FAQ - Spacecraft

1. How can the Hubble Spacecraft photograph so many new bodies in space? Is it accurate? Where are all these data stored?

The Hubble Space Telescope (HST) is actually not that big of a telescope. Its mirror is only 2.4 meters (less than 8 feet) in diameter. On Kitt Peak, astronomers regularly use the "small" 2.1 meter telescope. The largest telescopes are now 8 to 10 meters in diameter and much larger ones are being designed. The advantage that HST has is that it is in space, just above Earth's atmosphere. With bigger telescopes on the Earth and methods to correct for the blur of the Earth's atmosphere, telescopes on the ground can now image small areas, such as searching for planets around stars, as well as HST. However, for longer periods of time, or at wavelengths not easily doable from beneath the atmosphere, HST excels. HST can observe fainter objects because it does not have to worry about clouds and day and night, so can look at very faint galaxies. Yes, it is very accurate, again because it does not the atmospheric interference. The data are stored at the computers at Maryland where the operating center for HST is located.

2. Are there satellites used to help locate craters on Earth and on other planets? How far away are Venus, Mars, and Mercury?

There arent any Earth-orbiting satellites designed specifically to look at craters, but the Earth’s surface is mapped by imaging satellites (see Google Earth) and radar. People are discovering craters looking at these images. However, you still need ground truth to determine what may have caused the round feature you may think is an impact crater. Similar instruments are used to map the surface of other planets (Mercury, Venus, the Moon, Mars, Jovian and Saturnian satellites, and asteroids).

3. How do all of the fly-by objects, orbiters, and landers we put into space impact Earth and other planetary/celestial objects?

Lets put this into context. A flea weighs (mass) about 0.01 grams, which is 1/5,000,000 of a 110 pound (50 kilogram) person. For comparison, one of the largest spacecraft sent to any planet is Cassini, which has a mass (with fuel) about 5,000 kilograms. The Moon’s mass is 7x10²² kilograms, Mars is 6x10²³ kilograms, and Saturn is 6x10²⁶ kilograms. So, even when compared to the Moon, Cassini is 1x10¹⁷ times smaller (1/100,000,000,000,000,000) than a flea! The Apollo Lunar Module was only about 2 times the size of Cassini, so, still really small compared to the size of the Moon, etc. The bigger concern is the effect of the Shuttle launch on the atmosphere (destroying ozone), but, again, with the number of launches, the effect is very small.

4. How long does it take to travel to each planet with current technology?

This is not an easy question to answer since there are many factors involved, primarily dealing with things like weight and fuel (which weighs a lot). It also involves what you want to do once you get there (is flying by fast OK or do you want to orbit or land?). Below are the times it took/will take to get to various planets and the Moon (New Horizons is still on its way). All of the planets are in orbit around the Sun. To get to Mars, Jupiter, etc. you have to add energy to get away from the pull of the Sun. To get to Venus and Mercury, you have to lose energy. Gravity assists are used to help accomplish this. Many spacecraft have used Jupiter to gain the energy to go to the outer planets. Messenger has to lose a lot of energy to be able to orbit Mercury. In addition, it was a large spacecraft in a relatively small rocket, so it needed extra help!

Spacecraft	Target	Time	Comment
Apollo	Moon	3 days	Slowed down prior to orbit
Magellan	Venus	15 months	Slowed down prior to obrit
Phoenix	Mars	11 months	Slowed down prior to orbit
Dawn	Vesta	4 years	Mars flyby gravity assist; efficient fuel source
Galileo	Jupiter	6 years	Two Earth flyby gravity assists
Messenger	Mercury	6.5 years	Earth flyby gravity assist; two Venus flyby gravity assists; three Mercury flybys
Cassini	Saturn	7 years	Jupiter flyby gravity assist
Voyager 1 & 2	Jupiter; Saturn; Uranus; Neptune	13,23 months; 3,4 years; 8.5 years; 12 years	Voyager 1 fast orbit to Jupiter & Saturn; both now far out of the solar system; Voyager 2 is ~ 90 AU from the Sun and Voyager 1 is ~110 AU from the Sun
New Horizons	Pluto	9.5 years	Jupiter flyby gravity assist

5. Is the International Space Station used to study other planets?

The simple answer is no. It has been used to study the Earth, but it was determined long ago that it was not suited for astronomical studies. Too big to keep steady, especially with humans moving around and the space around it is not a clean environment. It is used primarily for low-gravity studies.

6. How will the inner planets be studied in the future? Are there serious plans to send a manned mission to the Moon or Mars?

MESSENGER reached Mercury in March, 2011. Venus Express (European Space Agency, ESA) is now in an extended mission around Venus. There are future missions planned by both ESA and JAXA (Japanese Space Agency). Mars Odyssey, Mars Express (ESA), and Mars Reconnaissance Orbiter are all in orbit around Mars and the two Mars Rovers are still functioning. The Mars Science Laboratory Rover (US) has been launched and is on its way to Mars. There are a number of future missions in the works: Phobos-Grunt (Russia and China) moon sample return, ExoMars rover (ESA), MAVEN (US), and MetNet (Finland and Russia). Selene (JAXA) orbited the Moon and was crashed onto the surface (to be studied from Earth). Chandrayaan-1 (India) and Lunar Reconnaissance Orbiter (LRO) are currently orbiting the Moon. LCROSS crashed onto the surface to look for water at the south pole. There are three or four other missions being discussed by the US and other countries. For manned missions, the US stated goals of putting astronauts back on the Moon by 2020 and on Mars by 2037.

