The New Horizons spacecraft is the size of a baby grand piano with a salad bowl — the dish antenna — on top. It will come closest to Pluto at 7:49 a.m. EDT Tuesday. Thirteen hours later, around 9 p.m. EDT, flight controllers will learn if everything went well. The spacecraft will have sent the confirmation signal 4½ hours earlier; that's the one-way, speed-of-light, data-transit time between New Horizons and Earth.