->The Conditions of the Arrival at Mars
Approach phase began 45 days before rovers' entry into Mars atmosphere. Due to craft being accurately tracked by Deep Space Network (DSN) antennas, team were able to design appropriate trajectory solutions. Interestingly they switched to Mars time: a Martian day is 40 mn longer than an Earth's; it is called a "sol". Rovers arrived at Mars in the second half of northern winter and southern summer. Both landed during Mars afternoon local time. During entry, descent and landing phases rovers' teams were mainly spectators, just watching correct process' unfolding and monitoring any data system was looking normal. Spirit landed at Gusev crater on January, 3rd 2004, 8:35 p.m. PST (4:35 UT January, 4th) as Opportunity touched down at Meridiani Planum on January, 24th 2004, 9:05 p.m. PST (5:05 UT January, 25th)
->The Most Accurate Ever Interplanetary Cruise!
Navigation teams set a new precision record in interplanetary missions: they led precision cruises as ever. Spirit journey is considered like the most accurately navigated in history. Spirit's cruise, trajectory tracking, and Trajectory Correction Maneuvers (TCMs) were so perfect that no trajectory correction maneuver was needed in the last 8 days preceding Mars. After a 300 million miles cruise, Spirit hit Martian atmosphere just 660 ft (200 m) from where planned! Some trouble was near to make the first arrival discomfortable however as a flaw was discovered in the entry, descent, and landing software just one week before Spirit's entry into Martian atmosphere. Such a flaw was preventing the airbags to inflate as the landing rockets to ignite. Odds were high that this occur in the reality. It was not until 3 hours and a half before Spirit entry that the faulty code was corrected and an upgraded software beamed to Mars!
| PREPARATIONS | |
|---|---|
| touchdown-1h 50 mn | S/C prepared for communications; switches from medium to low-gain antenna |
| about touchdown-1h 35 mn | S/C rotates to face heat shield appropriately |
| about touchdown-20 mn | S/C communicates with Earth through a 100 tones range only; cruise stage separation |
| NEXT 6 MINUTES BEGINNING AT TOUCHDOWN-6 MN | |
| lander grazes Martian atmosphere at 12,000 mph (5,400 m/s) and is heated to about 2,637° F (1,447° C). Heat shield brakes the craft too | |
| 30,000 ft above surface | S/C is now falling at 1,000 mph (450 m/s) only. A "supersonic" parachute is deployed |
| 10 seconds later | 10 seconds later main chute deployment. Heat shield jettisonned |
| 10 seconds later | lander descends from back shell along a 65 ft (20 m) tether. Altitude 20,000 ft |
| touchdown-1 mn | radar measurements determine how long and how retro rockets are fired |
| airbags inflation | |
| touchdown-6 s, 40ft from ground | 3 retro rockets firing, bringing vertical velocity to 0 |
| touchdown-3 s, a four-story building above ground | lander separation from the tether and freefall to the ground |
| LANDING | |
| touchdown | |
| rover may bounce up to a 4 or 5-story building's and as far as 0.6 mile (1 km). Bounces may last up to 10 mn | |
| standstill+4 mn and +7 mn | transmission of tones |
| landing platform deployment during 80 mn: airbags retracted, lander petals and solar arrays deployed, panoramic camera mast raised | |
| lander communicates Earth (even possibly first pictures) either via tow NASA orbiters (Mars Odyssey, Mars Global Surveyor), or directly via the Deep Space Network (DSN) | |
| lander turns back to sleep mode | |