7. How is imaging done for flybys?

First, if you really want to get a lot of pictures (thousands), you want to go into orbit and spend some time taking the pictures. However, if you do not have the energy to allow you to get into orbit, then all you can do is fly by and take pictures as you go by. That is what Voyager did in the outer Solar System and that is what the earlier Mariner missions did for Mercury, Venus, and Mars. In that case, it is like taking pictures out of a bus as you drive through a city. First you see things at a distance, then get a few close-ups, and then look back and get a few last pictures. The early Mariner spacecrafts only got a few dozen pictures of Mars (and only the side that they flew by). MESSENGER has gotten lots of pictures of Venus, Earth and Mercury as it has gone by, but not as many as it will once it gets into orbit.

8. How long does it take to get images (information) back from orbiters, landers, and rovers?

The short answer is the speed of light. It takes light 8 minutes to get from the Sun to the Earth (actually 8.33). So, for example, if Mars is 0.5 AU from Earth, it would take about 4 minutes for the information to get to Earth. If Earth and Mars are not lined up on the same side of the Sun, it could take as long as 20 minutes. That is the simple answer. It actually can take longer. Usually to save energy, a lander or rover may have a smaller transmitter and use an orbiter to relay the information/pictures, which will add a little time. Also, pictures can be big and it may take time to "upload" the pictures, depending on how fast the data can be transmitted. As an example, think about how long it used to take to download a movie using a modem compared to current-day high-speed connection.

9. When NASA launched Space Shuttles, did they reuse them for multiple launches?

Yes, the Shuttles are reused. There have been 132 flights: Challenger (10; destroyed in launch accident), Columbia (28; destroyed during re-entry), Discovery (38), Atlantis (32), and Endeavor (24; replacement for Challenger).

10. Is Earth more similar to Venus or Mars?

Venus and Mars have both similarities to the Earth. Venus is about the same size and it might be closer in geologic activity than Mars. Mars is colder than Earth, but closer to Earth in temperature. Mars has water, but presently this water is frozen. Mars may have been more similar to Earth in the past and appears to have had flowing water and maybe oceans (or at least lakes).

11. What would be the challenges of trying to get an astronaut off Mars so that they could return to Earth?

The biggest challenges for getting astronauts or any spacecraft off of Mars is gravity. The gravity of Mars is about 38% of Earth's, so we would need a fairly large rocket to escape the gravity of Mars. But, before that, you need to be able to soft land on the planet. Your choices are to bring all of your fuel with you or use the materials on Mars (water to make oxygen and hydrogen fuel) so that you would not need to bring all of your fuel with you. As an example of the how much fuel is needed, here are the numbers for the Shuttle: its total weight at launch is about 2 million kilograms, of this, about 1 million kilograms is solid fuel and 700,000 kilograms is liquid fuel. All this to get a 25,000 kilogram payload into Earth orbit!

12. How long does it take spacecraft to get to each planet?

When we send spacecraft to planets or other objects (asteroid or comet), the spacecraft is actually put into an orbit around the Sun in order to bring it close to the target planet. But, you have to deal with the gravity of the Sun. Here are some numbers: Mars - 7 months, Venus - 5 months, and Mercury - 5 months. From here, it gets complicated.

The closer a planet is to the Sun the faster it moves around the Sun. However, when you leave the Earth to go to another planet, you have to fight the gravity of the Earth and the Sun (like throwing something into the air). If you just want to fly by something, you are not too worried about how fast you go by. But, if you want to orbit or land, you want to be able to match the speed of the planet. For Mars, you have to give a spacecraft extra energy to move it away from the Earth and the Sun (if you throw something into the air, it slows down and stops, but to throw it higher, you have to give it more energy to begin with). When going closer to the Sun, however, you are still working against the gravity of the Sun. Drop a plate out of your hand and it may be moving fast enough to break it when it hits the ground. Drop it out of a second story window and it will hit the ground much faster thanks to gravity. The same is true for sending a spacecraft to Mercury. If you send something from the Earth to Mercury (the MESSENGER spacecraft), you have to fight against gravity to make sure it is not going too fast if you want to orbit around Mercury. But you can use a planet to speed you up or slow you down. This is called a gravity assist. You use the planet instead of using a lot of rocket fuel. To slow it down, MESSENGER flew by Earth once and Venus twice before it headed for Mercury. It flew by Mercury three times, slowing it down each time. It then "matched" Mercury's orbital speed and was eased into orbit in March, 2011. Its first flyby was 3.5 years after launch and it will be 6.5 years from launch until it goes into orbit!

13. Why are humans not going to the Moon anymore?

This is, quite simply, due to politics rather than science. Back during Apollo, the main reason for going to the Moon was to beat the Russians and science was secondary. People started getting bored with another trip to the Moon (really) and then there was the Vietnam war. So, congress cut back NASA funding. NASA decided it needed to concentrate more on developing a new, easier, and cheaper way to get into space and came up with a more complex and more expensive way called the shuttle. The bottom line is that we do not currently have the launch capability to go to the Moon. The shuttle can only make it to low Earth orbit and even getting to the Hubble telescope was an effort. So, to get back to the Moon, NASA (or some other country) needs to design new rockets to get us there and back.

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FAQ - Spacecraft

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