• Why not go into orbit around Pluto?
• What are some of the major challenges of this mission?
• How large is the spacecraft and what types of instruments will it carry?
  

• What is the projected cost of this mission?

There are two reasons. The first is an engineering reason. To get to Pluto (which is 5 billion kilometers or 3 billion miles from Earth) in just 9.5 years, as New Horizons plans, the spacecraft must travel very, very quickly. As a result, New Horizons will speed by Pluto at a velocity of about 43,000 kilometers per hour (27,000 miles per hour). To get into orbit, we would have to reduce that speed by over 90%, which would require more than 1,000 times the fuel that New Horizons can carry.

The second reason is scientific: If we did stop to go into orbit, we wouldn't be able to go on to explore the Kuiper Belt!

The huge distance of Pluto from the Sun, about 32 times farther than the Earth-Sun distance, creates "extreme" conditions in several respects. First, it takes a long time to get to Pluto (9.5 years with a gravity boost from Jupiter and about 12 years without), which means that the spacecraft and instruments must have long lifetimes (i.e., their "warranties" must be good for over a decade!). The large distance from the Sun also means that solar cells cannot be used to power the spacecraft, and the onboard systems must be designed to operate in a cold environment. Finally, sending a spacecraft all the way to Pluto requires a powerful rocket and places severe constraints on the weights of the instruments. The more mass you want to carry, the larger the rocket needs to be. Even using the Lockheed-Martin Atlas V rocket, one of the most powerful in the U.S. fleet, New Horizons must weigh less than 1,025 pounds (465 kilograms).

All of the above pose major technical challenges, but the New Horizons team has found ways to overcome all of them and will deliver a spacecraft that can meet all of NASA's primary scientific objectives at Pluto.

The New Horizons spacecraft is roughly 8 feet (2.5 meters) across and will weigh approximately 1,025 pounds (465 kilograms) — about half a ton — when fueled.

Its design includes seven scientific instruments:

1. Alice is an ultraviolet spectrometer used for measuring gas composition
2. Ralph combines an infrared spectrometer (LEISA) for mapping surface composition with a color optical imager (MVIC) for mapping surface structure and composition
3. REX is a radio experiment for measuring atmospheric composition and temperature
4. LORRI is an optical telescope that provides the highest resolution imaging of the surface
5. PEPSSI is a plasma-sensing instrument for measuring particles escaping from Pluto's atmosphere
6. SWAP is a plasma-sensing instrument for measuring the properties of the solar wind at Pluto, Pluto's atmospheric escape rate, and for searching for a magnetosphere around Pluto. The "solar wind" is a stream of charged particles streaming away from the Sun at high speed.
7. SDC, an instrument used to measure dust impacts at the New Horizons spacecraft during its entire trajectory, was built by students at the University of Colorado!