If all goes well, the Curiosity rover will be on the Mars surface at about 1:17 a.m. Eastern time, and 13 minutes, 48 seconds later (the time it takes for a radio signal to travel 154 million miles to Earth from Mars), there will be confirmation and cheering in the control room at 1:31 a.m., give or take a minute or so. 
 
 Or there could be silence – nothing from the rover, and probably a somber pall in mission control. 
 
 But it would not necessarily mean that the Curiosity had come to a quick, unfortunate demise. It could just be an interplanetary communications glitch. 
 
 There are several transmitters on the spacecraft that will broadcast at different frequencies. Using one of them, the so-called X-band, the Curiosity will send simple messages directly to Earth. But, a couple of minutes before landing, the landing site at Gale Crater will rotate out of view from Earth – that means the direct communications path will be blocked, too. 
 
 In addition, the spacecraft will be broadcasting a wealth a data using a UHF antenna. That is not powerful enough to be picked up by antenna on Earth, but a NASA orbiter, Mars Odyssey, will act as a relay, re-transmitting the data to Earth in real-time. 
 
 If anything goes wrong with the Curiosity-to-Odyssey-to-Earth communications, then the result will be silence. 
 
 That is not inconceivable, especially as Odyssey experienced a malfunction two months ago with one of three spinning wheels used to orient the spacecraft. A spare wheel was put into operation, but if it turns out that Odyssey cannot turn itself toward Curiosity, it will not hear anything. 
 
 If Odyssey misses Curiosity’s messages, a second orbiter, the Mars Reconnaissance Orbiter, will also be listening. But Reconnaissance Orbiter will be recording the data, not relaying it, and engineers on Earth will not get to sift through that information until hours later. 
 
 If silence persists, the two orbiters will make additional passes over Curiosity over the next day, and late on Monday, the Curiosity will be able to talk directly to Earth, bypassing the orbiters. 
 
 NASA engineers said it is quite possible for Curiosity to land successfully and that they would not find out for hours. Once they establish contact, the mission proceeds. 
 
 But if a full day passes without hearing from Curiosity, then pessimism will set in that something had gone terribly wrong. 
 
 — KENNETH CHANG ||||| That landing is scheduled for 1:31 a.m., and officials said they could know almost immediately if the rover was safely on the ground. That tracking would come from the Odyssey orbiter circling Mars, if the spacecraft is able to get to the right location at the right time. 
 
 If not, the waiting time for a final answer on whether the rover was safely on the surface could range from two to eight hours. If no signal arrives from Curiosity via three Mars orbiters and the Deep Space Network after 18 hours, NASA officials said, then they would start to worry about its safety. 
 
 The final descent has been pre-programmed and the army of engineers and scientists at the Jet Propulsion Lab’s Mission Control have no control over it. “Our position will be identical to anyone at home,” said Adam Steltzner, lead of the Entry, Descent and Landing (EDL) team. “We’re all along for the ride.” 
 
 Speaking for the team as a whole, Steltzner said they were “Rationally confident, emotionally terrified and ready for EDL.” 
 
 Because the rover is so much larger, more complicated and more ambitious than earlier models, it has to land in a new and far more hazardous way. The landing, which could never be tested in full on Earth, includes a hovering rocket stage, a kind of sky crane, to lower it to the ground. NASA’s chief scientist John Grunsfeld has said that because of that heightened landing difficulty, in addition to the unprecedented sophistication of the instruments on board, Curiosity is “the most important NASA mission of the decade.” 
 
 Worldwide spectacle 
 
 The Curiosity landing is shaping up to be an international spectacle. Formal “landing” parties have been scheduled from South Australia to Rome, from Israel to Crete; and in the United States from Atlanta to Seattle, Milwaukee to Honolulu. 
 
 NASA also has helped organize a landing gathering in New York’s Times Square, which will feature a large screen that will beam the streaming news from atop a building and high above the crowd. 
 
 Reaching, orbiting and landing on Mars is notoriously hard. In addition to the European Space Agency, nations including the United States, the former Soviet Union, Russia, the European Space Agency, China and Japan have sent missions to Mars since the late 1960s, but only about one-third of them have succeeded. 
 
 The United States is the only nation to land a vehicle on Mars and complete its mission, having done it six out of seven tries.
– The Curiosity rover landed safely on Mars early this morning, prompting whoops of joy and relief in NASA's mission control center, reports the New York Times. The rover quickly beamed back a picture of its own shadow cast on the surface of the Red Planet. "Touchdown confirmed. We are safe on the surface of Mars!" the team read out after receiving signals from the rover. After a journey of 354 million miles, the rover, which is much bigger and more complex than previous models, had to land in a new way that could never be fully tested on Earth, leading to what control room staff described as "seven minutes of terror" before confirmation was received, notes the Washington Post. As earlier reported, the spacecraft ferrying it had to rely on a supersonic parachute to slow it from 13,200mph to about 1.7mph; with seconds to go, the rover was then lowered to the surface using three nylon tethers and retro rockets.