions similar to ICESat. EUVE was a much larger satellite than ICESat and no debris was reported to have reached the surface.