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general FAQ's
aerogel FAQ's
Comet FAQ's

Note: A Spanish version of our FAQ is also available


How big is the Stardust spacecraft?

We are flying a small spacecraft, weighing only about 770 pounds (350 kg). It is the size of an average desk, except for the solar panels, which extend several feet in the front and back.

What will you find out by taking samples from the comet?

Since comets are thought to be the leftover material of the early Solar System, created before the time of the formation of the planets, it is hoped that scientists will find out more about the creation our universe. The planets have been altered by weathering, tectonics and other factors. In contrast, comets are believed to be the most unchanged, pristine bodies in the solar system. This means that their materials are the oldest and most basic available for study.

How come the comets don't change?

Most comets don't change once they are formed because they are kept in the deep freeze and isolation of space outside our Solar System. Comets come from the Kuiper Belt which is beyond Pluto, far from the Sun, where there is nothing to contaminate them. When comets approach the Sun they heat up and lose some of their material and during their travels, plus, they can potentially pick up foreign materials.

How long has this project been going on?

Stardust was selected to fly in Fall 1995, with work beginning in January 1996. It takes a long time to plan a mission, then build and fly a spacecraft. Because of the distances involved, missions can take many years to fly and complete.

Why does it take five years for the spacecraft to reach the comet?

Being in the right place at the right time is the major factor in determining the length of time of Stardust's journey. However, getting to the right place requires moving great distances at precise rates of travel. The spacecraft and comet need to encounter each other at similar speeds, so that the comet particles do not strike the spacecraft with such force that they destroy it.

To accomplish this rendezvous, the speed of the spacecraft must be increased beyond the initial push it received during launch. This maneuver requires swinging by the Earth for a gravity assist to increase its speed and enlarge the size of the spacecraft's orbit. This lengthens the distance it has to travel so that its path precisely intersects that of the comet. The return trip to Earth adds months to the journey, because the spacecraft must complete an entire orbit after its visit to the comet, so that it meets Earth at the proper position to successfully return the samples. All this adds up to five years of carefully planned and managed spaceflight.

What is involved in planning the entry speed and chute deployment to slow the landing of the return capsule?

The challenges of Sample Return Capsule (SRC) entry involved solving problems involving its travel at both supersonic and subsonic speeds. Engineers worked hard to determine the best capsule shape for speed, stability and survivability. One challenge was to make certain the capsule continuously orients its heat shield toward the atmosphere, which is made possible by the aerodynamics of its design and location of the center of gravity. During testing, design changes were made that included increasing the rotation speed upon separation from the Stardust spacecraft, to increase the capsule's stability. The size of the drogue chute was also increased beyond that already planned to better slow and direct the capsule during its descent.

What will the Stardust spacecraft be doing while on its way to the comet?

The spacecraft will be collecting interstellar dust samples, using the B-side of the aerogel collector in the mission while traveling to the comet at certain points. Real time interstellar dust analysis will also be conducted with the Cometary and Interstellar Dust Analyzer (CIDA) instrument. There are some planned imaging activities when the spacecraft flies past the Earth and Moon for the gravity assist. For the majority of the cruise to the comet, and after comet encounter, the spacecraft will be in a low power mode that saves energy while ensuring that all thermal environments are maintained.

What are the possibilities of inclement weather at the time of landing in Utah? Can the trajectory be adjusted to allow for landing at an alternate site?

There can be inclement weather for the Stardust landing but on average the January weather at UTTR is pretty good: only 6 days with visibility less than 7 miles, only 0.5 inches of precipitation, only 4 inches of snowfall, and the minimum mean temperature is 17 degrees F which will probably be close to our recovery temperature since the capsule comes in at 3 am. The trajectory cannot be changed to go to an alternate site - years of preparation and coordination are required to bring anything in from outer space.


To catch particles in space, the Stardust spacecraft uses a special material called aerogel. These are frequently asked questions about this material:

How is aerogel made?

Mixing four chemicals, which react to form a wet gel, similar to a gelatin dessert creates Aerogel. The gel is then dried in an autoclave, in essence a pressure cooker that applies pressure and heat.

What is it used for?

The Stardust Project is using aerogel as a capture media, where it will collect very small interstellar and cometary particles as they embed themselves in the porous aerogel. Because of its unique physical properties, aerogel has also been proposed for a wide variety of uses, including thermal insulation, acoustical insulation, optical components, catalytic supports and filters.

What does it feel like?

The microstructure of aerogel is extremely porous, so it feels like volcanic glass pumice or even a very fine, dry sponge, except that it is much lighter.

Why is it blue?

Aerogel has a blue cast for the same reason that the sky is blue. The very small particles that compose the aerogel scatter blue light, the same as our atmosphere scatters blue light. Similarly, when you look through the aerogel the light appears yellowish or reddish, like that of a sunrise or sunset.

Where can I get some aerogel?

Aerogel is commercially available in limited quantities from a few companies. These can be found quite easily by searching the Internet using the keyword: aerogel. JPL only produces specialized aerogel used for spaceflight.

How much does aerogel cost?

Aerogel is relatively expensive primarily because it is currently made in very limited quantities. While increasing the scale of aerogel production will reduce the cost, the basic process and raw materials are still somewhat costly. For relatively small quantities of aerogel the cost is about $1.00 per cubic centimeter for one liter.

What makes aerogel so special?

The fact that typical aerogels are between 95 and 99.5 percent porous gives them their unusual characteristics. Because of this highly porous quality they are characterized by extremely high surface area, high thermal and acoustical resistivity, low dielectric constant, and low refractive index. There are other materials that exhibit each of these properties, however, only aerogel exhibits all of these properties at the same time.

Who invented aerogel?

Aerogel was first made in the 1930s by Samuel S. Kistler, who obtained several patents for making a variety of aerogel, including silica, alumina, chromia, tin and carbon.

Why is it called a gel?

During the production of aerogel a wet gel is formed which when dried becomes filled with air. Thus the name aerogel, which means: air gel.

Is it solid?

Aerogel is made up of microscopic beads or strands connected to form a continuous network. Since the network fills space and supports itself, it is considered a solid.

What happens if I touch it?

Silica aerogel is semi-elastic because it returns to its original form if slightly deformed. If further deformed, a dimple will be created. However, if the elastic limit is exceeded, it will shatter catastrophically, like glass.

Is aerogel such a good insulator because the air within is trapped and immobile? And, is this why it doesn't melt?

Heat is transferred in three ways: convection, conduction, and radiation. Aerogel is a good thermal insulator for convective heat transfer because the air is severely limited in the distance that it can move and thus transport heat energy. The pores of a typical 20 mg/cc silica aerogel are roughly 0.00000001 meters in diameter. Aerogel is a good conductive insulator because the silica molecules are not as well "connected" as those in a metal (a good thermal conductor). Silica aerogel is a poor radiative insulator because infrared radiation (which transfers heat) passes right through silica aerogel. For this reason, carbon was added to the MER aerogel to stop infrared radiation from passing through it. This is also why one feels the heat from a flame. Air is a poor convective transporter of heat, but infrared radiation passes right through air, from the flame to your hand.

Note: the index of refraction depends on the density of the aerogel.

Would it be possible to create aerogel lighter than air by using helium instead of air?

Aerogel cannot be made less dense than air by filling it with helium. You might be able to make it less dense than the surrounding atmosphere by filling the aerogel with helium and then placing it in an atmosphere of radon or possibly xenon.

Last updated September 29, 2005

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