We're here at JPL, all set to cover the landing of the Mars Science Laboratory tomorrow night at about 10:30 PST. We'll be following along with the entry, descent, and landing (EDL) team as things happen. If you're going to stay up with us to watch how things go down (so to speak), here's what you can expect to see and when.
Before we get to the schedule, there are two key concepts to understand to put what's going to happen in proper perspective. First, there's the time delay that we're dealing with. Right now, Mars is hundreds of millions of kilometers away, meaning that even at the speed of light, signals take fourteen minutes to get from Earth to Mars. If you do the math, that means that seven minutes after the entire landing process is all finished, back here on Earth we'll just be getting our first signal that MSL has entered the Martian atmosphere. The upshot of this is that nobody can really do anything to help the rover out: it's completely on its own from start to finish, relying on hundreds of thousands of lines of code to help it cope with anything that Mars might throw at it.
The other thing to keep in mind is that when MSL lands, the landing site at Gale Crater won't be visible from here on Earth. We'll be able to receive signals directly from MSL approximately up to the parachute deployment, but after that, the rest of the landing will occur over the Martian horizon. So at that point, we're going to have to go through an orbital relay spacecraft: Mars Odyssey (pictured above). In order to act as a relay, though, Odyssey has to roll so that its pointing the right direction, and about five weeks ago, one of the reaction wheels that it depends on to do this stopped working. Engineers have a backup system that should work, but it's adding a little bit of extra stress into the mix, and since Odyssey's roll won't happen until 10-15 minutes prior to MSL's descent, we're not going to be sure what data we'll be able to see in real-time until that point.
Furthermore, with all the relaying that has to happen (and antenna changes caused by MSL's stage transitions), there's a risk of signal loss, which is the type of thing that's likely to stress everyone out a whole bunch but may not necessarily be a bad sign. Here's a cute video from JPL that takes you through the communications process:
So, during the landing itself, we'll be getting data from two sources: very simple X-band communication "tones" from MSL itself which are basically confirmations that things are going as planned, and then the much more detailed telemetry from Mars Odyssey, both in time-delayed real time. If for some reason Odyssey drops out, we're going to have to rely on two other spacecraft that will be watching the landing: Mars Reconnaissance Orbiter, and the European Space Agency's Mars Express. These spacecraft are both just recording data from MSL, though, and if we have to go to them for confirmation, it's going to be eight hours at the earliest before we get any data back.
Assuming everything goes according to plan, here's what's going to happen tomorrow night. All times are PST, and are when we'd expect to hear them on Earth: for when these things are happening on Mars, subtract 14 minutes. Also, these are just best estimates: they are likely to be off by seconds (or perhaps minutes), but the sequence won't change.
[UPDATED at 3PM with new times from JPL]
- 08:23:00 PM: The EDL team has one last chance to send course tweaks to MSL. They may not need to do this if everything looks good, but the opportunity is there anyway. At this point, MSL is 30,500 km from Mars and traveling nearly 4 km/s.
- 09:00:00 PM: Shortly after 9pm, as MSL's flight director Keith Comeaux told me, the entry, descent, and landing (EDL) team will make a final go or no go decision for turning off the command uplink from Earth to the spacecraft. After the uplink is disabled, MSL is completely on its own.
- 10:14:34 PM: The MSL landing system (the rover and sky crane inside the heat shield) separates from the cruise stage that has brought it to Mars from Earth.
- 10:15:34 PM: While traveling, MSL was slowly spinning (at about two rotations per minute) to keep it stable. MSL now enables its reaction control system and cancels out its spin over a period of about three minutes.
- 10:19:35 PM: MSL has a little bit of quiet time to calibrate its inertial measurement system.
- 10:24:34 PM: Entry begins. MSL is now traveling at about 5.8 km/s and is 125 km above the surface.
- 10:25:49 PM: The friction heating of the heat shield peaks at 2,100 degrees Celsius. MSL has already slowed down by about 2 km/s.
- 10:25:59 PM: Deceleration peaks at up to about 13 G. MSL has slowed down another 1 km/s, to about 2.8 km/s.
- 10:28:46 PM: At this point, MSL has decelerated to less than 500 m/s. It fires off six 25kg tungsten weights that it was using to offset its center of gravity straight out the side of the aeroshell to rebalance itself, reducing its angle of attack to close to zero.
- 10:28:48 PM: MSL deploys the largest supersonic parachute ever made at it continues to slow itself down.
- 10:29:12 PM: The heat shield falls away, exposing the bottom of the rover to Mars for the first time.
- 10:29:16 PM: Now that the heatshield is gone, MSL turns on its radar and starts trying to lock on to the surface. It also turns on the MARDI descent imager.
- 10:29:45 PM: Descending at about 150 m/s, MSL crosses over the Martian horizon, passing out of view of Earth. Back here at JPL, we stop receiving X-band tones directly from the craft, and from this point onwards, we'll be relying on Odyssey as a relay.
- 10:30:38 PM: The parachute and backshell separate, leaving the MSL rover and its sky crane completely exposed. MSL executes a horizontal maneuver to get away from the backshell.
- 10:30:20 PM: The skycrane's engines throttle to 100%. At about 1.5 km above the surface, the remainder of the descent will be powered.
- 10:30:57 PM: MSL is about 55 meters above the surface and descending at 20 m/s.
- 10:31:08 PM: At about 20 meters above the surface, MSL keeps decelerating down to 0.75 m/s.
- 10:31:14 PM: Less than 20 meters from the surface, the sky crane shuts off four of its eight engines as the rover separates and begins to descend on cables.
- 10:31:15 PM: MSL releases its "bogie" wheels, getting ready for touchdown.
- 10:31:30 PM: TOUCHDOWN! WOOHOO!!! Curiosity knows when she's on the ground when the load on the tether that she used to get from the skycrane to the ground goes slack.
- 10:31:33 PM: Cables connecting Curiosity to the skycrane are cut, and the skycrane flies off for a crash landing.
And that's it! We're putting together another post on what's going to happen after landing, like what kind of pics we can expect to see and when, so check back for that in a little bit.